JPWO2014021437A1 - Method for producing plate-like crystal powder, plate-like crystal powder, and crystal-oriented ceramics - Google Patents

Abstract

The method for producing a plate-like crystal powder disclosed in the present application includes a step (A) of preparing a first crystal powder having a layered structure in which (Bi2O2) 2+ layers and pseudo-perovskite layers are alternately laminated; And (B) obtaining a plate-like crystal powder in which the Bi component in the first crystal powder is reduced by heat-treating the crystal powder in a reducing atmosphere.

Description

  The present invention relates to a method for producing a plate-like crystal powder, a plate-like crystal powder, and a crystal-oriented ceramic that is a polycrystal having a crystal plane oriented, useful for a piezoelectric capacitor.

Piezoelectric devices using piezoelectric materials are widely used in the fields of electronics, mechatronics, automobiles, and the like, and are one of important electronic components in various industrial products. Various materials and forms of piezoelectric materials are used for piezoelectric devices, and piezoelectric ceramics are most widely used for piezoelectric devices. Specifically, Pb-based perovskite ferroelectric ceramics mainly composed of PbZrO ₃ —PbTiO ₃ (PZT) or the like are mainly used for piezoelectric devices.

Recently, there is a growing tendency not to use heavy metal elements such as Pb, Hg, Cd, Cr ⁶⁺ in industrial products etc. due to the heightened awareness of environmental conservation. Has been. The above-described Pb-based perovskite type ferroelectric ceramics also contain Pb, which is the object of regulation.

  In view of such circumstances, research on lead-free piezoelectric materials is urgent and important, and research and development of high-performance lead-free piezoelectric ceramics comparable to the performance of current PZT-based piezoelectric ceramics is progressing.

Among them, as a ceramic having a composition having relatively high piezoelectric characteristics in recent years, for example, Patent Document 1 is an isotropic perovskite type compound represented by the general formula: ABO ₃ , and the main component of the A site element is It is composed of a polycrystal having a main phase of the first perovskite type pentavalent metal acid alkali compound which is K and / or Na and the main component of the B site element is Nb, Sb and / or Ta, and is polycrystalline Disclosed is a crystallographically-oriented ceramic in which specific crystal planes of crystal grains constituting the body are oriented.

  In Patent Document 1, this crystal-oriented ceramic is produced by first producing a first anisotropic shaped powder such as a plate shape, a columnar shape, a scale shape, etc., mixing the first anisotropic shaped powder and other raw materials, It is described that the anisotropically shaped powder is shaped and fired so that it is oriented, and the whole crystal can be oriented by such a method.

JP 2003-12373 A (see columns 0094 to 0097)

  In view of the above problems, the present invention provides a plate-like crystal powder, a crystal-oriented ceramic, and a method for producing the plate-like crystal powder that are used to obtain a piezoelectric ceramic that does not contain Pb and can exhibit high piezoelectric characteristics. Objective.

The method for producing a plate-like crystal powder disclosed in the present application includes the step (A) of preparing a first crystal powder having a layered structure in which (Bi ₂ O ₂ ) ²⁺ layers and pseudo-perovskite layers are alternately laminated; And (B) obtaining a plate-like crystal powder in which the Bi component in the first crystal powder is reduced by heat-treating the first crystal powder in a reducing atmosphere.

  In the step (B), the first crystal powder, the first additive for producing the plate crystal powder, and the flux that melts at a temperature at which the first crystal powder and the first additive can react with each other. And a first intermediate firing by heat-treating the mixed material at a temperature at which the first crystal powder and the first additive can react with each other in the reducing atmosphere. And a step of removing the flux from the first intermediate fired body.

  In the step (B), the first crystal powder, the first additive for producing the plate crystal powder, and the flux that melts at a temperature at which the first crystal powder and the first additive can react with each other. To obtain a mixed material, heat-treating the mixed material at a temperature at which the first crystal powder and the first additive can react to form a second intermediate fired body, The step of removing the flux from the intermediate fired body of No. 2 and the step of heat treating the second intermediate fired body from which the flux has been removed in the reducing atmosphere may be included.

  In the step (B), the first crystal powder may be directly heat-treated in the reducing atmosphere.

The first crystal powder has a general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 A _m-1.5 Nb _m O _{3m + 1} ) ²⁻ (where A is at least selected from Li, K, or Na) It may be a compound represented by one element and m is an integer of 2 or more.

  In the step (A), a raw material containing Bi, A, and Nb and another flux that melts at a temperature at which the raw material reacts so as to contain Bi, A, and Nb at a composition ratio represented by the general formula. Preparing and mixing to obtain another mixed material, heating the other mixed material to obtain the first crystal powder covered with the other flux, and the other flux. Removing the other flux from the covered first crystal powder.

  The reducing atmosphere may be a hydrogen atmosphere, a nitrogen atmosphere, a carbon monoxide atmosphere, a hydrogen sulfide atmosphere, a sulfur dioxide atmosphere, a formaldehyde atmosphere, or a mixed atmosphere thereof.

  The plate-like crystal powder disclosed in the present application is a plate-like crystal powder obtained by any one of the production methods described above, and the Bi residual amount in the plate-like crystal powder is less than 8.5 mass%.

