JP6115163B2 - Multilayer piezoelectric ceramic element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a multilayer piezoelectric ceramic element and a method for manufacturing the same, and particularly to a multilayer piezoelectric ceramic element including an internal electrode layer containing Cu and a method for manufacturing the same.

  The multilayer piezoelectric ceramic element includes a piezoelectric multilayer body in which a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers are alternately stacked. The piezoelectric ceramic layer is usually composed of a piezoelectric ceramic containing lead oxide such as a lead zirconate titanate (PZT) based ceramic having a relatively large piezoelectric coefficient. On the other hand, as a conductive material to be included in the internal electrode layer, a noble metal such as an Ag—Pd alloy has been conventionally used. However, in recent years, use of a base metal such as Cu has been studied for cost reduction.

  However, in order to make the internal electrode layer as a base metal as described above, the following problems must be solved.

  In the firing step for obtaining a sintered piezoelectric laminate, a heat treatment for degreasing and a heat treatment for sintering are sequentially performed. In such a firing step, consideration must be given so that the base metal contained in the internal electrode layer is not oxidized. Therefore, if an atmosphere in which the base metal is not oxidized is applied, the amount of carbon may not be sufficiently reduced in the degreasing process. It is known that carbon causes reduction of lead contained in the piezoelectric ceramic and lowers the piezoelectricity of the piezoelectric ceramic in a subsequent heat treatment process for sintering.

  On the other hand, as a technique aiming at the base metal formation of the internal electrode layer as described above, for example, those described in JP-A-2006-196717 (Patent Document 1) and JP-A-2005-136260 (Patent Document 2), respectively. There is.

  In Patent Document 1, by reducing the amount of residual carbon contained in the raw laminate after degreasing to less than 350 ppm, the reduction of lead oxide by residual carbon is suppressed in the heat treatment step for sintering, and the piezoelectric ceramic layer By preventing the delamination at the interface between the internal electrode layer and the internal electrode layer, and coating the surface of the Cu powder used for the conductive paste forming the internal electrode layer with glass, oxidation resistance is not oxidized up to 400 ° C even in a nitrogen atmosphere. Is given to Cu powder.

  However, in the technique described in Patent Document 1, in the glass-coated Cu powder, Cu, which is a metal, has a larger coefficient of thermal expansion than that of glass, which is an oxide. In the heat treatment step for degreasing, As a result of the greater thermal expansion of Cu, there is a sufficient risk that the glass coat layer may be peeled off from the Cu powder. Therefore, Cu powder is exposed, causing a problem that the Cu component is oxidized.

  Next, in Patent Document 2, in order to improve the oxidation resistance in the degreasing process, the metal powder contained in the conductive paste used to form the internal electrode layer is dissolved in Cu and Cu. It is described that an alloy powder (Cu—Ni, Cu—Ir, Cu—Pd, Cu—Pt, Cu—Rh) with a metal having a high melting point is used. However, even when such an alloy powder is used, if degreasing is performed in an air atmosphere, the disadvantage that the Cu component is oxidized is unavoidable.

In Patent Document 2, PbO, Bi ₂ O ₃ , SiO ₂ , GeO ₂ , Li ₂ CO ₃ , ZnO, the surface of the metal powder contained in the conductive paste used for forming the internal electrode layer, It is described that the oxidation resistance of metal powder containing Cu is improved by forming a low-melting-point inorganic thin film layer composed of at least one of B ₂ O ₃ , BaO, SrO, CaO, CuO, and Ag. ing.

  In order to form the said inorganic thin film layer, patent document 2 describes applying the sol-gel method as an example. However, the inorganic thin film layer fixed by the sol-gel method has non-uniform coverage or insufficient thickness due to the nature of the sol-gel method. There is a problem that the oxidation of is inevitable.

JP 2006-196717 A Japanese Patent Laid-Open No. 2005-136260

  Accordingly, an object of the present invention is to solve the above-described problems, that is, in manufacturing a multilayer piezoelectric ceramic element having an internal electrode layer containing Cu, oxidation of Cu is performed even when degreasing in an air atmosphere. An object of the present invention is to provide a method for manufacturing a multilayer piezoelectric ceramic element that can be suppressed, and a multilayer piezoelectric ceramic element obtained by this manufacturing method.

  The present invention is first directed to a method for manufacturing a multilayer piezoelectric ceramic element.

  In the method for manufacturing a multilayer piezoelectric ceramic element according to the present invention, an alloy powder containing Cu and an easily oxidizable element that is easier to oxidize than Ni is prepared. Note that “Ni” in “easy to oxidize more than Ni” is selected to be a standard for defining the ease of oxidation, and has the significance of clearly defining the scope of the present invention.

  The alloy powder is heat-treated in an atmosphere having an oxygen concentration at which Cu does not oxidize and the oxidizable element oxidizes, thereby forming a core part mainly composed of Cu and an oxide containing the oxidizable element. A core-shell metal particle composed of a shell portion is formed. Here, since the easily oxidizable element is easier to oxidize than Ni, Cu is not oxidized, and it is easy to create a situation in which only the easily oxidizable element is oxidized. Therefore, the selection range of the heat treatment atmosphere can be widened. .

