JP4727458B2 - Sintering aid for piezoelectric ceramics, BNT-BT piezoelectric ceramics, multilayer piezoelectric device, and method for producing BNT-BT piezoelectric ceramics - Google Patents

Description

  The present invention relates to a sintering aid for piezoelectric ceramics, a BNT-BT piezoelectric ceramic, a laminated piezoelectric device, and a method for manufacturing a BNT-BT piezoelectric ceramic used for manufacturing a BNT-BT piezoelectric ceramic.

  In recent years, piezoelectric ceramic compositions containing no lead compound have attracted attention as piezoelectric ceramic element materials, and research and development have been promoted (for example, Patent Document 1). Since such a piezoelectric ceramic composition does not contain a lead compound, the load on the natural environment can be reduced.

The piezoelectric ceramic composition described in Patent Document 1 does not contain a lead compound, and the composition formula is x (Bi _1/2 Na _1/2 TiO ₃ ) + y (BaTiO ₃ ) + z (BaZrO ₃ ) (x + y + z = 1), the points represented by x, y, z in the triangular coordinates having these components as vertices have a composition that exists within a predetermined range. Since such a composition was found through experiments, the above-described three-component lead-free piezoelectric ceramic has been proposed.

In recent years, in order to enhance the function of the device, there is an increasing demand for a laminated piezoelectric device in which piezoelectric ceramics and an electrode are laminated. Inside the laminated piezoelectric device, a material such as Ag—Pd is provided. An internal electrode using is provided. A material such as Ag—Pd used for the internal electrode melts when it reaches a temperature exceeding 1100 ° C.
JP 2003-95737 A

Among the piezoelectric ceramic compositions described in Patent Document 1, x (Bi _1/2 Na _1/2 TiO ₃ ) + (1-x) (BaTiO ₃ ) (hereinafter referred to as BNT-BT) has piezoelectric characteristics. It is an excellent composition. However, the BNT-BT piezoelectric ceramics are sintered at a high temperature of 1150 ° C. to achieve densification of the sintered body. When a multilayer piezoelectric device is manufactured using a BNT-BT material, piezoelectric The densification temperature of the body layer exceeds the melting temperature of the internal electrode.

  On the other hand, if the firing temperature is set to 1100 ° C. or lower, the internal electrodes will not melt in the firing step, but densification is not achieved with the BNT-BT piezoelectric ceramics, and sufficient piezoelectric properties cannot be obtained. .

  The present invention has been made in view of such circumstances, and uses a sintering aid for piezoelectric ceramics and its aid that enables densification of BNT-BT piezoelectric ceramics at 1100 ° C. To provide a densified BNT-BT piezoelectric ceramic, a laminated piezoelectric device having a densified BNT-BT piezoelectric ceramic layer, and a method for producing a BNT-BT piezoelectric ceramic using the above-mentioned sintering aid. With the goal.

(1) To achieve the above object, a piezoelectric ceramic for sintering aid according to the present _{invention, x (Bi 0.5 Na 0.5 TiO} 3) - (1-x) BaTiO 3 ( where 0 < A sintering aid used in the production of a BNT-BT piezoelectric ceramic mainly composed of a perovskite type compound represented by x <1), having at least bismuth oxide and zinc oxide, with the remainder being boron oxide It is characterized by consisting of.

  By adding a sintering aid having such components to the piezoelectric ceramic in the manufacturing process of the BNT-BT piezoelectric ceramic, the BNT-BT piezoelectric ceramic can be densified at 1100 ° C. or lower.

  (2) Further, in the sintering aid for piezoelectric ceramics according to the present invention, the metal composition ratio of the bismuth oxide, zinc oxide, and boron oxide is mol%, 10 ≦ Bi ≦ 40, 20 ≦ Zn ≦ 90, and It is characterized by 0 ≦ B ≦ 40 (total 100 mol%).

  As described above, the sintering aid for piezoelectric ceramics of the present invention is configured so that the composition ratio of Bi: Zn: B is most effective for densification. By adding this sintering aid to the piezoelectric ceramics in the manufacturing process of the BNT-BT piezoelectric ceramics, the BNT-BT piezoelectric ceramics can be densified at 1100 ° C. or less and have sufficient piezoelectric properties. Can do.

