High-permittivity double rare-earth-doped barium titanate ceramics with diffuse phase transition

On the basis of Ti-vacancy defect compensation mode, high-permittivity La- and Ce-doped barium titanate ceramics (BLTC) with perovskite structure, i.e., (Ba1-xLax)(Ti1-x/4-yCey)O-3, where x=0.01-0.05 and y=0.05, were prepared by conventional ceramic processing techniques. Dielectric characteristics, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and hysteresis loops were measured. Defect chemistry and diffuse phase transition (DPT) in BLTC are discussed. Co-doping with the relatively smaller La3+ ions at Ba sites and the relatively larger Ce4+ ions at Ti sites in the BaTiO3 host lattice resulted in a fine-grained microstructure (0.8-1.1 mu m), marked raising, and broadening of the Curie peak characteristic of DPT. The Curie temperature (T-C) at 800 Hz decreased rapidly at a dramatic rate of -30 degrees C/at.% La when y=0.05. By means of co-doping with La and Ce, this is the first time that high k "Y5V" ceramics (BLTC: 0.03 <= x <= 0.04, y=0.05) with epsilon'(RT)> 10 000 over a frequency range of 1-100 kHz have been achieved in rare-earth-doped BaTiO3 ceramics.