  Next, a conductive paste containing at least the core-shell metal particles is prepared. On the other hand, a piezoelectric ceramic green sheet containing a piezoelectric ceramic material is prepared.

  Next, the conductive paste is printed on a piezoelectric ceramic green sheet, thereby forming a conductive paste film to be an internal electrode layer on the piezoelectric ceramic green sheet. And a raw laminated body is obtained by laminating | stacking the several piezoelectric ceramic green sheet containing the piezoelectric ceramic green sheet in which the electrically conductive paste film | membrane was formed.

  Next, a degreasing process is implemented with respect to a raw laminated body, and a degreasing laminated body is obtained. In this degreasing step, the raw laminate is heat-treated in an air atmosphere. Therefore, the amount of residual carbon can be sufficiently reduced in the degreased laminate. Moreover, in the core-shell metal particles contained in the conductive paste film, Cu contained in the core part is covered with the shell part made of an oxide containing an easily oxidizable element. Oxidation can be suppressed.

  Next, in order to sinter the degreased laminate, the degreased laminate is heat treated, thereby obtaining a sintered piezoelectric laminate. Here, an atmosphere having an oxygen concentration at which Cu is not oxidized and an easily oxidizable element is oxidized is applied.

  A multilayer piezoelectric ceramic element is manufactured as described above.

  In the method for manufacturing a multilayer piezoelectric ceramic element according to the present invention, preferably, the alloy powder is a Cu—Al based alloy powder or a Cu—Si based alloy powder. Since Al and Si are solid-dissolved in Cu and the difference in equilibrium oxygen partial pressure with Cu is relatively large, core-shell metal particles having a highly covering shell part can be produced.

  The content of the easily oxidizable element in the alloy powder is preferably 3 to 11% by weight. When the content of the easily oxidizable element is less than 3% by weight, Cu is oxidized in the step of forming the degreased laminate, and the Cu component diffuses into the piezoelectric ceramic green sheet or the piezoelectric ceramic layer, thereby forming the piezoelectric ceramic layer. The piezoelectric properties of the ceramic may be degraded. On the other hand, when the content of the easily oxidizable element exceeds 11% by weight, the shell part becomes too thick, and the sintering of Cu is hindered by the shell part when the degreasing laminate is sintered, thereby constituting the piezoelectric ceramic layer. The target piezoelectric characteristics may not be obtained in the piezoelectric ceramic.

  The core-shell metal particles produced in the step of producing the core-shell metal particles are such that the core part is made of an alloy containing Cu and an easily oxidizable element, that is, the alloy powder is heat-treated in a predetermined atmosphere. -When producing the shell metal particles, it is preferable that the easily oxidizable element remains in the core portion. According to such a configuration, since the core part is made of an alloy composed of Cu and an easily oxidizable element, the easily oxidizable element diffuses from the core part to the particle surface even in the temperature rising process of the degreasing process. In other words, since an oxide containing an easily oxidizable element can be formed on the particle surface, in other words, the core-shell metal particle can be given a self-healing capability, so that the core-shell metal particle is more resistant to acid. It can be made excellent in chemical properties.

  The conductive paste preferably further contains at least one metal compound selected from alkali metal compounds and alkaline earth metal compounds. In the step of sintering the degreased laminate by adding an alkali metal compound and / or alkaline earth metal compound to the conductive paste, the shell part in the core-shell metal particles is vitrified and Cu is liquid phase sintered. Therefore, it is possible to form an internal electrode layer with high coverage.

  In the step of producing the core-shell metal particles, the heat treatment temperature is preferably 400 ° C to 700 ° C. When the heat treatment temperature is less than 400 ° C., it is difficult to form a highly coverable shell portion, and Cu may be oxidized in the degreasing laminate manufacturing process. And in the process of sintering the subsequent degreased laminate, Cu diffuses into the piezoelectric ceramic layer and the piezoelectric characteristics of the piezoelectric ceramic tend to deteriorate. On the other hand, when the heat treatment temperature exceeds 700 ° C., part of the shell portion is destroyed, and Cu may be oxidized in the degreasing laminate manufacturing process. And in the process of sintering the subsequent degreased laminate, Cu diffuses into the piezoelectric ceramic layer and the piezoelectric characteristics of the piezoelectric ceramic tend to deteriorate.

  In the degreasing laminate manufacturing process, the heat treatment temperature is preferably 280 ° C to 700 ° C. When the heat treatment temperature is lower than 280 ° C., the resin decomposition is insufficient, the amount of residual carbon increases, and the lead component in the piezoelectric ceramic layer is reduced by the residual carbon in the subsequent sintering step of the degreasing laminate. Ceramic piezoelectric properties tend to degrade. On the other hand, when the heat treatment temperature exceeds 700 ° C., Cu in the core portion of the core-shell metal particles is exposed and oxidized, and there is a tendency that target piezoelectric characteristics cannot be secured in the piezoelectric ceramic.

  The present invention is also directed to the structure of the multilayer piezoelectric ceramic element obtained by the manufacturing method described above.

