1. A piezoelectric composition, wherein,

comprises a main component comprising an alkali metal niobate compound,

the carbon content is 350 ppm by weight or more and 700 ppm by weight or less.

2. The piezoelectric composition according to claim 1,

the alkali metal niobate series compound has a composition formula (K)_xNa_y)NbO₃It is shown that,

x is more than or equal to 0.5000 and less than or equal to 1.000,

the sum of said x and said y satisfies 0.980. ltoreq. x + y. ltoreq.1.000.

3. The piezoelectric composition according to claim 1 or 2,

the carbon content is 380 ppm by weight or more and 600 ppm by weight or less.

4. The piezoelectric composition according to claim 1 or 2,

the CV value of the concentration distribution relating to the carbon in the cross section of the piezoelectric composition is 0.5 or more and 2.5 or less.

5. An electronic component, wherein,

a piezoelectric composition comprising the piezoelectric composition according to any one of claims 1 to 4.

Background

The piezoelectric composition has an effect of generating charges on the surface by receiving a stress from the outside (piezoelectric effect) and an effect of generating distortion by applying an electric field from the outside (inverse piezoelectric effect) based on spontaneous polarization caused by variation of charges in a crystal. That is, the piezoelectric composition is capable of converting mechanical energy and electrical energy to each other.

As such a piezoelectric composition, as shown in patent document 1, lead zirconate (PbZrO) is often used₃) And lead titanate (PbTiO)₃) A lead-based piezoelectric composition (hereinafter, PZT-based compound) is formed. However,the lead-based piezoelectric composition contains about 60 to 70 wt% of lead oxide (PbO) having a low melting point, and the lead oxide is easily volatilized during firing. Therefore, from the viewpoint of environmental load, the lead-free piezoelectric composition is a very important problem.

In view of this problem, attention has recently been paid to alkali metal niobate compounds as shown in patent document 2 as environmentally friendly novel piezoelectric compositions. The alkali niobate-based compound has relatively high piezoelectric characteristics compared to other non-lead-based piezoelectric compositions. However, the alkali metal niobate-based compound is inferior to the PZT-based compound in piezoelectric characteristics, and is not sufficient as a substitute material for the PZT-based compound. In particular, improvement in the mechanical quality factor Qm and improvement in the stability of Qm over time are sought.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2006-196717

Patent document 2: japanese patent laid-open No. 2014-177355

Disclosure of Invention

Technical problem to be solved by the invention

In view of the above circumstances, an object of the present invention is to provide a non-lead-based piezoelectric composition having a high mechanical quality factor Qm and excellent stability of Qm over time, and an electronic component including the piezoelectric composition.

Technical solution for solving technical problem

In order to achieve the above object, a piezoelectric composition according to the present invention comprises a main component composed of an alkali metal niobate-based compound,

the carbon content is 350 ppm by weight or more and 700 ppm by weight or less.

Conventionally, in a piezoelectric composition, it is considered that the smaller the content of carbon, the better. Actually, patent document 1 discloses that in a piezoelectric element made of a PZT-based compound, reduction of lead oxide can be suppressed by reducing the amount of carbon contained in the laminate, and the piezoelectric characteristics are improved. As a result of intensive studies, the present inventors have found that a piezoelectric composition comprising an alkali metal niobate compound can have a high mechanical quality factor Qm and can have good stability of Qm over time by containing a predetermined amount of carbon, contrary to the conventional technical idea.

In the piezoelectric composition of the present invention, the alkali metal niobate-based compound has a composition formula (K)_xNa_y)NbO₃It is shown that the flow rate of the gas, preferably,

x is more than or equal to 0.5000 and less than or equal to 1.000,

the sum of said x and said y satisfies 0.980. ltoreq. x + y. ltoreq.1.000.

By satisfying the above composition with the alkali metal niobate-based compound, the deliquescence phenomenon is suppressed, and the requirements for high Qm and good stability over time can be satisfied.

The carbon content is preferably 380 ppm by weight or more and 600 ppm by weight or less. By controlling the content of carbon contained in the piezoelectric composition within the above range, Qm is further improved and stability over time becomes better. Further, the insulation resistance is also as high as 1 × 10¹⁰Omega cm or more. Since the insulation resistance becomes high, it is difficult for dielectric breakdown to occur even if a high voltage is applied at the time of polarization treatment or the like. That is, the withstand voltage characteristics of the piezoelectric composition are improved.

In the cross section of the piezoelectric composition of the present invention, the CV value (coefficient of variation) of the concentration distribution relating to carbon is preferably 0.5 or more and 2.5 or less.

The CV value is an index indicating the degree of dispersion of the concentration distribution, and means that the lower the CV value, the less the deviation of the concentration distribution. In the piezoelectric composition of the present invention, when the CV value of the carbon concentration distribution is within the above range, Qm is further improved and the stability of Qm with time is further improved. In addition, the insulation resistance is further as high as 1 × 10¹²Omega cm or more, the withstand voltage characteristics are further improved.

The element including the piezoelectric composition of the present invention can convert mechanical energy and electric energy into each other, and can be widely used as an electronic component in various fields. For example, the piezoelectric composition of the present invention can be suitably used for a piezoelectric actuator using the inverse piezoelectric effect. The piezoelectric actuator including the piezoelectric composition of the present invention can obtain a minute displacement with high accuracy against an applied voltage and has a high response speed, and therefore, can be used for, for example, a driving element of a construction member, a head driving element of an HDD, a head driving element of an ink jet printer, a driving element of a fuel injection valve, and a haptic device. In addition, the piezoelectric composition of the present invention can also be used as a piezoelectric buzzer or a piezoelectric speaker utilizing the inverse piezoelectric effect.

