WO2015093436A1

WO2015093436A1 - Piezoelectric ceramic with crystal orientation, production method therefor, and piezoelectric element

Info

Publication number: WO2015093436A1
Application number: PCT/JP2014/083134
Authority: WO
Inventors: 智紹加藤; 航士山田
Original assignee: 日立金属株式会社
Priority date: 2013-12-16
Filing date: 2014-12-15
Publication date: 2015-06-25
Also published as: JPWO2015093436A1

Abstract

The piezoelectric ceramic with crystal orientation includes a lead-free perovskite-type compound as the main component and is characterized in that: the piezoelectric ceramic is represented by the general formula (1-s)A1B1O₃-sBaMO₃ (where A1 represents at least one species of element selected from alkaline metals, B1 represents at least one species of element among the transition metal elements and contains Nb, M represents at least one species of element among the Group 4A and contains Zr, and 0< s ≤ 0.15); the piezoelectric ceramic has a plurality of oriented crystals, whereof the crystallographic orientation is aligned with one another, and a plurality of non-oriented crystals present in an irregular crystallographic orientation state; the average crystal particle size for the plurality of non-oriented crystals is between 1.0 μm exclusive and 5.0 μm inclusive; the degree of orientation is between 85% inclusive and 100% exclusive according to the Lotgering method; and the piezoelectric constant d33 is 350 pC/N or greater.

Description

Crystal-oriented piezoelectric ceramic, manufacturing method thereof, and piezoelectric element

The present invention relates to a crystal-oriented piezoelectric ceramic, a manufacturing method thereof, and a piezoelectric element.

Conventionally, various ceramic materials have been developed as piezoelectric materials used in piezoelectric devices. Among them, a piezoelectric ceramic made of PbZrO ₃ —PbTiO ₃ (PZT), which is a lead-containing perovskite ferroelectric, exhibits excellent piezoelectric characteristics. For this reason, PZT ceramics have been widely used in the fields of electronics, mechatronics, automobiles and the like.

However, in recent years, due to increasing awareness of environmental conservation, the tendency to not use metals such as Pb, Hg, Cd, and Cr ⁶⁺ in electronic and electrical equipment has increased, and a ban on use (RoHS Directive) has been issued mainly in Europe. It has been enforced.

Considering the wide use of conventional lead-containing piezoelectric ceramics, research on lead-free piezoelectric ceramics that are environmentally friendly is an important and urgent task. For this reason, there is an interest in lead-free piezoelectric ceramics that can exhibit performance comparable to that of conventional PZT piezoelectric ceramics.

Also, the piezoelectric ceramic is required to have a large piezoelectric constant d33 (mechanical displacement ratio per electric field in 33 directions).

As a polycrystalline ceramic having a relatively high piezoelectric constant d33, a piezoelectric ceramic in which a crystal is oriented (hereinafter referred to as a crystal oriented piezoelectric ceramic) is attracting attention as compared with a conventional non-oriented piezoelectric ceramic.

For example, Patent Document 1 discloses a lead-free crystal-oriented piezoelectric ceramic. Specifically, an isotropic perovskite compound represented by the general formula: ABO ₃ , wherein the main component of the A site element is K and / or Na, and the main component of the B site element is Nb, Sb, and Crystal-oriented piezoelectric ceramics comprising a polycrystal having a main phase of the first perovskite-type pentavalent metal acid alkali compound as Ta and / or a specific crystal plane of each crystal grain constituting the polycrystal Is disclosed.

JP 2003-12373 A

Conventional lead-free crystal-oriented piezoelectric ceramics have been required to have a higher piezoelectric constant d33.

An object of the present invention is to provide a lead-free crystal-oriented piezoelectric ceramic having a large piezoelectric constant d33, a piezoelectric element, and a method for manufacturing the piezoelectric ceramic.

The crystal-oriented piezoelectric ceramic of the present disclosure is a crystal-oriented piezoelectric ceramic containing a lead-free perovskite compound as a main component, and the perovskite compound has the general formula: (1-s) A1B1O ₃ -sBaMO ₃ (where A1 is at least one element selected from alkali metals, B1 is at least one element of transition metal elements and contains Nb, M is at least one element of Group 4A and contains Zr, and 0 < s ≦ 0.15), and the crystal-oriented piezoelectric ceramic includes a plurality of oriented crystals having crystal orientations aligned with each other, and a plurality of non-oriented crystals having crystal orientations in an irregular state. The average crystal grain size of the non-oriented crystal is larger than 1.0 μm and not larger than 5.0 μm, and the degree of orientation by the Lotgering method is 85% or more and less than 100%. The number d33 is 350 pC / N or more.

The above-mentioned crystal-oriented piezoelectric ceramic has a degree of orientation by the Lotgering method of 90% or more, an average crystal grain size of the plurality of non-oriented crystals of 1.3 μm to 4.5 μm, and a piezoelectric constant d33 of 400 pC / N or more. It is preferable that

The relative density is preferably 95.0% or more and 98.5% or less.

It is possible to form a piezoelectric element by forming a plurality of electrodes on these crystal-oriented piezoelectric ceramics.

Also, it is possible to form a piezoelectric element in which a plurality of ceramic layers including these crystal-oriented piezoelectric ceramics and a plurality of electrodes are formed, and the plurality of electrodes and the plurality of ceramic layers are alternately laminated.

The method for producing a crystal-oriented piezoelectric ceramic according to the present disclosure includes a step of preparing a first crystal powder of a bismuth layered structure compound including a (Bi ₂ O ₂ ) ²⁺ layer and a pseudo-perovskite layer, and reducing Bi from the first crystal powder. A step of preparing a plate-like crystal powder comprising the first perovskite compound obtained by mixing the additive raw material with the plate-like crystal powder, and the overall formula: (1-s) A1B1O ₃ — sBaMO ₃ (where A1 is at least one element selected from alkali metals, B1 is at least one element of a transition metal element and contains Nb, and M is at least one element of Group 4A and is Zr A process having a composition represented by 0 <s ≦ 0.15), a process using the mixture as a molded body, and the molded body having an oxygen partial pressure of 1 × 10 ⁻¹⁴ atm or more and 3 × 10 ^{-1 It includes} a step of sintering in a reducing atmosphere of ⁰ atm or less, and a step of subjecting the sintered body to a polarization treatment.

In the step of sintering in the reducing atmosphere, the oxygen partial pressure is preferably 7 × 10 ⁻¹⁴ atm or more and 4 × 10 ⁻¹³ atm or less.

In the sintering step, the sintering temperature is preferably 1135 ° C. or higher and 1170 ° C. or lower.

According to the present invention, it is possible to provide a crystal-oriented piezoelectric ceramic that is lead-free and has a large piezoelectric constant d33. Thereby, since the amount of displacement of ceramics increases even with a small voltage difference, a lead-free piezoelectric element with good response can be provided.

