JP5588771B2 - Piezoelectric material and method for manufacturing piezoelectric material - Google Patents

Description

  The present invention relates to a piezoelectric material, and more specifically, to an improved technique for a piezoelectric material not containing lead.

As a piezoelectric material, PZT (PbTiO ₃ —PbZrO ₃ ) composition ceramics are well known. PZT is excellent in piezoelectric characteristics such as an electromechanical coupling coefficient and a piezoelectric constant, and this PZT is widely used for piezoelectric elements such as sensors, ultrasonic motors, and filters.

  By the way, in recent years, there is an urgent need to make industrial products “lead-free” due to environmental demands. Naturally, since PZT is finally used for industrial products, it is necessary to replace the piezoelectric material from PZT containing lead (Pb) with another piezoelectric material not containing lead.

And as a piezoelectric material (lead-free piezoelectric material) which does not contain lead, for example, a compound represented by a chemical formula of K _x Na _(1-x) NbO ₃ as described in the following Patent Document 1 ( KNN) is obtained by adding an additive containing Co. Specifically, there is a KNN-Co ₂ O ₃ piezoelectric material in which Co ₂ O ₃ is added to KNN. This piezoelectric material has high sinterability and has attracted attention as a lead-free piezoelectric material. Note that general techniques related to piezoelectric materials are described in detail in Non-Patent Document 1 below.

Japanese Patent Publication No.56-12031

FDK Corporation, “Piezoelectric Ceramics (Technical Document)”, [online], [Search on February 9, 2010], Internet <URL: http://www.fdk.co.jp/cyber-j/pdf/ BZ-TEJ001.pdf>

The above-mentioned KNN-Co ₂ O ₃ piezoelectric material, which is expected as a lead-free piezoelectric material, has been densified and is excellent in productivity, but it is clear by the present inventors that it has poor moisture resistance. It was made. That is, it has been clarified that the piezoelectric characteristics deteriorate when exposed to a high humidity environment. Therefore, for example, there is a possibility of increasing the power consumption of the piezoelectric element using the piezoelectric material due to a decrease in the resistance value due to the absorbed water. Of course, not only such a possibility but various harmful effects derived from water absorption and low moisture resistance are expected.

  Therefore, the main object of the present invention is to provide a piezoelectric material that is environmentally friendly, excellent in piezoelectric characteristics, improved in denseness and moisture resistance, and has high reliability. Other purposes will be clarified in the following description.

In order to achieve the above object, the inventors of the present invention represented by the general formula Li _x K _y Na _(1-xy) Nb _a Ta _b Sb _(1-ab) O ₃ prior to the present invention. A piezoelectric material obtained by adding glass to the base material, and applied for a patent for the invention (Japanese Patent Application No. 2010-57735: hereinafter invention). In the piezoelectric material according to the present invention, the values of x, y, a, and b in the main component are 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.7, and 0.3 ≦ a, respectively. ≦ 0.9 and 0 ≦ b ≦ 0.2, and the glass is characterized in that it has a structure existing at the grain boundaries of the crystal grains of the base material.

Here, with respect to the piezoelectric material including the compound represented by the general formula Li _x K _y Na _(1-xy) Nb _a Ta _b Sb _(1-ab) O ₃ and glass, further improvement in characteristics For this purpose, the structure of the piezoelectric material was examined. As a result, even if the composition of the piezoelectric material and the composition ratio are the same, the characteristics change when the structure changes, and the structure is different from the structure in which glass exists at the grain boundaries of the base material crystal grains. It has been found that the piezoelectric material having the above structure has characteristics superior to those of the piezoelectric material according to the above-described invention. In addition, a method for manufacturing a piezoelectric material having the specific structure with high reproducibility was also examined, and the method was found.

And this invention is made | formed based on the said knowledge, The invention which concerns on a piezoelectric material is a piezoelectric material which consists of a sintered compact,
Including a base material represented by the general formula LixKyNa (1-xy) NbaTabSb (1-ab) O3 and glass as basic components;
In the general formula, on condition that x + y <1, 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9 , 0 ≦ b ≦ 0.2,
A compound represented by the general formula KyNa (1-xy) NbaO3 including K, Na, and Nb in the components of the base material is used as a core, and the core includes the KNN compound among the basic components. It has the structure covered with the film body which consists of components other than the component to comprise.
Then, the glass is a Bi-based glass containing compound _Bi 2 _{O 3} as a main component,
The addition amount of the Bi-based glass is more than 0.08 wt% and 15.0 wt% or less with respect to the basic compound .
Alternatively, the glass is a Zn-based glass containing a compound ZnO as a main component,
The added amount of the Zn-based glass may be more than 0.07 wt% and 15.0 wt% or less with respect to the basic compound.
The glass is a Si-based glass containing the compound SiO ₂ as a main component and not containing Li ₂ O,
The addition amount of the Si-based glass may be more than 0.07 wt% and 15.0 wt% or less with respect to the basic compound.
The glass is a Li-based glass containing a compound SiO ₂ as a main component and Li ₂ O,
The addition amount of the Li-based glass may be more than 0.1 wt% and 10.0 wt% or less with respect to the basic compound .

  In addition, a Cu compound is added, and the addition amount of the Cu compound is more than 0 mol% and 10 mol% or less. The softening point temperature of the glass is higher than the crystallization temperature of the base material. A low piezoelectric material can also be used.

The glass composition may contain no alkali metal. The glass not containing an alkali metal is selected from at least one selected from Bi glass containing the compound Bi ₂ O ₃ as a main component, Zn glass containing ZnO as a main component, and Si glass containing SiO ₂ as a main component. It can also be.

The glass may be Li-based glass containing SiO ₂ as a main component and Li ₂ O. And it is suitable if the addition amount of the said Li-type glass is more than 0.1 wt% with respect to the said basic compound, and 10.0 wt% or less.

