JP7206925B2 - Piezoelectric composition and piezoelectric element - Google Patents

Description

The present invention relates to a piezoelectric composition and a piezoelectric element having the piezoelectric composition.

Piezoelectric compositions have the effect of generating electric charges on the surface when subjected to external stress (piezoelectric effect) based on spontaneous polarization caused by the unevenness of electric charges in the crystal, and strain due to the application of an electric field from the outside. and the generated effect (inverse piezoelectric effect).

Piezoelectric elements to which such piezoelectric compositions capable of mutually converting mechanical energy and electrical energy are applied are widely used in various fields. For example, an actuator as a piezoelectric element that utilizes the inverse piezoelectric effect can accurately obtain minute displacement in proportion to the applied voltage and has a high response speed. It is used in head driving elements, inkjet printer head driving elements, and fuel injection valve driving elements.

In addition, it is also used as a sensor for reading minute force and deformation using the piezoelectric effect. Furthermore, since the piezoelectric composition has excellent responsiveness, it is possible to excite the piezoelectric composition itself or an elastic body in a bonding relationship with the piezoelectric composition to cause resonance by applying an AC electric field. They are also used as piezoelectric transformers and ultrasonic motors.

In general, a piezoelectric composition is composed of polycrystals, and is obtained by subjecting a fired ferroelectric composition to polarization treatment. In the ferroelectric composition after sintering, the direction of spontaneous polarization in each crystal is random, and the ferroelectric composition as a whole does not exhibit a biased charge, and does not exhibit a piezoelectric effect or an inverse piezoelectric effect. Therefore, by applying a DC electric field equal to or greater than the coercive electric field to the ferroelectric composition after sintering, an operation called polarization treatment is performed to align the direction of spontaneous polarization in a certain direction. The ferroelectric composition after polarization treatment can exhibit properties as a piezoelectric composition.

As piezoelectric compositions, lead-based piezoelectric compositions composed of lead zirconate (PbZrO ₃ ) and lead titanate (PbTiO ₃ ) are often used. However, lead-based piezoelectric compositions contain about 60 to 70% by weight of lead oxide (PbO), which has a low melting point, and lead oxide is likely to volatilize during firing. Therefore, from the viewpoint of environmental load, making the piezoelectric composition lead-free has become an extremely important issue.

Bismuth layered ferroelectrics and the like are known as lead-free piezoelectric compositions. However, since the bismuth layered ferroelectric has a large crystal anisotropy, it is necessary to orient the spontaneous polarization using the shear stress applied by the hot forging method, which poses a problem in terms of productivity.

On the other hand, recently, as a new eco-friendly piezoelectric composition, research is being conducted on alkali metal niobate-based compounds. In order to impart new properties to this alkali metal niobate-based compound, additives are added. For example, Patent Document 1 discloses a piezoelectric composition in which copper oxide is added to an alkali metal niobate compound. Non-Patent Document 1 discloses a piezoelectric composition in which germanium oxide is added to an alkali metal niobate compound.

Japanese Patent No. 4398635

K. Chen, et al, "Effects of GeO2 Addition on Sintering and Properties of (K0.5Na0.5)NbO3 Ceramics", J. Am. Ceram. Soc., 1-6 (2016)

2. Description of the Related Art In order to achieve high performance and miniaturization of equipment in which a piezoelectric element having a piezoelectric composition is mounted, it is necessary to reduce the size of the piezoelectric element while maintaining the performance of the piezoelectric element. In this case, it is necessary to reduce the size of the piezoelectric composition, but if the size of the piezoelectric composition is reduced, the mechanical strength of the piezoelectric composition is reduced. If the mechanical strength is lowered, defective products may occur during processing of the piezoelectric composition. Therefore, the piezoelectric composition is required to have good mechanical strength.

In addition, since devices equipped with piezoelectric elements are used in various environments, the piezoelectric elements are required to have high reliability in harsh environments. Examples of severe environments include high temperature and high humidity conditions.

