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

Nanopowders of Bi2Ti2O7 with various La modifications were fabricated by ch emical coprecipitation. As sintered at high temperature, the phase structur e in powders translates into (La0.22Bi0.78)(4)Ti3O12 and (La0.26Bi0.74)(2)T i4O11 with increasing La concentration, respectively. Dielectric and nonlin ear resistivity investigations in bulk ceramics show that oxygen vacancy re laxation or defect dipole polarization contributes considerably to the diel ectric permittivity, while the mechanism is shut off under a threshold fiel d dependent on phase transition as well as temperature. Furthermore, the qu antitative analysis of x-ray photoelectron spectroscopy indicates the devia tion of oxygen element composition at surfaces of (La0.22Bi0.78)(4)Ti3O12 c eramic grains from the standard ratio. (C) 1999 American Institute of Physi cs. [S0003-6951(99)03001-6].