JP5386848B2 - Piezoelectric ceramic - Google Patents

Description

The present invention relates to a pressure electromagnetic device.

  Piezoelectric ceramics exhibiting a so-called piezoelectric phenomenon that generates mechanical strain and stress when an electric field is applied are known. Such piezoelectric ceramics are used in various piezoelectric elements such as actuators, piezoelectric buzzers, sounding bodies, sensors, and the like.

  An actuator using a piezoelectric ceramic can obtain a small amount of displacement with high accuracy and has characteristics such as a large generated stress. For example, it is used for positioning a precision machine tool or an optical device. As a piezoelectric ceramic used for an actuator, lead zirconate titanate (PZT) having excellent piezoelectricity is most frequently used. However, since lead zirconate titanate contains a large amount of lead, recently, there is a concern about the influence on the global environment such as elution of lead by acid rain. Accordingly, there is a need for a piezoelectric ceramic material in which the amount of lead is sufficiently reduced instead of lead zirconate titanate. In response to such demands, various piezoelectric ceramic materials not containing lead have been proposed.

As a piezoelectric ceramic material not containing lead, barium titanate (BaTiO ₃ ) is known. In order to improve the piezoelectric characteristics of this barium titanate, two-component or three-component materials containing a plurality of perovskite compounds have been proposed.

For example, in Patent Documents 1 and 2, a perovskite-type oxide composed of a first element containing Na and K, a second element containing at least Nb in the group consisting of Nb and Ta, and oxygen (O). , A third material containing an alkaline earth metal element, a fourth element containing titanium (Ti), a perovskite oxide composed of oxygen, and a tungsten bronze oxide are proposed. Has been. This piezoelectric material exhibits a relatively large amount of displacement.
JP 2005-179143 A JP 2005-179144 A

  However, although the piezoelectric ceramics described in Patent Documents 1 and 2 show a large amount of displacement compared to conventional barium titanate and sodium potassium lithium niobate, the sintered body constituting this piezoelectric ceramic is not so high in resistance. The polarization voltage cannot be increased sufficiently. For this reason, the piezoelectric characteristics are still low compared with lead zirconate titanate, and further improvement is required.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a piezoelectric ceramic having a sufficiently reduced piezoelectric content and sufficiently excellent piezoelectric characteristics and a piezoelectric element including the piezoelectric ceramic. .

  In order to achieve the above object, the present inventors have conducted various studies on compositions and microstructures capable of obtaining a large amount of generated displacement. Usually, in order to sufficiently polarize the sintered body, it is necessary to enlarge the crystal grains of the sintered body. However, conventionally, there has been a problem that the dielectric loss (tan δ) increases when the firing temperature is increased in order to enlarge the crystal grains. However, the present inventors have found that an increase in dielectric loss (tan δ) can be suppressed even when the sintering temperature is increased by setting the firing atmosphere of the sintered body to a specific condition.

That is, the present invention contains a main component represented by the following general formula (1) and a subcomponent containing at least one compound containing Cr, Fe, Co, Cu or Ni as a constituent element, When converted into Cr ₂ O ₃ , Fe ₂ O ₃ , CoO, CuO and NiO, respectively, the content of subcomponents relative to the main component is 0.05 to 1.0% by mass, and includes a sintered body. The sintered body is fired in an atmosphere having an oxygen partial pressure of 0.1 atm or less , and provides a piezoelectric ceramic in which the average grain size of the sintered body is 0.9 μm or more.

_{a (Na x K y Li z} ) [Nb (1-α) Ta α] O 3 -bBa [Nb (1-α) Ta α] 2 O 6 -cABO 3 ···· (1)
In the formula (1), a, b, c, x, y, z, and α are respectively
a + b + c = 1,
0 ≦ b ≦ 0.01,
0 ≦ c ≦ 0.1,
0.35 ≦ x ≦ 0.65,
0.35 ≦ y ≦ 0.55,
A numerical value satisfying 0 ≦ z ≦ 0.1 and 0 ≦ α ≦ 0.2,
ABO ₃ is at least one compound selected from the group consisting of CaTiO ₃ , CaZrO ₃ , SrTiO ₃ , SrZrO ₃ , BaTiO ₃ , and BaZrO ₃ .

  Since the piezoelectric ceramic according to the present invention contains as a main component a composition composed of a complex oxide not containing lead as a constituent element, the lead content is sufficiently reduced and the environment is sufficiently excellent. The piezoelectric ceramic of the present invention has excellent piezoelectric characteristics because the average grain size of crystal grains is sufficiently large. The present inventors infer the reason why such an effect is obtained as follows. That is, since the sintered body provided in the piezoelectric ceramic according to the present invention is obtained by firing in an atmosphere with a reduced oxygen partial pressure, an increase in tan δ can be sufficiently suppressed. As one of the reasons why the increase in tan δ can be suppressed in this way, the value of the transition metal that is a constituent element of the subcomponent included in the piezoelectric ceramic is obtained by firing in an atmosphere with a reduced oxygen partial pressure. This is presumed to be because the variation in the number can be suppressed. Therefore, it is possible to increase the particle size of the sintered body by increasing the firing temperature as compared with the conventional case, and it is possible to sufficiently polarize by sufficiently increasing the electric resistance.

