Influence of Sb-doping on dielectric properties of NaCu3Ti3TaO12 ceramics and relevant mechanism(s)

A series of NaCu3Ti3Ta1−xSbxO12 ceramics were prepared by the conventional solid-state reaction technique, and their dielectric properties, crystalline structures, microstructures 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 the increasing Sb-doping. All these ceramics exhibit giant dielectric-permittivity properties, and impedance spectroscopy analysis reveals that NaCu3Ti3Ta1−xSbxO12 ceramics are electrically heterogeneous and composed of insulating grain boundaries and semiconducting grains. Moreover, CuO secondary phase and Cu2+/Cu1+, Ti4+/Ti3+, Sb5+/Sb3+ and Ta5+/Ta3+ aliovalences are found to exist in NaCu3Ti3Ta1−xSbxO12 ceramics through XRD, EDS and XPS analysis. Therefore, CuO segregation and aliovalences of metal ions were suggested to contribute greatly to the internal barrier layer capacitance effect formation in NaCu3Ti3Ta1−xSbxO12 ceramics. Furthermore, Sb-doping could decrease the tanδ of NaCu3Ti3Ta1−xSbxO12 ceramics at low frequencies, and the reason was discussed.