Novel trigonal ZrWMoO8 structure and its transformations

We found two new trigonal polymorphs of cubic ZrWMoO8 with a negative thermal expansion property and successfully solved and refined their structures using X-ray and/or neutron powder diffraction data. The space group of low temperature trigonal ZrWMoO8 is R (3) over bar with cell parameters a = 9.8722(1) angstrom and c = 17.5455(2) angstrom, a polytype of the layered trigonal ZrMo2O8 structure. The space group of high temperature trigonal ZrWMoO8 is P (3) over bar ml, and the cell parameters are a = 5.8404(1) angstrom and c = 6.0671(2) angstrom. The thermal expansion and phase transition properties of the trigonal and cubic phases were also studied, and consistent structure-property correlation in this system was found. The phase transitions between two forms of trigonal phases and between high temperature trigonal and cubic phases are reversible first order phase transitions. Utilizing the established polymorphous phase transitions, tailorable synthesis of solid oxide materials with controllable thermal expansion property is anticipated in this family.