  The crystal-oriented ceramic disclosed in the present application is a sintered body of the plate-like crystal powder and a second additive capable of forming a perovskite-type compound, and the sintered body is a crystal oriented in a predetermined direction. It consists of the sintered compact which is a polycrystal which has a surface.

  According to the method for producing a plate-like crystal powder disclosed in the present application, the Bi component can be reduced in a shorter time than before by heat-treating the first crystal powder in a reducing atmosphere. Therefore, a plate-like crystal powder with a small Bi component can be obtained. In addition, crystal oriented ceramics with high piezoelectric characteristics can be produced using this plate crystal powder.

It is a schematic diagram which shows the structure of the 1st crystal powder used with the manufacturing method of the plate-shaped crystal powder of this embodiment. It is a flowchart which shows the manufacturing method of the plate-shaped crystal powder by this embodiment. It is a flowchart which shows the manufacturing method of the crystal orientation ceramics by this embodiment. It is a flowchart which shows the manufacturing method of the 1st plate-shaped crystal powder by this embodiment. It is a flowchart which shows the manufacturing method of the 2nd plate-shaped crystal powder by this embodiment. It is a flowchart which shows the manufacturing method of the 3rd plate-shaped crystal powder by this embodiment. 2 is a SEM photograph of the first crystal powder according to Example 1. 2 is an X-ray diffraction measurement result of the first crystal powder according to Example 1. FIG. 2 is a compound analysis result of the first crystal powder according to Example 1. FIG. 2 is an X-ray diffraction peak of a plate-like crystal powder according to Example 1. FIG. It is a flowchart which shows the manufacturing method of the plate-shaped crystal powder by the comparative examples 1 and 2. FIG. 4 is an X-ray diffraction measurement result of an intermediate fired body according to Comparative Example 2. 4 is an X-ray diffraction result of a plate-like crystal powder according to Comparative Example 2.

The inventor of the present application studied in detail the crystal-oriented ceramic disclosed in Patent Document 1 and a method for producing the same. Patent Document 1 discloses a general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 A _m-1.5 Nb _m O _{3m + 1} ) ²⁻ (where m is an integer of 2 or more. A represents Na, K and Li At least one alkali metal element selected from the group consisting of: a second anisotropically shaped powder made of a bismuth layered perovskite type compound, and Bi is thermally or chemically produced from the second anisotropically shaped powder. A first anisotropically shaped powder is obtained by reduction.

  Here, Patent Document 1 describes that the Bi component is reduced as a method of reducing the thermal component or the chemical component. The method of heating at a temperature at which the components volatilize, the method of heating at a temperature at which the surplus components volatilize in the air or in oxygen for a long time, etc. are described as a preferred example (0095). In addition, as a method for chemically reducing the surplus component, it is described as “immersing the intermediate sintered body in a processing solution having a property of eroding only the surplus component and extracting the surplus component (0097)”.

As described in Patent Document 1, a composition that does not substantially contain Bi is considered promising as a composition that increases the piezoelectric constant d33 of crystal-oriented ceramics. When producing grain oriented ceramics having a composition substantially free of Bi is, Bi ₂ included in plate crystal powder (the first anisotropically shaped powder and the second anisotropically shaped powder referred to in Patent Document 1) It is preferable to reduce Bi compounds such as O ₃ (hereinafter referred to as Bi component) as much as possible.

  If the Bi component remains in the plate crystal powder, the Bi component remains as an impurity when the plate crystal powder and other raw materials (hereinafter referred to as the second additive) are fired, and the piezoelectric constant d33 is lowered. It is.

  However, according to the study of the present inventor, it has been found that long-time treatment is required to reduce the Bi component by the method described in Patent Document 1. Even if a method of heating under reduced pressure or vacuuming is used, it is difficult to perform the treatment in a short time, and if a method of heating in the atmosphere or oxygen is used, it is considered that a longer heat treatment is required.

  In addition, when the method of chemically reducing the Bi component is used, the Bi component is usually reduced by pickling in an acidic solution, but it is necessary to repeat pickling over and over, and the waste liquid treatment The processing steps including the above become complicated. For this reason, the processing time becomes longer even when the Bi component is chemically reduced.

  In view of the above problems, the inventor of the present application has come up with a novel method for producing a plate-like crystal powder capable of reducing the Bi component in a shorter time than before.

  First, the method for producing a plate-like crystal powder disclosed in the present application and the method for producing a crystal-oriented ceramic using the plate-like crystal powder produced by this method will be described below.

The method for producing a plate-like crystal powder of the present embodiment includes a step of preparing a first crystal powder having a layered structure in which (Bi ₂ O ₂ ) ²⁺ layers and pseudo-perovskite layers are alternately laminated, and a first crystal powder. And a step of obtaining a plate-like crystal powder in which the Bi component in the first crystal powder is reduced by heat-treating in a reducing atmosphere. Hereinafter, the step of preparing the first crystal powder and the step of obtaining the plate crystal powder will be described.

[Step of preparing first crystal powder (A)]
The first crystal powder is a bismuth layered structure compound composed of a (Bi ₂ O ₂ ) ²⁺ layer and a pseudo-perovskite layer. This bismuth layered structure compound has a crystal structure in which (Bi ₂ O ₂ ) ²⁺ layers 2 and pseudo-perovskite layers 1 are laminated in layers and alternately, as schematically shown in FIG. Since the first crystal powder having this crystal structure becomes plate-like during the crystal growth process, it can be used as a template of the plate-like crystal powder as described later.