The multilayer piezoelectric ceramic element according to the present invention includes a piezoelectric laminate formed by alternately laminating a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers, and the internal electrode layer includes a conductive portion mainly composed of Cu and , And a bond portion in which an easily oxidizable element is present that is easier to oxidize than Ni. The bond portion has a portion existing inside the internal electrode layer, and at least a portion of the bond portion is bonded to the piezoelectric ceramic layer. Yes, and the piezoelectric ceramic layer, is characterized in that the oxidizing ease element is present.

  In the manufacturing method described above, when Cu—Al based alloy powder or Cu—Si based alloy powder is used as the alloy powder, at least one element selected from Al and Si exists in the bonding portion in the internal electrode layer. .

  In the multilayer piezoelectric ceramic element according to the present invention, it is preferable that at least one metal selected from alkali metals and alkaline earth metals is further present in the joint portion. The presence of alkali metal and / or alkaline earth metal in the bonding portion reduces the viscosity of the bonding portion in the firing process for obtaining the multilayer piezoelectric ceramic element, and the bonding portion is made up of the internal electrode layer and the piezoelectric ceramic layer. Can be bonded more firmly.

Also, the coupling section of the internal electrode layers, and the piezoelectric ceramic layer laminated on one of the internal electrode layers, it is preferable that joining the piezoelectric ceramic layers stacked on the other inner electrode layers. According to this configuration, structural defects such as delamination can be made difficult to occur.

  Since the multilayer piezoelectric ceramic element according to the present invention is configured with an internal electrode layer mainly composed of Cu, it can be provided at low cost.

In addition, according to the multilayer piezoelectric ceramic element according to the present invention, since the internal electrode layer includes the coupling portion, the internal electrode layer and the piezoelectric ceramic layer are firmly coupled, and structural defects such as delamination are less likely to occur. Can do.
In the multilayer piezoelectric ceramic element according to the present invention, since the oxidizable element is present in the piezoelectric ceramic layer, such as at least one element selected from Al and Si, the internal electrode layer and the piezoelectric The ceramic layer can be more firmly bonded, and the effect of suppressing structural defects can be enhanced.

  According to the method for manufacturing a multilayer piezoelectric ceramic element according to the present invention, since the core-shell metal particles highly coated with the shell portion are used, the core-shell is not affected by exposure to the degreasing process in the air atmosphere. Cu contained in the core portion of the metal particles can be made difficult to oxidize.

  Therefore, the degreasing process can be carried out without problems in the air atmosphere, and the amount of residual carbon can be sufficiently reduced in the degreasing process, and as a result, the reduction of lead components in the piezoelectric ceramic by the residual carbon is suppressed in the sintering process. In the piezoelectric ceramic constituting the piezoelectric ceramic layer, good piezoelectric characteristics can be ensured.

1 is a cross-sectional view showing a multilayer piezoelectric ceramic element 1 according to an embodiment of the present invention. It is a figure which expands and shows the part A of FIG. FIG. 1 is a diagram for explaining a process of manufacturing core-shell metal particles 22 by heat-treating an alloy powder, which is performed in the method of manufacturing the multilayer piezoelectric ceramic element 1 shown in FIG. FIG.

  A laminated piezoelectric ceramic element 1 according to an embodiment of the present invention will be described with reference to FIG.

  The multilayer piezoelectric ceramic element 1 includes a piezoelectric multilayer body 11 in which a plurality of piezoelectric ceramic layers 2 to 5 and a plurality of internal electrode layers 7 to 9 are alternately stacked. In FIG. 1, four piezoelectric ceramic layers 2 to 5 and three internal electrode layers 7 to 9 are illustrated, but the number of each of the piezoelectric ceramic layers and the internal electrode layers may be arbitrarily changed. Of the three internal electrode layers 7 to 9, the internal electrode layers 7 and 9 are drawn to one end face 12 of the piezoelectric laminate 11, and the internal electrode layer 8 is drawn to the other end face 13. .

  An external terminal electrode 15 is formed on one end surface 12 of the piezoelectric laminate 11 so as to be electrically connected to the internal electrode layers 7 and 9, and the internal electrode layer 8 is formed on the other end surface 13. The external terminal electrode 16 is formed so as to be electrically connected. As a result, the internal electrode layers 7 and 9 connected to the first external terminal electrode 15 and the internal electrode layer 8 connected to the second external terminal electrode 16 face each other through the piezoelectric ceramic layer 3 or 4. However, they are alternately arranged.

  The piezoelectric ceramic layers 2 to 5 are made of a piezoelectric ceramic containing lead oxide such as a lead zirconate titanate (PZT) ceramic having a relatively large piezoelectric coefficient. The internal electrode layers 7 to 9 contain Cu as a main component, and details thereof will be described later with reference to FIG. External terminal electrodes 15 and 16 include, for example, a metal such as Cu or Ag as a conductive material.

  In FIG. 2, the internal electrode layer 8 sandwiched between the piezoelectric ceramic layers 3 and 4 is shown enlarged. The following description will be given with respect to the illustrated internal electrode layer 8, but the other internal electrode layers 7 and 9 have the same configuration, and therefore redundant description will be omitted.

