High dielectric-permittivity properties of NaCu3Ti3Sb0.5Nb0.5O12 ceramics

A series of NaCu3Ti3Sb0.5Nb0.5O12 ceramics were prepared by the conventional solid-state reaction technique under different sintering temperatures. Their crystalline structures, microstructures, dielectric properties and complex impedance were investigated systematically. All the ceramics show the main phases of perovskite-related crystallographic structure, and their dielectric properties change significantly with sintering temperature. Those ceramics sintered above 1293 K perform high dielectric-permittivity properties with ε′ over 5000. Impedance spectroscopy analysis reveals that NaCu3Ti3Sb0.5Nb0.5O12 ceramics are electrically heterogeneous and composed of semiconducting grains and insulating grain boundaries. Moreover, a small amount of CuO secondary phase and Cu2+/Cu1+, Ti4+/Ti3+, Sb5+/Sb3+ and Nb5+/Nb4+ aliovalences is found to exist in NaCu3Ti3Sb0.5Nb0.5O12 ceramics through XRD and XPS analysis. Internal barrier layer capacitance effect is suggested to be the origin of the high dielectric-permittivity properties in NaCu3Ti3Sb0.5Nb0.5O12 ceramics.