Further, the piezoelectric composition of the present invention can be suitably used for a sensor for reading a minute force or displacement amount by utilizing the piezoelectric effect. In addition, since the piezoelectric composition of the present invention has excellent responsiveness, the piezoelectric composition itself or an elastic body in a bonding relationship with the piezoelectric composition can be excited by application of an alternating electric field to generate resonance. Therefore, the present invention can be applied to a piezoelectric transformer, an ultrasonic motor, or the like.

Drawings

Fig. 1 is a schematic perspective view showing a piezoelectric element according to an embodiment of the present invention.

Fig. 2 is a schematic diagram showing a cross section of the piezoelectric composition.

Fig. 3 is a schematic cross-sectional view showing a modification of the piezoelectric element of the present invention.

Description of symbols:

5 … piezoelectric element

1 … piezoelectric body

4 … main phase particles

6 … grain boundaries

8 … out of phase

2. 3 … electrode

50 … (laminated) piezoelectric element

10 … laminate

11 … piezoelectric layer

12 … internal electrode layer

21. 22 … terminal electrode

Detailed Description

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

First, a piezoelectric element 5 (electronic component) to which the piezoelectric composition of the present embodiment is applied will be described. The 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 two principal surfaces of the piezoelectric body 1.

The piezoelectric body 1 is a sintered body and is composed of the piezoelectric composition of the present embodiment. Details of the piezoelectric composition will be described later. The pair of electrodes 2 and 3 are each made of a conductive material, and the conductive material is not particularly limited and can be arbitrarily set according to desired characteristics, applications, and the like. Examples of the conductive material included in the electrodes 2 and 3 include gold (Au), silver (Ag), platinum (Pt), palladium (Pd), Ni (nickel), copper (Cu), and the like, or an alloy containing any of the above elements.

In fig. 1, the piezoelectric body 1 has a rectangular parallelepiped shape, but the shape of the piezoelectric body 1 is not particularly limited and can be arbitrarily set according to desired characteristics, applications, and the like. The size of the piezoelectric body 1 is not particularly limited, and may be set arbitrarily according to desired characteristics, application, and the like.

The piezoelectric body 1 is polarized in a predetermined direction. For example, in the piezoelectric element 5 shown in fig. 1, polarization is performed in the thickness direction of the piezoelectric body 1, that is, in the direction in which the electrodes 2 and 3 face each other. For example, an external power supply, an external circuit, or the like is electrically connected to the electrodes 2 and 3 via unillustrated wirings or the like. Therefore, for example, if a predetermined voltage is applied to the piezoelectric body 1 from an external power supply via the electrodes 2 and 3, the piezoelectric body 1 converts electric energy into mechanical energy by the inverse piezoelectric effect, and the piezoelectric body 1 vibrates in a predetermined direction. When stress is applied to the piezoelectric body 1 from the outside, electric charges generated by the piezoelectric effect can be taken out to an external circuit through the electrodes 2 and 3.

Next, the piezoelectric composition of the present embodiment will be explained. Fig. 2 is a sectional view of the piezoelectric body 1 shown in fig. 1, that is, a sectional view of the piezoelectric composition. As shown in fig. 2, the piezoelectric composition of the present embodiment has main phase particles 4, grain boundaries 6, which are boundaries between the main phase particles 4, and a different phase 8 present between the main phase particles 4.

At the mainThe phase particles 4 contain a compound having the general formula ABO₃The perovskite-structured composite oxide is used as a main component. In the present embodiment, the main component is a component that accounts for 90 mol% or more of 100 mol% of the piezoelectric composition.

In the above perovskite structure, ABO is occupied by an element having a large ionic radius, for example, an alkali metal element, an alkaline earth metal element or the like₃The A site of (A), and ABO is occupied by an element having a small ionic radius, such as a transition metal element₃Trend of the B site of (1). And BO consisting of B site element and oxygen₆The oxygen octahedrons form a three-dimensional network sharing vertices, and the voids of the network are filled with a-site elements to form a perovskite structure.

In the present embodiment, the composite oxide which is the main component of the piezoelectric composition is an alkali metal niobate-based compound, and the general formula ABO described above₃By the composition formula (K)_xNa_y)NbO₃And (4) showing. That is, the a site element is potassium (K) and/or sodium (Na), and the B site element is niobium (Nb).

In the above composition formula, "x" represents the ratio of the number of atoms of K to the total number of atoms of the B site element, and "y" represents the ratio of the number of atoms of Na to the total number of atoms of the B site element. Thus, "x + y" represents the ratio of the total number of atoms of the a-site elements relative to the total number of atoms of the B-site elements, the so-called a/B ratio.

In the present embodiment, "x" can be 0 < x.ltoreq.1.000, preferably 0.5000 to 1.000, more preferably 0.800. ltoreq.x.ltoreq.1.000, and still more preferably 0.800. ltoreq.x.ltoreq.0.998. That is, in the present embodiment, it is preferable to increase the ratio of K in the a site.

Further, it is preferable that "x + y" is 0.970. ltoreq. x + y. ltoreq.1.000, more preferably 0.980 or more and 1.000 or less, and still more preferably 0.980 or more and 0.998 or less. In the present embodiment, a good mechanical strength can be obtained by making the B site element (Nb) present in an excess amount over the a site element (K, Na). In addition, in the case where "x + y" is larger than the above-mentioned range (in the case of exceeding 1.0), since the obtained piezoelectric composition shows high deliquescence, there is a tendency that the strength is significantly reduced. On the other hand, when "x + y" is less than the above range, the density of the obtained piezoelectric composition tends to decrease, and the mechanical strength tends to decrease.

