WO2023063007A1

WO2023063007A1 - Multilayer piezoelectric element

Info

Publication number: WO2023063007A1
Application number: PCT/JP2022/034339
Authority: WO
Inventors: 亮伊藤; 隆幸後藤
Original assignee: 太陽誘電株式会社
Priority date: 2021-10-12
Filing date: 2022-09-14
Publication date: 2023-04-20

Abstract

A multilayer piezoelectric element according to one aspect of the present invention is provided with piezoelectric ceramic layers which are mainly composed of an alkali niobate salt having a perovskite structure, and an internal electrode layer 20 which is arranged between the piezoelectric ceramic layers and has a conductive part 21 that has a silver content of 50% by mass or more, wherein: the area percentage (R1) occupied by the conductive part 21 is 75% to 95%; the internal electrode layer also has interstitial parts 22 in which the conductive part 21 is not present, and which have an average area percentage (R2) per one interstitial part of 5% or less; and at least one of the interstitial parts 22 contains lithium manganate 23.

Description

Laminated piezoelectric element

The present invention relates to laminated piezoelectric elements.

A piezoelectric element is an electronic component with a structure in which a piezoelectric ceramic (piezoelectric ceramic) is sandwiched between a pair of electrodes. Here, piezoelectricity is a property capable of mutually converting electrical energy and mechanical energy.

Piezoelectric elements use the aforementioned properties of piezoelectric ceramics to convert the voltage applied between a pair of electrodes into mechanical energy such as pressure or vibration, thereby moving other objects or moving itself. can do. On the other hand, piezoelectric elements can convert mechanical energy such as vibration and pressure into electrical energy, and extract the electrical energy as voltage between a pair of electrodes.

As for the structure of the piezoelectric element, in addition to the one in which electrodes are formed only on the surface of the piezoelectric ceramic, the one called laminated piezoelectric element in which multiple piezoelectric ceramic layers and internal electrode layers are alternately laminated is known. Laminated piezoelectric elements can be used, for example, as actuators because they can provide a large displacement in the lamination direction of the piezoelectric ceramic layers. Laminated piezoelectric elements are typically manufactured by simultaneously firing piezoelectric ceramic layers and internal electrode layers.

As piezoelectric ceramics constituting such piezoelectric elements, those mainly composed of lead zirconate titanate (Pb(Zr, Ti)O ₃ , PZT) and their solid solutions are widely used. Since PZT-based piezoelectric ceramics have a high Curie temperature, it is possible to obtain a piezoelectric element that can be used even in a high-temperature environment. It has the advantage that a piezoelectric element that can be converted efficiently can be obtained. Moreover, by selecting an appropriate composition, firing can be performed at a temperature below 1000° C., which has the advantage of reducing the manufacturing cost of the piezoelectric element. In particular, in the laminated piezoelectric element described above, the internal electrodes co-fired with the piezoelectric ceramics are made of a low-melting-point material that contains a large proportion of silver, in other words, contains a small proportion of expensive materials such as platinum and palladium. Being able to use it will bring significant cost savings.

However, PZT-based piezoelectric ceramics contain lead, which is a hazardous substance, which is regarded as a problem.

Alkali niobate ((Li, Na, K)NbO ₃ ) system, bismuth sodium titanate ((Bi _0.5 Na _0.5 )TiO ₃ , BNT) system, bismuth Various compositions have been reported, such as layered compound systems and tungsten bronze systems. Among these, alkaline niobate-based piezoelectric ceramics have a high Curie point and a relatively large electromechanical coupling coefficient, and are therefore attracting attention as alternatives to PZT-based ceramics (Patent Document 1).

Attempts have been made to reduce the manufacturing cost of laminated piezoelectric elements by firing the alkaline niobate-based piezoelectric ceramics at a low temperature, enabling them to be fired together with internal electrodes containing a large amount of silver. For example, in Patent Document 2, it is reported that by setting the composition of alkaline niobate-based piezoelectric ceramics to contain an alkaline earth metal and silver, it was possible to sinter integrally with internal electrodes of Ag0.7Pd0.3. It is In addition, Patent Document 2 reports that the obtained laminated piezoelectric element exhibited high electrical resistivity and exhibited a large amount of displacement when a voltage was applied.

On the other hand, in the laminated piezoelectric element, it has been reported that the internal electrode layers constrain the displacement of the piezoelectric ceramics, thereby suppressing the amount of displacement of the element (Patent Document 3). In Patent Document 3, a non-conductive portion composed of a ceramic portion filled with ceramic powder and a void portion is formed at a specific ratio in an internal electrode layer of a laminated piezoelectric element, thereby preventing displacement by the internal electrode layer. reported to be suppressed.

WO2007/094115 JP 2017-163055 A WO2006/068245

In Patent Document 2, Li ₂ O and SiO ₂ , which are components that contribute to improving the sinterability, and MnO, which is a component that contributes to improving the electrical resistance, are added to the above-described alkaline niobate-based piezoelectric ceramics. There is a statement to the effect that it is acceptable. However, depending on the content of these components _, _Li3NbO4 , which has conductivity, and lithium manganate, which has a lower electrical resistivity than alkali niobates, are generated in large amounts in the piezoelectric ceramics, and during use of the element, It has been found that the life of the element may be shortened due to the deterioration of the electrical insulation.

As described above, the laminated piezoelectric element described in Patent Document 2 exhibits a large amount of displacement when a voltage is applied. may restrain the displacement of the piezoelectric ceramic layer.

On the other hand, Patent Document 3 does not describe prevention of shortening of the life of the piezoelectric element due to deterioration of electrical insulation during use.

Therefore, an object of the present invention is to provide a multilayer piezoelectric element that does not contain lead as a constituent component, has a small decrease in electrical insulation during use, and has a large amount of displacement when a voltage is applied.

