A study was made of the effect of doping, with 1 to 8at%Nb, upon the properties of ceramic samples. A change in the Nb-doping effect was observed at about 3.5 to 4.5at%Nb. The impedance behavior revealed that specimens with a low Nb dopant content exhibited an activation energy of 1.85eV for carrier conduction in the bulk, or at grain boundaries. Specimens which had a high dopant content exhibited an energy of 1.30eV in the bulk, and of 1.85eV at grain boundaries. The capacitance-voltage relationship also revealed various effects of Nb doping upon the potential barrier height at grain boundaries. The results were explained in terms of a transition in compensating defect mode from pure Ba vacancies, to a combination of Ti vacancies in grain interiors and Ba vacancies at grain boundaries, as the Nb content was increased.

T.B.Wu, J.N.Lin: Journal of the American Ceramic Society, 1994, 77[3], 759-64