JPWO2020004670A1 - Dielectric materials showing polarization twist, dielectric structures that can control polarization, capacitors and piezoelectric elements using them, and ceramics, and capacitors and piezoelectric elements using them. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dielectric material exhibiting a polarization twist, a dielectric structure capable of controlling polarization, a capacitor and a piezoelectric element using the same, ceramics, and a capacitor and a piezoelectric element using the same. SOLUTION: The concentration of the pores of the anion X site introduced by the A site pores lacking the metal arranged at the A site of each apex of the cubic crystal or the pseudo cubic crystal is 1% or less, and the cubic crystal is described above. Alternatively, the octahedrons of the anions existing in the perovskite structure are rotated and arranged with respect to the crystal axis of the pseudo-cubic crystal with an angle ω, and both the angle ω and the polarization value change due to the application of an electric field. It is a dielectric material that exhibits twist. Further, for the ceramics represented by the general formula (A1 (1-x + δ) / 2A2 (1-x-3δ) / 2A3x □ δ) BO3, the combination of the amount δ of the A-site pores and the amount x of A3 is adjusted. , The properties of ceramics can be controlled. [Selection diagram] Fig. 1

Description

The present invention relates to a dielectric material exhibiting a polarization twist, a dielectric structure capable of controlling polarization, a capacitor and a piezoelectric element using the same, and ceramics, and a capacitor and a piezoelectric element using the same.

Dielectric materials are used in many applications such as insulating materials for electronic devices, inter-electrode insertion materials for capacitors, and piezoelectric elements. In particular, when used for a capacitor or a piezoelectric element, a dielectric material whose dielectric constant, piezoelectric strain constant, etc. can be controlled is required.

For example, Patent Document 1 below discloses a tunable capacitor that utilizes an electric field-induced phase transition of a ferroelectric substance and dielectric tunability in the vicinity of a critical point.

Further, as shown in Non-Patent Document 1, the present inventors show a polarization twist in a part of a dielectric crystal having a perovskite structure composed of a unit cell having a coordination polyhedron such as an oxygen octahedron. We found that it is related to polarization and that polarization can be controlled by voltage.

Japanese Unexamined Patent Publication No. 2014-36022

Scientific Reports volume 6, Article number: 32216 (2016) doi: 10.1038 / srep32216

However, in the above-mentioned conventional technique, there are problems that the value of the dielectric constant is not sufficiently large and that the control range of the dielectric constant is not sufficiently large. In addition, there was no mention of controlling the piezoelectric strain constant by voltage. Furthermore, there was no mention of controlling the properties related to the polarization characteristics of the dielectric material (ceramics).

An object of the present invention is a dielectric material exhibiting a polarization twist in which the dielectric constant and the piezoelectric strain constant can be significantly changed by an applied voltage through controlling the polarization by a voltage, a dielectric structure in which the polarization can be controlled, and the like. Another object of the present invention is to provide a capacitor and a piezoelectric element using the same, a ceramic having controllable polarization characteristics, and a capacitor and a piezoelectric element using the same.

In order to achieve the above object, one embodiment of the present invention is a dielectric material exhibiting a polarization twist and is arranged at the A site of each vertex of a cubic or pseudo-cubic crystal _{having a perovskite structure ABX 3.} An octahedron of anions present in the perovskite structure with respect to the crystal axis of the cubic or pseudo-cubic crystal, in which the concentration of the pores of the anion X site introduced by the metal-deficient A-site pores is 1% or less. Are rotated and arranged with an angle ω, and both the angle ω and the polarization value change due to the application of an electric field.

The dielectric material is preferably any of a normal dielectric, a ferrielectric, a ferroelectric, and an antiferroelectric.

Further, the octahedron is an octahedron composed of 6 oxygen atoms, and the concentration of oxygen vacancies introduced by the A site vacancies (number of oxygen vacancies / number of oxygen sites) is 1% or less. Is preferable. Here, the oxygen site indicates the site of oxide ion (O ^2- ).

Further, another embodiment of the present invention is a dielectric structure whose polarization can be controlled, wherein a dielectric material exhibiting any of the above polarization twists and an electric field are applied to the dielectric material to cause the angle ω. It is characterized by including a member for controlling polarization by changing the above.

Further, yet another embodiment of the present invention is characterized by being a capacitor or a piezoelectric element using the dielectric structure capable of controlling the polarization.

Further, still another embodiment of the present invention is a ceramic composed of a perovskite-type oxide represented by the following general formula (4).
(A1 _{(1-x + δ) / 2} A2 _{(1-x-3δ) / 2} A3 _x □ _δ ) BO ₃ ... (4)
A1 is a trivalent metal, A2 is a monovalent metal, A3 is a divalent metal, B is a tetravalent metal, □ represents A site vacancies, and the A site empty. The pore amount δ is 0 to 3%, and the A3 amount x is 2 to 25%.

Further, the perovskite type oxide preferably further contains a metal oxide M.

Further, it is preferable that A1 is Bi, A2 is Na, and A3 is Ba.

Further, it is preferable that M is Cu.

Further, yet another embodiment of the present invention is characterized by being a capacitor or a piezoelectric element using the above ceramics.

According to the present invention, a dielectric material showing a polarization twist that can greatly change the dielectric constant and the piezoelectric strain constant, a dielectric structure that can control polarization, a capacitor and a piezoelectric element using the same, and polarization characteristics are controlled. Possible ceramics and capacitors and piezoelectric elements using them can be realized.

It is explanatory drawing of the polarization twist. It is explanatory drawing when the electric field E is applied to the crystal of the dielectric material which shows a polarization twist. It is a figure which shows the example of the dielectric structure which can control the polarization P using the dielectric material which shows the polarization twist which concerns on Embodiment 1. FIG. It is a figure which shows the measurement result of the polarization twist. It is a figure which shows the measurement result of the polarization twist. It is a figure which shows the measurement result of the relationship between the rotation angle ω and the polarization P when the electric field changes. It is a figure which shows the measurement result of the relationship between the change of an electric field and the change of a dielectric constant. It is a figure which shows the measurement result of the relationship between the change of an electric field and the change of a piezoelectric strain constant. It is explanatory drawing of the manufacturing process of the ceramics which concerns on Embodiment 2. FIG. It is a figure which shows the P (polarization) -E (electric field) curve of the ceramics which concerns on Example 4. FIG. It is a figure which shows another example of the P (polarization) -E (electric field) curve of the ceramics which concerns on Example 4. FIG. It is a figure which shows the relationship between the electric field where a phase transition occurs between a strong dielectric phase (space group P4mm) and ferri dielectric phase (space group P4bm), and the amount δ of A site vacancy. It is a figure which shows the PE curve of the ceramics which concerns on Example 5. FIG. It is a figure which shows the P (polarization) -E (electric field) curve, and the electric susceptibility χ (E) when the electric field E is changed between the point A and the point B of FIG. It is a figure which shows another example of the P (polarization) -E (electric field) curve of the ceramics which concerns on Example 5. FIG. It is a figure which shows the P (polarization) -E (electric field) curve, and the electric susceptibility χ (E) when the electric field E is changed between the point A and the point B of FIG. It is a figure which shows still another example of the P (polarization) -E (electric field) curve of the ceramics which concerns on Example 5. FIG. It is a figure which shows the P (polarization) -E (electric field) curve, and the electric susceptibility χ (E) when the electric field E is changed between the point A and the point B of FIG. 17A. FIG. 17 (b) is a diagram showing a P (polarization) -E (electric field) curve and an electric susceptibility χ (E) when the electric field E is changed between points C and G in FIG. 17 (b). It is a figure which shows the summary of the state (phase) of ceramics before and after application of an electric field E (= 50 kV / cm) to ceramics.

Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

Embodiment 1.
1 (a) and 1 (b) show explanatory views of the polarization twist. FIG. 1A is a schematic diagram of a crystal lattice of a perovskite-type structure (ABX _{3) that is common in dielectric materials.} In FIG. 1 (a), the mother crystal of the perovskite structure (crystal phase with high symmetry) is represented by a cubic unit cell, and metal A is located at the A site at each apex of the cubic crystal, and metal A is located at the B site of the body center. The metal B is arranged, and six anions X are arranged at each face center of the cubic crystal centering on the metal B. Here, as the anion X, oxygen, fluorine, chlorine, bromine, arsenic and the like can be used, but oxygen is preferable because it is relatively easy to prepare and easy to handle.

The metal A includes metal elements such as Bi, La, Nd, Pr, Sm and other rare earth elements which are positive trivalent ions, and Pb, Ba and Sr which are metal elements which are positive divalent ions. , K, Na, Ag, Li, etc., which are metal elements that become positive monovalent ions, and as metal B, rare earths such as Y, which is a metal element that becomes positive trivalent ions, have a relatively small ionic radius. Elements, Sc, metal elements that are positive tetravalent ions such as Ti, Zr, Hf, metal elements that are positive pentavalent ions such as Nb and Ta, and Mo that are metal elements that are positive hexavalent ions. And W and the like. Further, the metal B also includes transition metal elements such as V, Cr, Mn, Fe, Co, Ni, and Cu, which are metal elements having a plurality of valences. Ca, Mg, and Zn, which are positive divalent ions, are elements that can enter both A site and B site.

As shown in FIG. 1 (a), in the unit cell of a crystal having a perovskite structure, an octahedron is formed by anions X.

FIG. 1B shows a schematic view when the crystal lattice is viewed from the direction of arrow D in FIG. 1A. In the example of FIG. 1 (b), four unit _{cells of ABX 3 shown in FIG. 1 (a) are shown.}

In a crystal whose crystal system is cubic or tetragonal (space group P4 mm), the rotation angle ω of the oxygen octahedron is zero, and there is no rotation of the octahedron. On the other hand, in the ferri dielectric phase (space group P4bm), as shown in FIG. 1 (b), each octahedron formed by the anion X has a cubic crystal axis (axis parallel to the line connecting the metal A). In the present specification, the static structure and the structure in which both the polarization value and the rotation angle ω of the octahedron change when an electric field is applied are referred to as a polarization twist. Further, each octahedron rotates about a line connecting two vertices (anion X) facing each other in the direction of arrow D in FIG. 1A as a rotation axis, and the rotation directions are opposite between two adjacent octahedrons. And the size of the rotation angle is the same (ω).

In addition to the dielectric material having the above-mentioned cubic crystal structure having high crystal symmetry, the symmetry of the crystal is lowered, and the symmetry of the crystal is lowered, so that the symmetry of the crystal is lowered, and the symmetric crystal, the orthogonal crystal, and the rhombic crystal (including the triclinic crystal) are used. Some materials have a monoclinic or triclinic crystal structure. These low-symmetry crystal systems can be approximated as pseudo-cubic crystals with distorted cubic crystals.

The dielectric material exhibiting the polarization twist is an ordinary dielectric, a ferrielectric, a ferroelectric or an antiferroelectric, and each of the cubic or pseudo-cubic crystals _{having a perovskite structure (composition formula: ABX 3).} Examples thereof include those having a low concentration of A-site vacancies in which the metal A arranged at the apex is missing. Here, the concentration of the A-site pores is calculated by the following formula.

Specifically, regarding the formal charge of the A-site metal arranged at each vertex (A-site), the concentration of the A-site vacancies is 3% or less in the case of plus trivalent, and the concentration is 3% or less in the case of plus divalent. It is preferable that the concentration of the A-site vacancies is 5% or less, and in the case of plus monovalent, the concentration of the A-site vacancies is 6% or less. In the case of such a concentration of A-site vacancies, the concentration of vacancies of anion X such as oxygen vacancies introduced by A-site vacancies becomes 1% or less, and the expression of polarization twist becomes easy. When the anion X is oxygen, the concentration of oxygen vacancies is calculated by the following formula.

The concentration of anion vacancies such as oxygen vacancies was measured by measuring the concentration of A site vacancies by quantitative analysis using inductively coupled plasma emission spectroscopy (ICP-AES) or a fluorescent X-ray analyzer (XRF). Based on the result, it can be determined from the electrically neutral condition. In the quantitative analysis by ICP-AES or XRF, all the compositions (amount of substance ratio) of the metal of A site are obtained based on the composition of the metal of B site, and the total of the number of A sites and the A site metal composition is obtained. From the difference, the A-site vacancy concentration (the total value of the vacancy concentrations of each metal) can be obtained. A specific method for calculating the A-site pore concentration will be described in Example 1.

Generally, when the A-site vacancies are formed, vacancies of anion X such as oxygen are also formed so as to satisfy the electrically neutral condition. In perovskite-type oxide (ABO ₃ ), when A-site vacancies are formed, oxygen vacancies are formed at the same time. For example, in the case of A = Bi, when ^{two Bi 3+} vacancies are formed, three vacancies (oxygen vacancies) are generated at oxygen sites (oxide ion (O ^{2-) sites).} Satisfy the electrical neutrality condition. In the case of A = Ag, when ^{two Ag +} vacancies are formed, one oxygen vacancies is generated, and the electrical neutrality condition is satisfied. As the concentration of the metal vacancies increases, so does the concentration of oxygen vacancies. In polarized dielectrics, oxygen vacancies interact with polarization to prevent macroscopic polarization changes due to electric fields. For this reason, even if the dielectric material potentially exhibits a polarization twist, in a sample having a high concentration of oxygen vacancies and a large influence thereof, the change in polarization due to an electric field is hindered, and the polarization twist due to the application of an electric field cannot be observed. There are many. On the other hand, when the concentration of the oxygen vacancies is reduced (1% or less), the influence of the oxygen vacancies is reduced, and a polarization twist due to the application of an electric field is observed.

The production of the dielectric material exhibiting the polarization twist is obtained through a heat treatment process. The lower the temperature under the heat treatment conditions, the lower the concentration of the A-site vacancies and the oxygen vacancies, and the higher the crystal integrity. Further, the higher the oxygen partial pressure during the heat treatment, the lower the concentration of the A-site pores and the higher the crystal integrity. When the crystal completeness is high, it becomes easy to induce a polarization twist due to the application of an electric field, and the dielectric constant and the piezoelectric strain constant can be greatly changed by the applied electric field through controlling the polarization by a voltage.

Usually, the above heat treatment is often performed in air (oxygen partial pressure is about 0.02 MPa). When heat treatment is performed in air (for example, heat treatment at a temperature of 1000 ° C. to 1300 ° C.), a defect formation reaction occurs in which elements having a high vapor pressure (Bi or Ag) volatilize, and the concentration of these A-site vacancies increases. When the oxygen partial pressure during this heat treatment is increased, the defect formation reaction is suppressed and the concentration of these A-site vacancies decreases. The higher the oxygen partial pressure during the heat treatment, the less likely it is that the defect formation reaction will occur, and the concentration of these A-site pores will decrease, resulting in a high-quality dielectric material with a small concentration of oxygen pores. In order to produce a high quality dielectric material, it is preferable that the oxygen partial pressure is 0.1 MPa to 1 MPa. If the oxygen partial pressure is further increased to about 10 MPa, there is a possibility that a higher quality dielectric material can be produced.

Further, in the case of heat treatment with the same oxygen partial pressure, the lower the heat treatment temperature, the more the defect formation reaction is suppressed, the concentration of A-site vacancies and oxygen vacancies becomes smaller, and a high-quality dielectric material can be obtained. Be done.

