Piezoelectric ceramic composition and piezoelectric transformer

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition suited, for example, for ultrasonic oscillators, actuators, piezoelectric transformers, or the like, and to a piezoelectric transformer used in electric power conversion devices such as an inverter for the back light of a liquid crystal display.
2. Description of the Prior Art
Piezoelectric materials are applied to various devices, such as ultrasonic oscillators, actuators, and piezoelectric transformers, as materials which can convert electrical energy to mechanical oscillation energy or mechanical oscillation energy to electrical energy. In these applications, piezoelectric materials having a large electromechanical coupling factor and a large mechanical quality factor are used. An example of such piezoelectric materials is a composition comprising Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 --Pb(Sn.sub.1/3 Nb.sub.2/3)O.sub.3 --PbTiO.sub.3 --PbZrO.sub.3 to which MnO.sub.2 is added, which has been known to have an excellent piezoelectric properties (see Japanese Patent Publication No. 56-30714).
In recent years, increase in the output of piezoelectric devices is demanded. However, the mechanical quality factor of piezoelectric materials lowers non-linearly due to high-field driving and increase in mechanical vibration, and piezoelectric materials abruptly generate large heat due to the loss of internal energy. Therefore, piezoelectric materials having a mechanical quality factor which lowers little even at high-field driving have been demanded.
With recent downsizing of office automation facilities, piezoelectric transformers have been diffused for producing inverters for cold cathode-ray tubes used as the back light of a liquid display, and for other applications. A piezoelectric transformer converts inputted electrical energy to mechanical oscillation energy, then to electrical energy again, thereby steps up or steps down the input voltage. For piezoelectric transformers used in such applications, high conversion efficiency and a small and thin size are demanded.
Also, a piezoelectric transformer is a device utilizing the resonance of a piezoelectric element, and when oscillation in the length direction is used, the resonant frequency increases with decrease in the length of the element. That is, downsizing leads to increase in driving frequencies. However, if driving frequencies are increased, the conversion efficiency of the entire circuit containing a piezoelectric transformer, such as an inverter circuit, is lowered by the effect of floating capacity in the vicinity of the circuit, the frequency characteristics of the cold cathode-ray tube, or the like. Therefore, small piezoelectric transformers which can be driven by a relatively low frequency are demanded.
BRIEF SUMMARY OF THE INVENTION
Object of the Invention
The above-described conventional materials exhibit excellent piezoelectric properties at low-field driving. However, their mechanical quality factor lowers significantly at high-field driving.
The first object of the present invention is to provide a piezoelectric ceramic composition having a large mechanical quality factor, which lowers little even at high-field driving, considering the problems of conventional piezoelectric materials; and to provide a piezoelectric device which generates little heat even at high-field driving, and enables high outputs, produced using such a piezoelectric ceramic composition as the piezoelectric material.
When a piezoelectric device of a laminated structure is formed, the effect of omitting the process for bonding the electrode and the piezoelectric material is obtained by sintering a silver-palladium paste and the piezoelectric ceramic composition at the same time, for facilitating the production of the piezoelectric device of a laminated structure. The upper limit of the sintering temperature when the silver-palladium paste and the piezoelectric ceramic composition at the same time is 1150.degree. C., and it was difficult for conventional materials to tolerate such a temperature. Furthermore, for decreasing the palladium content in the silver-palladium paste to reduce the material costs, the sintering temperature is preferably lower than 1100.degree. C.
The second object of the present invention is to provide a piezoelectric ceramic composition which can be sintered at a temperature lower than 1100.degree. C., and having a large mechanical quality factor, which lowers little even at high-field driving and to provide a piezoelectric device which generates little heat even at high-field driving, and enables high outputs, produced using such a piezoelectric ceramic composition as the piezoelectric material.
Also, on inputting a certain electrical energy to a piezoelectric transformer, if the piezoelectric material is made thin, the step up (step down) ratio increases, but conversion efficiency lowers.
The third object of the present invention is to provide a thin piezoelectric transformer having a high conversion efficiency.
Furthermore, on inputting a certain electrical energy to a piezoelectric transformer, if the driving frequency of the piezoelectric transformer is lowered, the amplitude of mechanical oscillation increases and conversion efficiency lowers.
The fourth object of the present invention is to provide a small piezoelectric transformer having a high conversion efficiency even at low driving -frequencies.
Summary of the Invention
The first invention of the present invention is a piezoelectric ceramic composition represented by a composition formula, (Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3, where the symbol A is at least one component selected from a group consisting of La, Nd, Pr, and Bi, and u, v, w, x, y, and z are within ranges represented by the following Equations, characterized in that 0.1 to 3 mole percent of a Mn compound calculated in terms of MnO.sub.2 is added to said piezoelectric ceramic composition.
w+x+y+z=1 [Equation 1]
0.85.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
According to a first aspect of the present invention, there can be provided a piezoelectric ceramic composition having a large mechanical quality factor, and achieving little lowering of the mechanical quality factor due to high-field driving.
The second invention of the present invention is a piezoelectric ceramic composition represented by a composition formula, [(Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3 ].sub.t --(YMnO.sub.3).sub.1-t, where the symbol A is at least one component selected from a group consisting of La, Nd, Pr, and Bi, and t, u, v, w, x, y, and z are within ranges represented by the following Equations.
w+x+y+z=1 [Equation 2]
0.960.ltoreq.t.ltoreq.0.999
0.90.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
According to a second aspect of the present invention, there can be provided a piezoelectric ceramic composition having a large mechanical quality factor, and achieving little lowering of the mechanical quality factor due to high-field driving.
The third invention of the present invention is a piezoelectric ceramic composition represented by a composition formula, (Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3, where the symbol A is at least one component selected from a group consisting of La, Nd, Pr, and Bi, and u, v, w, x, y, and z are within ranges represented by the following Equations, characterized in that 0.1 to 3 mole percent of a Mn compound calculated in terms of MnO.sub.2, and 0.5 to 2 mole percent of ZnO are added to said piezoelectric ceramic composition.
w+x+y+z=1 [Equation 1]
0.85.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
According to a third aspect of the present invention, there can be provided a piezoelectric ceramic composition which can be sintered at a temperature lower than 1100.degree. C., and having a large mechanical quality factor, and achieving little lowering of the mechanical quality factor due to high-field driving.
The fourth invention of the present invention is a piezoelectric ceramic composition represented by a composition formula, [(Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3 ].sub.t --(YMnO.sub.3).sub.1-t, where the symbol A is at least one component selected from a group consisting of La, Nd, Pr, and Bi, and t, u, v, w, x, y, and z are within ranges represented by the following Equations, characterized in that 0.5 to 2 mole percent of ZnO is added to said piezoelectric ceramic composition.
w+x+y+z=1 [Equation 2]
0.960.ltoreq.t.ltoreq.0.999
0.90.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
According to a fourth aspect of the present invention, there can be provided a piezoelectric ceramic composition which can be sintered at a temperature lower than 1100.degree. C., and having a large mechanical quality factor, and achieving little lowering of the mechanical quality factor due to high-field driving.
The fifth invention of the present invention is a piezoelectric device characterized in that the piezoelectric ceramic composition according to the first invention to the second invention is used as the piezoelectric body.
According to a fifth aspect of the present invention, there can be provided a piezoelectric device which generates little heat on high-field driving, and can produce a high output.
The sixth invention of the present invention is a piezoelectric transformer characterized in that the piezoelectric device according to the fifth invention is used as the piezoelectric transformer.
According to a sixth aspect of the present invention, there can be provided a piezoelectric transformer having a high conversion efficiency and a thin thickness.
The seventh invention of the present invention is the piezoelectric transformer according to the sixth invention comprising a polarizing portion in the length direction and a polarizing portion in the thickness direction.
According to a seventh aspect of the present invention, there can be provided a piezoelectric transformer having a high conversion efficiency and a thin thickness.
The eighth invention of the present invention is the piezoelectric transformer according to the seventh invention excited in a half-wavelength mode.