However, in the alkali metal niobate-based compound disclosed in Patent Document 1, the alkali metal element volatilizes during firing, and voids and defects tend to occur inside the piezoelectric composition after firing, resulting in low mechanical strength. There was a problem. However, Patent Document 1 does not evaluate the mechanical strength at all. Furthermore, it is considered that moisture or the like easily penetrates through voids, defects, etc. generated inside the fired piezoelectric composition disclosed in Patent Document 1, resulting in low reliability.

In addition, although it is described that the alkali metal niobate-based compound disclosed in Non-Patent Document 1 can be sintered at a low temperature, the piezoelectric properties such as the mechanical quality factor Qm are low, and the mechanical strength and No reliability has been evaluated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a highly reliable piezoelectric composition having both mechanical strength and piezoelectric properties, and a piezoelectric element comprising the piezoelectric composition. do.

To achieve the above objects, aspects of the present invention are:
[1] A piezoelectric composition represented by the composition formula K _m NbO ₃ and containing a composite oxide having a perovskite structure, copper, and germanium,
m in the composition formula satisfies the relationship 0.970 ≤ m ≤ 0.999,
x mol % of copper in terms of copper element and y mol % of germanium in terms of germanium element are contained in 1 mol of the composite oxide,
x satisfies the relationship 0.100 ≤ x ≤ 1.000,
The piezoelectric composition is characterized in that y satisfies the relationship of 0.000<y≦1.500.

[2] The piezoelectric composition according to [1], wherein m satisfies the relationship 0.991≤m≤0.999.

[3] A piezoelectric composition represented by the composition formula K _m NbO ₃ and containing a composite oxide having a perovskite structure, copper, and germanium,
The piezoelectric composition is composed of crystal grains having a perovskite structure and grain boundaries,
The piezoelectric composition is characterized in that germanium is contained in grain boundaries.

[4] The piezoelectric composition according to [3], wherein the grain boundaries contain at least one element selected from the group consisting of potassium, niobium and copper.

[5] A piezoelectric element comprising the piezoelectric composition according to any one of [1] to [4].

The piezoelectric composition according to the present invention has the characteristics described above, so that it is possible to achieve both mechanical strength and piezoelectric properties, and to provide a highly reliable piezoelectric composition, and a piezoelectric element comprising the piezoelectric composition. can be done.

FIG. 1 is a schematic perspective view of an example of a piezoelectric element according to this embodiment. FIG. 2 is a schematic cross-sectional view of another example of the piezoelectric element according to this embodiment. FIG. 3 is a STEM image of a sample cross section of a piezoelectric composition according to an example of the present invention. FIG. 4 is a diagram showing EDS point analysis results at points 1 to 5 shown in FIG.

Hereinafter, the present invention will be described in detail in the following order based on specific embodiments.
1. Piezoelectric element 1.1 Piezoelectric composition 2. Method for manufacturing piezoelectric element3. 4. Effect of this embodiment. Modification

(1. Piezoelectric element)
First, a piezoelectric element to which the piezoelectric composition according to this embodiment is applied will be described. The piezoelectric element is not particularly limited as long as it is an element to which the piezoelectric composition according to this embodiment can be applied. In this embodiment, for example, a piezoelectric transformer, a thin film sensor, and a piezoelectric ultrasonic motor are exemplified.

A piezoelectric element 5 shown in FIG. 1 includes a plate-shaped piezoelectric body 1 and a pair of electrodes 2 and 3 formed on a pair of opposing surfaces 1a and 1b, which are both main surfaces of the piezoelectric body 1. . The piezoelectric body portion 1 is made of the piezoelectric composition according to this embodiment, and details of the piezoelectric composition will be described later. Moreover, the conductive material contained in the electrodes 2 and 3 is not particularly limited, and can be arbitrarily set according to desired properties, applications, and the like. In this embodiment, gold (Au), silver (Ag), palladium (Pd), and the like are exemplified.