  In any one of the above piezoelectric materials, more preferably, the particle diameter of the coating body is set to be not more than twice the particle diameter of the core body.

In addition, the invention relating to the method for manufacturing a piezoelectric material includes a raw material of a base material represented by the general formula LixKyNa (1-xy) NbaTabSb (1-ab) O3, with x + y <1 as a condition. a matrix component weighing step for weighing so that x ≦ 0.3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, and 0 ≦ b ≦ 0.2;
First, a raw material of the KNN compound represented by the general formula KyNa (1-xy) NbaO3 is mixed among the weighed raw materials of the base material, and the mixture is pulverized to obtain a first powder. A mixing and grinding step;
Pre-baking step of pre-baking the first powder to produce a powder of the KNN compound;
Of the raw materials of the base material weighed, raw materials other than the raw material that is the origin of the first powder and glass raw material are mixed, and the mixture is pulverized to obtain a second powder. A second mixing and grinding step;
A sintering additive generating step of generating a powder of the sintering additive by heat-treating the second powder;
A firing step of sintering a mixture of the powder of the KNN compound and the powder of the sintering additive;
Only including,
In the second mixing and pulverizing step, Bi glass containing compound Bi ₂ O ₃ as a main component is mixed as a glass raw material with an addition amount of 0.08 wt% to 15.0 wt% with respect to the basic compound.
Alternatively, in the second mixing and pulverizing step, as a raw material of glass, Zn-based glass containing compound ZnO as a main component is mixed in an addition amount of 0.07 wt% to 15.0 wt% with respect to the basic compound. Also good.
In the second mixing and pulverizing step, Si glass containing compound SiO ₂ as a main component and not containing Li ₂ O as a glass raw material is added in an amount of 0.07 wt% to 15.0 wt% with respect to the basic compound. It can also be mixed in quantities.
In the second mixing and pulverizing step, an addition amount of Li-based glass containing the compound SiO ₂ as a main component and containing Li ₂ O as a glass raw material is more than 0.1 wt% and less than 10.0 wt% with respect to the basic compound. It is good also as mixing with.

  According to the present invention, it is possible to provide a piezoelectric material that is environmentally friendly, excellent in piezoelectric characteristics, and highly reliable.

It is a schematic structure figure of the conventional piezoelectric material. It is the schematic of the piezoelectric material of the structure a in which glass exists in a grain boundary. It is a flowchart which shows the manufacturing method of a piezoelectric material. (A) is a flowchart of the manufacturing method of the piezoelectric material of the said structure a, (B) is a flowchart of the manufacturing method of the piezoelectric material which concerns on the Example of this invention. It is a figure which shows the structure of the piezoelectric material which concerns on the Example of this invention. (A) is a micrograph of a piezoelectric material, (B) is a figure which shows the composition in each site | part of a piezoelectric material. (C) is the figure which showed the structure of the piezoelectric material typically.

=== About Prior Inventions ===
Prior to the present invention, the inventors have invented the piezoelectric material according to the above-described invention. In the following, the background up to the previous invention and the structure and characteristics of the piezoelectric material according to the previous invention will be described slightly. Then, the characteristics of the piezoelectric material of the present invention will be clarified.

<Piezoelectric material>
FIG. 1A shows a schematic structure of a conventional piezoelectric material. FIG. 1B shows an enlarged view in the circle 20 shown in FIG. As shown in FIG. 1A, the conventional piezoelectric material 1 has a structure in which crystal grains 10 of a compound that is the origin of piezoelectricity are connected in a mosaic pattern. The above-described KNN—Co ₂ O ₃ piezoelectric material also has this structure. Certainly, the KNN-Co ₂ O ₃ based piezoelectric material does not contain lead and is expected as a piezoelectric material excellent in environmental performance. As shown in the enlarged view of FIG. There is a possibility that the bonding structure between 10 is coarse and moisture is absorbed from the boundary (grain boundary) 11 between adjacent crystal grains 10. Indeed, the present inventors have made study in the process of the invention the piezoelectric material according to the earlier invention the properties of _KNN-Co 2 _{O 3} based piezoelectric material, _KNN-Co 2 _{O 3} based piezoelectric material, a crystal grain It has been found that densification is achieved and productivity is excellent, but moisture resistance is poor.

<Base material>
The present inventors have studied various compounds including other compositions together with K, Na, and Nb constituting KNN, and the general formula Li _x K _y Na _(1-xy) Nb _a Ta _b Sb _{( 1-ab) In a} piezoelectric material mainly composed of a compound represented by O ₃ (hereinafter referred to as a base material in the present specification), improvement in moisture resistance performance is expected by adding glass. I understood. On the other hand, it is also found that excellent piezoelectric properties cannot be obtained unless the values of x, y, a, and b in the above general formula, which is the composition of the base material, are carefully selected and the structure is taken into consideration. It was. It was also found that the piezoelectric properties and moisture resistance change depending on the type and amount of additive. The prior invention has been made based on such knowledge.

<Piezoelectric material according to the invention>
A piezoelectric material is a final product obtained by mixing an additive with a raw material of a piezoelectric substance and sintering it, and the prior invention has conducted extensive research on both the composition and structure for improving the moisture resistance performance of the piezoelectric material. It was made as a result of overlapping. In the piezoelectric material according to the present invention, glass is added to the base material, and x, y, a, and b in the composition of the base material are 0 ≦ x ≦ 0.3 and 0.1 ≦ y, respectively. ≤ 0.7, 0.3 ≤ a ≤ 0.9, 0 ≤ b ≤ 0.2, and, like the piezoelectric material 1a shown in FIG. It has the structure (henceforth structure a) which exists in the grain boundary 11 of the crystal grain 10a, It is characterized by the above-mentioned.

