Patent Grant
11515468
The present invention relates to a piezoelectric ceramics, and more particularly, to a lead-free piezoelectric ceramics and a manufacturing method therefor. The present invention also relates to a piezoelectric element, a vibration device, and an electronic device each using the piezoelectric ceramics.
A perovskite-type metal oxide of an ABO3 type, such as lead zirconate titanate (hereinafter referred to as “PZT”), which contains lead, is a typical piezoelectric material. A piezoelectric element obtained by forming electrodes on a surface of a piezoelectric material is used in a variety of piezoelectric devices and electronic devices, such as an actuator, an oscillator, a sensor, and a filter, by utilizing its piezoelectric effect.
However, PZT contains lead as an A site element, and hence its influence on an environment is regarded as a problem. For example, a lead component in a discarded piezoelectric material may elute into soil to adversely affect an ecosystem. Accordingly, there is a proposal of a piezoelectric ceramics using a lead-free perovskite-type oxide.
Barium titanate is known as a piezoelectric ceramics formed of the lead-free perovskite-type metal oxide. In Japanese Patent Application Laid-Open No. 2009-215111, there is a disclosure of a piezoelectric ceramics based on a pseudo-binary solid solution of barium zirconate titanate (Ba(Zr0.2Ti0.8)O3) and barium calcium titanate ((Ba0.7Ca0.3)TiO3), for improving a piezoelectric property of barium titanate at about room temperature. A piezoelectric ceramics of Examples shown in Table 2 of Japanese Patent Application Laid-Open No. 2009-215111 has an extremely high piezoelectric property with a piezoelectric constant d33 of more than 580 pC/N at room temperature. However, as shown in FIG. 5 of Japanese Patent Application Laid-Open No. 2009-215111, the piezoelectric constant significantly fluctuates depending on an ambient temperature. For example, a lowering in piezoelectric constant of about 20% per 10° C. was found in the vicinity of a peak of the property. When the piezoelectric constant significantly fluctuates depending on the ambient temperature in a practical temperature region as described above, a piezoelectric element including the piezoelectric ceramics does not have a stable displacement amount, and hence driving thereof is difficult to precisely control.
In order to suppress the fluctuation in piezoelectric constant depending on the ambient temperature in the practical temperature region, for example, in Japanese Patent Application Laid-Open No. 2003-128460, there is a disclosure of a technology for reducing a change in distortion amount with respect to a temperature change at around room temperature, without lowering a Curie temperature, by substituting part of Ba of barium titanate (BaTiO3) with Ca. However, as shown in Table 1 and FIG. 5 of Japanese Patent Application Laid-Open No. 2003-128460, there has been a problem in that, when temperature dependence at around room temperature is lowered, the piezoelectric constant itself takes a small value. In Japanese Patent Application Laid-Open No. 2003-128460, there is also a disclosure of a technology for increasing the piezoelectric constant by increasing an average grain diameter of crystal grains forming the piezoelectric ceramics to, for example, 60.9 μm. In this case, however, there has been a problem in that fine processability and mechanical strength of the ceramics are lowered.
The present invention has been made in order to solve such problems as described above, and provides a lead-free piezoelectric ceramics that stably exhibits an excellent piezoelectric constant in a practical temperature region, for example, the range of from 0° C. or more to 40° C. or less. The present invention also provides a manufacturing method for the piezoelectric ceramics, and a piezoelectric element, a vibration device, and an electronic device each using the piezoelectric ceramics.
In order to solve the above-mentioned problems, according to one embodiment of the present invention, there is provided a single-piece piezoelectric ceramics including as a main component a perovskite-type metal oxide represented by a compositional formula of ABO3, wherein the A site element contains Ba and M1, the M1 being formed of at least one kind selected from the group consisting of Ca and Bi, wherein the B site element contains T1 and M2, the M2 being formed of at least one kind selected from the group consisting of Zr, Sn, and Hf, wherein concentrations of the M1 and the M2 change in at least one direction of the piezoelectric ceramics, and wherein increase and decrease directions of concentration changes of the M1 and the M2 are directions opposite to each other.
According to one embodiment of the present invention, there is provided a manufacturing method for a piezoelectric ceramics including: stacking a first ceramics precursor and a second ceramics precursor with each other to obtain a multilayered body; and sintering the multilayered body to obtain a single-piece piezoelectric ceramics, wherein the following conditions are satisfied:
5° C.≤|TotA−TotB|≤30° C.
0≤2|d31A−d31B|/|d31A+d31B|≤0.2
where TotA and TotB represent respective orthorhombic-to-tetragonal phase transition temperatures of a first ceramics obtained by sintering the first ceramics precursor alone and a second ceramics obtained by sintering the second ceramics precursor alone, and d31A and d31B represent respective piezoelectric constants thereof after polarization treatment.
According to one embodiment of the present invention, there is provided a piezoelectric element including: a first electrode; a piezoelectric ceramics portion; and a second electrode, wherein a piezoelectric ceramics for forming the piezoelectric ceramics portion includes the piezoelectric ceramics according to the embodiment of the present invention.
According to one embodiment of the present invention, there is provided a vibration device including a vibration body including a diaphragm including the piezoelectric element according to the embodiment of the present invention.
According to one embodiment of the present invention, there is provided an electronic device including the piezoelectric element according to the embodiment of the present invention.
According to the present invention, the piezoelectric ceramics having a gradual change in piezoelectric constant in the practical temperature region, for example, the range of from 0° C. or more to 40° C. or less can be provided by integrating a plurality of piezoelectric materials different from each other in phase transition temperature, which is a temperature at which the piezoelectric constant becomes maximum with respect to temperature, with each other as ceramics without forming a solid solution. The present invention can also provide the manufacturing method for the piezoelectric ceramics, and the piezoelectric element, the vibration device, and the electronic device each using the piezoelectric ceramics.
In addition, the piezoelectric ceramics of the present invention uses substantially no lead, and hence has an extremely small load on the environment.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention are described below.
The present invention relates to a single-piece lead-free piezoelectric ceramics in which the Ba site and T1 site of barium titanate (BaTiO3) having a perovskite-type structure are partially substituted with other metal elements. A change in piezoelectric constant in a practical temperature region is reduced by changing local concentrations of the substituting elements depending on sites in the single-piece piezoelectric ceramics.
The average concentration of a substituting element in a barium titanate-based piezoelectric ceramics is associated with the phase transition temperature of the crystal structure of the piezoelectric ceramics. The barium titanate-based piezoelectric ceramics has such a property that its piezoelectric constant increases at a phase transition temperature between an orthorhombic structure and a tetragonal structure. Therefore, the phase transition temperature is preferably controlled to be in the practical temperature region of the piezoelectric ceramics, or in the vicinity of the practical temperature region.
It is known that the crystal structure of the barium titanate-based piezoelectric ceramics transitions from a rhombohedral structure to an orthorhombic structure, to a tetragonal structure, and to a cubic structure with a change in ambient temperature from a lower temperature side. A temperature at which the transition between the structures occurs is referred to as phase transition temperature. In the case of a piezoelectric ceramics, the piezoelectric constant takes a maximum value at around the phase transition temperature. Therefore, in the present invention, the temperature corresponding to the maximum value of the piezoelectric constant with respect to temperature is adopted as the phase transition temperature. The structures before and after the transition may be identified by X-ray diffraction measurement or electron beam diffraction measurement.
Meanwhile, the concentration change of a substituting element provides an effect of alleviating an abrupt change in piezoelectric constant at temperatures in the vicinity of the phase transition temperature.
The practical temperature region of the piezoelectric ceramics varies depending on its applications, but is generally from 0° C. or more to 40° C. or less. For example, when a temperature at which the piezoelectric constant becomes largest in the range of from 0° C. or more to 40° C. or less is represented by Tmax, and the absolute value of a piezoelectric constant d31 at Tmax is represented by dmax, if the extent of fluctuation in piezoelectric constant in the range of Tmax±10° C. falls within −15%, more preferably −10%, of dmax, the design of a device using such piezoelectric ceramics becomes easy. In addition, a case in which dmax is 140 pm/V or more is preferred because conversion efficiency between electrical energy and mechanical energy increases and the design of a device using such piezoelectric ceramics becomes easy.
When the phase transition temperature of the piezoelectric ceramics falls within the practical temperature region, the phase transition temperature coincides with Tmax.
The piezoelectric ceramics of the present invention also has reduced changes in relative dielectric constant and ferroelectricity with respect to temperature, and hence can be utilized as a dielectric material for various applications, such as a capacitor, a memory, and a sensor.
The piezoelectric ceramics of the present invention has the following features.
(Feature 1)
The piezoelectric ceramics of the present invention is formed of a single-piece piezoelectric ceramics. The term “single-piece piezoelectric ceramics” as used herein means a structurally seamless ceramics having piezoelectricity obtained by firing one compact.
The present invention has a feature in that composition and temperature properties are changed depending on sites in the single-piece piezoelectric ceramics. In contrast, a configuration that is not a single piece, obtained by bonding together a plurality of piezoelectric ceramics having different properties, is unsuitable for a piezoelectric actuator because modes of vibration generated from the piezoelectric ceramics are not unified.
It is preferred that at least part of the single-piece piezoelectric ceramics be subjected to polarization treatment to have the directions of spontaneous polarization axes aligned. When the polarization treatment is performed with an external electric field, the vibration generated from the piezoelectric ceramics of the present invention further increases.
