Oxidation-induced strain relaxation and related dielectric-temperature behavior in core/shell grained BaTiO3

Abstract

The effect of oxidation on dielectric-temperature behavior of core/shell grained BaTiO3 was studied in an attempt to reveal the prime governing parameter of dielectric-temperature behavior. BaTiO3 samples doped with 3 mol% Y2O3 or 3 mol% Dy2O3 with the same effective charges were sintered in a reducing atmosphere (Po2 < 10−13) and oxidized at 1050–1250 °C for 10 h in air. In the Y-doped samples, as the oxidation temperature increased, the fraction of the grains with ferroelectric domains in the shell increased from 18 to 54 % and the residual strain decreased. With an increased domain fraction, the dielectric-temperature behavior became poor, and a dielectric peak appeared. On the other hand, all the Dy-doped and air-annealed samples exhibited relatively high fractions of grains with ferroelectric domains in the shell, 32 % at 1050 °C and 63 % at 1250 °C, indicating a considerable reduction of residual strain in all the samples. The temperature stability of the Dy-doped samples was poor, and there was a dielectric peak, irrespective of the oxidation temperature. This difference in dielectric response between the Y-doped and Dy-doped samples reveals that the prime factor governing the dielectric-temperature stability is the residual strain in the core/shell grains rather than the previously suggested factors of defect concentration, dopant concentration in the shell and the occupational sites of rare-earth dopants.