JP2016108194A - Piezoelectric ceramic composition and method of producing piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition that is a HighQ material and has a high K constant and to provide a method of producing the piezoelectric ceramic composition.SOLUTION: A piezoelectric ceramic composition includes MgO as an additive in a base material represented by the general formula: A[PbSr(ZrTi)]+(1-A)[Pb{Mn(SbNb)}O] in which the A, x, y and z in the general formula satisfy 0.9≤A<1.0, 0.02≤x≤0.10, 0.45≤y≤0.53 and 0.00≤z≤1.00, respectively and the MgO is contained in a ratio of 0.25 wt% or less. The piezoelectric ceramic composition may have a particle size as measured by a line intercept method equal to or larger than a particle size of a piezoelectric ceramic composition having a base material of the same composition as that of the base material as mentioned above and containing no MgO.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a piezoelectric ceramic composition and a method for producing the same.

  The piezoelectric ceramic composition is a sintered body, and is formed by putting raw materials made of powder into a mold and molding the material into a target shape and firing the molded body. PZT is well known as a piezoelectric ceramic composition (hereinafter also referred to as a piezoelectric material). This piezoelectric material containing PZT or PZT as a main component (hereinafter also referred to as a PZT piezoelectric material) is a piezoelectric filter, ultrasonic wave Widely used in various piezoelectric elements such as vibrators, piezoelectric actuators, and piezoelectric buzzers.

By the way, characteristics of the piezoelectric material include an electromechanical coupling coefficient K (hereinafter also referred to as K constant), a relative dielectric constant (ε _r ), and a mechanical quality factor (Qm). The piezoelectric material includes a HighQ material having a Qm of 300 or more and a LowQ material having a Qm of less than 300. The PZT piezoelectric material classified as the HighQ material has a slightly low K constant, and the PZT piezoelectric material of the LowQ material has a high K. It is known to show constants. Non-Patent Document 1 below describes in detail a general technical explanation regarding piezoelectric materials, explanations of various characteristics, evaluation methods of characteristics, and the like. Non-Patent Document 2 describes a technique related to the present invention.

FDK Corporation, “Piezoelectric ceramics (technical document)”, [online], [searched on November 27, 2014], Internet <URL: http://www.fdk.co.jp/cyber-j/pdf/ BZ-TEJ001.pdf> T. Nagai, H. J. Hwang, M. Yasuoka, M. Sando and K. Niihara, J. Kor. Phys. Soc., 32, S1271-73 (1998).

  None of the PZT piezoelectric materials, which are the most widely used piezoelectric materials at the present time, belong to the HighQ material and have a high K constant. As is well known, Qm is a constant indicating the sharpness of mechanical vibration in the vicinity of the resonance frequency when the piezoelectric body causes natural vibration, and the piezoelectric material belonging to the HighQ material has low loss. The K constant is a constant representing the efficiency of converting electrical energy applied to the piezoelectric material into mechanical energy. The higher the value of K, the higher the efficiency of the piezoelectric material. Further, higher performance is required for the current piezoelectric element, and in order to meet the demand, a piezoelectric material having a high K constant belonging to the HighQ material is required. Therefore, an object of the present invention is to provide a piezoelectric ceramic composition that is a HighQ material and has a high K constant, and a method for producing the same.

To achieve the above object, the present invention provides:
Is represented by the general formula _{A [Pb 1-x Sr x} (Zr 1-y Ti y)] + (1-A) [Pb {Mn 1/3 (Sb 1-z Nb z) 2/3} O 3] The base material contains MgO as an additive, and the A, x, y, and z in the general formula are 0.9 ≦ A <1.0, respectively.
0.02 ≦ x ≦ 0.10
0.45 ≦ y ≦ 0.53
0.00 ≦ z ≦ 1.00
While satisfying
MgO is contained at a ratio of 0.25 wt% or less,
The piezoelectric ceramic composition is characterized by that.

  Moreover, it is good also as a piezoelectric ceramic composition whose average particle diameter measured by the line intercept method is more than the average particle diameter of the piezoelectric ceramic composition which the composition of the said base material is the same and does not contain MgO.

