JP5018649B2 - Piezoelectric ceramic, piezoelectric element and multilayer piezoelectric element - Google Patents

Description

  The present invention relates to a piezoelectric ceramic, a piezoelectric element, and a laminated piezoelectric element.

  Piezoelectric ceramics exhibiting a so-called piezoelectric phenomenon that generates mechanical strain and stress when an electric field is applied are known. Such a piezoelectric ceramic is used for an actuator, a piezoelectric buzzer, a sounding body, a sensor, or the like.

One of the characteristics required for the piezoelectric ceramic used for the piezoelectric layer of the piezoelectric element is that the piezoelectric strain constant that is an index representing the magnitude of the strain with respect to the strength of the electric field is large. Among materials forming a piezoelectric ceramic, materials capable of forming a piezoelectric ceramic having a large piezoelectric strain constant include nickel-lead niobate (Pb (Ni _1/3 Nb _2/3 ) O ₃ ; PNN) and titanic acid. A material containing lead (PbTiO ₃ ; PT) and lead zirconate (PbZrO ₃ ; PZ), that is, a PNN-PT-PZ-based material is known (for example, see Patent Document 1).
Japanese Patent No. 4018597

  Piezoelectric ceramics are used in various fields, and required characteristics differ depending on the field. For example, piezoelectric ceramics used in fuel injection actuators are required to exhibit excellent piezoelectric characteristics at high temperatures and high voltages, and to have excellent mechanical strength.

  However, according to studies by the present inventors, a piezoelectric ceramic made of a conventional PNN-PT-PZ-based composite oxide as described in Patent Document 1 has sufficient piezoelectric characteristics under high voltage. I knew it wasn't.

  The present invention has been made in view of such circumstances, a piezoelectric ceramic having sufficiently excellent piezoelectric characteristics even under a high voltage and excellent in mechanical strength, and a piezoelectric element including the piezoelectric ceramic having such characteristics, and An object is to provide a multilayer piezoelectric element.

In order to achieve the above object, the present invention includes a sintered body containing a composite oxide represented by the following general formula (1) as a main component, and Cu elements are unevenly distributed at grain boundaries of the sintered body. A piezoelectric ceramic is provided.
_{(Pb 1-x-y Me} x) [(Ni 1/3 Nb 2/3) a Ti b Zr c] O 3 -3 / 2y ... (1)

Here, in formula (1), Me represents at least one element selected from the group consisting of Ca, Sr, and Ba, and a, b, c, x, and y represent the following formulas (2) to (9). Fulfill.
0 <a ≦ 0.1 (2)
0 <b <1 (3)
0 <c <1 (4)
a + b + c = 1 (5)
0.788 ≦ b (1-a) /c≦0.941 (6)
0 ≦ x <1 (7)
0 ≦ y ≦ 0.05 (8)
0 <1-xy (9)

  By providing the piezoelectric ceramic of the present invention with the above-described configuration, the piezoelectric ceramic exhibits sufficiently excellent piezoelectric characteristics even under a high voltage and has excellent mechanical strength as compared with a piezoelectric ceramic without the above-described configuration. . In addition to such effects, the piezoelectric ceramic of the present invention has an effect that the Curie temperature is high and the temperature range is sufficiently wide and can be formed at a low firing temperature. Since the firing temperature can be lowered in this way, it is also possible to use an internal electrode layer containing copper (Cu) as a main component in the multilayer piezoelectric element. Since Cu is less expensive than an Ag—Pd alloy or the like, it is advantageous in terms of cost.

  The reason why such an effect is obtained is as follows. In the piezoelectric ceramic according to the present invention, when a satisfies the expression (2), the Curie temperature is increased, and the piezoelectric characteristics under a high voltage can be improved. Moreover, the specific resistance of the piezoelectric ceramic can be increased by having a fine structure in which Cu elements are unevenly distributed at the grain boundaries. Thereby, a sufficient polarization voltage can be applied, and a sufficiently large amount of generated displacement can be obtained. However, the reason why the above effect is obtained is not limited to this.

Y is satisfying the following formula (10) in the general formula (1).
0 <y ≦ 0.03 (10)

  By setting y in such a range, the piezoelectric characteristics of the piezoelectric ceramic can be further improved.

X in the general formula (1) is satisfying the following equation (11).
0 <x ≦ 0.05 (11)

  By setting x in such a range, the piezoelectric characteristics of the piezoelectric ceramic can be further improved.