(3) The BNT-BT piezoelectric ceramic according to the present invention is represented by x (Bi _0.5 Na _0.5 TiO ₃ )-(1-x) BaTiO ₃ (where 0 <x <1). A BNT-BT piezoelectric ceramic mainly comprising a perovskite type compound, wherein 3.0% by weight or more of the above-mentioned sintering aid for piezoelectric ceramic is added to the BNT-BT piezoelectric ceramic material. It is obtained by firing at a temperature of not higher than ° C., and has a density of 5.7 × 10 ³ kg / m ³ or more.

Thus, the BNT-BT piezoelectric ceramic having a density of 5.7 × 10 ³ kg / m ³ or more can be obtained by adding 3.0% by weight or more of the sintering aid and firing at 1100 ° C. or less. Obtainable. A sufficiently densified BNT-BT piezoelectric ceramic can be applied to a piezoelectric device as a lead-free material.

  (4) The multilayer piezoelectric device according to the present invention is formed by integrally laminating the piezoelectric layers made of the BNT-BT piezoelectric ceramics and the internal electrode layers made of Ag-Pd alternately. It is characterized by that. Such a lead-free multilayer piezoelectric device that is integrally fired can be applied as a small and highly functional piezoelectric device.

(5) The perovskite type compound represented by x (Bi _0.5 Na _0.5 TiO ₃ )-(1-x) BaTiO ₃ (where 0 <x <1) according to the present invention is used as a main component. An addition step of adding 3.0% by weight or more of the sintering aid for piezoelectric ceramics to the calcined powder of the BNT-BT piezoelectric ceramic material, and a molded body of the material obtained by the addition step And a firing step of firing at 1100 ° C. or lower.

  Thus, by adding 3.0% by weight or more of the above-mentioned sintering aid and firing at 1100 ° C. or less, a densified BNT-BT piezoelectric ceramic can be obtained. Thereby, a laminated piezoelectric device having an internal electrode made of Ag—Pd or the like can be manufactured by integral firing.

  According to the sintering aid for piezoelectric ceramics according to the present invention, at least bismuth oxide and zinc oxide are included, and the balance is composed of boron oxide. By adding this sintering aid to the piezoelectric ceramic in the manufacturing process of the BNT-BT piezoelectric ceramic, the BNT-BT piezoelectric ceramic can be densified at 1100 ° C. or lower.

  In recent years, the present inventors have sought to develop a multilayer piezoelectric device using a BNT-BT piezoelectric ceramic as a piezoelectric layer because there is a demand for a lead-free multilayer piezoelectric device that does not contain lead. In this process, the inventors pay attention to the need to fire the laminated piezoelectric device at a temperature at which the internal electrodes do not melt, and add a specific sintering aid to add BNT-BT piezoelectric ceramics. Has been found to be capable of being densified at low temperatures, and the present invention has been completed. Hereinafter, embodiments of the present invention will be described.

The BBZ piezoelectric ceramic sintering aid (hereinafter referred to as “BBZ sintering aid”) according to the present invention has at least bismuth oxide and zinc oxide, and the balance is made of boron oxide. Suitable for densification. By adding this BBZ sintering aid to the piezoelectric ceramic in the manufacturing process of the BNT-BT piezoelectric ceramic, the BNT-BT piezoelectric ceramic can be densified at 1100 ° C. or lower. The BNT-BT piezoelectric ceramic is mainly a perovskite type compound represented by x (Bi _0.5 Na _0.5 TiO ₃ )-(1-x) BaTiO ₃ (where 0 <x <1). Piezoelectric ceramics as a component.

In order to lower the sintering temperature without deteriorating the piezoelectric constant, it is effective to add ZnO or Bi ₂ O ₃ with high reactivity and low melting point to form a liquid phase in the grain boundary phase and promote low-temperature sintering. Is. For example, when ions with different valences such as trivalent Bi are added to tetravalent Ti, they are replaced with Ti sites, and oxygen ion vacancies are generated. These oxygen vacancies diffuse ions during sintering. Increase. As a result, the sintering temperature is effectively reduced.