The shape of the single-piece piezoelectric ceramics is not limited. With a view to forming a plurality of electrodes thereon to provide a piezoelectric element, the shape is preferably a plate shape having two or more flat surfaces, more preferably a flat plate shape, a rectangular plate shape, a disc shape, or a doughnut shape.
(Feature 2)
The piezoelectric ceramics of the present invention contains as a main component a perovskite-type metal oxide represented by the compositional formula of ABO3. It is more preferred that the crystal structure of the metal oxide forming the piezoelectric ceramics of the present invention be a so-called single phase formed only of a perovskite-type structure. For example, when the crystal structure of the metal oxide forming the piezoelectric ceramics has mixed therein a hexagonal structure, there is a risk in that the piezoelectric constant of the piezoelectric ceramics may be significantly lowered.
In the present invention, the perovskite-type metal oxide refers to a metal oxide having a perovskite-type structure (sometimes referred to as “perovskite structure”) that is ideally a cubic structure as described in Iwanami Rikagaku Jiten 5th Edition (published by Iwanami Shoten on Feb. 20, 1998). The metal oxide having a perovskite-type structure is generally represented by the compositional formula of ABO3. In the perovskite-type metal oxide, elements A and B occupy specific positions in a unit cell, which are called an A site and a B site, respectively, in the form of ions. For example, in the case of a cubic unit cell, the A site element occupies the corners of a cubic, and the B site element occupies a body-centered position of the cubic. An O element occupies the face-centered positions of the cubic as an anion of oxygen. The A site element is 12-coordinate, and the B site element is 6-coordinate. When the coordinates of each of the A site element, the B site element, and the O element slightly shift from a symmetrical position in a unit cell, the unit cell of the perovskite-type structure is distorted to become a crystal system such as a tetragonal, rhombohedral, or orthorhombic crystal system.
It is intended that, in the material of the present invention, ideally, Ba and M1 are positioned at the A site, and T1 and M2 are positioned at the B site. However, even when part of Ba and M1 are positioned at the B site, or part of T1 and M2 are positioned at the A site, the effect of the present invention is obtained.
In addition, the compositional formula of a perovskite-type metal oxide is generally expressed by ABO3. In actuality, however, owing to volatilization at the time of firing and an error in composition analysis, a quantitative ratio among the A site element, the B site element, and the oxygen element in the metal oxide as a whole is not necessarily 1:1:3. Such case also falls within the scope of the present invention as long as the oxide has a perovskite-type structure as a primary phase.
That the oxide has a perovskite-type structure may be judged from, for example, the measurement results of X-ray diffraction or electron beam diffraction on the piezoelectric ceramics. In the present invention, the concentrations of M1 and M2 undergo changes of increasing and decreasing in a certain direction, for example, a thickness direction. Therefore, it is preferred that the crystal structure be confirmed by performing diffraction measurement from a plurality of directions of the piezoelectric ceramics, or performing diffraction measurement for the piezoelectric ceramics that has been powdered.
A state in which the piezoelectric ceramics of the present invention contains as a main component the perovskite-type metal oxide represented by the compositional formula of ABO3 means that Ba, Ca, Bi, Ti, Zr, Sn, Hf, and O are detected as major components when the composition of the piezoelectric ceramics of the present invention is analyzed. For example, a case in which the sum total of Ba, Ca, Bi, Ti, Zr, Sn, Hf, and O is 97.5 mol % or more with respect to all elements detected in the composition analysis is preferred because the temperature stability of the piezoelectric constant, which is the effect of the present invention, is sufficiently obtained.
The piezoelectric ceramics of the present invention may contain auxiliary components for the purpose of adjusting properties. A case in which the content of the auxiliary components is less than 2.5 mol % in terms of sum total of elements with respect to all elements detected in the composition analysis is preferred because the temperature stability of the piezoelectric constant, which is the effect of the present invention, is hardly influenced.
Mn is given as an auxiliary component suitable for adjusting the properties of the piezoelectric ceramics of the present invention. When the piezoelectric ceramics of the present invention contains an appropriate amount of Mn, a high electrical insulation property is obtained. A piezoelectric ceramics having a high electrical insulation property reduces electric power to be consumed in the driving of an element including the piezoelectric ceramics. Mn has a property of varying in valence from divalent to tetravalent, and plays a role in compensating for a deficiency in charge balance in the piezoelectric ceramics.
When the amount of the Mn component contained in the piezoelectric ceramics is 0.3 part by mol or more and 1.5 parts by mol or less on a metal basis with respect to 100 parts by mol of the metal oxide (ABO3), a particularly high electrical insulation property is obtained.
Part or all of Mn serving as an auxiliary component may be positioned at any site in the unit cell of the perovskite-type metal oxide serving as the main component.
Elemental composition analysis of the main component and the auxiliary components contained in the piezoelectric ceramics of the present invention may be performed by ICP emission spectrometry, X-ray fluorescence analysis, atomic absorption spectrometry, mass spectrometry, or the like.
It is preferred that the piezoelectric ceramics of the present invention contain less than 1,000 ppm of a Pb component and a K component in total.
It is more preferred that the piezoelectric ceramics contain less than 500 ppm of the Pb component and less than 500 ppm of the K component. It is still more preferred that the piezoelectric ceramics contain less than 500 ppm of the Pb component and the K component in total.
When the amount of the Pb component contained in the piezoelectric ceramics of the present invention is reduced, the influence of the Pb component to be released into the environment when the piezoelectric ceramics is left in water or in soil can be reduced.
When the amount of the K component contained in the piezoelectric ceramics of the present invention is reduced, the moisture resistance of the piezoelectric ceramics and the efficiency in its high-speed vibration are enhanced.
(Feature 3)
The A site element in the metal oxide (ABO3) contains Ba and M1, and M1 is formed of at least one kind selected from the group consisting of Ca and Bi.
When Ba is mainly positioned at the A site of the perovskite-type structure, a barium titanate-type framework is stabilized, and hence a large piezoelectric constant is obtained in the practical temperature region including room temperature.
Besides, when the A site has mixed therein M1, namely, Ca or Bi, a temperature Tot, at which the kind of the perovskite-type structure of the metal oxide undergoes phase transition from an orthorhombic system to a tetragonal system can be shifted toward lower temperatures. A temperature Tto, at which transition from a tetragonal system to an orthorhombic system occurs, also shifts toward lower temperatures. As described later, the M2 element has an effect of shifting Tot and Tto to higher temperatures. By virtue of the combination of the M1 element and the M2 element, the phase transition temperature, namely, the temperature at which the piezoelectric constant becomes maximum can be adjusted to a desired temperature without sacrificing the piezoelectric constant.
The present invention has a feature in that the change in piezoelectric constant in the practical temperature region is reduced as a result of the concentration changes of components in the piezoelectric ceramics. The fluctuation in piezoelectric constant with respect to temperature resulting from the phase transition temperature can be alleviated by setting the concentration of M1 at a certain site in the ceramics to a relatively high level and setting the concentration of M1 at another site to a relatively low level.
In the A site element of the compositional formula, a case in which a ratio “x” of the molar amount of Ca to the total molar amount of Ba, Ca, and Bi falls within the range of 0.05≤x≤0.12 is preferred because the piezoelectric constant in the practical temperature region including room temperature becomes comparatively large. Similarly, a case in which a ratio “y” of the molar amount of Bi to the total molar amount of Ba, Ca, and Bi falls within the range of 0.001≤y≤0.005 is preferred because Tot can be lowered while the lowering of a Curie temperature is suppressed.
(Feature 4)
The B site element contains T1 and M2, and the M2 is formed of at least one kind selected from the group consisting of Zr, Sn, and Hf.
When Ti, which has a small ionic radius and has vacant d orbitals for electrons, is mainly positioned at the B site of the perovskite-type structure, the electrons of T1 and the electrons of O (oxygen) repulse each other and a large piezoelectric constant is obtained in the vicinity of room temperature.
Besides, when the B site has mixed therein M2, namely, Zr, Sn, or Hf, the anisotropy (c/a) of the tetragonal structure of the barium titanate-type framework reduces, and the stability of the tetragonal structure is lowered. As a result, the phase transition temperature Tot shifts to a higher temperature.
The coexistence of the M1 element and the M2 element provides the following advantage: even when local phase transition temperatures in the ceramics are distributed, local piezoelectric constants are kept uniform, and hence noise is not generated in a vibration wave generated from the piezoelectric ceramics.
In the B site element of the compositional formula, a case in which a ratio “1” of the molar amount of Zr to the total molar amount of Ti, Zr, Sn, and Hf, a ratio “m” of the molar amount of Sn to the total molar amount, and a ratio “n” of the molar amount of Hf to the total molar amount satisfy 0≤l≤0.08, 0≤m≤0.03, and 0≤n≤0.08, respectively, and in which “l”, “m”, and “n” have a relationship of 0.04≤l+2.5m+n≤0.08 is preferred because the piezoelectric constant in the practical temperature region increases.
The compositional formula ABO3 may be expressed as (Ba1-x-yCaxBiy)α(Ti1-t-m-nZr1SnmHfn)O3. The parameter “a” in the formula represents a ratio between the A site element number and the B site element number in the perovskite-type metal oxide. In order for the piezoelectric ceramics of the present invention to achieve a sufficient piezoelectric constant and to exhibit a high electrical insulation property, the range of “α” is preferably from 0.98 or more to 1.02 or less. An ideal value of “α” is 1.00, but in the case where a component for the Mn element is contained as an auxiliary component, part thereof can be positioned at the B site, and hence a particularly excellent piezoelectric property is exhibited when “a” represents 1.005 or more and 1.010 or less.
