JP2012072027A - Piezoelectric ceramic and piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic which is a non-lead system and capable of being fired at a low temperature, has high piezoelectric characteristics and can be variously applicable as a piezoelectric component, and a piezoelectric element using this.SOLUTION: The piezoelectric ceramic includes a perovskite type compound which is represented by Bi(NaK)TiOand has a molar ratio x filling 0.15<x<0.35 as a principal component, and 0.1 wt.% or more and 2.5 wt.% or less of an additive which consists of oxide of each element of manganese, bismuth and zinc relative to the amount of principal component. Thus, by making the so-called bismuth titanate sodium potassium (BNKT) into the principal component, when it is used for an electronic component, it can make its load to the natural environment small since lead is not included. Moreover, since it can be fired with the additive at below 1,100°C, firing integrally with internal electrode becomes possible. Moreover, since piezoelectric characteristics can be made high by the components, it is variously applicable as a piezoelectric component.

Description

  The present invention relates to a so-called bismuth sodium potassium titanate (BNKT) type piezoelectric ceramic which does not contain a lead compound and a piezoelectric element using the same.

  As conventional piezoelectric ceramics, lead zirconate titanate (PZT) and lead-based piezoelectric ceramics in which a third component is dissolved are used. However, from the recognition that the lead element contained in PZT is an environmental burden, such lead-based piezoelectric ceramics are becoming subject to environmental regulations. At present, the search for lead-free piezoelectric materials that can replace PZT as environmentally-friendly lead-free piezoelectric materials in various fields is continuing, and lead-free piezoelectric ceramics mainly composed of BNKT have also been developed.

For example, the piezoelectric ceramic described in Patent Document 1 includes BNT (bismuth sodium titanate (Bi _0.5 Na _0.5 ) TiO ₃ ), BT (barium titanate BaTiO ₃ ), and BKT (bismuth potassium titanate ( By including the three components of Bi _0.5 K _0.5 ) TiO ₃ ), it is intended to provide lead-free piezoelectric ceramics suitable as a knock sensor element. The piezoelectric element described in Patent Document 2 has three components of (Bi _0.5 Na _0.5 ) TiO ₃ , (Bi _0.5 K _0.5 ) TiO ₃ and BaTiO ₃ as main components, and has a good temperature characteristic. A resonance type knocking sensor is to be provided. The piezoelectric / electrostrictive ceramic described in Patent Document 3 is made of a material represented by the general formula xBNT-yBKT-zBT (x + y + z = 1), and is attempting to obtain a large electric field induced strain. Each document exemplifies additives such as Bi ₂ O ₃ and Mn ₂ O ₃ .

JP 2001-151666 A JP 2004-93197 A JP 2010-150126 A

  However, as a material having a large piezoelectric characteristic, a lead-free piezoelectric material having a main composition of BNKT, which has high specific dielectric constant εr, electromechanical coupling coefficient kr, and mechanical quality coefficient Qm, has not been obtained. The present invention has been made in view of such circumstances, and is a lead-free piezoelectric ceramic that can be fired at low temperature, has high piezoelectric characteristics, and can be applied in various ways as a piezoelectric component, and a piezoelectric element using the same The purpose is to provide.

(1) In order to achieve the above object, the piezoelectric ceramic of the present invention is represented by Bi _0.5 (Na _1-x K _x ) _0.5 TiO ₃ and the molar ratio x is 0.15 <x <0. The main component is a perovskite compound satisfying .35, and the additive contains 0.1 wt% or more and 2.5 wt% or less of an oxide of each element of manganese, bismuth and zinc. It is a feature.

  Thus, by using so-called potassium potassium bismuth titanate (BNKT) as a main component, it does not contain lead, and therefore, when used in an electronic component, the load on the natural environment can be reduced. In addition, since it can be fired at 1100 ° C. or less with an additive, it can be fired integrally with the internal electrode. In addition, the above-described components can enhance the piezoelectric characteristics, and can be applied in various ways as piezoelectric parts.

(2) Further, the piezoelectric ceramic of the present invention is characterized in that the electromechanical coupling coefficient is 0.14 or more, the mechanical quality coefficient is 185 or more, and the relative dielectric constant is 350 or more. Thus, since the electromechanical coupling coefficient kr is relatively large, the mechanical quality coefficient Qm, and the relative dielectric constant ε ₃₃ ^T / ε ₀ are also large, it can be applied to a wide range of products such as a piezoelectric buzzer and an ultrasonic motor.

  (3) Moreover, the piezoelectric element of the present invention is characterized in that the piezoelectric layer made of the piezoelectric ceramic and the internal electrode are integrally fired. Such a piezoelectric element integrally fired with the internal electrode can be fired at 1100 ° C. or less, and can be manufactured without melting the internal electrode.

  According to the present invention, it is possible to realize a piezoelectric ceramic that is non-leaded and can be fired at a low temperature and has high piezoelectric characteristics and can be applied in various ways as a piezoelectric component.

It is a table | surface which shows the piezoelectric characteristic with respect to the solid solution ratio of K element.

  Next, embodiments of the present invention will be described with reference to the drawings.