Further, a part of the B site element may be replaced with tantalum (Ta). However, when Nb is replaced with Ta, the ratio of the number of atoms of Ta in the B site is preferably 10% or less.

In addition, the piezoelectric composition of the present embodiment preferably contains copper (Cu) as an subcomponent. The content of Cu in the piezoelectric composition is preferably in the range of 0 to 1.5 parts by mole in terms of CuO with respect to 100 parts by mole of the alkali metal niobate-based compound as the main component. When Cu is contained as an accessory component, the form of existence thereof is not particularly limited, and Cu may be dissolved in the particles of the main phase particles 4 composed of the main component or may exist in the grain boundary 6. In the case where Cu exists in the grain boundary 6, it may form a compound with other elements.

Since Cu exists in the grains of the main phase particles 4 and/or the grain boundaries 6, the bonding force between the main phase particles 4 is enhanced, and the mechanical strength of the piezoelectric composition can be improved. The content of Cu is related to "x + y" described above, and by setting the content of Cu and the range of "x + y" to the above range, Cu can be dissolved in the main phase particles 4 or remain in the grain boundary 6. As a result, the bonding force between the main phase grains 4 can be further increased via the grain boundaries 6.

In addition, Cu added as a subcomponent contributes to an improvement in the mechanical quality factor Qm. However, if the Cu content is too large, a leakage current due to an applied voltage may be generated during the polarization treatment of the piezoelectric composition, and sufficient polarization may not be performed. In this case, the polarization is insufficient, and the piezoelectric properties exhibited by aligning the direction of spontaneous polarization with a predetermined direction are rather degraded. In the present embodiment, when Cu is added as a subcomponent, generation of a leakage current can be suppressed by controlling the content of Cu and the range of "x + y" to be within the above-described predetermined range, and sufficient polarization treatment can be performed. As a result, the mechanical quality factor Qm is improved.

In addition, the piezoelectric composition of the present embodiment may contain other components as subcomponents other than Cu. For example, at least one selected from transition metal elements (elements of groups 3 to 11 in the long periodic table), group 2 elements, group 12 elements, group 13 elements, and germanium (Ge) in the long periodic table may be contained in addition to Nd, Ta, and Cu.

Specifically, examples of the transition metal element other than the rare earth element include chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), tungsten (W), molybdenum (Mo), and the like. Examples of the rare earth element 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 the group 2 element include magnesium (Mg) and strontium (Sr), examples of the group 12 element include zinc (Zn), and examples of the group 13 element include aluminum (Al), gallium (Ga), and indium (In).

The subcomponent other than Cu may be added together with the subcomponent Cu or may be added in place of the subcomponent Cu. Among the above subcomponents (other than Cu), Ge, Cr, Ni, and Zn are preferably selected.

When Ge is added as a subcomponent, the content of Ge is GeO based on 100 parts by mole of the alkali metal niobate-based compound as the main component₂The content is preferably in the range of 0 to 1.5 parts by mole in terms. Ge is mainly contained in the grain boundary 6, and it is considered that the deliquescence phenomenon of the piezoelectric composition can be suppressed by containing Ge in the grain boundary 6. Therefore, the amount of Ge solid solution into the grains of the main phase grains 4 is preferably small, and Ge is more preferably not solid-dissolved in the grains of the main phase grains 4.

The deliquescence phenomenon of the alkali niobate-based compound is considered to be caused by hydration reaction between the alkali components (K, Na) contained in the compound and moisture in the air, and as a result, the portion becomes fragile, and the bonding force between the main phase particles 4 is weakened. It is considered that the inclusion of Ge in the grain boundary 6 makes it easy to convert the alkali metal component from a form in which the hydration reaction is likely to occur to a form in which the hydration reaction is unlikely to occur, and thereby suppresses the deterioration of the mechanical strength due to the deliquescence phenomenon.

On the other hand, when Cr, Ni or Zn is added as a subcomponent, the contents of these elements are CrO based on 100 parts by mole of the alkali metal niobate-based compound as a main component_3/2The content is preferably in the range of 0 to 2.0 parts by mole in terms of NiO or ZnO. The electromechanical coupling coefficient k is obtained by including the subcomponents of Cr, Ni or Zn in the above-mentioned ranges₃₁And a tendency to increase the dielectric breakdown strength.

The piezoelectric composition of the present embodiment may contain lead (Pb) as an impurity, but the content thereof is preferably 1 mass% or less with respect to 100 mass% of the piezoelectric composition, and more preferably contains no Pb.

The piezoelectric composition of the present embodiment contains carbon in addition to the main component and the subcomponent described above. Carbon is contained because unreacted alkali metal remains in the calcination process described later. In the present embodiment, the content of carbon contained in the piezoelectric composition is 350 ppm by weight or more and 700 ppm by weight or less, more preferably 380 ppm by weight or more and 600 ppm by weight or less, and still more preferably 400 ppm by weight or more and 500 ppm by weight or less. As described in detail later, when carbon is contained in the above range, high Qm can be obtained and the stability of Qm with time is good.

The mechanical quality factor Qm is an index representing the sharpness of mechanical vibration at the resonance frequency, and the higher the value, the more excellent the characteristics. The Qm is required to be stable and not to change (in particular, not to decline) with the passage of time, and the "stability of Qm with time" in the present embodiment is a measure representing the stability of Qm.

