GB881476A - Improvements in or relating to ceramic dielectric materials - Google Patents

Abstract

A ferroelectric ceramic material consisting of lead barium metaniobate is prepared from a mixture of powdered monoxide, carbonate or oxalate of lead; oxide, carbonate or oxalate of barium; and inobium pentoxide to give a product of Pb(1-x) Ba(x) Nb2 O6 where x lies between 0,25 and 0,6. The mixture is prepared at a temperature between 850 DEG C. and 1150 DEG C. in a non-reducing atmosphere for 2 or 3 hours, pulverized, compacted, and heated to between 1270 DEG C. and 1320 DEG C. in a non-reducing atmosphere for up to 30 minutes. In one method the lead metaniobate and barium metaniobate are first separately preformed by heating mixtures of the constituent oxides to 850 DEG C. and 1000 DEG C. respectively. In one example Pb0,7 Ba0,3 Nb2 O6 is prepared by heating a mixture of PbO, Nb2 O5 and Ba CO3 in appropriate proportions, with camphor in diethyl ether as a binder, in air. The material is then crushed, pressed into discs, heated up to 1280 DEG C., and cooled slowly. The addition of the barium to lead metaniobate has the effect of reducing the Currie temperature, facilitates formation of silver electrodes, and enables polarization to be carried out at a higher temperature by applying a 20 kv./cm. field to silvered discs in silicone oil at 250 DEG C. The material may be used in accelerometers for use at elevated temperatures, and generation of ultrasonic vibrations. A table is provided giving electrical characteristics of various materials according to the invention, including the electromechanical coupling coefficient in the radial mode and the variation of permittivity with temperature. Specifications 787,352, 812,343 and 828,066 are referred to.