(Feature 5)
Concentrations of the M1 and the M2 change in at least one direction of the piezoelectric ceramics, and increase and decrease directions of concentration changes of the M1 and the M2 are directions opposite to each other.
In general, when a single raw material powder for a ceramics is sintered at a temperature equal to or higher than its crystallization temperature, a sintered body having no variation in concentration is obtained. For example, when a perovskite-type metal oxide expressed by the compositional formula of (Ba,M1)(Ti,M2)O3 to be used in the present invention is sintered by a general technique, the local variation in concentration of each of the M1 element and the M2 element at any site in the sintered body is within 1%.
In the piezoelectric ceramics of the present invention, the concentrations of both the M1 element and the M2 element change in at least one direction of the piezoelectric ceramics, and the concentration changes of the M1 element and the M2 element increase and decrease in directions opposite to each other.
In
Through the formation of electrodes on two opposed plate planes of the piezoelectric ceramics of the composition as shown in
The piezoelectric constant is an amount that indicates the degree of the displacement (elongation, contraction, or shear) of the piezoelectric ceramics at a time when a voltage is applied to the piezoelectric ceramics. The piezoelectric constant d31 is the coefficient of proportionality of a voltage with respect to a contraction (elongation) displacement in a direction orthogonal to the polarization direction of the piezoelectric ceramics when the voltage is applied in the polarization direction (generally a direction in which a voltage is applied during the polarization treatment), namely a displacement amount per unit voltage. Conversely, the piezoelectric constant may also be defined as the amount of charge to be induced when a stress is applied to the material. The piezoelectric constant d31 is generally expressed as a negative value, but herein, its absolute value |d31| is evaluated. A larger value for |d31| is preferred in applications of piezoelectric devices.
The piezoelectric constant of the piezoelectric ceramics may be determined by calculation, from the measurement results of a resonance frequency and an antiresonance frequency, which are obtained with a commercially available impedance analyzer, based on the standard of Japan Electronics and Information Technology Industries Association (JEITA EM-4501). This measurement method is referred to as resonance-antiresonance method.
Herein, a case in which the resonance-antiresonance method is used as a method of measuring the piezoelectric constant is described. However, alternatively, the piezoelectric constant may be calculated through the measurement of a displacement amount at the time of voltage application, or through the measurement of the amount of charge induced at the time of stress application, or a test may be performed using, in place of the piezoelectric constant, a change in another kind of piezoelectric constant, such as a d33 constant, with respect to temperature.
As shown in
In
The Tmax value of a piezoelectric ceramics may be controlled using a conventional technology.
In
Similarly, in
On the other hand, in the case of the piezoelectric ceramics of the present invention, the concentrations of the M1 element and the M2 element change in at least one direction of the piezoelectric ceramics, which, in the example of
In each of the examples of
As shown in
The concentration of the Ca element at the left end of the chart, namely, on one surface of the disc is 5 mol % in terms of ratio of the element in question to the sum of the amounts of substance of Ba, Ca, Ti, and Zr serving as main components, but the Ca concentration gradually decreases as the observation point is moved to the inside of the disc. The minimum concentration in this decrease gradient is about 4.85 mol %, and the concentration change is −3% with reference to the reference point. The concentration of the Ca element abruptly decreases in the vicinity of the center in the thickness direction of the disc. The concentration change in this region is −35%. Beyond that region, as the observation point approaches the right end of the chart, the concentration of the Ca element gradually decreases again at a change ratio of about −3%, and reaches 3 mol % at the right end of the chart, namely, on the opposite surface of the disc. As described above, in the example of
In contrast, the concentration of the Zr element monotonically increases from the left to the right of the chart through three kinds of gradients. That is, the Zr concentration at the left end of the chart is 2 mol %, and the concentration of the Zr element gradually increases as the observation point is moved to the inside of the disc. The concentration change in this increase gradient is +4%. The concentration of the Zr element abruptly increases in the vicinity of the center. The concentration change in this region is +60%. Thereafter, as the observation point approaches the right end of the chart, the concentration of the Zr element gradually increases again at a change ratio of about +4%, and reaches 3.5 mol % at the right end of the chart. That is, the increase and decrease directions of the concentration changes of the M1 element and the M2 element are directions opposite to each other. When M1 contains Bi, or M2 contains Sn or Hf, the increase and decrease tendency of the M1 element or the M2 element may be judged based on the total number of moles of those elements.
When, as described above, the concentrations of the M1 element and the M2 element change in at least one direction of the piezoelectric ceramics, and the increase and decrease directions of the concentration changes of the M1 element and the M2 element are directions opposite to each other, the extent of fluctuation in piezoelectric constant in the range of the Tmax±10° C. can be caused to fall within −15%, more preferably −10%, of dmax.
In the example of the disc-like ceramics shown in
Such concentration change is seemingly achieved also by bonding the ceramics of
A case in which, as in the example of
However, when raw materials are integrally sintered so as to form a single-piece ceramics, the migration (diffusion) of an element occurs, and hence a slight concentration gradient cannot be avoided. In that case, it is preferred that a plurality of regions each having a stable local phase transition temperature and a region in which the concentration abruptly changes for transition between the plurality of regions be stacked in the form of layers because transition between the local phase transition temperatures can occur in a stepwise manner. That is, it is preferred that the plurality of regions include at least three or more regions, including a first region in which the concentration change of at least one kind of the M1 or the M2 in a perpendicular direction of the layers is 5% or less, a second region in which the concentration change is 5% or more, and a third region in which the concentration change is 5% or less.
As shown in
In
The reduction of the change in piezoelectric constant itself can be achieved, without involving a concentration change, by, for example, further increasing the Ca concentration to further shift the phase transition temperature to a lower temperature. In that case, however, the dmax value in the practical temperature region decreases, and hence, for example, consumed electric power increases.
As shown in
The concentration of M1, namely, the Ca element monotonically decreases from 5 mol % at the left end of the chart to 4 mol % in three kinds of gradient modes, and the change ratios thereof are −2%, −25%, and −2% in order from the left.
The concentration of M2, namely, the Zr element monotonically increases from 2 mol % at the left end of the chart to 2.5 mol % in three kinds of gradient modes, and the change ratios thereof are +5%, +35%, and +5% in order from the left. That is, the increase and decrease directions of the concentration changes of the M1 element and the M2 element are directions opposite to each other.
The piezoelectric ceramics of the present invention in
In
As shown in
The concentration of M1, namely, the Ca element monotonically decreases from 4 mol % at the left end of the chart to 3 mol % in three kinds of gradient modes, and the change ratios thereof are −3.5%, −19%, and −3.5% in order from the left.
The concentration of M2, namely, the Zr element monotonically increases from 2.5 mol % at the left end of the chart to 3.5 mol % in three kinds of gradient modes, and the change ratios thereof are +5%, +28%, and +5% in order from the left. That is, the increase and decrease directions of the concentration changes of the M1 element and the M2 element are directions opposite to each other.
The piezoelectric ceramics of the present invention in
In
As shown in
The concentration of M1, namely, the Ca element changes in five kinds of gradient modes of first decreasing from 4 mol % at the left end of the chart to 3 mol % and then increasing to 5 mol %, and the change ratios thereof are −3.5%, −19%, 0%, +35%, and +3% in order from the left.
The concentration of M2, namely, the Zr element changes in five kinds of gradient modes of first increasing from 2.5 mol % at the left end of the chart to 3.5 mol % and then decreasing to 2 mol %, and the change ratios thereof are +5%, +28%, 0%, −60%, and −4% in order from the left. That is, the increase and decrease directions of the concentration changes of the M1 element and the M2 element are directions opposite to each other.
The piezoelectric ceramics of the present invention in
In
Although a manufacturing method for a piezoelectric ceramics having the features of the present invention is not particularly limited, a particularly preferred manufacturing method is described below.
The manufacturing method for a piezoelectric ceramics of the present invention has the following features.
where TotA and TotB represent respective orthorhombic-to-tetragonal phase transition temperatures of a first ceramics obtained by sintering the first ceramics precursor alone and a second ceramics obtained by sintering the second ceramics precursor alone, and d31A and d31B represent respective piezoelectric constants thereof after polarization treatment.
(Feature 7)
As illustrated in
The multilayered body refers to a solid substance formed from raw material powder or granulated powder of raw material powder, i.e., a so-called compact. That is, the ceramics precursors forming the multilayered body each refer to any one of raw material powder, granulated powder, or raw material powder-dispersed slurry containing the components of the piezoelectric ceramics that is the target product. The granulated powder and the dispersed slurry are products obtained by processing the raw material powder. The first ceramics precursor and the second ceramics precursor differ from each other in chemical composition. When a piezoelectric ceramics as shown in
A case in which the first ceramics precursor and the second ceramics precursor each contain Ba and T1 is preferred because the piezoelectric constant of the piezoelectric ceramics after sintering is stably high against the ambient temperature.
The content ratio of Ba contained in each of the first ceramics precursor and the second ceramics precursor is preferably 40 mol % or more and 50 mol % or less with respect to the molar amount of all metals contained in the precursor. When the precursors each contain Ba in the range, the piezoelectric constant in the practical temperature region of the piezoelectric ceramics after sintering increases.
