JP5530140B2 - BNT-BT piezoelectric ceramics and manufacturing method thereof - Google Patents

Description

  The present invention relates to a BNT-BT piezoelectric ceramic and a manufacturing method thereof.

  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, see Patent Documents 1 and 2). Since such a piezoelectric ceramic composition does not contain a lead compound, the load on the natural environment can be reduced.

The sintering aid for piezoelectric ceramics described in Patent Document 1 is a perovskite type compound represented by x (Bi _0.5 Na _0.5 TiO ₃ )-(1-x) BaTiO (where 0 <x <1). In the production of the BNT-BT piezoelectric ceramics containing as a main component, at least bismuth oxide and zinc oxide are contained, and the balance is made of boron oxide. By adding a sintering aid having such components, the BNT-BT piezoelectric ceramic can be densified at 1100 ° C. or lower.

Furthermore, lead-free piezoelectric ceramics for sintering additive of Patent Document _{2, x (Bi 0.5 Na 0.5 TiO} 3) -y (BaTiO 3) -z (ZnO 2) ( provided that, x + y + z = 1 And at least bismuth oxide and zinc oxide, with the balance being boron oxide. Thus, the BNT-BT piezoelectric ceramic is densified by firing at 1100 ° C. or lower.

JP 2007-238376 A JP 2009-7181 A

  However, when a BNT-BT piezoelectric ceramic is produced by adding a sintering aid containing boron oxide as described above, since the boron oxide is dissolved in water, the aqueous solution binder cannot be used. Therefore, existing facilities for aqueous solutions cannot be used, which is uneconomical. On the other hand, when a sintering aid not containing boron oxide is added, a BNT-BT piezoelectric ceramic having high piezoelectric characteristics cannot always be produced by low-temperature firing.

  The present invention has been made in view of such circumstances, and BNT-BT piezoelectric ceramics that can use aqueous solutions for binders and the like in the manufacturing process and can maintain high piezoelectric characteristics even when manufactured by low-temperature firing, and their manufacture It aims to provide a method.

(1) In order to achieve the above object, the BNT-BT piezoelectric ceramic of the present invention has x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ -y (wt%) MnO. _A sintering aid comprising an oxide of each element having a perovskite type compound represented by ₂ as a main component and an element ratio of bismuth / zinc of 0.05 to 9 with respect to the main component is 0.1. Sintering is performed by adding at least 4.0% by weight and not more than 4.0% by weight, and y is an outer percent by weight of MnO ₂ with respect to x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ . X and y satisfy the conditions of 0.80 ≦ x <0.94 and 0.01 ≦ y ≦ 4.5.

  In this way, the sintering aid is composed of oxides of bismuth and zinc and does not contain boron, so aqueous solutions can be used during sheet production and powder production, eliminating the need for explosion-proof facilities when using organic solvents. . In addition, the piezoelectric ceramic can be sintered at a low temperature, and the mechanical electrical coupling coefficient can be increased.

(2) Further, the BNT-BT piezoelectric ceramic of the present invention is a perovskite represented by x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ -y (wt%) MnCO _3. A sintering aid comprising an oxide of each element having a bismuth / zinc element ratio of 0.05 to 9 with respect to the main component. When y is defined as the outer percent by weight of MnCO ₃ with respect to x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ , x and y are added. However, it is characterized by satisfying the conditions of 0.80 ≦ x <0.94 and 0.01 ≦ y ≦ 5.9. As a result, an aqueous solution can be used in the manufacturing process, and the piezoelectric characteristics can be maintained high even when fabricated by low-temperature firing.

(3) Moreover, the manufacturing method of the BNT-BT type piezoelectric ceramic of the present invention is expressed by x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ -y (wt%) MnO ₂ . A calcined powder containing a perovskite type compound as a main component, and sintering comprising an oxide of each element having a bismuth / zinc element ratio of 0.05 to 9 with respect to the calcined powder A step of adding 0.1% by weight or more and 4.0% by weight or less of an auxiliary agent, and a step of firing the calcined powder to which the sintering auxiliary agent has been added at 1100 ° C. or lower, wherein y is the x When the external weight% of MnO ₂ with respect to (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ is set, x and y are 0.80 ≦ x <0.94 and It is characterized by satisfying the condition of 01 ≦ y ≦ 4.5. As a result, an aqueous solution can be used in the manufacturing process, and the piezoelectric characteristics can be maintained high even when fabricated by low-temperature firing.