  In the piezoelectric ceramic according to the present invention, the sintered body contains a first subcomponent having at least one metal element R1 selected from the group consisting of Ta, Nb, and W as a constituent element. The content of one subcomponent is preferably greater than 0 and less than or equal to 0.9 mol in terms of metal element R1.

  When the piezoelectric ceramic contains the first subcomponent in a specific range, the mechanical strength and piezoelectric characteristics of the piezoelectric ceramic can be further improved.

In the piezoelectric ceramic according to the present invention, the sintered body is selected from the group consisting of at least one metal element R2 selected from the group consisting of Dy, Gd and Y and Ta, Nb and W as constituent elements. A second subcomponent having at least one metal element R3 is contained, and the content of the second subcomponent with respect to 100 moles of the main component is greater than 0 in terms of Pb (R2 _d R3 _e ) O ₃ and is less than 0.00. It is preferable that it is 6 mol or less.

Here, d and e are numerical values exceeding 0, respectively, and satisfy the following formula (12).
d + e = 1 (12)

  When the piezoelectric ceramic contains the above-mentioned second subcomponent in a specific range, the piezoelectric characteristics can be further improved.

  The present invention provides a piezoelectric element comprising the above-described piezoelectric ceramic. Since such a piezoelectric element includes the piezoelectric ceramic having the above characteristics, it exhibits excellent piezoelectric characteristics even under a high voltage, and is sufficiently excellent in mechanical strength.

  The present invention also provides a laminated piezoelectric element in which piezoelectric layers composed of the above-described piezoelectric ceramics and internal electrode layers containing Cu element are alternately laminated.

  Since such a laminated piezoelectric element includes the piezoelectric ceramic having the above-described characteristics, it exhibits excellent piezoelectric characteristics even under high voltage, and is sufficiently excellent in mechanical strength. In addition, the Curie temperature is high and it has a sufficiently wide operating temperature range. Further, by using the internal electrode layer containing Cu element, Cu element can be unevenly distributed in the grain boundary of the sintered body by utilizing diffusion from the electrode containing Cu element.

  According to the present invention, there are provided a piezoelectric ceramic having sufficiently excellent piezoelectric characteristics even under a high voltage and excellent in mechanical strength, and a piezoelectric element and a laminated piezoelectric element provided with the piezoelectric ceramic having such characteristics. Can do.

  In the following, preferred embodiments of the present invention will be described with reference to the drawings as the case may be. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted.

  FIG. 1 is a perspective view showing a preferred embodiment of the piezoelectric element of the present invention. The piezoelectric element 20 includes a piezoelectric ceramic 1 and a pair of electrodes 2 and 3 provided respectively on a pair of opposing surfaces of the piezoelectric ceramic 1.

  For example, the piezoelectric ceramic 1 is polarized in the thickness direction, that is, the direction in which the pair of electrodes 2 and 3 are opposed to each other. Can spread and vibrate in the direction. The electrodes 2 and 3 are made of metal such as gold (Au), for example. The electrodes 2 and 3 can be electrically connected to an external power source via wires or the like (not shown).

The piezoelectric ceramic 1 includes a sintered body containing a composite oxide represented by the following general formula (1) as a main component, and Cu elements are unevenly distributed at grain boundaries of the sintered body.
_{(Pb 1-x-y Me} x) [(Ni 1/3 Nb 2/3) a Ti b Zr c] O 3 -3 / 2y ... (1)

Here, in formula (1), Me represents at least one element selected from the group consisting of Ca, Sr, and Ba, and a, b, c, x, and y represent the following formulas (2) to (9). Fulfill.
0 <a ≦ 0.1 (2)
0 <b <1 (3)
0 <c <1 (4)
a + b + c = 1 (5)
0.788 ≦ b (1-a) /c≦0.941 (6)
0 ≦ x <1 (7)
0 ≦ y ≦ 0.05 (8)
0 <1-xy (9)

The composite oxide represented by the general formula (1) has a so-called perovskite structure (ABO ₃ ). Specifically, Pb and the substitution element Me are included at the A site, and Ni, Nb, Ti, and Zr are included at the B site.

As shown in the above general formula (6), the ratio (b / c) of the content of Ti and Zr at the B site is a substitution of (Ni _1/3 Nb _2/3 ) called a relaxer. It is adjusted to the amount a. By satisfying the general formula (6), the composite oxide has a composition in the vicinity of the morphotropic phase boundary, so that the piezoelectric strain constant can be increased.