  As shown in the region S of FIG. 1, the metal composition ratios of bismuth oxide, zinc oxide and boron oxide constituting the BBZ sintering aid are 10%, 10 ≦ Bi ≦ 40, 20 ≦ Zn ≦ 90, and 0. ≦ B ≦ 40 (total 100 mol%) is preferable. By making the composition ratio of Bi: Zn: B most effective for densification, the BNT-BT piezoelectric ceramic can be densified at 1100 ° C. or lower, and sufficient piezoelectric characteristics can be obtained. The BBZ sintering aid having the composition of the region S is preferable as the sintering aid for the BNT-BT piezoelectric ceramics. The sintering aid having the same composition is sufficient as the sintering aid for the PZT piezoelectric ceramics. Based on functioning.

  For example, a PBZ sintering aid having at least lead oxide and zinc oxide and the balance being boron oxide promotes low temperature sintering in the sintering process of PZT-based piezoelectric ceramics. As shown in FIG. 2, among the PBZ sintering aids, the metal composition ratios of lead oxide, zinc oxide, and boron oxide are 10 mol%, 10 ≦ Pb ≦ 40, 20 ≦ Zn ≦ 90, and 0 ≦ Experiments have shown that PZT piezoelectric ceramics fired at a low temperature using a PBZ sintering aid having a composition in the region of B ≦ 40 (total 100 mol%) have sufficient piezoelectric properties. The conditions for this experiment will be described later.

  The mechanism for creating a liquid phase in the grain boundary phase and promoting low-temperature sintering is the same whether it is a PBZ sintering aid for PZT piezoelectric ceramics or a BBZ sintering aid for BNT-BT piezoelectric ceramics. is there. Therefore, the metal composition ratio of bismuth oxide, zinc oxide, and boron oxide constituting the BBZ sintering aid is 10 mol%, 10 ≦ Bi ≦ 40, 20 ≦ Zn ≦ 90, and 0 ≦ B ≦ 40 (100 mol in total). %) Is preferable as the composition of the PBZ sintering aid. In addition, as the BNT-BT-based piezoelectric ceramics, good piezoelectric characteristics can be obtained when the BT composition is 5 to 15%. Can be mentioned.

The experimental conditions and results shown in FIG. 2 relate to the experiments performed on the PZT-based piezoelectric ceramics by the present inventors. In the following, the experiment for the PZT-based piezoelectric ceramic will be described. The sample preparation conditions are as follows. First, a base material calcined powder having a composition of (Pb _0.93 Sr _0.05 ) (Zr _0.52 Ti _0.45 Mn _0.01 Nb _0.02 ) O ₃ was prepared, while each sample number Each powder of Pb ₃ O ₄ , B ₂ O ₃ , and ZnO was mixed so that the composition of The auxiliary mixture was further mixed with the base material calcined powder. The auxiliary agent addition ratio shown in FIG. 2 is a ratio (H / E) of the weight (H) of the sintering auxiliary agent to the weight (E) of the base material. The molded body molded from the obtained mixed powder was fired at 1000 ° C. for 2 hours in the air, and the bulk density was determined by Archimedes method. Then, the silver paste was printed on both main surfaces of the sintered compact, and the electrode was formed by baking. Next, the sintered body was polarized in the thickness direction under conditions of 180 ° C., 10 minutes, and 2 kV / mm to produce a piezoelectric transformer.

  While measuring the temperature of this piezoelectric transformer, the output power was increased little by little, and the output characteristics of the piezoelectric transformer were measured when the temperature difference from the temperature before the power was turned on was 20 ° C. The power was applied by setting the frequency to about 150-170 kHz near the resonance frequency and connecting a matching load. In this way, the experimental result of FIG. 2 is obtained.

  In addition, the BNT-BT piezoelectric ceramics sintered using the BBZ sintering aid exhibit a great effect when used in a laminated piezoelectric device in which electrodes and piezoelectric layers are alternately laminated. For example, a multilayer piezoelectric transformer exists in the multilayer piezoelectric device. Multilayer piezoelectric transformers are increasing in demand for liquid crystal display backlights and the like as transformers that can achieve a large step-up ratio even if they are small in size. By using a BBZ sintering aid to realize a multilayer piezoelectric transformer having BNT-BT piezoelectric ceramics as a piezoelectric layer, a multilayer piezoelectric transformer that does not contain lead and has sufficient characteristics is obtained. Can do.

