Dielectric Relaxation of Al-Doped BaTiO3

The Curie point (T-c) of Ba(Ti1-xAlx)O3-delta shifted to lower temperatures as the Al content (x) was increased. In the high-temperature region (>350 degrees C), dielectric constants markedly increased with increasing temperature. At lower frequencies (<1 kHz), dielectric constants steeply decreased with increasing frequency. At >1 kHz, dielectric constants were independent of frequency regardless of Al doping level. Dielectric loss (tan delta) peaks moved to higher frequencies with increasing Al content (x) in the Ba(Ti1-xAlx)O3-delta system (0.0005 <= x <= 0.02) at 250 degrees C. The activation energy was estimated to be 0.42-0.65eV at 150-300 degrees C and 0.90-1.06eV at 350-500 degrees C. The activation energy at higher temperatures could be due to the extra energy required for the dissociation of the defect complex (Al-Ti'-V-O(center dot center dot)) in addition to the dipolar motion of oxygen vacancies. Second phases were detected in the specimen doped with 2.0 mol % Al. As the Al content was increased, the lattice parameters (a and c) of Ba(Ti1-xAlx)O3-delta decreased within the solubility limit (x <= 1.0 mol%). (C) 2009 The Japan Society of Applied Physics