Although the piezoelectric body 1 has a rectangular parallelepiped shape in FIG. 1, the shape of the piezoelectric body 1 is not particularly limited, and can be arbitrarily set according to desired characteristics, applications, and the like. Also, the dimensions of the piezoelectric body 1 are not particularly limited, and can be arbitrarily set according to desired characteristics, applications, and the like.

The piezoelectric portion 1 is polarized in a predetermined direction. For example, the piezoelectric element 5 shown in FIG. 1 is polarized in the thickness direction of the piezoelectric body 1, that is, in the direction in which the electrodes 2 and 3 face each other. An external power source (not shown) is electrically connected to the electrodes 2 and 3 via wires (not shown), for example, and a predetermined voltage is applied to the piezoelectric body 1 via the electrodes 2 and 3 . When a voltage is applied, electrical energy is converted into mechanical energy in the piezoelectric body 1 by the inverse piezoelectric effect, and the piezoelectric body 1 can vibrate in a predetermined direction.

(1.1 Piezoelectric Composition)
The piezoelectric composition according to this embodiment contains a composite oxide having a perovskite structure represented by the general formula ABO ₃ as a main component. Moreover, the piezoelectric composition according to the present embodiment contains copper (Cu) and germanium (Ge) in addition to the above composite oxide. In this embodiment, the main component is a component that accounts for 90 mol % or more in 100 mol % of the piezoelectric composition.

In the perovskite structure, elements with large ionic radii, such as alkali metal elements and alkaline earth metal elements, tend to occupy the A sites of _ABO3 , while elements with small ionic radii, such as transition metal elements, tend to occupy the A sites of _ABO3 . It tends to occupy the B site. BO ₆ oxygen octahedra composed of B-site elements and oxygen form a three-dimensional network in which the vertexes are shared with each other, and the perovskite structure is formed by filling the gaps of this network with A-site elements. It is formed.

In this embodiment, the general formula ABO ₃ can be represented by the composition formula K _m NbO ₃ . That is, the A-site element is potassium (K) and the B-site element is niobium (Nb).

In the above composition formula, "m" indicates the ratio of the total number of atoms of A-site elements to the total number of atoms of B-site elements, ie, the so-called A/B ratio. That is, it is the ratio of the number of K atoms to the number of Nb atoms. In this embodiment, "m" satisfies the relationship 0.970≤m≤0.999.

That is, good mechanical strength can be obtained by allowing the B-site element (Nb) to exist in excess of the A-site element (K). If "m" is larger than the above range, the resulting piezoelectric composition will exhibit high deliquescence, resulting in extremely low strength and a tendency to be unable to withstand processing. On the other hand, when "m" is smaller than the above range, the resulting piezoelectric composition tends to have a low density and low mechanical strength.

"m" is preferably 0.970 or more, more preferably 0.991 or more. On the other hand, "m" is preferably 0.999 or less.

In the piezoelectric composition according to the present embodiment, when the content of Cu in terms of Cu element is x mol % with respect to 1 mol (100 mol %) of the composite oxide, "x" is 0.100 ≤ x ≤ Satisfy the relation that is 1.000.

As long as Cu is contained within the above range, its existence form is not particularly limited. may When present at grain boundaries, they may form compounds with other elements. However, it is preferable that there are many crystal grains having a crystal phase composed of K _m NbO ₃ as described above, and it is not preferable that crystal grains other than the above are present as a different phase.

Presence of Cu in the grains and/or at the grain boundaries strengthens the bonding force between the crystal grains, thereby increasing the mechanical strength of the piezoelectric composition. In addition, the Cu content is related to the above-described “m”, and by setting the Cu content and the range of “m” to the above-described range, Cu becomes a solid solution in the crystal grains or grain boundaries. , and a heterogeneous phase containing Cu is less likely to be formed. As a result, the bonding strength between crystal grains can be further enhanced.