According to an eighth aspect of the present invention, there can be provided a piezoelectric transformer having a high conversion efficiency even at a low driving frequency, and having a small size.
The ninth invention of the present invention is a piezoelectric device, characterized by comprising the piezoelectric ceramic composition according to the third invention or the fourth invention, and silver-palladium paste electrodes.
According to a ninth aspect of the present invention, there can be provided a piezoelectric device which generates little heat on high-field driving, and can produce a high output.
The tenth invention of the present invention is a piezoelectric transformer characterized in that the piezoelectric device according to the ninth invention is used as the piezoelectric transformer.
According to a tenth aspect of the present invention, there can be provided a piezoelectric transformer having a high conversion efficiency and a thin thickness.
The eleventh invention of the present invention is the piezoelectric transformer according to the tenth invention, characterized by comprising a polarizing portion in the length direction and a polarizing portion in the thickness direction.
According to an eleventh aspect of the present invention, there can be provided a piezoelectric transformer having a high conversion efficiency and a thin thickness.
The twelfth invention of the present invention is the piezoelectric transformer according to the eleventh invention, characterized by excited in a half-wavelength mode.
According to a twelfth aspect of the present invention, there can be provided a piezoelectric transformer having a high conversion efficiency even at a low driving frequency, and having a small size.
The piezoelectric devices and piezoelectric transformers according to the ninth through twelfth aspects of the present invention have features that they are easily laminated by sintering a piezoelectric ceramic composition together with a silver-palladium paste.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing the appearance of a piezoelectric transformer according to the first and second embodiments of the present invention; and
FIG. 2 is a perspective view showing the appearance of a piezoelectric transformer according to the third and fourth embodiments of the present invention.

DESCRIPTION OF SYMBOLS
1, 5 Piezoelectric body driving portion
2, 6, 7 Piezoelectric body power generating portion
3, 8 Input electrode
4, 9 Output electrode
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention will be described below referring to attached drawings.
(First Embodiment)
First, the first embodiment of the present invention will be described below referring to attached drawings. FIG. 1 is a perspective view showing the appearance of the piezoelectric transformer according to the first embodiment of the present invention. Arrows in FIG. 1 show the directions of the polarizing axes of the piezoelectric body. A piezoelectric body driving portion 1 having input electrodes 3a and 3b formed on the major surface of the piezoelectric body has been subjected to the polarizing treatment in the thickness direction; and a piezoelectric body power generating portion 2 having an output electrode 4 formed on the end surface of the piezoelectric body has been subjected to the polarizing treatment in the length direction between the input electrodes 3a, 3b and the output electrode 4.
Next, the operation of the piezoelectric transformer according to this embodiment will be described. When AC electric signal is impressed between the input electrodes 3a and 3b, the piezoelectric body driving portion 1 is excited to make mechanical oscillation due to the reverse piezoelectric effect. By the piezoelectric effect of this mechanical oscillation, a voltage is generated between the output electrode 4 and the (common electrode of) input electrodes 3, and taken out as an electric signal. By this, the input voltage is converted into an output voltage. The relationship between the input voltage and the output voltage is determined by the size of the piezoelectric body, the frequency of the impressed AC electric signal, and so on. In this type of piezoelectric transformer, the voltage is most efficiently converted by the oscillation of the one-wavelength mode (.lambda.-mode) on the stretching oscillation in the length direction of the piezoelectric body (the piezoelectric body driving portion 1+the piezoelectric body power generating portion 2). The input electrodes 3a, 3b and the output electrode 4 have been formed by, for example, silver baking.
The piezoelectric body driving portion 1 and the piezoelectric body power generating portion 2 are piezoelectric ceramic compositions represented by a composition formula, (Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3, where the symbol A is at least one component selected from a group (A) consisting of La, Nd, Pr, and Bi, and u, v, w, x, y, and z are within ranges represented by the following Equations, to which 0.1 to 3 mole percent of a Mn compound calculated in terms of MnO.sub.2 is added.
w+x+y+z=1 [Equation 1]
0.85.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
The piezoelectric ceramic composition according to this embodiment has been proved to have a large mechanical quality factor, and to achieve little lowering of the mechanical quality factor due to high-field driving by satisfying the above requirements, the details of which will be described referring to Examples mentioned later.
Also, the piezoelectric transformer according to this embodiment has been proved to have a high conversion efficiency, and to realize a thin thickness by the use of the above-described piezoelectric ceramic composition, the details of which will be described referring to Examples mentioned later.
As a modification of this embodiment, in place of the piezoelectric ceramic composition according to this embodiment, there may be used a piezoelectric ceramic composition represented by a composition formula, [(Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3 ].sub.t --(YMnO.sub.3).sub.1-t, where the symbol A is at least one component selected from a group (A) consisting of La, Nd, Pr, and Bi, and t, u, v, w, x, y, and z are within ranges represented by the following Equations.
w+x+y+z=1 [Equation 2]
0.960.ltoreq.t.ltoreq.0.999
0.90.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
In this modified embodiment, it has also been proved that the same effects as those of the piezoelectric ceramic composition and the piezoelectric transformer according to the embodiment described above can be obtained, and the details will also be described referring to Examples mentioned later.
(Second Embodiment)
Next, the second embodiment of the present invention will be described below referring to attached drawings. This embodiment is similar to the piezoelectric transformer in the first embodiment described above except for the aspects related to the piezoelectric ceramic composition of the present invention. In this embodiment, therefore, what are not described are the same as those in the first embodiment, and the composing members having the same nominations have the same functions as those of the first embodiment unless otherwise described.
The construction of the piezoelectric transformer in this embodiment is the same as that shown in FIG. 1.
The input electrodes 3a and 3b, and the output electrode 4 are formed by silver baking, or by sintering a silver-palladium paste.
The piezoelectric body driving portion 1 and the piezoelectric body power generating portion 2 are piezoelectric ceramic compositions represented by a composition formula, (Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3, where the symbol A is at least one component selected from a group (A) consisting of La, Nd, Pr, and Bi, and u, v, w, x, y, and z are within ranges represented by the following Equations, to which 0.1 to 3 mole percent of a Mn compound calculated in terms of MnO.sub.2 and 0.5 to 2 mole percent of ZnO are added.
w+x+y+z=1 [Equation 1]
0.85.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
The piezoelectric ceramic composition according to this embodiment has been proved to be able to be sintered at a temperature below 1100.degree. C., to have a large mechanical quality factor, and to achieve little lowering of the mechanical quality factor due to high-field driving by satisfying the above requirements, the details of which will be described referring to Examples mentioned later.
Also, the piezoelectric transformer according to this embodiment has been proved to have a high conversion efficiency, and to realize a thin thickness by the use of the above-described piezoelectric ceramic composition, the details of which will be described referring to Examples mentioned later.
When a piezoelectric transformer in this embodiment is manufactured, since the above piezoelectric ceramic composition can be sintered at a temperature below 1100.degree. C., it can be sintered together with a silver-palladium paste forming the electrodes to form a laminated structure; therefore, a piezoelectric device having a laminated structure can be easily manufactured.
As a modification of this embodiment, in place of the piezoelectric ceramic composition according to this embodiment, there may be used a piezoelectric ceramic composition represented by a composition formula, [(Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3 ].sub.t --(YMnO.sub.3).sub.1-t, where the symbol A is at least one component selected from a group (A) consisting of La, Nd, Pr, and Bi, and t, u, v, w, x, y, and z are within ranges represented by the following Equations, to which 0.5 to 2 mole percent of ZnO is further added.
w+x+y+z=1 [Equation 2]
0.960.ltoreq.t.ltoreq.0.999
0.90.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
In this modified embodiment, it has also been proved that the same effects as those of the piezoelectric ceramic composition and the piezoelectric transformer according to the embodiment described above can be obtained, and the details will also be described referring to Examples mentioned later.
(Third Embodiment)
Next, the third embodiment of the present invention will be described below referring to attached drawings.