  Next, as an example of a method for producing a BNT-BT piezoelectric ceramic using a BBZ sintering aid, a method for producing a laminated piezoelectric transformer having a BNT-BT piezoelectric ceramic as a piezoelectric layer will be described.

_{First, Bi 2 O 3, N a} 2 CO 3, BaTiO 3, and blended appropriate amount of TiO ₂ is mixed uniformly with a ball mill or the like. The slurry after mixing is dried and calcined at 800 ° C. The calcining temperature is preferably 800 ° C. This is because, for example, the dielectric loss is smaller than those at 850 ° C. or 900 ° C. The calcined body is pulverized with a ball mill or the like to dry the slurry. Then, 3.0% by weight of BBZ sintering aid is added, and a binder is mixed to form a green sheet. BNT-BT piezoelectric ceramics having a density of 5.7 × 10 ³ kg / m ³ or more can be obtained by adding 3.0% by weight or more of BBZ sintering aid and firing at 1100 ° C. or less. According to the experimental results of the above PZT piezoelectric ceramics, the addition of 3.0% by weight or more of PBZ sintering aid to the PZT piezoelectric ceramics contributes to the densification by the same mechanism. This is because it is estimated that the density is increased by adding 3.0% by weight or more of the BBZ sintering aid to the BT piezoelectric ceramics.

  The green sheet can be produced by a known method such as a doctor blade method, an extrusion method, a calendar roll method, or the like. The thickness of the green sheet is adjusted so as to have a desired thickness after firing, for example. The green sheet thus manufactured is punched or cut in consideration of firing shrinkage and processing margin, and a printing sheet having a predetermined shape suitable for the rectangular shape of the piezoelectric transformer to be manufactured is obtained. An internal electrode paste containing Ag and Pd is printed by a screen printing method or the like on a half region in the longitudinal direction of the printing sheet. Here, in the printing of the internal electrode paste of Ag—Pd, for example, the printing thickness is adjusted to be about 2 μm to 5 μm after firing. Further, it is desirable to determine a pattern for printing the internal electrode paste so that the internal electrodes to be formed can be easily connected every other layer thereafter.

  Next, the printing sheets on which the internal electrode paste is printed are aligned and laminated by a predetermined number, and the printing sheets thus laminated are thermocompression bonded by a hot press or the like to be integrated. In this way, the press body in which the sheet is press-fitted in accordance with a predetermined position is punched to produce a molded body.

  Subsequently, the molded body is fired at 1100 ° C. or less according to a predetermined temperature pattern. If necessary, the shape and the shape of the fired body are adjusted by grinding or polishing. Next, using an Ag-Pd paste or the like, the internal electrodes of the input part are connected every other layer to form a pair of electrodes, and the output electrode is formed on the end face of the output part, and then at a predetermined temperature. The Ag-Pd paste or the like is baked by processing. Usually, the baking treatment of the Ag—Pd paste or the like is performed at a temperature lower than the firing temperature. And a lead wire is attached to the electrode formed as needed. The obtained sintered body is subjected to polarization treatment. A predetermined voltage is applied between the pair of electrodes provided in the input unit and the electrode provided on the end face of the output unit to perform polarization processing of the output unit, and then the pair of electrodes provided in the input unit A piezoelectric transformer is manufactured by applying a predetermined voltage between the electrodes and performing polarization processing of the input portion.

  The polarization treatment is performed for a predetermined time at a predetermined temperature lower than the Curie point of the piezoelectric ceramic. In this way, a lead-free BNT-BT multilayer piezoelectric transformer can be manufactured. Thus, by integrally firing the press body in which the piezoelectric layers made of BNT-BT piezoelectric ceramics and the internal electrode layers made of Ag-Pd or the like are alternately laminated, the lead-free laminated piezoelectric transformer Formation becomes possible.