The present invention also extends to a method for producing a piezoelectric ceramic composition,
Is represented by the general formula _{A [Pb 1-x Sr x} (Zr 1-y Ti y)] + (1-A) [Pb {Mn 1/3 (Sb 1-z Nb z) 2/3} O 3] A method for producing a piezoelectric ceramic composition containing MgO as an additive in a base material,
The raw materials of the base material are mixed so that 0.9 ≦ A <1.0, 0.02 ≦ x ≦ 0.10, 0.45 ≦ y ≦ 0.53, and 0.00 ≦ z ≦ 1.00. A first mixing step,
A pre-baking step of pre-baking the raw material of the base material mixed in the first mixing step;
A second mixing step of mixing the raw material powder obtained by the preliminary baking step and the MgO at a ratio of 0.25 wt% or less;
A baking step of baking the mixture obtained by adding the binder to the mixture obtained in the second mixing step and then forming the granulated product into a predetermined shape;
It is characterized by including.

  The piezoelectric ceramic composition according to the present invention can be a PZT piezoelectric material that is a HighQ material and has a high K constant. Further, according to the method for manufacturing a piezoelectric ceramic material according to the present invention, a PZT piezoelectric material that is a HighQ material and has a high K constant can be efficiently manufactured. Other effects will be clarified in the following description.

It is process drawing for demonstrating the manufacturing method of the piezoelectric ceramic composition which concerns on the Example of this invention. It is an electron micrograph which shows the difference in the crystal structure by the calcination temperature of a piezoelectric ceramic composition. It is a figure which shows the relationship between the calcination temperature of a piezoelectric ceramic composition, and an average particle diameter. It is an electron micrograph which shows the difference in the crystal structure by the addition amount of MgO in a piezoelectric ceramic composition. It is a figure which shows the relationship between the addition amount of MgO in a piezoelectric ceramic composition, and an average particle diameter.

=== The process of conceiving the present invention ===
In the process of developing a PZT-based piezoelectric material having a high K constant and a high K constant, the inventor has developed A [Pb _1-x Sr _x (Zr _1-y Ti _y )] + (1-A) [Pb {Mn _{1 / 3 (Sb 1-z Nb} z) 2/3} O 3 generally compounds described formula (hereinafter, also referred to as base material) was focused on, in HighQ material, K in spreading vibration mode of the disc A piezoelectric material having a constant (Kp) of about 50% could be obtained. However, even if the composition of the base material is adjusted, it is difficult to further improve the K constant while maintaining the HighQ material. In particular, it was difficult to make the Kp constant larger than that of the base material while maintaining a sufficiently high Qm ≧ 1000 as Qm. Therefore, when a wide variety of additives were examined with respect to the above base material, it was found that addition of MgO improves the K constant while belonging to the HighQ material. The present invention has been conceived as a result of intensive studies based on such knowledge.

=== Example according to the present invention ===
In the embodiment according to the present invention, an appropriate amount of MgO is added to the above-mentioned base material, thereby having a sufficient K constant without greatly deteriorating the excellent piezoelectric performance of the above-mentioned base material. Then, in order to evaluate the characteristics of the piezoelectric ceramic composition according to the example of the present invention, various piezoelectric materials in which the composition of the base material (values of A, x, y, and z) and the added amount of MgO are changed are sampled. And the piezoelectric characteristics of each sample were evaluated.

=== Procedure for Sample Production ===
FIG. 1 specifically shows a sample manufacturing procedure. As shown in this figure, first, the general formula becomes a raw material of the base material _{A [Pb 1-x Sr x} (Zr 1-y Ti y)] + (1-A) [Pb {Mn 1/3 (Sb _1-z Nb _z ) _2/3 } O ₃ ] is weighed (s1). At this time, if the amount and ratio of each raw material are changed, the values of A, x, y, and z in the above general formula change. Next, the raw material of the base material is wet mixed for 24 hours (h) by adding pure water as a solvent in a ball mill (s2). Thereby, the raw material mixture of the base material is pulverized into powder. Then, this powdery mixture is temporarily fired in the air at a temperature of 800 ° C. to 950 ° C. for 3 hours (s3).