FIG. 2 is a perspective view showing the appearance of the piezoelectric transformer according to the third embodiment of the present invention. Arrows in FIG. 2 show the directions of the polarizing axes of the piezoelectric body. A piezoelectric body driving portion 5 having input electrodes 8a and 8b formed on the major surface of the piezoelectric body has been subjected to the polarizing treatment in the thickness direction; and in a piezoelectric body power generating portions 6 and 7, both sides of the piezoelectric body driving portion 5 have been subjected to the polarizing treatment in the length direction and output electrodes 9a, 9b, 9c, and 9d are formed on the both surfaces of the both ends, respectively.
The operation of the piezoelectric transformer according to this embodiment will be described. When AC electric signal is impressed between the input electrodes 8a and 8b, the piezoelectric body driving portion 5 is excited to make mechanical oscillation due to the reverse piezoelectric effect. By the piezoelectric effect of this mechanical oscillation, a voltage is generated between the output electrodes 9a, 9b and the input electrodes 8a, 8b, and between the output electrodes 9c, 9d and the input electrodes 8a, 8b, and taken out as an electric signal. By this, the input voltage is converted into an output voltage. The relationship between the input voltage and the output voltage is determined by the size of the piezoelectric body, the frequency of the impressed AC electric signal, and so on. In this type of piezoelectric transformer, the voltage is most efficiently converted by the oscillation of the half-wavelength mode (.lambda./2-mode) on the stretching oscillation in the length direction of the piezoelectric body (the piezoelectric body driving portion 5+the piezoelectric body power generating portions 6 and 7). The oscillation frequency of the .lambda./2-mode is a half the oscillation frequency of the one-wavelength mode.
The input electrodes 8a, 8b, and the output electrodes 9a, 9b, 9c, and 9d have been formed by, for example, silver baking.
The piezoelectric body driving portion 5 and the piezoelectric body power generating portions 6 and 7 are piezoelectric ceramic compositions represented by a composition formula, (Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3, where the symbol A is at least one component selected from a group (A) consisting of La, Nd, Pr, and Bi, and u, v, w, x, y, and z are within ranges represented by the following Equations, to which 0.1 to 3 mole percent of a Mn compound calculated in terms of MnO.sub.2 is added.
w+x+y+z=1 [Equation 1]
0.85.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
The piezoelectric ceramic composition according to this embodiment has been proved to have a large mechanical quality factor, and to achieve little lowering of the mechanical quality factor due to high-field driving by satisfying the above requirements, the details of which will be described referring to Examples mentioned later.
Also, the piezoelectric transformer according to this embodiment has been proved to have a high conversion efficiency even at a low driving frequency, and to realize a thin thickness by the use of the above-described piezoelectric ceramic composition, the details of which will be described referring to Examples mentioned later.
Although a centrally driving type construction as shown in FIG. 2 is used as a .lambda./2-mode piezoelectric transformer according to this embodiment, the structure is not specifically limited, but the same effect can be obtained from the construction having a polarizing portion in the length direction and a polarizing portion in the thickness direction and which can be excited in .lambda./2 mode, such as the construction shown in FIG. 1.
As a modification of this embodiment, in place of the piezoelectric ceramic composition according to this embodiment, there may be used a piezoelectric ceramic composition represented by a composition formula, [(Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3 ].sub.t --(YMnO.sub.3).sub.1-t, where the symbol A is at least one component selected from a group (A) consisting of La, Nd, Pr, and Bi, and t, u, v, w, x, y, and z are within ranges represented by the following Equations.
w+x+y+z=1 [Equation 2]
0.960.ltoreq.t.ltoreq.0.999
0.90.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
In this modified embodiment, it has also been proved that the same effects as those of the piezoelectric ceramic composition and the piezoelectric transformer according to the embodiment described above can be obtained, and the details will also be described referring to Examples mentioned later.
(Fourth Embodiment)
Next, the fourth embodiment of the present invention will be described below referring to attached drawings. This embodiment is similar to the piezoelectric transformer in the third embodiment described above except for the aspects related to the piezoelectric ceramic composition of the present invention. In this embodiment, therefore, what are not described are the same as those in the third embodiment, and the composing members having the same nominations have the same functions as those of the third embodiment unless otherwise described. The construction of the piezoelectric transformer in this embodiment is the same as that shown in FIG. 2. The input electrodes 8a and 8b, and the output electrodes 9a, 9b, 9c, and 9d are formed, for example, by silver baking, or by sintering a silver-palladium paste.
The piezoelectric body driving portion 5 and the piezoelectric body power generating portions 6 and 7 are piezoelectric ceramic compositions represented by a composition formula, (Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3, where the symbol A is at least one component selected from a group (A) consisting of La, Nd, Pr, and Bi, and u, v, w, x, y, and z are within ranges represented by the following Equations, to which 0.1 to 3 mole percent of a Mn compound calculated in terms of MnO.sub.2 and 0.5 to 2 mole percent of ZnO are added.
w+x+y+z=1 [Equation 1]
0.85.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
The piezoelectric ceramic composition according to this embodiment has been proved to be able to sinter at a temperature below 1100.degree. C., to have a large mechanical quality factor, and to achieve little lowering of the mechanical quality factor due to high-field driving by satisfying the above requirements, the details of which will be described referring to Examples mentioned later.
Also, the piezoelectric transformer according to this embodiment has been proved to have a high conversion efficiency even at a low driving frequency, and to realize a thin thickness by the use of the above-described piezoelectric ceramic composition, the details of which will be described referring to Examples mentioned later.
Although a centrally driving type construction as shown in FIG. 2 is used as a .lambda./2-mode piezoelectric transformer according to this embodiment, the structure is not specifically limited, but the same effect can be obtained from the construction having a polarizing portion in the length direction and a polarizing portion in the thickness direction and which can be excited in .lambda./2 mode, such as the construction shown in FIG. 1.
When a piezoelectric transformer in this embodiment is manufactured, since the above piezoelectric ceramic composition can be sintered at a temperature below 1100.degree. C., it can be sintered together with a silver-palladium paste forming the electrodes to form a laminated structure; therefore, a piezoelectric device having a laminated structure can be easily manufactured.
As a modification of this embodiment, in place of the piezoelectric ceramic composition according to this embodiment, there may be used a piezoelectric ceramic composition represented by a composition formula, [(Pb.sub.u A.sub.1-u).sub.v {(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z }.sub.2-v O.sub.3 ].sub.t --(YMnO.sub.3).sub.1-t, where the symbol A is at least one component selected from a group (A) consisting of La, Nd, Pr, and Bi, and t, u, v, w, x, y, and z are within ranges represented by the following Equations, to which 0.5 to 2 mole percent of ZnO is further added.
w+x+y+z=1 [Equation 2]
0.960.ltoreq.t.ltoreq.0.999
0.90.ltoreq.u.ltoreq.0.99
0.97.ltoreq.v.ltoreq.1.03
0.01.ltoreq.w.ltoreq.0.20
0.01.ltoreq.x.ltoreq.0.15
0.35.ltoreq.y.ltoreq.0.48
0.30.ltoreq.z.ltoreq.0.50
In this modified embodiment, it has also been proved that the same effects as those of the piezoelectric ceramic composition and the piezoelectric transformer according to the embodiment described above can be obtained, and the details will also be described referring to Examples mentioned later.
In the first through fourth embodiments described above, although piezoelectric transformers using the piezoelectric ceramic composition of the present invention were described, the application of the piezoelectric ceramic composition of the present invention is not limited to piezoelectric transformers and it can also be applied to various piezoelectric devices including ultrasonic oscillators and actuators. Through the application of the piezoelectric ceramic composition of the present invention, piezoelectric devices with reduced thickness and size, and laminated piezoelectric devices which can be produced easily are realized.
EXAMPLES
The Examples of the present invention will be described below.
The following Examples correspond to the first through fourth embodiments described above and the modifications thereof, and show the results of the tests for the effects described above using Examples of the piezoelectric ceramic compositions and piezoelectric transformers corresponding to these embodiments, and Comparative Examples thereof.