  The internal electrode layer 8 includes a conductive portion 18 containing Cu as a main component and a bonding portion 19 in which at least one element selected from Al and Si is present, which is more easily oxidized than Ni. . The coupling portion 19 has a portion that joins the piezoelectric ceramic layers 3 and / or 4 at least in part. As can be seen from the illustrated connecting portion 19, the connecting portion 19 is bonded to both the piezoelectric ceramic layers 3 and 4, bonded to only one of the piezoelectric ceramic layers 3 and 4, and the piezoelectric ceramic layer 3. 4 and 4 are not bonded to each other, but bonding to at least one of the piezoelectric ceramic layers 3 and 4 makes the bonding between the internal electrode layer 8 and the piezoelectric ceramic layers 3 and 4 stronger. As a result, it contributes to making structural defects such as delamination difficult to occur.

  As described above, the coupling portion 19 is formed in the internal electrode layer 8 in addition to the conductive portion 18 due to the method for manufacturing the multilayer piezoelectric ceramic element 1 described below.

  In manufacturing the multilayer piezoelectric ceramic element 1, an alloy powder that is a material of the internal electrode layers 7 to 9 and includes Cu and an easily oxidizable element that is easier to oxidize than Ni is prepared. As the easily oxidizable element, Al or Si whose difference in equilibrium oxygen partial pressure with Cu is much larger than Ni is preferably used. Therefore, as the alloy powder, Cu-Al alloy powder or Cu-Si alloy powder is preferably used. The content of the easily oxidizable element in the alloy powder is preferably 3 to 11% by weight, as can be seen from the experimental examples described later.

  Next, the alloy powder includes a core portion mainly composed of Cu and an easily oxidizable element by being heat-treated in an atmosphere having an oxygen concentration at which Cu is not oxidized and an easily oxidizable element is oxidized. Core-shell metal particles composed of an oxide shell portion are produced. This core-shell metal particle preparation step will be described more specifically with reference to FIG. 3 assuming that the easily oxidizable element is Al. FIG. 3 (1) shows one alloy particle 21 constituting the alloy powder.

When the heat treatment step is performed in an atmosphere having an oxygen concentration at which Al does not oxidize and Al oxidizes, in the temperature rising process, the alloy particles 21 made of Cu and Al have Al as shown in FIG. As indicated by the arrows, it moves toward the surface of the alloy particle 21 and is oxidized when it reaches the surface to become Al ₂ O ₃ .

When the above heat treatment step proceeds, the core-shell metal particles 22 shown in FIG. The core-shell metal particles 22 are composed of a core portion 23 mainly composed of Cu and a shell portion 24 made of Al ₂ O ₃ . As can be seen from the phenomenon described with reference to FIG. 3 (1), Al may remain in the core portion 23 of the core-shell metal particle 22.

  The heat treatment temperature in the production process of the core-shell metal particles 22 is preferably 400 ° C to 700 ° C. This is because when the heat treatment temperature is less than 400 ° C., the highly coverable shell portion 24 is difficult to be formed, and when the heat treatment temperature exceeds 700 ° C., part of the shell portion 24 may be destroyed.

  Even when Al is replaced with another easily oxidizable element such as Si, the same phenomenon as described above occurs, and core-shell metal particles having the same form can be obtained.

  Next, a conductive paste containing at least core-shell metal particles is prepared. The conductive paste is for forming internal electrode layers 7-9. The conductive paste preferably further contains at least one metal compound selected from an alkali metal compound and an alkaline earth metal compound for the reason described later.

  On the other hand, a piezoelectric ceramic green sheet containing a piezoelectric ceramic material to be the piezoelectric ceramic layers 2 to 5 is prepared.

  Next, the conductive paste is printed on the piezoelectric ceramic green sheet, whereby a conductive paste film to be the internal electrode layers 7 to 9 is formed on the piezoelectric ceramic green sheet. Then, a plurality of piezoelectric ceramic green sheets including a piezoelectric ceramic green sheet on which a conductive paste film is formed are laminated, thereby obtaining a raw material of the piezoelectric laminate 11, that is, a raw laminate.

  Next, a degreasing process is implemented with respect to a raw laminated body. In this degreasing step, the raw laminate is heat-treated, but the heat treatment is performed in an air atmosphere. Therefore, in the obtained degreased laminate, the amount of residual carbon can be sufficiently reduced. Moreover, in the core-shell metal particles contained in the conductive paste film, Cu contained in the core is covered with a shell made of an oxide containing an easily oxidizable element, so that oxidation of Cu is suppressed. be able to.

  The heat treatment temperature in the degreasing step is preferably 280 ° C to 700 ° C. When the heat treatment temperature is less than 280 ° C., the resin decomposition is insufficient and the amount of residual carbon tends to increase. On the other hand, when the heat treatment temperature exceeds 700 ° C., Cu in the core portion of the core-shell metal particles may be exposed and oxidized.

