In situ high-pressure synchrotron x-ray diffraction study of Sc2W3O12 at up to 10 GPa -: art. no. 214106

Sc2W3O12 is known to display both negative thermal expansion and significant Sc3+ conductivity. Monochromatic synchrotron x-ray powder diffraction was used to study Sc-2(WO4)(3) at pressures up to 10 GPa in diamond anvil cells. Nitrogen and isopropanol were both used as pressure transmitting media. A phase transition from orthorhombic (Pnca) to monoclinic (P2(1)/a) symmetry was observed at similar to 0.3 GPa with a volume reduction of similar to 1.7%. A second crystalline to crystalline phase transition was seen at similar to 2.8 GPa. The latter was not reversible on decompression. The orthorhombic phase displays highly anisotropic compressibility, but that of the monoclinic phase is almost isotropic [orthorhombic in isopropanol beta(a)=6.32(16) x 10(-3) GPa(-1), beta(b) = 1.76(21) x 10(-2) GPa(-1), beta(c) = 6.84(32) x 10(-3) GPa(-1); monoclinic in isopropanol beta(a) = 1.85(3) x 10(-2) GPa(-1), beta(b) = 1.78(3) x 10(-2) GPa(-1), beta(c) = 1.69(9) x 10(-2) GPa(-1)]. Sc-2(WO4)(3) is very soft even when compared to most other NTE phases. Fitting a Birch-Murnaghan equation of state to data from the experiment in isopropanol gave a bulk modulus (K-0) of 31(3) for the orthorhombic and 14(1) GPa for the monoclinic phase. This reduction in bulk modulus at the phase transition and the reduction in volume per formula unit is almost entirely associated with changes in the orthorhombic a and c directions. The variation of b(ortho) and its monoclinic equivalent lattice constant is essentially continuous through the transition. The pressure of the orthorhombic to monoclinic phase transition in A(2)M(3)O(12) compounds does not have a strong dependence on the identity of the A(3+) cation. Amorphization did not occur in the pressure range studied.