The pseudo perovskite layer refers to a layer having a pseudo perovskite structure. The pseudo-perovskite structure is a crystal structure similar to the perovskite structure (ABO _{3 in the} general formula), but is strictly expressed by a different composition formula, for example, Bi _0.5 A _m-1.5 Nb _m O _{3m + 1} , A It refers to those having a crystal structure having a composition represented by the _{m-1 B m O 3m +} 1.

For example, in the present embodiment, the first crystal powder has a general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 Am _−1.5 Nb _m O _{3m + 1} ) ²⁻ (where A is Li, K, And a compound represented by at least one selected from the group consisting of Na and 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.

As the other first crystal powder in which the pseudo-perovskite layer does not contain Bi, the general formula: (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ²⁻ (where A is Li, K, Or at least one selected from the group consisting of Na, B is at least one selected from the group consisting of tetravalent, pentavalent and hexavalent elements such as Nb, Ta and Sb, and m is 2 or more It is also possible to use those represented by (integer).

  The first crystal powder may be manufactured by any method as long as it has the above composition and structure. For example, the first crystal powder can be prepared according to the flowchart shown in FIG. Specifically, raw materials each containing Bi, A and Nb or Bi, A and B are prepared, and the raw materials are weighed so as to have a composition ratio represented by any one of the above general formulas (S1).

  Next, the raw material for the first crystal powder is added to, for example, an organic solvent and mixed by a ball mill or the like (S2). After the mixed raw material is dried, a flux such as NaCl is added and further mixed ( S3). The flux is an auxiliary raw material that can be melted together with the raw material for the first crystal powder and that allows the first crystal powder to grow crystals from the melt as described later. The composition of the flux needs to be appropriately changed depending on the raw material for the first crystal powder. The amount of flux added is preferably 10 mass% or more, more preferably 30 mass% or more, relative to the raw material.

  As the flux, for example, alkali metal chlorides such as NaCl and KCl, fluorides, nitrates, sulfates, and the like can be used. In this embodiment, after the raw materials are mixed, the flux is added and mixed again. However, after the raw materials and the flux are weighed, they may be mixed at a time.

  The raw material to which the flux is added is heated at, for example, 700 ° C. or higher and 1300 ° C. or lower (S4). Thereby, in the state which flux melt | dissolved, the element in the said raw material becomes easy to move, and raw materials react. The heating atmosphere may be an oxygen-containing atmosphere and can be heated in the air. Multi-stage heat treatment may be used. By this heating, the first crystal powder containing the flux can be obtained. The heating time is preferably 1 minute or longer. When heating time is too long, productivity will fall and the aspect ratio of the obtained plate-shaped powder shape will become small. For this reason, it is preferable that heating time is 10 hours or less. By heating, a substantially integral fired body made of the first crystal powder whose periphery is covered with a flux is obtained.

  In order to remove the flux from the fired body, for example, the fired body may be immersed in warm water and melted (S5). Thereby, the flux covering the first crystal powder is removed, and only the first crystal powder separated individually can be taken out.

[Step of obtaining plate-like crystal powder (B)]
A plate-like crystal powder is obtained by heat-treating the first crystal powder in a reducing atmosphere to reduce the Bi component in the first crystal powder (S8). Since the plate-like crystal powder maintains the shape of the first crystal powder, it has a plate-like shape with a high aspect ratio.

In general, when the plate-like crystal powder in which the Bi component remains is used as an alignment material for crystal oriented ceramics, the Bi component volatilizes during firing and crystal growth, and many defects are generated in the crystal oriented ceramics. End up. Thereby, the volume resistivity of the fired body is lowered and the piezoelectric constant d33 is lowered. Further, the (Bi ₂ O ₂ ) ²⁺ layer 2 contained in the first crystal powder has almost no function of orienting the second additive described later. For this reason, when using the first crystal powder, it is preferable to reduce the Bi component from the first crystal powder as much as possible.

  As a result of studying various methods for reducing the Bi component, the present inventor has found that it is effective to perform heat treatment in a reducing atmosphere. In the present specification, the “reducing atmosphere” refers to an atmosphere that is more reducible than air. Specifically, the reducing atmosphere is a hydrogen atmosphere, a carbon monoxide atmosphere, a hydrogen sulfide atmosphere, a sulfur dioxide atmosphere, a formaldehyde atmosphere, or a mixed atmosphere thereof, and includes hydrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide or It refers to a reducing atmosphere containing formaldehyde at a rate of 0.1% to 100%.

  From the stoichiometric viewpoint for reducing Bi and volatilizing Bi in the first crystal powder in the case of a hydrogen atmosphere, for example, the hydrogen concentration is 0.5% or more with respect to the entire reducing atmosphere. It is preferable that The upper limit is preferably 4% or less from the standpoint that when the oxygen in the pseudo-perovskite layer 1 is reduced, the plate shape cannot be maintained, and the hydrogen explosion is suppressed.