Bi-based and Ag-based perovskite-type oxides showing a polarization twist are usually produced by heat treatment at a temperature of 1000 ° C. to 1200 ° C. When the oxygen partial pressure during this heat treatment is increased from 0.02 MPa to 0.1 MPa, the pore concentration of Bi and the pore concentration of Ag become smaller. In this case, the lower the heat treatment temperature, the smaller the pore concentration of the metal such as Bi and Ag. By the above operation, the concentration of oxygen vacancies can be reduced to 1% or less. Further, when the oxygen partial pressure is increased to about 1 MPa, the pore concentration of Bi and the pore concentration of Ag are reduced to 0.01% to less than 1%, and a clear polarization twist is induced in the obtained single crystal by an electric field. can.

When an electric field is applied to the crystal of the dielectric material showing the polarization twist in parallel with the arrow D in FIG. 1A, the present inventors change the rotation angle ω of the octahedron formed by the anion X and at the same time. We have found that the magnitude of polarization changes.

2 (a), (b), (c), and (d) show explanatory views when an electric field (E) is applied to a crystal of a dielectric material showing a polarization twist. _{In the perovskite-type structure ABX 3} shown in FIGS. 2 (a), (b), (c), and (d), the metals A, B, and anion X are omitted, and only the octahedron formed by the anion X is shown. ing. Further, the polarization P in FIG. 2A when the magnitude of the electric field is zero (no electric field is applied) is the spontaneous polarization Ps. The magnitude of the rotation angle ω of the octahedron is indicated by the arrow r. Further, as the magnitude of the electric field E applied in the order of FIGS. 2 (a), (b), (c), and (d) increases, the polarization P of the crystal also increases.

When the small electric field E shown in FIG. 2B is applied from the state where the electric field E is not applied as shown in FIG. 2A, the magnitude r of the rotation angle ω of the octahedron decreases and the polarization P The size of is increased. Next, as shown in FIG. 2C, when the applied electric field E is further increased, the magnitude r of the rotation angle ω is further reduced and the magnitude of the polarization P is further increased.

Here, when a larger electric field E is applied as shown in FIG. 2D, the magnitude r of the rotation angle ω of the octahedron becomes 0 (expressed by the fact that the arrow r is not shown in FIG. 2D). Along with this, the magnitude of the polarization P is significantly larger than that in the case of FIG. 2 (a). In this state, the properties of the dielectric material are transferred (phase transition) to the ferroelectric phase (ferroelectric state). When the magnitude r of the electric field E is reduced from the state of FIG. 2 (d), the magnitude r of the polarization P becomes smaller and the magnitude r of the rotation angle ω of the octahedron becomes larger, so that the electric field E becomes smaller. When it is set to zero, it returns to the state shown in FIG. 2 (a).

From the above, when the electric field E applied to the crystal of the dielectric material is increased, the magnitude r of the rotation angle ω of the octahedron becomes smaller and the polarization P becomes larger. On the other hand, when the electric field E is made small, the magnitude r of the rotation angle ω of the octahedron becomes large and the polarization P becomes small. The magnitude of polarization P in the polarization twist has a positive correlation with the applied electric field E.

As described in Non-Patent Document 1 and the like, the magnitude r of the rotation angle ω of the octahedron formed by the anion X can be measured by X-ray diffraction (XRD) or neutron diffraction.

When an electric field E is applied to a crystal of a dielectric material, the polarization P changes and the electric flux density D also changes. Assuming that the dielectric constant of the dielectric material is ε (ε = ε ₀ × ε _r , ε ₀ : vacuum dielectric constant, ε _r : relative permittivity) and the electric susceptibility of the dielectric is χ, the following relational expression is obtained. To establish.

By transforming the equation (1), the following equation (2) is obtained. Therefore, when the polarization P is measured with the electric field E applied, the electric susceptibility χ can be obtained experimentally by the equation (2), and the relative permittivity ε _r (ε _r = 1 + χ) can be obtained from the equation (1).

Here, ∂P / ∂E indicates the partial differential of the polarization P due to the electric field E. That is, ∂P / ∂E is equal to the gradient of the polarization P at a certain electric field E.

Further, when an electric field E is applied to the crystal of the dielectric material, the strain amount S (the length of the crystal at the electric field E / the length of the crystal when the electric field E is zero) changes. In a system in which the dielectric material has polarization Ps, assuming that the piezoelectric strain constant is d, these relationships are tentatively shown by the following equation (3).

Equation (3) is an equation that holds when the magnitude of the electric field E is as small as 1 kV / cm or less. In this case, since the piezoelectric strain constant d is a material constant (constant regardless of the electric field E), the slopes of the strain S and the electric field E are equal to the piezoelectric strain constant d.

On the other hand, when the electric field E becomes larger than several kV / cm, the piezoelectric strain constant d of the dielectric material depends on the electric field E. For example, when the directions of the electric field E and the spontaneous polarization Ps are different, the spontaneous polarization Ps is given in the direction in which the angle with the electric field E becomes smaller (the free energy of the system (the inner product of the Ps vector and the E vector (-Ps · E)). The driving force that rotates in the direction in which (is) becomes the minimum (most stable) works. As a result, when the spontaneous polarization Ps is rotated by the electric field E (including the rotation of the polarization domain), the electric field E dependence of the strain S shows hysteresis, and the piezoelectric strain constant d depends on the electric field E. Further, in a dielectric material exhibiting a polarization twist, when the electric field E is increased, the polarization P is also increased, and the piezoelectric strain constant d is also increased. Therefore, the piezoelectric strain constant d is evaluated by ∂S / ∂E.

Even in the dielectric material that potentially exhibits the polarization twist according to the first embodiment described above, when the concentration of the A-site pores is large and the concentration of the oxygen pores exceeds 1%, the polarization twist due to the application of an electric field is performed. Cannot induce. In the first embodiment, the concentration of the oxygen vacancies is set to 1% or less by devising the heat treatment conditions for producing the dielectric material as described above, so that the influence of the oxygen vacancies is reduced and the electric field E is affected. Polarization twist can be expressed by application. Therefore, the polarization P can be significantly changed by applying the electric field E to the crystal of the dielectric material, and the dielectric constant ε and the piezoelectric strain constant d of the dielectric material can be changed in a wide range through the change of the polarization P. Can be controlled.

3 (a), (b), and (c) show an example of a dielectric structure capable of controlling polarization using a dielectric material showing a polarization twist according to the first embodiment. In the example of FIG. 3A, electrodes 12a and 12b as members for controlling polarization are arranged on two opposing surfaces of the dielectric material 10 showing a polarization twist. Further, in the example of FIG. 3B, electrodes 12a and 12b are arranged on two opposing surfaces of the dielectric material 10 exhibiting a polarization twist as in FIG. 3A, and the electrodes 12a and 12b are further arranged. An intermediate electrode 14 is arranged between them (inside the dielectric material 10). In the examples of FIGS. 3A and 3B, the electrodes 12a and 12b and the intermediate electrode 14 are arranged in contact with the dielectric material 10, and an electric field can be arbitrarily applied to the dielectric material 10. ing. The number of intermediate electrodes 14 is not limited to one, and may be an appropriate number depending on the application. Further, the shape and the arrangement position of the intermediate electrode 14 can be appropriately determined according to the application.

Further, in the example of FIG. 3C, the electrodes 12a and 12b are arranged outside the dielectric material 10 without contacting the dielectric material 10. In FIG. 3C, the electric field generated by the electrodes 12a and 12b is applied to the dielectric material 10 arranged in the vicinity thereof.

In the example of the dielectric structure whose polarization can be controlled shown in FIGS. 3A, 3B, and 3C described above, an electric field is applied to the dielectric material 10 from the electrodes 12a and 12b and the intermediate electrode 14. By applying and changing the magnitude r of the rotation angle ω of the octahedron formed by the anion X according to the above-mentioned principle and changing the polarization P, the dielectric constant ε and the piezoelectric strain constant d of the dielectric material are controlled. be able to.

