Scandium tungstate above 2.5 GPa

Synchrotron x-ray powder diffraction was used to study Sc2W3O12 in a diamond anvil cell up to 6.2 GPa in order to better characterize the second high pressure phase observed in earlier in-situ diffraction studies. Two crystalline-to-crystalline phase transitions were observed, in line with the earlier work. Above 2.7 GPa, Sc2W3O12 adopted a monoclinic structure with probable space group P21/n, that is distinct from the monoclinic phase existing between 0.3 GPa and 2.7 GPa. The bulk modulous (K0)(K0) for this second high pressure phase was estimated to be 90(3) GPa using a Birch–Murnaghan equation of state with KpKp fixed at 4. Refining KpKp resulted in K0=72(3)GPa and Kp=12(1)Kp=12(1). The transition at ∼2.7 GPa on compression involved a unit cell volume reduction of almost 18% and was not reversible on decompression to atmospheric pressure at ambient temperature, suggesting that changes in bonding occur at the phase transition. Linear compressibility values for this high pressure monoclinic phase were estimated to be βa=3.6(1)×10−3GPa−1, βb=3.7(2)×10−3GPa−1, βc=2.0(1)×10−3GPa−1 by straight line fits to the lattice constants over the range 0–6.2 GPa.