The present inventor conducted various studies in order to solve the above problems, and found that the laminated piezoelectric element is composed of a piezoelectric ceramic layer containing alkali niobate as a main component and a conductive portion containing silver as a main component. and having an internal electrode layer containing lithium manganate in at least a part of the gap where the conductive portion does not exist. reached.

That is, one aspect of the present invention for solving the above problems is a piezoelectric ceramic layer mainly composed of alkali niobate having a perovskite structure, and a piezoelectric ceramic layer disposed between the piezoelectric ceramic layers and having a silver content of 50 mass. % or more, the area percentage (R ₁ ) occupied by the conductive part is 75% or more and 95% or less, and the gap part where the conductive part does not exist is the average area percentage (R ₂ ) is 5% or less, and an internal electrode layer containing lithium manganate is provided in at least one of the gaps.

According to the present invention, it is possible to provide a multilayer piezoelectric element that does not contain lead as a component, has a small decrease in electrical insulation during use, and has a large amount of displacement when a voltage is applied.

A cross-sectional view (XZ plane) showing the structure of a laminated piezoelectric element according to one aspect of the present invention. A cross-sectional view (YZ plane) showing the structure of a laminated piezoelectric element according to one aspect of the present invention. A perspective view showing a unit cell model of a perovskite structure FIG. 2 is a perspective view showing the state of internal electrode layers in the laminated piezoelectric element according to one aspect of the present invention; FIG. 4 is an explanatory diagram of the dimensions of each part necessary for calculating parameters R ₁ , R ₂ , R ₃ and R ₄ indicating the state of the internal electrode layers in the laminated piezoelectric element according to one aspect of the present invention;

Hereinafter, the configuration and effects of the present invention will be described with technical ideas, with reference to the drawings. However, the mechanism of action is presumed, and whether it is correct or not does not limit the present invention.

[Laminated piezoelectric element]
A multilayer piezoelectric element 100 according to one aspect of the present invention (hereinafter sometimes simply referred to as "this aspect") has piezoelectric ceramic layers, as schematically shown in cross-sectional views in FIGS. 10, internal electrode layers 20 arranged between the piezoelectric ceramic layers 10 and connection conductors 30 electrically connecting the internal electrode layers 20 every other layer. Among the internal electrode layers 20 shown in FIGS. 1 and 2 and the connection conductors 30 shown in FIG. or "-"). 1, the connection conductor 30 is formed on the surface of the laminated piezoelectric element 100. The connection conductor 30 is formed inside the laminated piezoelectric element 100 so as to penetrate the piezoelectric ceramic layer 10. may have been

As shown in FIG. 2, this side surface is provided with side margin portions 40 located between the Y-axis direction side surfaces and the internal electrode layers 20, and cover portions 50 located on the Z-axis direction upper and lower surfaces. good too. In addition, an external electrode (not shown) that electrically connects the connection conductor 30 and the drive circuit may be formed on the surface of this side surface.

Each part constituting the multilayer piezoelectric element 100 will be described in detail below.

(Piezoelectric ceramic layer)
The piezoelectric ceramic layer 10 is mainly composed of alkali niobate having a perovskite structure.

The alkali niobate, which is the main component, contains, as constituent elements, at least one alkali metal element selected from the group consisting of lithium (Li), sodium (Na) and potassium (K), and niobium (Nb). It is an oxide having a perovskite structure. Here, as shown in FIG. 3, the perovskite structure has an A site located at the vertex of the unit cell, an O site located at the face center of the unit cell, and an octahedron having the O site as a vertex. It is a crystal structure having a B site. In the alkali niobate according to the present embodiment, alkali metal ions are located at the A site, niobium ions are located at the B site, and oxide ions are located at the O site. In addition, each site may contain various ions other than those described above.

Here, confirmation that the piezoelectric ceramic layer 10 is mainly composed of alkali niobate having a perovskite structure is performed by the following procedure.
First, regarding the piezoelectric ceramic layer 10 exposed on the surface of the laminated piezoelectric element 100 or the powder obtained by pulverizing the laminated piezoelectric element 100, a diffraction line was obtained by an X-ray diffraction (XRD) apparatus using Cu—Kα rays. Measure your profile. The method of exposing the piezoelectric ceramic layer 10 on the surface of the laminated piezoelectric element 100 is not particularly limited, and a method of cutting or polishing the piezoelectric element can be employed. Moreover, the means for pulverizing the laminated piezoelectric element 100 is not particularly limited, and a hand mill (mortar/pestle) or the like can be used.
Next, when the ratio of the strongest diffraction line intensity in the diffraction profile derived from the other structure to the strongest diffraction line intensity in the profile derived from the perovskite structure in the obtained diffraction line profile is 10% or less, the piezoelectric ceramics It is determined that the layer 10 is mainly composed of a compound having a perovskite structure. At this time, when the XRD measurement is performed on the powder obtained by pulverizing the laminated piezoelectric element 100, the peak of the metal constituting the internal electrode layer 20 is also detected. comparison.
Next, for the piezoelectric ceramic layer 10 determined to be mainly composed of a compound having a perovskite structure or the powder prepared therefrom, high-frequency inductively coupled plasma (ICP) emission spectrometry, ion chromatography, or X-ray fluorescence (XRF) An analyzer measures the ratio of each element contained. As a result of the measurement, both the total content of alkali metal elements and the content of niobium expressed in mol % (or atomic %) were greater than the contents of other elements, indicating that the perovskite structure, which is the main component, is determined to be an alkali niobate.

The piezoelectric ceramic layer 10 may contain other components as long as the main component is alkali niobate having a perovskite structure. These other components may be dissolved in any of the A site, B site, and O site of the perovskite structure described above, or may exist as a different phase between sintered particles of the main component.