Moreover, the mechanical quality factor Qm can be improved by containing Cu. However, if the Cu content is too high, leakage current may occur due to voltage application during the polarization treatment of the piezoelectric composition, resulting in insufficient polarization. In this case, the polarization becomes insufficient, and the piezoelectric characteristics exhibited by aligning the direction of the spontaneous polarization in a predetermined direction are conversely deteriorated. Therefore, in the present embodiment, by containing Cu within the above range and by setting the range of "m" to the above range, it is possible to suppress the heterophase that is the main cause of the leakage current. As a result, sufficient polarization treatment can be performed. Therefore, since the effect of Qm improvement is obtained, Qm can be improved.

"x" is preferably 0.200 or more, more preferably 0.600 or more.

In the piezoelectric composition according to the present embodiment, when the content of Ge in terms of Ge element is y mol % with respect to 1 mol (100 mol %) of the composite oxide, "y" is 0.000<y≦ Satisfy the relation that is 1.500.

If Ge is contained within the above range, the expression of deliquescence peculiar to potassium niobate compounds is suppressed, and the potassium niobate compound-based piezoelectric composition exhibits high reliability even in a high-temperature and high-humidity environment. be able to. However, if the Ge content is too high, Ge-derived heterogeneous phases are likely to be formed, and the mechanical strength of the piezoelectric composition tends to decrease.

"y" is preferably 0.100 or more, more preferably 1.000 or more.

Moreover, the piezoelectric composition according to the present embodiment is composed of crystal grains having a perovskite structure, that is, crystal grains composed of a composite oxide, and grain boundaries.

In this embodiment, Ge is mainly contained in grain boundaries. It is considered that the deliquescence of the piezoelectric composition can be suppressed by including Ge in the grain boundaries. Therefore, it is preferable that the amount of solid solution of Ge in the grains of the crystal grains is small, and it is more preferable that Ge does not dissolve in the grains of the crystal grains.

The present inventors believe that the deliquescence phenomenon of the potassium niobate compound is that the potassium contained in the potassium niobate compound undergoes a hydration reaction with moisture in the air, and as a result, that portion becomes brittle, weakening the bonding force between crystal grains. We speculate that it is caused by

In the present embodiment, the inclusion of germanium in the grain boundaries facilitates the conversion of potassium from a form that readily reacts with hydration to a form that does not easily react with hydration, thereby suppressing deterioration in mechanical strength due to the deliquescence phenomenon. .

The piezoelectric composition according to this embodiment may contain other components in addition to the components described above. For example, transition metal elements other than Nb and Cu (elements of groups 3 to 11 in the long period periodic table), alkaline earth metal elements, group 12 elements in the long period periodic table and in the long period periodic table At least one of Group 13 metal elements may be contained. This is because other piezoelectric characteristics than Qm, particularly the electromechanical coupling coefficient (k), can be improved.

Specifically, examples of transition metal elements other than rare earth elements include chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), tungsten (W), molybdenum (Mo ) are exemplified. Examples of rare earth elements include yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb ), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb).

Examples of alkaline earth metal elements include magnesium (Mg) and strontium (Sr). Examples of group 12 elements include zinc (Zn). Examples of group 13 metal elements include aluminum (Al), gallium (Ga), and indium (In).

The piezoelectric composition according to the present embodiment may contain lead (Pb) as an impurity, but the content thereof is preferably 1% by mass or less in 100% by mass of the piezoelectric composition. More preferably no. From the viewpoint of pollution reduction, environmental friendliness, and ecology, the volatilization of Pb during firing can be suppressed to a minimum, and an electronic device equipped with a piezoelectric element containing the piezoelectric composition according to the present embodiment can be manufactured. This is because it is possible to minimize the release of Pb into the environment after being distributed in the market and discarded.

The average crystal grain size of crystal grains constituting the piezoelectric composition according to this embodiment may be controlled from the viewpoint of exhibiting piezoelectric properties and mechanical strength. In this embodiment, the average crystal grain size is preferably 0.5 μm to 20 μm, for example.

