Negative Thermal Expansion in Sc2(WO4)3

Sc2(WO4)3has been found to show the highly unusual property of negative thermal expansion over a temperature range of 10 to 1073 K. Powder neutron diffraction data from 10 to 450 K shows an essentially linear decrease in cell volume as a function of temperature. The intrinsic linear coefficient of thermal expansion from this data is −2.2×10−6K−1. The linear coefficient of thermal expansion measured on a ceramic bar of Sc2(WO4)3can be as negative as −11×10−6K−1due to microstructure changes as a function of temperature. Rietveld refinement as a function of temperature suggests that the intrinsic negative thermal expansion can be related to transverse vibrations of bridging oxygen atoms in the structure. The anharmonic nature of these vibrations leads to a coupled tilting of the quasi-rigid framework polyhedra. This tilting in turn causes the structure to become more dense with increasing temperature.