For example, the piezoelectric ceramic layer 10 may further contain at least one alkaline earth metal element selected from the group consisting of calcium (Ca), strontium (Sr) and barium (Ba), and silver (Ag). good. As a result, the piezoelectric ceramic layer 10 becomes dense with a small sintered particle size, and exhibits excellent piezoelectricity. From this point of view, the total content of alkaline earth metal elements is 100 mol % of the content of the elements in the B site of the alkali niobate, which is the main component (often in an ionic state). It is preferably more than 0.2 mol %, more preferably 0.3 mol % or more, even more preferably 0.5 mol % or more. For the same reason, the content of silver is preferably more than 0.5 mol %, more preferably 0.7 mol % or more, relative to 100 mol % of the elements in the B site. 0 mol % or more is more preferable. On the other hand, from the viewpoint of further improving the electrical insulation of the piezoelectric ceramic layer 10 to enable use under a high electric field and prolonging the device life, the total content of the alkaline earth metal elements is It is preferably 5.0 mol % or less, more preferably 3.0 mol % or less, even more preferably 1.0 mol % or less. For the same reason, the silver content is preferably 5.0 mol % or less, more preferably 4.0 mol % or less, and further preferably 3.0 mol % or less. preferable. In addition, for the reason described above, the total content of the alkaline earth metal elements and the content of silver are set so that the total content of the alkaline earth metal elements is 0.2 per 100 mol % of the elements in the B site. It is more than 5.0 mol % and less than or equal to 5.0 mol %, preferably more than 0.5 mol % and less than or equal to 5.0 mol % of silver, and the total content of alkaline earth metal elements is 0.3 mol % or more. 0 mol % or less, silver is more preferably 0.7 mol % or more and 4.0 mol % or less, and the total content of alkaline earth metal elements is 0.5 mol % or more and 1.0 mol % or less. and more preferably 1.0 mol % or more and 3.0 mol % or less of silver.

In addition, the piezoelectric ceramic layer 10 may further contain manganese (Mn). As a result, the electrical insulation of the piezoelectric ceramic layer 10 is improved, and the laminated piezoelectric element 100 with a long life can be obtained. From this point of view, the content of manganese should be 0.00% when the content of the element in the B site of the alkali niobate, which is the main component (actually, it is often in an ionic state), is 100 mol %. It is preferably 2 mol % or more, more preferably 0.3 mol % or more, and even more preferably 0.5 mol % or more. On the other hand, from the viewpoint of making the piezoelectric ceramic layer 10 excellent in piezoelectric characteristics, the content of manganese is preferably 2.0 mol % or less with respect to 100 mol % of the elements in the B site. It is more preferably 5 mol % or less, and even more preferably 1.0 mol % or less. For the reason described above, the manganese content is preferably 0.2 mol % or more and 2.0 mol % or less, and 0.3 mol % or more, relative to 100 mol % of the elements in the B site. It is more preferably 1.5 mol % or less, and even more preferably 0.5 mol % or more and 1.0 mol % or less.

Moreover, the piezoelectric ceramic layer 10 may further contain silicon (Si). As a result, the piezoelectric ceramic layer 10 is densified, and excess Li that has not completely dissolved in the main component reacts with silicon to form compounds such as Li ₂ SiO ₃ and Li ₄ SiO ₄ . can suppress the formation of conductive compounds such as Li ₃ NbO ₄ . From this point of view, the content of silicon should be 0.00% when the content of the element in the B site of the alkali niobate, which is the main component (actually, it is often in an ionic state), is 100 mol %. It is preferably 1 mol % or more, more preferably 0.5 mol % or more, and even more preferably 1.0 mol % or more. On the other hand, from the viewpoint of suppressing the amount of non-piezoelectric heterogeneous phases contained in the piezoelectric ceramic layer 10, the content of silicon is 3.0 mol % with respect to 100 mol % of the elements in the B site. or less, more preferably 2.5 mol % or less, and even more preferably 2.0 mol % or less. For the reason described above, the content of silicon is preferably 0.1 mol % or more and 3.0 mol % or less with respect to 100 mol % of the elements in the B site, and 0.5 mol % or more. 0.5 mol % or less is more preferable, and 1.0 mol % or more and 2.0 mol % or less is even more preferable.

In addition to these components, the piezoelectric ceramic layer 10 may optionally contain at least one selected from first transition elements such as Sc, Ti, V, Cr, Fe, Co, Ni, Cu and Zn. good. By including these elements in appropriate amounts, it is possible to adjust the firing temperature of the laminated piezoelectric element 100, control grain growth, and extend the life in a high electric field.

In addition, the piezoelectric ceramic layer 10 may contain at least one selected from Y, Mo, Ru, Rh and Pd, which are second transition elements, if necessary. By including these elements in appropriate amounts, it is possible to adjust the firing temperature of the laminated piezoelectric element 100, control grain growth, and extend the life in a high electric field.

Further, the piezoelectric ceramic layer 10 may include third transition elements such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, and W, if necessary. , Re, Os, Ir, Pt and Au. By including these elements in appropriate amounts, it is possible to adjust the firing temperature of the laminated piezoelectric element 100, control grain growth, and extend the life in a high electric field.

Of course, in the present embodiment, the piezoelectric ceramic layer 10 can contain a plurality of types of the above-described first transition element, second transition element, and third transition element.

The alkali niobate is represented by the following composition formula (1) from the viewpoint of exhibiting excellent piezoelectric properties and obtaining a long-life element when used under a high electric field. preferable.