  As described above, in the core-shell metal particle 22 shown in FIG. 3 (2), when Al remains in the core portion 23, that is, when the core portion 23 is made of an alloy containing Cu and Al, the degreasing step is increased. Even in the temperature process, Al diffuses from the core portion 23 toward the particle surface, and an oxide containing Al can be formed on the particle surface. In other words, the ability of the core-shell metal particles 22 to be self-repaired Therefore, the core-shell metal particles 22 can be made more excellent in oxidation resistance. This is also true when other easily oxidizable elements such as Si are used instead of Al.

  Next, in order to sinter the degreased laminate, heat treatment is performed, whereby the sintered piezoelectric laminate 11 is obtained. In this heat treatment, an atmosphere having an oxygen concentration at which Cu is not oxidized and an easily oxidizable element is oxidized is applied.

  As described above, the multilayer piezoelectric ceramic element 1 is obtained.

  As described above, when the conductive paste used to form the internal electrode layers 7 to 9 further contains at least one metal compound selected from an alkali metal compound and an alkaline earth metal compound, a degreasing step. , The shell portion in the core-shell metal particles is vitrified, and Cu can be liquid phase sintered in the sintering process, so that the high-coverage internal electrode layers 7 to 9 can be formed.

  Moreover, in the obtained multilayer piezoelectric ceramic element 1, the above-mentioned easily oxidizable element may be present in the piezoelectric ceramic layers 2 to 5, such as at least one element selected from Al and Si. When the easily oxidizable elements are present in the piezoelectric ceramic layers 2 to 5, the internal electrode layers 7 to 9 and the piezoelectric ceramic layers 2 to 5 are more strongly bonded to increase the effect of suppressing structural defects. Can do.

  The multilayer piezoelectric ceramic element according to the present invention can be used as, for example, a speaker, a shock sensor or the like. In the laminated piezoelectric ceramic elements used as these speakers or shock sensors, it is necessary to increase the area of the internal electrode layer. According to the present invention, since the main component of the internal electrode layer having a large area can be Cu, the cost reduction effect due to the use of Cu is great.

  Next, experimental examples carried out to confirm the effects of the present invention will be described.

<Preparation of evaluation sample>
(1) Production of Alloy Powder Alloy powders S-1 to S-9 each having “composition” and “D50” shown in Table 1 were produced by an atomizing method. In addition, although the alloy powder S-9 has Cu of 100% by weight and is not precisely an alloy powder, in the following description, it will be referred to as “alloy powder” for convenience.

  In Table 1, “composition” was determined by ICP-AES method (inductively coupled plasma emission analysis). “D50” was determined by a laser diffraction particle size distribution method.

  In the alloy powder shown in Table 1, the content of Al or Si was in the range of 3 to 11% by weight. However, in the case of less than 3% by weight, Cu is oxidized in a degreasing process described later, and the piezoelectric ceramic It has been confirmed that the Cu component may diffuse into the green sheet or the piezoelectric ceramic layer and the piezoelectric characteristics of the piezoelectric ceramic constituting the piezoelectric ceramic layer may deteriorate. On the other hand, when the content of Al or Si exceeds 11% by weight, in the core-shell metal particle preparation process described later, the shell part becomes too thick, and in the sintering process, the sintering of Cu is inhibited by the shell part, It has been confirmed that the target piezoelectric characteristics may not be obtained in the piezoelectric ceramic constituting the piezoelectric ceramic layer.

(2) Production of Core-Shell Metal Particles Next, while applying the heating profiles shown in “Temperature” and “Holding Time” in Table 2 to Alloy Powders S-1 to S-9 shown in Table 1, Table 2 As shown in FIG. 4, heat treatment is performed in an atmosphere having an oxygen partial pressure indicated by “PO ₂ ” while controlling the flow rates of “N ₂ ”, “air”, “H ₂ O”, and “H ₂ ”. Metal particles M-1 to M-12 were obtained.

  Regarding the metal particles M-1 to M-12, as shown in Table 2, “the presence or absence of the core-shell structure”, “the thickness of the shell part”, “the existing element in the shell part”, and “the existing element in the core part” Was evaluated.

  The evaluation of “presence / absence of core-shell structure”, “thickness of shell part”, “existing element of shell part” and “existing element of core part” was performed by the following methods.

[With or without core-shell structure]
Each metal particle was embedded in an epoxy resin and cured. After curing, the metal particle cross section was exposed by polishing. Next, FIB (focused ion beam) processing was performed on the metal particle cross section exposed by polishing. STEM (scanning transmission electron microscope) observation was performed on the metal particle cross-section sampled by FIB processing. The STEM observation was performed at 5000 times and 25000 times at an acceleration voltage of 5 kV.

  In STEM observation, the peripheral length L0 of the core portion and the peripheral length L1 of the core portion covered with the metal oxide were calculated. A case where L1 / L0 ≧ 75% is determined to be a core-shell structure, “◯” is displayed in the column “Presence / absence of core-shell structure” in Table 2, and L1 / L0 <75%. It was judged that the thing was not a core-shell structure, and "x" was displayed.

  In addition, what was judged not to have a core-shell structure was not evaluated for “thickness of shell part”, “existing element of shell part”, and “existing element of core part”.

[Thickness of shell part]
The thickness of the shell portion was calculated from the STEM image described above.