Example 1
Examples of the piezoelectric ceramic compositions according to the first through fourth embodiments, and Comparative Examples thereof, will be described below.
As the starting materials of the Examples, PbO, La.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Pr.sub.2 O.sub.3, Bi.sub.2 O.sub.3, ZnO, SnO.sub.2, Nb.sub.2 O.sub.5, TiO.sub.2, ZrO.sub.2, MnCO.sub.3, and Y.sub.2 O.sub.3 of chemically high purity were used. These were weighed to form a predetermined composition, and wet-mixed with a ball mill using zirconia balls. Here, the quantity of MnCO.sub.3 was calculated to obtain a required quantity of MnO.sub.2. As the starting materials, any of oxides, hydroxides, carbonates, or alkoxides of each component element described above can also be used. The mixture was taken out from the ball mill, dried, and calcined in the air at 850-1100.degree. C. for 2 hours. The calcined powder was wet-ground with the above-described ball mill, then the ground slurry was taken out from the ball mill, dried, and granulated with a polyvinyl alcohol solution.
Granules thus obtained were molded into a disc having a diameter of 20 mm and a thickness of about 2 mm using a mold and a press. After the binder was removed from the molded article by allowing the molded article to stand in the air at 700.degree. C. for 1 hour, the molded article was sintered in the air at 1000-1260.degree. C. for 2 hours. After the sintered article was machined into a disc having a diameter of about 16 mm and a thickness of about 1 mm, silver electrodes were formed on the both major surface of the disc by baking, and polarization treatment was performed in an insulation oil at 100.degree. C. by impressing a DC electric field of 1-5 kV/mm. From the measurement of the obtained disc specimen with the resonance-antiresonance method using an impedance analyzer, the mechanical quality factor Qm of the oscillation in the radial direction of the disc was obtained. Here, the Qm values when the impressed voltage was 0.1 Vrms and when it was 5 Vrms were obtained to evaluate the degree of Qm lowering due to high-field driving.
Table 1 shows the compositions, sintering temperatures, and Qm values when the impressed voltage was 0.1 Vrms and when it was 5 Vrms. Asterisks (*) indicated to the right of the specimen numbers indicate that such samples are beyond the scope of the claim of the present invention.
TABLE 1__________________________________________________________________________ SinteringSpecimen MnO.sub.2 ZnO temperature QmNo. A u v w x y z (Mole %) (Mole %) (.degree. C.) 0.1 5__________________________________________________________________________ V 1* -- 1 1 0.09 0.09 0.42 0.40 1 0 1230 2200 700 2 La 0.99 1 0.09 0.09 0.42 0.40 1 0 1230 2180 1200 3 La 0.94 1 0.09 0.09 0.42 0.40 1 0 1230 2350 1830 4 La 0.85 1 0.09 0.09 0.42 0.40 1 0 1230 1560 1420 5* La 0.75 1 0.09 0.09 0.42 0.40 1 0 1260 980 500 6 Bi 0.99 1 0.09 0.09 0.42 0.40 1 0 1230 2010 1310 7 Bi 0.94 1 0.09 0.09 0.42 0.40 1 0 1200 1870 1700 8 Bi 0.90 1 0.09 0.09 0.42 0.40 1 0 1170 1650 1580 9 La1/2Bi1/2 0.94 1 0.09 0.09 0.42 0.40 1 0 1200 2150 205010* La 0.94 0.90 0.09 0.09 0.42 0.40 1 0 1260 320 12011 La 0.94 0.97 0.09 0.09 0.42 0.40 1 0 1260 1600 135012 La 0.94 1.03 0.09 0.09 0.42 0.40 1 0 1200 2210 174013* La 0.94 1.1 0.09 0.09 0.42 0.40 1 0 1170 560 33014* -- 1 1 0 0 0.48 0.52 1 0 1140 700 15015 La 0.96 1 0.01 0.01 0.48 0.50 1 0 1110 1520 112016 La 0.96 1 0.20 0.15 0.35 0.30 1 0 1260 1750 153017* La 0.96 1 0.25 0.25 0.29 0.21 1 0 1260 850 73018* La 0.94 1 0.09 0.09 0.42 0.40 0 0 1260 530 12019 La 0.94 1 0.09 0.09 0.42 0.40 0.1 0 1260 1230 110020 La 0.94 1 0.09 0.09 0.42 0.40 2 0 1260 1890 178021 La 0.94 1 0.09 0.09 0.42 0.40 3 0 1260 1580 142022* La 0.94 1 0.09 0.09 0.42 0.40 4 0 1260 620 31023 La 0.99 1 0.12 0.06 0.42 0.40 1 0 1110 2150 150024 La 0.94 1 0.12 0.06 0.42 0.40 1 0 1140 2350 212025 La 0.96 1 0.09 0.05 0.43 0.43 1 0 1110 2260 184026 La 0.96 1 0.09 0.05 0.43 0.43 0.1 0 1110 1420 121027 La 0.96 1 0.09 0.05 0.43 0.43 3 0 1110 1830 170028 Nd 0.94 1 0.09 0.09 0.42 0.40 1 0 1260 2430 223029 Nd 0.94 1 0.09 0.09 0.42 0.40 1 0.5 1080 2250 203030 Nd 0.94 1 0.09 0.09 0.42 0.40 1 1 1080 2000 176031 Nd 0.94 1 0.09 0.09 0.42 0.40 1 2 1000 1750 152032* Nd 0.94 1 0.09 0.09 0.42 0.40 1 4 1000 800 68033 Pr 0.94 1 0.09 0.09 0.42 0.40 1 0 1230 2000 188034 Pr 0.94 1 0.09 0.09 0.42 0.40 1 1 1080 1960 1790__________________________________________________________________________
As is obvious from the results shown in Table 1, specimens corresponding to the piezoelectric ceramic compositions according to the first and third embodiments of the present invention exhibited high mechanical quality factors Qm not lower than 1200 in low-field driving (0.1 Vrms), and also exhibited high Qm values not lower than 1100 even in high-field driving (5 Vrms). Also, specimens corresponding to the piezoelectric ceramic compositions according to the second and fourth embodiments of the present invention (specimens of Nos. 29, 30, 31, and 34) exhibited high Qm values at a sintering temperature lower than 1100.degree. C., indicating that they could be sintered together with a silver-palladium paste.
Whereas the specimens of Comparative Examples (specimens of Nos. 1, 5, 10, 13, 14, 17, 18, 22, and 32) exhibited significantly lower Qm values in high-field driving.
Example 2
Examples and Comparative Examples of the piezoelectric ceramic compositions according to the first through fourth embodiments and modifications thereof will be described below.
Granules obtained in the same manner as Example 1 were molded into a disc having a diameter of 20 mm and a thickness of about 2 mm using a mold and a press. After the binder was removed from the molded article by allowing the molded article to stand in the air at 700.degree. C. for 1 hour, the molded article was sintered in the air at 1000-1260.degree. C. for 2 hours. After the sintered article was machined into a disc having a diameter of about 16 mm and a thickness of about 1 mm, silver electrodes were formed on the both major surface of the disc by baking, and polarization treatment was performed in an insulation oil at 100.degree. C. by impressing a DC electric field of 1-5 kV/mm. From the measurement of the obtained disc specimen with the resonance-antiresonance method using an impedance analyzer, the mechanical quality factor Qm of the oscillation in the radial direction of the disc was obtained. Here, the Qm values when the impressed voltage was 0.1 Vrms and when it was 5 Vrms were obtained to evaluate the degree of Qm lowering due to high-field driving.
Table 2 shows the compositions, sintering temperatures, and Qm values when the impressed voltage was 0.1 Vrms and when it was 5 Vrms. Asterisks (*) indicated to the right of the specimen numbers indicate that such samples are beyond the scope of the claim of the present invention.