(Ag _u M2 _v (K _1-w-x Na _w Li _x ) _1-u-v ) _a
(Sb _y Ta _z Nb _1-yz )O ₃ (1)

However, M2 in the formula represents at least one alkaline earth metal element selected from the group consisting of calcium (Ca), strontium (Sr) and barium (Ba). Further, u, v, w, x, y, z and a are respectively 0.005<u≦0.05, 0.002<v≦0.05, 0.007<u+v≦0.1, 0≦ w≤1, 0.02<x≤0.1, 0.02<w+x≤1, 0≤y≤0.1, 0≤z≤0.4, 1<a≤1.1 A numerical value that satisfies an inequality.

Here, it is confirmed by the following procedure that the alkali niobate is represented by the above compositional formula (1).
First, the piezoelectric ceramic layer 10, which has been confirmed to contain an alkali niobate having a perovskite structure as a main component, or a powder prepared therefrom, is subjected to high-frequency inductively coupled plasma (ICP) emission spectroscopy and ion chromatography. Equipment or X-ray fluorescence (XRF) analyzer, silver (Ag), calcium (Ca), strontium (Sr), barium (Ba), potassium (K), sodium (Na), lithium (Li), antimony ( Sb), tantalum (Ta) and niobium (Nb) contents are measured.
Next, the total number of moles of antimony, tantalum and niobium is calculated, and the ratio of the number of moles of each element to this is calculated.
When the obtained ratio of each element is within the range of the above composition formula (1), it is determined that the alkali niobate is represented by the above composition formula (1).

(Internal electrode layer)
The internal electrode layer 20 has, as schematically shown in FIG. The area percentage is 75% or more and 95% or less, the size of the gap 22 is 5% or less in average area percentage per location, and lithium manganate is present in at least one location of the gap 22 23.

The internal electrode layer 20 has a conductive portion 21 made of metal with a silver content of 50% by mass or more. Since the content of silver in the conductive portion 21 is 50% by mass or more, the amount of expensive metals such as platinum and palladium used can be reduced, and the material cost of the laminated piezoelectric element 100 can be suppressed. In addition, since the ratio of silver, which is excellent in conductivity, increases, the electrical resistivity decreases, and the electrical loss when driving the multilayer piezoelectric element 100 is reduced. A silver-palladium alloy is exemplified as a metal having a silver content of 50% by mass or more. The content of silver in the conductive portion 21 is preferably 70% by mass or more, more preferably 80% by mass or more.

The content of silver in the internal electrode layer 20 can be confirmed by performing elemental analysis of the internal electrode layer 20 using various measuring instruments and calculating the mass ratio of silver to all the detected elements. The measuring instrument used is a scanning electron microscope (SEM) or an energy dispersive X-ray spectrometer (EDS) attached to a transmission electron microscope (TEM). Or wavelength dispersive X-ray spectrometer (Wavelength Dispersive X-ray Spectrometer, WDS), electron probe microanalyzer (Electron Probe Micro Analyzer, EPMA) and laser irradiation type inductively coupled plasma mass spectrometer (LA-ICP-MS), etc. exemplified.

The area percentage of the conductive portions 21 in the internal electrode layers 20 is set to 75% or more and 95% or less. By setting the area percentage (hereinafter sometimes simply referred to as “R ₁ ”) to 75% or more, a sufficient voltage is applied to the piezoelectric ceramic layer 10 when driving the multilayer piezoelectric element 100, A large displacement can be obtained. From this point of view, _R1 is preferably 80% or more. On the other hand, by setting _R1 to 95% or less, the restraining force by the internal electrode layers 20 generated when the piezoelectric ceramic layers 10 are displaced is reduced, and a large displacement can be obtained. From this point of view, R ₁ is preferably 93% or less. For the reason described above, _R1 is preferably 80% or more and 93% or less.

The internal electrode layer 20 has a gap portion 22 where the conductive portion 21 does not exist. The gaps 22 are sized such that the average area percentage (hereinafter sometimes simply referred to as “R ₂ ”) per portion of the entire internal electrode layer 20 is 5% or less. As a result, when driving the laminated piezoelectric element 100, a sufficient voltage can be applied to the piezoelectric ceramic layer 10 to obtain a large displacement. From the viewpoint of applying a higher voltage across the piezoelectric ceramic layer 10, _R2 is preferably 3% or less. Although the lower limit of _R2 is not limited, it is often 0.01% or more in the laminated piezoelectric element 100 having _R1 of 75% or more and 95% or less, which is obtained by a general manufacturing method. The ratio of the total area of the gaps 22 to the area of the internal electrode layers 20 is 5% or more and 25% or less in terms of area percentage, that is, the value obtained by subtracting the aforementioned _R1 from 100%. Therefore, the area percentage of the total area of the gaps 22 corresponding to the above-mentioned preferable value of _R1 is 7% or more and 20% or less.

The gap 22 contains lithium manganate 23 in at least one location. As a result, deterioration in electrical insulation during use of the laminated piezoelectric element 100 is reduced. This is thought to be suppressed by the following mechanism. Lithium manganate 23 is a compound having a lower electrical resistivity than alkaline niobate, which is the main component of piezoelectric ceramic layer 10 . The presence of such a compound in the piezoelectric ceramic layer 10 causes a decrease in electrical resistivity of the piezoelectric ceramic layer 10 and the multilayer piezoelectric element 100 as a whole during use. On the other hand, when the lithium manganate 23 is present in the interstices 22 of the internal electrode layers 20, although the electrical resistivity of the interstices 22 is lower than in the case where the alkali niobate is present, the interstices 22 are included. Since the internal electrode layer 20 is originally conductive, the adverse effect on the electrical resistivity of the laminated piezoelectric element 100 is limited. Therefore, the presence of the lithium manganate 23 in the interstices 22 of the internal electrode layers 20 reduces the amount of lithium manganate in the piezoelectric ceramic layer 10, and the entire piezoelectric ceramic layer 10 and the laminated piezoelectric element 100 in use. decrease in electrical resistivity is suppressed.

