JP2005194150A - Piezoelectric ceramics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic which can be formed by firing at a lower temperature without practically lowering the piezoelectric characteristics. <P>SOLUTION: The piezoelectric ceramic is expressed by the general formula ABO<SB>3</SB>where the site A has lead as a main component and the site B has zirconium and titanium as main components, and it is characterised in that the electromechanical coupling factor Kr of the piezoelectric ceramic after adding 0.5 to 3.0 wt.% of a sintering auxiliary containing at least two kinds selected from among bismuth oxides, boron oxides, and zinc oxides to the total weight of the ABO<SB>3</SB>and firing at a temperature of 1,000 °C or lower, is 0.6 or larger, and the composition of respective components of the sintering auxiliaries after firing is 30 to 55 mol% of a Bi component, 0 to 25 mol% of the B component, and 45 to 70 mol% of a Zn component, respectively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a piezoelectric ceramic that can be fired at a low temperature and has an electromechanical coupling coefficient comparable to that of the prior art.

  Piezoelectric ceramics mainly composed of lead zirconate titanate (so-called PZT) have a high piezoelectric constant (such as d31), and thus are useful, for example, as materials for stacked piezoelectric actuators.

Conventionally, piezoelectric ceramics used in multilayer piezoelectric actuators need to be fired at about 1100 ° C. or higher in order to exhibit good characteristics. For this reason, a silver / palladium paste containing a large amount of palladium as an electrode paste. It was necessary to use (Ag / Pd = 70/30) or platinum paste (Pt). However, the use of such an electrode paste containing a large amount of expensive noble metal leads to an increase in production cost. For example, as disclosed in Patent Document 1, a piezoelectric ceramic is formed using a sintering aid. A study of firing at a lower temperature is underway.
Japanese Patent No. 3406611

  However, as a result of tests conducted by the inventors in accordance with the disclosure of Patent Document 1, the deterioration of piezoelectric characteristics becomes large, and it is difficult to produce piezoelectric ceramics having desired displacement characteristics with desired sizes. I found out.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a piezoelectric ceramic that can be fired at a lower temperature without substantially deteriorating piezoelectric characteristics.

The present invention is a piezoelectric ceramic represented by a general formula ABO ₃ , wherein the A site is mainly composed of lead, and the B site is composed of zirconium and titanium as main components,
A sintering aid containing at least two kinds of bismuth oxide, boron oxide and zinc oxide is added in an amount of 0.5 wt% to 3.0 wt% with respect to the total weight of the ABO ₃ , and fired at 1000 ° C. or lower. The piezoelectric ceramic after the electromechanical coupling coefficient Kr is 0.6 or more, and the composition of each component of the sintering aid after firing is 30 to 55 mol% Bi component and 0 to 25 mol% A piezoelectric ceramic comprising a B component and 45 to 70 mol% of a Zn component.

  The piezoelectric ceramic according to the present invention can lower the sintering temperature to, for example, 1000 ° C. without substantially reducing the piezoelectric characteristics as compared with a composition having the same main component but not using a sintering aid. it can. For this reason, when a co-fired multilayer piezoelectric element is manufactured using the piezoelectric ceramic of the present invention, an electrode material having a low palladium content can be used, which greatly reduces the manufacturing cost. become able to.

Hereinafter, embodiments for carrying out the present invention will be described in detail.
The piezoelectric ceramic of the present invention has a perovskite type crystal structure represented by the general formula ABO ₃ . Here, the A site contains lead (Pb) as a main component, and the B site contains zirconium (Zr) and titanium (Ti) as main components. Other components that enter the A site include strontium (Sr), calcium (Ca), barium (Ba), silver (Ag), and the like.
Other components entering the B site include nickel (Ni), niobium (Nb), tantalum (Ta), antimony (Sb), magnesium (Mg), manganese (Mn), zinc (Zn), and the like.

Next, the piezoelectric ceramic of the present invention has at least two kinds of bismuth oxide (B ₂ O ₃ ), boron oxide (B ₂ O), and zinc oxide (ZnO) with respect to the total weight of ABO ₃ having the components described above. The above-mentioned sintering aid is added in an amount of 0.5 wt% to 3.0 wt%. That is, a raw material powder (hereinafter referred to as “base raw material powder”) containing lead, zirconium, titanium or the like used for forming ABO ₃ contains 0.5% by weight or more of sintering aid with respect to the total weight. The piezoelectric ceramic of the present invention can be obtained by molding a mixed powder (hereinafter referred to as “molding powder”) obtained by adding and mixing 0.0% by weight or less into a predetermined shape and firing.

Here, the addition ratio of the sintering aid to the base material powder and the ratio of the sintering aid component to the weight of the ABO ₃ component in the piezoelectric ceramic (fired body) produced using the molding powder are calcined. In consideration of the possibility that part of the components forming ABO ₃ and part of the sintering aid component may evaporate during the process, the above-mentioned sintering aid is not necessarily added. The numerical limits of the quantities are as follows.

  That is, when the amount of the sintering aid added is less than 0.5% by weight, a sufficiently dense body cannot be obtained when the sintering temperature is 1000 ° C. or lower, and the piezoelectric characteristics are further deteriorated. Further, if the amount of the sintering aid added exceeds 3.0% by weight, the piezoelectric characteristics are deteriorated, which is not preferable.