(4) The method for producing the BNT-BT piezoelectric ceramic of the present invention is represented by x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ -y (wt%) MnCO ₃ . A calcined powder containing a perovskite type compound as a main component, and sintering comprising an oxide of each element having a bismuth / zinc element ratio of 0.05 to 9 with respect to the calcined powder A step of adding 0.1% by weight or more and 4.0% by weight or less of an auxiliary agent, and a step of firing the calcined powder to which the sintering auxiliary agent has been added at 1100 ° C. or lower, wherein y is the x X and y are 0.80 ≦ x <0.94 and 0.8% when the outer weight% of MnCO ₃ with respect to (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ is used. It is characterized by satisfying the condition of 01 ≦ y ≦ 5.9. As a result, an aqueous solution can be used in the manufacturing process, and the piezoelectric characteristics can be maintained high even when fabricated by low-temperature firing.

  (5) Moreover, the manufacturing method of the BNT-BT type piezoelectric ceramic of the present invention is to produce the calcined powder by pulverizing and mixing the powder containing the perovskite type compound as a main component using an aqueous solution. It is a feature. Thus, since it can grind and mix using aqueous solution, it is easy to use the equipment for an aqueous binder, an explosion-proof facility etc. can be made unnecessary, and cost can be reduced.

  (6) Moreover, the manufacturing method of the BNT-BT type piezoelectric ceramic of this invention further includes the process of mixing a water-soluble binder with the calcining powder to which the said sintering auxiliary agent was added, The mixture obtained by the said mixing It is characterized in that a molded body obtained using the above is fired. Thus, since a molded object can be produced using an aqueous solution binder and fired, facilities for an aqueous binder can be easily used, an explosion-proof facility or the like can be dispensed with, and costs can be reduced.

  According to the present invention, an aqueous solution can be used in the manufacturing process, and the piezoelectric characteristics can be maintained high even when manufactured by low-temperature firing.

It is a graph which shows the relationship between the temperature about each sample, and a dielectric constant.

  The present inventor has attempted to develop a multilayer piezoelectric device using a BNT-BT piezoelectric ceramic as a piezoelectric layer in order to produce a lead-free multilayer piezoelectric device not containing lead. In the process, the present inventor noticed that there is a demand for firing a laminated piezoelectric device having high piezoelectric characteristics at low temperature using an aqueous solution, and adding a manganese compound and a specific sintering aid. The present inventors have found that a BNT-BT piezoelectric ceramic is produced. Hereinafter, embodiments of the present invention will be described.

(Configuration of BNT-BT piezoelectric ceramics)
The BNT-BT piezoelectric ceramic of the present invention is x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ -y (wt%) MnO ₂ or x (Bi _0.5 Na _{0 .5} ) A lead-free piezoelectric ceramic mainly composed of a perovskite compound represented by TiO _3- (1-x) BaTiO ₃ -y (wt%) MnCO ₃ . The BNT-BT piezoelectric ceramic is sintered by adding a sintering aid (hereinafter referred to as “BZ sintering aid”) to a base material having a predetermined composition as described above.

The composition of the base _{metal, x (Bi 0.5 Na 0.5)} TiO 3 - (1-x) BaTiO 3 -y (wt%) when expressed as MnO _2, in 0.80 ≦ x <0.94 Yes, and y satisfying the condition of 0.01 ≦ y ≦ 4.5 where y is the external weight% of MnO ₂ with respect to x (Bi _0.5 Na _0.5 ) TiO ₃ — (1-x) BaTiO ₃ is there. In the case where MnCO ₃ is used instead of MnO ₂ , it is preferable that the outer weight percent satisfies the condition of 0.01 ≦ y ≦ 5.9.