The carbon contained in the piezoelectric composition is mainly present in the grain boundary 6 and the hetero-phase 8. The carbon is preferably not dissolved in the particles of the main phase particles 4. The hetero-phase 8 containing carbon may be present between the main phase particles 4, i.e., in a part of the grain boundary 6, and contains oxygen, K, Na, Nb, Cu, Zn, or the like in addition to carbon. It is considered that the presence of the heterogeneous phase 8 containing carbon makes the piezoelectric composition as a sintered body denser. Further, it is considered that the inclusion of K, Na, Nb, and the like, which are also included in the main component, in the heterogeneous phase 8 including carbon enables the binding force between the main phase particles 4 to be maintained in a higher state.

The average particle diameter of the heterogeneous phase 8 containing carbon is preferably about the same as or larger than the average particle diameter of the main phase particles 4. Here, the average particle diameter of the main phase particles 4 may be controlled from the viewpoint of the exertion of piezoelectric characteristics and mechanical strength, and in the present embodiment, for example, is preferably set to 0.5 μm or more and 20 μm or less in terms of circle-equivalent diameter. On the other hand, the average particle diameter of the heterogeneous phase 8 containing carbon is preferably 1.0 to 3.0 times the average particle diameter of the main phase particles 4 in terms of circle-equivalent diameter. The average particle size of the main phase particles 4 and the average particle size of the hetero-phase 8 can be determined by observing a cross section of the piezoelectric composition with a Scanning Electron Microscope (SEM), a Scanning Transmission Electron Microscope (STEM), or the like, and analyzing the obtained cross-sectional photograph.

Further, it is preferable that the carbon contained in the piezoelectric composition is not locally concentrated but dispersed under a predetermined condition. Specifically, in any cross section of the piezoelectric composition of the present embodiment, the CV value (coefficient of variation) of the concentration distribution with respect to carbon is preferably 0.50 or more and 2.50 or less, and more preferably 0.50 or more and 2.00 or less. Further, the CV value is expressed in terms of standard deviation/average value, and is an index indicating the degree of dispersion. A lower CV value means more uniform dispersion.

Here, in the present embodiment, the CV value of the carbon content and the concentration distribution thereof can be measured by, for example, the following method. First, the carbon content can be measured using a carbon sulfur analyzer (CS analyzer). In this CS analyzer, the piezoelectric composition is pulverized in a mortar or the like, and the pulverized powder is used as a measurement sample. Then, the powder sample is heated and burned in a high-frequency furnace in the apparatus to convert carbon contained in the sample into carbon dioxide (CO)₂) Converting sulfur to sulfur dioxide (SO)₂) The gas of (2). Further by measuring the produced CO by non-dispersive infrared absorption method or the like₂And SO₂And calculating the contents of carbon and sulfur contained in the measured sample. Therefore, the above-mentioned carbon content is a net content of carbon contained in the measurement sample (piezoelectric composition), and is preferablyThe measurement was carried out at least three times and calculated as an average value.

The CV value can be calculated by performing a mapping analysis using an electron beam microanalyzer (EPMA). In map analysis by EPMA, a predetermined cross section (measurement region) is irradiated with an electron beam at a constant interval, and component analysis is performed for each measurement point, whereby the concentration distribution of a specific element (measurement element) can be visualized, that is, mapped. The concentration of the specific element in each measurement point is represented as a luminance corresponding to the integrated intensity of the detection peak (peak of the characteristic X-ray of the specific element), and a higher level of the luminance means a higher proportion of the specific element existing in the measurement point. The measurement interval in the mapping analysis corresponds to the size of one pixel in the obtained mapping data, and the number of measurement points corresponds to the number of pixels in the mapping data.

The CV value of the concentration distribution related to carbon was calculated based on the average value and standard deviation of the population, with the data of the brightness at each measurement point as the population. In the calculation of the CV value, the measurement interval in the mapping analysis is preferably less than 1 μm square, and the number of measurement points is preferably at least 128 × 128 or more. The size of the measurement region is preferably a region corresponding to a 50 μm square to 250 μm square (rectangular region may be used). Further, the CV value is preferably evaluated by changing the measurement area, performing the mapping analysis at least twice, and using the average value.

Next, an example of a method for manufacturing the piezoelectric element 5 shown in fig. 1 will be described below.

First, starting materials for the piezoelectric composition are prepared. As a starting material of the alkali metal niobate-based compound as a main component, a compound containing K, a compound containing Nb, and if necessary, a compound containing Na can be used. Examples of the compound containing K and the compound containing Na include a carbonate, a hydrogencarbonate compound, and the like. Examples of the Nb-containing compound include oxides and the like.

In addition, when the piezoelectric composition contains a subcomponent, a starting material of the subcomponent can be usedSuch as simple metals, oxides, complex oxides, carbonates, oxalates, acetates, aqueous oxides, halides, organometallic compounds, and the like. For example, when Cu is added as a subcomponent, the starting materials of Cu include Cu simple substance, copper oxide, and K_αCu_βTa_γO_δOr K_αCu_βNb_γO_δAnd the like, and copper oxide (CuO) is particularly preferably used.

The starting material for the main component and the starting material for the subcomponent are both powders, and the average particle diameter thereof is preferably in the range of 0.1 to 5.0. mu.m.

Next, the prepared starting materials of the main components are weighed in a predetermined ratio and mixed for 5 to 20 hours using a mixer such as a ball mill. The mixing method may be wet mixing or dry mixing. In the case of wet mixing, the mixed powder obtained after mixing is dried.

Next, the starting materials mixed in the above-described step are calcined. Here, it is considered that the carbon contained in the piezoelectric composition enters the piezoelectric composition by the reaction of the unreacted alkali metal component remaining after firing with carbon dioxide or the like in the atmosphere. That is, it is considered that the content of carbon contained in the piezoelectric composition is proportional to the remaining amount of the unreacted alkali metal component. Therefore, in order to control the carbon content or the degree of carbon dispersion within the above range, the form and conditions during the calcination are preferably controlled.