The piezoelectric ceramic of the present invention is obtained by processing the above-mentioned molding powder by a known molding method to produce a molded body, and firing the molded body at 1000 ° C. or lower. The best piezoelectric characteristics are obtained. Furthermore, it is a case where it bakes at 900 degreeC or more. Firing at such a low temperature is possible because the sintering aid component is uniformly dispersed in the molding powder, and a part of the sintering aid becomes liquid phase during firing of the compact. It is thought that liquid phase sintering proceeds uniformly throughout the fired sample.
The piezoelectric ceramic according to the present invention ensures high performance when used as various piezoelectric elements such as multilayer piezoelectric actuators and multilayer piezoelectric transformers when fired at a firing temperature lower than the conventional one. Further, the composition of the sintering aid is adjusted so that the electromechanical coupling coefficient Kr is 0.6 or more.
That is, a sintering aid containing at least two kinds of bismuth oxide, boron oxide, and zinc oxide is added in an amount of 0.5 wt% to 3.0 wt% with respect to the total weight of ABO ₃ , and 1000 ° C. or less. It is preferable that the composition of each component of the sintering aid after firing is 30 to 55 mol% Bi component, 0 to 25 mol% B component, and 45 to 70 mol% Zn component. .

(Test example)
(Pb _0.92 Sr _0.06 ) (Zr _0.52 Ti _0.46 Nb _0.02 ) Each powder of lead oxide, strontium carbonate, zirconium oxide, titanium oxide and niobium oxide is weighed so as to be O _3, and this is wet-mixed (for example, ball mill And calcined at 900 ° C. for 3 hours. Subsequently, 3 kg of the calcined powder is added to 3 liters of pure water to prepare a slurry, which is pulverized using a medium stirring mill so that the average particle size is 1 μm or less, and then dried. Thus, a base material powder was prepared.
Various weights were measured using powders of bismuth oxide (B ₂ O ₃ ), boron oxide (B ₂ O), and zinc oxide (ZnO), and these were wet mixed in a ball mill.
After mixing, the solvent was removed, and the powder that passed through a 100 mesh sieve was used as the sintering aid powder.
Here, the compounding amount of the powders of bismuth oxide (B ₂ O ₃ ), boron oxide (B ₂ O), and zinc oxide (ZnO) is as follows. It adjusted so that the composition (mol%) of each component of an agent might change variously.
The composition of the sintering aid after being baked at 1000 ° C. was measured by IPC emission spectroscopic analysis.

The additive amount of the sintering aid powder to the base raw material powder thus obtained is 1% by weight, and the composition (mol%) of each component of the sintering aid after firing at 1000 ° C. is as shown in Table 1. Various changes were made, and each composition was mixed for 16 hours with a ball mill, then dried, and further granulated using a nylon mesh. The obtained granulated powder was uniaxially press-formed into a disk shape having a diameter of 16 mmφ and a thickness of 1.5 mm, and this press-formed body was subjected to CIP (cold isostatic pressing) treatment at 1200 kgf / cm ² (= 17.6 MPa). did.
The CIP molded body thus produced was placed on an alumina setter, covered with a nickel sheath, placed in a firing furnace, and fired at 1000 ° C. for 3 hours in the atmosphere. After polishing the surface of the obtained fired body, its density was measured by Archimedes method.

  Next, a conductive paste (for example, silver paste) was applied to the polished surface of the fired body and baked at 860 ° C. The piezoelectric plate thus formed with the electrodes was subjected to a polarization treatment at 2 kV / mm in silicon oil at 120 ° C. for 20 minutes. The electromechanical coupling coefficient Kr and relative dielectric constant εr of the polarization-treated piezoelectric plate were measured with an impedance analyzer. The results are summarized in Table 1.

From the results of Table 1, test No. which is an example of the present invention is shown. Although 2,3,4,5,8,9,10,11,14,15,16 were baked at a low temperature of 1000 ° C, all of them were high in density and densified. Further, the electromechanical coupling coefficient Kr was 0.6 or more, and the piezoelectric characteristics were excellent. The relative dielectric constant εr was as large as 1800 or more.
That is, according to the present invention, it was found that firing can be performed at a lower temperature without substantially reducing the piezoelectric characteristics.

On the other hand, test No. which is a comparative example of the present invention. 1, 6, 7, 12, 13, 17, and 18 all had an electromechanical coupling coefficient Kr of less than 0.6, which was inferior in piezoelectric characteristics. It was also confirmed that the relative dielectric constant was lowered.
From this, the sintering aid containing at least two or more of bismuth oxide, boron oxide and zinc oxide is added to the base material powder, and each component of the sintering aid after firing at 1000 ° C. or lower is added. It has been found that the composition is preferably 30 to 55 mol% Bi component, 0 to 25 mol% B component, and 45 to 70 mol% Zn component.

Claims (1)

Represented by the general formula ABO ₃ , the A site is a piezoelectric ceramic mainly composed of lead, and the B site is a piezoelectric ceramic mainly composed of zirconium and titanium,
A sintering aid containing at least two kinds of bismuth oxide, boron oxide and zinc oxide is added in an amount of 0.5 wt% to 3.0 wt% with respect to the total weight of the ABO ₃ , and fired at 1000 ° C. or lower. The piezoelectric ceramic after the electromechanical coupling coefficient Kr is 0.6 or more, and the composition of each component of the sintering aid after firing is 30 to 55 mol% Bi component and 0 to 25 mol% A piezoelectric ceramic comprising a B component and 45 to 70 mol% of a Zn component.