Further, y representing the decrease in Pb from the stoichiometric composition at the A site is adjusted to the range represented by the general formula (8). In addition, the reduction | decrease of Pb from a stoichiometric composition shows the reduction | decrease of Pb from the compound represented by following General formula (13). The composite oxide in the present embodiment may have a maximum of 5 mol% of Pb reduced with respect to the stoichiometric composition of formula (13), but if it is within 3 mol%, the sinterability is particularly good. Can keep.
_{(Pb 1-x Me x)} [(Ni 1/3 Nb 2/3) a Ti b Zr c] O 3 ... (13)

  In the formula (1), the oxygen composition is obtained stoichiometrically, and in the actual composition, there is a slight deviation from the stoichiometric composition (for example, 95% based on the stoichiometric composition. ˜105 mol%) is acceptable.

  FIG. 2 is a TEM (transmission electron microscope) photograph showing the fine structure of the piezoelectric ceramic according to the present embodiment. FIG. 2 shows a crystal grain 30 of the composite oxide and a grain boundary 50 that is a boundary portion between the crystal grains 30. The state in which the Cu element is unevenly distributed means, for example, a state in which almost no Cu element is present in the crystal grain 30 and the Cu element is present in the grain boundary 50 of the sintered body.

  Table 1 shows the result of measuring the change in the element distribution according to the distance from the grain boundary 50 using the energy dispersive X-ray spectrometer (EDS) along the direction of the arrow L11 in FIG.

  The numerical value shown in Table 1 has shown the content [mol%] of the conversion element of the detection element with respect to the main component. As shown in Table 1, Cu element (CuO) is detected in the grains, that is, at a point where the distance from the grain boundary is 0 nm, but no Cu element is detected at the points of 5 nm and 10 nm.

  The piezoelectric ceramic 1 has a high specific resistance by including a microstructure in which Cu elements are unevenly distributed at the grain boundaries of the sintered body. The Cu element segregated at the grain boundary exists, for example, in the state of a Cu compound. Examples of the Cu compound include Cu oxides such as CuO.

  The content of the Cu element in the piezoelectric ceramic 1 is preferably 0.1 to 1.0% by mass in terms of CuO with respect to the composite oxide represented by the general formula (1) as the main component, It is more preferable that it is 0.2-1.0 mass%. When the content is less than 0.1% by mass, there is a tendency that a sufficient improvement effect of piezoelectric characteristics cannot be obtained. On the other hand, when the content exceeds 1.0% by mass, the Cu component tends to enter the composite oxide particles, and excellent piezoelectric characteristics tend to be impaired.

It is preferable that x and y in the general formula (1) satisfy the following formulas (10) and (11), respectively.
0 <y ≦ 0.03 (10)
0 <x ≦ 0.05 (11)

  In the piezoelectric ceramic 1, the sintered body contains a first subcomponent having at least one metal element R1 selected from the group consisting of Ta, Nb, and W as a constituent element, and the first subcomponent with respect to 100 mol of the main component. The component content is preferably greater than 0 and less than or equal to 0.9 mol in terms of metal element R1.

In the piezoelectric ceramic 1, the sintered body is at least one metal element R2 selected from the group consisting of Dy, Gd and Y as a constituent element, and at least one selected from the group consisting of Ta, Nb and W. And the content of the second subcomponent with respect to 100 moles of the main component is 0 in terms of Pb (R2 _d R3 _e ) O ₃ which is a perovskite oxide. It is preferably larger than 0.6 mol. The reason for converting to the perovskite type oxide is that the second subcomponent is usually considered to exist as a perovskite type oxide. However, the second subcomponent is not limited to the perovskite oxide.

Here, d and e are numerical values exceeding 0 and satisfying the following formula (12), and (d, e) = (1/2, 1/2), (2/3) as specific combinations. , 1/3) and (1/3, 2/3).
d + e = 1 (12)

That is, d and e indicating the content ratio of R2 and R3 are adjusted so that (R2 _d R3 _e ) is a tetravalent stoichiometric.

  Next, a method for manufacturing the piezoelectric element 20 shown in FIG. 1 will be described below. First, oxide powders containing lead, nickel, niobium, titanium, and zirconium are respectively prepared as raw materials for the composite oxide that is the main component of the piezoelectric ceramic 1.

  Further, as a Cu element material unevenly distributed in the grain boundary, for example, a Cu compound such as Cu oxide powder or Cu powder is prepared. The raw material of the complex oxide as the main component and the Cu element that is unevenly distributed in the grain boundary may not be the above-described one, and for example, a material that becomes an oxide by firing, such as carbonate or oxalate, is used. May be. These raw material powders are usually those having an average particle diameter of about 0.5 to 10 μm.

