JPH012383A - Manufacturing method of piezoelectric ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of manufacturing piezoelectric ceramics used for ceramic filters and the like, and particularly relates to a method of heat treatment after polarization treatment.

[Prior art and its problems]

BACKGROUND ART Various devices such as ceramic filters, resonators, actuators, etc., which utilize the piezoelectric properties of polarized ceramic substrates having ferroelectric properties, are used.

In this method, polarization is performed by applying a high DC voltage between electrodes formed on both sides of the substrate. After polarization, 80-15
Leave it at a temperature of about 0'. This treatment can stabilize the characteristics and is effective against changes over time.

However, no effect has been observed on deterioration of electrical characteristics due to thermal shock cycles (-45° to -80'C), resulting in problems such as large changes in resonance frequency, for example.

〔the purpose〕

An object of the present invention is to solve the above-mentioned problems and obtain a piezoelectric ceramic whose characteristics are less degraded by thermal shock cycles.

This is intended to improve the reliability of elements used in devices and the like that are subject to severe temperature changes.

[Means for solving problems]

The present invention achieves the above object by performing heat treatment for a short time at a temperature close to the Curie point.

That is, in a method for manufacturing a piezoelectric ceramic in which a polarized piezoelectric ceramic is heat-treated, the method is characterized in that the polarized piezoelectric ceramic is heat-treated at a temperature near the Curie point for a short time.

Although this causes depolarization and the coupling coefficient to decrease slightly, a piezoelectric ceramic with extremely stable characteristics can be obtained.

C Example] Examples of the present invention will be described below.

An example of a piezoelectric ceramic made of Pb-Ti-Zr oxide partially substituted with La, Ni, and sintered, and sintered with the addition of 0.5χ MnO□ will be described.

The above piezoelectric ceramic was heated at 80'C, 4KV/mm (7
) Polarization treatment was performed by applying a DC electric field for 30 seconds. Thereafter, heat treatment was performed after aging for 30 minutes.

The heat treatment was carried out for a short time of 5 to 10 seconds in air at a temperature of 290"C.The Curie point of this piezoelectric ceramic is 300"C, and the heat treatment temperature was very close to the Curie point. It is.

As shown in FIG. 1, when a piezoelectric material is exposed to a temperature near the Curie point, it is depolarized and its electromechanical coupling coefficient decreases. The above heat treatment also lowered the electromechanical coupling coefficient, which decreased by 20 to 30x, making the initial value smaller.

The piezoelectric ceramic heat-treated in this way was heated to -45°C and +80°C.
Changes in properties in response to thermal shock cycles at °C were measured. The measurement was performed by examining the change in resonance frequency of the resonator.

The following table shows the results of measuring how much the resonance frequency changes from the initial value of the element at 0, 5, 10, 25, and 100 cycles.

As mentioned above, the value of the change in frequency is almost constant for those depolarized by heat treatment, and the rate of change is very small. On the other hand, for those that are only polarized, there is a difference in the change value, which is 10% or more. Although this comparative example had saturated polarization, the value of change was larger in the element with unsaturated polarization.

FIG. 2 is a graph showing the above results, and curve 21 shows the characteristics of the material heat-treated according to the present invention. Curves 22 and 23 show the characteristics of elements that have been subjected to saturated and unsaturated polarization treatments, respectively, and which have not been heat treated.

In this way, the piezoelectric ceramic subjected to the heat treatment according to the present invention,
It shows stable characteristics against thermal shock cycles.

〔effect〕

According to the present invention, a piezoelectric ceramic exhibiting stable characteristics against thermal shock cycles can be obtained.

Thereby, elements suitable for piezoelectric devices such as filters, vibrators, actuators, etc. used in environments with severe temperature changes can be easily obtained.

Furthermore, the elements heat-treated according to the present invention were found to be effective against changes over time.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the relationship between temperature and depolarization, and FIG. 2 is an explanatory diagram showing the state of frequency change.

Claims (1)

[Claims] A method for producing a piezoelectric ceramic, the method comprising heat treating the polarized piezoelectric ceramic at a temperature near the Curie point for a short period of time.