Dielectric Relaxation of Al-Doped BaTiO3

The Curie point (Tc) of Ba(Ti1-xAlx)O3-δ shifted to lower temperatures as the Al content (x) was increased. In the high-temperature region (>350 °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 δ) peaks moved to higher frequencies with increasing Al content (x) in the Ba(Ti1-xAlx)O3-δ system (0.0005 ≤x ≤0.02) at 250 °C. The activation energy was estimated to be 0.42–0.65 eV at 150–300 °C and 0.90–1.06 eV at 350–500 °C. The activation energy at higher temperatures could be due to the extra energy required for the dissociation of the defect complex (AlTi'–VO••) 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-δ decreased within the solubility limit (x≤1.0 mol %).