(Composition of base material)
The lead-free piezoelectric ceramic of the present invention is a perovskite type compound represented by Bi _0.5 (Na _1-x K _x ) _0.5 TiO ₃ and having a molar ratio x satisfying 0.15 <x <0.35. It is a so-called bismuth sodium potassium titanate (BNKT) type piezoelectric ceramic as a main component. In this way, by using a lead-free material as a main component, the load on the natural environment can be reduced when used for electronic components.

(Additive composition)
In order to lower the sintering temperature of the ceramic member without deteriorating the piezoelectric properties of the base material such as BNKT-based piezoelectric ceramics, ZnO or Bi ₂ O ₃ having a high reactivity and a low melting point is added, and the grain boundary phase is added. It is effective to promote low temperature sintering by forming a liquid phase. 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.

Further, MnCO ₃ is further added to the piezoelectric ceramic of the present invention. These additives are added to the piezoelectric ceramic material in an amount of 0.1 wt% to 2.5 wt% in the manufacturing process. When such an additive acts, it is densified at a firing temperature of 1100 ° C. or lower. In addition, the above-described components can enhance the piezoelectric characteristics, and can be applied in various ways as piezoelectric parts.

(Production method)
The piezoelectric ceramic of the present invention can be produced by the following method. First, Bi ₂ O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , and TiO ₂ powders are weighed and mixed together with a solvent in a mill. 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 , MnCO ₃ , and ZnO is added together with the binder, followed by drying and granulation. If the powder thus obtained is molded into a desired shape and fired at 1100 ° C., a dense body of the piezoelectric ceramic of the present invention can be obtained by low-temperature firing.

(Experiment)
The K element solid solution ratio (molar ratio) x of the main component Bi _0.5 (Na _1-x K _x ) _0.5 TiO ₃ is appropriately selected within a range satisfying 0.15 <x <0.35 (x = 0.10, 0.25, 0.30), 1.5% by weight of BiZn oxide and 0.5% by weight of MnCO ₃ are added to the main components and fired at 1100 ° C. A sintered body was obtained. And the silver paste was printed on both the main surfaces of the sintered compact pellet, and the electrode was provided and polarized by baking, and each characteristic was measured. The sintered body was polarized in the thickness direction under the conditions of 60 to 150 ° C., 5 to 20 minutes, and 2 to 4 kV / mm. And the piezoelectric characteristic of the obtained sintered compact was measured. FIG. 1 is a table showing the piezoelectric characteristics with respect to the solid solution ratio of the K element. As shown in FIG. 1, when x = 0.10, the electromechanical coupling coefficient kr and the mechanical quality coefficient Qm are 0.23 and 742, respectively, and the highest characteristics are obtained. On the other hand, the relative dielectric constant ε ₃₃ ^T / ε ₀ is 837 when x = 0.30, which is the highest.

  As a result of measuring the density of the piezoelectric ceramic, it was confirmed that all were sintered without any problem. There is no direct relationship between low temperature sinterability or mechanical quality factor magnitude. The bulk density is measured as the density, and the Archimedes method is used for the measurement.

(Piezoelectric element)
In addition, the lead-free piezoelectric ceramic of the present invention provides a great effect when used in a laminated piezoelectric element in which electrodes and piezoelectric layers are alternately laminated. The piezoelectric ceramic of the present invention has an advantage that solid-phase sintering is simple and is suitable for lamination. Examples of the laminated piezoelectric element include a piezoelectric transformer and a piezoelectric actuator. By producing a laminated piezoelectric element using a BNKT piezoelectric ceramic as a piezoelectric layer using an additive composed of an oxide of each element of manganese, bismuth and zinc, a laminated piezoelectric element containing no lead is obtained. be able to.

As an example of a method for manufacturing a multilayer piezoelectric element to which the piezoelectric ceramic of the present invention is applied, a method for manufacturing a multilayer piezoelectric transformer will be described below. Appropriate amounts of Bi ₂ O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , and TiO ₂ powders are blended and mixed uniformly 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, predetermined amounts of not less than 0.1 wt% and not more than 2.5 wt% of additives made of oxides of manganese, bismuth and zinc are added, and a binder is mixed to form a green sheet. And by sintering at 1100 degrees C or less, the piezoelectric ceramic of this invention fully sintered can be obtained.

  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 BNKT laminated piezoelectric transformer can be manufactured. In this way, a press body in which piezoelectric layers made of the piezoelectric ceramic of the present invention 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. Can do.

Claims (3)

The main component is a perovskite compound represented by Bi _0.5 (Na _1-x K _x ) _0.5 TiO ₃ and having a molar ratio x satisfying 0.15 <x <0.35.
A piezoelectric ceramic comprising 0.1 to 2.5% by weight of an additive composed of oxides of manganese, bismuth and zinc with respect to the main component.   2. The piezoelectric ceramic according to claim 1, wherein an electromechanical coupling coefficient is 0.14 or more, a mechanical quality coefficient is 185 or more, and a relative dielectric constant is 350 or more.   A piezoelectric element comprising a piezoelectric layer made of the piezoelectric ceramic according to claim 1 and an internal electrode and integrally fired.

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