  The heat treatment is preferably performed at 650 ° C. or more and 1300 ° C. or less in terms of thermal conditions for reducing Bi and volatilizing Bi in the first crystal powder. If the heat treatment is less than 650 ° C., it is difficult to reduce the Bi component. If the heat treatment is above 1300 ° C., the first crystal powder is dissolved and integrally fired, making it difficult to form a powder. In order to sufficiently remove Bi, the heat treatment temperature is preferably 700 ° C. or higher, more preferably 800 ° C. or higher.

  In the heat treatment, the first crystal powder is preferably held at the above temperature for a time in the range of 0.5 hours to 24 hours. If it is less than 0.5 hour, the Bi component cannot be sufficiently reduced. It is preferably 1 hour or longer, more preferably 3 hours or longer. If it exceeds 24 hours, the production time becomes longer and the productivity is lowered. More preferably, it is 20 hours or less.

The melting point of Bi ₂ O ₃ is 820 ° C., whereas the melting point of metal Bi is 271 ° C. Therefore, if heat treatment is performed in a reducing atmosphere, the (Bi ₂ O ₂ ) ²⁺ layer 2 of the first crystal powder is reduced and metal Bi is generated, so that the Bi component can be volatilized even in a short time treatment. . Therefore, a plate-like crystal powder having a Bi content of less than 8.5 mass% can be obtained.

In the plate-like crystal powder produced in this way, (Bi ₂ O ₂ ) ²⁺ layer 2 is almost disappeared due to the volatilization of Bi. Accordingly, the plate-like crystal powder mainly includes only the pseudo-perovskite layer 1 and has a pseudo-perovskite structure (however, Bi is not included) as a whole. For this reason, it is suitable as a template for producing oriented ceramics having a composition of ABO ₂ .

Further, as described below, in the step of obtaining the plate crystal powder, if the first additive is added so that the plate crystal powder has a composition of ABO ₃ , the plate crystal powder having a perovskite structure is obtained. Can be obtained.

  That is, the plate crystal powder is a first perovskite type compound having a pseudo perovskite structure or a perovskite structure.

  According to the present embodiment, it is easy to reduce the Bi component from the first crystal powder, so that a plate-like crystal powder with less Bi remaining than in the prior art can be obtained. In addition, when removing the Bi component, it is difficult to apply physical force from the outside to the first crystal powder, so the plate crystal powder maintains the shape of the first crystal powder, and the plate crystal powder having a high aspect ratio. Is obtained. Therefore, crystal oriented ceramics having a high degree of orientation and a high piezoelectric constant d33 can be obtained using the plate-like crystal powder of this embodiment.

In contrast, according to the conventional Bi component disclosed in Patent Document 1 a method for reducing thermally, BiO ₂ is hardly reduced, BiO ₂ is considered difficult to volatilize than metal Bi. Further, according to the method of removing the Bi component with the treatment liquid, it is considered difficult to remove the Bi component inside the powder because the treatment liquid hardly penetrates into the first crystal powder. For these reasons, it is difficult to reduce the Bi component from the first crystal powder in the short time treatment as in the conventional method, and the Bi component remains in the plate crystal powder at a rate of 8.5 mass% or more. It is possible. Further, when the Bi component is removed by the treatment liquid, in order to increase the removal efficiency, it is necessary to perform agitation of the treatment liquid. It is conceivable that the aspect ratio of the obtained plate-like crystal powder becomes small because destruction occurs.

[Crystal-oriented ceramics]
Crystal oriented ceramics can be produced using the plate-like crystal powder disclosed in the present application. A method for producing a crystallographically-oriented ceramic using the plate-like crystal powder of the present embodiment will be described with reference to FIG.

  The plate-like crystal powder produced by the procedure described above and the second additive are mixed. As the second additive, a material capable of obtaining a crystallographically-oriented ceramic made of the second perovskite compound by reacting with the plate-like crystal powder is used.

As the second additive, for example, a general formula: ABO ₃ (where A is at least one element selected from Li, K, or Na, and B is selected from 4, 5, and 6-valent elements such as Nb and Ta) The raw material used as the perovskite type compound represented by (at least one element) can be used.

  A sheet-like molded body in which the plate-like crystal powder and the second additive are dispersed is produced. First, a plate crystal powder, a second additive, a binder, a plasticizer and a solvent are mixed to form a slurry (S11).

  As the binder, polyvinyl butyral (PVB) resin, polyvinyl acetal resin, acrylic resin, or the like can be used. Among them, the use of polyvinyl butyral is preferable in that a sufficient strength can be obtained even if the sheet is thinned, and the crystallographically oriented ceramic is easily thinned.

  As the plasticizer, a glycol plasticizer or a phthalic acid plasticizer can be used. As the glycol plasticizer, glycerin is preferable. For example, ethylene glycol, diethylene glycol, triethylene glycol, hexamethylene glycol, polyethylene glycol, butyl phthalyl glycolate, triethylene glycol-2-ethyl butyrate, etc. may be used. it can. Examples of the phthalic acid plasticizer include dioctyl phthalate (DOP), dimethyl phthalate, diethyl phthalate, dipropyl phthalate, and dibutyl phthalate.

  In addition to ethanol and butanol, alcohols such as toluene and isopropyl alcohol can also be used as the solvent.

  Next, it shape | molds so that plate-shaped crystal powder may be orientated inside (S12).