For example, the form during firing is preferably not a powder but a block (a temporary molded body). In this case, the mixed powder of the starting materials is press-molded in advance before the calcination to obtain a temporary molded body. In this case, a uniaxial press machine is preferably used as the molding machine, and the pressure during molding is set to about 10 to 50 MPa. Alternatively, a temporary molded body may be obtained using a cold isostatic press (CIP molding machine) or the like.

The conditions for the calcination are preferably such that the furnace atmosphere is an atmospheric atmosphere, the holding temperature is preferably 850 to 1030 ℃, and the holding time is preferably 1 to 20 hours. By calcining the temporary molded body under the above-mentioned conditions, a calcined body of the composite oxide can be obtained, in which an appropriate amount of unreacted alkali metal component is generated.

Further, the composite oxide constituting the calcined body obtained has a general formula of KNbO₃Or (K, Na) NbO₃The perovskite structure shown. The calcined body thus obtained is pulverized for a predetermined time by using a pulverizer such as a ball mill. The average particle diameter of the pulverized powder thus obtained is preferably 0.5 to 2.0. mu.m.

In addition, when the subcomponent is added, a starting material of the subcomponent weighed in a predetermined ratio is added to the pulverized powder and mixed to obtain a raw material powder of the piezoelectric composition. The mixing of the main component and the subcomponents can be carried out by wet mixing or dry mixing using various mixers such as a ball mill or a bead mill, similarly to the mixing of the main component starting material.

Using the thus obtained raw material powder, a molded body of the piezoelectric composition was produced. The method for molding the raw material powder of the piezoelectric composition is not particularly limited, and may be appropriately selected depending on the desired shape, size, and the like. When the piezoelectric composition is press-molded, a predetermined binder and, if necessary, additives such as a plasticizer, a dispersant, and a solvent are added to the raw material powder of the piezoelectric composition, and then the composite is molded into a predetermined shape to obtain a molded body. Further, the above binder and the like may be added to the raw material powder of the piezoelectric composition to granulate the powder, and the obtained granulated powder may be used to produce a molded body. Further, the molded article obtained may be subjected to a further pressure treatment by CIP or the like as necessary. As the binder, an acrylic binder, an ethyl cellulose binder, a polyvinyl butyral binder, or the like can be used.

The obtained molded article was subjected to binder removal treatment. The binder removal condition is preferably a holding temperature of 400 to 800 ℃, and a temperature holding time of 2 to 4 hours.

Subsequently, the binder-removed molded body is subjected to main firing. The conditions for the main firing are preferably 1000 to 1100 ℃, and the holding time is preferably 2 to 4 hours. In addition, it is preferable that both the temperature increase rate and the temperature decrease rate during the main firing are set to be in the range of 1.5 ℃/min to 5.0 ℃/min. Further, the furnace atmosphere at the time of firing is preferably an oxygen-containing atmosphere, and may be an atmospheric atmosphere.

After the above-described main firing, a piezoelectric composition as a sintered body was obtained. The content of carbon contained in the piezoelectric composition may vary depending on the composition of the main component and the kind of the added subcomponent.

The obtained sintered body is polished as necessary, and an electrode paste is applied to both principal surfaces thereof and baked, thereby forming a temporary electrode. The method for forming the temporary electrode is not particularly limited, and may be performed by vapor deposition, sputtering, or the like.

Next, the sintered body on which the temporary electrode is formed is subjected to polarization treatment. The sintered body is polarized by applying an electric field of 2kV/mm to 5kV/mm for about 5 minutes to 1 hour in an oil at a predetermined temperature (about 80 ℃ to 150 ℃). By this polarization treatment, a piezoelectric composition having spontaneous polarization aligned in a predetermined direction can be obtained.

Then, the piezoelectric composition after polarization treatment is processed into a predetermined size as necessary to form a plate-shaped piezoelectric body 1. Next, electrodes 2 and 3 are formed on the piezoelectric body 1 by a method such as baking of an electrode paste, vapor deposition, sputtering, or plating, thereby obtaining a piezoelectric element 5 shown in fig. 1. Further, the electrodes 2 and 3 may be directly transferred to temporary electrodes formed before the polarization treatment.

(summary of the present embodiment)

The piezoelectric composition of the present embodiment contains an alkali metal niobate-based compound as a main component, and contains carbon in the above range (350 to 700 ppm by weight).

As a result of intensive studies, the present inventors have found that a piezoelectric composition comprising an alkali metal niobate compound can have a high mechanical quality factor Qm and good stability of Qm over time by containing a predetermined amount of carbon, contrary to the conventional technical idea.

The reason why Qm and Qm have improved stability over time is not necessarily clear, but the following reasons are considered, for example. In conventional alkali niobate compounds, an alkali metal element volatilizes during firing, and voids, defects, and the like are likely to occur in the interior of the piezoelectric composition after firing. If a void or a defect exists in the piezoelectric composition, moisture or the like in the air is adsorbed in the void or the defect, and vibration (driving) of the piezoelectric composition is inhibited. Further, it is considered that moisture and the like in the air react with the alkali metal component contained in the piezoelectric composition, thereby causing deterioration of Qm with time.

In contrast, in the piezoelectric composition of the present embodiment, it is considered that the carbon component mainly exists as the hetero-phase 8 between the main phase particles 4. Further, it is considered that generation of voids or defects is suppressed by the carbon component present in the hetero-phase 8. Therefore, it is considered that in the piezoelectric composition of the present embodiment, inhibition of vibration due to adsorption of moisture or the like or reaction of moisture with an alkali metal component can be suppressed, Qm is improved, and Qm is less likely to deteriorate with time.