=== Embodiment of the Invention ===
The piezoelectric material according to the embodiment of the present invention has the same composition as the piezoelectric material according to the previous invention. However, the structure is different from the piezoelectric material of the previous invention. In the piezoelectric material of the present embodiment, the above-described KNN (general formula K _y Na _(1-xy) Nb _a O ₃ ) containing K, Na, and Nb as constituent elements of the base material is used as a core body. However, it has the structure (henceforth structure b) covered with the film body which consists of components other than said KNN in a base material, and glass. The piezoelectric material according to the embodiment of the present invention has a moisture resistance equivalent to that of the piezoelectric material according to the previous invention, and has a piezoelectric property superior to that of the piezoelectric material according to the previous invention due to the structure different from the piezoelectric material according to the previous invention. It has.

=== Sample Production Method ===
In order to evaluate the characteristics of the piezoelectric material according to the embodiment of the present invention, the above-described base material is used as a piezoelectric substance, and the conventional piezoelectric material that does not contain glass, and the base material composition, additive type, and addition amount A large number of piezoelectric materials having different structures a and b were produced as samples.
The piezoelectric material can be manufactured by mixing and sintering the raw material of the base material, which is a piezoelectric substance, and the raw material of an additive such as glass. However, each of the piezoelectric materials having the structure a and the structure b has a unique structure, and a method for manufacturing the piezoelectric material having the structure with high reproducibility is required. FIG. 3 shows a method for manufacturing the piezoelectric materials of the structures a and b with good reproducibility.

<Method for Manufacturing Piezoelectric Material of Structure a>
FIG. 3A shows the procedure of a method for manufacturing the piezoelectric material having the structure a with good reproducibility. First, a predetermined amount of a raw material of a compound serving as a base material of a piezoelectric material is weighed and compounded (s1), and the raw material and an alcohol (such as ethanol) as a solvent are placed in a ball mill and pulverized while wet-mixing (s2). ). Thereby, the raw materials of the base material are mixed and pulverized into powder. And this mixture is calcined for 1 hour (h) -3h at the temperature of 800 to 1000 degreeC in air | atmosphere (s3), and a base material is produced | generated by solid-phase reaction. That is, in this manufacturing procedure, not all the raw materials of the piezoelectric material including the additives are mixed, but a powder only of the base material is first generated.
Next, glass is added as an additive to the powder of only the base material obtained by preliminary firing (s4). The glass serving as the additive is finally the most important factor for obtaining a piezoelectric material having excellent moisture resistance. At this time, all raw materials constituting the piezoelectric material are mixed.

Next, an aqueous PVA solution as a binder is added to and mixed with the mixture of all raw materials, and granulated into a powder having an appropriate particle size (s5), and the granulated powder is formed into a desired shape. (S6). Then, the molded product is placed under a predetermined temperature (for example, about 300 ° C. to 500 ° C.) to remove the binder (s7), and further fired in the atmosphere at a temperature of 900 ° C. to 1200 ° C. for 1 h (s8). Obtain piezoelectric ceramics.
Finally, the piezoelectric ceramic is processed into a disk shape having a diameter Φ ≧ 15 mm and a thickness t = 1.0 mm, and Ag electrodes are baked on both surfaces of the disk (s9, s10). The piezoelectric ceramic is polarized in an electric field of 4 Kv / mm in silicon oil at 120 ° C. (s11) to obtain a piezoelectric material.

<Procedure for Fabricating Piezoelectric Material of Structure b>
FIG. 3B shows the procedure of a method for manufacturing the piezoelectric material having the structure b with good reproducibility. First, a predetermined amount of a raw material of a compound that becomes a base material of a piezoelectric material is weighed (s21). However, in the sample of the structure b, the raw materials of the base material are not calcined collectively, but only the raw material of the KNN among the weighed raw materials of the base material is mixed and pulverized (s22). Then, the pulverized product (first powder) is temporarily fired under the same conditions as the temporary firing step (s3) in the sample of the structure a (s23). Thereby, a powder of KNN is generated.
Next or in parallel with the preliminary firing, raw materials other than KNN are mixed and pulverized (s24), and the pulverized product (second powder) is heated (s25). The heating temperature is preferably about 100 ° C. to 200 ° C. higher than the temperature at which KNN is temporarily fired.

Next, the KNN powder and a second powder (hereinafter, sintering additive) made of raw materials other than KNN are mixed (s26). In addition, about the conventional piezoelectric material which has a structure as shown in FIG. 1 without adding glass, it does not need to mix glass in the procedure (s24) of mixing raw materials other than this KNN. And the subsequent procedure (s27 to s33) is the same as the procedure from granulation (s5) to polarization (s11) in the method for producing the sample of structure a, granulation (s27), molding (s28), The sample of the structure b is completed by the steps of binder removal (s29), baking (s30), processing (s31), electrode baking (s32), and polarization (s33).

  By the way, the piezoelectric material of the structure b can also be produced by a general piezoelectric material production procedure (see Non-Patent Document 1, page 15). That is, there is a case where the piezoelectric material having the structure b can be formed even if KNN and the sintering additive are not separately mixed but all raw materials are first mixed. However, when comparing the piezoelectric material of the structure b produced by this general procedure with the piezoelectric material of the structure b produced by the procedure shown in FIG. 3B, the piezoelectric material produced by the general procedure is Even with the same composition, there was some variation in characteristics. Moreover, in order to manufacture the piezoelectric material having the structure b with a high probability by a general procedure, it is expected that complicated and ambiguous conditions such as a mixing method and firing conditions need to be accurately set. Therefore, in order to manufacture the piezoelectric material having the structure b with high reproducibility so as to have more stable characteristics, the procedure shown in FIG. 3B is desirable. That is, among the components of the base material, first, the powder obtained by pre-baking the KNN raw material and the sintering additive powder obtained by heat-treating the raw material other than the KNN raw material are mixed and sintered. It was found that the procedure is important.

