Giant dielectric response and mixed-valent structure in the layered-ordered double-perovskite ceramics

Abstract

Origin of giant dielectric response in the layered-ordered double-perovskite La 2CuSnO 6 ceramics was investigated in the present work. Apart from the main layered-ordered double-perovskite La 2CuSnO 6 phase, minor La 2Sn 2O 7 secondary phase was detected. There were two dielectric relaxations in the curve of temperature dependence of dielectric properties of La 2CuSnO 6 ceramics. Both of dielectric relaxations were thermal activated process. The low temperature relaxation should be attributed to the mixed-valent structure (Cu 2+/Cu 3+) since the activation energy was similar to that of La 2CuTiO 6 ceramics. While the high temperature relaxation was closely related to the thermal activated hopping process of electrical conduction. After annealing the sample in N 2 and O 2 atmosphere, the trend of dielectric behaviors and ac conductivities were the same at high temperature. This result confirmed that the high temperature relaxation was closely related to the electrical conduction.