Shift of the Curie point of barium titanate ceramics with sintering temperature

Definite increases in the Curie point (T-C of undoped and lanthanum- (La-) doped (<0.5 at.%) barium titanate (BaTiO3) ceramics sintered at elevated temperatures in the range of 1300 degrees-1450 degrees C were observed. Both undoped and 0.3 at.% La-doped BaTiO3 (chosen as a typical doping concentration to yield semiconducting materials) ceramics showed almost the same T-C behavior; their T-C values increased by similar to 3.5 degrees C as the sintering temperature was increased from 1300 degrees to 1450 degrees C. Semiconducting 0.3 at.% La-doped materials increased in room-temperature bulk resistivity and T-C with increased sintering temperature. The bulk resistivity of the La-doped materials, which was obtained from complex impedance analysis, increased from similar to 2 Omega.cm for the material sintered at 1350 degrees C to similar to 6 Omega.cm at 1450 degrees C. The phenomenon of bulk resistivity increase with sintering temperature was observed in the materials with a doping concentration of greater than or equal to 0.2 at.% La, but was not observed in those doped with <0.2 at.% La. The mechanisms of T-C and the bulk resistivity increase observed in the present materials with increased sintering temperature are discussed based on various models found in the literature, particularly in terms of the defect chemistry in semiconducting BaTiO3 ceramics and the influence of liquid phases present during sintering.