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

Origin of giant dielectric response in the layered-ordered double-perovskite La2CuSnO6 ceramics was investigated in the present work. Apart from the main layered-ordered double-perovskite La2CuSnO6 phase, minor La2Sn2O7 secondary phase was detected. There were two dielectric relaxations in the curve of temperature dependence of dielectric properties of La2CuSnO6 ceramics. Both of dielectric relaxations were thermal activated process. The low temperature relaxation should be attributed to the mixed-valent structure (Cu2+/Cu3+) since the activation energy was similar to that of La2CuTiO6 ceramics. While the high temperature relaxation was closely related to the thermal activated hopping process of electrical conduction. After annealing the sample in N2 and O2 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.