Piezoelectric ceramic and piezoelectric element

Abstract

A piezoelectric ceramic according to the present disclosure contains potassium sodium niobate and at least one of strontium zirconate, barium zirconate, strontium titanate and barium titanate. A piezoelectric element according to the present disclosure comprises a pair of electrodes on one surface of the above-described piezoelectric ceramic and on the other surface that is on the reverse side of the one surface.

Description

Piezoelectric ceramics and piezoelectric elements

[0001] The present disclosure relates to piezoelectric ceramics and piezoelectric elements.

[0002] Conventionally, PZT (lead zirconate titanate) based materials and PT (lead titanate) based materials have been used for parts that require piezoelectric properties. However, in recent years, there has been a growing movement to restrict the use of lead from the viewpoint of protecting the global environment, and there are high expectations for lead-free piezoelectric materials, and research and development is being actively carried out. Patent Document 1 describes a piezoelectric material with a perovskite structure (general formula ABO ３ ) an alkali niobate-based piezoelectric material in which an alkali metal is arranged at the A site and niobium is arranged at the B site is shown.

[0003] Japanese Patent Application Laid-Open No. 2006-028001

[0004] The piezoelectric ceramic of the present disclosure is made of potassium sodium niobate (KNN) and strontium zirconate (SrZrO ３ ), barium zirconate (BaZrO ３ ), strontium titanate (SrTiO ３ ), barium titanate (BaTiO ３ ) at least one of the following.

[0005] Conventionally, PZT (lead zirconate titanate) based materials and PT (lead titanate) based materials have been used for parts that require piezoelectric properties. However, in recent years, there has been a growing movement to restrict the use of lead from the viewpoint of protecting the global environment, and there are high expectations for lead-free piezoelectric materials, and research and development is being actively carried out. Patent Document 1 describes a piezoelectric material with a perovskite structure (general formula ABO ３ ) an alkali niobate-based piezoelectric material in which an alkali metal is arranged at the A site and niobium is arranged at the B site is shown.

[0006] Lead-free piezoelectric materials have inferior piezoelectric properties compared to PZT-based and PT-based materials. However, in recent years, from the perspective of protecting the global environment, there has been a movement to put lead-free piezoelectric materials into practical use even if they do not have the same piezoelectric properties as PZT-based and PT-based materials.

[0007] Despite these trends, for example, piezoelectric elements are naturally required to have excellent element characteristics, and therefore there is a demand for improved piezoelectric characteristics in lead-free materials.

[0008] Therefore, there is a need for a technology that can overcome the above-mentioned problems and provide piezoelectric ceramics and piezoelectric elements that are made of lead-free materials and have excellent piezoelectric properties.

[0009] The piezoelectric ceramic of the present disclosure is made of potassium sodium niobate (KNN) and strontium zirconate (SrZrO ３ ), barium zirconate (BaZrO ３ ), strontium titanate (SrTiO ３ ), barium titanate (BaTiO ３ The potassium sodium niobate is a main component of the piezoelectric ceramic, and the main component here means that sodium is contained in 100% by mass of all components constituting the piezoelectric ceramic. ２ O, potassium to K ２ O, niobium Nb ２ O ５ The total of the converted values ​​of the components accounts for 95 mass % or more.

[0010] The piezoelectric ceramic of the present disclosure contains potassium sodium niobate and at least one of strontium zirconate, barium zirconate, strontium titanate, and barium titanate, and thus has superior piezoelectric properties, specifically a larger value of the piezoelectric constant d31, compared to those not containing these.

[0011] Next, an example of the compounded composition formula of potassium sodium niobate in the piezoelectric ceramic of the present disclosure will be described.