The content ratio of T1 contained in each of the first ceramics precursor and the second ceramics precursor is preferably 45 mol % or more and 50 mol % or less with respect to the molar amount of all metals contained in the precursor. When the precursors each contain T1 in the range, the piezoelectric constant in the practical temperature region of the piezoelectric ceramics after sintering increases.
The raw material powder to be contained in each of the first and second ceramics precursors preferably has a high purity. For example, when the ceramics precursors are each produced using only raw material powder having a purity of 99.9% or more, the lowering of the piezoelectric constant due to the influence of an unintentional impurity component can be avoided in the piezoelectric ceramics after sintering.
Examples of a metal compound that may be used for the raw material powder may include a Ba compound, a Ca compound, a Bi compound, a T1 compound, a Zr compound, a Sn compound, a Hf compound, a Mn compound, and composite compounds thereof.
Examples of the Ba compound that may be used include barium oxide, barium carbonate, barium oxalate, barium acetate, barium nitrate, barium titanate, barium zirconate, barium stannate, barium calcium titanate, and calcined composite powders of various metals.
Examples of the Ca compound that may be used include calcium oxide, calcium carbonate, calcium oxalate, calcium acetate, calcium titanate, calcium zirconate, calcium stannate, calcium zirconate titanate, barium calcium titanate, and calcined composite powders of various metals.
Examples of the Bi compound that may be used include bismuth oxide, bismuth nitrate, bismuth chloride, bismuth titanate, and calcined composite powders of various metals.
Examples of the T1 compound that may be used include titanium oxide, barium titanate, barium calcium titanate, bismuth titanate, and calcined composite powders of various metals.
Examples of the Zr compound that may be used include zirconium oxide, barium zirconate, calcium zirconate, barium zirconate titanate, calcium zirconate titanate, and calcined composite powder of various metals.
Examples of the Sn compound that may be used include tin oxide containing divalent or tetravalent Sn, barium stannate, calcium stannate, barium calcium stannate, and calcined composite powders of various metals.
Examples of the Hf compound that may be used include hafnium oxide, barium hafnate, and calcined composite powders of various metals.
Examples of the Mn compound that may be used include manganese oxide containing divalent to tetravalent Mn, manganese carbonate, manganese acetate, manganese oxalate, and calcined composite powders of various metals.
Raw material powder particularly desired for forming each of the ceramics precursors is powder of barium titanate, calcium titanate, barium zirconate, calcium zirconate, bismuth oxide, or manganese oxide. Such raw material powder can be obtained at a high purity, and moreover, has rich chemical reactivity for forming complex perovskite-type metal oxides forming a solid solution with each other.
The raw material powder may be subjected to calcining treatment at a maximum temperature of 800° C. or more and 1,000° C. or less before being used for granulation, slurrying, and forming.
When the ceramics precursors are to be obtained as granulated powders, the raw material powder is subjected to granulation treatment. When a multilayered body is manufactured by stacking granulated powders as the ceramics precursors, there is an advantage in that crystal grains of a sintered body using the multilayered body are likely to have a uniform size distribution. A method for the granulation treatment is not particularly limited. From the viewpoint that the particle diameters of the granulated powder can be made more uniform, a spray drying method is the most preferred granulation method. Examples of a binder that may be used in the granulation include polyvinyl alcohol (PVA), polyvinyl butyral (PVB), and an acrylic resin. The amount of the binder to be added is preferably from 1 part by weight to 10 parts by weight with respect to the raw material powder of the piezoelectric ceramics, and is more preferably from 2 parts by weight to 7 parts by weight from the viewpoint that the density of the compact increases.
A method of obtaining the ceramics precursors in dispersed slurry form is described later in the section for a manufacturing method for a piezoelectric element based on sheet forming.
A method of stacking the first and second ceramics precursors in powder form is not particularly limited, but the stacking may be performed by a technique involving, for example, sequentially loading the precursors in powder form into a mold for compressing and pressing a compact, followed by uniaxial pressing. When the first and second ceramics precursors in slurry form are to be stacked, the stacking may be performed by forming each of the first and second ceramics precursors into green sheets in advance and stacking a required number of sheets, followed by compression bonding.
In order to increase its density, the multilayered body is more preferably subjected to external pressing treatment, such as uniaxial pressing, cold isostatic pressing, or hot isostatic pressing.
(Feature 8)
The multilayered body is sintered to become a single-piece piezoelectric ceramics.
A method of sintering the multilayered body is not particularly limited.
Examples of the sintering method include sintering using an electric furnace, sintering using a gas furnace, a conduction heating method, a microwave sintering method, a millimeter-wave sintering method, and hot isostatic pressing (HIP). The electric furnace and the gas furnace for the sintering may each be a continuous furnace or a batch furnace.
A sintering temperature in the sintering method is not particularly limited, but is preferably a temperature at which each compound reacts to cause sufficient crystal growth. However, when the sintering is performed at an excessively high temperature, there is a risk in that the diffusion of the M1 element and the M2 element progresses excessively, with the result that a desired concentration distribution cannot be obtained.
When the viewpoint of causing the grain diameter of the ceramics to fall within the range of from 1 μm to 100 in which processability is good, is also taken into consideration in addition to the viewpoints of crystal growth and concentration distribution, the sintering temperature is preferably 1,150° C. or more and 1,400° C. or less, more preferably 1,250° C. or more and 1,360° C. or less. A piezoelectric ceramics sintered in the above-mentioned temperature range exhibits a satisfactory insulation property and a high piezoelectric constant. In order to stabilize the properties of the piezoelectric ceramics to be obtained by the sintering treatment with good reproducibility, it is appropriate that the sintering treatment be performed with the sintering temperature being set constant in the above-mentioned range for 1 hour or more and 48 hours or less, more preferably 2 hours or more and 24 hours or less. In addition, a sintering method such as a two-stage sintering method may be used, and a method that does not involve an abrupt temperature change is preferred in consideration of productivity.
(Feature 9)
The first ceramics precursor and the second ceramics precursor differ from each other in chemical composition, and it is a feature of the manufacturing method of the present invention that, in the preparation of the compositions, such compositions as to satisfy 5° C.≤|TotA−TotB|≤30° C. and 0≤2|d31A−d31B|/|d31A+d31B|≤0.2 are selected.
For example, when a single-piece piezoelectric ceramics having the composition distribution as shown in
In this case, the orthorhombic-to-tetragonal phase transition temperature TotA of the first ceramics obtained by sintering the first ceramics precursor alone is 5° C. as can be read from the chart of
In order that, while the same base material, for example, a barium titanate-based material is used for each of the first ceramics precursor and the second ceramics precursor, TotA and TotB may differ by 5° C. or more and 30° C. or less and d31A and d31B may not differ too much, it is preferred that the first ceramics precursor and the second ceramics precursor each contain at least one element selected from the group consisting of Ca, Zr, Sn, Hf, and Bi. Ca and Bi each have an effect of shifting Tot to a lower temperature side depending on the substitution amount thereof. Zr, Sn, and Hf each have an effect of shifting Tot to a higher temperature side depending on the substitution amount thereof. In particular, the substitution of the T1 site with Zr is preferred because the degree of lowering of the Curie temperature of the piezoelectric ceramics is comparatively small.
When |TotA−TotB| is 5° C. or more, the following effect is obtained: the change ratio of the piezoelectric constant in the range of Tmax±10° C. is remarkably smaller than that of a piezoelectric ceramics obtained from a single ceramics precursor. In addition, when |TotA−TotB| is 30° C. or less, a large piezoelectric constant can be obtained as a whole in the range of Tmax±10° C. A more preferred range of |TotA−TotB| is from 10° C. or more to 30° C. or less.
In addition, in order to cause Tmax to fall within the practical temperature region of the piezoelectric ceramics, it is preferred that the average value of TotA and TotB, namely, (TotA+TotB)/2 be 0° C. or more and 30° C. or less. It is more preferred that (TotA+TotB)/2 be 10° C. or more and 30° C. or less.
(Piezoelectric Element)
Next, the piezoelectric element of the present invention is described.
The piezoelectric property of the piezoelectric ceramics of the present invention may be evaluated by forming the piezoelectric element including at least the first electrode 1 and the second electrode 3. The first electrode 1 and the second electrode 3 are each formed of a conductive layer having a thickness of from about 5 nm to about 10 μm. A material therefor is not particularly limited, and only needs to be one to be generally used for a piezoelectric element. Examples thereof may include metals, such as Ti, Pt, Ta, Ir, Sr, In, Sn, Au, Al, Fe, Cr, Ni, Pd, Ag, and Cu, and compounds thereof.
Each of the first electrode 1 and the second electrode 3 may be formed of one kind of those materials, or may be obtained by stacking two or more kinds thereof. In addition, the first electrode 1 and the second electrode 3 may be formed of materials different from each other.
A production method for each of the first electrode 1 and the second electrode 3 is not limited. The first electrode 1 and the second electrode 3 may each be formed by baking a metal paste or by sputtering, vapor deposition, or the like. In addition, both the first electrode 1 and the second electrode 3 may be patterned in desired shapes before use.
(Polarization)
It is more preferred that the piezoelectric element have spontaneous polarization axes aligned in a certain direction. When the spontaneous polarization axes are aligned in a certain direction, the piezoelectric constant of the piezoelectric element increases.
