Patent Application
20090170685
The present invention relates to a method of producing a lead zirconium titanate-based sintered body having a perovskite structure that excessively contains a lead oxide (PbO) component, a lead zirconium titanate-based sintered body, and a lead zirconium titanate-based sputtering target.
Lead zirconium titanate (hereinafter, also referred to as “PZT”) has large permittivity, piezoelectricity, and ferroelectricity, and is in wide industrial use as a thinfilm device among fields of a piezoelectric device, a dielectric memory, an actuator, a sensor, and the like. A sputtering method is often used as a method of producing a PZT thinfilm.
In the case of depositing PZT by the sputtering method, however, there is a problem that a content of PbO (lead oxide) contained in the film is reduced as compared to that contained in a target composition. Specifically, for obtaining a highly-oriented film of PZT, a substrate on which PZT is deposited needs to be heated during deposition or after the deposition. In this case, a phenomenon in which PbO contained in the PZT (Pb(ZrxTi1−x)O3) composition is decomposed by the heat, and Pb or PbO itself is volatilized occurs. Therefore, in the case of depositing PZT by the sputtering method, the target composition and the thin film composition are differed.
When using PZT for the dielectric memory, for example, since properties of a remanent polarization, coercive electric field, and the like become important, it is desirable that the PZT thinfilm has a stoichiometric composition. However, when using a target having the stoichiometric composition, the film composition results in a PbO diminution as compared to the stoichiometric composition.
In this regard, for compensating the content reduced by the volatilization of the PbO, a technique of excessively adding PbO in a target is known. By producing a target using a bulk material formed of PZT excessively containing PbO (hereinafter, referred to as PbO-excess PZT), a thinfilm having a stoichiometric composition can be deposited.
Specifically, Japanese Patent Application Laid-open No. Hei 11-335825 (paragraph [0035]) discloses a method of producing a PZT sintered body that involves mixing and pre-sintering (calcining) raw material powder excessively containing Pb, pulverizing the pre-sintered body thereafter, and carrying out primary sintering and secondary sintering at a temperature higher than the pre-sintering temperature. Moreover, Japanese Patent Application Laid-open No. Hei 11-1367 (paragraphs [0011] and [0012]) discloses a method of producing a PZT sintered body that involves pre-sintering raw material powder having a stoichiometric composition at 800° C., mixing Pb3O4 powder as an excessive lead oxide thereafter, and sintering the resultant at 1,100° C. Furthermore, Japanese Patent Application Laid-open No. Hei 7-18427 discloses a technique in which, focusing on a crystalline structure of Pb, a main body of the excessive PbO has a tetragonal system crystalline structure.
Meanwhile, the following conditions are required for a quality of a sputtering target. First, a crystalline organization distribution needs to be fine and uniform, and a composition distribution also needs to be uniform. Second, purity needs to be controlled. Finally, a relative density needs to be as high as 95% or more in a case of using powder as a raw material. Here, the relative density refers to a ratio of a density of a porous body to a density of a material having the same composition as the porous body but with no pores (the same holds true in descriptions below).
The sputtering target formed of PZT that excessively contains PbO needs to have a sufficient PbO content and a high-density and uniform crystalline structure.
However, because PbO has poor stability in terms of heat as described above, there is a problem that, when the PZT mixed powder excessively containing PbO as compared to the stoichiometric composition is sintered at as high a temperature as 1,000° C. or more as described in Japanese Patent Application Laid-open No. Hei 11-335825, a PbO diminution becomes large and composition control becomes difficult. Moreover, it becomes difficult to increase the relative density of the sintered body due to the loss of PbO.
Japanese Patent Application Laid-open No. Hei 11-335825 also discloses a method of repeating sintering and pulverization a predetermined number of times, as a measure to uniformize the crystalline organization. However, there arises a problem that the compositions may become non-uniform as the number of times the sintering/pulverization are carried out increases, or a new issue concerning an increase in impurities may be caused due to an increase in the number of processes.