[0012] (1-x) {(K １－ａ Na ａ ) １－ｂ Li ｂ} ｃ (Nb １－ｄ－ｅ Ta ｄ Sb ｅ ) O ３ +xBi α (A1 １－β A2 β ) O３ ...Formula 1 Here, x, a, b, c, d, e, α, and β are in the ranges of 0≦x≦0.005, 0.30≦a≦0.60, 0.01≦b≦0.06, 0.99≦c≦1.01, 0.08≦d≦0.13, 0.05≦e≦0.09, 2 / 3≦α≦1, 1 / 3≦β≦2 / 3, respectively, A1 is at least one kind selected from the group of elements consisting of Mg, Cu, and Zn, and A2 is at least one kind selected from the group of elements consisting of Nb, Ta, Sb, Ti, Zr, Hf, Ge, Sn, and Ce. {(K １－ａ Na ａ ) １－ｂ Li ｂ} ｃ (Nb １－ｄ－ｅ Ta ｄ Sb ｅ ) O ３ has a perovskite structure. In the following description, {(K １－ａ Na ａ ) １－ｂ Li ｂ} ｃ (Nb １－ｄ－ｅ Ta ｄ Sb ｅ ) O ３ Since is also the main component of the piezoelectric ceramic, it may be hereinafter simply referred to as the main component.

[0013] The composition range satisfying x, a, b, c, d, and e expressed by formula 1 is a composition range including a boundary where the crystal structure changes, that is, a so-called MPB (Morphotropic Phase Boundary) region and a PPT (Polymorphic Phase Transition) region.

[0014] Next, Formula 1 will be explained by dividing it into a plurality of components. Potassium sodium niobate having a composition represented by the following formula 2 is a main component of piezoelectric ceramics and has a perovskite structure.

[0015] {(K １－ａ Na ａ ) １－ｂ Li ｂ} ｃ (Nb １－ｄ－ｅ Taｄ Sb ｅ ) O ３ ...Formula 2

[0016] In formula 2, by setting a in the range of 0.30≦a≦0.60 and substituting a part of K with Na, the piezoelectric constant can be increased.

[0017] Furthermore, by setting b in the range of 0.01≦b≦0.06, the piezoelectric constant can be increased.

[0018] The reason why d is set to the range of 0.08≦d≦0.13 is that the piezoelectric constant can be increased by substituting a part of Nb with Ta.

[0019] The reason why e is set to the range of 0.05≦e≦0.09 is that the sinterability can be improved by substituting a part of Nb with Sb as required.

[0020] Next, by introducing a Bi composite oxide represented by the following formula 3 into such potassium sodium niobate, the piezoelectric properties become even more excellent. Specifically, the value of the piezoelectric constant d31 is large.

[0021] xBi α (A1 １－β A2 β ) O ３ ...Formula 3

[0022] The Bi composite oxide represented by Formula 3 has a complex perovskite structure, and since Bi has a 6s2 lone electron pair, there is a large distortion in the crystal structure. By introducing a predetermined amount of this Bi composite oxide into potassium sodium niobate represented by Formula 2, distortion is introduced into the crystal structure of the potassium sodium niobate, increasing polarization and resulting in excellent piezoelectric properties.

[0023] Furthermore, since compounds containing Bi form a liquid phase at a relatively low temperature, the introduction of a Bi composite oxide also has the effect of lowering the firing temperature of the piezoelectric ceramic.

[0024] Here, α is in the range of 2 / 3≦α≦1. By setting α in this range, it is possible to incorporate the Bi composite oxide into potassium sodium niobate in just the right amount.

[0025] The first metal element A1 in formula 3 includes one of Mg, Cu, and Zn, and the second metal element A2 includes one of Nb, Ta, Sb, Ti, Zr, Hf, Ge, Sn, and Ce. When the first metal element is Zn and the second metal element A2 is Sn, the piezoelectric constant is particularly excellent.

[0026] β is in the range of 1 / 3≦β≦2 / 3. By setting β in this range, the ratio of A1 to A2 can be set within the range of the stoichiometric ratio.

[0027] When A2 is an element that forms a pentavalent ion, i.e., Nb, Ta, or Sb, it is preferable to set α+β to 4 / 3, which allows A1 and A2 to fall within the stoichiometric ratio range.When A2 is an element that forms a tetravalent ion, i.e., Ti, Zr, Hf, Ge, Sn, or Ce, it is preferable to set β to 1 / 2, which allows A1 and A2 to fall within the stoichiometric ratio range.