  The slurry is adjusted to a predetermined kinematic viscosity and formed into a sheet shape by a doctor blade or the like. Depending on the viscosity of the slurry and the thickness of the sheet to be formed, the degree of orientation of the plate-like crystal powder dispersed in the sheet-like formed body varies. Basically, the higher the slurry viscosity, the higher the orientation degree the thinner the sheet to be molded. If necessary, a plurality of molded sheets are stacked. When using crystal oriented ceramics as the actuator, the sheet serving as the conductive layer and the sheet containing the plate-like powder and the second additive described above may be laminated alternately or every predetermined number.

  Then, a sheet-like molded object or its laminated body is baked (S13).

  By firing, a crystal composed of the second additive or a compound of the plate crystal powder and the second additive grows in accordance with the crystal direction of the oriented plate crystal powder. Thereby, a ceramic made of a polycrystalline sintered body oriented in a predetermined direction is obtained. That is, the microcrystals constituting the polycrystal are oriented in a predetermined direction, and the crystal planes of the microcrystals are oriented in the same direction. For this reason, a piezoelectric body having a high piezoelectric constant d33 can be obtained by subjecting the obtained ceramic to polarization treatment.

  Hereinafter, various embodiments in the process of producing a plate-like crystal powder from the first crystal powder will be described.

[Method for Producing Plate-like Crystal Powder (Embodiment 1)]
As shown in FIG. 4, first, as described above, the first crystal powder is prepared (S1 to S5).

Subsequently, a first crystal powder, a first additive such as Na ₂ CO ₃ for producing a plate crystal powder, and a flux such as NaCl that melts at a temperature at which the first crystal powder and the first additive can react. (Second flux) is mixed (S6, S7).

As the first additive, it is possible to use a compound of element A of the crystal-oriented ceramic shown by ABO ₂ described above, such as an oxide or carbonate of element A. The addition amount of the first additive is adjusted so that the molar ratio of the A element and Nb to the first crystal powder becomes 1: 1 after the Bi component is removed.

  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 flux is used to promote crystal growth by reacting 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 flux is easily dissolved in water or a solvent, the flux is added and mixed after drying an organic solvent or the like. The addition amount of the flux is preferably 10 mass% or more, more preferably 30 mass% or more with respect to the first crystal powder.

  The mixed material is heat-treated in a reducing atmosphere at a temperature at which the first crystal powder and the first additive can react (S8a).

  In the manufacturing process of the plate crystal powder, the firing process in which the first crystal powder reacts with the first additive also serves as a heat treatment for reducing the Bi component. Therefore, the firing is sometimes referred to as heat treatment.

  The heat treatment conditions are as described above. Since Bi is reduced in the reaction process of the first crystal powder and the first additive, the first intermediate in which the solid substance of the flux adheres to the plate crystal powder of the pentavalent metal acid alkali compound having a perovskite structure after the heat treatment. A fired body is obtained. Therefore, the thermal or chemical removal process for reducing only the Bi component after firing can be omitted.

  Next, the flux is removed from the first intermediate fired body (S9). In order to remove the flux from the first intermediate fired body, a means for immersing the first intermediate fired body in warm water and stirring it, and filtering the melted flux can be employed. Thereby, only plate-like crystal powder can be taken out.

This plate-like crystal powder has the general formula ABO ₃ (where A is at least one selected from the group consisting of Li, K and Na, and B is at least one element selected from 4, 5, and 6-valent elements) ) Perovskite type compounds represented by

  Hereinafter, the plate-like crystal powder obtained in Embodiment 1 is referred to as a first plate-like crystal powder.

[Method for Producing Plate-like Crystal Powder (Embodiment 2)]
A method for producing a plate-like crystal powder different from the first embodiment will be described.

  As shown in FIG. 5, first, as described above, the first crystal powder is prepared (S1 to S5).

  Subsequently, a plate-like crystal powder is produced using the first crystal powder. The difference from the method for producing the first plate-like crystal powder is that the method for producing the first plate-like crystal powder reacts the first crystal powder with the first additive, and reduction for reducing the Bi component. In contrast to the heat treatment step in the neutral atmosphere, the method for producing the plate-like crystal powder according to the second embodiment reacts the first crystal powder with the first additive to perform the second intermediate firing including the Bi component. It is the point which has the process of heat-processing in a reducing atmosphere after obtaining a body. Since other steps are the same as those of the first method for producing the plate crystal powder, description thereof will be omitted.

  The obtained first crystal powder, the first additive for producing the plate-like crystal powder, and the flux (second flux) that melts at a temperature at which the first crystal powder and the first additive can react are mixed. (S6, S7).

  The mixed material is heated to a temperature at which the first crystal powder and the first additive can react to form a second intermediate fired body (S8).

  Here, in order to react the first crystal powder and the first additive, the mixed material is preferably heated at 700 ° C. or higher and 1300 ° C. or lower. Even if the flux can be melted, the first crystal powder and the first additive do not react if the heating temperature is less than 700 ° C. On the other hand, when the heating temperature exceeds 1300 ° C., the first crystal powder is melted and integrally fired, making it difficult to form a powder.

  The heating atmosphere may be an atmosphere containing oxygen, and can be performed in the air, for example.

  By heating, the first crystal powder and the first additive react to obtain the second intermediate fired body in which the Bi component and the solid flux are adhered to the plate-like crystal powder according to Embodiment 2 of the compound having a perovskite structure. .