=== About Glass ===
By the procedure shown in FIG. 3B, the composition ratio (x, y, 1-xy) of Li, K, and Na in the base material, and the composition ratio (a, b, 1-a) of Nb, Ta, and Sb. -B) Multiple types of samples were prepared according to the presence or absence of additives, the type of additives, the amount of additives added, and the difference in structure.

<Composition of glass>
Glass is added to all samples other than the conventional example that does not contain glass. The glass used for these samples is generally commercially available for industrial use. Here, glass containing SiO ₂ as a main component (hereinafter, Si-based glass), glass containing Bi ₂ O ₃ as a main component ( hereinafter, Bi-based glass), ZnO glass (hereinafter referred to as main components, Zn-based glass), and glass containing Li ₂ O and SiO ₂ as a main component (hereinafter, is either Li-based glass). For reference, the composition of each glass is shown below.
· Si based glass _{SiO 2: 80mol%, B 2} O 3: 18mol%, Al 2 O 3: 2mol%
Bi-based glass Bi ₂ O ₃ : 60 mol%, B ₂ O ₃ : 30 mol%, CuO: 7 mol%, SiO ₂ : 3 mol%
· Zn-based glass _{ZnO: 45mol%, MgO: 27mol} %, B 2 O 3: 25mol%, SiO 2: 3mol%
· Li based glass _{SiO 2: 50mol%, Li 2} O: 20mol%, B 2 O 3: 20mol%, CaO: 5 BaO: 5mol%

=== Sample condition ===
As described above, the compound serving as the base material is represented by the composition formula of Li _x K _y Na _(1-xy) Nb _a Ta _b Sb _(1-ab) , and is used to distribute the raw materials of the base material. The values of x, y, a and b change accordingly. Therefore, first, two types of samples of the conventional example, 125 samples of the structure a, and 125 samples of the structure b were prepared. Each sample is a base material having a different composition, that is, a base material having different values of x, y, a, and b. is there.

  Tables 1 to 5 below show the composition of the base material in each sample, the types of additives, and the amounts added. In Tables 1 to 5, Si-based glass, Bi-based glass, Zn-based glass, and Li-based glass as additives are indicated by Si, Bi, Zn, and Li, respectively. In addition, samples of structure a and structure b other than the sample of the conventional example are given the same sample number (No.) if they have the same composition, followed by “a” or “b” indicating the structure. It is added. In Tables 1 to 5, since the compositions of the samples of the structure a and the structure b are the same, a and b are appended together after the sample number, such as “S1a, b”.

Table 1 shows the compositions of Samples 1 and 2 of the conventional example.

Table 2 shows the compositions of the samples S1a to S31a and S1b to S31b (S1a, b to S31a, b) having the structure a or the structure b to which Si-based glass is added.

Table 3 shows the compositions of the samples B1a to B35a and B1b to B35b (B1a, b to B35a, b) having the structure a or the structure b to which Bi-based glass is added.

Table 4 shows the compositions of the samples Z1a to Z30a and Z1b to Z30b (Z1a, b to Z30a, b) having the structure a or the structure b to which Zn-based glass is added.

Table 5 shows the compositions of the samples L1a to L29a and L1b to L29b (L1a, b to L29a, b) having the structure a or the structure b to which Li-based glass is added.

  As shown in Tables 1 to 5, the breakdown of the produced samples is that the two types of samples according to the conventional example to which no glass is added are No. 1 and No. 2 types, samples of structure a and structure b to which Si-based glass is added 31 types each (S1a to S31a, S1b to S31b), hereinafter, a structure to which Bi-based glass, Zn-based glass, and Li-based glass are added Samples of a and structure b are 35 types (B1a to B35a, B1b to B35b), 30 types (Z1a to Z30a, Z1b to Z30b), and 29 types (L1a to L29a, L1b to L29b), respectively. ing.

  In Tables 1 to 5, sample 1 is a sample for evaluating the performance of the base material itself, and sample 2 is a piezoelectric material obtained by adding a Cu compound to the base material. Here, CuO is added as a Cu compound. A sample other than the conventional example is a piezoelectric material having a structure a or a structure b including a base material and glass.

=== Characteristic evaluation of sample ===
For each sample shown in Tables 1 to 5, first, the piezoelectric characteristics immediately after the production were measured. Here, the electromechanical coupling coefficient Kr, the mechanical quality factor Qm, and measures each piezoelectric properties of dielectric constant epsilon _33, and the measured value as an initial value. Further, for the sample of structure b, whether or not the initial characteristics are improved with respect to the sample of structure a is evaluated, and the sample of structure b is left in an oven at 85 ° C. and 85% RH for 100 hours. performed humidity shelf test that, after 4h is removed from the constant temperature bath, was measured Qm and epsilon _33. Then, the ratio of the measured value (measured value after the moisture resistance test) to the initial value {(measured value after the moisture resistance test−initial value) / initial value} is used as the evaluation value, and the moisture resistance performance is evaluated based on the evaluation value. did. And about the sample of the structure b, pass / fail was judged based on the initial characteristic and the evaluation value.

Pass / fail criteria must have predetermined initial characteristics. The initial characteristics are superior to the sample of structure a having the same composition. The evaluation value was 3 points or less. Specifically, first, in each of the samples shown in Tables 1 to 5, the initial values of the Kr, Qm, and ε ₃₃ are measured for the conventional example and the samples of the structure a and the structure b. in a sample structure b, Kr, Qm, and the initial value of the epsilon _33, respectively 10 or more, 10 or more, and is 20 or more and, in the sample of a construct a the same composition Qm, and epsilon ₃₃ initial values of On the other hand, if the numerical value increased, the initial characteristics were accepted. Moreover, subjected to humidity shelf test on samples pass the A structure b for the initial characteristics, the values of Qm and epsilon ₃₃ after the moisture resistance standing test, if the fluctuation of within 10% of the initial value, the final Therefore, it was judged as “pass”.

