DIELECTRIC AND PIEZOELECTRIC CERAMICS FOR HIGH TEMPERATURE APPLICATIONS

Perovskite materials have been widely embedded in many consumer and industrial electronics, both for capacitor applications in the case of dielectric materials, and for actuator, transducer and sensor applications in the case of piezoelectric materials. Functional devices used in high temperature environments, such as deep oil well instrumentation, geothermal exploration, and devices for aerospace applications require the persistence of materials' properties at high temperatures. In this paper, high potential capacitor and piezoelectric ceramics for high temperature applications are presented. High dielectric constant (K) materials based on 0.8BaTiO(3) - 0.2Bi(Zn1/2Ti1/2)O-3 solid solutions have been shown to have superior properties for high temperature capacitor applications. Studies of the temperature dependence of the dielectric properties have shown that the composition with Ba vacancies exhibits a high relative permittivity (epsilon(r) > 1150) and a low dielectric loss (tan delta < 0.05) that persist up to a temperature of 460 degrees C. This composition also shows a high resistivity in excess of 7.0 x 10(10) Omega-cm which remains unchanged up to a temperature of 270 degrees C as well as a large RC time constant (RC > 20 s). In the case of high temperature piezoelectric ceramics, solid solutions of PbTiO3 - BiScO3 - Bi(M1/2Ti1/2)O-3 ternary systems were studied, where M is Mg and Zn. The ratio of BiScO3 to Bi(M1/2T1/2)O-3 was kept at 1:1, while the concentration of PbTiO3 was varied. X-ray diffraction patterns showed that tetragonal symmetry was observed in compositions which contain a high concentration of PbTiO3 (> 60 mol%). Evidence of a morphotropic phase boundary (MPB) was observed with compositions containing PbTiO3 in the range of 52 56 mol%. At 70 mol% PbTiO3 compositions, high Curie temperatures (T-C) of 490 degrees C and 533 degrees C were observed for compositions containing Mg and Zn, respectively.