In order to reduce the sintering temperature of the ceramic member while maintaining high piezoelectric properties of the base material such as BNT-BT piezoelectric ceramics, ZnO or Bi ₂ O ₃ having a high reactivity and a low melting point is added, and the grain boundary It is effective to create a liquid phase in the phase and promote low temperature sintering. 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.

  The BZ sintering aid used in the present invention comprises bismuth oxide and zinc oxide, and is suitable for densifying BNT-BT piezoelectric ceramics. By adding the BZ sintering aid to the piezoelectric ceramic in the manufacturing process of the BNT-BT piezoelectric ceramic, the BNT-BT piezoelectric ceramic is densified at a firing temperature of 1100 ° C. or lower.

  The metal composition ratio of bismuth oxide and zinc oxide constituting the BZ sintering aid is a molar ratio of Bi: Zn in the range of 0.05: 0.95 to 0.1: 0.9 (bismuth / zinc The element ratio is preferably 0.05 to 9). By making the composition ratio of Bi: Zn the most effective for densification, the BNT-BT piezoelectric ceramic can be densified at 1100 ° C. or lower, and high piezoelectric characteristics can be obtained.

(Manufacturing method of BNT-BT piezoelectric ceramic)
A manufacturing method for manufacturing a BNT-BT piezoelectric ceramic by low-temperature firing using a BZ sintering aid is as follows. First, powders of Bi ₂ O ₃ , Na ₂ CO ₃ , BaTiO ₃ , MnO ₂ (or MnCO ₃ ) are weighed and mixed by a mill together with a solvent. Then, the mixed powder is dried and granulated by a mesh pass. Subsequently, the powder is calcined at 800 ° C. and pulverized. Then, a predetermined amount of Bi ₂ O ₃ and ZnO are added together with the binder, dried and granulated. If the powder thus obtained is formed into a desired shape and fired at 1100 ° C., a sintered body of BNT-BT piezoelectric ceramics by low-temperature firing can be obtained. As described above, the piezoelectric ceramic can be sintered at a low temperature by adding Mn and BZ sintering aids. Moreover, the mechanical electrical coupling coefficient can be increased by adding Mn. Note that Mn may be added by either MnCO ₃ or MnO ₂ .

  In the above manufacturing process, it is preferable to pulverize and mix the BNT-BT piezoelectric ceramic powder using an aqueous solution and calcine it to produce a calcined powder. Moreover, it is preferable to mix a water-soluble binder with the calcined powder to which the sintering aid is added, and to fire the molded body formed from the mixture obtained by mixing. In this way, the sintering aid is composed of oxides of bismuth and zinc and does not contain boron, so aqueous solutions can be used during sheet production and powder production, eliminating the need for explosion-proof facilities when using organic solvents. . As a result, the manufacturing cost can be reduced.

(Composition trace experiment of main component)
In order to obtain a BNT-BT piezoelectric ceramic having sufficient piezoelectric properties, the composition of the base material to which the BZ sintering aid is added needs to be suitable for the purpose. In the composition trace experiment, a certain amount of each BZ sintering aid was added to produce BNT-BT piezoelectric ceramics having different compositions. The composition ratio x was appropriately selected within a range satisfying 0.83 ≦ x ≦ 0.89. Further, MnCO ₃ was added in such an amount that y was 0.5% by weight. In this manner, a main component calcined body was obtained.

Bi ₂ O ₃ and ZnO powders were mixed to prepare an auxiliary mixture. And the auxiliary agent mixture was mixed with the base material calcined powder having the above composition. The sintering aid was added during pulverization after calcination. The added amount was Bi: Zn = 3: 4, and added in an external weight ratio with respect to the calcined powder. 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. In this way, 2% by weight of BZ was added, and the molded body was fired at 1100 ° C. And about the sintered compact of each composition, the density, the mechanical electrical coupling coefficient, and the dielectric constant were measured.