A polarization method for the piezoelectric element is not particularly limited. The polarization treatment may be performed in the air or may be performed in silicone oil. A temperature at which the polarization is performed is preferably a temperature of from 60° C. to 150° C. However, optimum conditions slightly vary depending on the composition of the piezoelectric ceramics for forming the element. An electric field to be applied for performing the polarization treatment is preferably from 800 V/mm to 3.0 kV/mm.
(Multilayered Piezoelectric Element)
Next, a multilayered piezoelectric element serving as one embodiment of the piezoelectric element is described.
In the multilayered piezoelectric element according to the present invention, the piezoelectric ceramics portion 2 includes at least one internal electrode, and the piezoelectric element has a multilayered structure in which piezoelectric ceramics layers each formed of the piezoelectric ceramics and the at least one internal electrode in a form of a layer are alternately stacked.
That is, in each of the piezoelectric ceramics layers 54, 504, the concentrations of the M1 element and the M2 element change in directions opposite to each other.
The electrode layer may include external electrodes, such as a first electrode 51, 501 and a second electrode 53, 503, in addition to the internal electrode 55, 505.
The internal electrodes 55, 505a, and 505b, the external electrodes 506a and 506b, the first electrodes 51 and 501, and the second electrodes 53 and 503 do not need to be identical in size and shape to the piezoelectric ceramics layers 54 and 504, and may each be divided into a plurality of portions.
The internal electrodes 55 and 505, the external electrodes 506a and 506b, the first electrodes 51 and 501, and the second electrodes 53 and 503 are each formed of a conductive layer having a thickness of from about 5 nm to about 10 μm. A material for each of the electrodes is not particularly limited and only needs to be one to be generally used for a piezoelectric element. Examples thereof may include metals, such as Ti, Pt, Ta, Ir, Sr, In, Sn, Au, Al, Fe, Cr, Ni, Pd, Ag, and Cu, and compounds thereof. Each of the internal electrodes 55 and 505 and the external electrodes 506a and 506b may be formed of one kind thereof, may be formed of a mixture or alloy of two or more kinds, or may be formed of a multilayered body of two or more kinds thereof. In addition, a plurality of electrodes may be respectively formed of materials different from each other.
In the multilayered piezoelectric element using the piezoelectric ceramics of the present invention, the internal electrode 55, 505 contains Ag and Pd, and a weight ratio MAg/MPd between the content weight MAg of the Ag and the content weight MPd of the Pd preferably falls within the range of 1.5≤MAg/MPd≤9.0. A case in which the weight ratio MAg/MPd is less than 1.5 is not desired because the increase of the Pd component increases electrode cost, though the heat resistance of the internal electrode 55, 505 is high. Meanwhile, a case in which the weight ratio MAg/MPd is more than 9.0 is not desired because, owing to the lack of the heat-resistant temperature of the internal electrode, the internal electrode is formed in an island shape, resulting in in-plane non-uniformity. From the viewpoints of heat resistance and cost, the weight ratio MAg/MPd more preferably falls within the range of 2.0≤MAg/MPd≤5.0.
From the viewpoint that an electrode material is inexpensive, it is preferred that the internal electrode 55, 505 contain at least any one kind selected from the group consisting of Ni and Cu. When at least any one kind selected from the group consisting of Ni and Cu is used for the internal electrode 55, 505, the multilayered piezoelectric element of the present invention is preferably fired in a reducing atmosphere.
As illustrated in
(Manufacturing Method for Piezoelectric Element or Multilayered Piezoelectric Element based on Sheet Forming)
Although a manufacturing method for the multilayered piezoelectric element according to the present invention is not particularly limited, a production method therefor is exemplified below. First, a step (A) of obtaining each of a slurry 1 serving as the first ceramics precursor and a slurry 2 serving as the second ceramics precursor from metal oxide powder, and a step (B) including separately placing the slurry 1 and the slurry 2 on base materials to form sheets, and integrating the sheets to obtain a compact are performed. After that, a step (C) of forming electrodes on the compact and a step (D) of sintering the compact having the electrodes formed thereon to obtain a multilayered piezoelectric element are performed.
In this case, when the step (C) is omitted and external electrodes are formed after the sintering of the step (D), a single plate-type piezoelectric element as illustrated in
The metal oxide powder that may be used in the step (A) is as exemplified as the raw material powder. A method of selecting each of the compositions of the slurry 1 and the slurry 2 is as described in the feature (9). The metal oxide powder is more preferably subjected to calcining treatment at a maximum temperature of 800° C. or more and 1,200° C. or less before being slurried.
A method of preparing each of the slurries in the step (A) is exemplified. A solvent is added in a weight of 1.6-fold to 1.7-fold with respect to the metal compound powder, followed by mixing. As the solvent, for example, toluene, ethanol, a mixed solvent of toluene and ethanol, n-butyl acetate, or water may be used. The components are mixed in a ball mill for 24 hours, and then minute amounts of the binder and the plasticizer are added.
Examples of the binder include polyvinyl alcohol (PVA), polyvinyl butyral (PVB), and an acrylic resin. Examples of the plasticizer include dioctyl sebacate, dioctyl phthalate, and dibutyl phthalate. When dibutyl phthalate is used as the plasticizer, equal weights of dibutyl phthalate and the binder are weighed. Then, mixing in a ball mill is performed again overnight. The amounts of the solvent and the binder are adjusted so that the viscosity of each of the slurries is from 300 mPa·s to 500 mPa·s.
The sheets in the step (B) are each a sheet-shaped mixture of the metal compound powder, the binder, and the plasticizer. As a method of obtaining each of the sheets in the step (B), for example, there is given sheet forming. For example, a doctor blade method may be used for the sheet forming. The doctor blade method is a method of forming a sheet-shaped compact involving applying the slurry onto the base material with a doctor blade and drying the applied slurry.
As each of the base materials, for example, a PET film may be used. It is desired that the surface of the PET film onto which the slurry is applied be coated with, for example, fluorine because the coating facilitates the peeling of the compact. The drying may be natural drying or hot-air drying. The thickness of the compact is not particularly limited, and may be adjusted depending on the thickness of the multilayered piezoelectric element. The thickness of the compact may be increased by, for example, increasing the viscosity of each of the slurries.
A sheet 1 obtained from the slurry 1 and a sheet 2 obtained from the slurry 2 are stacked and subjected to compression bonding to be used as one sheet in the next step (C). In order to adjust a thickness after the sintering, a stack of a plurality of the sheets 1 and a stack of a plurality of the sheets 2 may be subjected to compression bonding. As a method for the compression bonding, there are given uniaxial pressing, cold isostatic pressing, and hot isostatic pressing.
A production method for each of the electrodes in the step (C), that is, the internal electrodes 505 and the external electrodes 506a and 506b is not limited. The electrodes may each be formed by baking a metal paste or by sputtering, vapor deposition, a printing method, or the like. For the purpose of reducing a driving voltage, the layer thicknesses and pitch interval of the piezoelectric ceramics layers 504 are reduced in some cases. In that case, there is selected a process involving forming a multilayered body including precursors for the piezoelectric ceramics layers 504 and the internal electrodes 505a and 505b, and then firing the multilayered body simultaneously. In that case, there is demanded an internal electrode material that does not undergo deformation or conductivity deterioration at a temperature required for sintering the piezoelectric ceramics layers 504. A metal that has a low melting point and is inexpensive as compared to Pt, such as Ag, Pd, Au, Cu, or Ni, or an alloy thereof may be used for each of the internal electrodes 505a and 505b and the external electrodes 506a and 506b. In this connection, the external electrodes 506a and 506b may be formed after the firing of the multilayered body. In that case, Al or a carbon-based electrode material may be used in addition to Ag, Pd, Cu, or Ni.
A method of forming each of the electrodes is desirably a screen printing method. The screen printing method is a method involving placing a screen printing plate on a compact placed on a base material and applying a metal paste with a spatula from above the screen printing plate. A screen mesh is formed on at least part of the screen printing plate. Thus, the metal paste at a portion on which the screen mesh is formed is applied onto the compact. The screen mesh in the screen printing plate desirably has a pattern formed therein. An electrode may be patterned onto the compact by transferring the pattern onto the compact through the use of the metal paste.
After the formation of the electrodes in the step (C), one or a plurality of sheets of the compact peeled from the base material are stacked and subjected to compression bonding. As a method for the compression bonding, there are given uniaxial pressing, cold isostatic pressing, and hot isostatic pressing. The hot isostatic pressing is desired because a pressure can be applied isotropically and uniformly. It is desired to heat the compact to around the glass transition temperature of the binder during the compression bonding because more satisfactory compression bonding can be achieved. A plurality of sheets of the compact may be stacked and subjected to compression bonding so as to achieve a desired thickness. For example, 5 to 100 sheets of the compact may be stacked and then subjected to thermocompression bonding involving applying a pressure of from 10 MPa to 60 MPa in a stacking direction over 10 seconds to 10 minutes at from 50° C. to 80° C., to thereby stack the sheets of the compact. In addition, a plurality of sheets of the compact may be aligned and stacked with good accuracy by providing the electrodes with alignment marks. Of course, a plurality of sheets of the compact may also be stacked with good accuracy by forming a through-hole for positioning in the compact.