  And based on the pass / fail judgment result in each sample of the structure b, the correlation tendency between the composition and the pass / fail, etc., an appropriate composition of the base material in the piezoelectric material of the structure b was defined. Further, more preferable values (recommended values) were defined for the addition amounts of various additives other than the base material contained in the piezoelectric material having the structure b.

Table 6 shows the evaluation results for the samples 1 and 2 of the conventional example.

Table 7 shows the initial characteristics of the samples S1a to S31a having the structure a and the evaluation results of the samples S1b to S31b having the structure b.

Table 8 shows the initial characteristics of the structure a samples B1a to B35a and the evaluation results of the samples B1b to B35b of the structure b.

Table 9 shows the initial characteristics of the samples Z1a to Z30a and the evaluation results of the samples Z1b to Z30b having the structure b.

Table 10 shows the initial characteristics of the samples L1a to L29a and the evaluation results of the samples L1b to L29b having the structure b.

Table 6 shows the evaluation value of the initial characteristics and moisture shelf test after Qm and epsilon ₃₃ of conventional piezoelectric materials. Although the initial characteristics have reached the acceptance standard, the evaluation value is large, that is, Qm and ε ₃₃ after the moisture resistance test are greatly varied with respect to the initial value. Moreover, the evaluation value of Qm is minus, and it can be seen that the Qm value after the moisture resistance test is lowered from the initial value, and the piezoelectric characteristics are deteriorated.

In Tables 7 to 10, the initial characteristic change rate is an index for evaluating the initial characteristics of the sample of the structure b, and the superiority or inferiority of the initial values of Qm and ε ₃₃ in the samples of the structure a and the structure b having the same composition. Is shown. Initial characteristics change rate, for example, the initial value of Qm or epsilon ₃₃ samples of the structure of a composition a is a, the same composition of the structure b samples the initial value when the b of (b-a) / a It is a numerical value when the value of is expressed as a percentage. That is, if the characteristic is deteriorated with respect to the initial value of the sample of the structure a having the same composition, the initial characteristic variation rate becomes a negative value. As shown in Tables 7 to 10, the samples of the structure b had the initial characteristics improved with respect to the samples of the structure a at all compositions. Moreover, about the sample which passed about the initial characteristic, all the evaluation values after a moisture-resistant leaving test were less than 10%, and the acceptance criteria were satisfy | filled.

=== Condition of x, y, a, b ===
From the evaluation results in Tables 7 to 10, the numerical ranges for the values of x, y, a, and b are defined. As shown in Tables 2 to 5, the values of x, y, a, and b of each sample of the structure b are 0 to 0.31, 0.09 to 0.71, 0.29 to 0.00, respectively. 91, 0 to 0.21. In these numerical ranges, the outermost value (limit values: x = 0.31, y = 0.09, y = 0. 71, a = 0.29, a = 0.91, b = 0.21) (for example, S12b to S14b, S18b, S19b, S24b, S25b, S30b, S31b), both pass and fail are mixed doing. All other samples were acceptable except for samples that were rejected due to excessive or insufficient amounts of glass and Cu compound added as described later. Here, when considering the rejected sample, only one of the values of x, y, a, and b is a limit value. Appropriate values can be said to be 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, and 0 ≦ b ≦ 0.2. Therefore, the sample of the structure b in the above numerical range is an example of the present invention. Although not described here, the appropriate values of the values of x, y, a, and b are not limited to the above glasses, and similar results were obtained for other general glasses.

=== About Structure b ===
From Table 6, in Samples 1 and 2 of the conventional example not containing glass, both x, y, a, and b were in the above numerical range, but both failed. That is, even if the composition of the base material was the same, it was proved that the moisture resistance performance was inferior if glass was not included. By the way, the structure b starts from the knowledge that the piezoelectric material produced by the procedure shown in FIG. 3B improves the piezoelectric characteristics while maintaining the moisture resistance as compared with the piezoelectric material of the previous invention. This was confirmed in the subsequent structural analysis process. Therefore, in Tables 7 to 10, the microscopic structure of the samples that were determined to be acceptable was reconfirmed.

  FIG. 4 shows the structure of the piezoelectric material 1b according to the example of the present invention. FIG. 4A is a photomicrograph of the sample Z1b of the structure b that was determined to be acceptable by adding Zn-based glass among the samples shown in Tables 2 to 5. FIG. 4 (B) shows an analysis using energy dispersive X-ray fluorescence (EDX) for the portion marked with “x” marked by numbers “1” to “5” in the micrograph of (A). The results are shown. FIG. 4C is a diagram schematically showing a cross section taken along the line aa in FIG. In addition, in the figure of (C), the location to be analyzed by the EDX is indicated by a one-dot chain line and a number.

  In the photograph of FIG. 4 (A) and the part (number 1) of the grain boundary 11 in the schematic diagram of (C), as shown in (B), other than the composition (K, Na, Nb) constituting KNN. There are many compositions. It can also be seen that the composition of KNN increases on the surface of the crystal grain 10b as the distance from the grain boundary 11 increases, that is, as the number increases. However, compositions other than KNN are certainly present. Therefore, the piezoelectric material 1b according to the embodiment of the present invention has a structure in which the crystal grains 10b of KNN are used as the core and the other composition including glass is covered as the film 12b as shown in FIG. Can be determined.

  In (B), the values of Li and Sb contained in the base material are not included, but this is the values of x and a−b, which are the ratio of Li and Sb in the sample used for EDX analysis. Is close to the lower limit, below the measurement limit, and could not be detected. In any case, it is certain that KNN is covered with a sintering additive composed of other composition including glass.

