Synthesis and Characterization of Oxynitrides in the ZrO2-Rich Part of the Systems Ca–Zr–O–N and Mg–Zr–O–N☆

Abstract Oxynitrides in the ZrO 2 -rich part of the systems Ca–Zr–O–N and Mg–Zr–O–N have been prepared by nitridation of the corresponding oxides in nitrogen atmosphere at temperatures between 1400 and 2000°C. A thermodynamic model of the nitridation is presented. The crystal structures of the resulting oxynitride phases are derived from the fluorite-type structure of the cubic high temperature phase of ZrO 2 . The structure of the β′ phase in the Mg–Zr–O–N system has been investigated using X-ray powder methods. Its trigonally distorted fluorite-type structure (ordered anion vacancies) can be described by an arrangement of Bevan clusters ( A 7 X 12 units) and A 7 X 14 units. At ∼975°C, a transition into a cubic fluorite-type phase with randomly distributed vacancies has been observed.