The members for controlling polarization by applying an electric field to a dielectric material such as the electrodes 12a and 12b and the intermediate electrode 14 are not limited to the examples of FIGS. 3A, 3B, and 3C, and are dielectric. If the electric field applied to the body material 10 can be controlled, the number, shape, and arrangement location of the electric field can be arbitrarily determined.

The dielectric structure according to the first embodiment, which can control the polarization, can control the dielectric constant ε and the piezoelectric strain constant d by applying an electric field. Specifically, the dielectric constant ε and the piezoelectric strain constant d can be changed to large values by applying an electric field. Therefore, it can be suitably used for capacitors, piezoelectric elements and the like.

When the dielectric structure having controllable polarization according to the first embodiment is used as a capacitor, for example, the configurations shown in FIGS. 3A and 3B can be used as they are. In this case, when the electrodes 12a and 12b are charged with electric charges, the dielectric constant ε of the dielectric material 10 is greatly increased by the electric field generated by the electric field, so that the capacitance of the capacitor is greatly increased and the charging charge is greatly increased. Can be made to.

According to the configuration of FIG. 3C, the capacitance of the capacitor can be greatly increased by applying an electric field from the outside of the capacitor.

Further, when the dielectric structure having controllable polarization according to the first embodiment is used as the piezoelectric element, the configurations shown in FIGS. 3A and 3B can be used as they are. In this case, when a voltage is applied to the electrodes 12a and 12b, the piezoelectric strain constant d of the dielectric material 10 is greatly increased by the electric field generated by the voltage, so that a piezoelectric element having a large strain amount S can be realized.

According to the configuration of FIG. 3C, the strain amount S of the piezoelectric element can be greatly increased by applying an electric field from the outside of the piezoelectric element.

Embodiment 2.
The ceramic according to the second embodiment is a ceramic composed of a perovskite-type oxide (ABO ₃ ), which is a crystal having a perovskite-type structure.

A specific example is a ceramic composed of polycrystals of perovskite-type oxide represented by the following general formula (4).
(A1 _{(1-x + δ) / 2} A2 _{(1-x-3δ) / 2} A3 _x □ _δ ) BO ₃ ... (4)
A1 is a trivalent metal, A2 is a monovalent metal, A3 is a divalent metal, B is a tetravalent metal, □ represents A site vacancies, and A site empty. The amount of pores (mole fraction) δ is 0 to 3%, and the amount (mole fraction) x of A3 is 2 to 25%.

Here, examples of A1 include rare earth elements such as Bi and La, examples of A2 include Li, Na, and K, and examples of A3 include Ca, Sr, and Ba. Further, examples of B include Ti, Zr, Hf and the like.

The perovskite-type oxide may further contain a metal M. By adding a compound containing M such as a metal of M or an oxide or fluoride, this may act as an additive to improve the sinterability and various properties of the perovskite type oxide. For example, if the sinterability is improved by adding the metal M, dense ceramics can be produced at a lower firing temperature, and as a result, high-quality crystalline ceramics having a small oxygen pore concentration can be produced. Further, since the added metal M ions trap the vacancy (oxygen vacancy) of the oxygen ion site, the adverse effect of the oxygen vacancy can be reduced, so that various characteristics such as dielectric property, polarization property and piezoelectric property are improved. do.

The perovskite-type oxide when the oxide of the metal M is contained is represented by the following general formula (5).
(A1 _{(1-x + δ) / 2} A2 _{(1-x-3δ) / 2} A3 _x □ _δ ) (B _{1- y My} ) O ₃ ... (5)
However, A1, A2, A3, B and □ are the same as the above general formula (4), and y is the composition of the metal M (molar fraction of M at the B site). Examples of M include transition metal elements such as Cu, Mn, and Co. Further, y is preferably 0.001 to 5%.

The perovskite-type oxide represented by the above general formula (5) is, for example, (Bi _{(1-x + δ) / 2} Na _{(1-x-3δ) / 2} Ba _x □ _δ ) (Ti _0.999 Cu _0.001 ). O ₃
The crystal represented by is preferable.

The perovskite-type oxide ceramics represented by the general formulas (4) and (5) can control the polarization characteristics by adjusting the amount δ of the A-site pores and the amount x of A3. Therefore, the polarization characteristics can be adjusted according to the application of the ceramics.

For example, in applications where the change in the electric field is large, such as a capacitor for a high-power transistor, a ferroelectric material (for example, a phase in which the space group is P4 mm) that can keep the fluctuation of the dielectric constant small with respect to the change in the electric field is used as the dielectric material. Can be used as. Further, in applications such as multilayer ceramic capacitors (MLCC) where the change in electric field is small, as a dielectric material whose dielectric constant increases when an electric field is applied due to the action of polarization twist such as ferri dielectric phase (P4bm phase). Can be used. Further, when used as a piezoelectric element, a large piezoelectric constant of the ferri-dielectric phase (P4bm phase) can be used for applications in which a conventional soft piezoelectric material having a relatively large piezoelectric strain constant is used. Specifically, actuators for micro-positioning and nano-positioning, various sensors, ultrasonic transmitters and receivers, flow rate and liquid level measurement, object identification / monitoring, electroacoustics such as acoustic transducers, microphones, and pickups. Can be used for. A ferroelectric constant with good linearity of a ferroelectric phase (P4 mm phase) can be used for applications in which a conventional hard piezoelectric material having a relatively small piezoelectric strain constant and a small electrical loss is used. Specifically, it can be used for high-power acoustics, various applications using ultrasonic waves, material processing (ultrasonic welding, bonding, drilling, etc.), and medical sensors.

FIG. 9 shows an explanatory diagram of the ceramic manufacturing process according to the second embodiment. In FIG. 9, first, the oxide or carbonate as a raw material is weighed (I). Weighing is performed precisely after the high-purity reagent has been sufficiently dried.

Next, the weighed oxide or carbonate (raw material containing A1, A2, A3, B, M) is pulverized and mixed (II), and pre-baked in air at 600 to 1000 ° C. for 0.5 to 20 hours. Do (III). The oxide of the metal M or the like may be added after the preliminary firing. As described above, the calcination can be performed in air, but it is desirable that the calcination is performed in oxygen having a high oxygen partial pressure (oxygen partial pressure of about 0.1 MPa) or in a high-pressure oxygen atmosphere (oxygen partial pressure of about 10 MPa).

After the pre-baking, PVA (polyvinyl alcohol) and PMMA (polymethylmethacrylate) are mixed as a binder (IV). The powder mixed with the binder is press-molded to prepare a green compact pellet (V). For press molding, an isotropic pressure press is performed after the uniaxial pressure press. The molding pressure at the time of pressing is about 150 MPa. Then, in the same manner as in (III) above, main firing is performed at 1000 to 1250 ° C. for 0.5 to 20 hours in the air or in a high-concentration oxygen atmosphere (oxygen partial pressure of about 0.1 to 10 MPa) (VI). As described above, the ceramics according to the second embodiment are manufactured. Further, a step of removing the binder at a relatively low temperature (200-500 ° C.) may be provided before firing.

Hereinafter, examples of the present invention will be specifically described. The following examples are for facilitating the understanding of the present invention, and the present invention is not limited to these examples.

Example 1. Relationship between oxygen vacancy concentration and polarization twist based on A-site vacancy concentration <Measurement of A-site vacancy concentration>
An ICP emission spectroscopic analyzer SPS-3100 manufactured by SII Nanotechnology Co., Ltd. was used as the ICP-AES apparatus.

As the XRF apparatus, a scanning fluorescent X-ray analyzer ZSX Primus III manufactured by Rigaku Co., Ltd. was used.