TABLE 2__________________________________________________________________________ SinteringSpecimen ZnO temperature QmNo. A u v w x y z t (Mole %) (.degree. C.) 0.1 V 5__________________________________________________________________________ V35* -- 1 1 0.12 0.09 0.41 0.38 0.980 0 1230 2350 61036 La 0.99 1 0.12 0.09 0.41 0.38 0.980 0 1230 2250 145037 La 0.94 1 0.12 0.09 0.41 0.38 0.980 0 1230 2540 198038 La 0.90 1 0.12 0.09 0.41 0.38 0.980 0 1260 1750 160039* La 0.80 1 0.12 0.09 0.41 0.38 0.980 0 1260 650 32040 Bi 0.99 1 0.12 0.09 0.41 0.38 0.980 0 1230 2120 146041 Bi 0.94 1 0.12 0.09 0.41 0.38 0.980 0 1170 1780 160042 Bi 0.90 1 0.12 0.09 0.41 0.38 0.980 0 1170 1540 141043 La1/2Bi1/2 0.94 1 0.12 0.09 0.41 0.38 0.980 0 1200 1850 170044* La 0.94 0.90 0.12 0.09 0.41 0.38 0.980 0 1260 450 18045 La 0.94 0.97 0.12 0.09 0.41 0.38 0.980 0 1260 1520 120046 La 0.94 1.03 0.12 0.09 0.41 0.38 0.980 0 1200 2020 163047* La 0.94 1.1 0.12 0.09 0.41 0.38 0.980 0 1170 420 2148* -- 1 1 0 0 0.48 0.52 0.980 0 1140 750 23049 La 0.96 1 0.01 0.01 0.48 0.50 0.980 0 1110 1650 140050 La 0.96 1 0.20 0.15 0.35 0.30 0.980 0 1260 1890 171051* La 0.96 1 0.25 0.25 0.28 0.22 0.980 0 1260 630 48052* La 0.96 1 0.09 0.09 0.42 0.40 1.000 0 1260 320 8053 La 0.96 1 0.09 0.09 0.42 0.40 0.999 0 1260 1180 109054 La 0.96 1 0.09 0.09 0.42 0.40 0.970 0 1230 1950 162055 La 0.96 1 0.09 0.09 0.42 0.40 0.960 0 1200 1630 154056* La 0.96 1 0.09 0.09 0.42 0.40 0.900 0 1200 390 15057 La 0.99 1 0.12 0.06 0.42 0.40 0.980 0 1110 2420 181058 La 0.92 1 0.12 0.06 0.42 0.40 0.980 0 1140 2680 232059 La 0.96 1 0.09 0.05 0.43 0.43 0.999 0 1110 1520 123060 La 0.96 1 0.09 0.05 0.43 0.43 0.970 0 1110 2010 169061 La 0.96 1 0.09 0.05 0.43 0.43 0.960 0 1110 1820 141062 Nd 0.94 1 0.12 0.09 0.41 0.38 0.980 0 1230 2470 185063 Nd 0.94 1 0.12 0.09 0.41 0.38 0.980 0.5 1080 2320 182064 Nd 0.94 1 0.12 0.09 0.41 0.38 0.980 1 1080 1930 171065 Nd 0.94 1 0.12 0.09 0.41 0.38 0.980 2 1000 1600 135066* Nd 0.94 1 0.12 0.09 0.41 0.38 0.980 4 1000 710 53067 Pr 0.94 1 0.12 0.09 0.41 0.38 0.980 0 1260 2150 192068 Pr 0.94 1 0.12 0.09 0.41 0.38 0.980 1 1080 1790 1600__________________________________________________________________________
As is obvious from the results shown in Table 2, specimens corresponding to the piezoelectric ceramic compositions according to the modifications of the first and third embodiments of the present invention exhibited high mechanical quality factors Qm not lower than 1100 in low-field driving (0.1 Vrms), and also exhibited high Qm values not lower than 1000 even in high-field driving (5 Vrms) . Also, specimens corresponding to the piezoelectric ceramic compositions according to the second and fourth embodiments of the present invention (specimens of Nos. 63, 64, 65, and 68) further exhibited high Qm values at a sintering temperature lower than 1100.degree. C., indicating that they could be sintered together with a silver-palladium paste.
Whereas the specimens of Comparative Examples (specimens of Nos. 35, 39, 44, 47, 48, 51, 52, 56, and 66) exhibited significantly lower Qm values in high-field driving.
Example 3
Examples and Comparative Examples of the piezoelectric transformers according to the first and second embodiments will be described below referring to FIG. 1. FIG. 1 shows the appearance of a piezoelectric transformer according to the present invention.
Granules obtained in the same manner as Example 1 were molded into a rectangular plate having a length of 50 mm, a width of 10 mm, and a thickness of about 3 mm using a mold and a press. After the binder was removed from the molded article by allowing the molded article to stand in the air at 700.degree. C. for 1 hour, the molded article was sintered in the air at 1000-1260.degree. C. for 2 hours. The sintered article was machined into rectangular plates having a length of 40 mm, a width of 7 mm, and a thickness of 2 mm and 1 mm. The piezoelectric body driving portion 1 was formed by the silver baking of input electrodes 3a and 3b on the major surface, and subjected to polarization treatment in the thickness direction. The piezoelectric body power generating portion 2 was formed by forming the output electrode 4 having a width of 1 mm, and subjected to polarization treatment in the length direction between the input electrodes 3a, 3b and the output electrode 4. Arrows in FIG. 1 show the directions of polarization axes. The length of each of the piezoelectric body driving portion 1 and the piezoelectric body power generating portion 2 was 20 mm, respectively. A load resistance of 100 k.OMEGA. was connected to the output electrode 4, and AC electric signals were supplied to the input electrodes 3a and 3b to excite them to make mechanical oscillation. The evaluation of efficiency was performed for the one-wavelength mode (.lambda.-mode) of stretching oscillation in the length direction. The input electric power Win was 3 W, and the resonant frequency was about 80 kHz.
Table 3 shows the compositions, the thickness of piezoelectric elements, and the efficiencies of piezoelectric transformers. Asterisks (*) indicated to the right of the specimen numbers indicate that such samples are beyond the scope of the claim of the present invention.