[Existing elements in the shell] and [Existing elements in the core]
In the STEM observation described above, each of the existing elements in the shell part and the core part was qualitatively determined by EDS (energy dispersive X-ray analyzer).

  The metal particles M-1, M-2, and M-4 to M-9 that are heat-treated under the conditions within the scope of the present invention are oxidizable elements that are more easily oxidized than Cu and more easily oxidized than Ni. It was confirmed that the core-shell structure has a shell part mainly composed of an oxide of Al or Si and a core part mainly composed of Cu.

  In metal particles M-1, M-2, and M-4 to M-9, a small amount of Cu component was diffused in the shell portion. In this way, the presence of a small amount of Cu component in the shell portion improves the bondability between the shell portion and the core portion, and reduces the destruction of the shell portion due to mechanical shear force in the dispersion process of the subsequent paste manufacturing process. I guess it can be done.

  Further, in the metal particles M-1, M-2, and M-4 to M-9, Al or Si as an easily oxidizable element that is more easily oxidized than Ni was present in the core portion. As described above, the presence of the easily oxidizable element in the core portion allows the easily oxidizable element to diffuse from the core portion to the surface and oxidize when the metal particles thermally expand in the temperature rising process of the subsequent degreasing process. It is estimated that the Cu component of the core part can be suppressed from being oxidized.

  On the other hand, for the metal particles M-3, the alloy powder S-2 within the scope of the present invention was used. However, in the heat treatment, the oxygen partial pressure that also oxidizes the Cu component was applied. -A shell structure was not formed.

  Further, as the metal particles M-12, alloy powder S-2 within the scope of the present invention was used. However, since the heat treatment was not performed, naturally, the core-shell structure was not formed.

  Metal particles M-10 and M-11 were prepared using alloy powders S-8 and S-9, respectively, which are outside the scope of the present invention, and the Cu component was also oxidized, resulting in a core-shell structure. Did not form.

  In addition, although the heat processing temperature applied in the core-shell metal particle preparation process shown in Table 2 was in the range of 400 ° C. to 700 ° C., when the heat processing temperature was less than 400 ° C., the highly coverable shell portion was It is difficult to form, and Cu may be oxidized in a subsequent degreasing process, and it has been confirmed that Cu may diffuse into the piezoelectric ceramic layer in the subsequent sintering process and deteriorate the piezoelectric characteristics of the piezoelectric ceramic. On the other hand, when the heat treatment temperature exceeds 700 ° C., part of the shell portion is destroyed, Cu may be oxidized in the degreasing process, and Cu is diffused into the piezoelectric ceramic layer in the subsequent sintering process. It has been confirmed that the characteristics may deteriorate.

(3) Production of conductive paste for internal electrode layer Metal particles shown in Table 2, terpineol / ethocell resin = 90/10 wt% organic vehicle, sodium carbonate (NaCO ₃ ) powder, barium carbonate (BaCO ₃₎ ) The powder was prepared so as to have the composition shown in Table 3, and dispersed with a three roll to obtain conductive pastes P-1 to P-14 for forming an internal electrode layer.

In Table 3, it is noted that the conductive paste P-13 contains NaCO ₃ as an alkali metal compound, and the conductive paste P-14 contains BaCO ₃ as an alkaline earth metal compound. Is done.

(4) Production of raw laminate A piezoelectric ceramic green sheet made of lead zirconate titanate containing bismuth, lanthanoid and nickel was prepared. Next, the conductive paste shown in Table 3 was applied and dried on the piezoelectric ceramic green sheet to form a conductive paste film to be the internal electrode layer. Next, a plurality of piezoelectric ceramic green sheets including three piezoelectric ceramic green sheets on which a conductive paste film was formed were laminated to obtain a raw laminate.

(5) Heat treatment for degreasing and sintering The raw laminate was subjected to heat treatment for degreasing and subsequent sintering under the conditions shown in Table 4, and samples 1 to 19 were subjected to heat treatment. Sintered piezoelectric laminates according to each were obtained.

In the column of “degreasing step” in Table 4, “temperature” in heat treatment for degreasing, and each flow rate and oxygen partial pressure of “N ₂ ”, “air”, “H ₂ O”, and “H ₂ ” “PO ₂ ” is shown, and in the “sintering step” column, “temperature” in the heat treatment for sintering, and “N ₂ ”, “air”, “H ₂ O” and “H ₂ ” Each flow rate and oxygen partial pressure “PO ₂ ” are shown.

  In addition, although the heat treatment temperature in the “degreasing step” in Table 4 was in the range of 280 ° C. to 700 ° C., when the heat treatment temperature is less than 280 ° C., the resin decomposition is insufficient, and the amount of residual carbon increases, In the subsequent sintering process, it has been confirmed that the lead component in the piezoelectric ceramic layer is reduced by residual carbon and the piezoelectric characteristics of the piezoelectric ceramic tend to deteriorate. On the other hand, it has been confirmed that when the heat treatment temperature exceeds 700 ° C., Cu in the core portion of the core-shell metal particles is exposed and oxidized, and the target piezoelectric characteristics tend not to be secured in the piezoelectric ceramic.

<Evaluation>
Next, evaluation of the sintered piezoelectric laminated body according to each sample produced as described above was performed for the following items.