  The flux is removed from the second intermediate fired body (S9). In order to remove the flux, the intermediate fired body may be immersed in warm water and melted as in the above example.

  Next, the second intermediate fired body after flux removal is heat-treated in a reducing atmosphere to reduce the Bi component (S10b). The heat treatment conditions are as described above.

The plate-like crystal powder according to Embodiment 2 is similar to the first plate-like crystal powder in general formula ABO ₃ (where A is at least one selected from the group consisting of Li, K and Na, B is 4, Perovskite type compound represented by at least one element selected from pentavalent and hexavalent elements).

  Hereinafter, the plate-like crystal powder obtained in Embodiment 2 is referred to as a second plate-like crystal powder.

[Method for Producing Plate-like Crystal Powder (Embodiment 3)]
As shown in FIG. 6, first, as described above, the first crystal powder is prepared (S1 to S5).

  Subsequently, a third plate-like crystal powder is produced using the first crystal powder. The difference from the first plate crystal powder manufacturing method is that the first plate crystal powder manufacturing method mixes the first crystal powder, the first additive, and the flux and then heat-treats in a reducing atmosphere. On the other hand, the third method for producing a plate-like crystal powder is to heat-treat the first crystal powder alone in a reducing atmosphere.

  That is, Bi component is reduced by heat-treating the first crystal powder directly in a reducing atmosphere (S8c). Heat treatment in a direct reducing atmosphere means heat treatment in a reducing atmosphere without performing other heat treatment steps. The heat treatment conditions are as described above.

  As described above, the plate crystal powder according to the third embodiment is obtained by heat-treating the first crystal powder in a reducing atmosphere.

The composition of the plate crystal powder also depends on the composition of the first crystal powder. For example, the first crystal powder may have a general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 A _m-1.5 Nb _m O _{3m + 1} ) ²⁻ (where A is selected from the group consisting of Li, K, and Na) And m is an integer greater than or equal to 2), the general formula: A _m-1.5 Nb _m O _{3m + 1} (where A consists of Li, K and Na) A third plate-like crystal powder having a composition represented by at least one selected from the group and m is an integer of 2 or more is obtained. In addition, the first crystal powder has a general formula: (Bi ₂ O ₂ ) ²⁺ (A _m-1 B _m O _{3m + 1} ) ^2- (where A is at least selected from the group consisting of Li, K and Na) One, B is at least one selected from the group consisting of tetravalent, pentavalent and hexavalent elements such as Nb and Ta, and m is an integer of 2 or more. Formula: A _m-1 B _m O _{3m + 1} (where A is at least one selected from the group consisting of Li, K, and Na, and B is composed of 4, 5, 6 valent elements such as Nb, Ta, etc. A plate-like crystal powder having a composition represented by at least one selected from the group and m is an integer of 2 or more is obtained.

  The manufacturing method according to the third embodiment has fewer manufacturing steps than the first and second plate-like crystal powder manufacturing methods, and can produce the same crystal-oriented ceramics, so that the manufacturing steps can be shortened.

  Hereinafter, the plate-like crystal powder obtained in Embodiment 3 is referred to as a third plate-like crystal powder.

  Hereinafter, specific examples of producing the plate-like crystal powder according to the above-described embodiment will be described.

Example 1
A first plate crystal powder was produced according to the procedure shown in FIG.

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 raw 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).

  To the separated raw material, 100 mass% of NaCl as a flux (first flux) was mixed with the raw material, and dry mixed for 10 minutes with a coarse pulverizer (S3).

  The raw material after the addition of the flux was subjected to a two-stage calcination that was held at 850 ° C. for 1 hour in the air 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 intermediate fired body, it was immersed in warm water of 95 ° C. to 100 ° C. and left for 3 hours. Then, the process of stirring and dehydrating in warm water for 60 minutes was repeated three times, and finally filtered. As a result, a first crystal powder composed of the general formula: Bi _2.5 Na _3.5 Nb ₅ O ₁₈ was obtained (S5).

  FIG. 7 is a SEM observation photograph of the first crystal powder. It can be confirmed that the crystals are plate-like. From the SEM observation, it was found that the aspect ratio of the first crystal powder was 4-30. Here, the aspect ratio is defined as the ratio of the maximum longitudinal length of the plate to the thickness of the plate.

  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. A Cu Kα radiation source was used for all X-ray diffraction.

From FIG. 9, most of the obtained first crystal powder is represented by the general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 A _m-1.5 Nb _m O _{3m + 1} ) ²⁻ , where m = 5. It was found to be Bi _2.5 Na _3.5 Nb ₅ O ₁₈ . It was also found that the compounds represented by m = 2 and m = 4 were included slightly.

Next, a first plate crystal powder of a perovskite type pentavalent metal acid alkali compound having the general formula: NaNbO ₃ was produced from the first crystal powder.

Na ₂ CO ₃ is used as the first additive to the first crystal powder mainly composed of Bi _2.5 Na _3.5 Nb ₅ O ₁₈ , and Na ₂ CO ₃ is added in an amount that makes Na and Nb 1: 1 after the reaction. did. Thereafter, the first crystal powder and the first additive 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).

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

The mixed material of the first crystal powder, the first additive, and the flux is heat-treated in an N ₂ reducing atmosphere containing 3% H ₂ at 950 ° C. × 2 hours to obtain a first intermediate fired body It was. The temperature rise and fall of the heat treatment was about 200 ° C./h (S8a).