  In general, a material for a piezoelectric ceramic mainly composed of a composite oxide is fired at a lower oxygen partial pressure than air in order to prevent scattering of oxygen ions and metal ions constituting the composite oxide. It wasn't. For this reason, it was thought that it was preferable to bake in an atmosphere with a high oxygen partial pressure. However, in the present invention, the specific composition containing the main component represented by the general formula (1) and the specific subcomponent in a predetermined ratio is used, and the oxygen partial pressure is made lower than that of air and fired. However, the piezoelectric characteristics can be greatly improved without damaging the crystal structure of the composite oxide.

In the present invention, the sintered body, Ru der those fired at 1150 to 1300 ° C.. As a result, the sintering proceeds sufficiently and the piezoelectric characteristics can be further improved.

The present invention relates to a perovskite oxide containing at least one compound selected from the group consisting of CaTiO ₃ , CaZrO ₃ , SrTiO ₃ , SrZrO ₃ , BaTiO ₃ , and BaZrO ₃ , a sodium compound, a potassium compound, a niobium compound, and A raw material composition comprising an essential component comprising a barium compound and an optional component comprising a lithium compound and / or a tantalum compound, and an additive comprising at least one compound having Cr, Fe, Co, Cu or Ni as a constituent element; , And the mixture is calcined at 750 to 1100 ° C., then molded and fired in an atmosphere having an oxygen partial pressure of 0.1 atm or less , and the following general formula (1) And at least a constituent element composed of Cr, Fe, Co, Cu or Ni It contains a subcomponent including one compound, subcomponent, respectively _{Cr 2 O 3, Fe 2 O} 3, CoO, when converted to CuO and NiO, 0.05 to the content of subcomponents with respect to the main component There is provided a method for manufacturing a piezoelectric ceramic, comprising: a firing step for obtaining a sintered body of 1.0% by mass; and a polarization treatment step for obtaining a piezoelectric ceramic by subjecting the sintered body to polarization treatment.

In the method for manufacturing a piezoelectric ceramic according to the present invention, a perovskite oxide containing at least one compound selected from the group consisting of CaTiO ₃ , CaZrO ₃ , SrTiO ₃ , SrZrO ₃ , BaTiO ₃ , and BaZrO ₃ , and other raw materials , _{i.e., (Na x K y Li z} ) [Nb (1-α) Ta α] O 3 and _{Ba [Nb (1-α)} Ta α] and ₂ O ₆ subcomponent material, i.e. the above additives It is mixed and sintered. Thereby, a sintered body containing the composition represented by the general formula (1) as a main component and a specific metal compound as a subcomponent can be obtained. A sintered body having such a composition is suitably used as a piezoelectric ceramic. In the manufacturing method of the present invention, the sintered body is prepared by firing in an atmosphere with a reduced oxygen partial pressure. ing. For this reason, compared with the case where it bakes in air, increase of tan-delta can fully be suppressed.

  As one of the reasons why the increase in tan δ can be suppressed in this way, the fluctuation of the valence of the transition metal, which is a constituent element of the additive, is suppressed by firing in an atmosphere with a reduced oxygen partial pressure. I guess it is because it became possible to do. Therefore, in the method for manufacturing a piezoelectric ceramic according to the present invention, the firing temperature range for obtaining a sintered body can be sufficiently widened. In addition, by increasing the firing temperature to promote grain growth of the sintered body and increasing the grain size, the electrical resistance can be increased and polarization can be sufficiently achieved. For this reason, according to the piezoelectric ceramic manufacturing method of the present invention, it is possible to manufacture a piezoelectric ceramic that is sufficiently excellent in piezoelectric characteristics.

In the manufacturing method of the piezoelectric ceramic of the present invention, _{additive, Cr 2 O 3, F e} 2 O 3, CoO, preferably contains at least one compound selected from the group consisting of CuO and NiO. Thereby, the piezoelectric characteristics of the obtained piezoelectric ceramic can be further improved.

  In the method for manufacturing a piezoelectric ceramic according to the present invention, a sodium compound, a potassium compound, a niobium compound, a barium compound, a lithium compound, and a tantalum compound included as essential or optional components in the raw material composition are oxides, carbonates, and oxalic acid. It is preferably a salt or a hydroxide. By using such a compound, it can fully suppress that the unreacted component which is an impurity remains in the obtained sintered compact. In addition, since the reaction proceeds smoothly during firing, the firing time can be shortened.

