SEMICONDUCTING INSULATING TRANSITION FOR HIGHLY DONOR-DOPED BARIUM-TITANATE CERAMICS

BaTiO3 ceramics doped with La (0.01-0.84 at.%) were prepared only with the addition of La and stoichiometric TiO2. As a result, even when BaTiO3 was doped with 0.53 at. % La, it could be converted to a semiconductor by sintering at 1540-degrees-C for 2 h in air and cooled slowly in the furnace. Differential thermal analysis data clearly demonstrated that the Curie point in the materials shifted toward lower temperatures with increased content of La substituted at the Ba site up to a critical concentration that varied with the sintering temperature. The obtained results suggest that the semiconducting-insulating transition for highly donor-doped BaTiO3 was closely related to the incorporation of donor into the grains and to the resultant grain size, which were significantly affected by the sinterability of the BaTiO3 starting powders and sintering conditions used.