(2. Manufacturing method of piezoelectric element)
Next, an example of a method for manufacturing a piezoelectric element will be described below.

First, starting materials for the piezoelectric composition are prepared. A compound containing K and a compound containing Nb can be used as starting materials for the composite oxide. Compounds containing K include, for example, carbonates and hydrogen carbonate compounds. Examples of compounds containing Nb include oxides.

As a starting raw material of copper, copper alone or a compound containing copper may be used. In this embodiment, it is preferably an oxide containing copper. As a starting material for germanium, germanium alone or a compound containing germanium may be used as in the case of copper. In this embodiment, an oxide containing germanium is preferable.

After weighing the prepared starting materials of the composite oxide in a predetermined ratio, they are mixed for 5 to 20 hours using, for example, a ball mill. The mixing method may be wet mixing or dry mixing. For wet blending, dry the blended powder. Subsequently, the mixed powder or a molded body obtained by molding the mixed powder is heat-treated (calcined) in the atmosphere at 750 to 1050 ° C. for 1 to 20 hours to obtain a calcined powder of a composite oxide. .

The composite oxide constituting the obtained calcined powder has a perovskite structure represented by the general formula _KNbO3 .

When the obtained calcined powder is agglomerated, it is preferable to pulverize the calcined powder for a predetermined time using a ball mill, for example, to obtain pulverized powder. A starting raw material of copper and a starting raw material of germanium weighed in a predetermined ratio are added to the calcined powder or pulverized powder, and mixed for 5 to 20 hours using, for example, a ball mill to obtain a mixed powder of the piezoelectric composition. obtain. The mixing method may be wet mixing or dry mixing. In the case of wet mixing, the powder mixture is dried to obtain a powder mixture of the piezoelectric composition.

The method of molding the mixed powder of the piezoelectric composition is not particularly limited, and may be appropriately selected according to the desired shape, dimensions, and the like. When performing press molding, a predetermined binder and, if necessary, additives are added to the mixed powder of the piezoelectric composition, and the mixture is molded into a predetermined shape to obtain a compact. Alternatively, a compact may be obtained by using a granulated powder obtained by adding a predetermined binder or the like to a mixed powder of the piezoelectric composition and granulating the mixture. If necessary, the obtained compact may be subjected to further pressure treatment such as CIP.

The resulting compact is subjected to binder removal treatment. As the binder removal conditions, the holding temperature is preferably 400° C. to 800° C., and the temperature holding time is preferably 2 hours to 8 hours.

Subsequently, the compact after the binder removal treatment is fired. As the firing conditions, the holding temperature is preferably 950° C. to 1060° C., the temperature holding time is preferably 2 hours to 4 hours, and the temperature rising and cooling rate is preferably about 50° C./hour to 300° C./hour. is preferably an oxygen-containing atmosphere.

The piezoelectric composition obtained as a sintered body is polished, if necessary, and an electrode paste is applied and baked to form an electrode. The method of forming the electrodes is not particularly limited, and the electrodes may be formed by vapor deposition, sputtering, or the like.

By applying an electric field of 2 kV/mm to 5 kV/mm in oil at a predetermined temperature for about 5 minutes to 1 hour, the sintered body on which the electrodes are formed is subjected to polarization treatment. After the polarization treatment, a piezoelectric composition having spontaneous polarization aligned in a predetermined direction is obtained.

The piezoelectric composition after the polarization treatment is processed into a predetermined size as necessary to form a plate-like piezoelectric body portion 1 . Next, electrodes 2 and 3 are formed on the piezoelectric portion 1 by vapor deposition or the like, thereby obtaining the piezoelectric element shown in FIG.