  The present invention also provides a piezoelectric element including the above-described piezoelectric ceramic. This piezoelectric element may be, for example, a piezoelectric element including a plurality of electrodes and the above-described piezoelectric ceramic provided between the plurality of electrodes. Also, an element body in which electrodes and the above-described piezoelectric ceramics are alternately stacked, and a pair of terminal electrodes provided on both end faces of the element body so as to sandwich the element body and electrically connected to the electrodes A piezoelectric element comprising: Since such a piezoelectric element includes the piezoelectric ceramic having the above-described characteristics, it has excellent environmental characteristics and sufficiently excellent piezoelectric characteristics.

  ADVANTAGE OF THE INVENTION According to this invention, while content of lead is fully reduced, a piezoelectric ceramic which has the piezoelectric characteristic which was fully excellent, and a piezoelectric element provided with the said piezoelectric ceramic can be provided.

  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 an 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 is composed of a sintered body. The said sintered compact contains the main component represented by the said General formula (1). The main component includes a first perovskite oxide having Nb and alkali metal elements as constituent elements, a tungsten bronze oxide having Nb and Ta as constituent elements, and an alkaline earth metal as constituent elements. And a second perovskite oxide different from the perovskite oxide.

  The main component of the sintered body is composed of a solid solution of three kinds of complex oxides. Specifically, the first perovskite oxide represented by the following general formula (2) and the following general formula ( 3) a tungsten bronze type oxide, and a second perovskite type oxide represented by the following general formula (4).

(Na _x K _y Li _z ) [Nb _(1-α) Ta _α ] O ₃ (2)
Ba [Nb _(1-α) Ta _α ] ₂ O ₆ (3)
ABO ₃ (4)

In the general formulas (2) and (3), x, y, z, and α are 0.35 ≦ x ≦ 0.65, 0.35 ≦ y ≦ 0.55, and 0 ≦ z ≦ 0.1, respectively. Numerical values satisfying 0 ≦ α ≦ 0.2 are shown. The second perovskite oxide contains at least one compound selected from the group consisting of CaTiO ₃ , CaZrO ₃ , SrTiO ₃ , SrZrO ₃ , BaTiO ₃ , and BaZrO ₃ .

  The molar ratio of each compound of general formula (2), (3), (4) in the main component of the sintered body is relative to the total amount of each compound of general formula (2), (3), (4). The first perovskite oxide of the formula (2) is 0.89 to 0.97, the tungsten bronze oxide of the formula (3) is 0 to 0.01, and the second perovskite oxide of the formula (4) It is preferable that a thing is 0-0.1. The molar ratio is 0.92 to 0.97 for the first perovskite oxide of the formula (2) with respect to the total amount of the compounds of the general formulas (2), (3) and (4). More preferably, the tungsten bronze type oxide of the formula (3) is 0.002 to 0.003, and the second perovskite type oxide of the formula (4) is 0.03 to 0.07.

  The sintered body preferably contains at least one oxide selected from the group consisting of chromium oxide, manganese oxide, iron oxide, cobalt oxide, copper oxide and nickel oxide as a subcomponent. The sintered body may contain a compound having a Cr, Mn, Fe, Co, Cu, or Ni element different from the oxide other than these oxides or instead of the oxide. By containing the above oxide as a subcomponent, a piezoelectric ceramic having sufficiently more excellent piezoelectric characteristics can be obtained.

  The content of the main component of the sintered body is preferably 95% by mass or more, more preferably 98% by mass or more, based on the whole sintered body from the viewpoint of obtaining more excellent piezoelectric characteristics. More preferably, it is at least mass%. A sintered compact contains 0.05-1.0 mass% in total of a subcomponent in conversion to an oxide with respect to the whole main component. When the content of the subcomponent is less than 0.05% by mass, excellent piezoelectric characteristics cannot be obtained. On the other hand, when the content exceeds 1.0% by mass, excellent piezoelectric characteristics cannot be obtained. The subcomponent may be present in a granular form in the sintered body or may be dissolved in the main component particles.

  The compounds represented by the general formulas (2), (3), and (4) are preferably in solid solution with each other in the sintered body. As a result, variations in piezoelectric characteristics can be sufficiently suppressed.

  The composition of the piezoelectric ceramic 1 can be specified by fluorescent X-ray analysis, X-ray diffraction, and ICP emission spectroscopic analysis. These analyzes can be performed by a usual method using a commercially available analyzer.

  The average grain size of the crystal grains constituting the sintered body is 0.9 μm or more, preferably 2 μm or more, and more preferably 4 μm or more. In general, the larger the average particle size, the better the piezoelectric characteristics. However, when the average particle size becomes excessively large, voids are likely to occur and the relative density tends to decrease. From this viewpoint, the upper limit of the average particle diameter is preferably 50 μm or less, more preferably 30 μm or less, and further preferably 10 μm or less.

