Effects of reoxidation process on positive temperature coefficient of resistance properties of Sm-doped Ba0.85Ca0.15TiO3

Abstract

The positive temperature coefficient resistance (PTCR) effects of Sm-doped BaTiO3 have been studied in terms of annealing temperature, annealing time, and additive content. (Ba0.85-xCa0.15Smx)(0.997)TiO3 samples were prepared by a liquid mix method developed by Pechini. The specimen was sintered in a reducing atmosphere (P-O2 < 10(-9) atm) at 1350 degrees C, followed by annealing processes at 900-1200 degrees C and P-O2 = 1 atm. Room-temperature resistances were dependent on the donor concentration. At 0.5 mol % Sm, the electrical compensation mode of the donor impurity switched from electrons to cation vacancies. The specimens doped with Sm <= 0.5 mol % showed low resistivities and large grains, whereas high resistivities and small grains were observed with Sm > 0.5 mol %. The oxidation degree of grain boundaries increased with annealing temperature and time, leading to increased room-temperature resistances. This implies that the acceptor-state density at grain boundaries increases the potential barrier height.