In order to remove the flux component from the obtained first intermediate fired body, it was immersed in warm water of 95 ° C. to 100 ° C. and left for 3 hours. Then, the process of stirring and dehydrating in warm water for 60 minutes was repeated three times, and finally filtered. Thus the general formula: NaNb0 obtain a first plate-like crystal powder composed of ₃ (S9).

  The first plate crystal powder was the same plate shape as the first crystal powder, and the aspect ratio was 4 to 30.

  FIG. 10 is an X-ray diffraction result of the first plate crystal powder obtained in Example 1.

The peak in X-ray diffraction shown in FIG. 10 is sharper than the peak in X-ray diffraction obtained from the plate-like crystal powder of Comparative Example 2 described later, and is considered to be a substantially single-phase NaNbO ₃ compound. Further, of the two count peaks from the diffraction angle of 44 ° to 48 °, the half width on the lower angle side was 0.16 °. This count peak is of the (200) plane of pseudo cubic crystal. Therefore, the obtained first plate crystal powder is considered to have a pseudo-perovskite structure.

  The amount of Bi remaining in the first plate crystal powder of Example 1 is shown in Table 1. The amount of Bi remaining was measured by ICP quantitative analysis.

(Comparative Example 1)
Using the manufacturing process of FIG. 11, a method of thermally reducing (heating in a reduced pressure atmosphere) was used as a method of reducing the Bi component.

First, in the same steps (S1 to S5) as in Example 1, a first crystal powder made of the general formula: Bi _2.5 Na _3.5 Nb ₅ O ₁₈ was obtained.

Next, Na ₂ CO ₃ was used as the first additive, and Na ₂ CO ₃ was added in such an amount that Na and Nb were 1: 1 after the reaction. 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 separated raw material was mixed with NaCl as a flux at 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 heated to be held 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 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, and finally filtered (S9).

Then, it was kept at 950 ° C. for 8 hours in a reduced pressure atmosphere of 5 × 10 ⁻⁴ torr to reduce the Bi component, and a plate crystal powder composed of the general formula: NaNbO ₃ was obtained (S10).

  When the Bi remaining amount was measured in the same manner as in Example 1, the Bi remaining amount exceeded 8.5 mass%, and the Bi component could not be sufficiently reduced. Moreover, the peak in the X-ray diffraction result was very broad.

(Comparative Example 2)
Using the manufacturing process of FIG. 11, a method of chemically reducing was used as a method of reducing the Bi component.

First, in the same steps (S1 to S5) as in Example 1, a first crystal powder made of the general formula: Bi _2.5 Na _3.5 Nb ₅ O ₁₈ was obtained.

Next, Na ₂ CO ₃ was used as the first additive, and Na ₂ CO ₃ was added in such an amount that Na and Nb were 1: 1 after the reaction. 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 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 (S6).

  The separated raw material was mixed with NaCl as a flux at 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 heated to be held 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 remove the 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, and finally filtered (S9).

  FIG. 12 is an X-ray diffraction result of the second intermediate fired body after removing the flux. Since a Bi component is included, a Bi compound count peak is observed in the range of 27 to 30 °.

Thereafter, the second intermediate fired body after flux removal was immersed in an aqueous solution having a nitric acid concentration of 4% at a rate of 50 g with respect to 1 L of the solution, stirred for 1 hour, and left for 1 hour after stirring. The solution was discarded, washed with pure water and dried to general formula: NaNb0 ₃ to obtain a plate-like crystal powder composed of (S10).

  Table 1 shows the amount of Bi remaining in the plate crystal powder and the half width of (100). Bi residual amount was 8.5 mass%, and Bi component could not be reduced sufficiently. FIG. 13 is an X-ray diffraction result of the plate-like crystal powder of Comparative Example 2. The peak is broader than the X-ray diffraction result of Example 1.

(Example 2)
A second plate crystal powder was produced by the production method shown in FIG.

First, in the same steps (S1 to S5) as in Example 1, a first crystal powder made of the general formula: Bi _2.5 Na _3.5 Nb ₅ O ₁₈ was obtained.

Na ₂ CO ₃ was used as the first additive, and Na ₂ CO ₃ was added in such an amount that Na and Nb were 1: 1 after the reaction. 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 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 (S6).

  To the separated raw material, 100 mass% of NaCl as the second flux was mixed with the first crystal powder, and 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 heated to be held 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 remove the 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, and finally filtered (S9).

The Bi component was volatilized by performing a heat treatment for holding the second intermediate fired body from which the flux component had been removed at 950 ° C. for 8 hours in an N ₂ reducing atmosphere containing 3% H ₂ . The temperature increase and decrease were about 200 ° C./h (S10b).

  Similar to Example 1, it was possible to easily obtain the second plate-like crystal powder having less Bi component than before.

  The removal of the second flux in the manufacturing process of FIG. 5 may be performed after the heat treatment (S10b) process.

Example 3
A third plate-like crystal powder was produced by the production method shown in FIG.

First, in the same steps (S1 to S5) as in Example 1, a first crystal powder made of the general formula: Bi _2.5 Na _3.5 Nb ₅ O ₁₈ was obtained.