  The average particle diameter of the sintered body can be measured by observing the surface or cross section of the sintered body with a scanning electron microscope (SEM). The average particle diameter of the present embodiment can be obtained by extracting 150 particles randomly from the surface or cross-sectional image magnified 5000 times and calculating the average value thereof.

Next, a method for manufacturing the piezoelectric ceramic 1 and the piezoelectric element 20 shown in FIG. 1 will be described below. The manufacturing method of the piezoelectric ceramic 1 of the present embodiment includes a preparation step for preparing a second perovskite oxide, the second perovskite oxide, a sodium compound, a potassium compound, a niobium compound, and a barium compound. A raw material composition containing an essential component and an optional component containing a lithium compound and / or a tantalum compound, and an additive containing at least one compound containing Cr, Mn, Fe, Co, Cu, or Ni as a constituent element; Mixing step for preparing a mixture by mixing the mixture, calcining step for granulating the mixture to obtain granulated powder, and forming the granulated powder into an oxygen partial pressure of 2.1 × 10 ⁻ Firing in an atmosphere of less than ¹ atm, containing the composition represented by the general formula (1) and at least one metal compound containing Cr, Mn, Fe, Co, Cu, or Ni as a constituent element A firing step for obtaining a sintered body having a content of the entire metal compound of 0.05 to 1.0% by mass relative to the whole composition, and a polarization treatment step for obtaining a piezoelectric ceramic by subjecting the sintered body to polarization treatment And having. Hereinafter, each step will be described in detail.

In the preparation step, a second perovskite oxide represented by the general formula (4) is prepared. After the raw material containing an element A and B in the general formula (4) were mixed well in an organic solvent or water by a ball mill etc. and dried and baked for 2 to 4 hours at 1000 to 1300 ° C., in ABO ₃ A composite oxide represented (second perovskite oxide) is prepared. The second perovskite oxide contains at least one compound selected from the group consisting of CaTiO ₃ , CaZrO ₃ , SrTiO ₃ , SrZrO ₃ , BaTiO ₃ , and BaZrO ₃ .

  In the mixing step, first, a raw material composition that is a raw material of the main component of the piezoelectric ceramic 1 is prepared. The raw material composition contains, as essential components, a sodium compound containing Na as a constituent element, a potassium compound containing K as a constituent element, a niobium compound containing Nb as a constituent element, and a barium compound containing Ba as a constituent element. To do. Moreover, this raw material composition may contain a lithium compound containing Li as a constituent element and / or a tantalum compound containing Ta as a constituent element as an optional component. As each of the above-mentioned compounds contained in the raw material composition, an easily available powdered oxide can be used. In addition to oxides, those that become oxides upon firing, such as carbonates or oxalates, may be used.

Separately from the above raw material composition, Cr compound having Cr as a constituent element, Mn compound having Mn as a constituent element, Fe compound having Fe as a constituent element, Co compound having Co as a constituent element, Cu as a constituent element An additive containing at least one compound selected from the group consisting of a Cu compound and a Ni compound having Ni as a constituent element is prepared. The additive can be a subcomponent of the piezoelectric ceramic, and preferably contains at least one compound selected from the group consisting of Cr ₂ O ₃ , MnCO ₃ , Fe ₂ O ₃ , CoO, CuO and NiO. By using such a compound, the piezoelectric characteristics of the obtained piezoelectric ceramic can be further improved.

  The raw material composition and the second perovskite oxide prepared as described above are sufficiently dried, and then each raw material of the main component is weighed in such a ratio that the composition of the general formula (1) is obtained. In addition, the total content of the composition of the above general formula (1) generated according to each raw material of this main component is 0.05 to 1. The additive which is a raw material of the auxiliary component is weighed so that it becomes 0% by mass.

  After weighing, the raw materials of the main component and the raw materials (additives) of the subcomponent are sufficiently mixed in an organic solvent or water by a ball mill or the like to prepare a mixture.

  The reason for mixing the second perovskite oxide and other main component materials and additives after preparing the second perovskite oxide represented by the general formula (4) in the preparation step is as follows. It is as follows. When the raw material of the second perovskite compound and the raw materials and additives of other main components are mixed and calcined as described later, the second perovskite compound is not produced, and the target general formula ( This is because the main component represented by 1) cannot be obtained.

  In the calcining step, the mixture obtained in the mixing step is dried, press-molded, and calcined at 750 to 1100 ° C. for 1 to 4 hours in an air atmosphere. Thereby, a calcined product containing the composition represented by the general formula (1) and at least one metal compound containing Cr, Mn, Fe, Co, Cu, or Ni as constituent elements is obtained. The calcined product is sufficiently pulverized in an organic solvent or water using a ball mill or the like, dried again, and granulated with a binder.

