Electrical and structural characteristics of lanthanum-doped barium titanate ceramics

Single phase La-doped BaTiO3 with the formula Ba1-xLaxTi1-x/4O3: 0 less than or equal to x less than or equal to 0.20 was prepared by solid state reaction of oxide mixtures at 1350 degrees C, 3 days, in O-2. The tetragonal distortion in undoped BaTiO3 decreased with x and samples were cubic for x greater than or equal to 0.05. Both the tetragonal/cubic and orthorhombic/tetragonal transition temperatures decreased with x, but at different rates, and appeared to coalesce at x similar to 0.08. The value of the permittivity maximum at the tetragonal/cubic phase transition in ceramic samples increased from similar to 10 000 for x = 0 at 130 degrees C to similar to 25 000 for x = 0.06 at similar to-9 degrees C. At larger x, the permittivity maximum broadened, showed "relaxor"-type frequency dependent permittivity characteristics and continued to move to lower temperatures. Samples fired in O-2 were insulating and showed no signs of donor doping whereas air-fired samples were semiconducting, attributable to oxygen loss. (C) 1999 American Institute of Physics. [S0021-8979(99)04423-0].