Colossal permittivity and dielectric relaxations in (La0.5Nb0.5)xTi1-xO2 ceramics

A series of La+Nb co-doped TiO2 (La0.5Nb0.5)(x)Ti1-xO2 (0.25% <= x <= 5%) ceramics were prepared using a solid-state reaction method. Colossal permittivity (CP) (epsilon' > 10(4)) and low dielectric loss (tan delta < 0.05) were obtained when the ceramics were sintered at 1673 K in an N-2 atmosphere and annealed at 1073-1173 K in air. A pure rutile phase was achieved when x = 0.25% and secondary phase La2TiO5 was detected when x >= 0.5%. The optimum dielectric performance of epsilon' > 10(4) and tand < 0.05 within 1 Hz-2 MHz and 25-350 K was obtained for x = 0.5%. Three types of dielectric relaxations were observed through the dielectric-temperature spectrum: electron-pinned defect-dipoles (EPDD) polarization, electron hopping, and Maxwelle Wagner polarization. The CP (> 25 K at 1 kHz) was primarily related to EPDD polarization. The high activation energy of the grain boundary (E-gb = 1.98 eV) is one of the reasons for the low tan delta in this study. (C) 2018 Elsevier B.V. All rights reserved.