  In the piezoelectric ceramic 1, when a part of Pb is replaced with Me, an oxide powder containing at least one element selected from the group consisting of Ca, Sr and Ba is used as the first subcomponent having the metal element R1. When oxide is included, oxide powders of Ta, Nb and W are prepared.

Further, when the second subcomponent having the metal elements R2 and R3 is included, for example, an oxide powder containing R2 and an oxide powder containing R3 are prepared. Here, R2 represents at least one metal element selected from the group consisting of Dy, Gd and Y, and R3 represents at least one metal element selected from the group consisting of Ta, Nb and W. Note that examples of the oxide containing R2 include Dy ₂ O ₃ , and examples of the oxide containing R ₃ include Ta ₂ O ₅ .

  Subsequently, after sufficiently drying the prepared raw material, the raw material is weighed at a ratio such that the composition of the piezoelectric ceramic 1 becomes a desired composition.

  The weighed raw materials are wet pulverized and mixed using, for example, a ball mill to obtain a raw material mixture. The Cu element material, the first subcomponent, and the second subcomponent material that are unevenly distributed at the grain boundaries may be added after pre-baking described later. However, from the viewpoint of producing a homogeneous piezoelectric ceramic, it is preferable to add it before the preliminary firing. In addition, when adding after temporary baking, it is preferable to use an oxide for the raw material.

  Then, this mixture is dried and, for example, calcined at 750 to 950 ° C. for 1 to 6 hours. The pre-baking may be performed in the air, or may be performed in an atmosphere having a higher oxygen partial pressure than in the air or a pure oxygen atmosphere. The obtained calcined product is finely pulverized, then wet pulverized using a ball mill, and dried again to obtain a calcined powder. Furthermore, after adding an acrylic resin as a binder to the calcined powder and granulating, a compact can be obtained by press molding using a uniaxial press molding machine.

For example, the obtained compact is fired at 950 ° C. for 8 hours in a low oxygen reducing atmosphere with an oxygen partial pressure of about 1 × 10 ⁻¹⁰ to 1 × 10 ⁻⁶ atm to obtain a sintered body. Can do. The firing temperature and firing atmosphere can be appropriately changed according to the composition of each component. From the viewpoint of unevenly distributing the Cu element at a higher concentration in the grain boundary, the firing is preferably performed in the low oxygen reducing atmosphere as described above.

  As described above, it is possible to unevenly distribute the Cu compound at the grain boundaries of the sintered body by adding a Cu compound such as Cu oxide to the raw material of the main component. Good. For example, it is possible to segregate a molded body not containing a Cu compound by firing it under appropriate firing conditions while being in contact with a compound containing Cu. In this way, by firing in a state where the compact contains a compound containing Cu, Cu is diffused into the sintered body, and a sintered body in which Cu elements are unevenly distributed at grain boundaries can be obtained.

  Next, the obtained sintered body is processed as necessary to form the piezoelectric ceramic 1, electrodes 2 and 3 are provided, and an electric field is applied in heated silicone oil to perform polarization treatment. Thereby, the piezoelectric ceramic 1 and the piezoelectric element 20 shown in FIG. 1 can be obtained. The electrodes 2 and 3 can be formed by applying a paste such as Ag (silver) and then drying and baking.

  Next, another embodiment of the piezoelectric element of the present invention will be described.

  FIG. 3 is a side view showing another embodiment of the piezoelectric element of the present invention. A laminated piezoelectric element 10 that is a laminated piezoelectric element shown in FIG. 3 includes a rectangular parallelepiped laminated body 11 and a pair of terminal electrodes 17A and 17B formed on opposing end surfaces of the laminated body 11, respectively. Yes.

  The laminated body 11 includes an element body 14 formed by alternately laminating internal electrode layers (electrode layers) 13A and 13B via piezoelectric layers 12, and the element body 14 is disposed on both end surfaces in the laminating direction (upper and lower sides in the figure). It is comprised from a pair of protective layers 15 and 16 provided so that it may pinch | interpose from direction. In the element body 14, the piezoelectric layers 12 and the internal electrode layers 13A and 13B are alternately stacked.

  The piezoelectric layer 12 is a layer composed of a piezoelectric ceramic. As a piezoelectric ceramic, the thing similar to the piezoelectric ceramic 1 with which the above-mentioned piezoelectric element 20 is equipped can be used.

  Although the thickness per layer of the piezoelectric layer 12 can be set arbitrarily, it can be set to 1 to 100 μm, for example.