The sintering temperature of the compact in the step (D) is not particularly limited, but is preferably a temperature at which each compound reacts to cause sufficient crystal growth. A preferred sintering temperature is 1,100° C. or more and 1,400° C. or less, more preferably 1,150° C. or more and 1,300° C. or less, from the viewpoint of causing the grain diameter of the ceramics to fall within the range of from 0.2 μm to 50 μm. A multilayered piezoelectric element sintered in the above-mentioned temperature range exhibits satisfactory piezoelectric performance.
However, when a material containing Ni as a main component is used for each of the electrodes in the step (C), the step (D) is preferably performed in a furnace capable of atmosphere firing. The binder is removed by combustion at a temperature of from 200° C. to 600° C. in an air atmosphere, and then the atmosphere is changed to a reducing atmosphere, in which sintering is performed at a temperature of from 1,200° C. to 1,550° C. The term “reducing atmosphere” as used herein refers to an atmosphere mainly formed of a mixed gas of hydrogen (H2) and nitrogen (N2). A volume ratio between hydrogen and nitrogen preferably falls within the range of from H2:N2=1:99 to H2:N2=10:90. In addition, the mixed gas may contain oxygen. The oxygen concentration thereof when the total pressure of the mixed gas is 1 Pa is 10−12 Pa or more and 10−4 Pa or less, more preferably 10−8 Pa or more and 10−5 Pa or less. The oxygen concentration may be measured with a zirconia-type oxygen sensor. When a Ni electrode is used, the multilayered piezoelectric element of the present invention can be inexpensively manufactured. After firing in the reducing atmosphere, it is preferred that the temperature be decreased to 600° C., the atmosphere be replaced with an air atmosphere (oxidizing atmosphere), and oxidation treatment be performed. After removal from the firing furnace, a conductive paste is applied to a side surface of the compact on which end portions of the internal electrodes are exposed, followed by drying, to form external electrodes.
(Vibration Device, and Image Pickup Apparatus serving as Electronic Device)
The shapes and arrangement of the members are not limited to the examples of
The piezoelectric element 330 includes a piezoelectric ceramics 331, a first electrode 332, and a second electrode 333, and the first electrode 332 and the second electrode 333 are arranged so as to be opposed to each other on the plate planes of the piezoelectric ceramics 331. In the case of the multilayered piezoelectric element, the piezoelectric ceramics 331 has an alternate structure of a piezoelectric ceramics layer and an internal electrode, and can provide driving waveforms different from each other in phase depending on layers of the piezoelectric ceramics by short-circuiting the internal electrode with the first electrode 332 or the second electrode 333 alternately. In
When an alternating voltage is externally applied to the piezoelectric element 330, a stress is generated between the piezoelectric element 330 and the diaphragm 320 to generate out-of-plane oscillation in the diaphragm 320. The dust removing device 310 is a device configured to remove foreign matter, such as dust, sticking to the surface of the diaphragm 320 by the out-of-plane oscillation of the diaphragm 320. The out-of-plane oscillation refers to elastic vibration in which the diaphragm is displaced in an optical axis direction, namely in the thickness direction of the diaphragm.
Next, an image pickup apparatus using the dust removing device is described.
The image pickup apparatus may also be said to be an example of the electronic device of the present invention. In
In the camera main body 601 illustrated in
In
Herein, the digital single-lens reflex camera has been described as an example of the image pickup apparatus, but the image pickup apparatus may be a camera with an interchangeable imaging lens unit, such as a mirrorless digital single-lens camera without the mirror box 605. In addition, the present invention may also be applied to various types of image pickup apparatus or electronic and electric devices including the image pickup apparatus, such as a video camera with an interchangeable imaging lens unit, a copying machine, a facsimile, and a scanner, in particular, a device that is required to remove dust sticking to the surface of an optical component.
(Other Electronic Device Examples 1: Liquid Ejection Head and Liquid Ejection Apparatus)
As illustrated in
The liquid ejection head includes discharge ports 105, independent liquid chambers 103, communicating holes 106 for connecting the independent liquid chambers 103 and the discharge ports 105, liquid chamber partition walls 104, a common liquid chamber 107, a diaphragm 102, and the piezoelectric element 101. In general, the piezoelectric ceramics 1012 has a shape in conformity with the shape of the independent liquid chamber 103.
When the liquid ejection head serving as an example of the electronic device of the present invention is driven by inputting an electric signal thereinto, the diaphragm 102 vibrates up and down in accordance with the deformation of the piezoelectric element 101 to apply a pressure to a liquid stored in each of the independent liquid chambers 103. As a result, the liquid is discharged from each of the discharge ports 105. The liquid ejection head may be used for incorporation into a printer configured to perform printing on various media or manufacture of an electronic device.
Next, a liquid ejection apparatus using the liquid ejection head is described.
The liquid ejection apparatus may also be said to be an example of the electronic device of the present invention. In
The liquid ejection apparatus of
In such liquid ejection apparatus, the carriage 892 carries the liquid ejection head in accordance with an instruction from an external computer, and ink is discharged from the discharge ports 105 of the liquid ejection head in response to a voltage applied to the piezoelectric element 101. Thus, printing is performed.
In the example described above, the printer is exemplified. However, the liquid ejection apparatus of the present invention may be used as a printing apparatus, such as an ink jet recording apparatus, e.g., a facsimile, a multifunctional peripheral, or a copying machine, or as an industrial liquid ejection apparatus or a drawing apparatus for an object. In addition, a user may select a desired transfer material depending on applications.
(Other Electronic Device Examples 2: Vibration Wave Motor and Optical Device)
The application of two alternating voltages different from each other in phase by an odd multiple of π/2 to the piezoelectric element 2012 results in the generation of a flexural traveling wave in the vibration body 201, and hence each point on the sliding surface of the vibration body 201 undergoes an elliptical motion. The moving body 202 receives a frictional force from the vibration body 201 to rotate in the direction opposite to the flexural traveling wave. A body to be driven (not shown) is joined to the output shaft 203, and is driven by the rotary force of the moving body 202.
Next, a vibration wave motor including a piezoelectric element having a multilayered structure (multilayered piezoelectric element) is illustrated in
The application of alternating voltages different from each other in phase to the multilayered piezoelectric element 2042 causes the vibration body 204 to excite two vibrations orthogonal to each other. The two vibrations are combined to form a circular vibration for driving the tip portion of the vibration body 204. A constricted annular groove is formed in the upper portion of the vibration body 204 to enlarge the displacement of the vibration for driving.
A moving body 205 (also referred to as rotor) is brought into contact with the vibration body 204 under pressure by a spring 206 for pressurization to obtain a frictional force for driving. The moving body 205 is rotatably supported by a bearing.
Next, an optical device using the vibration wave motor is described.
The optical device may also be said to be an example of the electronic device of the present invention. In
A fixed barrel 712, a linear guide barrel 713, and a front unit barrel 714 are fixed to an attaching/detaching mount 711 for a camera. Those members are fixed members of the interchangeable lens barrel.
A linear guide groove 713a in an optical axis direction for a focus lens 702 is formed on the linear guide barrel 713. Cam rollers 717a and 717b protruding outward in a radial direction are fixed to a rear unit barrel 716 holding the focus lens 702 via axial screws 718, and the cam roller 717a is fitted in the linear guide groove 713a.
A cam ring 715 is fitted on the inner periphery of the linear guide barrel 713 in a rotatable manner. Relative movement between the linear guide barrel 713 and the cam ring 715 in the optical axis direction is restricted because a roller 719 fixed to the cam ring 715 is fitted in an annular groove 713b of the linear guide barrel 713. A cam groove 715a for the focus lens 702 is formed on the cam ring 715, and the above-mentioned cam roller 717b is simultaneously fitted in the cam groove 715a.
On the outer peripheral side of the fixed barrel 712, there is arranged a rotation transmission ring 720 held by a ball race 727 in a rotatable manner at a constant position with respect to the fixed barrel 712. The rotation transmission ring 720 has shafts 720f extending radially from the rotation transmission ring 720, and rollers 722 are held by the shafts 720f in a rotatable manner. A large diameter part 722a of the roller 722 is brought into contact with a mount side end surface 724b of a manual focus ring 724. In addition, a small diameter part 722b of the roller 722 is brought into contact with a joining member 729. Six rollers 722 are arranged on the outer periphery of the rotation transmission ring 720 at regular intervals, and each roller is arranged in the relationship as described above.
A low friction sheet (washer member) 733 is arranged on an inner diameter part of the manual focus ring 724, and this low friction sheet is sandwiched between a mount side end surface 712a of the fixed barrel 712 and a front side end surface 724a of the manual focus ring 724. In addition, an outer diameter surface of the low friction sheet 733 is formed in a ring shape so as to be circumferentially fitted on an inner diameter part 724c of the manual focus ring 724. Further, the inner diameter part 724c of the manual focus ring 724 is circumferentially fitted on an outer diameter part 712b of the fixed barrel 712. The low friction sheet 733 has a role of reducing friction in a rotation ring mechanism in which the manual focus ring 724 rotates relatively to the fixed barrel 712 about the optical axis.
The large diameter part 722a of the roller 722 is brought into contact with the mount side end surface 724b of the manual focus ring under a state in which a pressure is applied by a pressing force of a waved washer 726 pressing a vibration wave motor 725 to the front of the lens. In addition, similarly, the small diameter part 722b of the roller 722 is brought into contact with the joining member 729 under a state in which an appropriate pressure is applied by a pressing force of the waved washer 726 pressing the vibration wave motor 725 to the front of the lens. Movement of the waved washer 726 in the mount direction is restricted by a washer 732 connected to the fixed barrel 712 by bayonet joint. A spring force (biasing force) generated by the waved washer 726 is transmitted to the vibration wave motor 725, and further to the roller 722, to be a force for the manual focus ring 724 to press the mount side end surface 712a of the fixed barrel 712. In other words, the manual focus ring 724 is integrated under a state in which the manual focus ring 724 is pressed to the mount side end surface 712a of the fixed barrel 712 via the low friction sheet 733.
