Preparation and dielectric properties of CaTaO2N and SrNbO2N ceramics

A new approach for the synthesis of perovskite oxynitride ceramics via ammonolysis of thin pellets of their corresponding oxide precursors is reported. Phase-pure CaTaO2N- and SrNbO2N-ceramics with relative densities up to 78% were obtained by ammonolysis of Ca2Ta2O7- and Sr2Nb2O7-pellets with ≈10% porosities at 950 °C (SrNbO2N) and 1100 °C (CaTaO2N). The oxynitride samples were investigated with respect to their optical, thermal and dielectric properties. Temperature- and frequency-dependent impedance measurements revealed that CaTaO2N is an insulator at room temperature with a relative permittivity in the order of 100. In contrast, SrNbO2N exhibits a high relative bulk permittivity of ε′ = 25000 and a comparatively high bulk conductivity of 1.6 × 10−4 S cm−1 at room temperature. At elevated temperatures, the evolving small electrical conductivity of CaTaO2N can be assigned to the formation of thermally activated electron-hole pairs. For SrNbO2N two defect-dominated conduction paths can be distinguished and related to grain boundary and bulk conductivity, respectively.