  The internal electrode layers 13A and 13B are provided so as to be parallel to each other. The internal electrode layer 13 </ b> A is formed so that one end is exposed to the end surface of the multilayer body 11 where the terminal electrode 17 </ b> A is formed. Further, the internal electrode layer 13B is formed such that one end portion is exposed on the end surface of the multilayer body 11 where the terminal electrode 17B is formed. Furthermore, the internal electrode layer 13A and the internal electrode 13B are arranged so that most of them overlap in the stacking direction. The active region 18 of the piezoelectric layer 12 sandwiched between the internal electrodes 13A and 13B becomes an active portion that expands and contracts (displaces) in the stacking direction when a voltage is applied to the internal electrodes 13A and 13B. On the other hand, the region 19 not sandwiched between the internal electrodes 13A and 13B is an inactive portion.

  As a material for the internal electrode layers 13A and 13B, a Pt, Au, Pd, or Ag—Pd alloy is usually used, but it may contain Cu. By using a material containing Cu as the internal electrode layers 13A and 13B, Cu in the internal electrode layers 13A and 13B can be diffused into the piezoelectric layer 12 at the time of firing described later. As a result, the Cu compound can be segregated at the grain boundaries of the piezoelectric ceramic constituting the piezoelectric layer 12 without adding a Cu compound such as Cu oxide to the raw material of the main component.

  The protective layers 15 and 16 are preferably made of ceramics and made of piezoelectric ceramics. Examples of the piezoelectric ceramic for forming the protective layers 15 and 16 include those similar to the piezoelectric layer 12. The piezoelectric ceramics constituting the protective layers 15 and 16 and the piezoelectric layer 12 may be the same or different.

  The terminal electrodes 17A and 17B are in contact with the end portions of the internal electrodes 13A and 13B exposed at the end surfaces at the end surfaces where the terminal electrodes 17A and 17B are provided. Thereby, the terminal electrodes 17A and 17B are electrically connected to the internal electrodes 13A and 13B, respectively. The terminal electrodes 17A and 17B can be made of a conductive material whose main component is Ag, Au, Cu or the like. The thicknesses of the terminal electrodes 17A and 17B are appropriately set depending on the application, the size of the multilayer piezoelectric element, and the like, and can be set to 10 to 50 μm, for example.

  Next, a method for manufacturing the multilayer piezoelectric element 10 will be described. The piezoelectric layer 12 is composed of a piezoelectric ceramic. In addition, the process until temporary baking and obtaining temporary baking powder is the same as the manufacturing method of the piezoelectric element 20 described above. Hereinafter, the process after obtaining the calcined powder will be described.

  The obtained calcined powder is wet pulverized in a solvent using a ball mill or the like to obtain a calcined powder slurry. At this time, as the solvent, water or alcohol such as ethanol, or a mixed solvent of water and ethanol can be used. The wet pulverization is preferably performed until the average particle size of the calcined powder becomes about 0.5 to 2.0 μm.

  Next, the obtained calcined powder slurry is dispersed in an organic vehicle obtained by dissolving the binder in an organic solvent to obtain a piezoelectric paste. The binder used in the organic vehicle is not particularly limited as long as it functions as a binder, and can be appropriately selected from various ordinary binders such as ethyl cellulose, polyvinyl butyral, and acrylic. Also, the organic solvent used in the organic vehicle is not particularly limited, and from organic solvents such as terpineol, butyl carbitol, acetone, toluene, MEK (methyl ethyl ketone), terpineol, etc. What is necessary is just to select suitably. The contents of the binder and the organic solvent in the piezoelectric paste are not particularly limited, but usually the binder is about 5 to 10% by mass and the organic solvent is about 10 to 50% by mass. In addition, the piezoelectric paste may contain additives selected from various dispersants, plasticizers, dielectrics, insulators, and the like as necessary.

  In the above-described method, an organic vehicle is used, but an aqueous vehicle in which a water-soluble binder, a dispersant, or the like is dissolved in water may be used instead of the organic vehicle. The water-soluble binder used in the water-based vehicle is not particularly limited as long as it is soluble in water, and for example, polyvinyl alcohol, cellulose, water-soluble acrylic resin, and the like can be used.