Because the method disclosed in Japanese Patent Application Laid-open No. Hei 11-1367 also involves carrying out the sintering of the powder obtained by mixing the pre-sintered powder having the stoichiometric composition and the PbO powder at 1,100° C., there is a problem that composition control becomes difficult due to the reduction of PbO, and a high relative density cannot be obtained.
It should be noted that for suppressing dispersion of PbO during sintering, a method in which pre-sintering and sintering are carried out at a low temperature is conceivable. However, the sintered body obtained by this method most often has a low-density (relative density of about 70%) organization that is not formed with a complete PZT phase, contains many crystalline phases that reflect the raw material powders, and has a non-uniform composition distribution.
Furthermore, Japanese Patent Application Laid-open No. Hei 7-18427 only defines the PbO crystalline structure and does not describe about the density or PbO volatilization amount of the obtained sintered body.
As described above, when producing a PZT sintered body that excessively contains PbO, a crystalline phase from before the final sintering process remains as it is, thus causing a low density of the sintered body. In addition, due to the volatility of PbO, the composition and density of the PZT sintered body become non-uniform, and a mixed composition with a crystalline phase of three phases or more is obtained. When such poor conditions occur at the same time, there have been caused a fluctuation of a voltage/current, generation of particles, and a crack of a target during deposition by the sputtering. Therefore, a target constituted of a high-density, high-quality sintered body having uniform crystalline phases is desired to be developed.
In view of the circumstances as described above, an object of the present invention is to provide a method of producing a high-density lead zirconium titanate-based sintered body having uniform crystalline phases and containing a large amount of PbO, a lead zirconium titanate-based sintered body, and a method of producing a lead zirconium titanate-based sputtering target.
To achieve the above object, according to an embodiment of the present invention, there is provided a method of producing a lead zirconium titanate-based sintered body, including: producing a pre-sintered body by sintering raw material powder of lead zirconium titanate in which PbO, ZrO2, and TiO2 are mixed to have a stoichiometric composition, at a temperature of 900° C. or more and 1,200° C. or less; pulverizing the pre-sintered body; producing lead-excessive mixed powder by adding PbO powder to powder obtained by pulverizing the pre-sintered body; and sintering the lead-excessive mixed powder at a temperature lower than the sintering temperature of the pre-sintered body.
Further, according to another embodiment of the present invention, there is provided a lead zirconium titanate-based sintered body, including: a first crystalline phase formed of lead zirconium titanate having a stoichiometric composition; and a second crystalline phase formed of a lead oxide distributed in the first crystalline phase.
Furthermore, according to another embodiment of the present invention, there is provided a lead zirconium titanate-based sputtering target, including: a first crystalline phase formed of lead zirconium titanate having a stoichiometric composition; and a second crystalline phase formed of a lead oxide distributed in the first crystalline phase.
A method of producing a lead zirconium titanate-based sintered body according to an embodiment of the present invention includes: producing a pre-sintered body (green body) by sintering raw material powder of lead zirconium titanate in which PbO, ZrO2, and TiO2 are mixed to have a stoichiometric composition, at a temperature of 900° C. or more and 1,200° C. or less; pulverizing the pre-sintered body; producing lead-excessive mixed powder by adding PbO powder to powder obtained by pulverizing the pre-sintered body; and sintering the lead-excessive mixed powder at a temperature lower than the sintering temperature of the pre-sintered body.
Because the sintering process is divided into two stages, a high-density (e.g., 95% or more) PZT sintered body constituted only of two types of crystalline phases of PZT having a stoichiometric composition (Pb(ZrTi)O3) in which PbZrO3, PbTiO3, ZrO2, TiO2, PbO, and other intermediate compounds are absent, and excessive PbO can be obtained.
In this embodiment of the present invention, the pre-sintered body is produced by mixing lead oxide powder, zirconium oxide powder, and titanium oxide powder at a stoichiometric composition, and sintering the mixed raw material powder at a temperature of 900° C. or more and 1,200° C. or less. Accordingly, it becomes possible to suppress PbO volatilization and increase the relative density.