It is a SEM observation photograph (1500 times) of the crystal | crystallization of the crystal orientation piezoelectric ceramic of this invention. It is a figure which shows an example of the process (until preparation of plate-shaped crystal powder) of the manufacturing method of this invention. It is a figure which shows an example of the process (after the process of FIG. 2) of the manufacturing method of this invention. It is a schematic diagram of the layered structure of the 1st crystal powder used for the manufacturing method of this invention. It is a cross-sectional schematic diagram which shows the sheet-like molded object which the plate-shaped crystal powder orientated used for the manufacturing method of this invention. It is a SEM observation photograph (5000 times) of the non-oriented crystal | crystallization of the crystal orientation piezoelectric ceramic of this invention. It is a figure which shows the SEM observation photograph (500 times) of the 1st crystal powder used for the manufacturing method of this invention. It is a figure which shows the X-ray-diffraction result of the 1st crystal powder used for the manufacturing method of this invention. It is a figure which shows the detail of a composition of the 1st crystal powder used for the manufacturing method of this invention. Orientation degree of the oxygen partial pressure in the firing atmosphere (PO ₂₎ in the manufacturing method of the grain-oriented piezoelectric ceramic of the present invention, is a diagram showing the relationship between the piezoelectric constant d33 and the oxygen partial pressure (PO _2). Is a diagram showing the relationship between the oxygen partial pressure (PO ₂₎ and the relative density in the firing atmosphere in the method for manufacturing a grain-oriented piezoelectric ceramic of the present invention. It is a figure which shows the relationship between the sintering temperature and relative density of the crystal orientation piezoelectric ceramic of this invention, and a sintering temperature and orientation degree. It is a figure which shows the relationship between the relative density and orientation degree of the crystal orientation piezoelectric ceramic of this invention. It is a figure which shows the relationship between the sintering temperature and relative density of a crystal orientation piezoelectric ceramic of a comparative example, and a sintering temperature and orientation degree. It is a figure which shows the relationship between the relative density and orientation degree of the crystal orientation piezoelectric ceramic of a comparative example.

The crystal-oriented piezoelectric ceramic generally has a larger piezoelectric constant d33 as the relative density after sintering is higher. However, as a result of investigation by the present inventor, it is sufficient that the crystal-oriented piezoelectric ceramic using the piezoelectric material having the composition system represented by the general formula: (1-s) A1B1O ₃ -sBaMO ₃ is sufficient only by increasing the relative density. It has been found that the piezoelectric constant d33 may not be obtained. As a result of further detailed studies, the present inventors have obtained crystal-oriented piezoelectric ceramics having extremely high d33 by setting the average crystal grain size of non-oriented crystals (hereinafter referred to as non-oriented crystals) within a predetermined range. I found out that Hereinafter, embodiments of the crystal-oriented piezoelectric ceramic, the manufacturing method thereof, and the piezoelectric element of the present invention will be described. First, the crystal-oriented piezoelectric ceramic will be described.

1. Crystal Oriented Piezoelectric Ceramics [Composition of Crystal Oriented Piezoelectric Ceramics]
The crystal-oriented piezoelectric ceramic of the present embodiment contains a ceramic represented by the following general formula (1) as a main component. The main component is a lead-free perovskite type compound.
(1-s) A1B1O ₃ -sBaMO ₃ (0 <s ≦ 0.15) (1)
Here, A1 is at least one element selected from alkali metals, B1 is at least one element of transition metal elements and contains Nb, and M is at least one element of Group 4A and contains Zr.

The crystal-oriented piezoelectric ceramic may not be composed of only the perovskite type compound having the composition defined by the general formula (1), and contains 80 mol% or more of the ceramic having the composition represented by the general formula (1). In other words, a high piezoelectric constant d33 is exhibited. That is, it is sufficient if the composition represented by the general formula (1) is included as a main component. In this case, the relative density of the main component may be 95.0% or more and 98.5% or less.

Composition represented by A1B1O ₃ is an alkali metal-containing niobium oxide. Specifically, A1 is at least one element selected from alkali metals, and B1 is at least one element of transition metal elements and contains Nb. The alkali metal-containing niobium oxide having this composition is known as a composition of piezoelectric ceramics having a tetragonal perovskite structure that is easy to obtain a high piezoelectric constant while being lead-free.

More specifically, in the composition represented by A1B1O _3, A1 is at least one selected from alkali metal (Li, Na, K). Preferably, A1 includes all of Li, K and Na.

Preferably, A1B1O ₃ is expressed by the formula is represented by _{_{_{K 1-xy Na x Li y}}} (Nb 1-z Q z) O 3. Here, Q is at least one transition metal element other than Nb, preferably Nb. x, y, and z satisfy 0 <x <1, 0 <y <1, and 0 ≦ z ≦ 0.3.

By including both K and Na as the alkali metal, a higher piezoelectric constant can be exhibited than when K or Na is included alone. Li can also have the effect of increasing the Curie temperature of crystal-oriented piezoelectric ceramics and the effect of increasing the piezoelectric constant by increasing the sinterability. Moreover, the effect which improves mechanical strength can also be show | played. However, when the Li content y exceeds 0.3, the piezoelectric constant tends to decrease. For this reason, the content y of Li in the alkali metal is preferably 0 <y ≦ 0.3. Q is not essential, but can be added within the range of x. The ranges of x, y, and z are more preferably 0.3 ≦ x ≦ 0.7, 0.05 ≦ y ≦ 0.2, and 0 ≦ z ≦ 0.2.

BaMO ₃ can have the effect of increasing the dielectric constant. M preferably contains 80 mass% or more of Zr as group 4A.

A1B1O ₃ and BaMO ₃ are contained in the piezoelectric ceramic in a ratio represented by the general formula (1).

When the content ratio s of BaMO ₃ is in the range of 0 <s ≦ 0.15, a piezoelectric ceramic having a high piezoelectric constant d33 and a high Curie temperature can be obtained. On the other hand, when s is 0 or s exceeds 0.15, the piezoelectric constant d33 becomes too low, making it difficult to obtain a practical piezoelectric ceramic. s is preferably greater than 0.05. Thereby, a higher piezoelectric constant d33 can be obtained. A more preferable range of s is 0.065 ≦ s ≦ 0.10.

A material having a composition represented by (R · A2) TiO ₃ can be further added to the above composition. In that case, the above general formula is represented by the following general formula (1 ′).
(1-st) A1B1O ₃ —sBaMO ₃ —t (R · A2) TiO ₃
... (1 ')
Here, A1 is at least one element selected from alkali metals, B1 is at least one element of transition metal elements and contains Nb, M is at least one element of Group 4A and contains Zr , R is at least one element of rare earth elements (including Y), A2 is at least one element selected from alkali metals, and s and t are 0 <s ≦ 0.15, 0 <t ≦ 0.03 is satisfied.