In the sintering step, the granulated powder is press-molded using a uniaxial press molding machine, a hydrostatic pressure molding machine (CIP), or the like to obtain a compact. Thereafter, for example, the molded body is heated to remove the binder, and sintered at 1150 to 1300 ° C. for 2 to 10 hours to obtain a sintered body. The atmosphere during firing needs to have a lower oxygen partial pressure than air (less than 0.21 atm), and the oxygen partial pressure is preferably 0.1 atm or less, preferably 3 × 10 ⁻⁶ atm or less. Is more preferable. The atmosphere during firing is preferably an inert gas atmosphere such as N ₂ or Ar.

  When the firing temperature exceeds 1350 ° C., the electrical resistance tends to decrease even if the particle size is sufficiently increased by firing in an atmosphere having a low oxygen partial pressure. The firing temperature is preferably 1200 to 1300 ° C., more preferably 1250 to 1300 ° C., from the viewpoint of obtaining a piezoelectric ceramic having more sufficiently excellent piezoelectric characteristics.

  In the polarization treatment step, the obtained sintered body is processed as necessary to form a desired shape, and then electrodes 2 and 3 are provided on a pair of surfaces of the sintered body so as to sandwich the sintered body. Then, polarization treatment is performed by applying an electric field in heated silicone oil. Thereby, the piezoelectric ceramic 20 provided with the piezoelectric ceramic 1 and the piezoelectric ceramic 1 shown in FIG. 1 and a pair of electrodes 2 and 3 provided so as to sandwich the piezoelectric ceramic 1 can be obtained. The electrodes 2 and 3 can be formed by applying a paste such as silver, then drying and baking.

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

  FIG. 2 is a side view showing another embodiment of the piezoelectric element of the present invention. A multilayer piezoelectric element 10 which is a multilayer piezoelectric element shown in FIG. 2 includes a rectangular parallelepiped multilayer body 11 and a pair of terminal electrodes 17A and 17B formed on opposite end surfaces of the multilayer 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 the material of the internal electrode layers 13A and 13B, for example, a metal such as Au, Pt, Pd, Ni, Cu, or Ag, or an alloy containing two or more of these metals (Ag—Pd alloy or the like) is used.

  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. The piezoelectric ceramic includes a main component represented by the general formula (1) and a subcomponent including at least one compound containing Cr, Mn, Fe, Co, Cu, or Ni as a constituent element. Is converted into Cr ₂ O ₃ , MnO, Fe ₂ O ₃ , CoO, CuO and NiO, respectively, from a sintered body in which the total content of subcomponents relative to the main component is 0.05 to 1.0 mass%. Become.

  In the method of manufacturing the multilayer piezoelectric element 10, first, a starting material such as a piezoelectric ceramic material compound for forming the piezoelectric layer 12 and other additive components is prepared as a starting material. Specifically, for example, each oxide powder having sodium, potassium, lithium, niobium, tantalum, and barium as constituent elements is used as a raw material of the composite oxide that is a main component of the piezoelectric ceramic constituting the piezoelectric layer 22. prepare. As a raw material for these main components, not an oxide but a material that becomes an oxide by firing, such as carbonate or oxalate, may be used.

  Apart from the above raw materials, the second perovskite oxide shown in the general formula (4) is prepared. The second perovskite oxide is prepared by, for example, thoroughly mixing raw materials each containing A and B elements in an organic solvent or water using a ball mill or the like, then drying and baking at 1000 ° C. to 1300 ° C. for 2 to 4 hours. By doing so, it can be prepared.

In addition to the above raw materials, an additive containing at least one compound containing Cr, Mn, Fe, Co, Cu, or Ni as a constituent element is prepared. The additive can be a subcomponent of the piezoelectric ceramic, and preferably contains at least one compound selected from the group consisting of Cr ₂ O ₃ , MnCO ₃ , Fe ₂ O ₃ , CoO, CuO and NiO. Thereby, the piezoelectric characteristics of the obtained piezoelectric ceramic can be further improved.

  Next, after sufficiently drying the raw materials of the main components and the raw materials of the subcomponents, the raw materials of the main components are weighed at a ratio such that the composition of the general formula (1) is obtained. Moreover, the total content of the subcomponents converted to oxides is 0.05 to 1.0% by mass with respect to the main component represented by the general formula (1). Weigh. Then, the weighed main component materials and subcomponent materials are thoroughly mixed in an organic solvent or water by a ball mill or the like.

  Thereafter, the mixture is dried, and calcined, for example, at a temperature of 750 to 1100 ° C. for 1 to 4 hours. Thereby, a calcined product containing the composition represented by the general formula (1) and at least one compound having Cr, Mn, Fe, Co, Cu, or Ni as constituent elements is obtained.