  The density of the sintered body was measured by the Archimedes method. In the characteristic measurement, a silver paste is printed on both main surfaces of the pellet-shaped sintered body formed under each condition, and an electrode is formed by firing, 60 to 150 ° C., 5 to 20 minutes, 2 to 4 kV. The sintered body was polarized in the thickness direction under the condition of / mm. In this manner, the fired sample was provided with an electrode and polarized, and the mechanical coupling coefficient kr and the like were measured.

Table 1 is a table showing the results of measuring the density, the mechanical electrical coupling coefficient, and the relative dielectric constant of the BNT-BT piezoelectric ceramics having each composition. As shown in FIG. 1, when BNT-BT piezoelectric ceramics were produced by changing the composition, a mechanical electrical coupling coefficient kr of 0.11 or more was obtained in most compositions, and the mechanical electrical coupling of the lead-free piezoelectric material was obtained. A sufficiently large value was obtained as the coefficient kr.

In any BNT-BT piezoelectric ceramics having any composition shown in Table 1, the density is 5.7 kg / m ³ or more, the mechanical electrical coupling coefficient kr is 0.11 or more, the relative dielectric constant is 520 or more, and the dielectric loss tan δ is 0. .6 or less and had preferable piezoelectric characteristics. Based on such a result, it was decided to conduct an experiment on the presence or absence of addition of an auxiliary agent using Sample No. 3 having a composition within the above range and close to the median.

(Experiment of BZ sintering aid)
As a sample to which a BZ sintering aid was added, a BNT-BT piezoelectric ceramic having the composition of Sample No. 3 was used. On the other hand, the molded body to which no BZ sintering aid was added was fired at 1200 ° C, 1150 ° C, and 1100 ° C. And when the density of the sintered body was measured by the Archimedes method, the composition of sample number 3 was used as the base material, and the BNT-BT piezoelectric ceramic obtained under the conditions of a firing temperature of 1200 ° C. and no added amount of BZ sintering aid The density of was 5.76 × 10 ³ kg / m ³ . Further, the density of the BNT-BT piezoelectric ceramics obtained under the conditions where the firing temperature is 1150 ° C. and 1100 ° C. and the amount of the BZ sintering aid is not added is 5.45 × 10 ³ kg / m ³ , 5.00 × The density was 10 ³ kg / m ³ and the densification was insufficient. On the other hand, the density of the BNT-BT piezoelectric ceramics obtained under the conditions of the firing temperature of 1100 ° C. and the addition amount of 2 wt% of BZ sintering aid is 5.77 × 10 ³ kg / m ^3, which is sufficiently densified. It was. Table 2 summarizes the production conditions and characteristics of each sample.

  As described above, with respect to the BNT-BT piezoelectric ceramic having the composition of Sample No. 3, a dense sintered body can be obtained even when the firing temperature is set to 1100 ° C. by adding the BZ sintering additive to 2% by weight or more. I understood.

The measurement of the mechanical electrical coupling coefficient kr and the relative dielectric constant ε _33T / ε ₀ was performed by producing a pellet-like sintered body in the same manner as described above. In Example 1, the electromechanical coupling coefficient was 0.11, and the relative dielectric constant was 521, indicating that both were sufficiently high. And especially dielectric loss tan-delta is 0.5, and it turned out that it is remarkably excellent compared with the sample which does not add a BZ sintering auxiliary agent.

  “−” In the table indicates that polarization is not possible or measurement is impossible. In Comparative Example 3, polarization was impossible, but all other samples could be polarized. In consideration of the effect of the usual sintering aid, the BZ sintering aid is actually densified with an addition amount of 2% by weight or more, but the sintered body is densified even with an addition amount of 0.01% by weight or more. It is thought to do.