Meanwhile, in the process of sintering the mixed powder in which the powder obtained by pulverizing the pre-sintered body and the lead oxide powder are mixed, the mixed powder is sintered at a temperature lower than the sintering temperature of the pre-sintered body. Accordingly, a PbO-excessive lead zirconium titanate-based sintered body in which volatilization of the added PbO is suppressed and that has a high relative density can be obtained. Moreover, since the PbO volatilization can be suppressed, composition control of the lead zirconium titanate-based sintered body is facilitated. As a result, a fine crystalline organization in which crystalline phases (two phases) are dispersed uniformly can be obtained.
By carrying out the sintering of the pre-sintered body and the sintering of the lead-excessive mixed powder in an oxidizing atmosphere, PbO volatilization can additionally be suppressed. Here, the oxidizing atmosphere refers to, for example, an air atmosphere or an oxygen gas atmosphere. An effect of suppressing the PbO volatilization is higher in the oxygen gas atmosphere than in the air atmosphere.
The lead zirconium titanate-based sintered body produced as described above includes a first crystalline phase formed of lead zirconium titanate having a stoichiometric composition, and a second crystalline phase formed of a lead oxide distributed in the first crystalline phase. In other words, a high-density lead zirconium titanate-based sintered body having a uniform chemical composition and crystalline structure and excessively containing PbO can be obtained.
Further, a lead zirconium titanate-based sputtering target according to an embodiment of the present invention includes a first crystalline phase formed of lead zirconium titanate having a stoichiometric composition, and a second crystalline phase formed of a lead oxide distributed in the first crystalline phase. When the lead zirconium titanate-based sputtering target includes two types of crystalline phases, an enlargement of crystals (>10 μm) facilitates anomalous discharge and generation of particles during sputtering. However, according to the embodiment, because the two types of crystals are fine and can be dispersed uniformly, a high-density lead zirconium titanate-based sputtering target having uniform crystalline phases and excessively containing PbO can be obtained. Furthermore, it becomes possible to suppress a fluctuation of a voltage/current, generation of particles, and a crack of a target during sputtering.
As described above, according to the present invention, a lead zirconium titanate-based sintered body with suppressed PbO volatilization and that has uniform crystalline phases and a high density, and excessively contains PbO can be obtained.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
First, a pre-sintered body constituted of a PZT sintered body having a stoichiometric composition is produced (Step 101).
For obtaining the pre-sintered body, lead oxide, zirconium oxide, and titanium oxide are mixed at such a mix ratio as to obtain Pb(Zr0.52Ti0.48)O3 as raw material powder, and sintering is carried out at a temperature of 900° C. or more and 1,200° C. or less while applying a constant pressure. The pressure is desirably 500 kg/cm2 or more. Accordingly, PbO volatilization can be suppressed and a Pb content can be kept constant.
Here, for producing a PZT target excessively containing PbO (hereinafter, also referred to as “PbO-excessive”), sintering has been carried out after excessively adding PbO at a time of mixing raw material powders in the related art. When applying a temperature condition normally used for sintering PZT (e.g., 1,200° C.), PbO is volatilized and dispersed to thus cause a deviation from a mix composition, that is, degradation of uniformity of an average composition or composition distribution is caused, and a value of a density is also lowered.
As is apparent from
As described above, the PZT sintered body in which the raw material powders are mixed at a stoichiometric composition has a suppressed PbO diminution and is excellent in composition controllability. It should be noted that a ceramic crucible or an MgO crucible can be used for sintering the preform.
Next, a sintering temperature of the pre-sintered body will be described.
In producing the pre-sintered body in Step 101, the sintering temperature is set within the range of 900° C. or more and 1,200° C. or less. When the sintering temperature is lower than 900° C., sintering does not progress due to a low temperature, and thus a treatment time is prolonged and a density is not increased. On the other hand, when the sintering temperature is higher than 1,200° C., a speed of PbO volatilization or dispersion is increased, and thus the PbO diminution becomes large and a composition deviation from the mix composition occurs.
As shown in
The sintering of the pre-sintered body in Step 101 is desirably carried out in an oxidizing atmosphere. Particularly in the oxygen gas atmosphere, the relative density is confirmed to increase at the sintering temperature of 1,100° C. or more, as compared to the air atmosphere.