  Further, MgO as an additive is weighed according to the sample, and the raw material of the powdery base material obtained by pre-baking and the weighed MgO are pulverized while mixing in pure water for 5 h by a ball mill. (S4 → s5, s6). In addition, about the sample which does not add MgO, these mixing processes (s5) and a grinding | pulverization process (s6) are abbreviate | omitted.

  Then, a mixture of the raw material of the base material and the additive that has undergone preliminary firing, or a raw material of the base material that has undergone the preliminary firing is added and mixed with a PVA aqueous solution serving as a binder, and an appropriate particle size (for example, 1 μm) Granulate to form powder (s7). Thereafter, the granulated powder is formed into a desired shape (s8). A sample for evaluating piezoelectric characteristics is processed into a disk shape having a diameter Φ = 17 mm and a thickness t = 1.0 mm at a pressure of 250 MPa. And the molding is baked at 1130-1310 degreeC in air | atmosphere for 3 hours, and it is set as a disk shaped piezoelectric ceramic composition (s9). Furthermore, Ag electrodes were formed on both surfaces of the disk-shaped piezoelectric ceramic composition (s10). The Ag electrode was formed by holding the piezoelectric ceramic composition coated with the Ag paste at a temperature of 680 ° C. for 1 min. Then, a polarization process was performed by applying an electric field of 2.5 Kv / mm for 30 min in 120 ° C. silicone oil to complete a piezoelectric element (s11). This piezoelectric element was used as a sample for evaluating the characteristics of the piezoelectric ceramic composition (piezoelectric material).

=== Characteristic evaluation ===
For various samples having different compositions, the electromechanical coupling coefficient Kp (%), the relative dielectric constant ε _r (= ε ₃₃ ^T / ε ₀ ), and the mechanical quality factor Qm were measured using a known impedance analyzer. For the evaluation of piezoelectric characteristics, samples fired at the same temperature (1280 ° C.) were used.

By the way, an object of the present invention is to improve the K constant of the PZT piezoelectric material belonging to the HighQ material. Therefore, regarding the piezoelectric characteristics of each sample produced, if Qm> 1000, which is necessary and sufficient for Qm ≧ 300, which is the condition of the HighQ material, this Qm> 1000 is regarded as an acceptable standard as having excellent Qm characteristics. It was. Also, in terms of permittivity ε _r , ε _r > 1000, which is practically sufficient, was set as a pass criterion.

  Table 1 shows the composition of each sample and the measurement results of various piezoelectric characteristics.

<Effect of MgO>
First, the effect of adding MgO was examined based on the characteristic measurement results of each sample shown in Table 1. In Table 1, Samples 1, 16, and 17 are piezoelectric materials composed only of a base material to which no MgO is added, and MgO is added to a base material having the same composition as those of Samples 1, 16, and 17. Let's look at the piezoelectric properties of the sample.

First, samples 19 to 21 are piezoelectric materials having the same base material composition as sample 1. Looking at the piezoelectric characteristics of Samples 19 to 21, Samples 19, 20, and 21 have MgO addition rates of 0.05 wt%, 0.25 wt%, and 0.26 wt%, and the MgO addition rate is 0.26%. The sample 21 did not satisfy ε _r > 1000 and Qm> 1000. However, Sample 19 with an MgO addition rate of 0.05 wt% and Sample 20 with an addition amount of 0.25 wt% had a higher Kp than Sample 1 while satisfying the passing conditions of ε _r > 1000 and Qm> 1000. . Therefore, the upper limit of the added amount of MgO can be defined as 0.25 wt% from Samples 1 and 19-21.

  Samples 14 and 18 have the same base material composition as Samples 16 and 17 and added with MgO. Samples 14 and 18 have MgO added at 0.25 wt%, which is the upper limit of the specified range. When samples 16 and 14 and samples 17 and 18 are compared here, it can be seen that samples 14 and 18 have an increase in Kp with respect to samples 16 and 17 having the same base material composition by adding MgO. . Samples 14 and 18 also have a higher Kp than sample 1 although the compositions of the base materials are different. That is, it was confirmed that Kp was increased by adding MgO regardless of the composition of the base material.