(3. Effects of this embodiment)
In this embodiment, potassium niobate having a perovskite structure is employed as the composite oxide contained as a main component in the piezoelectric composition, and copper (Cu) and germanium (Ge) are added to the piezoelectric composition within the above ranges. is contained in

Since Cu contained within the above range is not excessively contained in the composite oxide, it is difficult to form a different phase different from the crystal grains forming the composite oxide. That is, Cu is dissolved in the inside of the crystal grains forming the composite oxide, or exists in the grain boundaries formed between the crystal grains. Presence of Cu in such a form strengthens the bonding force between crystal grains, thereby improving the mechanical strength of the piezoelectric composition.

The fired piezoelectric composition may be processed during, for example, polarization treatment and production of piezoelectric elements. If the piezoelectric composition does not have good mechanical strength, there will be a problem that defective products will be produced due to chipping, cracking, etc. caused by insufficient strength of the piezoelectric composition during processing. If such defective products occur, the yield decreases and high productivity cannot be achieved. In addition, since mechanical energy and electrical energy are repeatedly applied to the piezoelectric composition, it is necessary to have strength to withstand these. Since the piezoelectric composition according to the present embodiment has good mechanical strength, it has good workability, so that the yield can be increased and the production efficiency of piezoelectric elements can be improved. Furthermore, the piezoelectric composition according to this embodiment has sufficient strength to withstand mechanical energy and electrical energy that are repeatedly applied.

Also, although Cu has the effect of improving the mechanical quality factor Qm, when the content of Cu increases, the leakage current increases during the polarization treatment of the piezoelectric composition, resulting in insufficient polarization treatment. On the contrary, there is a problem that Qm is lowered. Therefore, in the present embodiment, by controlling the "m" of the composite oxide together with the Cu content, the occurrence of heterogeneous phases is suppressed, and the range of the Cu content in which sufficient polarization processing can be performed is increased. High Qm can be realized.

Ge contained within the above range can improve the reliability in a high-temperature and high-humidity environment while maintaining the mechanical strength and piezoelectric properties of the piezoelectric composition.

In addition, since Ge is included in the grain boundaries, potassium, which is easily hydrated, is easily converted into a form which is difficult to be hydrated. As a result, deterioration of the piezoelectric composition due to the deliquescence phenomenon is suppressed, and reliability in a high-temperature, high-humidity environment can be enhanced.

(4. Modification)
In the above-described embodiment, the piezoelectric element having a single-layered piezoelectric portion has been described, but the piezoelectric element may have a structure in which the piezoelectric portions are laminated. Alternatively, a piezoelectric element having a configuration in which these are combined may be used.

As a piezoelectric element having a structure in which piezoelectric portions are laminated, for example, a piezoelectric element 50 shown in FIG. 2 is exemplified. This piezoelectric element 50 includes a laminate 10 in which a plurality of piezoelectric layers 11 made of the piezoelectric composition according to the present embodiment and a plurality of internal electrodes 12 are alternately laminated. A pair of terminal electrodes 21 and 22 are formed at both ends of the laminate 10 so as to be electrically connected to the internal electrode layers 12 alternately arranged inside the laminate 10 .

The thickness of each layer (interlayer thickness) of the piezoelectric layer 11 is not particularly limited, and can be arbitrarily set according to the desired characteristics, application, and the like. Usually, the interlayer thickness is preferably about 1 μm to 100 μm. The number of layers of the piezoelectric layer 11 is not particularly limited, and can be arbitrarily set according to the desired properties, application, and the like.

As a method for manufacturing the piezoelectric element 50 shown in FIG. 2, a known method may be used. For example, a green chip that becomes the laminate 10 shown in FIG. After that, the laminate 10 is manufactured by printing or transferring the terminal electrodes to the laminate 10 and baking the laminate. Examples of methods for manufacturing green chips include a normal printing method using paste and a sheet method. In the printing method and the sheet method, a green chip is formed using a paste obtained by mixing raw material powder of the piezoelectric composition described above and a vehicle in which a binder is dissolved in a solvent to form a paste.

