Vacancy Ordering in the ZrO2Rich Part of the Systems Ca–Zr–O–N, Mg–Zr–O–N, and Y–Zr–O–N

Abstract

CaO, MgO, and Y2O3doped zirconia samples were nitrided at temperatures between 1400 and 2000°C in a graphite heated resistance furnace in a nitrogen atmosphere. Depending on the content of nitrogen and aliovalent oxides, different types of ordered (β type) and disordered (tetragonal, cubic) phases were observed. Nitridation of pure ZrO2results in the formation of the β″ phase. With increasing content of the aliovalent oxides, other β type phases (β′, β) are detectable. The stability fields of the individual β type phases are determined by the ratio ofVN/Vtotaland by the kind of dopant oxide. In the system Y–Zr–O–N, the transition tetragonal–cubic was observed for higher Y2O3concentrations. In this case, the “effective” total concentration of vacancies is the dominant factor which controls the transition.