In the piezoelectric composition of the present embodiment, the alkali metal niobate-based compound has the composition formula (K) as described above_xNa_y)NbO₃It is shown that "x" and "x + y" in the composition formula satisfy a predetermined relationship. When the main component is in a predetermined composition range, Qm is further improved and the deliquescence phenomenon can be suppressed.

In the piezoelectric composition of the present embodiment, the carbon content is controlled within a predetermined range (380 to 600 ppm by weight, 400 to 500 ppm by weight), so that Qm can be maintained high and the stability of Qm over time can be further improved. Further, the insulation resistance is also as high as 1 × 10¹⁰Omega cm or more. Since the insulation resistance is increased, dielectric breakdown is less likely to occur even if a high voltage is applied during polarization treatment or the like. That is, the withstand voltage characteristics of the piezoelectric composition are improved.

In the piezoelectric composition of the present embodiment, the CV value of the concentration distribution related to carbon in an arbitrary cross section is controlled within the above range. Thereby Qm advancesThe improvement is one-step, and the stability of Qm is better. In addition, the insulation resistance is further as high as 1 × 10¹²Omega cm or more, the withstand voltage characteristics are further improved.

(modification example)

In the above-described embodiment, the piezoelectric element 5 in which the piezoelectric portion 1 is a single layer was described, but may be a piezoelectric element having a structure in which piezoelectric portions are stacked. Further, a piezoelectric element having a structure in which these elements are combined may be used. The term "structure in which these are combined" refers to a case where a region in which piezoelectric layers and internal electrode layers are stacked and a region in which electrode layers are not stacked but only a piezoelectric portion is provided in a piezoelectric element.

An example of a piezoelectric element having a structure in which piezoelectric portions are stacked is a piezoelectric element 50 shown in fig. 3. The piezoelectric element 50 includes a laminate 10 in which a plurality of piezoelectric layers 11 and a plurality of internal electrode layers 12 made of the piezoelectric composition of the present embodiment are alternately laminated. A pair of terminal electrodes 21 and 22 that are electrically connected to the internal electrode layers 12 alternately arranged inside the laminate 10 are formed at both end portions of 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 desired characteristics, use, or the like. Generally, the interlayer thickness is preferably about 1 μm to 100. mu.m. The number of stacked piezoelectric layers 11 is not particularly limited, and can be arbitrarily set according to desired characteristics, applications, and the like.

The internal electrode layers 12 are made of a conductive material, and mainly contain a noble metal element such as Ag, Pd, Au, or Pt, a base metal element such as Cu or Ni, or an alloy containing at least one of these elements. The thickness of each of the internal electrode layers is not particularly limited, and may be, for example, 0.5 to 2.0 μm. The terminal electrodes 21 and 22 may have the same configuration as the electrodes 2 and 3 shown in fig. 1.

The piezoelectric element 50 shown in fig. 3 can be manufactured, for example, by preparing green chips to be the laminate 10, firing the green chips to obtain the laminate 10, and then printing or transferring the terminal electrodes 21 and 22 on the laminate 10 and firing the terminal electrodes. As a method for producing a green chip, for example, a general printing method using a paste, a sheet method, or the like is exemplified. In both the printing method and the sheet method, a paste obtained by mixing the above-described raw material powder of the piezoelectric composition and a vehicle in which a binder is dissolved in a solvent and forming the mixture into a coating material is used.

The conditions for binder removal treatment or main firing may be the same as those in the above-described embodiment. However, when the internal electrode layers 12 are made of a base metal, the main firing is preferably performed in a nitrogen or nitrogen-hydrogen mixed atmosphere. In this case, it is preferable to perform the re-oxidation treatment after the main firing.

By laminating a plurality of piezoelectric layers 11 as in the piezoelectric element 50 shown in fig. 3, the displacement amount or driving force per unit volume can be made larger than that of the non-laminated piezoelectric element 1. Further, since the piezoelectric element 50 also contains the piezoelectric composition of the present embodiment, the same effects as those of the above-described embodiments can be obtained.

The piezoelectric elements 5 and 50 shown in fig. 1 and 3 can convert mechanical energy and electric energy into each other, and can be widely used as electronic components in various fields. For example, the present invention can be applied to a piezoelectric actuator utilizing an inverse piezoelectric effect. The piezoelectric actuator including the piezoelectric composition of the present invention can obtain a minute displacement with high accuracy against an applied voltage and has a high response speed, and therefore, can be used for, for example, a driving element of a construction member, a head driving element of an HDD, a head driving element of an ink jet printer, a driving element of a fuel injection valve, and a haptic element. The piezoelectric elements 5 and 50 can also be used as piezoelectric buzzers and piezoelectric speakers using the inverse piezoelectric effect.

Further, the piezoelectric elements 5, 50 can be applied to a sensor for reading a minute force or displacement amount using a piezoelectric effect. Since the piezoelectric elements 5 and 50 including the piezoelectric composition of the present invention have excellent response, the piezoelectric composition itself or an elastic body in a bonding relationship with the piezoelectric composition can be excited by application of an alternating electric field to generate resonance. Therefore, the present invention can be applied to a piezoelectric transformer, an ultrasonic motor, or the like.

While the embodiments of the present invention have been described above, the present invention is not limited to any of the embodiments described above, and may be modified according to various embodiments within the scope of the present invention. For example, the piezoelectric element 5 shown in fig. 1 has a substantially rectangular shape in plan view, but is not limited thereto, and may have a shape in plan view such as an oval shape, a circular shape, or a polygonal shape. In the piezoelectric element 50 shown in fig. 3, the terminal electrodes 21 and 22 are electrically connected to the internal electrode layers 12, but the present invention is not limited thereto. For example, each of the internal electrode layers 12 may be electrically connected to a pair of via electrodes and the via electrodes may be connected to extraction electrodes formed on the main surface of the laminate 10, thereby achieving electrical conduction with the internal electrode layers 12.

