JPH04224168A - Piezoelectric ceramic composition - Google Patents

Abstract

PURPOSE:To improve mechanical strength of a piezoelectric ceramic compsn. comprising lead titanate zirconate (PZT) without decreasing its electric characteristics. CONSTITUTION:SiO2 and PbO are added by 2-5mol% in total to Pb(ZrxTi1-x)O3 satisfying 0.3<=x<=0.7, and the mixture is molded and fired to obtain a piezoelectric ceramic compsn. The mixture of SiO2 and PbO changes into glasses at the sintering temp. of PZT, so that the obtd. sintered compact has a granular phase of PZT particles embedded in a glass phase and has no vacancy. Thereby, mechanical strength of the PZT is improved with reduction of deterioration of electric characteristics with the elapse of time. When only SiO2 is used, the glass phase is not formed at the sintering temp. of PZT, which makes vacancy among granules and does not improve the strength of the sintered compact.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to piezoelectric ceramic compositions.

0002

2. Description of the Related Art When piezoelectric materials are applied to actuators, mechanical properties (particularly strength) are important as well as electrical properties. Therefore, a method is known in which SiC whiskers are added to a piezoelectric material to strengthen the piezoelectric ceramic composition. Also,
Pb (
Mg1/3N2/3)O3, PbTiO3, PbZ
Composition Pb (Mg1/3N2
A piezoelectric ceramic composition has been proposed in which SiO2 is added in an amount of 0.05 to 1.0 wt.
15344).

0003

[Problem to be solved by the invention] However, SiC
In the method of adding whiskers, the electrical properties are impaired as the amount added increases, so a significant improvement in strength cannot be expected. Furthermore, in Japanese Patent Application Laid-Open No. 45-15344, SiO2 forms a grain boundary phase, but SiO2 has a high sintering temperature, so P
There is a problem that sufficient sintering does not occur at the sintering temperature of ZT (lead zirconate titanate)-based materials, and the mechanical strength of the sintered body does not become sufficiently high.

[0004] Therefore, an object of the present invention is to improve the mechanical strength of piezoelectric ceramic compositions.

[0005]

[Means for Solving the Problems] The present invention achieves the above objects,
Pb(Zrx Ti1-x)O3 where 0.3≦
A total of 2 to 5 SiO2 and PbO for x≦0.7
This is achieved by providing a piezoelectric ceramic composition characterized by the addition of mol %. The basic piezoelectric material of the piezoelectric ceramic composition of the present invention is PZT, more specifically Pb (Zrx
Ti1-x)O3 where 0.3≦x≦0.7
It is. Since particularly high piezoelectric properties can be obtained when x is within the range of 0.51 to 0.56, this range is preferable. Pb
(Zrx Ti1-x)O3 itself is a PbO source, Z
It can be manufactured by mixing an rO 2 source and a TiO 2 source into a predetermined composition and firing the mixture.

In the piezoelectric ceramic composition of the present invention, this PZT
It is characterized in that SiO2 and PbO2 are added in a total amount of 2 to 5 mol%. Since the mixture of SiO2 and PbO forms a liquid phase at the firing temperature of PZT, the glass phase consisting of SiO2 and PbO occupies the grain boundaries of the PZT sintered body, reducing the number of pores and improving the mechanical properties of the sintered body. Strength is improved. The mixing ratio of SiO2 and PbO2 is preferably 4:1.

[0007] The piezoelectric ceramic composition of the present invention can be produced using PZT.
This is done by firing a mixed powder of powder, SiO2 powder, and PbO powder. PZT powder, SiO2 powder, Pb
The particle size of the O powder is preferably 0.3 to 1.0 μm. The firing temperature is about 1200 to 1300°C. The firing atmosphere is an oxygen-containing atmosphere.

[0008]

[Operation] The mixture of SiO2 and PbO is vitrified at the firing temperature of PZT, and as shown in Fig. 1, the grain boundaries 2 of PZT particles 1 are filled with the grain boundary phase consisting of vitrified SiO2 and PbO, and the sintered body is formed. Improve mechanical strength. but,
Unlike the addition of whiskers, the electrical properties of the piezoelectric ceramic composition are not deteriorated.

[0009]

[Example] Example The composition of the piezoelectric ceramics used in the example was Pb (Zr
0.52, Ti0.48) was used. SiO2 powder,
The PbO 2 powder had a purity of 98% or more and a particle size of 0.5 μm or less, and was added to the PZT powder in a total amount of 1 to 8 mol %. (Table 1) This mixed powder was mixed in a ball mill for 48 hours and then granulated in a spray dryer. This granulated powder was molded at a pressure of 1000 kg/cm2 and fired at 1250°C for 2 hours.

The obtained fired body has a diameter of 15 mm and a thickness of 0.
It was processed into a 5 mm disk, and silver electrodes were baked on the top and bottom surfaces of the disk. A disk with baked silver electrodes was immersed in silicone oil at 100° C., and a voltage of 1.5 KV was applied to the top and bottom surfaces of the disk for 30 minutes to polarize it. After polarization, electrical characteristics were measured using an impedance meter. The method of measuring and calculating the electrical properties was in accordance with the Electronic Materials Association Standards (EMAS-6001 to 6007).

Further, the bending strength was evaluated by processing the fired body obtained in the same manner as above into a rectangular plate having a width of 4 mm, a length of 15 mm, and a thickness of 0.5 mm, and performing three-point bending with a span of 10 mm. Table 1 shows the electrical properties and mechanical strength of each composition prepared by the above method.

0012

[Table 1]

Comparative Example PZ obtained by mixing, molding, and firing in the same manner as in the example, but without adding SiO2 powder and PbO powder.
The electrical properties and mechanical strength of the T sintered body were observed and measured in the same manner as in the examples. As a result, the three-point bending strength was 53 MPa, and the SiO2 and PbO
The results show that the three-point bending strength (119 MPa) of a mixture of 4:1 ratio and a total addition of 5 mol % was significantly improved (see FIG. 2). In addition, regarding other properties, ε33T/ε0 and Kp are 5% and 4%, respectively, compared to those without the addition of SiO2 powder and PbO powder.
It only declined.

[0014] When only SiO2 powder is added, the three-point bending strength is slightly improved compared to the case without addition, but ε33T/ε
0 and Kp caused performance deterioration of 34-36% and 60-70%, respectively.

[0015]

[Effects of the Invention] According to the present invention, the mechanical strength of the lead zirconate titanate sintered body can be improved without deteriorating the electrical properties, and therefore the deterioration of the piezoelectric properties over time can be reduced. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the structure of a sintered body of a piezoelectric ceramic composition of the present invention.

[Figure 2] Piezoelectric ceramic composition sintered body 3 of Examples and Comparative Examples
It is a graph diagram showing point bending strength.

[Explanation of symbols]

1...PZT particles 2...Glass grain boundary phase

Claims (1)

[Claims] [Claim 1] Pb(Zrx Ti1-x)O3
In the formula, 0.3≦x≦0.7 contains SiO2 and PbO
A piezoelectric ceramic composition comprising a total of 2 to 5 mol% of the following.