The lithium manganate 23 contained in the gap 22 includes those represented by various composition formulas such as Li ₂ MnO ₃ , LiMn ₂ O ₄ and LiMnO ₂ . Express.

The area ratio of the lithium manganate 23 contained in the gaps 22 to the total area of the internal electrode layers 20 (hereinafter sometimes simply referred to as “R ₃ ”) is preferably 1% or more. , more preferably 2% or more. As a result, deterioration of the electrical insulation of the laminated piezoelectric element 100 during use is significantly reduced. Although the upper limit of _R3 is not limited, as described above, the upper limit of the ratio of the total area of the gaps 22 to the area of the internal electrode layers 20 is 25%, and the preferable upper limit is 20%. necessarily lower than these values. For the reasons described above, _R3 is preferably 1% or more and 25% or less, more preferably 2% or more and 20% or less.

The ratio of the area of the lithium manganate 23 contained in the gap 22 to the total area of the gap 22 (hereinafter sometimes simply referred to as “R ₄ ”) is preferably 10% or more, It is more preferably 20% or more. As a result, deterioration of the electrical insulation of the laminated piezoelectric element 100 during use is significantly reduced. The upper limit of R ₄ is not limited, and may be 100%, that is, a state in which all the gaps 22 are filled with lithium manganate 23 .

Here, whether lithium manganate 23 is contained in at least one of gaps 22 in internal electrode layer 20 is confirmed by the following procedure.
First, the laminated piezoelectric element 100 is cut along a plane perpendicular to the plane perpendicular to the lamination direction, passing near the center of gravity, and the cut surface is polished to expose the internal electrode layers 20 . However, in the laminated element in which the connecting conductor 30 is formed through the piezoelectric ceramic layer 10, the cutting is performed while avoiding the connecting conductor 30. FIG.
Next, the exposed internal electrode layers 20 are observed with an optical microscope to identify the conductive portions 21 having metallic luster and the gaps 22 where the conductive portions are interrupted. Identify the location of the speckled portion that is recognized by the difference in lightness or saturation. In addition, the spotted portion often has an orange or black color due to the coloring of manganese.
Next, Li, Mn and Nb were analyzed using a laser irradiation type inductively coupled plasma mass spectrometer (LA-ICP-MS) for each of the speckled portions and portions where similar specks did not exist in the piezoelectric ceramic layer 10. Measure the content.
Next, from the obtained measurement results, the ratio of the amount of Li to the amount of Nb expressed in atomic % (Li/Nb) and the ratio of the amount of Mn to the amount of Nb expressed in atomic % (Mn/Nb) were determined at each measurement point. are calculated respectively.
Next, when the values of Li/Nb and Mn/Nb calculated for the spotted portion became larger than the respective values calculated for the measurement points in the piezoelectric ceramic layer 10, the spotted portion was replaced with manganic acid. Determined to be lithium-23. If there are a large number of speckled portions having the same appearance, the Li/Nb and Mn/Nb values at three of them are larger than the measured portions in the piezoelectric ceramic layer 10, and the remaining is also determined to be lithium manganate 23.

Moreover, the values of R ₁ , R ₂ , R ₃ and R ₄ described above are measured and calculated in the following procedure.
First, an optical microscope image of a cross section of the laminated piezoelectric element 100 determined to contain lithium manganate 23 in the interstices 22 of the internal electrode layers 20 by the above-described procedure is taken from the internal electrode layers 20 exposed there. , arbitrarily select three consecutive sheets (layers).
_Next , for _the selected internal _electrode layers 20, as schematically shown in _FIG . Length _occupied by _{each lithium manganate 23 (L M11} _, _L _M12 _, _. ₎ , the length _occupied _by _{each lithium manganate 23 (L M21} _, L _M22 , . , L _d3c ) and the length occupied by each lithium manganate 23 (L _M31 , L _M32 , . . . , L _M3r ) are measured. The suffixes a, b, and c respectively denote the number of gaps 22 present in each layer, and the suffixes p, q, and r denote the number of lithium manganate 23 present in each layer.
Next, from the measured lengths, R ₁ is determined by the following formula (2), R ₂ is determined by the following formula (3), R ₃ is determined by the following formula (4), and R ₄ is determined by the following formula (5). calculate.

(connection conductor)
The connection conductor 30 electrically connects every other internal electrode layer 20 . When the connection conductor 30 is formed on the surface of the laminated piezoelectric element 100, the material of the connection conductor 30 has high conductivity and is physically and chemically stable under the polarization conditions and the usage environment of the element, which will be described later. is not particularly limited. Examples include silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), and alloys thereof. On the other hand, when the connecting conductor 30 is formed inside the laminated piezoelectric element 100 so as to penetrate the piezoelectric ceramic layer 10, the silver content is 50%, similarly to the conductive portion 21 of the internal electrode layer 20 described above. It is preferable to use the metal in mass % or more.

(Side margin and cover)
The side margin portion 40 and the cover portion 50 function as protection portions that protect the piezoelectric ceramic layers 10 and the internal electrode layers 20 .

The side margin portion 40 and the cover portion 50 are made of alkali niobate, similar to the piezoelectric ceramic layer 10, from the viewpoint of the shrinkage rate during firing of the laminated piezoelectric element 100 and the relaxation of internal stress in the laminated piezoelectric element 100. It is preferably formed of a sintered body containing salt as a main component. However, the material for forming the side margin portions 40 and the cover portion 50 need not contain alkali niobate as a main component as long as the material has high insulating properties.