  The calcined product is wet pulverized by a ball mill or the like and then dried to obtain granulated powder. Subsequently, an organic binder, an organic solvent, an organic plasticizer, and the like are added to the granulated powder and mixed for about 20 hours by a ball mill or the like to obtain a piezoelectric paste.

  This piezoelectric paste is applied onto, for example, a polyethylene terephthalate (PET) base film by a doctor blade method to obtain a piezoelectric green sheet for forming the piezoelectric layer 12. This piezoelectric green sheet mainly contains the composition represented by the general formula (1), at least one compound containing Cr, Mn, Fe, Co, Cu, or Ni as constituent elements, and a binder. .

  Thereafter, an electrode paste for forming the internal electrodes 13A and 13B is applied on the piezoelectric green sheet by a screen printing method or the like, and an electrode paste layer made of this electrode paste is formed. In this way, a lamination sheet having an electrode paste layer on the piezoelectric green sheet is obtained. At this time, the electrode paste layers are respectively formed in patterns that can obtain the shapes of the internal electrodes 13A and 13B described above.

  Here, the electrode paste for forming the electrode paste layer is, for example, a metal such as Au, Pt, Pd, Ni, Cu, or Ag, or an alloy containing two or more of these metals (Ag—Pd alloy or the like). And a binder and an organic solvent. Known binders and organic solvents can be used. The total content of metals in the electrode paste is preferably 40% by mass or more, and more preferably 50 to 60% by mass.

  Next, a plurality of lamination sheets are stacked so that the electrode paste layers and the piezoelectric green sheets are alternately arranged, and a plurality of piezoelectric green sheets are further provided on the surfaces of both end surfaces in the stacking direction of this stacked structure. Laminate layer by layer. The laminated body thus obtained is pressurized in the laminating direction while being appropriately heated, and further cut into a desired size as necessary, whereby a laminated green (laminate) can be obtained.

  Then, after placing this laminate green on a stabilized zirconia setter or the like, a degreasing treatment is performed to remove the binder and organic solvent contained in the piezoelectric green sheet and the electrode paste layer by heating in an air atmosphere. Do.

  Then, the laminate green after the binder removal is subjected to a firing treatment (main firing) in which, for example, heating is performed at 1150 to 1300 ° C. for 2 to 10 hours in an atmosphere having an oxygen partial pressure of less than 0.21 atm. 11 is obtained. 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.

  In this embodiment, since the main firing is performed in an atmosphere having a lower oxygen partial pressure than air, an increase in dielectric loss can be sufficiently suppressed even if the firing temperature is increased. Therefore, by firing at a higher firing temperature, grain growth of the sintered body can be promoted, and a sintered body having particles having a large particle diameter can be obtained. Since such a sintered body has a sufficiently large electric resistance, a sufficiently large polarization voltage can be applied in the polarization treatment described later, and a piezoelectric ceramic having sufficiently excellent piezoelectric characteristics can be obtained.

  Next, the terminal electrodes 17A and 17B are baked on 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. 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 multilayer piezoelectric element 10 having the structure shown in FIG. 1 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.

  For example, a voltage is applied to the laminated piezoelectric element 10 for about 10 to 30 minutes in an environment of room temperature to 120 ° C. so that the electric field strength is about 2 to 5 kV / mm between the terminal electrodes 17A and 17B. By performing the polarization treatment, it is possible to obtain the multilayer piezoelectric element 10 that functions as a piezoelectric actuator.

  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.

( Reference Examples 1-1 to 1-12, Comparative Examples 1-1 to 1-3)
<Production of piezoelectric element>

A piezoelectric element 20 as shown in FIG. 1 was produced by the following procedure. First, sodium carbonate (Na ₂ CO ₃ ) powder, potassium carbonate (K ₂ CO ₃ ) powder, lithium carbonate (Li ₂ CO ₃ ) powder, niobium oxide (Nb ₂ O ₅ ) powder, tantalum oxide (Ta ₂ O ₅ ) Powder, strontium carbonate (SrCO ₃ ) powder, zirconium oxide (ZrO ₂ ) powder and barium carbonate (BaCO ₃ ) powder were prepared. In addition, manganese carbonate (MnCO ₃ ) powder was prepared as a raw material (additive) for the accessory component. After sufficiently drying these raw materials, each raw material was weighed so that the composition of the composite oxide as the main component of the piezoelectric ceramic would be the following formula (5).

0.9475 (Na _0.57 K _0.38 Li _0.05 ) (Nb _0.9 Ta _0.1 ) O ₃ -0.0025Ba (Nb _0.9 Ta _0.1 ) ₂ O ₆ -0.05 SrZrO ₃ ... (5)

Then, the MnCO ₃ powder, the total composition of the above formula (5) with respect to, were weighed to be 0.5 mass% in terms of MnO.

