TRANSITION OF COMPENSATING DEFECT MODE IN NIOBIUM-DOPED BARIUM-TITANATE

The influence of Nb-doping from 1.0 to 8.0 at.% on grain size, ferroelectric phase transition, lattice strain, and electrical properties of BaTiO3 ceramics has been studied. A change in the Nb-doping effect was observed at compositions around 3.5-4.5 at.% Nb. The impedance behavior revealed that specimens of low Nb-doping had an activation energy of 1.85 eV for carrier conduction either in bulk or at grain boundaries, but specimens having a high Nb-doping content showed an energy of 1.30 eV in bulk and 1.85 eV at grain boundaries. The capacitance-voltage relation also disclosed different influences of Nb-doping on the potential barrier height at grain boundaries. The above results are explained by the transition of a compensating defect mode from pure barium vacancies to a combination of titanium vacancies in grain interiors and barium vacancies at grain boundaries as the Nb-doping content in BaTiO3 is increased.