=== About the amount of glass added ===
From the evaluation results shown in Tables 6 to 10, some samples to which glass was added passed even if the composition of the base material was outside the above appropriate range. Therefore, the recommended value of the addition amount in each glass was defined as a condition for obtaining stable characteristics. In the prepared sample, 0.06 wt% to 15.1 wt% is added for Si glass and Zn glass, 0.07 wt1 to 15.1 wt% is added for Bi glass, and Li glass is added. 0.09 wt% to 10.1 wt% was added.

And about Si type | system | group glass, most of the samples which added 15.1 wt% failed. Moreover, when comparing the sample added with 0.06% and the sample added with 0.07%, for example, comparing samples having the same composition other than the added amount of glass, such as S13b and S30b, or S26b and S27b, found the following sample added 0.06%, such as larger difference between the values of Qm and epsilon _33, unstable elements were seen. Therefore, the recommended value for the addition amount of Si-based glass is defined as 0.07% or more and 15.0% or less.

  Bi-type glass, Zn-type glass, and Li-type glass were found to have a tendency in the relationship between the added amount of glass and the initial characteristics and pass / fail as in the case of Si-type glass. The recommended values for the addition amounts of Zn-based glass, Bi-based glass, and Li-based glass are 0.08 wt% to 15.0 wt%, 0.07 wt% to 15.0 wt%, and 0.1 wt%, respectively. The content was 10.0 wt% or less.

=== Addition of Cu Compound ===
Initially, the present inventor studied the piezoelectric material mainly composed of the base material mainly for the purpose of improving the moisture resistance. And it has confirmed that moisture resistance improved by adding glass. However, although moisture resistance had the improved, focusing on the characteristics of Qm and epsilon _33, it has been found in the creative process of prior invention that these characteristics are in a trade-off relationship. In a piezoelectric material, it is also important that certain piezoelectric characteristics are superior, but since a piezoelectric material is finally incorporated into an industrial product as a piezoelectric element, it is important to operate stably. It is important that the individual characteristics are at a practical level and the characteristics are averaged.

Therefore, for the piezoelectric material of structure b, samples with the addition amount of Cu compound set to 0 mol%, 2 mol%, 10 mol%, and 10.1 mol% were prepared, and the characteristics were evaluated. As a result, as shown in Tables 7 to 10, most of the samples in which the composition of the base material was out of the above range and the addition amount of the Cu compound was 10.1 mol% were rejected. That is, it has been found that the base material having a composition close to the upper limit or the lower limit of the appropriate value may deteriorate the characteristics when a large amount of Cu compound is added. Therefore, in a piezoelectric material in which glass is added to the basic compound, a more practical lead-free piezoelectric material can be obtained by adding more than 0 mol% and 10 mol% or less of a Cu compound. For example, from the initial characteristics of samples S12b and S13b, B15b and B16b, Z21b and Z25b, L20b and L24b, etc., when the composition of the base material is close to the upper limit or lower limit, Qm and ε ₃₃ can be obtained by adding a Cu compound. It was confirmed that the characteristics were uniform.

=== Dependence on particle size ===
In the sample of the structure b, in the KNN powder generation procedure (s23) in FIG. 3B, the average particle diameter of KNN is adjusted to 0.8 μm, and the particle diameter of the sintering additive is adjusted. In the sintering additive production procedure (s25), the average particle size was adjusted to 1.5 μm. Here, in order to find out the conditions of the piezoelectric material having further excellent characteristics, it was examined whether or not the piezoelectric characteristics depend on the particle size of the base material or glass. Here, first, in the samples shown in Tables 2 to 5, the values of x, y, a, and b, the addition amount of the Cu compound, and the addition amount of the glass are 0.02, 0.49, For each sample of S2b, B5b, Z1b, and L1b, which are the same at 0.86, 0.10, 2 mol%, and 0.3 wt%, the core body KNN and the coating composition including the other composition Samples with various ratios (sintering additive particle size / KNN particle size) to the particle size of the resulting sintering additive were prepared. And about each sample, the initial value of Qm and (epsilon) ₃₃ was measured and the initial characteristic change rate with respect to the sample of the structure a of the same composition was calculated | required. The particle size of the core was 0.8 μm. Table 11 Table 14 below shows the relationship between the initial value of the a particle diameter ratio, Qm and epsilon _33. In Tables 11 to 14, samples with different particle diameter ratios were respectively obtained for S2b, B5b, Z1b, and L1b, and S2-A to S2-H, B5-A to B5-H, respectively. , Z1-A to Z1-H, L1-A to L1-H.

Table 11 below shows the relationship between the particle size ratio between the sintering additive containing Si-based glass and KNN and the initial characteristic change rate.

Table 12 below shows the relationship between the particle size ratio of the sintering additive containing Bi-based glass and KNN and the initial characteristic change rate.

Table 13 below shows the relationship between the particle size ratio of the sintering additive containing Zn-based glass and KNN and the initial characteristic change rate.

Table 14 below shows the relationship between the particle size ratio of the sintering additive containing Li-based glass and KNN and the initial characteristic change rate.

From Tables 11-14, when the particle diameter of the sintering additive which is a coating body becomes smaller than the particle diameter of KNN which is a core body, the characteristics of Qm are gradually improved. On the other hand, the epsilon _33, the particle size of the sintered additive, gradually the value until twice the particle size of a nucleus KNN and (particle diameter ratio = 0.5) is gradually increased together, when it is 2 times or less, the value of the epsilon ₃₃ is remained almost constant. That is, the value of ε ₃₃ is stabilized. Therefore, in the piezoelectric material of the structure b in which the composition of the base material is the above appropriate value, excellent initial characteristics can be obtained if the particle diameter of the coating is not more than twice the particle diameter of the core. It was confirmed that the variation was small.