(R · A2) TiO ₃ is a ceramic composition having a rhombohedral perovskite structure. By mixing the composition represented by (R · A2) TiO ₃ with the composition represented by A1B1O ₃ , a piezoelectric ceramic having a phase boundary such as a tetragonal crystal-rhombus crystal can be obtained.

In the case of the above general formula, when t exceeds 0.03, the amount of expensive rare earth used increases and the raw material cost increases. A preferable range of t is 0.005 ≦ t ≦ 0.02.

The (R · A2) of the (R · A2) TiO ₃ refers to (R _0.5 A2 _0.5 ). 0.5 includes a range of significant digits, that is, the ratio of R to A2 is in the range of R: A2 = 0.45: 0.54 to 0.54: 0.45.

R is particularly preferably at least one selected from Y, La and Ce, and among them, La is more preferable. Since rare earth elements such as La, Y, and Ce, which have a low standard free energy of formation of oxides, are used, these elements cause little volatilization during sintering and can suppress fluctuations in the composition of the ceramic.

A2 is particularly preferably at least one selected from the group consisting of Li, Na, and K, and Na is more preferable among them. By using this element, the piezoelectric constant d33 can be increased.

[Crystal structure of crystal-oriented piezoelectric ceramics]
FIG. 1 shows a cross section perpendicular to the thickness direction of the oriented plate crystal powder of the crystal oriented piezoelectric ceramic of the present embodiment. As can be seen from FIG. 1, the crystal-oriented piezoelectric ceramic of the present embodiment includes a plurality of oriented crystals a (crystal orientation is (100)) in which crystal orientations are aligned with each other, and a plurality of crystal orientations that exist in an irregular state. It has a non-oriented crystal b. Each oriented crystal a is obtained by growing a plate-like crystal powder, and each non-oriented crystal b is obtained by crystallizing an additive raw material.

The plurality of oriented crystals a have crystal orientations aligned in the thickness direction (100) of the plate. The plurality of non-oriented crystals b have an isotropic (random) crystal orientation. That is, the crystal orientations of the plurality of non-oriented crystals b do not match (align). In the oriented crystal region a, the granular black portion is a void. The oriented crystal a often has a larger particle size than the non-oriented crystal b. Here, the crystal refers to a region of crystal grains that is generally a single crystal.

A non-oriented crystal can be identified by analyzing the orientation of the crystal with an electron backscattering pattern EBSP (Electron Back Scattering Pattern). In the analysis by EBSP, each crystal can be displayed in different colors depending on the angle at which the crystal orientation is shifted from the (100) direction. Each crystal in a region that is clustered in an irregular crystal orientation is this non-oriented crystal.

The average crystal grain size of non-oriented crystals is larger than 1.0 μm and not larger than 5.0 μm. When the average crystal grain size of the non-oriented crystal is 1.0 μm or less, grain growth due to diffusion does not occur sufficiently, and the piezoelectric constant d33 is relatively small. This is considered to be caused by the fact that the plate-like crystal powder does not grow.

On the other hand, when the average crystal grain size of the non-oriented crystal exceeds 5.0 μm, the non-oriented crystal grows excessively, and on the contrary, the grain growth of the plate-like crystal powder is suppressed. In this case as well, the piezoelectric constant d33 is improved. It is thought that it is not connected. A method for measuring the average crystal grain size of the non-oriented crystal will be described later.

According to the knowledge of the present inventor, in order to control the size of the non-oriented crystal, the oxygen partial pressure (hereinafter sometimes referred to as PO ₂ ) of the atmosphere during sintering can be set within a predetermined range. It is valid. It is considered that oxygen vacancies introduced into the ceramics are related to the diffusion rate, and high diffusivity is ensured by introducing sufficient oxygen vacancies.

The atmosphere during sintering is preferably a reducing atmosphere having an oxygen partial pressure of 1 × 10 ⁻¹⁴ atm or more and 3 × 10 ⁻¹⁰ atm or less.

By setting the oxygen partial pressure to 3 × 10 ⁻¹⁰ atm or less, the average crystal grain size of the non-oriented crystal can be increased to more than 1.0 μm. In addition, crystal oriented piezoelectric ceramics having a piezoelectric constant d33 of 350 pC / N or more can be obtained. Under a high oxygen partial pressure exceeding 3 × 10 ⁻¹⁰ atm, sufficient oxygen defects are not introduced, grain growth due to diffusion does not occur sufficiently, and plate-like crystal powder does not grow. For this reason, it is considered that the piezoelectric constant d33 is not improved.

On the other hand, by setting the oxygen partial pressure to 1 × 10 ⁻¹⁴ atm or more, the average crystal grain size of the non-oriented crystal can be set to 5.0 μm or less. At a low oxygen partial pressure of less than 1 × 10 ⁻¹⁴ atm, it is considered that the grain growth of the plate-like crystal powder is suppressed and does not lead to an improvement in the piezoelectric constant d33.

[Physical properties of crystal-oriented piezoelectric ceramics]
The crystal-oriented piezoelectric ceramic of the present embodiment has an orientation degree by the Lotgering method of 85% or more and less than 100%. Preferably, the degree of orientation is 90% or more and less than 100%.

Further, the crystal-oriented piezoelectric ceramic of the present embodiment has a piezoelectric constant d33 of 350 pC / N or more. Preferably, the piezoelectric constant is 400 pC / N or more.

In the crystal-oriented piezoelectric ceramic of this embodiment, when the degree of orientation is 90% or more and less than 100%, a piezoelectric constant d33 of 400 pC / N or more is obtained.

2. Piezoelectric Element The crystal-oriented piezoelectric ceramic of the present embodiment has a high piezoelectric constant, and can be used for various applications as a bulk sintered body. Moreover, an electrode can be formed to form a piezoelectric element. For example, it is possible to form a piezoelectric element by forming electrodes on two main surfaces of a crystal-oriented piezoelectric ceramic that is a bulk sintered body. The piezoelectric element may include a plurality of ceramic layers including crystal-oriented piezoelectric ceramics and a plurality of electrodes, and the plurality of electrodes and the plurality of ceramic layers may be alternately stacked. In this case, for example, a metal such as Ag can be used for the electrode.