TABLE 3__________________________________________________________________________ ElementSpecimen MnO.sub.2 ZnO thickness EfficiencyNo. A u v w x y z (Mole %) (Mole %) (mm) (%)__________________________________________________________________________ 69* -- 1 1 0.09 0.09 0.42 0.40 1 0 2 84.3 70* -- 1 1 0.09 0.09 0.42 0.40 1 0 1 75.0 71 La 0.99 1 0.09 0.09 0.42 0.40 1 0 2 95.3 72 La 0.99 1 0.09 0.09 0.42 0.40 1 0 1 90.8 73 La 0.94 1 0.09 0.09 0.42 0.40 1 0 2 97.8 74 La 0.94 1 0.09 0.09 0.42 0.40 1 0 1 94.2 75 La 0.85 1 0.09 0.09 0.42 0.40 1 0 2 93.6 76 La 0.85 1 0.09 0.09 0.42 0.40 1 0 1 90.2 77 La1/2Bi1/2 0.94 1 0.09 0.09 0.42 0.40 1 0 2 98.5 78 La1/2bi1/2 0.94 1 0.09 0.09 0.42 0.40 1 0 1 93.8 79* La 0.94 0.90 0.09 0.09 0.42 0.40 1 0 2 75.2 80* La 0.94 0.90 0.09 0.09 0.42 0.40 1 0 1 52.9 81 La 0.94 0.97 0.09 0.09 0.42 0.40 1 0 2 97.5 82 La 0.94 0.97 0.09 0.09 0.42 0.40 1 0 1 91.3 83 La 0.94 1.03 0.09 0.09 0.42 0.40 1 0 2 98.6 84 La 0.94 1.03 0.09 0.09 0.42 0.40 1 0 1 93.1 85* La 0.94 1.1 0.09 0.09 0.42 0.40 1 0 2 63.2 86* La 0.94 1.1 0.09 0.09 0.42 0.40 1 0 1 42.3 87* -- 1 1 0 0 0.48 0.52 1 0 2 52.1 88* -- 1 1 0 0 0.48 0.52 1 0 1 37.3 89 La 0.96 1 0.01 0.01 0.48 0.50 1 0 2 93.8 90 La 0.96 1 0.01 0.01 0.48 0.50 1 0 1 90.2 91 La 0.96 1 0.20 0.15 0.35 0.30 1 0 2 96.5 92 La 0.96 1 0.20 0.15 0.35 0.30 1 0 1 92.3 93* La 0.94 1 0.09 0.09 0.42 0.40 0 0 2 68.9 94* La 0.94 1 0.09 0.09 0.42 0.40 0 0 1 42.1 95 La 0.94 1 0.09 0.09 0.42 0.40 0.1 0 2 94.1 96 La 0.94 1 0.09 0.09 0.42 0.40 0.1 0 1 90.9 97 La 0.94 1 0.09 0.09 0.42 0.40 3 0 2 96.3 98 La 0.94 1 0.09 0.09 0.42 0.40 3 0 1 92.1 99 La 0.99 1 0.12 0.06 0.42 0.40 1 0 2 98.9100 La 0.99 1 0.12 0.06 0.42 0.40 1 0 1 93.6101 La 0.94 1 0.12 0.06 0.42 0.40 1 0 2 98.6102 La 0.94 1 0.12 0.06 0.42 0.40 1 0 1 96.3103 La 0.96 1 0.09 0.05 0.43 0.43 1 0 2 98.1104 La 0.96 1 0.09 0.05 0.43 0.43 1 0 1 97.0105 La 0.96 1 0.09 0.05 0.43 0.43 0.1 0 2 93.2106 La 0.96 1 0.09 0.05 0.43 0.43 0.1 0 1 90.1107 La 0.96 1 0.09 0.05 0.43 0.43 3 0 2 96.2108 La 0.96 1 0.09 0.05 0.43 0.43 3 0 1 92.6109 Nd 0.94 1 0.09 0.09 0.42 0.40 1 0 2 98.3110 Nd 0.94 1 0.09 0.09 0.42 0.40 1 0 1 94.5111 Nd 0.94 1 0.09 0.09 0.42 0.40 1 1 2 97.9112 Nd 0.94 1 0.09 0.09 0.42 0.40 1 1 1 94.3113 Pr 0.94 1 0.09 0.09 0.42 0.40 1 0 2 97.2114 Pr 0.94 1 0.09 0.09 0.42 0.40 1 0 1 93.0115 Pr 0.94 1 0.09 0.09 0.42 0.40 1 1 2 96.1116 Pr 0.94 1 0.09 0.09 0.42 0.40 1 1 1 93.6__________________________________________________________________________
As is obvious from the results shown in Table 3, specimens corresponding to the piezoelectric transformer according to the first embodiment of the present invention exhibited a high efficiency of 90% or more even when the thickness of the piezoelectric element is as thin as 1 mm. Also, specimens corresponding to the piezoelectric transformers according to the second embodiment of the present invention (specimens of Nos. 111, 112, 115, and 116) further exhibited high efficiencies at a sintering temperature lower than 1100.degree. C., indicating that they could be sintered together with a silver-palladium paste to form a laminated structure. Actually, a high conversion efficiency and a high boosting ratio were verified when a laminated piezoelectric transformer comprising 9 layers of piezoelectric bodies (having the composition of the specimen No. 111) and 10 layers of silver-palladium electrodes was fabricated, and its transformer properties were evaluated.
On the contrary, the specimens of Comparative Examples (specimens of Nos. 69, 70, 79, 80, 85, 86, 87, 88, 93, and 94) were known to have significantly lowered efficiencies especially when the thickness of the piezoelectric element was as thin as 1 mm.
The evaluation of temperature rise of the specimen No. 70 (Comparative Example) and specimen No. 110 after continuous driving for 20 minutes showed that their temperature rises when the room temperature was 25.degree. C. were 36.degree. C. and 16.degree. C., respectively, and that the piezoelectric devices using piezoelectric ceramic compositions according to the first and second embodiment of the present invention produced little heat in high-field driving, enabling a high output.
Example 4
Examples and Comparative Examples of the piezoelectric transformers according to the modifications of the first and second embodiments will be described below referring to FIG. 1. FIG. 1 shows the appearance of a piezoelectric transformer according to the present invention.
Granules obtained in the same manner as Example 1 were molded into a rectangular plate having a length of 50 mm, a width of 10 mm, and a thickness of about 3 mm using a mold and a press. After the binder was removed from the molded article by allowing the molded article to stand in the air at 700.degree. C. for 1 hour, the molded article was sintered in the air at 1000-1260.degree. C. for 2 hours. The sintered article was machined into rectangular plates having a length of 40 mm, a width of 7 mm, and a thickness of 2 mm and 1 mm. The piezoelectric body driving portion 1 was formed by the silver baking of input electrodes 3a and 3b on the major surface, and subjected to polarization treatment in the thickness direction. The piezoelectric body power generating portion 2 was formed by forming the output electrode 4 having a width of 1 mm, and subjected to polarization treatment in the length direction between the input electrodes 3a, 3b and the output electrode 4. Arrows in FIG. 1 show the directions of polarization axes. The length of each of the piezoelectric body driving portion 1 and the piezoelectric body power generating portion 2 was 20 mm, respectively. A load resistance of 100 k.OMEGA. was connected to the output electrode 4, and AC electric signals were supplied to the input electrodes 3a and 3b to excite them to make mechanical oscillation. The evaluation of efficiency was performed for the one-wavelength mode (.lambda.-mode) of stretching oscillation in the length direction. The input electric power Win was 3 W, and the resonant frequency was about 80 kHz.
Table 4 shows the compositions, the thickness of piezoelectric elements, and the efficiencies of piezoelectric transformers. Asterisks (*) indicated to the right of the specimen numbers indicate that such samples are beyond the scope of the claim of the present invention.
