JPH0269352A - Piezoelectric ceramics - Google Patents

Abstract

PURPOSE:To improve piezoelectric characteristics by using TiO2 the main crystal structure of which is rutile type as the essential raw material. CONSTITUTION:The TiO2 is heated to change the crystal structure thereof from anatase type to rutile type and to obtain the TiO2 which is the rutile type in >=97% of the crystal structure. This TiO2 and respective carbonates or oxides of Pb, Mg, Nd, and Zr are wet mixed in a ball mill and are dried, then the dried mixture is subjected to preliminary calcination and pulverizing to obtain the pulverized matter. This pulverized matter is dried and a binder is added thereto. The pulverized matter is then molded and calcined by which the piezoelectric ceramics of the formula Pb(Mg1/3Nb2/3)O3-PbTiO2-PbZrO3 system is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to piezoelectric ceramics used as elements that convert electrical energy to mechanical energy.

(Prior art) Two-component Pb is used as piezoelectric ceramics used as actuators, lighter ignition elements, sensors, etc.
Three-component system Pb(Mg
%Nb%) 03-PbT103-PbZyOi is known as Japanese Patent Publication No. 42-9716, and further p in the above composition.
The one in which a part of the b atoms were replaced with Sr was published in 1977.
It was proposed as No. 103 and is known as a piezoelectric ceramic with excellent various properties.

(Problems to be Solved by the Invention) As described above, piezoelectric ceramics with excellent various properties have recently been proposed, but further improvements in properties are desired. For example, for piezoelectric ceramics used as actuators, etc., it is preferable that the dielectric constant (ε3./ε.) is small and the piezoelectric strain constant (d3h) and electromechanical coupling coefficient (KP) are large. Further improvements are desired.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides that TiO2 used as a starting material for piezoelectric ceramics has a crystal structure of
It was assumed that 7% or more was rutile (high temperature type) and the rest was anatase (low temperature type).

(Function) By heating TIO□, its crystal structure changes from anatase to rutile, and by using TMURO 2 whose crystal structure is rutile, the characteristics of the fired piezoelectric ceramics are improved.

(Example) The present invention will be described in detail below with reference to specific numerical values.

First, in the present invention, 97% of the crystal structure of TiO2 (rJ!L titanium anatase) is heated.
% or more is rutile (high temperature type) as shown in Figure 1, and the rest is anatase (low temperature type). In the experiment, anatase was rutiled by changing the heating conditions at a temperature of 1000 to 1200°C to create T, O, and raw materials with different rutile rates. Moreover, the rutilation rate was determined by X-ray diffraction method.

Next, the following composition is obtained using the heat-treated Tr02.

37, 5Pb (Mg% Nb%) 03”37P
A piezoelectric ceramic (element) is produced from a composition having a composition of bT 103''25 , 5PbZr03 or more using the following procedure.

First, in addition to pre-rutilized TIO□, chemical purity 9
Prepare 8% or more oxides or carbonates, weigh them as raw materials so that they have the compounding composition of each formula above, and perform 12-hour mixing in a rubber-lined ball mill to make a homogeneous mixture. . After drying this mixture,
Preliminary firing was carried out at 50° C. for 2 hours, followed by pulverization for 12 hours in a ball mill. After that, the pulverized material was dried, a small amount of organic binder was added, and the granules were sized at a pressure of 100.
It is molded into a disk with a diameter of 22 mm and a thickness of 2 mm at 0 kg/cm2, and this disk is held and fired at a predetermined temperature for 2 hours in a closed container of a crucible. Here, the predetermined temperature is 1260℃
, 1270°C, 1280°C, and 1290°C.

Next, after polishing the fired disc, g! is applied to both sides of the disc. The desired piezoelectric ceramics are obtained by applying an electrode, baking it, immersing it in silicone oil, and applying a DC electric field of 2.5 kv/+m for 20 minutes at room temperature to perform polarization.

The piezoelectric ceramics obtained as above (rutilation rate 9
7% and 100%) and conventional piezoelectric ceramics, that is, those whose crystal structures are 100% anatase and 93% rutile, are shown in FIGS. 2 to 5. Here, the meanings of the symbols in the figure are as follows.

ε33/ε. : Specific dielectric constant.

Kp (%F): Electromechanical coupling coefficient. The larger this value is, the better the properties of piezoelectric ceramics will be.

d3□: Piezoelectric strain constant. Strain in the direction perpendicular to the direction of application when voltage is applied. The larger this value, the better the characteristics when used as an actuator or the like.

(Effects of the Invention) As is clear from the above explanation and the results shown in FIGS. 2 to 4, according to the present invention, when T,02 is used as a starting material, the crystal structure of TiO2 is 97% By making the above material rutile, it is possible to obtain piezoelectric ceramics that exhibit piezoelectric properties superior to those of conventional ceramics.

[Brief explanation of the drawing]

Figure 1 shows the crystal structure of TiO7, Figures 2 to 4
The figure is a graph comparing the characteristics of the piezoelectric ceramic according to the present invention and the conventional piezoelectric ceramic.

Claims (2)

[Claims] (1) A piezoelectric ceramic using TiO_2 (titanium oxide) as a part of the starting material, wherein the crystal structure of the TiO_2 is 97% or more of rutile. (2) The piezoelectric ceramic is Pb(Mg_1_/_3
Nb_2_/_3)O_3-PbTiO_3-PbZr
The piezoelectric ceramic according to claim 1, wherein the piezoelectric ceramic is O_3-based.