  Further, apart from the above-described piezoelectric paste, an internal electrode paste and a terminal electrode paste are prepared. The internal electrode paste and the terminal electrode paste are prepared by kneading the above-described organic vehicle with a conductive material containing at least one metal selected from the group consisting of Pt, Au, Pd, Ag, Cu and Ni. Is done. Further, if necessary, components equivalent to the piezoelectric layer 12 may be added to the internal electrode paste in order to alleviate shrinkage during firing of the electrode and to prevent the internal electrode layers 13A and 13B from peeling off the piezoelectric layer 12. it can. In addition, when Cu is contained as a conductive material in the internal electrode paste, Cu can be diffused into the piezoelectric layer 12 formed by firing the piezoelectric layer paste in the firing step described later. Thereby, a piezoelectric ceramic having further excellent piezoelectric characteristics can be obtained.

  The contents of the binder and the organic solvent in the internal electrode paste and the terminal electrode paste are not particularly limited, but are usually about 5 to 10% by mass of the binder and about 10 to 50% by mass of the organic solvent. In addition, the piezoelectric paste may contain additives selected from various dispersants, plasticizers, dielectrics, insulators, and the like as necessary.

  Next, the piezoelectric green sheet for forming the piezoelectric layer 12 by applying the piezoelectric paste prepared as described above onto a substrate made of polyethylene terephthalate (PET) with a predetermined thickness by a printing method, for example. Get.

  Thereafter, an electrode paste for forming the internal electrodes 13A and 13B is applied on the piezoelectric green sheet by a printing method to form an electrode paste layer made of the electrode paste. Further, similarly, a plurality of piezoelectric green sheets and electrode paste layers are alternately provided by repeating the application of the piezoelectric paste on the electrode paste layer and the application of the electrode paste layer on the piezoelectric paste a predetermined number of times. A laminated sheet is obtained. At the time of printing, the electrode paste layer is formed in a pattern that can obtain the shapes of the internal electrodes 13A and 13B described above. The obtained laminated sheet is pressed in the laminating direction while being appropriately heated, and further cut into a desired size as necessary, whereby a laminated green (green chip) can be obtained.

  In addition, although the manufacturing method of the laminated body green by the printing method was illustrated here, the laminated body green is, for example, a sheet in which a plurality of sheets each having an electrode paste layer formed on a piezoelectric green sheet are laminated and heated and pressed. It can also be obtained by a molding method.

Next, a binder removal process is performed on the produced laminate green. In the binder removal treatment, the atmosphere is preferably determined by the conductive material in the internal electrode precursor. For example, when the conductive material contains Cu element, considering the oxidation of Cu and the reduction of an oxide such as PbO contained in the piezoelectric layer precursor, the equilibrium oxygen partial pressure of Cu and Cu ₂ O and Pb It is preferable to set the atmosphere based on the equilibrium oxygen partial pressure of PbO.

  The binder removal processing is usually performed at 300 ° C to 650 ° C. The binder removal time needs to be determined depending on the temperature and atmosphere, but is preferably selected in the range of 0.5 to 50 hours.

Subsequently, the laminate green subjected to the binder removal treatment is fired (main firing) at, for example, 800 to 1050 ° C. to obtain the laminate 11. Note that in the case where the conductive material contains a Cu element, the firing is preferably performed in a low oxygen reducing atmosphere with an oxygen partial pressure of 1 × 10 ⁻¹⁰ to 1 × 10 ⁻⁶ atm. If the oxygen partial pressure is less than 1 × 10 ⁻¹⁰ atm, the oxide contained in the piezoelectric layer precursor, such as PbO, may be reduced and deposited as metal Pb, possibly reducing the piezoelectric properties of the finally obtained fired body. is there. On the other hand, if it exceeds 1 × 10 ⁻⁶ atm, oxidation of Cu is a concern. A more preferable oxygen partial pressure is 1 × 10 ⁻⁹ to 1 × 10 ⁻⁸ atm.

  Here, although the method of performing the binder removal process as a process different from the firing described later has been described, the binder removal treatment may be performed continuously with the firing. In the case where the firing is continuously performed, the binder removal process may be performed in the temperature raising process of the firing.

  In the main firing process, the piezoelectric green sheet and the electrode paste layer are integrally fired to form the internal electrodes 13A and 13B from the electrode paste layer, and the piezoelectric green sheet is sandwiched between the internal electrodes 13A and 13B. 12 is formed. In addition, protective layers 15 and 16 are formed from piezoelectric green sheets stacked on both end faces in the stacking direction of the stacked green. When the internal electrode contains Cu or a compound (alloy) containing Cu, the Cu component diffuses from the internal electrodes 13A and 13B to the piezoelectric layer 12 during firing. Thereby, it is also possible to segregate the Cu compound at the grain boundaries of the piezoelectric ceramic constituting the piezoelectric layer 12. In this case, the amount of diffusion of the Cu component from the internal electrode can be adjusted by adjusting the firing temperature, firing time, and atmosphere. The firing conditions can be adjusted as appropriate according to the composition of the complex oxide constituting the piezoelectric layer 12.