TABLE 4__________________________________________________________________________ ElementSpecimen ZnO thickness EfficiencyNo. A u v w x y z t (Mole %) (mm) (%)__________________________________________________________________________117 La 0.99 1 0.12 0.09 0.41 0.38 0.980 0 2 97.2118 La 0.99 1 0.12 0.09 0.41 0.38 0.980 0 1 91.0119 La 0.90 1 0.12 0.09 0.41 0.38 0.980 0 2 96.8120 La 0.90 1 0.12 0.09 0.41 0.38 0.980 0 1 94.8121 La1/2Bi1/2 0.94 1 0.12 0.09 0.41 0.38 0.980 0 2 97.3122 La1/2Bi1/2 0.94 1 0.12 0.09 0.41 0.38 0.980 0 1 92.8123* La 0.94 0.90 0.12 0.09 0.41 0.38 0.980 0 2 65.4124* La 0.94 0.90 0.12 0.09 0.41 0.38 0.980 0 1 46.0125 La 0.94 0.97 0.12 0.09 0.41 0.38 0.980 0 2 94.5126 La 0.94 0.97 0.12 0.09 0.41 0.38 0.980 0 1 91.1127 La 0.94 1.03 0.12 0.09 0.41 0.38 0.980 0 2 98.6128 La 0.94 1.03 0.12 0.09 0.41 0.38 0.980 0 1 96.2129* -- 1 1 0 0 0.48 0.52 0.980 0 2 64.9130* -- 1 1 0 0 0.48 0.52 0.980 0 1 38.7131 La 0.96 1 0.01 0.01 0.48 0.50 0.980 0 2 93.8132 La 0.96 1 0.01 0.01 0.48 0.50 0.980 0 1 90.2133 La 0.96 1 0.20 0.15 0.35 0.30 0.980 0 2 97.5134 La 0.96 1 0.20 0.15 0.35 0.30 0.980 0 1 93.6135* La 0.96 1 0.09 0.09 0.42 0.40 1.000 0 2 42.1136* La 0.96 1 0.09 0.09 0.42 0.40 1.000 0 1 32.9137 La 0.96 1 0.09 0.09 0.42 0.40 0.999 0 2 92.7138 La 0.96 1 0.09 0.09 0.42 0.40 0.999 0 1 90.1139 La 0.96 1 0.09 0.09 0.42 0.40 0.960 0 2 98.3140 La 0.96 1 0.09 0.09 0.42 0.40 0.960 0 1 92.0141 La 0.99 1 0.12 0.06 0.42 0.40 0.980 0 2 98.7142 La 0.99 1 0.12 0.06 0.42 0.40 0.980 0 1 95.1143 La 0.92 1 0.12 0.06 0.42 0.40 0.980 0 2 98.6144 La 0.92 1 0.12 0.06 0.42 0.40 0.980 0 1 96.7145 La 0.96 1 0.09 0.05 0.43 0.43 0.999 0 2 96.4146 La 0.96 1 0.09 0.05 0.43 0.43 0.999 0 1 93.0147 La 0.96 1 0.09 0.05 0.43 0.43 0.970 0 2 97.0148 La 0.96 1 0.09 0.05 0.43 0.43 0.970 0 1 93.5149 La 0.96 1 0.09 0.05 0.43 0.43 0.960 0 2 94.9150 La 0.96 1 0.09 0.05 0.43 0.43 0.960 0 1 90.8151 Nd 0.92 1 0.12 0.06 0.42 0.40 0.980 0 2 98.3152 Nd 0.92 1 0.12 0.06 0.42 0.40 0.980 0 1 97.1153 Nd 0.92 1 0.12 0.06 0.42 0.40 0.980 1 2 97.1154 Nd 0.92 1 0.12 0.06 0.42 0.40 0.980 1 1 95.7155 Pr 0.92 1 0.12 0.06 0.42 0.40 0.980 0 2 97.4156 Pr 0.92 1 0.12 0.06 0.42 0.40 0.980 0 1 95.1157 Pr 0.92 1 0.12 0.06 0.42 0.40 0.980 1 2 96.3158 Pr 0.92 1 0.12 0.06 0.42 0.40 0.980 1 1 93.0__________________________________________________________________________
As is obvious from the results shown in Table 4, specimens corresponding to the piezoelectric transformer according to the modification of the first embodiment of the present invention exhibited a high efficiency of 90% or more even when the thickness of the piezoelectric element is as thin as 1 mm. Also, specimens corresponding to the piezoelectric transformers according to the modification of the second embodiment of the present invention (specimens of Nos. 153, 154, 157, and 158) further exhibited high efficiencies at a sintering temperature lower than 1100.degree. C., indicating that they could be sintered together with a silver-palladium paste to form a laminated structure. Actually, a high conversion efficiency and a high boosting ratio were verified when a laminated piezoelectric transformer comprising 9 layers of piezoelectric bodies (having the composition of the specimen No. 153) and 10 layers of silver-palladium electrodes was fabricated, and its transformer properties were evaluated.
Whereas, the specimens of Comparative Examples (specimens of Nos. 123, 124, 129, 130, 135, and 136) were known to have significantly lowered efficiencies especially when the thickness of the piezoelectric element was as thin as 1 mm.
The evaluation of temperature rise of the specimen No. 124 (Comparative Example) and specimen No. 154 after continuous driving for 20 minutes showed that their temperature rises when the room temperature was 25.degree. C. were 62.degree. C. and 18.degree. C., respectively, and that the piezoelectric devices using piezoelectric ceramic compositions according to the modifications of the first and second embodiment of the present invention produced little heat in high-field driving, enabling a high output.
Example 5
Examples and Comparative Examples of the piezoelectric transformers according to the third and fourth embodiments will be described below referring to the drawing. FIG. 2 shows the appearance of a piezoelectric transformer according to the present invention.
Granules obtained in the same manner as Example 1 were molded into a rectangular plate having a length of 50 mm, a width of 10 mm, and a thickness of about 3 mm using a mold and a press. After the binder was removed from the molded article by allowing the molded article to stand in the air at 700.degree. C. for 1 hour, the molded article was sintered in the air at 1000-1260.degree. C. for 2 hours. The sintered article was machined into rectangular plate having a length of 40 mm, a width of 7 mm, and a thickness of 1 mm. The piezoelectric body driving portion 5 was formed by the silver baking of input electrodes 8a and 8b on the major surface, and subjected to polarization treatment in the thickness direction. The piezoelectric body power generating portions 6 and 7 were formed by forming the output electrodes 9a, 9b, 9c, and 9d having a width of 1 mm, and subjected to polarization treatment in the length direction between the input electrodes 8a, 8b and the output electrodes 9a, 9b and the output electrodes 9c, 9d, respectively. Arrows in FIG. 2 show the directions of polarization axes. The length of the piezoelectric body driving portion 5 was 24 mm and that of the piezoelectric body power generating portions 6 and 7 was 8 mm, respectively. Four lead wires were connected to a load resistance of 120 k.OMEGA., and each of the lead wires was connected to the output electrodes 9a, 9b, 9c, and 9d. AC electric signals were supplied to the input electrodes 8a and 8b to excite them to make mechanical oscillation. The evaluation of efficiency was performed for the half-wavelength mode (.lambda./2-mode) of stretching oscillation in the length direction. The input electric power Win was 3 W, and the resonant frequency was about 40 kHz.
Table 5 shows the compositions and the efficiencies of piezoelectric transformers in the half-wavelength mode. Asterisks (*) indicated to the right of the specimen numbers indicate that such samples are beyond the scope of the claim of the present invention.
TABLE 5__________________________________________________________________________Specimen MnO.sub.2 ZnO EfficiencyNo. A u v w x y z (Mole %) (Mole %) (%)__________________________________________________________________________159* -- 1 1 0.09 0.09 0.42 0.40 1 0 71.3160 La 0.99 1 0.09 0.09 0.42 0.40 1 0 86.2161 La 0.94 1 0.09 0.09 0.42 0.40 1 0 91.6162 La 0.85 1 0.09 0.09 0.42 0.40 1 0 85.9163 La1/2Bi1/2 0.94 1 0.09 0.09 0.42 0.40 1 0 89.0164* La 0.94 0.90 0.09 0.09 0.42 0.40 1 0 46.0165 La 0.94 0.97 0.09 0.09 0.42 0.40 1 0 88.9166 La 0.94 1.03 0.09 0.09 0.42 0.40 1 0 90.8167* La 0.94 1.1 0.09 0.09 0.42 0.40 1 0 35.2168* -- 1 1 0 0 0.48 0.52 1 0 30.2169 La 0.96 1 0.01 0.01 0.48 0.50 1 0 86.9170 La 0.96 1 0.20 0.15 0.35 0.30 1 0 88.7171* La 0.94 1 0.09 0.09 0.42 0.40 0 0 31.6172 La 0.94 1 0.09 0.09 0.42 0.40 0.1 0 88.3173 La 0.94 1 0.09 0.09 0.42 0.40 3 0 89.6174 La 0.99 1 0.12 0.06 0.42 0.40 1 0 90.3175 La 0.94 1 0.12 0.06 0.42 0.40 1 0 92.1176 La 0.96 1 0.09 0.05 0.43 0.43 1 0 93.5177 La 0.96 1 0.09 0.05 0.43 0.43 0.1 0 86.3178 La 0.96 1 0.09 0.05 0.43 0.43 3 0 89.3179 Nd 0.94 1 0.09 0.09 0.42 0.40 1 0 92.4180 Nd 0.94 1 0.09 0.09 0.42 0.40 1 1 91.9181 Pr 0.94 1 0.09 0.09 0.42 0.40 1 0 90.8182 Pr 0.94 1 0.09 0.09 0.42 0.40 1 1 89.6__________________________________________________________________________
Resonant frequencies of stretching oscillation in the length direction vary depending on the oscillation mode. When the resonant frequency is 40 kHz, the length of the piezoelectric element in the one-wavelength mode (.lambda.-mode) is about 80 mm, while the length of the piezoelectric element in the half-wavelength mode (.lambda./2-mode) is about 40 mm. That is, in order to realize a piezoelectric transformer of a reduced size, it is effective to make the oscillation mode the half-wavelength mode. However, since the oscillation amplitude increases and mechanical strain increases as the resonant frequency is lowered, the efficiency of the piezoelectric transformer lowers.