[0028] In this way, by introducing a complex perovskite structure with large strain of Bi composite oxide represented by formula 3 into a perovskite structure of potassium sodium niobate represented by formula 2, it is possible to increase the piezoelectric constant and reduce the temperature dependence of the piezoelectric characteristics.

[0029] The ratio of the Bi composite oxide to potassium sodium niobate is represented by x in formula 1, where x is 0≦x≦0.005. By setting x in this range, an appropriate amount of strain is introduced into the perovskite structure of potassium sodium niobate, thereby increasing the piezoelectric constant.

[0030] Furthermore, the piezoelectric ceramic of the present disclosure contains Mn in an amount of MnO relative to 100 parts by mass of the component represented by the formula 1 shown above. ２ The content of Sr is 0 to 1.04 parts by mass in terms of SrZrO relative to 100 parts by mass of the component represented by the formula 1 shown above. ３ The content is converted to 0.351 to 1.287 parts by mass.

[0031] The purpose of including Mn is to improve the insulating properties of the piezoelectric ceramic. By including Mn, the insulating properties of the piezoelectric ceramic are improved, making it difficult for current to flow outside of specified locations during operation. Therefore, the inclusion of Mn gives the piezoelectric ceramic excellent reliability.

[0032] Strontium zirconate (SrZrO ３ By including the above-mentioned SiO 2 , the piezoelectric ceramic can have a high piezoelectric constant.

[0033] Strontium zirconate (SrZrO ３ ) instead of barium zirconate (BaZrO ３ ), strontium titanate (SrTiO ３ ) and barium titanate (BaTiO ３ Similarly, the piezoelectric constant can be increased.

[0034] In addition, silicon dioxide (SiO ２ ), the piezoelectric constant can be increased. ２ ) silicon dioxide exists at the grain boundaries of the crystal structure, making it difficult for the electrodes to diffuse into the interior of the piezoelectric element when it is formed.

[0035] A piezoelectric ceramic having a compounded composition containing the above formula 1 and the above-mentioned Mn and Sr contents exhibits excellent piezoelectric properties, such as a piezoelectric constant d31 of 100 or more and a Curie temperature of 200°C or more.

[0036] Regarding the range of x described above, when x = 0, the material does not contain Bi, Al, and A2 and is composed only of the main components. Even in such cases, excellent piezoelectric properties are exhibited as long as a desired amount of Sr is contained.

[0037] In the piezoelectric ceramic of the present disclosure, the components containing Mn and Sr as defined in Formula 1 above and in the amounts shown above may account for a total of 99% by mass or more. The total amount of other impurity elements, calculated as oxides, may be less than 0.5% by mass, less than 0.2% by mass, or even less than 0.1% by mass. Examples of impurity elements include those resulting from the manufacturing process of the piezoelectric ceramic, such as Fe, Ni, Co, Cr, and Al. A trace amount of less than 0.5% by mass calculated as oxides does not affect the characteristics. The composition and impurity element content of the piezoelectric ceramic can be confirmed by elemental analysis such as X-ray fluorescence analysis or ICP atomic emission spectroscopy.

[0038] An example of a method for producing the piezoelectric ceramic of the present disclosure will be described. ２ CO ３ , K. ２ CO ３ , Li ２ CO ３ and MgCO ３ Carbonates such as CuO, Cu ２ O, CaO, BaO, MgO, SiO ２ , Fe ２ O ３ , ZnO, Nb ２ O ５ , Ta ２ O ５ , Sb ２ O ３ , TiO ２ , ZrO ２ , HfO ２ , GeO ２ , SnO ２ , Ce ２ O ３ , Bi ２ O ３ , MnO ２ and SrZrO ３ The raw materials are not limited to these, and metal salts such as nitrates that produce oxides when fired may also be used.