Although the embodiments of the present invention have been described above, the present invention is by no means limited to the above embodiments, and may be modified in various ways within the scope of the present invention.

The present invention will be described in more detail below using examples and comparative examples. However, the present invention is not limited to the following examples.

First, potassium hydrogen carbonate (KHCO ₃ ) powder and niobium oxide (Nb ₂ O ₅ ) powder were prepared as starting materials for composite oxide (K _m NbO ₃ ), which is the main component of the piezoelectric composition. Powders of copper oxide (CuO) and germanium oxide (GeO ₂ ) were prepared as starting materials for copper (Cu) and germanium (Ge) as components contained in the piezoelectric composition.

The prepared starting materials were weighed so that the fired piezoelectric composition (sintered body) had the composition shown in Table 1. The weighed powders of KHCO ₃ and Nb ₂ O ₅ were mixed by a ball mill for 16 hours and then dried at 120° C. to obtain a mixed powder. The obtained mixed powder was press-molded and calcined at 1000° C. for 4 hours to obtain a calcined composite oxide. Subsequently, this calcined body was pulverized by a ball mill for 16 hours to obtain a pulverized powder.

Weighed powders of CuO and GeO ₂ were added to the pulverized powder obtained, mixed for 16 hours in a ball mill, and then dried at 120° C. to obtain raw material powder of the piezoelectric composition. PVA as a binder was added to the obtained raw material powder of the piezoelectric composition and granulated by a known method. Next, the obtained granulated powder was press-molded with a press molding machine under a load of 196 MPa to obtain a flat plate-shaped compact.

The plate-like molded body thus obtained was subjected to binder removal treatment at 550° C. for 2 hours. The molded body after the binder removal treatment was fired at 1050° C. for 2 hours in an air atmosphere to obtain a piezoelectric composition (sintered body).

The obtained sintered body was polished to form a parallel plate with a thickness of 1.0 mm, and after printing silver paste on both sides of the parallel plate-shaped sintered body, baking was performed at 800 ° C. to form a counter silver electrode. The sintered body was cut into a length of 12 mm and a width of 3 mm with a dicing saw according to JEITA EM-4501M of the Japan Electronics and Information Technology Industries Association standard to obtain a sample before polarization. Finally, an electric field of 3 kV/mm was applied to the pre-polarized sample in silicone oil at 150° C. for 5 minutes to polarize the piezoelectric composition. 1 to 8) were obtained.

The obtained samples were measured for mechanical strength and mechanical quality factor Qm as follows.

Using a double-sided lapping machine and a dicing saw, the piezoelectric composition (sintered body) was ground and cut into a length of 7.2 mm, a width of 2.5 mm, and a thickness of 0.32 mm, and a sample for mechanical strength measurement was obtained. got Using INSTRON 5543, the maximum load (N) when the samples for mechanical strength measurement were broken by 3-point bending with a distance between fulcrums of 5 mm was measured for 20 samples, and the mechanical strength was calculated. In this example, in consideration of practical workability, samples having a mechanical strength of 70 MPa or more were judged to be good. Table 1 shows the results.

Qm was measured by 4194A IMPEDANCE/GAIN-PHASE ANALYZER (manufactured by HEWLETT PACKARD). In this example, samples with a Qm of 200 or more were judged to be good. Table 1 shows the results.

In addition, in the column of the mechanical quality factor Qm in Table 1, when "-" is indicated, the predetermined piezoelectric characteristics were not obtained because the polarization treatment of the piezoelectric composition was not sufficiently performed or dielectric breakdown occurred during the polarization treatment. was not obtained, indicating that Qm could not be measured.