Further, comparing Samples 18 and 23 or Samples 14 and 22 with the same base material composition but different MgO addition amounts, Kp increases as the MgO addition amount decreases with the same base material composition. You can see that That is, it can be said that MgO is desirably contained in a very small amount. Therefore, it can be said that the optimum addition amount of MgO only needs to be included at a ratio higher than 0 wt% unless the upper limit 0.25 wt% specified above is exceeded. The piezoelectric material MgO relative to the base material is added in an appropriate amount as is What is a also epsilon _r and Qm is the composition of the base material satisfy the the above acceptance criteria, and Hahazai only the piezoelectric of It shows a higher Kp than the material.

<About composition of base material>
Next, based on the results shown in Table 1, the appropriate values of the values of A, x, y, and z in the above general formula for determining the composition of the base material will be examined. Here, first, an appropriate value of z will be examined. Composition [Pb {Mn _1/3 (Sb _1-z Nb _z ) _2/3 } O ₃ ] (hereinafter also referred to as B site) represented by the chemical formula of the second item in the above general formula representing the composition of the base material. In addition, Sb and Nb contained in the first item {Pb _1-x Sr _x (Zr _1-y Ti _y ) O ₃ }, which is also referred to as A site) increase or decrease in a complementary manner depending on the value of z. . Therefore, Sample 1 with z = 0 does not contain Nb in the composition of the base material. Accordingly, when the piezoelectric characteristics of samples 16 and 17 made of only the base material are examined as in sample 1, sample 16 is z = 0.5, sample 17 is z = 1, and half or all of Sb is respectively. Substituted with Nb. The samples 16 and 17 the proportion of Nb is increased from the piezoelectric characteristics of the (z increases) the value of epsilon _r gradually decreases in accordance with the, it can be seen that the value of Qm is increasing gradually. However, samples 16 and 17 both satisfy ε _r > 1000 and Qm> 1000. As for Kp, no significant difference was observed with the increase or decrease of Nb. That is, it is sufficient that at least one of Sb and Nb is included in the B site, and an appropriate value of z is 0 ≦ z ≦ 1.

Then the value of A in the base material, i.e. the ratio of the A site and B site, looking at the piezoelectric characteristics of samples 11 to 15 satisfy the acceptance criteria for the sample 11, epsilon _r and Qm of A = of 0.89 However, it decreased with respect to Kp = 52% in Sample 1 at Kp = 47%. Sample 15 has A = 1.00, and the base material is composed of only the component of A site. That is, the B site does not exist. Therefore, in the column of z of the composition of the sample 15 in Table 1, “-” is described because the value of z indicating the ratio of Nb contained in the B site is meaningless. And although this Sample 15 epsilon _r and Qm is met the acceptance criteria are the same as Sample 1 with Kp = 52%, improvement in Kp was observed. Therefore, the appropriate range of A can be defined as 0.90 ≦ A <1.00. The value of x can be defined as 0.02 ≦ x ≦ 0.10 from samples 2 to 6, and the value of y should be defined as 0.45 ≦ y ≦ 0.53 from samples 7 to 10. Can do.

<About particle size>
As described above, the piezoelectric material in which an appropriate amount of MgO is added to the base material is a high-Q material having a sufficiently large Qm (Qm> 1000) and a base material having the same composition while having a practical εr (> 1000). A high Kp is shown for a piezoelectric material made of Therefore, the mechanism of increasing Kp by adding MgO was examined from the viewpoint of change in crystal structure. Specifically, various piezoelectric materials having the same composition as Samples 1 and 19 in Table 1 but different firing temperatures were produced, and the crystal structures of the various piezoelectric materials were observed with an electron microscope. FIG. 2 shows electron micrographs of piezoelectric materials fired at 1190 ° C., 1250 ° C., and 1310 ° C. among various piezoelectric materials produced. 2A, 2B, and 2C are piezoelectric materials that have the same composition as sample 1 and do not contain MgO. Figures (A), (B), and (C) show the crystal structures of the piezoelectric material when the firing temperatures are 1190 ° C, 1250 ° C, and 1310 ° C, respectively. 2 (D), (E), and (F) are piezoelectric materials containing the same composition as sample 19 and containing MgO, and the crystal structures when the firing temperatures are 1190 ° C., 1250 ° C., and 1310 ° C., respectively. Show.

