Significantly Improved Colossal Dielectric Properties and Maxwell-Wagner Relaxation of TiO2-Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

Abstract

In this work, the colossal dielectric properties and Maxwell-Wagner relaxation of TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 (x = 0-0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na1/2Y1/2Cu3Ti4O12 is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (R-gb). The colossal permittivities of epsilon' similar to 0.7-1.4 x 10(4) with slightly dependent on frequency in the frequency range of 10(2)-10(6) Hz are obtained in the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics, while the dielectric loss tangent is reduced to tan delta similar to 0.016-0.020 at 1 kHz due to the increased R-gb. The semiconducting grain resistance (R-g) of the Na1/2Y1/2Cu3Ti4+xO12 ceramics increases with increasing x, corresponding to the decrease in Cu+/Cu2+ ratio. The nonlinear electrical properties of the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO2-rich Na1/2Y1/2Cu3Ti4+xO12 ceramics are explained by the Maxwell-Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.