Is a perovskite oxide ABO ₃ below _{(Bi 1/2} Na _1/2) single crystal sample (hereinafter, referred to as single-crystal sample 1) of TiO ₃ -7% BaTiO 3 and single crystal samples AgNbO ₃ (hereinafter, The composition analysis result of (referred to as single crystal sample 2) is shown. In the following, Po ₂ represents the oxygen partial pressure during single crystal growth. In this case, the oxygen gas used was manufactured by Suzuki Shokan Co., Ltd. with a purity of 99.9 vol. %. The oxygen vacancies concentration was determined from the electrically neutral conditions based on the composition of other metal elements.

_{· (Bi 1/2 Na 1/2) TiO} 3 -7% BaTiO 3 single crystal (single crystal sample 1)
The measurement sample was grown by the TSSG method (top seeded solution growth method) described in Non-Patent Document 1. The growth of the single crystal sample 1 was carried out at _{Po 2 = 0.9 MPa.} In addition, as a comparative example _{, cultivation was also carried out at Po 2} = 0.02 MPa (hereinafter referred to as Comparative Example 1).

The orientation of the single crystal sample 1 and the single crystal sample of Comparative Example 1 was determined by an X-ray diffraction experiment, and the single crystal sample was cut out so that an electric field could be applied to the [100] orientation, and platinum electrodes were sputtered on the upper and lower surfaces of the cut out crystal. Provided by law. A step cutter MC-171 manufactured by Maruto Co., Ltd. was used for cutting. The size of the sample used for the measurement is approximately 1 mm square on the electrode surface and 0.1-0.2 mm in thickness. Therefore, a voltage is applied to a sample having a thickness of 0.1-0.2 mm. With respect to the single crystal sample 1 and the single crystal sample of Comparative Example 1 processed as described above, the concentration of A-site vacancies and the concentration of oxygen vacancies were measured by the following methods.
Measuring method: Inductively coupled plasma atomic emission spectrometry (ICP-AES) method Measuring device: ICP emission spectroscopic analyzer SPS-3100 manufactured by SII Nanotechnology Co., Ltd.
Measurement results: Table 1 below.

As shown in the composition formula of the perovskite-type structure ABX ₃ (number of A sites 1, number of B sites 1, number of X sites 3), the A site vacancy concentration shown in Table 1 is the A site. It is calculated from the number (1) and the substance amount ratio of Bi, Na, and Ba. Specifically, it is (1- (total of substance amount ratios of Bi, Na, and Ba)).

-AgNbO ₃ single crystal (single crystal sample 2)
The measurement sample was prepared by the Czochralski (Cz) method. The growth of the single crystal sample 2 was carried out at _{Po 2 = 0.9 MPa.} In addition, as a comparative example _{, the growth was carried out at Po 2} = 0.1 MPa by the static slow cooling method (hereinafter referred to as Comparative Example 2).

The orientation of the single crystal sample 2 and the single crystal sample of Comparative Example 2 was determined by an X-ray diffraction experiment in the same manner as the single crystal sample 1 and Comparative Example 1, and an electric field was applied to the [110] orientation. It was cut out as much as possible, and platinum electrodes were provided on the upper surface and the lower surface of the cut out crystal by a sputtering method (the size is the same as that of the single crystal sample 1 and the single crystal sample of Comparative Example 1). With respect to the single crystal sample 2 and the single crystal sample of Comparative Example 2 processed as described above, the concentration of A-site vacancies and the concentration of oxygen vacancies were measured by the following methods.
Measuring method: X-ray fluorescence analysis (XRF) method Measuring device: Scanning fluorescent X-ray analyzer ZSX Primus III manufactured by Rigaku Co., Ltd.
Measurement results: Table 2 below.

The A-site vacancy concentration shown in Table 2 is the vacancy concentration of Ag. Specifically, it is (amount of substance ratio of 1-Ag).

_{As shown in Tables 1 and 2 above, it can be seen that the higher the oxygen partial pressure (Po 2} ) during the growth of the single crystal as a sample, the lower the oxygen vacancy concentration in the single crystal.

<Measurement of polarization twist>
The single crystal sample 1 and Comparative Example 1 (a sample cut out so that an electric field can be applied in the [100] orientation (main surface is 1 mm square, thickness is 0.1-0.2 mm, with a platinum electrode)), and a single sample. Toyo Technica Co., Ltd. regarding crystal sample 2 and Comparative Example 2 (a sample cut out so that an electric field can be applied in the [110] direction (main surface is 1 mm square, thickness is 0.1-0.2 mm, and has a platinum electrode)). Using a ferroelectric measurement system (Toyo 6252 Rev. B) manufactured by the company, the dependence of the polarization P on the electric field E at 25 ° C. (the relationship between the change in the polarization P and the change in the electric field E) was measured. In this measurement, the frequency of the applied electric field E was set to 1 Hz, and a data set of about 1000 points was measured.

The measurement results are shown in FIGS. 4 and 5. FIG. 4A is the measurement result of Comparative Example 1, and FIG. 4B is the measurement result of the single crystal sample 1. Further, FIG. 5 (a) is the measurement result of Comparative Example 2, and FIG. 5 (b) is the measurement result of the single crystal sample 2.

FIG. 4B shows that in the process of increasing and decreasing the electric field, the polarization P rapidly rises and falls when the electric field is in the range of -30 to 30 kV / cm. This indicates that the polarization twist was expressed in the single crystal sample 1, and the polarization P changed significantly in response to the change in the electric field.

On the other hand, in FIG. 4A, the polarization P changes substantially linearly with the change in the electric field in the process of increasing and decreasing the electric field. This indicates that the polarization twist does not appear (difficultly) in the single crystal sample of Comparative Example 1.

Further, also in FIG. 5 (b), it is shown that the polarization P rapidly rises and falls in the two ranges of -100 to 0 kV / cm and 0 to 100 kV / cm in the process of increasing and decreasing the electric field. ing. This indicates that the polarization twist was expressed in the single crystal sample 2, and the polarization P changed significantly in response to the change in the electric field.

On the other hand, in FIG. 5A, the polarization P changes substantially linearly with the change in the electric field in the process of increasing and decreasing the electric field. This indicates that the polarization twist does not appear (difficultly) in the single crystal sample of Comparative Example 2.

From the above results, Polarization twist is expressed in the single crystal sample 1 and the single crystal sample 2 in which the oxygen vacancy concentration in the single crystal is 1% or less, but the oxygen vacancy concentration exceeds 1% in Comparative Example 1. In Comparative Example 2, it can be seen that the polarization twist does not occur (it is difficult).

Example 2. Effect of polarization twist <Preparation of dielectric material showing polarization twist>
· _{(Bi 0.96} Na _0.5) Preparation present single crystal sample of single crystal sample of TiO 3 -7% BaTiO ₃ (hereinafter referred to as a single crystal sample 3) are described in Non-Patent Document 1 TSSG It was grown by the method (top seeded solution growth method). The single crystal was grown under high pressure oxygen (Po ₂ = 1 MPa) (oxygen gas was manufactured by Suzuki Shokan Co., Ltd. with a purity of 99.9 vol.%).

-Preparation of (Ag _0.96 Li _{0.04 ) NbO 3} single crystal sample This single crystal sample (hereinafter referred to as single crystal sample 4) is described in the Japanese Journal of Applied Physics 55, 10TB03 (2016). It was grown by the Cz method (Czochralski method). Incidentally, with _Ag 0.96 _Li 0.04 NbO ₃ powder instead of AgNbO ₃ described in the above document as a starting material. Further, when the crystals were grown by the Cz method, about 4% of Ag was excessively added. The single crystal was also grown under high pressure oxygen (Po ₂ = 1 MPa) (oxygen gas was manufactured by Suzuki Shokan Co., Ltd. with a purity of 99.9 vol.%).