Examples

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

(experiment 1)

In experiment 1, samples of piezoelectric compositions of examples 1 to 7 were produced while varying the level of the carbon content. The experimental conditions will be described in detail below.

First, potassium bicarbonate (KHCO) is prepared₃) Powder of (2) and niobium oxide (Nb)₂O₅) The powder of (3) is used as a starting material of an alkali metal niobate compound which is a main component of the piezoelectric composition. In addition, a powder of copper oxide (CuO) was prepared as a starting material for the subcomponents.

Then, the prepared starting materials of the main components were weighed so that the piezoelectric composition (sintered body) after firing had the composition shown in table 1. Weighing KHCO by ball mill₃And Nb₂O₅The respective powders of (a) were wet-mixed for 16 hours, and then dried at 120 ℃ to obtain mixed powders.

Next, the mixed powder of the starting materials was pressed with a uniaxial press under a molding pressure of 20MPa to obtain a temporary molded body. Further, the temporary molded body was calcined at a predetermined temperature for 4 hours to obtain a calcined body of the alkali niobate-based compound. In experiment 1, the content of carbon contained in each example sample was adjusted according to the holding temperature at the time of calcination. Table 1 shows the holding temperatures at the time of calcination in examples 1 to 7. The atmosphere during the firing was set to the atmospheric atmosphere.

Next, the calcined body was pulverized for 16 hours by a ball mill to obtain a pulverized powder. Then, a predetermined amount of CuO powder was added to the pulverized powder, wet-mixed by a ball mill for 16 hours, and then dried in a constant temperature bath at 120 ℃. In this case, the amount of CuO added was 1.0 part by mole based on 100 parts by mole of the main component. Next, a binder is added to the raw material powder, mixed, and granulated with a screen to obtain a granulated powder. Then, the obtained granulated powder was subjected to a load of 196MPa by a press molding machine to be molded, thereby obtaining a flat plate-like molded body.

The flat plate-like molded article thus obtained was subjected to a binder removal treatment at 550 ℃ for 3 hours. Then, the binder-removed molded body was subjected to main firing at 1050 ℃ for 2 hours in an atmospheric atmosphere to obtain a sintered body. In the main firing, the temperature increase rate and the temperature decrease rate were both set to 5 ℃/min.

The obtained sintered body was then polished to form a parallel flat plate having a thickness of 1.0 mm. Further, silver paste was printed on both surfaces of the parallel flat plate-like sintered body, and then firing was performed at 800 ℃. Then, the sintered body after the electrode formation was cut into a length of 12mm and a width of 3 mm. Finally, an electric field of 3kV/mm was applied to silicone oil at 150 ℃ for 5 minutes to polarize the piezoelectric composition, thereby obtaining piezoelectric composition samples of examples 1 to 7. In addition, at least 5 or more samples of the piezoelectric composition were prepared in each example, and the following evaluations were performed.

Determination of carbon content

The content of carbon contained in the piezoelectric composition sample was measured using a carbon/sulfur analyzer (CS600) manufactured by LECO japan contract corporation. In addition, as a sample for measurement, a powder obtained by pulverizing a piezoelectric composition sample with an agate mortar was used. In addition, CS analysis was performed three times, and the average value thereof was calculated as the carbon content of each example.

Determination of mechanical quality factor Qm

Qm of the piezoelectric composition sample was measured by an impedance analyzer (4194A) manufactured by KEYSIGHT TECHNOLOGIES. In addition, Qm was measured after a sample of the piezoelectric composition was left at room temperature for 24 hours after the polarization treatment. In the present embodiment, the criterion of the qualification of Qm is 1000 or more, 1500 or more is judged to be good, and 1800 or more is judged to be more good.

Evaluation of stability with time

The stability with time of the piezoelectric composition sample was evaluated by calculating the rate of change of Qm over a long period of time. Specifically, after the lapse of 100 hours after the polarization treatment, Qm was measured again by the same method as described above, and the rate of change of Qm (Δ Qm) was obtained by the following calculation formula.

Δ Qm (unit%) { (Qm after 100 hours from polarization-Qm after 24 hours from polarization)/Qm after 24 hours from polarization } × 100

In the present example, the criterion for the acceptability of Δ Qm is 20% or less, and 10% or less is judged to be satisfactory.

In addition to the above evaluation, elemental analysis by EPMA and a fluorescent X-ray analyzer (XRF) was performed on the obtained piezoelectric composition sample. As a result, in all examples, it was confirmed that the main component having the same composition as the target value was contained and the subcomponent (Cu) having the same composition as the target value was contained.

Comparative example 1 and comparative example 2

In comparative examples 1 and 2, the form and the holding temperature during firing were changed from those of examples 1 to 7 described above, and piezoelectric composition samples were produced. Specifically, in comparative example 1, the form during firing was referred to as "temporary molded body", and the holding temperature was set to 1040 ℃. On the other hand, in comparative example 2, the form during calcination was defined as "powder", and the holding temperature was set to be as low as 800 ℃.

The piezoelectric composition samples of comparative examples 1 and 2 were prepared under the same experimental conditions as in examples 1 to 7 except for the above, and the above evaluations were performed.

Evaluation results 1

The evaluation results of experiment 1 are shown in table 1.

