Significantly improved dielectric properties of TiO2 ceramics through acceptor-doping and Ar/H2 annealing

The acceptor-doped rutile TiO2 ceramics, x mol% M2O3-(1-x) mol% TiO2 (M = Al3+, Ga3+, and In3+), were prepared by solid state reaction method. The influence of Ar/H-2 annealing on the structural and dielectric properties of the ceramics were systematically investigated. Our results reveal that the dielectric properties of the ceramics can be significantly improved by the Ar/H-2 annealing. Ga3+ is found to be the most suitable dopant with the best doping level of 5 mol%. Excellent dielectric properties of colossal and flat dielectric permittivity (-1.2 x 105 (@1 kHz and 25 degrees C), low dielectric loss (-0.1), and good frequency stability were achieved over the temperature range of -70-150 degrees C in the Ar/H-2-annealed 5 mol% Ga2O3-95 mol% TiO2 ceramic. This approach of acceptor-doping and Ar/H-2 annealing leads to two thermally activated relaxations in the sample. The low temperature relaxation is argued to be a Maxwell-Wagner relaxation caused by frozen electrons, while the high-temperature relaxation is a glass-transition-like relaxation associated with the freezing process of the electrons. This work highlights that engineering low-temperature Maxwell-Wagner relaxation paves a new way other than the frequently used acceptor-donor dual doping to design superior dielectric properties in the TiO2 system.