  Next, end face polishing such as barrel polishing or sand blasting is applied to end faces (end faces where the end portions of the internal electrodes 13A and 13B are exposed) parallel to the stacking direction of the obtained laminate 11 and facing each other. After that, terminal electrodes 17A and 17B are baked on the end faces, respectively. Specifically, after applying a terminal electrode forming paste containing the metal constituting the terminal electrodes 17A and 17B, an organic binder, and the like to the end face of the laminate 11, the terminal electrodes 17A and 17B are fired. Is formed. In this way, the laminated piezoelectric element 10 having the structure shown in FIG. 3 is obtained. The terminal electrodes 17A and 17B can be formed by a method such as sputtering, vapor deposition, or electroless plating in addition to the above-described baking.

  Then, for example, a polarization process is performed on the multilayer piezoelectric element 10 by applying a voltage for about 10 minutes so that the electric field strength is about 2 to 5 kV / mm between the terminal electrodes 17A and 17B in an environment of 120 ° C. Thus, the laminated piezoelectric element 10 that functions as a piezoelectric actuator can be obtained.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example at all.

(Examples 1 to 20, 22 to 28, 30 to 43, Reference Examples 21 and 29 , Comparative Examples 1 and 3 to 5)
First, PbO powder, SrCO ₃ powder, NiO powder, Nb ₂ O ₅ powder, TiO ₂ powder, and ZrO ₂ powder are prepared as raw materials for the main components, and the composition of the main components after firing is shown in Tables 2 to 4 described later. It weighed so that it might become the composition shown in this. Furthermore, each raw material oxide was weighed so that the compositions after firing of the first subcomponent and the second subcomponent had the compositions shown in Tables 2 to 4. Further, the Cu ₂ O, and weighed 0.03 wt% with respect to the main component in Table 2-4.

In Tables 2 to 4, PNN [mol%], PT [mol%], and PZ [mol%] are values obtained by multiplying a, b, and c in the general formula (1) by 100, respectively. Further, the Pb loss [mol%] and the Pb substitution amount [mol%] are values obtained by multiplying y and x in the general formula (1) by 100, respectively, and the Pb substitution element is an element used as Me. Further, R1 and R2 _d R3 _e represent elements used as the first subcomponent and the second subcomponent, respectively, R1 [mol%] is the content of the first subcomponent with respect to the main component, and R2 _d R3 _e [mol%] is the content of _{Pb (R2 d R3 e) O} 3 in terms of the second subcomponent with respect to the main component.

Next, using a ball mill, the weighed main component raw material, subcomponent raw material oxide and Cu ₂ O were blended and wet mixed for 16 hours, and calcined at 700 to 900 ° C. for 2 hours in the air.

The obtained calcined product was finely pulverized and then wet pulverized for 16 hours using a ball mill. After drying this, an acrylic resin was added as a binder and granulated, and then formed into a disk shape having a diameter of 17 mm and a thickness of 3 mm using a uniaxial press molding machine at a pressure of about 3 to 5 ton / cm ² .

The obtained molded body was fired at 950 ° C. for 8 hours in a low oxygen reducing atmosphere (oxygen partial pressure 1 × 10 ⁻¹⁰ to 1 × 10 ⁻⁶ atm, total pressure 1 atm).

Obtained was sintered body sliced and lapped by a thickness 2.0mm disc-shaped, and processed into evaluable shape of the piezoelectric constant d _33. After forming the Ag whole surface electrode by vapor deposition on both surfaces of the obtained sample and grinding the outer periphery, an electric field of 3 kV / mm was applied for 15 minutes in silicone oil at 120 ° C., and polarization treatment was performed. A sample was prepared.

(Comparative Example 2)
The sample was prepared in the same manner as in Example 1 above, except that the raw material of the main component was blended so that the composition of the main component after firing was the composition shown in Table 3, and that Cu ₂ O was not blended. Was made.

(Comparative Example 6)
The examples described above, except that the raw materials for the main components were blended so that the composition of the main components after firing was the composition shown in Table 4 and that the firing was performed in an air atmosphere instead of a low oxygen reducing atmosphere. A sample was prepared in the same manner as in 1.