(1) Piezoelectric properties The piezoelectric laminate according to each sample was cut into a size of 13 mm x 3 mm. The thickness was about 0.12 mm.

Electrodes were formed by vapor deposition on the surface of the cut piezoelectric laminate. Further, after performing polarization treatment, d ₃₁ was calculated by a resonance method. The results are shown in Table 5.

As shown in Table 5, Samples 1, 3, 6, 8-14, 18 and 19 within the scope of the present invention exhibited excellent piezoelectric characteristics with d ₃₁ (pC / N) of 210 or more.

On the other hand, in Samples 2, 4, 7, 15 and 16 outside the scope of the present invention, d ₃₁ (pC / N) was less than 50, and piezoelectric properties that could be put to practical use were not obtained. These reasons are presumed as follows.

  In Samples 2 and 4, as shown in Table 4, since the heat treatment in the sintering process was performed in the atmosphere, the shell portion was destroyed by the thermal expansion of the metal particles during the temperature rising process from the degreasing process to the sintering process. This is presumably because the core portion mainly composed of Cu was exposed and Cu which is the main component of the exposed core portion was oxidized.

  In Sample 7, it is presumed that the metal particles M-3 shown in Table 2 were used as the metal particles. As shown in Table 2, the metal particles M-3 are subjected to heat treatment in the atmosphere as shown in Table 2, and therefore, the Cu component is not oxidized to become core-shell metal particles. It is presumed that it was not reduced to Cu in the subsequent sintering step under a reducing atmosphere.

  In Sample 15, it is presumed that the metal particles M-10 obtained by heat-treating the alloy powder S-8 made of a Cu—Ni alloy as shown in Table 1 as shown in Table 2 were used. . As shown in Table 2, the metal particles M-10 did not become core-shell metal particles in the core-shell metal particle production step. This is because both the Ni component and the Cu component were oxidized in the core-shell metal particle preparation step, and the oxidized Cu component was not reduced to Cu in the subsequent sintering step in a reducing atmosphere. Guessed.

  In Sample 16, it is presumed that metal particles M-11 obtained by heat-treating alloy powder S-9 with 100% Cu as shown in Table 1 and heat-treated as shown in Table 2 were used. Since the metal particles M-11 have 100% Cu, the core-shell metal particles are not core-shell metal particles as shown in Table 2 in the core-shell metal particle manufacturing step.

Further, in Sample 5 outside the scope of the present invention, d ₃₁ (pC / N) was less than 150, and piezoelectric characteristics that could be put to practical use were not obtained. This is because, as shown in the column of “Degreasing Process” in Table 4, since the heat treatment for degreasing was not performed in the atmosphere, the amount of residual carbon in the degreased laminate increased, and in the subsequent sintering process, This is presumably because the lead component in the piezoelectric ceramic was reduced by the residual carbon in the laminate formation process.

Further, even in the sample 17 outside the scope of the present invention, d ₃₁ (pC / N) was less than 150, and piezoelectric characteristics that could be put to practical use were not obtained. This is presumably because the sample 17 used the metal particles M-12 shown in Table 2 as the metal particles. The metal particles M-12 are not subjected to heat treatment in the core-shell metal particle preparation step, and thus do not have a core-shell structure. Therefore, as shown in Table 4, the degreasing step is performed in the atmosphere. In this case, it is presumed that the Cu component was completely oxidized and was not reduced to Cu in the subsequent sintering step under a reducing atmosphere.

As a result of the evaluation of the piezoelectric characteristics as described above, when d ₃₁ (pC / N) is less than 150, it was determined that the piezoelectric characteristics were defective, and the subsequent characteristics evaluation was not performed. That is, the following characteristic evaluation was performed only for samples 1, 3, 6, 8-14, 18 and 19, and the subsequent characteristic evaluation was not performed for samples 2, 4, 5, 7 and 15-17.

(2) Presence / absence of bonding portion and existing elements The piezoelectric laminate according to each sample was filled with resin and then subjected to cross-section polishing to expose the interface between the internal electrode layer and the piezoelectric ceramic layer. SEM observation and WDX observation of the cross section of the internal electrode layer were performed, and the presence of the joint existing in the internal electrode layer and joining the piezoelectric ceramic layer and the elements present in the joint were identified.

  For all of Samples 1, 3, 6, 8-14, 18 and 19, the presence of a bond was observed, and Al or Si was observed in the bond.

  In Samples 18 and 19, Na as an alkali metal or Ba as an alkaline earth metal was observed at the joint.

(3) Presence element of piezoelectric ceramic layer The piezoelectric laminated body which concerns on each sample was resin-filled, and it cross-sectional-polished and exposed the interface of an internal electrode layer and a piezoelectric ceramic layer. WDX observation of the cross section of the piezoelectric ceramic layer was performed to identify elements present in the piezoelectric ceramic layer.

  For all of Samples 1, 3, 6, 8-14, 18 and 19, Al or Si was observed in the piezoelectric ceramic layer.

