Colossal dielectric properties in (Ta0.5Al0.5)xTi1-xO2 ceramics

In this study, (Ta0.5Al0.5)(x)Ti1-xO2 (x = 0-0.125) and Ta-doped ceramics were fabricated by conventional solid-state method. The phases and microstructures indicate that all ceramics show pure tetragonal rutile TiO2 with different grain size. Notably, by co-doping TiO2 with 0.08 (Ta+Al) ions, a colossal permittivity (epsilon(r), similar to 6.24 x 10(4)) and low dielectric loss (tan delta, similar to 0.05) at room temperature were achieved. While the ceramic doped with same amount of Ta displays the giant er but higher tan delta value, and the pure TiO2 exhibits a low permittivity value. The co-doped ceramics exhibit more excellent dielectric properties than that of pure TiO2 and Ta-doped TiO2 ceramics when they are subjected to temperature (20-200 degrees C) and frequency (10(2)-10(6) Hz) variations. Moreover, the detailed dielectric and impedance spectra analyses for all samples indicate that the colossal permittivity could be explained by the internal barrier layer capacitance (IBLC) model. According to the model, the microstructures of ceramics are consisting of semiconducting grains and insulating grain boundaries, leading to formation of numerous micro-capacitors. (c) 2018 Elsevier B.V. All rights reserved.