Therefore, when a control unit (not shown) drives the vibration wave motor 725 to rotate with respect to the fixed barrel 712, the rollers 722 rotate about the shafts 720f because the joining member 729 is brought into frictional contact with the small diameter parts 722b of the rollers 722. As a result of the rotation of the rollers 722 about the shafts 720f, the rotation transmission ring 720 rotates about the optical axis.
Two focus keys 728 are mounted to the rotation transmission ring 720 at opposing positions, and the focus key 728 is fitted to a notch portion 715b arranged on the tip of the cam ring 715. Therefore, when the rotation transmission ring 720 rotates about the optical axis, the rotation force is transmitted to the cam ring 715 via the focus key 728. When the cam ring is rotated about the optical axis, the rear unit barrel 716 whose rotation is restricted by the cam roller 717a and the linear guide groove 713a is moved forward and backward along the cam groove 715a of the cam ring 715 by the cam roller 717b. Thus, the focus lens 702 is driven, and the focus operation is performed.
While the interchangeable lens barrel for the single-lens reflex camera has been described as the optical device using the vibration wave motor, the vibration wave motor can be applied to any optical device including the drive unit including the vibration wave motor, regardless of a type of the camera, including a compact camera, an electronic still camera, and the like.
The vibration device, the image pickup apparatus, the liquid ejection head, the liquid ejection apparatus, the vibration wave motor, and the optical device have been described above as examples of the electronic device of the present invention, but the kind of the electronic device is not limited thereto. The piezoelectric element of the present invention is applicable to all of the following: electronic devices each configured to detect an electric signal resulting from a positive piezoelectric effect or extract energy by extracting electric power from a piezoelectric element; and electronic devices each utilizing a displacement based on a converse piezoelectric effect obtained by inputting electric power into a piezoelectric element. For example, a piezoelectric acoustic component and a sound reproduction device, a sound recording device, a cellular phone, and an information terminal each including the piezoelectric acoustic component are also encompassed in the electronic device of the present invention.
The piezoelectric ceramics, piezoelectric element, vibration device, and electronic device of the present invention are hereinafter described more specifically by way of Examples. However, the present invention is not limited to the following Examples.
(Preparation of Ceramics Precursor)
A ceramics precursor containing Ba, Ca, Bi, Ti, Zr, Sn, and Hf and further containing Mn was prepared.
Raw material powders needed to form a composition of interest were selected from the following group of raw materials and used.
Commercially available powder of barium titanate (BaTiO3), barium zirconate (BaZrO3), or barium carbonate (BaCO3, purity: 99.9% or more) was used as a Ba raw material. Commercially available powder of calcium titanate (CaTiO3) was used as a Ca raw material. Commercially available powder of bismuth oxide (Bi2O3, purity: 99.9% or more, particle diameter: less than 500 nm) was used as a Bi raw material.
Commercially available powder of barium titanate (BaTiO3), calcium titanate (CaTiO3), or titanium oxide (TiO2, purity: 99.9% or more) was used as a T1 raw material. Commercially available powder of barium zirconate (BaZrO3) or calcium zirconate (CaZrO3) was used as a Zr raw material.
Commercially available powder of barium stannate (BaSnO3) or calcium stannate (CaSnO3) was used as a Sn raw material.
Commercially available powder of hafnium titanate (HfTiO3) was used as a Hf raw material.
First, in order to prepare a ceramics precursor of Production Example 1, the raw material powders were weighed so as to achieve a compositional ratio shown in Table 1, and were subjected to rotary mixing with a dry ball mill apparatus for 24 hours. Barium carbonate was used to adjust the “α” value. 3 mass % of a PVA binder was added to the mixed powder, and the mixture was subjected to granulation treatment with a spray dryer to provide the ceramics precursor of Production Example 1.
Ceramics precursors of Production Example 2 to Production Example 5, which were granulated powders of compositions shown in Table 1, were produced in the same manner as in Production Example 1.
Next, in order to find out the properties of each ceramics precursor alone, the granulated powder was filled into a mold and compressed to produce a disc-like compact. The resultant compact was put into an electric furnace having an air atmosphere, and was fired at a maximum temperature of 1,340° C. for 12 hours to provide a piezoelectric ceramics corresponding to each Production Example.
Next, the piezoelectric ceramics of each Production Example was polished so as to have a thickness of about 0.5 mm. In order to remove the internal stress of the piezoelectric ceramics resulting from the polishing treatment and organic components on the surface of the piezoelectric ceramics, the piezoelectric ceramics was subjected to heat treatment in an air atmosphere at 400° C. for 30 minutes.
Gold (Au) electrodes each having a thickness of 400 nm were formed on both front and rear surfaces of the piezoelectric ceramics after the heat treatment by a DC sputtering method. Titanium (Ti) was formed into a film having a thickness of 30 nm as a contact layer between the electrodes and the piezoelectric ceramics.
The piezoelectric ceramics with the electrodes was cut into a rectangular plate shape of 10 mm×2.5 mm×0.5 mmt suitable for the evaluation of properties. Thus, a piezoelectric element was produced.
For the purpose of aligning the spontaneous polarization axes of the piezoelectric element in a certain direction, the piezoelectric element was subjected to polarization treatment. Specifically, in a silicone oil bath kept at 150° C., a voltage of 1.2 kV/mm was applied to the sample for 30 minutes. While the voltage was applied, the sample was cooled to room temperature.
For the piezoelectric element that had been subjected to the polarization treatment, a resonance-antiresonance method was performed using an environmental test box and an impedance analyzer while the temperature was changed from −30° C. to +45° C. For example, in the case of the piezoelectric element using Production Example 1, measurement results as shown in
A piezoelectric ceramics of Example 1 was manufactured using the granulated powder of Production Example 3 as a first ceramics precursor, and using the granulated powder of Production Example 1 as a second ceramics precursor.
In this combination, |TotA−TotB| was 30° C., 2|d31A−d31B|/|d31A+d31B| was 0.05, and (TotA+TotB)/2 was 20° C.
The powder of the first ceramics precursor (Production Example 3) was placed on the inner bottom surface of a cylindrical mold, and the same weight of the powder of the second ceramics precursor (Production Example 1) was placed and filled thereon. The granulated powders were subjected to uniaxial compressing to provide a disc-like multilayered body (compact). The filling amounts of the powders were adjusted so that a thickness after firing was 0.8 mm.
The resultant compact was put into an electric furnace having an air atmosphere, and was fired at a maximum temperature of 1,340° C. for 4 hours to provide a single-piece piezoelectric ceramics of Example 1 of the present invention. The piezoelectric ceramics had a disc shape, and had a thickness of 0.8 mm.
Part (1 g or more) of the piezoelectric ceramics was powdered and subjected to X-ray diffraction measurement, and its crystal structure was identified by Rietveld analysis. As a result, it was found that the sample was mostly formed of a single perovskite-type structure of an ABO3 type.
The plate-like (disc-like) piezoelectric ceramics was analyzed for the composition in the depth direction thereof by alternately repeating X-ray fluorescence analysis and polishing from one surface side thereof. As a result, in each case of measurement, Ba, Ca, Ti, Zr, Mn, and O were detected. The content of Mn was 0.6 part by mol with respect to 100 parts by mol of the total number of moles of T1 and Zr, and there was no concentration change depending on sites in the ceramics. The content of a metal element other than Ba, Ca, Ti, Zr, and Mn was 0.1 mol % or less with respect to the total amount of all metal elements. The piezoelectric ceramics contained less than 100 ppm of Pb, and less than 200 ppm of K.
The concentrations of Ba, Ca, Ti, and Zr changed in the thickness direction of the plate-like piezoelectric ceramics. In particular, for Ca (Mi) and Zr (M2), change tendencies of the concentrations as shown in
That is, in Example 1, the concentrations of M1 and M2 changed in at least one direction of the piezoelectric ceramics, and the increase and decrease directions of the concentration changes of M1 and M2 were directions opposite to each other. In addition, the piezoelectric ceramics of Example 1 contained a plurality of regions different from each other in average composition in the form of layers. The plurality of regions included three regions, including a first region in which the concentration change of each of M1 and M2 in a perpendicular direction of the layers was 5% or less, a second region in which the concentration change was 5% or more, and a third region in which the concentration change was 5% or less.
A photograph obtained by magnified observation of a cross-section of the piezoelectric ceramics of Example 1 with a scanning electron microscope is shown in
Next, a piezoelectric element of the present invention using the piezoelectric ceramics of Example 1 was produced.
First, the baked disc-like piezoelectric ceramics was polished so as to have a thickness of about 0.5 mm. The treatment was performed so that the losses of thickness due to the polishing on both surfaces of the disc were equal to each other. In order to remove the internal stress of the piezoelectric ceramics resulting from the polishing treatment and organic components on the surface of the piezoelectric ceramics, the piezoelectric ceramics was subjected to heat treatment in an air atmosphere at 400° C. for 30 minutes.