<Preparation and evaluation of samples for measurement of electric susceptibility χ and piezoelectric strain constant d>
The orientation of the obtained single crystal sample is determined by an X-ray diffraction experiment, and an electric field can be applied to the [001] orientation in the case of the single crystal sample 3 and the [011] orientation in the case of the single crystal sample 4. Platinum electrodes were provided on the upper surface and the lower surface of the cut crystal by a sputtering method. A step cutter MC-171 manufactured by Maruto Co., Ltd. was used for cutting. The size of the sample used for the measurement is approximately 1 mm square on the electrode surface and 0.1-0.2 mm in thickness. Therefore, a voltage is applied to a sample having a thickness of 0.1-0.2 mm.

In evaluating the electric susceptibility χ, the electric field E dependence of the polarization P (the relationship between the change in the polarization P and the change in the electric field E) was determined using a ferroelectric measurement system (Toyo 6252 Rev. B) manufactured by Toyo Technica Co., Ltd. Was measured. Further, in evaluating the piezoelectric strain constant d, the dependence of the strain S on the electric field E (the relationship between the change in the strain S and the change in the electric field E) was determined by the optical heterodyne micro-vibration measuring device (MLD-221V-STN RP) manufactured by NeoArc Corporation. ) Was used for measurement. The electric field E dependence of the strain S was measured at the same time as the electric field E dependence of the polarization P. In both measurements, the frequency of the applied electric field E was set to 1 Hz, and the electric susceptibility χ and the piezoelectric strain constant d were evaluated from the data of the polarization P and the strain S obtained when the electric field E increased as follows. A data set of about 1000 points was measured for both the polarization P and the strain S.

The electric susceptibility χ uses _{the relational expression of ∂P / ∂E = ε 0} χ to determine the electric field E dependence of the electric susceptibility χ from the inclination of the data points (10 points) in the electric field E dependence of the polarization P. evaluated. Similarly, the piezoelectric strain constant d is the electric field of the piezoelectric strain constant d from the slope of the electric field E-dependent data points (10 points) of the strain S with respect to the electric field E, using the relational expression of ∂S / ∂E = d. E-dependency was evaluated.

The results of the measurements as described above are shown in FIG. 6 for the single crystal sample 3 and in FIG. 7 for the single crystal sample 4.

<Measurement of the relationship between rotation angle ω and polarization when the electric field changes>
A sample obtained by cutting out the single crystal sample 3 so that an electric field can be applied in the [001] direction (main surface is 1 mm square, thickness is 0.1-0.2 mm, with platinum electrode, same as the measurement sample in FIG. 6). The beamline BL02B1 of the large-scale radiation facility SPring-8 was used to irradiate 35 keV single-color X-rays [wavelength: 0.035313 nm], and the X-ray diffraction data of the single crystal sample 3 was acquired to obtain the X-ray diffraction data of the oxygen octahedron. The rotation angle ω was calculated. In this case, the measurement of the X-ray diffraction data is performed in the state where the electric field E is applied in the [001] direction, as in the measurement of the dependence of the polarization P on the electric field E, which was performed in the evaluation of the electric susceptibility χ in FIG. went.

The oxygen octahedron rotation angle ω obtained as described above is plotted on the horizontal axis, and the polarization P obtained from the measurement of the dependence of the polarization P on the electric field E in FIG. 6 is plotted on the vertical axis to obtain FIG. rice field. Therefore, FIG. 8 shows the relationship between the rotation angle ω and the polarization P when the electric field E changes.

The details of the measurement of the X-ray diffraction data are as follows.

・ When the electric field E increases 1 (E is a low electric field of 0 → 20 kV / cm, the crystal phase is a ferri-dielectric phase of the low electric field phase P4 bm)
When the electric field E is increased from zero, the rotation angle ω of the oxygen octahedron gradually decreases from about 3 °, and the polarization P increases significantly as shown in FIG. As the rotation angle ω decreases, the polarization P increases. In this case, the crystal phase of the dielectric material (single crystal sample 3) is a ferri-dielectric phase (feri-dielectric P4 mb phase) having a space group of P4 mb, which is a low electric field phase.

Since the slope ∂P / ∂E of the polarization P dependence on the electric field E is proportional to the electric susceptibility χ, the electric susceptibility χ increases significantly as the electric field E increases. This corresponds to a large increase in the electric susceptibility χ when the electric field E in FIG. 6 increases from zero to about 20 kV / cm.

・ When the electric field E increases 2 (E is a high electric field of 20 → 100 kV / cm, the crystal phase is a high electric field phase P4 mm ferroelectric phase)
When the electric field E is further increased beyond 20 kV / cm, as shown in FIG. 8, the space group, which is a high electric field phase, undergoes a phase transition to a ferroelectric phase of P4 mm (ferroelectric P4 mm phase). Since the ferroelectric P4 mm phase does not rotate the oxygen octahedron, its rotation angle ω becomes zero. Therefore, in the region where the electric field E in FIG. 8 is large. ω = 0. In the high electric field phase, the polarization P does not change much even if the electric field E is increased. This is equivalent to the fact that the electric susceptibility χ does not depend on the electric field E. This is observed in the region where the electric field E in FIG. 6 is large.

・ When the electric field E decreases 1 (E is a high electric field of 100 → 10 kV / cm, the crystal phase is a high electric field phase P4 mm ferroelectric phase)
Even if the electric field E is lowered, the rotation angle ω remains zero because the high electric field phase P4 mm remains. Also, the polarization P of the high electric field phase remains large.

・ When the electric field E decreases 2 (E is a low electric field of 10 → 0 kV / cm, the crystal phase is a ferri-dielectric phase of the low electric field phase P4 bm)
When the electric field E becomes 10 kV / cm or less, the phase transition to the ferric dielectric P4 bm occurs. The phase transition electric field between the ferri dielectric phase and the strong dielectric phase is different from about 20 kV / cm when the electric field increases and 3-10 kV / cm when the electric field decreases. In the ferri-dielectric P4bm, when the electric field E becomes smaller, the rotation angle ω becomes larger and the polarization P decreases. Then, when the electric field E becomes zero, the oxygen octahedron rotation angle ω becomes 3 degrees, and the original structure is restored.

As shown in FIGS. 6 to 8 above, when the applied electric field is 20 kV / cm or less, the dielectric constant ε (polarization P) and the piezoelectric strain constant d with respect to the change in the electric field can be significantly changed by the polarization twist. can. Therefore, the characteristics (capacitance, strain amount S) of the capacitor and the piezoelectric element can be significantly changed.

Example 3. Manufacture of Ceramics According to the process shown in Fig. 9, bismuth oxide (Bi ₂ O ₃ ), sodium carbonate (Na ₂ CO ₃ ), barium carbonate (BaCO ₃ ), titanium oxide (TIO ₂ ) and copper oxide (CuO) are used as raw materials. Dry at 110 ° C for 12 hours or more (DOV-450A constant temperature dryer manufactured by AS ONE Co., Ltd.) and use precision weighing (electronic balance PRACTUM513-1SJP manufactured by Sartorius Japan Co., Ltd.) in a globe box (UN-800L) manufactured by UNICO Co., Ltd. )did. The weight ratio of each is (Bi ₂ O ₃ ) :( Na ₂ CO ₃ ) :( BaCO ₃ ) :( TiO ₂ ) :( CuO) = 116.49 × (1-x + δ): 26.50 × (1). −X-3δ): 197.34 × x: 79.79: 0.080. However, δ is the amount of A-site vacancies (mole fraction), and x is the amount of Ba (mole fraction).