Furthermore, the samples after measuring the mechanical strength and Qm were subjected to a test of exposure to a high-temperature and high-humidity environment, and then the mechanical strength and Qm were measured to evaluate the reliability of the samples. Specifically, the sample after measuring the mechanical strength and Qm is placed in a constant temperature bath kept at room temperature, and the target temperature in the constant temperature bath is 85 ° C. (with an error of ± 2 ° C.). The target relative humidity was an environment of 85% RH (with an error of ±2% allowed). After maintaining this environment for 1000 hours, the sample was taken out from the constant temperature bath, and the mechanical strength and Qm were measured in the same manner as above. From the obtained measured values, the mechanical strength and Qm deterioration rate were calculated according to the following equations. In this example, a sample with a mechanical strength of 70 MPa or more and both deterioration rates of 10% or less is indicated as "A" in Table 1, and the mechanical strength is less than 70 MPa and both deterioration rates are 10%. The following samples are denoted as "B" in Table 1, and the mechanical strength is less than 70 MPa and at least one of the deterioration rates exceeds 10%, or at least one of the deterioration rates is unmeasurable. In Table 1, it was described as "C". Table 1 shows the results.
Mechanical strength deterioration rate (%) = (mechanical strength before high temperature and high humidity test - mechanical strength after high temperature and high humidity test) x 100 / deterioration rate (%) of mechanical strength Qm before high temperature and high humidity test = (Qm before high temperature and high humidity test - Qm after high temperature and high humidity test) × 100 / Qm before high temperature and high humidity test

Further, STEM-EDS analysis of the cross section of the sample confirmed that Ge was present at the grain boundary between two grains or the grain boundary triple point, except for the samples of Comparative Examples 5 and 7.

A cross-sectional STEM image of the sample of Example 7 is shown in FIG. FIG. 4 shows the result of EDS point analysis of the STEM image shown in FIG. EDS point analysis was performed at points 1 to 5 shown in FIG. Points 1 to 3 are analysis points on two grain boundaries, and points 4 and 5 are analysis points on crystal grains.

From Table 1, in the composite oxide represented by the composition formula K _m NbO ₃ , by setting “m” within the above range and the content of copper and germanium with respect to the composite oxide within the above range, good It was confirmed that a high mechanical strength was obtained, Qm was improved, and high reliability was obtained. In particular, Comparative Examples 5 and 7, which do not contain germanium, were confirmed to have a large deterioration rate.

From FIGS. 3 and 4, it was confirmed that germanium was mainly contained in grain boundaries and hardly contained in crystal grains.

INDUSTRIAL APPLICABILITY The piezoelectric composition according to the present invention can achieve both good mechanical strength and good Qm, and has high reliability, so that it can be suitably used for piezoelectric elements in various fields.

DESCRIPTION OF SYMBOLS 5... Piezoelectric element 1... Piezoelectric part 2, 3... Electrode 50... Piezoelectric element 10... Laminated body 11... Piezoelectric layer 12... Internal electrode layer 21, 22... Terminal electrode

Claims (5)

A piezoelectric composition represented by the composition formula K _m NbO ₃ and containing a composite oxide having a perovskite structure, copper, and germanium,
m in the composition formula satisfies the relationship 0.970 ≤ m ≤ 0.999,
With respect to 1 mol of the composite oxide, x mol % of the copper is contained in terms of copper element, and y mol % of the germanium is contained in terms of germanium element,
The x satisfies the relationship 0.100 ≤ x ≤ 1.000,
A piezoelectric composition, wherein y satisfies the relationship 0.000<y≦1.500. 2. The piezoelectric composition according to claim 1, wherein said m satisfies the relationship 0.991≤m≤0.999. A piezoelectric composition represented by the composition formula K _m NbO ₃ and containing a composite oxide having a perovskite structure, copper, and germanium,
m in the composition formula satisfies the relationship 0.970 ≤ m ≤ 0.999,
The piezoelectric composition is composed of crystal grains having a perovskite structure and grain boundaries,
The piezoelectric composition, wherein the grain boundary contains the germanium. 4. The piezoelectric composition according to claim 3, wherein the grain boundaries contain one or more elements selected from the group consisting of potassium, niobium and copper. A piezoelectric element comprising the piezoelectric composition according to claim 1 .

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