<Evaluation of sample>
Specific resistance, bending strength, and piezoelectric d constant (d ₃₃ ) as piezoelectric characteristics were measured for the samples of each of Examples , Reference Examples, and Comparative Examples. The specific resistance was measured using a digital ultrahigh resistance meter (trade name: R8340A manufactured by ADVANTEST). The bending strength was measured by a three-point bending test in accordance with JIS-R1602. The piezoelectric d constant (d ₃₃ ) was measured by using a fringe counter type laser displacement meter for displacement when an electric field of 2.0 kV / mm was applied. The piezoelectric constant d ₃₃ is based on strain in the direction perpendicular to the electrode surface (thickness). Tables 5 to 7 show measurement results of specific resistance, bending strength, and piezoelectric d constant (d ₃₃ ).

Moreover, about the produced sample of each Example , each reference example, and a comparative example, the presence or absence of Cu uneven distribution was evaluated using the energy dispersive X-ray-spectral-analysis apparatus (EDS). In addition, although Cu element is detected at a point where the distance from the grain boundary is 0 nm, Cu uneven distribution is “existing” when the Cu element is not detected at the points of 5 nm and 10 nm, and the distance from the grain boundary is 5 nm and 10 nm. However, those in which the Cu element was detected were evaluated as Cu uneven distribution “none”. The presence or absence of Cu uneven distribution of each sample is shown in Tables 5-7.

From the above, the piezoelectric ceramics of Examples 1 to 20, 22 to 28, and 30 to 43 have sufficiently superior piezoelectric characteristics even under high voltage and mechanical strength as compared with the piezoelectric ceramics of Comparative Examples 1 to 6. It was confirmed to be excellent.

Further, for the sample prepared in Example 11 and Comparative Example 4, by changing the measurement field, to confirm the electric field dependence of the d _33. The results are shown in Table 8.

  It was confirmed that the sample of Example 11 was particularly excellent in piezoelectric characteristics under a high voltage as compared with the sample of Comparative Example 4.

It is a perspective view which shows suitable one Embodiment of the piezoelectric element of this invention. It is a TEM (transmission electron microscope) photograph which shows the fine structure of the piezoelectric ceramic which concerns on this embodiment. It is one side view which shows another embodiment of the piezoelectric element of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Piezoelectric ceramic, 2, 3 ... Electrode, 10 ... Laminated piezoelectric element, 11 ... Laminated body, 12 ... Piezoelectric layer, 13A, 13B ... Internal electrode, 14 ... Element body, 15, 16 ... Protective layer, 17A, 17B ... terminal electrode, 18 ... active region, 19 ... inactive region, 20 ... piezoelectric element.

Claims (5)

A sintered body containing a composite oxide represented by the following general formula (1) as a main component is provided,
A piezoelectric ceramic in which Cu elements are unevenly distributed at grain boundaries of the sintered body.
_{(Pb 1-x-y Me} x) [(Ni 1/3 Nb 2/3) a Ti b Zr c] O 3 -3 / 2y ... (1)
[In the formula (1), Me represents at least one element selected from the group consisting of Ca, Sr and Ba, and a, b, c, x and y satisfy the following formulas (2) to (9).
0 <a ≦ 0.1 (2)
0 <b <1 (3)
0 <c <1 (4)
a + b + c = 1 (5)
0.788 ≦ b (1-a) /c≦0.941 (6)
0 <x ≦ 0.05 (7)
0 <y ≦ 0.03 (8)
0 <1-xy (9)] The sintered body contains a first subcomponent having at least one metal element R1 selected from the group consisting of Ta, Nb and W as a constituent element;
2. The piezoelectric ceramic according to claim 1, wherein the content of the first subcomponent with respect to 100 mol of the main component is greater than 0 and less than or equal to 0.9 mol in terms of metal element R1. The sintered body has as constituent elements at least one metal element R2 selected from the group consisting of Dy, Gd and Y, and at least one metal element R3 selected from the group consisting of Ta, Nb and W; A second subcomponent having
The content of the second subcomponent with respect to 100 moles of the _{main, Pb (R2 d R3 e)} O 3 in terms of (d and e satisfy the following equation (12).) In large at 0.6 mol or less than 0 The piezoelectric ceramic according to claim 1 or 2 .
d + e = 1 (12) A piezoelectric element provided with the piezoelectric ceramic as described in any one of Claims 1-3 . A laminated piezoelectric element in which piezoelectric layers made of the piezoelectric ceramic according to any one of claims 1 to 3 and internal electrode layers containing a Cu element are alternately laminated.