By thoroughly mixing strontium carbonate (SrCO ₃ ) powder and zirconium oxide (ZrO ₂ ) powder weighed as described above in water using a ball mill, drying, and firing at 1000 to 1300 ° C. for 2 to 4 hours , SrZrO ₃ (second perovskite oxide) was prepared.

This second perovskite oxide, sodium carbonate (Na ₂ CO ₃ ) powder, potassium carbonate (K ₂ CO ₃ ) powder, lithium carbonate (Li ₂ CO ₃ ) powder, niobium oxide (Nb ₂ ) weighed as described above. O ₅ ) powder, tantalum oxide (Ta ₂ O ₅ ) powder, and manganese carbonate (MnCO ₃ ) powder were thoroughly mixed in ethanol using a ball mill, dried, press-molded, and 750-500 Calcination was performed at 1100 ° C. for 1 to 4 hours.

  After calcining the mixture, the calcined product was sufficiently pulverized in ethanol using a ball mill, dried again, and granulated by adding a binder (PVA) solution. The obtained granulated powder was press-molded using a uniaxial press molding machine to obtain a molded body. Thereafter, the molded body was heated to 600 ° C. to remove the binder, and fired at the firing temperature shown in Table 1 for 1 to 4 hours to obtain a sintered body. The firing atmosphere was adjusted to the oxygen partial pressure shown in Table 1 by adjusting the mixing ratio of commercially available nitrogen gas, oxygen gas and air (total pressure = atmospheric pressure).

  A conductive paste was applied to the obtained sintered body, dried and fired to provide electrodes 2 and 3. Thereafter, an electric field was applied in heated silicone oil to perform polarization treatment, and a piezoelectric element 20 provided with the piezoelectric ceramic 1 was obtained (FIG. 1).

<Evaluation of piezoelectric characteristics>
After the obtained piezoelectric element 20 was allowed to stand for 24 hours, the electrical resistance and the dielectric loss (tan δ), the relative dielectric constant (εr), and the piezoelectric d constant (d ₃₃ ) were measured as piezoelectric characteristics. The electrical resistance was measured using a digital ultrahigh resistance meter (manufactured by ADVANTEST, trade name: R8340A). The relative dielectric constant (εr) and dielectric loss (tan δ) were measured at a frequency of 1 kHz using an impedance analyzer (trade name: HP4294A, manufactured by Agilent Technologies). The piezoelectric d constant (d ₃₃ ) was measured by using a d ₃₃ meter (product name: ZJ-4B, manufactured by Institute of Acoustics Academia Sinica). The measurement results are shown in Table 1.

<Evaluation of microstructure and composition>
The microstructure of the obtained piezoelectric ceramic 1 was observed with a scanning electron microscope (SEM) (magnification 5000 times). And 150 particles projected on the screen were extracted at random, the particle size was measured, and the average value was obtained as the average particle size. The measurement results are shown in Table 1.

( Reference Examples 2-1 to 2-5, Comparative Examples 2-1 to 2-5)
Each raw material was weighed and used so that the composition of the main component of the piezoelectric ceramic was represented by the following formula (6), and the firing temperature and the oxygen partial pressure of the firing atmosphere at the time of producing the sintered body were as shown in Table 2. A piezoelectric element was fabricated and evaluated in the same manner as Reference Example 1-5 except that the above was performed. The results are shown in Table 2.

(1-b-c) (Na _0.57 K _0.38 Li _0.05 ) (Nb _0.9 Ta _0.1 ) O ₃ -bBa (Nb _0.9 Ta _0.1 ) ₂ O ₆ -cSrZrO ₃ ... (6)
In addition, in said formula (6), b and c show the numerical value of Table 2.

( Reference Examples 3-1 to 3-6, Comparative Examples 3-1 to 3-6)
Each raw material was weighed and used so that the composition of the main component of the piezoelectric ceramic was represented by the following formula (7), and the firing temperature and the oxygen partial pressure of the firing atmosphere at the time of producing the sintered body were as shown in Table 3 A piezoelectric element was fabricated and evaluated in the same manner as Reference Example 1-5 except that the above was performed. The results are shown in Table 3.

_{0.9475 (Na x K y Li z} ) (Nb 0.9 Ta 0.1) O 3 -0.0025Ba (Nb 0.9 Ta 0.1) 2 O 6 -0.05SrZrO 3 ··· (7 )
In addition, in said formula (7), x, y, and z show the numerical value of Table 3.

( Reference Examples 4-1 to 4-2, Comparative Examples 4-1 to 4-3)
Each raw material was weighed and used so that the composition of the main component of the piezoelectric ceramic was represented by the following formula (8), and the firing temperature and the oxygen partial pressure of the firing atmosphere at the time of producing the sintered body were as shown in Table 4 A piezoelectric element was fabricated and evaluated in the same manner as Reference Example 1-9 except that the above was performed. The results are shown in Table 4.