When a laminated piezoelectric body is composed of crystal-oriented piezoelectric ceramics, it is common to measure the relative density of crystal-oriented piezoelectric ceramics in such piezoelectric elements because other materials such as electrodes exist between the ceramic layers. It is difficult to do. In this case, the relative density can be obtained by measuring the porosity. The porosity φ can be calculated from the equation φ = Sp / S as the cross-sectional area S of the ceramic and the area Sp of the void existing on the cross-sectional area, and can also be calculated from the laminated piezoelectric material. Since the value obtained by dividing the value of porosity φ from 100 (%) is the same value as the relative density, the crystal orientation piezoelectric ceramic of the present embodiment depends on whether the porosity φ is 1.5% or more and 5% or less. Further, it can be determined whether it is preferable.

3. Method for Producing Crystal Oriented Piezoelectric Ceramics One embodiment of the method for producing crystal oriented piezoelectric ceramics of the present invention will be described below. The crystal-oriented piezoelectric ceramic according to the present embodiment can be manufactured, for example, by the following manufacturing process.
(1) preparing a first crystal powder of a bismuth layered structure compound comprising a (Bi ₂ O ₂ ) ²⁺ layer and a pseudo-perovskite layer;
(2) preparing a plate-like crystal powder comprising the first perovskite type compound with reduced Bi from the first crystal powder;
(3) An additive raw material is mixed with the plate-like crystal powder, and the general formula: (1-s) A1B1O ₃ —sBaMO ₃ (where A1 is at least one element selected from alkali metals) , B1 is at least one element of transition metal elements and contains Nb, M is at least one element of Group 4A and contains Zr, and a mixture having a composition represented by 0 <s ≦ 0.15) The process of
(4) a step of using the mixture as a molded body,
(5) sintering the molded body in a reducing atmosphere having an oxygen partial pressure of 1 × 10 ⁻¹⁴ atm to 3 × 10 ⁻¹⁰ atm;
(6) Step of applying polarization treatment to the sintered body

Hereinafter, each process will be described with reference to the flowcharts shown in FIGS.

(1) Step of Preparing First Crystal Powder A step of preparing a first crystal powder of a bismuth layered structure compound comprising a (Bi ₂ O ₂ ) ²⁺ layer and a pseudo-perovskite layer, which is the first step (1). Will be explained.

As shown schematically in FIG. 4, the first crystal powder has a crystal structure in which (Bi ₂ O ₂ ) ²⁺ layers 2 and pseudo-perovskite layers 1 are alternately stacked. Since the crystal is grown in a plate shape in the subsequent steps, it can be used as a template for the plate crystal powder as described later.

In the present embodiment, for example, the first crystal powder is a general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 A3 _m-1.5 Nb _m O _{3m + 1} ) ²⁻ (where A3 is selected from alkali metals). Or an element represented by m is an integer of 2 or more. In this general formula, the left side shows the (Bi ₂ O ₂ ) ²⁺ layer, and the right side shows the composition of the pseudo-perovskite layer.

In addition, as the first crystal powder in which the pseudo-perovskite layer does not contain Bi, the general formula: (Bi ₂ O ₂ ) ²⁺ (A3 _m-1 B2 _m O _{3m + 1} ) ²⁻ (where A3 is an alkali metal) And B2 is at least one element selected from 4, 5 and 6 valent elements, and m is an integer of 2 or more. A3 is preferably at least one element selected from Li, K, or Na. B2 is preferably at least one element of Nb and Ta.

First, raw materials are prepared (S1), mixed (S2), the mixed raw materials are dried, and a first flux such as NaCl is added (S3). As the first flux, for example, an alkali metal chloride or fluoride such as NaCl or KCl, nitrate, sulfate, or the like can be used.

Thereafter, the raw material to which the first flux is added is heated in the air at 700 ° C. or higher and 1300 ° C. or lower (S4), and the raw material is reacted to grow a crystal that becomes the first crystal powder. By this heating, a reaction product composed of the first crystal powder and the flux can be obtained. When heating, multistage heat treatment can also be employed. In order to sufficiently react the first crystal powder and the flux, the heating time is preferably set to 1 minute or longer. Long-time heating tends to decrease the aspect ratio of the obtained plate-like powder shape as the treatment time becomes longer, and is preferably 10 hours or less. The reaction product (first intermediate fired body) after heating is filled with flux around it and becomes a lump.

Thereafter, the first flux is removed from the reaction product (S5). In this step, a method of melting the first flux by immersing the reactant in warm water may be used. Thereby, only the first crystal powder can be taken out.

(2) Step of obtaining plate-like crystal powder The step of preparing plate-like crystal powder made of the first perovskite type compound in which Bi is reduced from the first crystal powder, which is step (2), will be described below. . This step is shown in steps S6 to S10 in FIG.

The first crystal powder, the first additive such as Na ₂ CO ₃ for generating the plate crystal powder, and the flux of NaCl or the like that melts at a temperature at which the first crystal powder and the first additive can react. 2 flux) (S6, S7).

As the first additive, the above-described A1 element compound of the crystal-oriented ceramic represented by A1B1O ₃ , for example, an A1 element oxide or carbonate material can be used. The amount of the first additive added is adjusted so that the molar ratio of the A1 element to the B1 element becomes 1: 1 after the reduction of the Bi component (S10) with respect to the first crystal powder.

In order to mix the first additive, for example, a means of adding a raw material in an organic solvent and mixing with a ball mill or the like can be used.

The second flux is used to promote crystal growth by the reaction between the first crystal powder and the first additive in the solution. Therefore, it is preferable to use a material that has a melting point that is lower than that of the first crystal powder or the first additive. Moreover, it is preferable that it is a composition which does not contain elements other than the composition of the desired plate-like crystal powder by reaction. For example, alkali metal chlorides such as NaCl and KCl can be used.

Since this second flux is easily dissolved in water or a solvent, the second flux is added and mixed after drying the organic solvent or the like. The amount of the second flux added is preferably 10 mass% or more, more preferably 30 mass% or more with respect to the first crystal powder.

Thereafter, the mixed material is fired at a temperature at which the first crystal powder and the first additive can react (S8). A first intermediate fired body is obtained by this firing.

Calcination is preferably performed at 600 ° C. or higher and 1300 ° C. or lower. If the firing is less than 600 ° C., composition conversion from the first crystal powder to the plate-like crystal powder hardly occurs, and if it exceeds 1300 ° C., the first crystal powder dissolves and is integrally fired to form a powder. It becomes difficult to do.

Calcination is preferably held at the above temperature for 0.5 hour or more. If it is less than 0.5 hour, composition conversion from the first crystal powder to the plate-like crystal powder hardly occurs. The firing time is more preferably 3 hours or more. Further, if the firing time exceeds 24 hours, the production time becomes long and the productivity is lowered, so that it is preferably 24 hours or less, and more preferably 20 hours or less.

Next, the second flux is removed from the first intermediate fired body (S9). In order to remove the second flux from the first intermediate fired body, means for immersing the first intermediate fired body in warm water and stirring it, and filtering the melted second flux can be employed. Thereby, the second flux can be removed.