  2 (A) and (D), (B) and (E), and (C) and (F) are compared, when the firing temperature is the same, the addition of MgO increases the crystal particle size. I understand that. That is, grain growth is promoted. From this, MgO is considered to act as a sintering aid or a grain growth accelerator. In other words, the cause of the increase in Kp due to the addition of MgO can be considered as a result of the accelerated grain growth.

  Certainly, as shown in FIG. 2C, if it is fired at a high temperature of 1310 ° C., grain growth is promoted without adding MgO. However, Pb in the mother may be volatilized at this firing temperature. If Pb volatilizes, the raw material mixing ratio of the base material mixed at the time of manufacturing the piezoelectric material will deviate from the composition ratio of the base material in the actually fired piezoelectric material. Of course, if the ratio of Pb, which is the main component in the PZT-based piezoelectric material, is relatively reduced, the piezoelectric characteristics are greatly deteriorated. Therefore, the relationship between the firing temperature and the particle diameter of each piezoelectric material was examined. FIG. 3 shows the relationship between the firing temperature and the particle diameter in the piezoelectric material with and without MgO added. The particle diameter is the average particle diameter specified by a well-known line intercept method. As shown in FIG. 3, in the piezoelectric material to which MgO is not added, the particle diameter increases rapidly from the firing temperature of around 1300 ° C. On the other hand, in the piezoelectric material to which MgO is added, the particle diameter gradually increases as the firing temperature increases. That is, it was confirmed that by adding MgO, grain growth can be surely promoted without volatilizing Pb.

  By the way, considering that the increase in Kp due to the addition of MgO is due to the promotion of grain growth, the difference in piezoelectric properties due to the composition of the base material is mainly influenced by the characteristics of the element itself, while the addition of MgO It can be considered that the difference in the piezoelectric characteristics due to this depends on the size of the particle diameter. Therefore, the particle diameters of various piezoelectric materials having the same base material composition and different MgO addition amounts were examined. FIG. 4 is an electron micrograph showing crystal structures of various piezoelectric materials having different amounts of MgO added to the base material having the same composition as Sample 1 in Table 1. The various piezoelectric materials shown in FIG. 4 are all fired at 1280 ° C., and are piezoelectric materials to which samples 1, 19, and 20 in Table 1 and 0.20 wt% of MgO are added. 4A, 4 </ b> B, 4 </ b> C, and 4 </ b> D correspond to sample 1, sample 19, piezoelectric material to which 0.20 wt% of MgO is added, and sample 20, respectively. FIG. 5 is a diagram showing the relationship between the added amount of MgO specified based on the electron micrograph shown in FIG. 4 and the particle diameter. The particle size in FIG. 5 is also an average particle size based on the line intercept method. As shown in FIGS. 4A and 4D and FIG. 5, a piezoelectric material (sample 20) in which MgO is added to the base material up to the upper limit (0.25 wt%), and a piezoelectric material with only the base material (sample 1) The particle size is almost the same. This means that if the composition of the base material is the same, if the particle diameter when adding MgO is equal to or larger than the particle diameter when not adding MgO, a higher Kp can be obtained than the piezoelectric material of the base material alone. Suggests. Therefore, after defining the composition of the base material, if the particle diameter of the piezoelectric material in which MgO is added to the base material at a ratio of 0.25 wt% or less is equal to or larger than the particle diameter of the piezoelectric material consisting only of the base material, The piezoelectric material to which MgO is added has a high K constant while belonging to the HighQ material more reliably.

=== About Manufacturing Method ===
Each sample shown in Table 1 was created by the procedure shown in FIG. That is, first, a mixture of raw materials of a base material is temporarily fired, and MgO as an additive is added to the powder obtained by the temporary firing, followed by firing. However, as a manufacturing procedure of the piezoelectric material, there is also a procedure (hereinafter, also referred to as a raw material mixing method) in which a raw material of a base material and an additive are first mixed, and the mixture is molded and fired. Therefore, samples having the same composition as Samples 19, 20, 22, and 23 in Table 1 and employing a raw material mixing method in the production procedure were prepared, and the piezoelectric characteristics of each sample were examined.

