Temperature- and composition-dependence of the ferroelastic phase transition in (CuxZn1-x)WO4

Abstract

The lattice parameters of(CuxZn1-x)WO4 have been determined as a function of composition and temperature by high-temperature Guinier X-ray diffraction. The ferroelastic phase transition from PT to P 2 c (with increasing X and T) appears to be continuous (second-order) as a function of temperature for the sample (Zn0.75Cu0.25)WO4. As the Cu-content increases, however, the high-temperature transition behaviour becomes increasingly first-order in character with a tricritical transition occurring at about (Zn0.32Cu0.68)WO4 and about 650°C. The triclinic-monoclinic phase boundary has been mapped out in temperature-composition space. The critical transition temperature varies non-linearly as a function of composition. A modified Landau potential successfully models the transition as a function of both temperature and composition. © 1993.