=== Discussion ===
<Piezoelectric material of structure b>
In the piezoelectric material having the structure b according to the example of the present invention, as shown in Tables 7 to 10, the initial characteristics of all the samples were improved as compared with the samples having the structure a. Moreover, the characteristic fluctuations before and after the moisture resistance test were all suppressed to less than 10%. And even if the composition of the base material is outside the above appropriate range, there is a sample that has passed the evaluation. Therefore, it can be concluded that the piezoelectric material of the structure b is environmentally friendly, has a moisture resistance equivalent to that of the piezoelectric material of the structure a, and has piezoelectric characteristics superior to those of the piezoelectric material of the structure a. That is, in the piezoelectric material excellent in all of the environmental performance, piezoelectric characteristics, and moisture resistance performance, in addition to the composition including the base material and glass, KNN is used as a core, and other compositions have the core. It is an important condition that the covering structure b is provided.

<Recommended value of glass addition>
From the results of the performance evaluation tests for the above samples, it was found that the piezoelectric material including the base material and glass has a more preferable value (recommended value) for the amount of glass added. The reason why this recommended value exists is that if the addition amount is small, the coating body covering KNN lacks the glass that affects the moisture resistance, and if it is large, the glass foams and a part of the coating body is lost. The reason can be considered.

<Glass melting point>
In order to efficiently coat the core of KNN with a sintering additive having a composition other than KNN, the glass is first softened during the temperature rising process during the sintering of the piezoelectric material, and the sintering additive is added to KNN. In the process of coating the agent, it is desirable that the softened glass is uniformly dispersed in the coating while flowing. For this purpose, it is more desirable to use a glass having a softening point lower than the crystallization temperature of the base material. In the piezoelectric material having the structure b according to the example of the present invention, the crystallization temperature of the base material is 1100 ° C. to 1200 ° C., and the softening point of each glass is 790 ° C. for Si glass and 450 for Bi glass. The temperature is 580 ° C. for Zn-based glass and 550 ° C. for Li-based glass.

<Particle size ratio>
In particular, the value of ε ₃₃ of the piezoelectric characteristics depends on the ratio of the particle diameter of KNN to the particle diameter of the sintering additive, and there is an optimum numerical range for the ratio of the particle diameter of KNN and the particle diameter of the sintering additive. Were present. And since the particle size ratio is not a chemical property but expresses a physical structure exclusively, the optimum numerical range of the particle size ratio is not limited to the above four types of glass, but the base material and glass. It can be said that the present invention can be applied to all piezoelectric materials having a structure b including:

<Li-based glass>
Among the above four types of glass, the piezoelectric material to which Li-based glass was added had a narrow range of recommended values for the amount of glass added compared to the other three types of glass. This given that Li is an alkali metal, absorbent, piezoelectric characteristics of the glass during the sintering additive is expressed by covering the surface of the core body of KNN is inhibited by water absorption by alkali metal It is reasonable to assume that this has happened.

  The present invention can be used for devices and elements using piezoelectricity such as ultrasonic motors and filters.

1, 1a, 1b piezoelectric material, 10, 10a, 10b crystal grains, 11 grain boundaries,
12a glass, 12b coating

Claims (11)