[ Table 1]

As shown in Table 1, in comparative example 1 in which the carbon content was as low as 200 ppm by weight, Qm was 1000 or more, but Δ Qm was very high, as high as 45%, and the stability with time of Qm was very poor. Generally, Qm and Δ Qm have an inverse relationship, and if Qm becomes higher, the value of Δ Qm tends to become larger, and stability tends to deteriorate. That is, as shown in the evaluation results of comparative example 1, it is difficult to satisfy both high Qm and good Δ Qm.

In comparative example 2 having a carbon content as high as 720 ppm by weight, polarization was not sufficiently achieved, and Qm and Δ Qm could not be measured. The reason why the polarization was not possible in comparative example 2 is considered to be due to: after firing, the unreacted K component remains as much as necessary, and a large amount of moisture is adsorbed in the piezoelectric composition, thereby significantly lowering the resistivity.

Examples 1 to 7 obtained results in which Qm and Δ Qm both satisfied the criterion of pass or fail, compared with the results of comparative examples 1 and 2. From this result, it can be confirmed that: when the carbon content is in the range of 350 ppm by weight or more and 700 ppm by weight or less, both high Qm and good stability over time can be satisfied.

(experiment 2)

In experiment 2, the piezoelectric composition samples of examples 12 to 21 were produced while changing the composition of the main component and the kind of the added subcomponent. Specifically, examples 12 to 15 were conducted except for KHCO₃And Nb₂O₅In addition, sodium bicarbonate (NaHCO) was prepared₃) As a starting material for the main component, the K and Na atoms in the obtained piezoelectric compositionThe ratio of the number of subgroups (i.e., x and y in the composition formula) was set to the value shown in table 2. In examples 12 to 15, "x + y" was 1.000.

In examples 16 to 17, piezoelectric composition samples were prepared with the ratio of the total number of atoms in the a site to the total number of atoms in the B site (i.e., "x + y" in the composition formula) as shown in table 2.

Further, in examples 18 to 21, the structures of subcomponents were changed from those of experiment 1. In example 18, as subcomponents, in addition to 1.0 molar part of CuO to 100 molar parts of the main component, 0.5 molar part of zinc oxide (ZnO) was added to 100 molar parts of the main component. In example 19, as subcomponents, in addition to 1.0 molar part of CuO with respect to 100 molar parts of the main component, 0.8 molar part of germanium oxide (GeO) was added with respect to 100 molar parts of the main component₂). In example 20, 1.6 parts by mole of magnesium carbonate (MnCO) was added as a subcomponent to 100 parts by mole of the main component in place of CuO₃) In example 21, 0.38 molar parts of a composite oxide (K) containing Cu was added to 100 molar parts of the main component in place of CuO_5.4Cu_1.3Ta₁₀O₂₉)。

In each example of experiment 2, the form during firing was defined as "temporary molded body (block)" and the holding temperature during firing was defined as 1000 ℃. In experiment 2, samples of piezoelectric compositions of examples 12 to 21 were obtained under the same experimental conditions as in experiment 1 except for the above.

Further, in experiment 2, in addition to the evaluation performed in experiment 1, the measurement of the resistivity ρ of the piezoelectric composition sample was also performed. The resistivity ρ was measured by applying a voltage of 40V to a sample of the piezoelectric composition using a digital ultra high resistance/micro ammeter (R8340) manufactured by Advantest. The standard for whether the resistivity is acceptable or not is set to 1X 10¹⁰Omega. cm or more, 1X 10¹¹The omega cm or more is judged to be good, 1X 10¹²Omega cm or more is judged to be more preferable. The evaluation results of experiment 2 are shown in table 2.

[ Table 2]

As shown in table 2, it was found that the carbon content was changed even when the composition of the main component or the kind of the added sub-component was changed. In addition, if comparative examples 12 to 15, it can be confirmed that Qm becomes higher and the stability of Qm over time becomes further improved (Δ Qm becomes lower) if the proportion of K is larger than Na.

Further, when examples 18 to 21 are compared, it is found that Qm is higher and Δ Qm is lower in the other examples in which Cu is added than in example 20 in which Mn is added. From these results, it is found that a compound containing Cu is preferable as an added subcomponent, and CuO is particularly preferable.

(experiment 3)

In experiment 3, samples of piezoelectric compositions of examples 31 and 35 were prepared while varying the CV value level. In experiment 3, the degree of carbon dispersion (CV value) was adjusted by controlling the holding temperature during firing and the holding temperature during main firing. Specifically, in example 31, the holding temperature during firing was 1000 ℃ and the holding temperature during main firing was 1050 ℃. On the other hand, in example 35, the holding temperature during firing was 990 ℃ and the holding temperature for main firing was 1040 ℃.

In addition, in experiment 3, the CV value of the obtained piezoelectric composition sample was determined by map analysis of EPMA. Specifically, mapping analysis of three fields was performed under conditions in which the measurement interval was 0.5 μm × 0.5 μm and the number of measurement spots was 256 × 256, and the CV value (average value of three fields) was calculated from the result of the mapping analysis. Table 3 shows CV values of example 31 and example 35.

In addition, in experiment 3, the ratio of the starting materials was adjusted so as to satisfy the composition formula K in any of the examples_0.995NbO₃1.0 molar part of CuO and 0.5 molar part of ZnO were added as subcomponents. The test conditions other than the above were set to the same conditions as in experiment 2, and Qm, Δ Qm and resistivity of the obtained piezoelectric composition sample were measured. The evaluation results are shown in table 3.

[ Table 3]

As shown in table 3, example 35, which has a smaller CV value, has a higher Qm and a higher resistivity than example 31. From this result, it can be confirmed that: in the piezoelectric composition, the more uniformly the carbon is dispersed, the higher Qm and the better the insulation resistance.