Gold (Au) electrodes each having a thickness of 400 nm were formed on both front and rear surfaces of the piezoelectric ceramics after the heat treatment by a DC sputtering method. Titanium (Ti) was formed into a film having a thickness of 30 nm as a contact layer between the electrodes and the piezoelectric ceramics.
The piezoelectric ceramics with the electrodes was cut into a rectangular plate shape of 10 mm×2.5 mm×0.5 mm suitable for the evaluation of properties. Thus, the piezoelectric element of the present invention was obtained. The mechanical strength of the piezoelectric material of Example 1 was high enough to allow the polishing and the cutting to be performed without any problem.
For the purpose of aligning the spontaneous polarization axes of the piezoelectric element in a certain direction, the piezoelectric element was subjected to polarization treatment. Specifically, in a silicone oil bath kept at 150° C., a voltage of 1.2 kV/mm was applied to the sample for 30 minutes. While the voltage was applied, the sample was cooled to room temperature.
For the piezoelectric element that had been subjected to the polarization treatment, a resonance-antiresonance method was performed using an environmental test box and an impedance analyzer while the temperature was changed from −30° C. to +45° C. As a result, measurement results as shown in
As shown in Table 2, dmax was 143 pm/V, Tmax was 35° C., and the change ratio of the piezoelectric constant in the range of Tmax±10° C. was a decrease of 8.3%.
Next, piezoelectric ceramics of the present invention were manufactured in the same manner as in Example 1 except that the combination of the ceramics precursors was changed.
The combination of the ceramics precursors in each Example, and |TotA−TotB|, 2|d31A−d31B|/|d31A+d31B|, and (TotA+TotB)/2 in the combination are as shown in Table 2.
Example 4 differs from other Examples in that three kinds of ceramics precursors are used. In this case, the first ceramics precursor, the second ceramics precursor, and the third ceramics precursor were placed and filled in the stated order on the inner bottom surface of the cylindrical mold. Placed weights were set so that the precursors had equal weights.
In each of Examples, the single-piece piezoelectric ceramics of the present invention was obtained, and was found by X-ray diffraction measurement to have a perovskite-type structure of an ABO3 type as a primary phase.
The plate-like piezoelectric ceramics was analyzed for the composition in the depth direction thereof by alternately repeating X-ray fluorescence analysis and polishing from one surface side thereof. As a result, the following was found. For Examples 2, 3, and 4, Ba, Ca, Ti, Zr, Mn, and O were detected, and the content of any other metal element was 0.1 mol % or less with respect to the total amount of all metal elements. For Example 5, Ba, Ca, Bi, Zr, Sn, Mn, and O were detected, and the content of any other metal element was 0.1 mol % or less with respect to the total amount of all metal elements. For Example 6, Ba, Ca, Bi, Zr, Hf, Mn, and O were detected, and the content of any other metal element was 0.1 mol % or less with respect to the total amount of all metal elements. The content of Mn with respect to 100 parts by mol of the total number of moles of Ti, Zr, Sn, and Hf was as shown in Table 2, and there was no concentration change of Mn depending on sites in the ceramics. In each of Examples, the piezoelectric ceramics contained less than 100 ppm of Pb, and less than 200 ppm of K.
In all Examples, the concentrations of Ba, Ca, Bi, Ti, Zr, Sn, and Hf (except for undetected elements) changed in the thickness direction of the plate-like piezoelectric ceramics. For example, in the case of Example 2, change tendencies of the concentrations as shown in
That is, in all Examples, the concentrations of M1 and M2 changed in at least one direction of the piezoelectric ceramics, and the increase and decrease directions of the concentration changes of M1 and M2 were directions opposite to each other.
Next, the piezoelectric element of the present invention was produced in the same manner as in Example 1 using each of the piezoelectric ceramics of Examples 2 to 6.
For the piezoelectric element that had been subjected to polarization treatment, a resonance-antiresonance method was performed using an environmental test box and an impedance analyzer while the temperature was changed from −30° C. to +45° C. As a result, measurement results as shown in
For all Examples, dmax, Tmax, and the change ratio of the piezoelectric constant in the range of Tmax±10° C. are shown in Table 2. The minus sign in the change ratio means a decrease in piezoelectric constant. The change ratio of the piezoelectric constant in the range of Tmax±10° C. was less than −15% in each of Examples, and particularly in each of Examples 1, 3, and 4, the change was as small as less than −10%.
Next, piezoelectric ceramics for comparison were manufactured in the same manner as in Examples 1 to 6.
As shown in Table 2, the granulated powder of the same Production Example was used for each of the first ceramics precursor and the second ceramics precursor.
In each of Comparative Examples, a single-piece ceramics was obtained, and was found by X-ray diffraction measurement to have a perovskite-type structure as a primary phase.
The composition in the depth direction was analyzed in the same manner as in Examples. As a result, for all the samples of Comparative Examples, Ba, Ca, Ti, Zr, Mn, and O were detected, and the content of any other metal element was 0.1 mol % or less with respect to the total amount of all metal elements. The content of Mn with respect to 100 parts by mol of the total number of moles of T1 and Zr was as shown in Table 2.
The concentration changes of Ca and Zr depending on sites in the ceramics were as shown in
Next, the piezoelectric element for comparison was produced in the same manner as in Example 1 using each of the ceramics of Comparative Examples 1 to 3.
For the piezoelectric element that had been subjected to polarization treatment, a resonance-antiresonance method was performed using an environmental test box and an impedance analyzer while the temperature was changed from +45° C. to −30° C. As a result, measurement results as shown in
For all Comparative Examples, dmax, Tmax, and the change ratio of the piezoelectric constant in the range of Tmax±10° C. are shown in Table 2. The change ratio of the piezoelectric constant in the range of Tmax±10° C. was −24% or more in each of Comparative Examples, and was significantly larger than that of each of Examples.
The multilayered piezoelectric element of the present invention was produced in the following manner.
The mixed powders before spray drying granulation in Production Examples 1 to 5 were slurried with the addition of a PVB binder to provide ceramics precursors. Next, each of the ceramic precursors was formed into a sheet by a doctor blade method to provide a green sheet having a thickness of 50 μm.
In the same manner as in Examples 1 to 6, the first ceramics precursor and the second ceramics precursor, and as required, the third ceramics precursor were selected, and two or three green sheets were subjected to compression bonding to provide a green sheet having a composition distribution. The multilayered piezoelectric element of the present invention is obtained by alternately stacking the green sheet having a composition distribution and an internal electrode.
Correspondences between Examples and the kinds of ceramics precursors are shown in Table 3.
A conductive paste for an internal electrode was printed on the surface of the green sheet having a composition distribution. As the conductive paste, an Ag70%-Pd30% alloy (Ag/Pd=2.33) paste was used. Nine of the green sheets coated with the conductive paste were stacked, and the multilayered body was fired at 1,200° C. for 5 hours to obtain a sintered body. The thickness after the sintering was 0.6 mm in each of Examples 7 to 9, 11, and 12. The thickness of the sintered body in Example 10 was 0.9 mm. The sintered body was cut to a size of 10 mm×2.5 mm, and then side surfaces thereof were polished. A pair of external electrodes (first electrode and second electrode) for short-circuiting the internal electrodes alternately was formed by Au sputtering to produce the multilayered piezoelectric element as illustrated in
A cross-section of each of the multilayered piezoelectric elements of Example 7 to Example 12 was observed. As a result, it was found that the internal electrodes formed of Ag-Pd and the piezoelectric ceramics layers were alternately formed, and the M1 element and the M2 element increased and decreased in directions opposite to each other in the layer thickness direction in each of the piezoelectric ceramics layers.
The multilayered piezoelectric elements of Example 7 to Example 12 were each subjected to polarization treatment. Specifically, the sample was heated to 150° C. in an oil bath, and a voltage of 1.5 kV/mm was applied between the first electrode and the second electrode for 30 minutes. While the voltage was applied, the sample was cooled to room temperature.
The resultant multilayered piezoelectric elements were evaluated for their piezoelectric constants with respect to the ambient temperature in the same manner as in Examples 1 to 6. The results are shown in Table 3. Also in each of the piezoelectric elements of Examples 7 to 12, the extent of fluctuation in piezoelectric constant in the range of Tmax±10° C. was less than −15%, comparable to that in each of the piezoelectric elements of Examples 1 to 6.
Through the use of each of the piezoelectric elements of Examples 1 to 12, the dust removing device illustrated in
Through the use of the dust removing device, the image pickup apparatus illustrated in
Through the use of each of the piezoelectric elements of Examples 1 to 12, the liquid ejection head illustrated in
Through the use of the liquid ejection head, the liquid ejection apparatus illustrated in
Through the use of each of the piezoelectric elements of Examples 1 to 12, the ultrasonic motor illustrated in
Through the use of the ultrasonic motor, the optical device illustrated in
The piezoelectric material of the present invention has a gradual change in piezoelectric constant depending on an ambient temperature. In addition, the piezoelectric material of the present invention is free of lead, and hence has a small load on the environment. Accordingly, the piezoelectric ceramics of the present invention can be utilized for an electronic device required to be stably operated at various ambient temperatures, such as a dust removing device, a liquid ejection head, or a vibration wave motor.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2018-020321, filed Feb. 7, 2018, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
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| JP2018-020321 | Feb 2018 | JP | national |
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| Number | Date | Country | |
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| 20190245135 A1 | Aug 2019 | US |
