Structures and phase transitions of trigonal ZrMo2O8 and HfMo2O8

Abstract

This paper describes the structures, thermal-expansion properties and phase transitions of the trigonal forms of ZrMo2O8 and HfMo2O8. Both phases adopt a P\overline 3 m structure at room temperature and show positive thermal expansion. Both phases also undergo a displacive phase transition at high temperature (ZrMo2O8 at 487 K and HfMo2O8 at 463 K) to a higher-symmetry structure that has lower thermal expansion. The structure of the high-temperature α′-AMo2O8 form (A = Zr and Hf) has been refined from powder diffraction data in space group P\overline 3m1.