  Further, regarding the sample (Example 1) fired at 1100 ° C. with 2% by weight of BZ sintering aid and the sample fired at 1200 ° C. without adding the BZ sintering aid (Comparative Example 1), the temperature and The relationship with the relative dielectric constant was measured. FIG. 1 is a graph showing the relationship between temperature and relative dielectric constant for each sample. As shown in FIG. 1, the graph B of Comparative Example 1 without the addition of an auxiliary agent has an inflection point in the vicinity of 150 ° C., and when the temperature is raised, the piezoelectric characteristics may begin to be lost at this temperature. I understand. On the other hand, graph A of Example 1 to which an auxiliary agent was added had an inflection point near 180 ° C., and the piezoelectric characteristics were stable in a temperature range 30 ° C. wider than the sample to which no auxiliary agent was added. I understand. Therefore, it can be seen that the BNT-BT piezoelectric ceramic according to the present invention has improved high-temperature characteristics.

  As described above, by adding a sintering aid made of bismuth oxide and zinc oxide and containing no boron to a base material having a BNT-BT-Mn type composition, It has been demonstrated that the piezoelectric properties can be improved, the Curie point can be raised, and low temperature sintering is also possible.

(Laminated piezoelectric device)
BNT-BT piezoelectric ceramics sintered using a BZ sintering aid can be used for laminated piezoelectric devices in which electrodes and piezoelectric layers are alternately laminated, thereby obtaining a great effect. BNT-BT piezoelectric ceramics have the advantage that solid-phase sintering is simple and are suitable for lamination. An example of the multilayer piezoelectric device is a multilayer piezoelectric transformer. Multilayer piezoelectric transformers are small and can provide a large step-up ratio, so there is a demand for backlights for liquid crystal displays. By using a BZ sintering aid to realize a multilayer piezoelectric transformer having a BNT-BT piezoelectric ceramic as a piezoelectric layer, a multilayer piezoelectric transformer that does not contain lead and has sufficient characteristics is obtained. Can do.

As an application example of BNT-BT piezoelectric ceramics using a BZ sintering aid, a manufacturing method of a laminated piezoelectric transformer using BNT-BT piezoelectric ceramics as a piezoelectric layer will be described below. First, appropriate amounts of Bi ₂ O ₃ , Na ₂ CO ₃ , BaTiO ₃ , TiO ₂ and MnO ₂ (or MnCO ₃ ) are mixed and uniformly mixed by a ball mill or the like. The slurry after mixing is dried and calcined at 800 ° C. The calcining temperature is preferably 800 ° C. or lower. For example, the dielectric loss of a sintered compact becomes small by setting it as 800 degrees C or less.

  Next, the calcined body is pulverized with a ball mill or the like to dry the slurry. Then, an appropriate amount of 0.01 to 4.0% by weight of BZ sintering aid is added, and a binder is mixed to form a green sheet. A densified BNT-BT piezoelectric ceramic can be obtained by adding a BZ sintering aid and firing at 1100 ° C. or lower.

  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 process 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, a press body in which piezoelectric layers made of BNT-BT piezoelectric ceramics and internal electrode layers made of Ag-Pd or the like are alternately laminated is integrally fired to produce a lead-free laminated piezoelectric transformer. be able to.

A Graph of Example 1 B Graph of Comparative Example 1

Claims (2)

a step of producing a calcined powder mainly comprising a perovskite type compound represented by x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ -y (wt%) MnCO ₃ ;
Adding 2% by weight of a sintering aid comprising an oxide of each element with a bismuth / zinc element ratio of 0.75 to the calcined powder;
Mixing a water-soluble binder into the calcined powder to which the sintering aid is added using an aqueous solution;
Firing the molded body obtained using the mixture obtained by the mixing at 1100 ° C. or less,
When y is an external weight% of MnCO ₃ with respect to x (Bi _0.5 Na _0.5 ) TiO _3- (1-x) BaTiO ₃ ,
A method for producing a BNT-BT piezoelectric ceramic, wherein x and y satisfy the conditions of 0.83 ≦ x <0.89 and y = 2 . The method for producing a BNT-BT piezoelectric ceramic according to claim 1 , wherein the powder containing the perovskite compound as a main component is pulverized, mixed and calcined using an aqueous solution to produce the calcined powder.

Images