The weighed raw material powder was pulverized and mixed (using a planetary ball mill P-5 manufactured by Fritsch Japan Co., Ltd.), and calcined in air at 800 ° C. for 4 hours. Then, PMMA was mixed as a binder. After that, a uniaxial pressure press (using a hydraulic press WMP-5 manufactured by NAPAC Co., Ltd.) at a molding pressure of 150 MPa and then an isotropic pressure press at the same pressure (cold hydrostatic isobaric press machine manufactured by NPA System Co., Ltd.) CPP-25 was used) and press-molded into a cylindrical shape or a coin shape. Then, it was fired in air at 1195 ° C. for 4 hours to produce ceramics.

The composition of the perovskite-type oxides that make up the manufactured ceramics is
(Bi _{(1-x + δ) / 2} Na _{(1-x-3δ) / 2} Ba _x □ _δ ) (Ti _0.999 Cu _0.001 ) O ₃
The weight of the raw material and the oxygen concentration at the time of firing were adjusted to control the amount of A-site pores (mole fraction) δ and the amount of Ba (mole fraction) x. For example, the raw material weights are 15.279 g (Bi ₂ O ₃ ), 3.416 g (Na ₂ CO ₃ ), 1.940 g (BaCO ₃ ), 11.205 g (TiO ₂ ) and 0.011 g (CuO), respectively. By calcining in air, samples of x = 7% and δ = 0.40% were prepared. The ICP emission spectroscopic analyzer SPS-3100 manufactured by SII Nanotechnology Co., Ltd. was used for the measurement of δ and x, and the measurement was performed by the inductively coupled plasma atomic emission spectrometry (ICP-AES) method.

Example 4.
Ceramics having the above x of 7% and δ of 0.00%, 0.75% and 1.00%, respectively, were produced by the method of Example 3, and a ferroelectric measurement system manufactured by Toyo Corporation (MODEL 6252) was manufactured. Using Rev. B), the dependence of polarization P on electric field E at 25 ° C. (the relationship between the change in polarization P and the change in electric field E, sometimes referred to as the PE curve) was measured. In this measurement, the frequency of the applied electric field E was set to 1 Hz, and a data set of about 1000 points was measured. As the measurement sample, a plate-shaped sample having an in-plane size of about 3 mm × 6 mm square and a thickness of about 0.1 to 0.2 mm, which was formed by press molding, was used.

The PE curves of the measurement results are shown in FIGS. 10A, 10B, and 10C. FIG. 10 (a) is a PE curve when δ = 0.00%, (b) is δ = 0.75%, and (c) is δ = 1.00%. Each PE curve is a plot of the above-mentioned data set of about 1000 points. The vertical axis of FIGS. 10A, 10B, and 10C shows the polarization P, and the horizontal axis shows the applied electric field E. Further, Pr in each figure is a residual polarization (a polarization value across E = 0 and a polarization amount held by the sample in a state where the electric field is off).

In the case of FIG. 10A, the ferroelectric phase (P4 mm) is always maintained. This is an effect of setting the pore amount δ to 0.00% when x = 7%. On the other hand, in FIGS. 10 (b) and 10 (c), between the ferroelectric phase (P4 mm) and the ferri dielectric phase (P4 bm) at the four inflection points (indicated by circles in the figure). A phase transition is occurring. In the cases of FIGS. 10 (b) and 10 (c), as the value of δ ^{increases, the constriction of the PE curve near the polarization P = 0 μC / cm 2} increases, and the region of the ferri-dielectric phase expands.

11 (a), (b), and (c) show the PE curve when the value of δ is further increased. 11 (a) is a PE curve when δ = 1.20%, (b) is δ = 1.50%, and (c) is δ = 1.80%. Also in FIGS. 11A, 11B, and 11C, the constriction of the PE curve becomes larger (the region of the ferrielectric phase expands) as the value of δ increases, and the four inflection points ( In (indicated by a circle in the figure), a phase transition occurs between the ferroelectric phase (P4 mm) and the ferri dielectric phase (P4 bm).

FIG. 12 shows the relationship between the electric field in which a phase transition occurs between the ferroelectric phase (P4 mm) and the ferri dielectric phase (P4 bm) and the amount δ of A-site vacancies. An electric field _{E threshold The} axis of ordinate is the phase transition occurs in FIG. 12, the horizontal axis is [delta].

The relationship of FIG. 12 is the upper left shoulder of the inflection points (○ marks) shown in FIGS. 10 (a), (b), (c) and 11 (a), (b), (c). It is a plot of the electric fields E and δ at the inflection points of (indicated by Su) and the lower right shoulder (indicated by Sl). In FIG. 12, the Su plot is indicated by a diamond (◆) and the Sl plot is indicated by a square (■). As shown in FIG. 12, it can be seen that the stable range of the ferroelectric phase (P4 mm) and the ferri dielectric phase (P4 bm) with respect to the electric field E changes depending on the amount of pores δ.

Example 5.
FIG. 13 shows the PE curve when δ = 0.75% and x = 12%. As shown in FIG. 13, in the combination of the values of δ and x, the ceramic always maintains a ferroelectric phase (P4 mm).

14 (a) and 14 (b) show the polarization P and the electric susceptibility χ (E) when the electric field E is changed between the points A and B in FIG. 13 (however, ∂P / ∂E = ε ₀ χ (E)) is shown.

As shown in FIGS. 14 (a) and 14 (b), even if the applied electric field E fluctuates, the gradient of the polarization P, that is, the electric susceptibility χ (E) is constant in the ceramics which are ferroelectrics. It can be seen that the relative permittivity ε _r = 1 + χ (E) is also constant (it does not depend on the electric field E).

FIG. 15 shows the PE curve when δ = 1.50% and x = 8%. As shown in FIG. 15, in the combination of the values of δ and x, the ceramics have a ferroelectric phase (P4 mm) and a ferri dielectric phase (P4 bm) at four inflection points (indicated by ○ in the figure). A phase transition is occurring between and.

16 (a) and 16 (b) show the polarization P and the electric susceptibility χ (E) when the electric field E is changed between the points A and B in FIG. 15 (however, ∂P / ∂E = ε ₀ χ (E)) is shown.

As shown in FIG. 15, since the phase transition occurs according to the fluctuation of the applied electric field E, in FIG. 16A, the electric field is zero and the phase is in the ferri-dielectric phase. When the electric field E is increased, the phase transitions to the ferroelectric phase at the points indicated by ○. In the larger electric field region, the ferroelectric phase state is stabilized. When the electric field strength is reduced from the point B (strong dielectric phase), the phase transitions to the ferri dielectric phase at the electric field indicated by the circle, and the phase remains the ferri dielectric phase even at the zero electric field.

Further, as shown in FIG. 16B, when the applied electric field E is increased from the point A, the electric susceptibility χ (E) increases in the state of the ferri dielectric phase (P4bm), and the relative permittivity ε. _r = 1 + χ (E) also increases (denoted as electrically enhanced permittivity). In the process of further increasing the applied electric field E and approaching point B, the phase transitions from the ferri-dielectric phase (P4bm) to the ferroelectric phase (P4mm), and the electric susceptibility χ (E) also has a relative permittivity ε _r = 1 + χ (E) is also constant (it does not depend on the electric field E).