0.9475 (Na _0.57 K _0.38 Li _0.05 ) (Nb _1-α Ta _α ) O ₃ -0.0025Ba (Nb _0.9 Ta _0.1 ) ₂ O ₆ -0.05 SrZrO _3. (8)
In the above formula (8), α represents a numerical value described in Table 4.

( Reference Examples 5-1 to 5-3, Comparative Examples 5-1 to 5-4)
The MnCO ₃ powder was weighed and used so as to have the content described in Table 5 in terms of MnO with respect to the entire main component represented by the above formula (5), and when the sintered body was produced. A piezoelectric element was fabricated and evaluated in the same manner as in Reference Example 1-5 except that the firing temperature and the oxygen partial pressure of the firing atmosphere were set as shown in Table 5. The results are shown in Table 5.

( Reference Examples 6-1 to 6-5, Comparative Examples 6-1 to 6-2)
Of the main components represented by the above formula (5), the compound shown in Table 6 was used as the second perovskite oxide instead of SrZrO ₃ , and the firing temperature and firing during the production of the sintered body A piezoelectric element was produced and evaluated in the same manner as in Reference Example 1-5 except that the oxygen partial pressure in the atmosphere was changed to the conditions described in Table 6. The results are shown in Table 6. CaTiO ₃ is CaCO ₃ powder and TiO ₂ powder, CaZrO ₃ is CaCO ₃ powder and ZrO ₂ powder, SrTiO ₃ is SrCO ₃ powder and TiO ₂ powder, and BaTiO ₃ is BaCO ₃ powder and TiO ₂ powder. BaZrO ₃ was prepared using BaCO ₃ powder and ZrO ₂ powder, and CaZrO ₃ was used using CaCO ₃ powder and ZrO ₂ powder to prepare a second perovskite oxide. Preparation method were the same as the preparation of SrZrO ₃ in Reference Example 1 -1.

(Example 7-1～7- 5, Comparative Example 7-1～7-2)
As an additive which is a raw material of the auxiliary component, the powder of the compound shown in Table 7 was used instead of MnCO ₃ , and the firing temperature and the oxygen partial pressure of the firing atmosphere at the time of producing the sintered body were as shown in Table 7. A piezoelectric element was fabricated and evaluated in the same manner as in Reference Example 1-9 except that. The results are shown in Table 7. When MnCO ₃ was used as an additive, the piezoelectric constant could be further improved while maintaining a low dielectric loss.

  From the results shown in Tables 1 to 7, the piezoelectric ceramic of each example had a high electric resistance and a sufficiently low dielectric loss. It was also found that all the characteristics of the electromechanical coupling coefficient, the relative dielectric constant, and the piezoelectric constant can be made to high level values.

<Evaluation of composition>
Some of the piezoelectric ceramics prepared as described above were selected, and the composition of the piezoelectric ceramics was confirmed by fluorescent X-ray analysis (EDX). The results are shown in Table 8. As a result of composition analysis by EDX, it was confirmed that the composition of the piezoelectric ceramic after sintering substantially coincided with the composition of the raw materials. From this result, it was confirmed that even when firing under conditions where the oxygen partial pressure was lower than that of air, no disappearance of oxygen ions or metal ions occurred.

It is a perspective view which shows one Embodiment of the piezoelectric element of this invention. 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 (1)

It contains a main component represented by the following general formula (1) and a subcomponent containing at least one compound containing Cr, Fe, Co, Cu, or Ni as a constituent element, and each of the subcomponents is Cr ₂ O _3. , Fe ₂ O ₃ , CoO, CuO, and NiO, when the content of the subcomponent with respect to the main component is 0.05 to 1.0 mass%, comprising a sintered body,
_{a (Na x K y Li z} ) [Nb (1-α) Ta α] O 3 -bBa [Nb (1-α) Ta α] 2 O 6 -cABO 3 ···· (1)
[Wherein a, b, c, x, y, z, α are respectively
a + b + c = 1,
0 ≦ b ≦ 0.01,
0 ≦ c ≦ 0.1,
0.35 ≦ x ≦ 0.65,
0.35 ≦ y ≦ 0.55,
A numerical value satisfying 0 ≦ z ≦ 0.1 and 0 ≦ α ≦ 0.2,
ABO ₃ is at least one compound selected from the group consisting of CaTiO ₃ , CaZrO ₃ , SrTiO ₃ , SrZrO ₃ , BaTiO ₃ , and BaZrO ₃ . ]
The sintered body is fired at 1150 to 1300 ° C. in an atmosphere having an oxygen partial pressure of 0.1 atm or less ,
A piezoelectric ceramic in which an average grain size of crystal grains of the sintered body is 0.9 μm or more.

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