(external electrode)
The external electrode has a function of electrically connecting the connection conductor 30 and the drive circuit. Moreover, when this is formed on the piezoelectric ceramics layer 10, it also has a function of applying a voltage thereto. The material of the external electrode is not particularly limited as long as it has high conductivity and is physically and chemically stable under the polarization conditions and the usage environment of the piezoelectric element. Examples include silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), and alloys thereof.

[Manufacturing Method of Laminated Piezoelectric Ceramics]
The laminated piezoelectric element according to this aspect is obtained by, for example, mixing raw material powders in a predetermined ratio to obtain a raw material mixed powder, calcining the raw material mixed powder, and Obtaining a calcined powder as a component, mixing the calcined powder with a binder and a dispersion medium to prepare a slurry, forming the slurry into a sheet to obtain a green sheet, silver on the green sheet A paste containing a metal and a manganese compound whose After removing the binder from the green compact, firing it to obtain a laminated piezoelectric ceramic, applying a conductor paste to the surface of the laminated piezoelectric ceramic where the internal electrode layer is exposed, and baking it to connect conductor and applying a high voltage between the connection conductors to polarize the piezoelectric ceramic layer. Each operation will be described in detail below.

(Preparation of raw material mixed powder)
First, raw material powders are mixed at a predetermined ratio to obtain a raw material mixed powder. Examples of raw material powders to be used include lithium carbonate (Li ₂ CO ₃ ) as a lithium compound, sodium carbonate (Na ₂ CO ₃ ) and sodium hydrogen carbonate (NaHCO ₃ ) as sodium compounds, and potassium carbonate ( K ₂ CO ₃ ) and potassium hydrogen carbonate (KHCO ₃ ), and niobium pentoxide (Nb ₂ O ₅ ) as a niobium compound. Although optional components, frequently used compounds include tantalum pentoxide (Ta ₂ O ₅ ) as a tantalum compound and antimony trioxide (Sb ₂ O ₃ ) as an antimony compound.

The method of mixing the raw material powders is not particularly limited as long as each powder is uniformly mixed while suppressing the contamination of impurities, and either dry mixing or wet mixing may be employed. When wet mixing using a ball mill is adopted as the mixing method, for example, partially stabilized zirconia (PSZ) balls are used, and after stirring for about 8 to 60 hours with a ball mill using an organic solvent such as ethanol as a dispersion medium, The organic solvent may be evaporated and dried.

(Preparation of calcined powder)
Next, the mixed raw material powder is calcined to obtain a calcined powder. The calcination is carried out under conditions under which raw material powders react with each other to obtain an alkali niobate having a predetermined composition. One example is firing in air at a temperature of 700 to 1000° C. for 1 to 10 hours. The calcined powder may be directly used to prepare a slurry, but it is preferable to pulverize the powder with a ball mill, a stamp mill, or the like prior to this, in order to obtain a smooth green sheet through a uniform slurry.

If a commercially available alkali niobate powder can be used, the subsequent operations may be performed on this powder without preparing the raw material mixed powder and preparing the calcined powder described above.

(Preparation of slurry)
Next, the calcined powder is mixed with a binder and a dispersion medium to prepare a slurry. As the binder, a binder that can hold the shape of the green sheet to be described later and is volatilized without leaving carbon or the like by firing or a binder removal treatment prior thereto is used. Examples of binders that can be used include polyvinyl alcohol-based, polyvinyl butyral-based, cellulose-based, urethane-based and vinyl acetate-based binders. The amount of the binder used is also not particularly limited, but since it is removed in the post-process, it is preferable to reduce the amount as much as possible within the range where the desired moldability and shape retention can be obtained, in terms of reducing raw material costs. .

As the dispersion medium, one that does not cause aggregation of the calcined powder and the binder and can be easily removed by volatilization or the like after forming the green sheet described later is used. Examples of usable dispersion media include water and alcoholic solvents.

Components that adjust the properties of the slurry, such as dispersants, plasticizers and thickeners, may be added to the slurry.

Moreover, various components to be contained in the piezoelectric ceramic layer may be added to the slurry. Examples of such components include alkaline earths such as calcium carbonate ( _CaCO3 ), calcium metasilicate ( _CaSiO3 ) and calcium orthosilicate ( _Ca2SiO4 ), strontium carbonate ( _SrCO3 ₎ and barium carbonate ( _BaCO3 ). metal-containing compounds, silver-containing compounds such as silver oxide (AgO), lithium-containing compounds such as lithium carbonate, lithium fluoride and lithium manganate, manganese-containing compounds such as manganese oxide, manganese carbonate, manganese acetate and lithium manganate, and Examples include silicon-containing compounds _such as silicon dioxide ( _SiO2 ), calcium metasilicate ( _CaSiO3 ) and calcium orthosilicate ( _Ca2SiO4 ).

The method of mixing the calcined powder, binder, and dispersion medium is not particularly limited as long as each component is uniformly mixed while preventing impurities from being mixed. One example is ball mill mixing.

(Preparation of green sheet)
Next, the obtained slurry is molded to obtain a green sheet. As a molding method, a commonly used method such as a doctor blade method can be adopted.

(Printing of metal paste)
Next, an internal electrode paste containing a metal with a silver content of 50% by mass or more and a manganese compound is printed on the obtained green sheets. Since the internal electrode paste contains a manganese compound, the lithium that did not fully dissolve into the perovskite structure during firing, which will be described later, reacts with the manganese compound in the internal electrode layer to generate lithium manganate, thereby creating a gap. part is formed. In order to keep the area ratio _R1 of the gap and the average area percentage _R2 per gap within a predetermined range, the amount of the manganese compound added to the internal electrode paste should be 0.1% by mass or more and 3% by mass or less. preferably. The values of _R1 and _R2 are also affected by the composition of the piezoelectric ceramic layer, the amount of vehicle in the internal electrode paste, the printed film thickness, and the like. For this reason, the amount of the manganese compound added to the paste is controlled under _the manufacturing conditions that are actually employed. The value of ₂ may be determined to be a predetermined value.