In order to demonstrate that the BNT-BT piezoelectric ceramic can be fired at a low temperature by adding the BBZ sintering aid, the present inventors conducted the following experiment. FIG. 3 is a table summarizing the experimental conditions and results. First, each oxide was mixed at an element ratio of Bi: B: Zn = 3: 3: 4 to prepare a BBZ sintering aid. _{Then, Bi 0.5 Na 0.5 TiO 3:} BaTiO 3 = 86: addition of BBZ sintering aid BNT-BT calcined powder fabricated such that the 14 proportion of. The auxiliary agent addition ratio is a ratio (H / E) of the weight (H) of the sintering auxiliary agent to the weight (E) of the base material. The calcining temperature was 800 ° C.

When the density of the sintered body obtained by firing amount 1.0 wt% of the compacts and added amount of 3.0% by weight of the molded body at 1000 ° C. as measured by the Archimedes method, respectively 3.64 × ¹⁰ 3 kg / m ³ and 4.12 × 10 ³ kg / m ³ . Next, When the addition amount of 3.0% by weight of the molded article was measured density of the fired sintered body at 1050 ° C. and 1100 ° C., respectively, the density of the sintered body of 1050 ℃ 5.38 × ¹⁰ 3 kg / Although m ³ was not sufficient, the density of the sintered body at 1100 ° C. is 5.74 × 10 ³ kg / m ³ , which is a standard for being densely sintered. A density of ³ kg / m ³ or more could be achieved. All the sintered bodies were produced in the form of pellets.

Next, the electrical characteristics of the pellets of Example 1 that were able to achieve a sufficient density were measured. As a result, a relative dielectric constant εr = 1290, a radial coupling coefficient kr = 13.7%, and a dielectric loss tan δ = 5.4% were measured. As a result, by setting the element ratio of Bi: Zn: B in the BBZ sintering aid to a composition of 3: 3: 4, the BNT-BT piezoelectric ceramic can be densified at 1100 ° C. or less and sufficiently It has been proved that excellent piezoelectric characteristics can be obtained.

  In the above-described embodiment, the BBZ sintering aid having at least bismuth oxide and zinc oxide and the balance being boron oxide has been described. However, the same applies to a BB-Cd sintering aid in which zinc is replaced with cadmium. It is thought that an effect is acquired. Zinc or cadmium is believed to produce a liquid phase suitable for grain growth in liquid phase sintering and to help dissolved bismuth enter the ceramic.

It is a diagram which shows the composition of the BBZ sintering aid which concerns on this invention. It is a table | surface which shows the conditions and result of an experiment regarding PZT piezoelectric ceramics. It is a table | surface which shows an Example.

Explanation of symbols

S area

Claims (4)

Production of BNT-BT piezoelectric ceramics mainly composed of perovskite type compounds represented by x (Bi _0.5 Na _0.5 TiO ₃ )-(1-x) BaTiO ₃ (where 0 <x <1) A sintering aid used in
Having at least bismuth oxide and zinc oxide, the balance being boron oxide,
A sintering aid for piezoelectric ceramics, wherein the metal composition ratio of the bismuth oxide, zinc oxide and boron oxide is Bi: B: Zn = 3: 3: 4 . x (Bi _0.5 Na _0.5 TiO ₃ )-(1-x) BaTiO ₃ (where 0 <x <1) is a BNT-BT piezoelectric ceramic mainly composed of a perovskite type compound. And
It is obtained by adding 3.0% by weight or more of the sintering aid for piezoelectric ceramics according to claim 1 to BNT-BT piezoelectric ceramic material and firing at 1100 ° C. or lower.
A BNT-BT piezoelectric ceramic characterized by having a density of 5.7 × 10 ³ kg / m ³ or more.   A multilayer piezoelectric device comprising: piezoelectric layers made of BNT-BT piezoelectric ceramics according to claim 2 and internal electrode layers made of Ag-Pd, which are alternately laminated and integrally fired. x (Bi _0.5 Na _0.5 TiO ₃ )-(1-x) BaTiO ₃ (where 0 <x <1) as a main component of a BNT-BT piezoelectric ceramic material mainly composed of a perovskite compound An addition step of adding 3.0% by weight or more of the sintering aid for piezoelectric ceramic according to claim 1 to the calcined powder;
And a firing step of firing the molded body of the material obtained by the addition step at 1100 ° C. or lower. A method for producing a BNT-BT piezoelectric ceramic, comprising:

Images