In producing the pre-sintered body in Step 101, a forming pressure of the PZT powder having the stoichiometric composition is desirably 500 kg/cm2 or more.
Next, a process of pulverizing the obtained pre-sintered body is carried out (Step 102).
A suitable pulverizer is used for pulverizing the pre-sintered body. Powder of the pulverized pre-sintered body is sieved to an arbitrary size. In this embodiment, the pre-sintered body is pulverized into powder having an average powder size of 5 μm or less. Accordingly, as will be described later, it becomes possible to increase the relative density and suppress the reduction of the PbO content in the later secondary sintering with PbO powder.
Next, a process of adding and mixing the powder of the pre-sintered body obtained in the pulverizing process described above and excessive PbO powder is carried out (Step 103). The powder of the pre-sintered body and the PbO powder are mixed uniformly by a rod mill or a mixer. Though the excess PbO content to be added is not particularly limited, a range is set within 0.3≦y≦1.0 when the PZT sintered body to be obtained is represented by Pb1+y(ZrxTi1−x)O3+y, for example.
Subsequently, a process of pressure-forming the mixed powder obtained by mixing the powder of the pre-sintered body and the PbO powder into a predetermined shape is carried out (Step 104). Then, a process of sintering the obtained compressed compact of the mixed powder is carried out (Step 105). It should be noted that a ceramic crucible or an MgO crucible, or a plate-like ceramics can be used for sintering the preform.
In the sintering process of Step 105, the compressed compact of the mixed powder is sintered at a temperature lower than the sintering temperature of the pre-sintered body in Step 101. In this embodiment, the sintering temperature is 850° C. or more and 1,000° C. or less, desirably 850° C. or more and 950° C. or less. A ceramic plate containing MgO can be used for sintering the compact.
Since a melting point of PbO itself is 888° C., it has been presumed that, depending on the excess PbO content, melting occurs locally at a temperature around the melting point, and non-uniform sintering progresses. However, by employing the method of producing a sintered body of the present invention described above, it has been confirmed that a precise sintered body can actually be obtained. It should be noted that under the temperature condition of 800° C. or less, the sintering of PbO took a long time, and the relative density was not increased even when the temperature was maintained for a time period about several times the time period that had been considered adequate.
In the forming process of Step 104, the powder size of the powder obtained by pulverizing the pre-sintered body is desirably 5 μm or less.
On the other hand,
Also in producing the preform in Step 104, the forming pressure of the mixed powder obtained by mixing the powder having the stoichiometric composition and the PbO powder is preferably 500 kg/cm2 or more.
In addition, a sintering time in the sintering process of Step 105 was discussed.
The PbO-excess PZT sintered body can be produced as described above. Moreover, a sputtering target is constituted by cutting out the PZT sintered body in a predetermined shape and bonding it to a backing plate (not shown).
According to this embodiment, because the sintering process is divided into two stages, a PbO-excess PZT sintered body that includes a uniform 2-phase mixed organization structure constituted of a first crystalline phase P1 formed of PZT having the stoichiometric composition and a second crystalline phase P2 formed of PbO distributed in the first crystalline phase P1, and has a high relative density, as shown in
Further, the PZT sintered body produced as described above was mechanically processed using a cutting machine and a grinding machine to thus form a sputtering target plate, and the sputtering target plate was then bonded to the backing plate. In this case, while 3 out of 10 targets were cracked with a low-density (80% or less) PZT sintered body of the related art, none were cracked with the PZT sintered body of this embodiment.
It should be noted that in the descriptions above, although the pressure-forming process and sintering process of the mixed powder have been carried out separately in the production of the PZT pre-sintered body having the stoichiometric composition and the production of the PbO-excess PZT sintered body, a hot-press method (vacuum high-temperature high-pressure sintering method) in which the pressure-forming and sintering are carried out at the same time may also be employed.
Hereinafter, examples of the present invention will be described.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an MgO crucible and pre-sintered at 1,200° C. for 1.0 hour in an oxygen atmosphere, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 2.00:0.52:0.48. The obtained mixed powder was subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 900° C. for 0.5 hour in the oxygen atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 98.0%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, only peaks of two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an MgO crucible and pre-sintered at 1,100° C. for 1.0 hour in an oxygen atmosphere, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 2.00:0.52:0.48. The obtained mixed powder was subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 850° C. for 0.5 hour in the oxygen atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 97.2%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, only peaks of two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an MgO crucible and pre-sintered at 1,100° C. for 1.0 hour in an oxygen atmosphere, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 1.80:0.52:0.48. The obtained mixed powder was subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 850° C. for 0.5 hour in the oxygen atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 97.2%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, only peaks of two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an Al2O3 crucible and pre-sintered at 900° C. for 1.0 hour in an air atmosphere, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 1.80:0.52:0.48. The obtained mixed powder was subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 850° C. for 1.0 hour in the air atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 95.3%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, only peaks of two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an MgO crucible and pre-sintered at 1,200° C. for 1.0 hour in an oxygen atmosphere, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 1.50:0.52:0.48. The obtained mixed powder was subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 900° C. for 1.0 hour in the oxygen atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 96.2%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, only peaks of two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an MgO crucible and pre-sintered at 1,200° C. for 1.0 hour in an oxygen atmosphere, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 1.30:0.52:0.48. The obtained mixed powder was subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 850° C. for 1.0 hour in the oxygen atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 95.1%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, only peaks of two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an MgO crucible and pre-sintered at 1,100° C. for 1.0 hour in an oxygen atmosphere, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 1.30:0.52:0.48. The obtained mixed powder was subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 900° C. for 1.0 hour in the oxygen atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 97.2%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, only peaks of two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an MgO crucible and pre-sintered at 1,200° C. for 1.0 hour, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 1.30:0.52:0.48. The obtained mixed powder was subjected to vacuum high-temperature high-pressure sintering (HP) at 850° C. for 1.0 hour, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 97.5%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, only peaks of two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.00:0.40:0.60, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an Al2O3 crucible and pre-sintered at 800° C. for 1.0 hour, to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm, and PbO powder was added and mixed so that the mol ratio became 1.50:0.52:0.48. The obtained mixed powder was subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 700° C. for 1.0 hour in the air atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 74.5%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, peaks indicating many other phases than two phases of PZT and PbO were confirmed.
Raw material powders of PbO, ZrO2, and TiO2 were mixed at a mol ratio of Pb:Zr:Ti=1.30:0.52:0.48, and the mixed powder was subjected to hydrostatic pressure forming at a pressure of 1,000 kg/cm2, to thus obtain a preform. The preform was put in an MgO crucible and pre-sintered at 900° C. for 1.0 hours to thus obtain a PZT pre-sintered body having a stoichiometric composition. The PZT pre-sintered body was then pulverized into powder having an average powder size of 5 μm and subjected to hydrostatic pressure forming at a pressure of 2,000 kg/cm2. The obtained compact was placed on an MgO plate and sintered at 950° C. for 1.0 hour in the oxygen atmosphere, to thus obtain a PbO-excess PZT sintered body.
A measurement of a relative density of the PbO-excess PZT sintered body showed a result of 70.0%. Moreover, as a result of conducting a powder XRD measurement on a part of the PbO-excess PZT sintered body that has been changed into powder, peaks indicating many other phases than two phases of PZT and PbO were confirmed.
Of the examples above, Examples 1 to 8 each show a PbO-excess PZT sintered body produced by the method described in the embodiment of the present invention, whereas Comparative Example 1 shows a PbO-excess PZT sintered body sintered at a lower temperature. Moreover, Comparative Example 2 shows a PbO-excess PZT sintered body produced by the production method of the related art, that is, by adding excessive PbO at a stage of mixing the raw materials.
Meanwhile, the PZT sintered body produced by the method described in Example 7 (relative density of 97%) and the PZT sintered body produced by the method described in Comparative Example 2 (relative density of 70%) were compared for its mechanical strength. In the experiment, the number of defective sintered bodies (generation of cracks in sintered bodies) at a time of processing the sintered body into a target and a time of bonding the sintered body to the backing plate was checked.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-336437 | Dec 2007 | JP | national |