To the internal electrode paste, glass frit or powder having the same composition as the alkali niobate powder contained in the green sheet may be added in order to improve the adhesion strength to the piezoelectric ceramic layer after firing.

When printing the internal electrode paste on the green sheet, it may be printed with a space that will be the side margin when the laminated piezoelectric element is formed.

(Production of green body)
Next, a predetermined number of green sheets printed with the internal electrode paste are laminated, and the green sheets are pressure-bonded to each other to produce a green body. Lamination and pressure bonding may be carried out by a commonly used method, such as a method in which laminated green sheets are heated and pressed in the direction of lamination, and thermocompression bonding is performed by the action of a binder.

At the time of lamination and pressure bonding, green sheets may be added to both ends in the lamination direction to serve as cover portions when the laminated piezoelectric element is formed. In this case, the green sheet to be added may have the same composition as the green sheet on which the internal electrode paste is printed, or may have a different composition. From the viewpoint of uniforming the shrinkage rate during firing, the composition of the green sheets to be added is preferably the same as or similar to the composition of the green sheets printed with the internal electrode paste.

(Fabrication of laminated piezoelectric ceramics)
Next, the obtained green body is fired to obtain a laminated piezoelectric ceramic. The binder may be removed from the green body prior to firing. In this case, removal of the binder and firing may be performed continuously using the same firing apparatus. The conditions for removing and firing the binder may be appropriately set in consideration of the volatilization temperature and content of the binder, the sinterability of the alkali niobate, the heat resistance of the metal contained in the internal electrode paste, and the like. An example of the conditions for removing the binder is an atmospheric atmosphere at a temperature of 300 to 500° C. for 5 to 20 hours. Examples of firing conditions include 800° C. to 1100° C. for 1 hour to 5 hours in an air atmosphere. When obtaining a plurality of laminated piezoelectric ceramics from one green body, the green body may be divided into several blocks prior to firing.

As described above, during firing of the green compact, lithium that did not fully dissolve in the perovskite structure reacts with the manganese compound in the internal electrode layer to form lithium manganate, thereby forming gaps. be done. In addition, silver in the internal electrode layers diffuses into the piezoelectric ceramic layers during firing, which may form gaps.

When the green sheet forming the green body contains at least one alkaline earth metal element selected from the group consisting of calcium, strontium and barium, silver and alkaline earth elements diffused from the internal electrode layers during firing. Due to the interaction with the metal element, the obtained piezoelectric ceramic layer becomes dense with fine sintered particles.

In addition, when the green sheet forming the green body contains silicon, it can act as a sintering aid to lower the firing temperature. In addition, silicon reacts with elements contained in the alkali niobate or separately added elements during firing to form Li ₂ SiO ₃ , Li ₄ SiO ₄ , K ₃ Nb ₃ O ₆ Si ₂ O ₇ , KNbSi _{2 .} By precipitating a crystalline phase such as O ₇ , K ₃ LiSiO ₄ or KLi ₃ SiO ₄ or an amorphous phase containing these elements, the volatilization of alkali metals and precipitation between sintered particles can be suppressed. .

(Formation of connection conductor)
Next, a conductive paste is applied to the surfaces of the obtained laminated piezoelectric ceramics where the internal electrode layers are exposed, and then baked to form connection conductors.

(Polarization treatment)
Finally, a high voltage is applied between the connecting conductors to perform polarization treatment, thereby obtaining a laminated piezoelectric element. Conditions for the polarization treatment are not particularly limited as long as the direction of spontaneous polarization in each piezoelectric ceramic layer can be aligned without causing damage such as cracks in the laminated piezoelectric ceramics. An example is applying an electric field of 4 kV/mm to 6 kV/mm at a temperature of 100.degree. C. to 150.degree.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples.

(Example 1)
A calcined powder represented by the composition formula Li _0.06 Na _0.52 K _0.42 NbO ₃ was prepared as an alkali niobate powder having a perovskite structure. _With respect to 100 mol% of this calcined powder, 0.65 mol% _Li2CO3 , 1.3 mol% _SiO2 , 0.5 mol% _CaCO3 and 0.5 mol% _MnCO3 , and polyvinyl A butyral-based binder was added, respectively, and wet-ball-mill mixed. The resulting mixed slurry was molded with a doctor blade to obtain a green sheet with a thickness of 30 μm. On the other hand, an internal electrode paste was prepared by mixing 0.1% by mass of manganese oxide (MnO) with Ag—Pd alloy paste (Ag/Pd mass ratio=9/1). After forming an electrode pattern by screen-printing the internal electrode paste on the green sheet, 26 layers of the green sheet are laminated and pressed at a pressure of about 50 MPa while heating to obtain a laminate. rice field. After separating the laminate into individual pieces, binder removal treatment was performed in the air, followed by firing in the air at 980° C. for 2 hours to obtain a fired body (laminated piezoelectric ceramics). A conductive paste containing Ag was applied to the surface of this fired body, heated to 600° C. and baked to form a pair of connecting conductors and external electrodes. Finally, an electric field of 3.0 kV/mm was applied between the pair of external electrodes for 3 minutes in a constant temperature bath at 80° C. to perform polarization treatment, thereby obtaining the laminated piezoelectric element of Example 1.

(Examples 2 and 3)
In the same manner as in Example 1, except that the amount of manganese oxide (MnO) added to the Ag—Pd alloy paste was set to 0.5% by mass (Example 2) and 3% by mass (Example 3). Laminated piezoelectric elements according to Examples 2 and 3 were obtained.