(4) Bondability The piezoelectric laminated body according to each sample was filled with a resin and then subjected to cross-sectional polishing to expose the interface between the internal electrode layer and the piezoelectric ceramic layer. When the presence or absence of delamination was evaluated at the joint between the internal electrode layer and the piezoelectric ceramic layer, no delamination was observed in all of Samples 1, 3, 6, 8-14, 18 and 19.

  Next, the piezoelectric laminate was mechanically broken with pliers. When the fragments after destruction were observed with a magnifying glass, in Samples 1, 3, 6 and 8 to 14, some interface destruction between the internal electrode layer and the piezoelectric ceramic layer was observed. No interface breakdown between the layer and the piezoelectric ceramic layer was observed.

  From the results described above, it was found that Samples 1, 3, 6, 8-14, 18 and 19 within the scope of the present invention have good bondability between the internal electrode layer and the piezoelectric ceramic layer. In particular, Samples 18 and 19 showed better bondability. This is presumed to be because an alkali metal or an alkaline earth metal was included in the bonding portion. In Samples 18 and 19, an alkali metal compound and / or an alkaline earth metal compound was added to the conductive paste. Therefore, in the step of sintering the degreased laminate, it is presumed that the shell part in the core-shell metal particles can be vitrified and Cu can be liquid phase sintered, which is also the internal electrode layer and the piezoelectric ceramic layer. It is presumed that this contributed to the improvement of the bondability.

DESCRIPTION OF SYMBOLS 1 Laminated piezoelectric ceramic elements 2-5 Piezoelectric ceramic layers 7-9 Internal electrode layer 11 Piezoelectric laminated body 18 Conductive part 19 Coupling part 21 Alloy particle 22 Core-shell metal particle 23 Core part 24 Shell part

Claims (11)

Comprising a piezoelectric laminate in which a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers are alternately laminated;
The internal electrode layer includes a conductive portion containing Cu as a main component and a bonding portion where an easily oxidizable element that is easier to oxidize than Ni exists.
The coupling portion, and having a portion present in the interior of the inner electrode layer, have a portion to be bonded to the piezoelectric ceramic layer at at least a portion,
The easily oxidizable element is present in the piezoelectric ceramic layer ,
Multilayer piezoelectric ceramic element.   The multilayer piezoelectric ceramic element according to claim 1, wherein the easily oxidizable element is at least one element selected from Al and Si.   The multilayer piezoelectric ceramic element according to claim 1 or 2, wherein at least one metal selected from an alkali metal and an alkaline earth metal is further present in the joint portion.   2. The multilayer according to claim 1, wherein the coupling portion joins the piezoelectric ceramic layer stacked on one of the internal electrode layers and the piezoelectric ceramic layer stacked on the other of the internal electrode layers. Type piezoelectric ceramic element. Preparing an alloy powder containing Cu and an easily oxidizable element that is easier to oxidize than Ni;
The alloy powder is heat-treated in an atmosphere having an oxygen concentration at which Cu does not oxidize and the easily oxidizable element oxidizes, whereby a core portion mainly composed of Cu and an oxide including the easily oxidizable element Producing a core-shell metal particle composed of a shell portion comprising:
Preparing a conductive paste containing at least the core-shell metal particles;
Preparing a piezoelectric ceramic green sheet containing a piezoelectric ceramic material;
Forming a conductive paste film to be an internal electrode layer on the piezoelectric ceramic green sheet by printing the conductive paste on the piezoelectric ceramic green sheet;
A step of obtaining a raw laminate by laminating a plurality of piezoelectric ceramic green sheets including the piezoelectric ceramic green sheet on which the conductive paste film is formed;
In order to degrease the raw laminate, a step of obtaining a degreased laminate by heat-treating the raw laminate in an air atmosphere;
In order to sinter the degreased laminate, the degreased laminate is heat-treated in an atmosphere having an oxygen concentration in which Cu is not oxidized and the easily oxidizable element is oxidized, thereby obtaining a sintered piezoelectric laminate. Process,
A method for manufacturing a laminated piezoelectric ceramic element, comprising: The method for producing a multilayer piezoelectric ceramic element according to claim 5 , wherein the alloy powder is a Cu—Al based alloy powder or a Cu—Si based alloy powder. The method for producing a multilayer piezoelectric ceramic element according to claim 5 or 6 , wherein a content of the easily oxidizable element in the alloy powder is 3 to 11% by weight. The core - the core is prepared in the step of preparing a shell metal particles - shell metal particles, the core portion is made of an alloy containing Cu and the oxidizing ease element according to any one of claims 5 to 7 A method for manufacturing a multilayer piezoelectric ceramic element. The conductive paste includes at least one further comprising a metal compound, the method of fabricating the multilayer piezoelectric ceramic element according to any one of claims 5 to 8 selected from alkali metal compounds and alkaline earth metal compounds. The method for producing a multilayer piezoelectric ceramic element according to any one of claims 5 to 9 , wherein in the step of producing the core-shell metal particles, a heat treatment temperature is 400 ° C to 700 ° C. The method for producing a multilayer piezoelectric ceramic element according to any one of claims 5 to 10 , wherein in the step of obtaining the degreased laminate, a heat treatment temperature is 280 ° C to 700 ° C.

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