[0039] In the above formula 1, A1 is selected from the group of elements consisting of Mg, Cu, and Zn, and A2 is selected from the group of elements consisting of Nb, Ta, Sb, Ti, Zr, Hf, Ge, Sn, and Ce, and the above raw materials are used to adjust the content within a predetermined range, and Mn is selected from the group of elements consisting of MnO relative to 100 parts by mass of the components of formula 1. ２ 0 to 1.04 parts by mass in terms of SrZrO ３ The raw materials are weighed out so that the total mass is 0.351 to 1.287 parts by mass in terms of the total mass. The weighed raw materials are mixed to form a mixture, and the mixture is pulverized so that the average particle size (D50) in the particle size distribution is in the range of 0.1 to 30 μm. This mixture is calcined and synthesized at 600°C to 1000°C to obtain a composite. The resulting composite is pulverized to adjust the average particle size (D50) in the particle size distribution to a range of 10 μm. A specified binder is then added and wet-mixed to obtain a granulated powder.

[0040] The resulting granulated powder is molded into a predetermined shape by a known molding method such as press molding or tape molding, and fired in an oxidizing atmosphere such as air at a temperature in the range of 850°C to 1150°C for 2 to 10 hours to obtain a piezoelectric ceramic.

[0041] A piezoelectric element can be obtained by placing a pair of electrodes on one side of such a piezoelectric ceramic and the other side opposite the first side.Possible materials for the electrodes include an Ag-Pd alloy and a metal such as Ni.

[0042] Piezoelectric elements can also be stacked to obtain a laminate. Specifically, a conductive paste is first prepared by adding a binder and a plasticizer to a metal powder, such as an Ag-Pd alloy or Ni, which will become the internal electrodes, and mixing them. This conductive paste is then printed onto the piezoelectric elements using a screen printing method. Next, a plurality of piezoelectric elements with the printed conductive paste are stacked together with a plurality of ceramic green sheets, each with no printed conductive paste, at both ends in the stacking direction, to obtain a laminated compact. This laminated compact is then subjected to a binder removal treatment at a predetermined temperature and then fired to obtain a laminate.

[0043] Further advantages and modifications may readily occur to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

[0044] Piezoelectric ceramics having various compositions shown in Tables 1, 2, 3 and 4 were prepared, and the piezoelectric constants and Curie temperatures were measured. The results are shown in Tables 3 and 4.

[0045]

[0046]

[0047]

[0048]

[0049] It was found that a piezoelectric ceramic having a compounded composition containing Formula 1 and desired contents of Mn and Sr has a piezoelectric constant d31 of 100 or more, a Curie temperature of 200°C or more, and excellent piezoelectric properties.

[0050] The present technology can also be configured as follows: (1) A piezoelectric ceramic containing potassium sodium niobate and at least one of strontium zirconate, barium zirconate, strontium titanate, and barium titanate. (2) The piezoelectric ceramic according to (1), containing a Bi composite oxide having a composite perovskite structure. (3) The Bi composite oxide is Bi α (A1 １－β A2 β ) O ３(3) The piezoelectric ceramic according to any one of (1) to (2), wherein A1 comprises one of Mg, Cu, and Zn, and A2 comprises one of Nb, Ta, Sb, Ti, Zr, Hf, Ge, Sn, and Ce. (4) The piezoelectric ceramic according to any one of (3), wherein A1 is Zn and A2 is Sn. (5) The piezoelectric ceramic according to any one of (1) to (4), comprising silicon dioxide. (6) A piezoelectric element comprising a pair of electrodes on one surface of the piezoelectric ceramic according to any one of (1) to (5) and on the other surface opposite to the one surface.

Claims

1. A piezoelectric ceramic comprising potassium sodium niobate and at least one of strontium zirconate, barium zirconate, strontium titanate, and barium titanate.

2. 2. The piezoelectric ceramic according to claim 1, comprising a Bi composite oxide having a composite perovskite structure.

3. The Bi composite oxide is α (A1 １－β A2 β ) O ３ When expressed as A1 contains any one of Mg, Cu and Zn; 3. The piezoelectric ceramic according to claim 2, wherein A2 comprises any one of Nb, Ta, Sb, Ti, Zr, Hf, Ge, Sn and Ce.

4. 4. The piezoelectric ceramic according to claim 3, wherein said A1 is Zn and said A2 is Sn.

5. The piezoelectric ceramic of claim 1 comprising silicon dioxide.

6. 6. A piezoelectric element comprising the piezoelectric ceramic according to claim 1, and a pair of electrodes on one surface of the piezoelectric ceramic and on another surface opposite to the one surface.