(Comparative example 1)
A multilayer piezoelectric element according to Comparative Example 1 was obtained in the same manner as in Example 1, except that manganese oxide (MnO) was not added to the Ag—Pd alloy paste.

(Comparative example 2)
A laminated piezoelectric element according to Comparative Example 2 was obtained in the same manner as in Example 1, except that the amount of manganese oxide (MnO) added to the Ag—Pd alloy paste was 10% by mass.

<Evaluation>
[Confirmation of presence or absence of interstices in internal electrode layers and lithium manganate]
For each laminated piezoelectric element thus obtained, cross-sectional observation was performed by the above-described method, and composition analysis was performed for those in which spots were confirmed. was confirmed, and the presence of lithium manganate in the gap was also confirmed.

[Calculation of R ₁ , R ₂ , R ₃ and R ₄ of internal electrode layers]
For each laminated piezoelectric element thus obtained, the cross section was observed and the lengths of the internal electrode layers, gaps, and lithium manganate were measured by the method described above, and R ₁ , R ₂ , R ₃ and R ₄ of the internal electrode layers were measured. was calculated. Table 1 shows the results.

[Measurement of electrical resistivity]
Each laminated piezoelectric element thus obtained was placed in a constant temperature bath at 80° C., and an electric field of 5 kV/mm was applied for 5 minutes to measure the voltage value and the current value. Then, based on the obtained measured values and element dimensions, the electrical resistivity of the laminated piezoelectric element was calculated. Table 1 shows the results.

[Measurement of change in electrical insulation over time (average life)]
Each laminated piezoelectric element thus obtained was placed in a constant temperature bath at 100° C., a DC electric field of 8 kV/mm was applied between the external electrodes, and the time until the current value flowing between the external electrodes reached 1 mA or more was measured. It was measured. Then, the average value for 10 devices at this time was taken as the average life. Table 1 shows the obtained average life as a ratio of the average life of the laminated piezoelectric element according to Comparative Example 1 to 100.

[Evaluation of Piezoelectric Properties]
The piezoelectric characteristics of each laminated piezoelectric element obtained were evaluated by displacement performance d ^* ₃₃ (pm/V). First, a unipolar sine wave having a maximum electric field of 6 kV/mm was applied to the laminated piezoelectric ceramics at about 100 Hz, and the displacement of the laminated piezoelectric element was measured with a laser Doppler displacement meter. Then, the displacement amount of the obtained laminated piezoelectric element is calculated from the thickness of the piezoelectric ceramic layer (the distance between the electrodes), the maximum voltage calculated from the maximum electric field, and the number of piezoelectric ceramic layers constituting the laminated piezoelectric element. By dividing, the displacement performance d ^* ₃₃ per unit voltage in one piezoelectric ceramic layer was calculated. The obtained displacement performance d ^* ₃₃ is shown in Table 1 as a ratio when the displacement performance d ^* ₃₃ of the multilayer piezoelectric element according to Comparative Example 1 is set to 100.

From the above results, it can be seen that the laminated piezoelectric element having the alkaline niobate-based piezoelectric ceramic layers includes gaps of a predetermined ratio and size in the internal electrode layers, and lithium manganate is contained in the gaps. It can be said that by using the material as a material, the deterioration of the electrical insulation during use is reduced and the displacement performance is also improved.

According to the present invention, it is possible to make a laminated piezoelectric element using an alkali niobate-based piezoelectric ceramic less degraded in electrical insulation during use and to have a large displacement when a voltage is applied. can. Such a laminated piezoelectric element is suitable for a haptic module that requires a large amount of displacement and a long life. Moreover, since the laminated piezoelectric element does not contain lead as a component, it is useful in that it can reduce the load on the environment during its life cycle.

REFERENCE SIGNS LIST 100 Laminated piezoelectric element 10 Piezoelectric

ceramic layers

20, 20a, 20b Internal electrode layer 21 Conductive portion 22 Gap portion 23

Lithium manganate

30, 30a, 30b Connection conductor 40 Side margin portion 50 Cover portion

Claims

A piezoelectric ceramic layer mainly composed of an alkali niobate having a perovskite structure, and disposed between the piezoelectric ceramic layers,
Having a conductive part with a silver content of 50% by mass or more,
The area percentage (R 1 ) occupied by the conductive portion is 75% or more and 95% or less,
An internal electrode having gaps in which the conductive part is not present and having an average area percentage (R 2 ) of 5% or less per one gap, and containing lithium manganate in at least one of the gaps. A laminated piezoelectric element comprising layers.
2. The method of claim 1, wherein the piezoelectric ceramic layer further contains at least one alkaline earth metal selected from the group consisting of calcium (Ca), strontium (Sr), and barium (Ba), and silver (Ag). Laminated piezoelectric element as described.
3. The laminated piezoelectric element according to claim 1, wherein said piezoelectric alkali niobate is represented by the following compositional formula.

(Ag u M2 v (K 1-w-x Na w Li x ) 1-u-v ) a
(Sb y Ta z Nb 1-yz )O 3 (1)

(However, M2 in the formula represents at least one alkaline earth metal selected from the group consisting of calcium (Ca), strontium (Sr) and barium (Ba). w, x, y, z and a are 0.005<u≤0.05, 0.002<v≤0.05, 0.007<u+v≤0.1, 0≤w≤1, 0.005<u≤0.05;02<x≦0.1,0.02<w+x≦1, 0≦y≦0.1, 0≦z≦0.4, and 1<a≦1.1. .)
4. The multilayer piezoelectric element according to claim 1, wherein the area percentage ( R3 ) of said lithium manganate in said internal electrode layer is 1% or more.
5. The laminated piezoelectric element according to claim 1, wherein the area percentage ( R4 ) of said lithium manganate in said gap is 10% or more.