The induced phase transformation and oxygen vacancy relaxation in La-modified bismuth titanate ceramics

Abstract

Nanopowders of Bi2Ti2O7 with various La modifications were fabricated by chemical coprecipitation. As sintered at high temperature, the phase structure in powders translates into (La0.22Bi0.78)4Ti3O12 and (La0.26Bi0.74)2Ti4O11 with increasing La concentration, respectively. Dielectric and nonlinear resistivity investigations in bulk ceramics show that oxygen vacancy relaxation or defect dipole polarization contributes considerably to the dielectric permittivity, while the mechanism is shut off under a threshold field dependent on phase transition as well as temperature. Furthermore, the quantitative analysis of x-ray photoelectron spectroscopy indicates the deviation of oxygen element composition at surfaces of (La0.22Bi0.78)4Ti3O12 ceramic grains from the standard ratio.