17 (a) and 17 (b) show the PE curve when δ = 0.40% and x = 7%. In the combination of the values of δ and x, as shown in the PE curve of FIG. 17 (a), when the electric field E is first applied, as-prepared (the state in which the electric field E is not applied) (the state in which the electric field E is not applied). When the applied electric field E is increased from point A (ferridielectric phase (P4bm)) at the point A (when the electric field E is first applied from before the application of the electric field), the ferroelectric phase (P4mm) is at the bending point of the PE curve. ). When the applied electric field E reaches 60 kV / cm (point B), the applied electric field E is lowered until the point C (ferroelectric phase) of the polled (sample after the electric field is applied once) in FIG. 17 (a). The PE curve changes. After that, the PE curve changes according to FIG. 17B as the PE curve of the sample (poled) after the electric field is once applied. As shown in FIG. 17B, when the applied electric field E is lowered and the applied electric field E is raised when it reaches −97 kV / cm (point D), the applied electric field E becomes 0 kV / cm and the point E is reached. After passing through, the polarization P ^{passes through the F point of 0 μC / cm 2} at 20 kV / cm, and reaches the G point at 97 kV / cm where the electric field E is higher than the B point in FIG. The PE curve (the curve that passes through the point of GCDEF) is repeated. In the PE curve shown in FIG. 17 (b), from the strong dielectric phase (P4 mm) to the ferri dielectric phase (P4 bm) at the inflection point (indicated by a circle) when transitioning from the point E to the point F. The phase transition from the ferri dielectric phase (P4bm) to the strong dielectric phase (P4mm) occurs at the inflection point (indicated by a circle) at the transition from the F point to the G point. When the applied electric field E is set to 0 kV / cm when the point F is reached, the point returns to the point A in FIG. 17 (a) and changes according to the PE curve shown in FIG. 17 (a).

18 (a) and 18 (b) show the polarization P and the electric susceptibility χ (E) when the electric field E is changed between the points A and B in FIG. 17 (a) (however, ∂P / ∂E = ε ₀ χ (E)) is shown. Note that FIG. 18A is the same as FIG. 17A.

As shown in FIGS. 18A and 18B, when the applied electric field E is increased from the point A, the electric susceptibility χ (E) increases in the ferri-dielectric phase (P4bm) state, and the relative permittivity increases. The rate ε _r = 1 + χ (E) also increases (denoted as electrically enhanced permittivity). Furthermore, in the process of increasing the applied electric field E and approaching point B (20 kV / cm or more), the phase shifts from the ferri-dielectric phase (P4 bm) to the ferroelectric phase (P4 mm), and the electric susceptibility χ (E) also increases. The relative permittivity ε _r = 1 + χ (E) is also constant (it does not depend on the electric field E).

When the applied electric field E is increased in FIG. 17 (a), the phase transitions to the ferroelectric phase (P4 mm) at point B, and thereafter, the phase transitions along the PE curve shown in FIG. 17 (b). When ceramics are used in the ferrielectric phase (P4bm) shown in 18 (a) and 18 (b), the applied electric field E is maintained at an electric field less than point B, specifically, an electric field smaller than about 20 kV / cm. There is a need.

19 (a) and 19 (b) show the polarization P and the electric susceptibility χ (E) when the electric field E is changed between the points C and G in FIG. 17 (b) (however, ∂P / ∂E = ε ₀ χ (E)) is shown.

As shown in FIGS. 19A and 19B, even if the applied electric field E fluctuates, the gradient of polarization P, that is, the electric susceptibility χ (E) is constant in the ceramics in the ferroelectric phase. It can be seen that the relative permittivity ε _r = 1 + χ (E) is also constant (it does not depend on the electric field E). This is the same as the case shown in FIGS. 14 (a) and 14 (b) above.

Example 6.
20 (a) and 20 (b) show the images before and after the application of the electric field E to the ceramics (before and after the application of the electric field: as-prepared), which were investigated in the same manner as in Examples 4 and 5 described above. A summary of the states (phases) of the ceramics after applying an electric field (poled) is shown. In FIGS. 20 (a) and 20 (b), the vertical axis is the amount of A-site vacancies δ, and the horizontal axis is the amount x of Ba. Further, FIG. 20A shows the state of the ceramics before applying the electric field E (before applying the electric field: as-prepared), and FIG. 20B shows the application of the electric field after applying the electric field of 50 kV / cm. The state of the ceramics when stopped (after applying an electric field: polled). That is, it is shown that what was in the state shown in FIG. 20 (a) immediately after production transitions to the state shown in FIG. 20 (b) after the application of an electric field (partially unchanged).

In FIGS. 20 (a) and 20 (b), the diamonds (◇) shown by diagonal lines indicate the single phase of the ferroelectric phase (P4 mm), and the circles (○) indicate the single phase of the ferroelectric phase (P4 bm). , The triangle (Δ) indicated by the diagonal line indicates the single phase of the ferroelectric phase (R3c). Further, the quadrangle (□) indicates a state in which the ferroelectric phase and the ferri-dielectric phase (P4bm) are mixed. Specifically, the diagonal line on the left side of the quadrangle (□) indicates a two-phase coexistence state of the ferroelectric phase (R3c) and the ferri-dielectric phase (P4bm). A diagonal line on the right side of the quadrangle (□) indicates a two-phase coexistence state of the ferroelectric phase (P4 mm) and the ferri dielectric phase (P4 bm).

In FIG. 20 (b), the ceramics in the range surrounded by the broken line are the ferroelectric phase (R3c phase) according to the magnitude of the applied electric field, similarly to those shown in FIGS. 15 to 19 above. Alternatively, a phase transition occurs between the P4 mm phase) and the ferrielectric phase (P4 bm). Therefore, it is a ceramic in which the property of the electrically enhanced permittivity and the property that the permittivity does not depend on the electric field are switched according to the electric field. Further, the ceramics outside the range surrounded by the broken line maintain the ferroelectric phase (P4 mm or R3c) regardless of the magnitude of the applied electric field, and the dielectric constant does not always depend on the electric field. ing.

As shown in FIGS. 20A and 20B, the properties of the ceramics produced in Example 3 can be controlled by adjusting the combination of the amount δ of the A-site pores and the amount x of Ba. Understand.

10 Dielectric material, 12a, 12b electrodes, 14 intermediate electrodes.

Claims (12)

The concentration of pores in the anion X-site introduced by the metal-deficient A-site pores located at the A-site of each apex of a cubic or pseudo-cubic crystal having a perovskite-type structure ABX _{3 is 1% or less.} The octahedrons of anions existing in the perovskite-type structure are rotated and arranged with respect to the crystal axis of the cubic or pseudo-cubic crystal with an angle ω, and both the angle ω and the polarization value are both due to the application of an electric field. A dielectric material exhibiting a polarization twist, characterized by varying. The dielectric material exhibiting a polarization twist according to claim 1, wherein the dielectric material is any of an ordinary dielectric, a ferrielectric, and an antiferroelectric. The polarization according to claim 1 or 2, wherein the octahedron is an octahedron composed of 6 oxygen atoms, and the concentration of oxygen vacancies introduced by A-site vacancies is 1% or less. A dielectric material that exhibits twist. The dielectric material exhibiting the polarization twist according to any one of claims 1 to 3, and the dielectric material.
A member that controls polarization by applying an electric field to the dielectric material and changing the angle ω.
A dielectric structure in which polarization can be controlled. A capacitor using the dielectric structure according to claim 4, wherein the polarization can be controlled. A piezoelectric element using the dielectric structure according to claim 4, wherein the polarization can be controlled. A ceramic composed of a perovskite-type oxide represented by the following general formula (4).
(A1 _{(1-x + δ) / 2} A2 _{(1-x-3δ) / 2} A3 _x □ _δ ) BO ₃ ... (4)
A1 is a trivalent metal, A2 is a monovalent metal, A3 is a divalent metal, B is a tetravalent metal, and □ represents A site vacancies.
A ceramic having an A-site pore amount δ of 0 to 3% and an A3 amount x of 2 to 25%. The ceramic according to claim 7, wherein the perovskite-type oxide further contains a metal oxide M. The ceramic according to claim 7 or 8, wherein A1 is Bi, A2 is Na, and A3 is Ba. The ceramic according to any one of claims 7 to 9, wherein M is Cu. A capacitor using the ceramics according to any one of claims 7 to 10. A piezoelectric element using the ceramics according to any one of claims 7 to 10.

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