However, as is obvious from the results shown in Table 5, the specimen corresponding to the piezoelectric transformer according to the third embodiment of the present invention exhibits a high efficiency of 85% or more even when the driving frequency is as low as 40 kHz. Also, specimens corresponding to the piezoelectric transformers according to the fourth embodiment of the present invention (specimens of Nos. 180 and 182) further exhibited high efficiencies at a sintering temperature lower than 1100.degree. C., indicating that they could be sintered together with a silver-palladium paste to form a laminated structure. Actually, a high conversion efficiency and a high boosting ratio were verified when a laminated piezoelectric transformer comprising 9 layers of piezoelectric bodies (having the composition of the specimen No. 180) and 10 layers of silver-palladium electrodes was fabricated, and its transformer properties were evaluated.
Whereas, the specimens of Comparative Examples (specimens of Nos. 159, 164, 167, 168, and 171) had significantly low efficiencies.
Example 6
Examples and Comparative Examples of the piezoelectric transformers according to the modifications of the third and fourth embodiments will be described below referring to the drawing. FIG. 2 shows the appearance of a piezoelectric transformer according to the present invention.
Granules obtained in the same manner as Example 1 were molded into a rectangular plate having a length of 50 mm, a width of 10 mm, and a thickness of about 3 mm using a mold and a press. After the binder was removed from the molded article by allowing the molded article to stand in the air at 700.degree. C. for 1 hour, the molded article was sintered in the air at 1000-1260.degree. C. for 2 hours. The sintered article was machined into a rectangular plate having a length of 40 mm, a width of 7 mm, and a thickness of 1 mm. The piezoelectric body driving portion 5 was formed by the silver baking of input electrodes 8a and 8b on the major surface, and subjected to polarization treatment in the thickness direction. The piezoelectric body power generating portions 6 and 7 were formed by forming the output electrodes 9a, 9b, 9c, and 9d having a width of 1 mm, and subjected to polarization treatment in the length direction between the input electrodes 8a, 8b and the output electrodes 9a, 9b and the output electrodes 9c, 9d, respectively. Arrows in FIG. 2 show the directions of polarization axes. The length of the piezoelectric body driving portion 5 was 24 mm and that of the piezoelectric body power generating portions 6 and 7 8 mm, respectively. Four lead wires were connected to a load resistance of 120 k.OMEGA., and each of the lead wires was connected to the output electrodes 9a, 9b, 9c, and 9d. AC electric signals were supplied to the input electrodes 8a and 8b to excite them to make mechanical oscillation. The evaluation of efficiency was performed for the half-wavelength mode (.lambda./2-mode) of stretching oscillation in the length direction. The input electric power Win was 3 W, and the resonant frequency was about 40 kHz.
Table 6 shows the compositions and the efficiencies of piezoelectric transformers in the half-wavelength mode. Asterisks (*) indicated to the right of the specimen numbers indicate that such samples are beyond the scope of the claim of the present invention.
TABLE 6__________________________________________________________________________Specimen ZnO EfficiencyNo. A u v w x y z t (Mole %) (%)__________________________________________________________________________183 La 0.99 1 0.12 0.09 0.41 0.38 0.980 0 87.9184 La 0.90 1 0.12 0.09 0.41 0.38 0.980 0 91.8185 La1/2Bi1/2 0.94 1 0.12 0.09 0.41 0.38 0.980 0 90.5186* La 0.94 0.90 0.12 0.09 0.41 0.38 0.980 0 32.6187 La 0.94 0.97 0.12 0.09 0.41 0.38 0.980 0 87.2188 La 0.94 1.03 0.12 0.09 0.41 0.38 0.980 0 94.8189* -- 1 1 0 0 0.48 0.52 0.980 0 31.0190 La 0.96 1 0.01 0.01 0.48 0.50 0.980 0 86.9191 La 0.96 1 0.20 0.15 0.35 0.30 0.980 0 90.4192* La 0.96 1 0.09 0.09 0.42 0.40 1.000 0 23.0193 La 0.96 1 0.09 0.09 0.42 0.40 0.999 0 87.8194 La 0.96 1 0.09 0.09 0.42 0.40 0.960 0 89.9195 La 0.99 1 0.12 0.06 0.42 0.40 0.980 0 93.8196 La 0.92 1 0.12 0.06 0.42 0.40 0.980 0 94.0197 La 0.96 1 0.09 0.05 0.43 0.43 0.999 0 90.1198 La 0.96 1 0.09 0.05 0.43 0.43 0.970 0 91.3199 La 0.96 1 0.09 0.05 0.43 0.43 0.960 0 86.3200 Nd 0.92 1 0.12 0.06 0.42 0.40 0.980 0 92.5201 Nd 0.92 1 0.12 0.06 0.42 0.40 0.980 1 92.0202 Pr 0.92 1 0.12 0.06 0.42 0.40 0.980 0 91.8203 Pr 0.92 1 0.12 0.06 0.42 0.40 0.980 1 90.5__________________________________________________________________________
As is obvious from the results shown in Table 6, specimens corresponding to the piezoelectric transformer according to the modification of the third embodiment of the present invention exhibited a high efficiency of 85% or more even when the driving frequency is as low as 40 kHz. Also, specimens corresponding to the piezoelectric transformers according to the modification of the fourth embodiment of the present invention (specimens of Nos. 201 and 203) further exhibited high efficiencies at a sintering temperature lower than 1100.degree. C., indicating that they could be sintered together with a silver-palladium paste to form a laminated structure. Actually, a high conversion efficiency and a high boosting ratio were verified when a laminated piezoelectric transformer comprising 9 layers of piezoelectric bodies (having the composition of the specimen No. 203) and 10 layers of silver-palladium electrodes was fabricated, and its transformer properties were evaluated.
On the contrary, the specimens of Comparative Examples (specimens of Nos. 186, 188, and 192) had significantly low efficiencies.
Although a centrally driving type construction as FIG. 2 shows was used as a .lambda./2-mode piezoelectric transformer according to this embodiment, the structure is not specifically limited thereto, but the similar effects can be expected from the construction having a polarizing portion in the length direction and a polarizing portion in the thickness direction, and which can be excited in the .lambda./2-mode, such as the construction shown in FIG. 1.
As described above, the present invention according to claims 1 and 2 can provide a piezoelectric ceramic composition having a large mechanical quality factor, which little lowers due to high-field driving.
The present invention according to claims 3 and 4 can provide a piezoelectric ceramic composition which can be sintered at a temperature lower than 1100.degree. C., having a large mechanical quality factor, which little lowers due to high-field driving.
The present invention according to claims 5 and 9 can provide a piezoelectric device which generates little heat during high-field driving, and enables a high output.
The present invention according to claims 6, 7, 10 and 11 can provide a piezoelectric transformer which has a high conversion efficiency and a thin thickness.
The present invention according to claims 8 and 12 can provide a piezoelectric transformer which has a high conversion efficiency even if the driving frequency is low, and has a small size.
The piezoelectric device and the piezoelectric transformer of the present invention according to claims 9 through 12 have the advantage that they can be easily laminated by sintering a piezoelectric ceramic composition together with a silver-palladium paste.

Number	Date	Country	Kind
10-173662	Jun 1998	JPX
11-126423	May 1999	JPX

Number	Name	Date
3998748	Nishida et al.	Dec 1976
5320910	Banno	Jun 1994
5402791	Saitoh et al.	Apr 1995
5410209	Yamashita et al.	Apr 1995
5721464	Dibbern et al.	Feb 1998

Piezoelectric ceramic composition and piezoelectric transformer

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