  Table 2 shows the piezoelectric characteristics of the samples prepared by the raw material mixing method.

Samples 24, 25, 26, and 27 shown in Table 2 have the same compositions as Samples 19, 20, 22, and 23 shown in Table 1, respectively. However composition despite the same, the Kp and epsilon _r is a sample prepared by the raw materials mixing method was reduced. For Sample 25 the added amount of MgO is the upper limit (0.25 wt%) is the degree to which the epsilon _r was slightly above the acceptance criteria. Moreover, a plurality of samples having the same composition are prepared instead of one, and the characteristics shown in Tables 1 and 2 are values obtained by averaging the characteristics of a plurality of solids having the same composition. And about the sample 25, the solid below the acceptance standard also existed. Therefore, the piezoelectric material according to the embodiment of the present invention is preferably manufactured by the procedure shown in FIG.

<Action and effect by temporary firing>
As described above, the piezoelectric material according to the embodiment of the present invention has a high K constant by adding an appropriate amount of MgO to the base material. However, it is also a fact that the piezoelectric characteristics vary depending on the manufacturing method. Therefore, consider the relationship between the manufacturing method and the piezoelectric characteristics. In general, when MgO is added to PZT, Mg ²⁺ acts as an acceptor ion, and oxygen vacancies are generated by solid solution at the B site. Consequently epsilon _r decreases, limited movement of the domain wall in the crystal structure is Qm is increased. On the other hand, it is known that the K constant decreases when an oxide that can be an acceptor ion is added to the composition near the morphotopic layer boundary (MPB). However, in the piezoelectric material according to the example of the present invention, it seems that it is easy to introduce MgO into the base material without acting as an acceptor ion. That is, the reactivity of MgO to the PZT base material is poor, and MgO is hardly dissolved in the PZT base material. As a result, the K constant is considered to be improved.

  Furthermore, in the manufacturing method in which MgO is added after calcining the raw material of the base material and then calcined thereon, an appropriate amount of MgO is added to the base material that has become a pre-stable state by the temporary firing, and MgO is accepted as an acceptor. It is considered that it can be introduced into the base material more reliably without acting as ions.

s1 base material raw material weighing step, s2 mixing and pulverizing step, s3 pre-baking step, s5 MgO mixing step, s7 granulating step, s8 forming step, s9 baking step, s11 polarization step

Claims (3)

Is represented by the general formula _{A [Pb 1-x Sr x} (Zr 1-y Ti y)] + (1-A) [Pb {Mn 1/3 (Sb 1-z Nb z) 2/3} O 3] The base material contains MgO as an additive, and the A, x, y, and z in the general formula are 0.9 ≦ A <1.0, respectively.
0.02 ≦ x ≦ 0.10
0.45 ≦ y ≦ 0.53
0.00 ≦ z ≦ 1.00
While satisfying
MgO is contained at a ratio of 0.25 wt% or less,
A piezoelectric ceramic composition characterized by that.   2. The piezoelectric ceramic composition according to claim 1, wherein an average particle diameter measured by a line intercept method is equal to or greater than an average particle diameter of a piezoelectric ceramic composition having the same base material composition and containing no MgO. Is represented by the general formula _{A [Pb 1-x Sr x} (Zr 1-y Ti y)] + (1-A) [Pb {Mn 1/3 (Sb 1-z Nb z) 2/3} O 3] A method for producing a piezoelectric ceramic composition containing MgO as an additive in a base material,
The raw materials of the base material are mixed so that 0.9 ≦ A <1.0, 0.02 ≦ x ≦ 0.10, 0.45 ≦ y ≦ 0.53, and 0.00 ≦ z ≦ 1.00. A first mixing step,
A pre-baking step of pre-baking the raw material of the base material mixed in the first mixing step;
A second mixing step of mixing the raw material powder obtained by the preliminary baking step and the MgO at a ratio of 0.25 wt% or less;
A baking step of baking the mixture obtained by adding the binder to the mixture obtained in the second mixing step and then forming the granulated product into a predetermined shape;
The manufacturing method of the piezoelectric ceramic composition characterized by including.