A piezoelectric material made of a sintered body,
And the base material represented by the general formula _{Li x K y Na (1-} x-y) Nb a Ta b Sb (1-a-b) O 3, and a glass as a base component,
In the above general formula , 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, and 0 ≦ b ≦ 0.2, provided that x + y <1. And
A compound represented by the general formula K _y Na _(1-xy) Nb _a O _{3 including} K, Na, and Nb in the components of the base material is used as a core, and the core is the basic component. , Having a structure covered with a film composed of components other than the components constituting the KNN compound,
The glass is a Bi-based glass containing the compound Bi ₂ O ₃ as a main component,
The addition amount of the Bi-based glass is more than 0.08 wt% and 15.0 wt% or less with respect to the basic compound.
A piezoelectric material characterized by that. A piezoelectric material made of a sintered body,
And the base material represented by the general formula _{Li x K y Na (1-} x-y) Nb a Ta b Sb (1-a-b) O 3, and a glass as a base component,
In the general formula, 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, and 0 ≦ b ≦ 0.2, provided that x + y <1. And
A compound represented by the general formula K _y Na _(1-xy) Nb _a O _{3 including} K, Na, and Nb in the components of the base material is used as a core, and the core is the basic component. , Having a structure covered with a film composed of components other than the components constituting the KNN compound,
The glass is a Zn-based glass containing a compound ZnO as a main component,
The added amount of the Zn-based glass is more than 0.07 wt% and 15.0 wt% or less with respect to the basic compound.
A piezoelectric material characterized by that. A piezoelectric material made of a sintered body,
And the base material represented by the general formula _{Li x K y Na (1-} x-y) Nb a Ta b Sb (1-a-b) O 3, and a glass as a base component,
In the general formula, 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, and 0 ≦ b ≦ 0.2, provided that x + y <1. And
A compound represented by the general formula K _y Na _(1-xy) Nb _a O _{3 including} K, Na, and Nb in the components of the base material is used as a core, and the core is the basic component. , Having a structure covered with a film composed of components other than the components constituting the KNN compound,
The glass is a Si-based glass containing the compound SiO ₂ as a main component and not containing Li ₂ O,
The piezoelectric material characterized in that the addition amount of the Si-based glass is more than 0.07 wt% and not more than 15.0 wt% with respect to the basic compound . A piezoelectric material made of a sintered body,
And the base material represented by the general formula _{Li x K y Na (1-} x-y) Nb a Ta b Sb (1-a-b) O 3, and a glass as a base component,
In the general formula, 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, and 0 ≦ b ≦ 0.2, provided that x + y <1. And
A compound represented by the general formula K _y Na _(1-xy) Nb _a O _{3 including} K, Na, and Nb in the components of the base material is used as a core, and the core is the basic component. , Having a structure covered with a film composed of components other than the components constituting the KNN compound,
The glass is a Li-based glass containing a compound SiO ₂ as a main component and Li ₂ O,
The Li-based glass is added in an amount of more than 0.1 wt% and 10.0 wt% or less with respect to the basic compound . In any one of claims 1-4, together with Cu compound is added, the addition amount of the Cu compound, a piezoelectric material, characterized by more than 0 mol%, or less 10 mol%. 6. The piezoelectric material according to claim 1, wherein a softening point temperature of the glass is lower than a crystallization temperature of the base material. 7. The piezoelectric material according to claim 1, wherein the particle diameter of the coating is not more than twice the particle diameter of the core. A method for manufacturing a piezoelectric material, comprising:
The raw materials of the general formula _{Li x K y Na (1-} x-y) Nb a Ta b Sb (1-a-b) the base material represented by _{O 3,} while subject to x + y <1, 0 ≦ x ≦ 0 .3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, 0 ≦ b ≦ 0.2, and a base material component weighing step for weighing.
Among the weighed raw materials of the base material, the raw material of the KNN compound represented by the general formula K _y Na _(1-xy) Nb _a O ₃ is mixed, and the mixture is pulverized to obtain the first powder A first mixing and grinding step to obtain a body;
Pre-baking step of pre-baking the first powder to produce a powder of the KNN compound;
0.08 wt% of Bi based glass containing compound Bi ₂ O ₃ as a main component in the weighed raw materials other than the raw material that is the origin of the first powder. A second mixing and pulverizing step in which the mixture is mixed at an addition amount of more than 1% and 15.0 wt% or less, and the mixture is pulverized to obtain a second powder;
A sintering additive generating step of generating a powder of the sintering additive by heat-treating the second powder;
A firing step of sintering a mixture of the powder of the KNN compound and the powder of the sintering additive;
A method for producing a piezoelectric material, comprising: A method for manufacturing a piezoelectric material, comprising:
The raw materials of the general formula _{Li x K y Na (1-} x-y) Nb a Ta b Sb (1-a-b) the base material represented by _{O 3,} while subject to x + y <1, 0 ≦ x ≦ 0 .3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, 0 ≦ b ≦ 0.2, and a base material component weighing step for weighing.
Among the weighed raw materials of the base material, the raw material of the KNN compound represented by the general formula K _y Na _(1-xy) Nb _a O ₃ is mixed, and the mixture is pulverized to obtain the first powder A first mixing and grinding step to obtain a body;
Pre-baking step of pre-baking the first powder to produce a powder of the KNN compound;
Of the raw materials of the base material weighed, a Zn-based glass containing a compound ZnO as a main component in a raw material other than the raw material from which the first powder originated is less than 0.07 wt% with respect to the basic compound. A second mixing and pulverizing step of mixing at an addition amount of not more than 15.0 wt% and pulverizing the mixture to obtain a second powder;
A sintering additive generating step of generating a powder of the sintering additive by heat-treating the second powder;
A firing step of sintering a mixture of the powder of the KNN compound and the powder of the sintering additive;
A method for producing a piezoelectric material, comprising: A method for manufacturing a piezoelectric material, comprising:
The raw materials of the general formula _{Li x K y Na (1-} x-y) Nb a Ta b Sb (1-a-b) the base material represented by _{O 3,} while subject to x + y <1, 0 ≦ x ≦ 0 .3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, 0 ≦ b ≦ 0.2, and a base material component weighing step for weighing.
Among the weighed raw materials of the base material, the raw material of the KNN compound represented by the general formula K _y Na _(1-xy) Nb _a O ₃ is mixed, and the mixture is pulverized to obtain the first powder A first mixing and grinding step to obtain a body;
Pre-baking step of pre-baking the first powder to produce a powder of the KNN compound;
Of the raw materials of the base material weighed, raw materials other than the raw material from which the first powder is derived include Si-based glass containing the compound SiO ₂ as a main component and not containing Li ₂ O as the basic compound. And a second mixing and pulverizing step of mixing the mixture in an addition amount of 0.07 wt% to 15.0 wt% , and pulverizing the mixture to obtain a second powder;
A sintering additive generating step of generating a powder of the sintering additive by heat-treating the second powder;
A firing step of sintering a mixture of the powder of the KNN compound and the powder of the sintering additive;
A method for producing a piezoelectric material, comprising: A method for manufacturing a piezoelectric material, comprising:
The raw materials of the general formula _{Li x K y Na (1-} x-y) Nb a Ta b Sb (1-a-b) the base material represented by _{O 3,} while subject to x + y <1, 0 ≦ x ≦ 0 .3, 0.1 ≦ y ≦ 0.7, 0.3 ≦ a ≦ 0.9, 0 ≦ b ≦ 0.2, and a base material component weighing step for weighing.
Among the weighed raw materials of the base material, the raw material of the KNN compound represented by the general formula K _y Na _(1-xy) Nb _a O ₃ is mixed, and the mixture is pulverized to obtain the first powder A first mixing and grinding step to obtain a body;
Pre-baking step of pre-baking the first powder to produce a powder of the KNN compound;
Of the raw materials of the base material weighed, a raw material other than the raw material from which the first powder originated, and a Li-based glass containing Li ₂ O as a main component and a compound SiO ₂ as a main component is used as the basic compound. A second mixing and pulverizing step in which the mixture is mixed at an addition amount of more than 0.1 wt% and not more than 10.0 wt% , and the mixture is pulverized to obtain a second powder;
A sintering additive generating step of generating a powder of the sintering additive by heat-treating the second powder;
A sintering additive generating step of generating a powder of the sintering additive by heat-treating the second powder;
A firing step of sintering a mixture of the powder of the KNN compound and the powder of the sintering additive;
A method for producing a piezoelectric material, comprising: