Phase behaviour, thermal expansion and compressibility of SnMo2O8

Abstract

The phase behaviour and thermoelastic properties of SnMo2O8, derived from variable temperature and pressure synchrotron powder diffraction data, are reported. SnMo2O8 is a member of the AM2O8 family of negative thermal expansion (NTE) materials, but unexpectedly, has positive thermal expansion. Over the P-T space explored (298–513K, ambient to 310MPa) four different forms of SnMo2O8 are observed: α, β, γ and γ′. The γ to β transition is temperature-, pressure-, and time-dependent. SnMo2O8 is a much softer material (α and γ form have BT = 29 and 26GPa at 298K) than other members of the AM2O8 family. Counter-intuitively, its high temperature β phase becomes stiffer with increasing temperature (BT ∼36GPa at 490K). The pressure dependence of the thermal expansion for each phase is reported.