The first crystal powder was heat-treated in an N ₂ reducing atmosphere containing 3% H ₂ at 950 ° C. × 8 hours to volatilize the Bi component. The temperature increase and decrease were about 200 ° C./h (S8c).

  Compared to the conventional manufacturing method, the steps of adding the first additive (S6), adding the second flux (S7), and removing the second flux (S9) in the manufacturing process of the plate crystal powder are no longer necessary. The manufacturing process was simplified compared to Example 1.

  A third plate-like crystal powder with less Bi component could be easily obtained. If the amount of Bi component is the same, processing in a short time is possible.

  The flux removal in the manufacturing process of FIG. 6 may be performed after the heat treatment (S8c) process.

Example 4
Crystal-oriented ceramics can be produced using the first to third plate-like crystal powders of the examples. An example of the manufacturing process of the crystallographically-oriented ceramic will be described with reference to FIG.

  The obtained plate crystal powder and the second reaction raw material are mixed at 5 mass%: 95 mass%, and mixed for 3 hours by a ball mill. Thereafter, a binder (polyvinyl butyral), a plasticizer (dioctyl phthalate), and an organic solvent (ethanol) for viscosity adjustment are mixed and vacuum degassed to prepare a slurry (S11).

  In the sheet molding, the laminating sheet in which the plate-like crystal powder is oriented is formed by putting the slurry in an extrusion apparatus having a width of 300 μm on the opening side and a width of 200 μm on the discharge side (S12). A plurality (10) of the laminating sheets are laminated and pressure-bonded with a warm CIP of 85 ° C. and 11.6 MPa to obtain a laminated body. You may form the electrode which consists of Ni, Ag, etc. in the interlayer and outer peripheral part of a laminated body.

  By firing this laminated body at a temperature of 700 to 1400 ° C. (1200 ° C. in the present embodiment) (S13), a crystallographically oriented ceramic is obtained.

  The plate crystal powder manufacturing method, plate crystal powder, and crystal oriented ceramics disclosed in the present application are used for manufacturing piezoelectric ceramics having various compositions, for example, suitable for manufacturing lead-free piezoelectric ceramics. .

1 Pseudo perovskite layer 2 (Bi ₂ O ₂ ) ²⁺ layer

Claims (9)

A step (A) of preparing a plate-like first crystal powder having a layered structure in which (Bi ₂ O ₂ ) ²⁺ layers and pseudo-perovskite layers are alternately laminated;
(B) obtaining a plate-like crystal powder in which the Bi component in the first crystal powder is reduced by heat-treating the first crystal powder in a reducing atmosphere;
A method for producing a plate-like crystal powder comprising The step (B)
The first crystal powder, a first additive for producing the plate crystal powder, and a flux that melts at a temperature at which the first crystal powder and the first additive can react, are mixed materials Obtaining
Heat treating the mixed material at a temperature at which the first crystal powder and the first additive can react and in the reducing atmosphere to form a first intermediate fired body;
Removing the flux from the first intermediate fired body;
The manufacturing method of the plate-shaped crystal powder of Claim 1 containing. The step (B)
The first crystal powder, a first additive for producing the plate crystal powder, and a flux that melts at a temperature at which the first crystal powder and the first additive can react, are mixed materials Obtaining
Heat-treating the mixed material at a temperature at which the first crystal powder and the first additive can react to form a second intermediate fired body;
Removing the flux from the second intermediate fired body;
Heat-treating the second intermediate fired body from which the flux has been removed in the reducing atmosphere;
The manufacturing method of the plate-shaped crystal powder of Claim 1 containing.   The said process (B) is a manufacturing method of the plate-shaped crystal powder of Claim 1 which heat-processes the said 1st crystal powder directly in the said reducing atmosphere. The first crystal powder has a general formula: (Bi ₂ O ₂ ) ²⁺ (Bi _0.5 A _m-1.5 Nb _m O _{3m + 1} ) ²⁻ (where A is at least selected from Li, K, or Na) 5. The method for producing a plate-like crystal powder according to claim 1, wherein the compound is a compound represented by the following formula: one element and m is an integer of 2 or more. The step (A)
By preparing and mixing a raw material containing Bi, A and Nb and another flux which melts at a temperature at which the raw material reacts so as to contain Bi, A and Nb at a composition ratio represented by the general formula Obtaining other mixed materials;
Obtaining the first crystal powder covered with the other flux by heating the other mixed material;
Removing the other flux from the first crystal powder covered with the other flux;
The manufacturing method of the plate-shaped crystal powder of Claim 2 or 3 containing this.   The method for producing a plate-like crystal powder according to any one of claims 1 to 4, wherein the reducing atmosphere is a hydrogen atmosphere, a carbon monoxide atmosphere, a hydrogen sulfide atmosphere, a sulfur dioxide atmosphere, a formaldehyde atmosphere, or a mixed atmosphere thereof. A plate-like crystal powder obtained by the production method according to claim 1,
A plate-like crystal powder wherein the Bi amount in the plate-like crystal powder is less than 8.5 mass%.   A sintered body of the plate-like crystal powder according to claim 8 and a second additive capable of forming a perovskite type compound, wherein the sintered body is a polycrystal having a crystal plane oriented in a predetermined direction. A crystal-oriented ceramic comprising a sintered body.

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