Next, the Bi component remaining in the plate-like powder remaining after removing the second flux is reduced (S10). This powder is put into a pickling solution in which water and an acid such as nitric acid are mixed and pickled, and the Bi component is dissolved in the solution. The powder from which the Bi component has been removed becomes a plate-like crystal powder used in the present invention, and is precipitated in the pickling solution. The plate-like crystal powder can be extracted by removing the pickling solution from the supernatant and drying the residue. Pickling can be repeated multiple times.

Since this plate-like crystal powder maintains the same shape using the plate-like shape of the first crystal powder as a template, a plate-like crystal powder with a high aspect ratio can be obtained.

The plate-like crystal powder may be a perovskite-type compound represented by the general formula A1B1O _3. In this plate-like crystal powder, A1 is particularly preferably at least one selected from the group consisting of Li, K and Na. B1 is particularly preferably at least one element selected from 4, 5, and 6-valent elements.

(3) Step of obtaining a mixture having the composition represented by the general formula (1) Below, an additive raw material is mixed with the plate-like crystal powder which is the step (3) of the production method of the present invention. A general formula: (1-s) A1B1O ₃ —sBaMO ₃ (where A1 is at least one element selected from alkali metals, B1 is at least one element of transition metal elements and contains Nb; M represents at least one element of Group 4A, which includes Zr, and describes a process of making a mixture having a composition represented by 0 <s ≦ 0.15). This step is shown as step S11 in FIG.

As shown in step S11, the plate crystal powder and the additive raw material are mixed.

The additive raw material is mixed with the plate crystal powder to obtain a general formula: (1-s) A1B1O ₃ —sBaMO ₃ (where A1 is at least one element selected from alkali metals, and B1 is a transition metal) A raw material having a composition represented by 0 <s ≦ 0.15), which is at least one kind of element and contains Nb, is used.

The plate-like crystal powder is preferably added at a ratio of 0.1 to 10 mol% with respect to the additive raw material.

(4) Step of Obtaining Molded Body Hereinafter, the step of using the mixture as the molded body, which is the fourth step of the production method of the present invention, will be described. This step is shown as step S12 in FIG.

After the plate crystal powder and the additive raw material are mixed, the plate crystal powder is molded so as to be oriented. For example, by mixing plate crystal powder, additive raw material, binder, plasticizer, and solvent into a slurry and forming a sheet-like molded body, plate crystal powder 3 as shown in FIG. The sheet-like oriented molded body 10 existing in an oriented state is obtained.

The additive raw material is powdery, and the BET value is preferably 2.0 m ² / g or more and 10 m ² / g or less.

Depending on the viscosity of the slurry and the thickness of the sheet to be molded, the degree of orientation of the plate-like crystal powder dispersed in the sheet-like molded body can be changed.

As the oriented molded body, a laminated body in which sheet-like molded bodies are laminated can be used, or one in which electrodes such as Ag, Ni, and Cu are formed between the layers can be used.

(5) Step of obtaining sintered body Hereinafter, the oriented molded body as the step (5) is subjected to reduction in an oxygen partial pressure of 1 × 10 ⁻¹⁴ atm or more and 3 × 10 ⁻¹⁰ atm or less. A process of sintering will be described. This step is indicated by step S13 in FIG.

The obtained oriented molded body is sintered. By sintering in a reducing atmosphere with an oxygen partial pressure of 1 × 10 ⁻¹⁴ atm or more and 3 × 10 ⁻¹⁰ atm or less, the degree of orientation by the Lotgering method is 85% or more and less than 100%, and the piezoelectric constant d33 jumps. Thus, a crystallographically oriented piezoelectric ceramic of 350 pC / N or higher can be obtained.

At this time, by setting the oxygen partial pressure to 7 × 10 ⁻¹⁴ atm or more and 4 × 10 ⁻¹³ atm or less, the degree of orientation by the Lotgering method is 90% or more, and the crystal orientation in which the piezoelectric constant d33 is 400 pC / N or more. Piezoelectric ceramics are obtained.

Furthermore, by setting the oxygen partial pressure to 1.1 × 10 ⁻¹³ atm or more and 3 × 10 ⁻¹³ atm or less, the degree of orientation by the Lotgering method is 90.5% or more, and the piezoelectric constant d33 is 420 pC / N or more. A crystal-oriented piezoelectric ceramic is obtained.

The oxygen partial pressure can be adjusted by using a known preparation method, for example, by adjusting the supply amount of water vapor and hydrogen.

Sintering is preferably performed at a temperature of 1135 ° C. or higher and 1170 ° C. or lower in a reducing atmosphere. By sintering at this temperature, a sintered body having a relative density of 95% or more and 98.5% or less, and further 96% or more and less than 97.5% can be obtained. In general, it is recognized that the crystal orientation piezoelectric ceramic increases in the degree of orientation by increasing the relative density (density relative to the true density), and accordingly, the piezoelectric constant d33 increases. It is considered that a large piezoelectric constant d33 can be obtained. However, the composition-type piezoelectric material represented by the general formula: (1-s) A1B1O ₃ —sBaMO ₃ does not always have a correlation between the relative density and the degree of orientation. It turned out that it does not contribute to the improvement of the constant d33. If the relative density is in the range of 95% or more and 98.5% or less, which is a little lower, the degree of orientation is the highest, and accordingly, a high piezoelectric constant d33 is obtained.
(6) Step of applying polarization treatment to the sintered body

An electrode is formed on the ceramic, which is a sintered body obtained by the above process, and subjected to polarization treatment. Due to the polarization treatment, the direction of spontaneous polarization in the ceramic is aligned, and the piezoelectric characteristics are exhibited. For the polarization treatment, a known polarization treatment generally used in the production of piezoelectric ceramics can be used. For example, the fired body on which the electrode is formed is held at a temperature of room temperature to 200 ° C. with a silicone bath or the like, and a voltage of about 0.5 kV / mm to 6 kV / mm is applied. Thereby, crystal-oriented piezoelectric ceramics having piezoelectric characteristics can be obtained.

4). Measurement of physical properties, etc. Hereinafter, methods for measuring oxygen partial pressure, composition, orientation degree, average crystal grain size of non-oriented crystals, piezoelectric constant d33, true density, and relative density in the present application will be described.

[Oxygen partial pressure]
The oxygen partial pressure can be evaluated using an oxygen concentration meter having a commercially available YTZ (yttrium stabilized zirconia) sensor. The measurement method used a method such as extracting from the furnace using an alumina tube so that the atmosphere in the vicinity of the work in the electric furnace that creates a gas atmosphere can be directly sampled.

The partial pressure of oxygen can be adjusted by a method of containing a certain amount of water vapor by a method such as bubbling in a gas containing 0 to 4 mol% of hydrogen based on an inert gas such as nitrogen or argon. The oxygen partial pressure that can be created at this time can be calculated from the following equations 1 and 2 using the hydrogen partial pressure PH ₂ and the water vapor partial pressure PH ₂ O. In Equation 1, ΔG _f is the standard production Gibbs energy of water vapor, R is a gas constant, and T is an absolute temperature.

[composition]
The composition was measured by SEM-EDX (Energy Dispersive X-ray spectroscopy). As measurement conditions, the acceleration voltage was 15 kV, the current was 100 nA, and the beam diameter was 1 μm.

[Piezoelectric constant d33]
After the polarization treatment, the piezoelectric constant d33 is measured. For the polarization treatment, an Ag electrode was formed on the ceramic by sputtering, and a 4.0 kV / mm DC electric field was applied for 10 minutes at 413 K (140 ° C.).

The piezoelectric constant d33 was measured with a d33 meter (manufactured by Institute of Speech, Chinese Academy of Sciences).

[Orientation]
The degree of orientation was measured by the Lotgering method.

Specifically, it was obtained from the XRD result using Cu-Kα rays. XRD was measured in the range of 2θ: 5 ° to 80 ° on a surface obtained by grinding the surface of the sintered body. From the measurement results of XRD, the degree of orientation f was calculated by the following

Lotgering numbers

3 and 4. Here, P is the remanent polarization value of the piezoelectric ceramic, ΣI {h00} is the sum of all integrated intensities of diffraction peaks derived from {h00}, and ΣI {hkl} is the integrated intensities of all observed diffraction peaks. The sum is shown. P ₀ is the remanent polarization value of the non-oriented piezoelectric ceramic. A sintered body was prepared without using the plate-like crystal powder, and was calculated from Equation 3 in the same manner as described above.

[Average crystal grain size of non-oriented crystals]
The region of the non-oriented crystal is confirmed by EBSP, and as shown in FIG. 6, the back-scattered electron image (BSE: 5000 times) is taken with a scanning electron microscope (SEM). The maximum diameter L and area S of each crystal (n1, n2, .. nz) are measured with image analysis software (free software: ImageJ, http://rsb.info.nih.gov/ij/) The sum Σ (L · S) of the product values (L · S) (= L · S1 + L · S2 + ·· + L · Sz) is calculated. Further, the total area Σ (S) (= S1 + S2 + .. + Sz) of the non-oriented crystal is calculated by image analysis software. The value obtained by dividing Σ (L · S) by Σ (S) was defined as the average grain size of the non-oriented crystals.

[True density]
The true density is calculated by calculating the mass of the perovskite-type unit cell from the charged composition, calculating the volume of the unit cell from the XRD (X-Ray Diffraction) measurement result of the sintered body, and dividing the mass of the unit cell. This was adopted as the true density.

[Relative density]
The relative density was expressed as a percentage of the actually measured density (measured by Archimedes method) with respect to the true density as 100%.

5. Examples of the present invention will be described in more detail.

Example 1
First, by the steps (S1 to S5) shown in FIG. 2, a first crystal powder of a bismuth layer structure compound composed of a (Bi ₂ O ₂ ) ²⁺ layer and a pseudo-perovskite layer was prepared.

In the general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 A _m-1.5 Nb _m O _{3m + 1} ) ²⁻ , so that A becomes Na, m = 5, Bi _2.5 Na _3.5 Nb ₅ O ₁₈ , Bi ₂ O ₃ , Na ₂ CO ₃ , and Nb ₂ O ₅ were weighed (S1).

These materials were mixed by a ball mill. Ethanol was used as a solvent and zirconia balls were used as a medium, and mixed for 24 hours at a rotation speed of 94 rpm. The media and raw materials were taken out from the ball mill container and dried in the air at 130 ° C. Thereafter, the media and the raw material were separated by a sieve (S2).

The mixed raw material was mixed with 100% by mass of NaCl as a flux with respect to the raw material, and then dry mixed for 10 minutes with a coarse pulverizer (S3).

The raw material after flux addition was subjected to two-stage calcination which was held in air at 850 ° C. for 1 hour and then held at 1100 ° C. for 2 hours. The temperature increase and decrease were about 200 ° C./h (S4).

In order to remove the flux component from the obtained first intermediate fired body, it was immersed in warm water at 95 ° C. to 100 ° C. and left for 3 hours. Thereafter, the process of stirring and dehydrating in warm water for 60 minutes was repeated three times (S5). Thus the general formula: to give a first crystalline powder consisting of _{_{_{_{Bi 2.5 Na 3.5 Nb 5 O 18}}}} .

FIG. 7 is a SEM observation photograph of the first crystal powder. It can be confirmed that the crystals are plate-like.

FIG. 8 shows the X-ray diffraction result of the first crystal powder, and FIG. 9 shows the result of specifying the compound using the X-ray diffraction result. All X-ray diffraction was performed using a Cu Kα radiation source.

Most of the crystals obtained are represented by the general formula: Bi _2.5 Na _3.5 Nb ₅ O ₁₈ . However, in addition to the general formula: Bi _2.5 Na _3.5 Nb ₅ O ₁₈ , in the general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 A _m-1.5 Nb _m O _{3m + 1} ) ²⁻ , m = 2 A compound of Bi _2.5 Na _0.5 Nb ₂ O ₉ and Bi _2.5 Na _2.5 Nb ₄ O ₁₅ of m = 4 can be confirmed.

Next, a plate-like crystal powder made of the first perovskite compound obtained by reducing Bi from the first crystal powder by the manufacturing steps (S6 to S10) shown in FIG. 2 was prepared.

Na ₂ CO ₃ was used as the first additive, and an amount such that Na and Nb were 1: 1 after the reaction was added. These were mixed by a ball mill. Ethanol was used as a solvent and zirconia balls were used as media, and the mixture was mixed at 94 rpm for 4 hours. The mixture was taken out from the ball mill container and dried in an atmosphere of 130 ° C. Thereafter, the media was separated by a sieve (S6).

The mixed raw material was mixed with NaCl as a second flux by 100 mass% with respect to the first crystal powder, and then dry-mixed for 10 minutes with a coarse pulverizer (S7).

The mixed material composed of the first crystal powder, the first additive, and the flux was fired at 950 ° C. for 8 hours in the atmosphere to obtain a second intermediate fired body. The temperature increase and decrease were about 200 ° C./h (S8).

In order to reduce the second flux component from the second intermediate fired body, it was immersed in warm water of 95 ° C. to 100 ° C. and left for 3 hours. Thereafter, the step of stirring and dehydrating in warm water for 60 minutes was repeated three times (S9).

Thereafter, pickling was performed to reduce the Bi component from the second intermediate fired body. The material to be treated obtained in step S9 was placed in a pickling solution in which pure water and nitric acid were mixed at a ratio of about 3: 1 to 10: 1 and stirred. Thereafter, the supernatant liquid in which the Bi component was melted was removed. Further, the pickling solution was added, stirred, and the supernatant was removed repeatedly. Thereafter, the residue was dried to obtain a plate-like crystal powder made of NaNbO ₃ (S10). The obtained plate crystal powder had an aspect ratio (ratio of plate thickness to maximum diameter) of about 10.

Next, the additive raw material is mixed with the plate-like crystal powder in the step (S11) shown in FIG. 3, and the general formula: (1-s) A1B1O ₃ -sBaMO ₃ (where A1 is selected from alkali metals) B1 is at least one element of transition metal elements and contains Nb, M is at least one element of Group 4A and contains Zr, and 0 <s ≦ 0.15) The mixture of the composition represented by this was obtained.

In this embodiment, with respect to the plate-like crystal powder Xmol consisting NaNbO _3, it was mixed with added raw materials consisting of _{_{(K 0.414 Na 0.46-X Li}} 0.046 Ba 0.08) (Nb 0.92-X Zr 0.08) O 3. In this example, the value of X of the plate-like crystal powder was 1 (mol). As a result, a composition represented by (K _0.414 Na _0.46 Li _0.046 Ba _0.08 ) (Nb _0.92 Zr _0.08 ) O ₃ containing 1 mol% of plate crystal powder as a whole was obtained. The value of s in the above general formula is 0.08 (S11).

Next, a molded body of the mixture was obtained by the step (S12) shown in FIG.

First, in order to make the mixture into a slurry, ethanol was added at 200 to 300 mass% with respect to the mixture and butanol was added at 50 to 100 mass% with respect to the mixture. A plasticizer was also added. In this example, dioctyl phthalate was added as a plasticizer in an amount of 5 to 15 mass% with respect to the mixture. A binder was also added. In this example, 5 to 15 mass% of polyvinyl butyral was added as a binder to the mixture. The slurry thus obtained was formed into a sheet (S12).

Next, the oriented molded body was sintered by the step (S13) shown in FIG.

Considering that a sample for comparison is prepared by mixing nitrogen and water containing 0.01 to 2% of hydrogen, the atmosphere in the furnace is changed from 2.4 × 10 ⁻⁸ atm to 3.9 × 10. A reducing atmosphere was prepared so that the oxygen partial pressure was ^-15 atm. The sintering temperature was 1150 ° C.

The obtained crystal-oriented piezoelectric ceramic was measured for oxygen partial pressure PO ₂ , degree of orientation, average crystal grain size of non-oriented crystals, piezoelectric constant d33, and relative density. Table 1 shows the results. FIG. 10 shows the relationship between oxygen partial pressure (PO ₂ ) and orientation degree, oxygen partial pressure (PO ₂ ), and piezoelectric constant d33. FIG. 11 shows the relationship between oxygen partial pressure (PO ₂ ) and relative density. FIG. 6 is an observation result of the structure of sample No. 3 in Table 1.

As shown in FIG. 10, the degree of orientation with respect to the oxygen partial pressure PO ₂ draws a gentle curve and takes a maximum value in the vicinity of about 1 × 10 ⁻¹² to 1 × 10 ⁻¹¹ atm, whereas the oxygen partial pressure PO _2. The piezoelectric constant d33 with respect to takes a maximum value locally. That is, when sintered in a reducing atmosphere with an oxygen partial pressure PO ₂ of less than 1 × 10 ⁻¹⁴ atm or more than 3 × 10 ⁻¹⁰ atm, a crystal having a piezoelectric constant d33 of less than 350 pC / N, even if the degree of orientation is high. It tends to be oriented piezoelectric ceramics.

On the other hand, in the range of 1 × 10 ⁻¹⁴ to 1 × 10 ⁻¹⁰ atm, the piezoelectric constant d33 can be rapidly increased by slightly changing the oxygen partial pressure PO ₂ . Specifically, when the oxygen partial pressure during firing is a reducing atmosphere of 1 × 10 ⁻¹⁴ atm or more and 3 × 10 ⁻¹⁰ atm or less, a crystal-oriented piezoelectric ceramic having a piezoelectric constant d33 of 350 pC / N or more is obtained. Can do. Further, the average crystal grain size of the non-oriented crystal of the crystal oriented piezoelectric ceramic obtained at this time is larger than 1.0 μm and not larger than 5.0 μm.

In particular, in this example, when the oxygen partial pressure is 7 × 10 ⁻¹⁴ atm or more and 4 × 10 ⁻¹³ atm or less, a crystal-oriented piezoelectric ceramic having a piezoelectric constant d33 of 400 pC / N or more is obtained, and the oxygen partial pressure is A crystal-oriented piezoelectric ceramic having a piezoelectric constant d33 of 420 pC / N or more was obtained when it was 1.1 × 10 ⁻¹³ atm or more and 3 × 10 ⁻¹³ atm or less.

As shown in FIG. 11, the crystal-oriented piezoelectric ceramic obtained in this example has a relative density in the range of 96% or more and 97.0% or less.

In addition, evaluation was performed in the same manner as in Example 1 except that the range of s in the general formula: (1-s) A1B1O ₃ —sBaMO ₃ was changed within the range of 0 <s ≦ 0.15. As a result, the average crystal grain size of the non-oriented crystals could be within the above range by setting the oxygen partial pressure PO ₂ to be the same as in Example 1. Moreover, crystal orientation piezoelectric ceramics having a large piezoelectric constant d33 were obtained by using this oxygen partial pressure PO ₂ .

(Example 2)
The relationship between the relative density and the degree of orientation was examined by changing the sintering temperature. A sample was prepared in the same manner as in Example 1 except for the conditions described below.

The sintering temperature was 1110 ° C, 1130 ° C, 1145 ° C (Example), 1150 ° C (Example), 1175 ° C, 1190 ° C.

The reducing atmosphere was an atmosphere of 2% hydrogen in nitrogen, and the oxygen partial pressure PO ₂ was 3 × 10 ⁻¹³ atm.

The true density, relative density, orientation degree, and piezoelectric constant d33 of the obtained crystal-oriented piezoelectric ceramic were measured. The results are shown in Table 2. FIG. 12 shows the relationship between the sintering temperature and the relative density, and the relationship between the sintering temperature and the degree of orientation.

The crystal-oriented piezoelectric ceramic of the example sintered at a temperature of 1145 ° C. or more and 1150 ° C. or less has a relative density of 95% or more and 98.5% or less. The degree of orientation is 85% or more and less than 100%.

As shown in FIG. 12, the crystal-oriented piezoelectric ceramic of this embodiment has a tendency that the relative density increases as the sintering temperature becomes higher in the range of 1110 ° C. to 1190 ° C., but the degree of orientation is around 1140 ° C. Sintered one shows high value. That is, the relative density and the degree of orientation do not have a linear relationship, and the degree of orientation takes the maximum value in the range of 1135 ° C. to 1170 ° C.

FIG. 13 shows the relationship between the relative density and the degree of orientation. It can be seen that the degree of orientation takes the maximum value when the relative density is in the range of 95% to 98.5%.

The crystal-oriented piezoelectric ceramic obtained at a sintering temperature of less than 1135 ° C. or more than 1170 ° C. has a relative density of less than 95% or more than 98.5% and an orientation degree of less than 85%. The piezoelectric constant d33 was not measurable because the piezoelectric constant was not expressed because the electrodes were energized (shorted) during the polarization process.

On the other hand, the crystal-oriented piezoelectric ceramic obtained at a sintering temperature of 1135 ° C. or higher and 1170 ° C. or lower has a relative density of 95% or higher and 98.5% or lower, and an orientation degree of 85% or higher. The piezoelectric constant d33 showed a large value of 300 pC / N or more.

The value obtained by dividing the porosity (%) value from 100% was the same value as the relative density.

The same tendency was observed even in the composition in which the value of s was changed in the range of 0 <s ≦ 0.15 in the general formula: (1-s) A1B1O ₃ —sBaMO ₃ .

From the above, the general formula: (1-s) A1B1O ₃ —sBaMO ₃ (where A1 is at least one element selected from alkali metals, B1 is at least one element of transition metal elements, and Nb The crystal orientation piezoelectric ceramic represented by 0 <s ≦ 0.15) does not necessarily increase the degree of orientation and increase the piezoelectric constant d33 if the relative density is high. It was found that the relative density of 95% or more and 98.5% or less, which is slightly lower than before, is good.

(Comparative Example 1)
A comparative experiment was conducted using a composition of A1B1O ₃ (NaNbO ₃ ) that does not contain BaMO ₃ as the ceramic composition.

In the same manner as in Example 1, plate-like crystal powder (NaNbO ₃ ) was obtained.

The Na materials and Nb raw material to be NaNbO ₃ of 96mol against the plate-like crystal powder 4mol was added to obtain a mixture having a composition represented by NaNbO _3.

Using this mixture, crystal oriented piezoelectric ceramics were produced in the same manner as in Example 1 along the steps (S11 to S13) shown in FIG.

In the same manner as in Example 1, the true density, relative density, orientation degree, and piezoelectric constant d33 of the obtained crystal-oriented piezoelectric ceramic were measured.

FIG. 14 shows the relationship between the sintering temperature and relative density, and the sintering temperature and orientation degree. The comparatively oriented crystallographic piezoelectric ceramics of NaNbO ₃ composition has a tendency that the relative density increases on the high temperature side when the sintering temperature is in the range of 1100 ° C. to 1140 ° C., and the degree of orientation tends to increase accordingly. is there.

FIG. 15 shows the relationship between the relative density and the degree of orientation in the crystal-oriented piezoelectric ceramic of the comparative example. When the relative density is 96% or more, the degree of orientation is as large as 80% or more. Unlike the crystal-oriented piezoelectric ceramic of the present invention, only the correlation that the degree of orientation becomes higher as the relative density is higher can be confirmed as in the conventional knowledge.

These results, and the ceramic represented by the general formula (1), for example, in the A1B1O _3, the relationship between the degree of orientation and the relative density is found to be different.

1 Pseudo-Perovskite Layer 2 (Bi ₂ O ₂ ) ²⁺ Layer 3 Plate-like Crystal Powder 4 Additive Raw Material 10 Oriented Molded Body

Claims

A crystal-oriented piezoelectric ceramic containing a lead-free perovskite compound as a main component,
The perovskite type compound has the general formula: (1-s) A1B1O 3 —sBaMO 3 (where A1 is at least one element selected from alkali metals, and B1 is at least one element of a transition metal element) Nb is included, M is at least one element of Group 4A, includes Zr, and is represented by 0 <s ≦ 0.15)
The crystal-oriented piezoelectric ceramic is
A plurality of oriented crystals in which the crystal orientations are aligned with each other and a plurality of non-oriented crystals in which the crystal orientations are irregular. The average crystal grain size of the plurality of non-oriented crystals is larger than 1.0 μm. 0.0 μm or less,
A crystallographically oriented piezoelectric ceramic having an orientation degree by the Lotgering method of 85% or more and less than 100% and a piezoelectric constant d33 of 350 pC / N or more.
The degree of orientation by the Lotgering method is 90% or more, the average crystal grain size of the plurality of non-oriented crystals is 1.3 μm or more and 4.5 μm or less,
The crystal-oriented piezoelectric ceramic according to claim 1, wherein the piezoelectric constant d33 is 400 pC / N or more.
3. The crystal-oriented piezoelectric ceramic according to claim 1, wherein the relative density is 95% or more and 98.5% or less.
A piezoelectric element comprising the crystal-oriented piezoelectric ceramic according to any one of claims 1 to 3 and a plurality of electrodes in contact with the crystal-oriented piezoelectric ceramic.
A plurality of ceramic layers comprising the crystal-oriented piezoelectric ceramic according to claim 1;
A piezoelectric element comprising a plurality of electrodes, wherein the plurality of electrodes and the plurality of ceramic layers are alternately laminated.
Preparing a first crystal powder of a bismuth layered structure compound comprising a (Bi 2 O 2 ) 2+ layer and a pseudo-perovskite layer;
Preparing a plate-like crystal powder made of the first perovskite compound in which Bi is reduced from the first crystal powder;
An additive raw material is mixed with the plate-like crystal powder, and the general formula: (1-s) A1B1O 3 —sBaMO 3 (where A1 is at least one element selected from alkali metals, and B1 is A step of forming a mixture having a composition represented by 0 <s ≦ 0.15), which is at least one element of a transition metal element and includes Nb, and M is at least one element of Group 4A and includes Zr;
A step of using the mixture as a molded body,
Sintering the molded body in a reducing atmosphere having an oxygen partial pressure of 1 × 10 −14 atm to 3 × 10 −10 atm; and
Applying a polarization treatment to the sintered body;
A method for producing a crystal-oriented piezoelectric ceramic comprising:
The method for producing a crystal-oriented piezoelectric ceramic according to claim 6, wherein, in the sintering step, an oxygen partial pressure is 7 × 10 −14 atm or more and 4 × 10 −13 atm or less.
The method for producing a crystal-oriented piezoelectric ceramic according to claim 6 or 7, wherein in the sintering step, a sintering temperature is 1135 ° C or higher and 1170 ° C or lower.