Scandium tungstate above 2.5 GPa

Abstract

Synchrotron x-ray powder diffraction was used to study Sc 2W 3O 12 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, Sc 2W 3O 12 adopted a monoclinic structure with probable space group P2 1/n, that is distinct from the monoclinic phase existing between 0.3 GPa and 2.7 GPa. The bulk modulous ( K 0 ) for this second high pressure phase was estimated to be 90(3) GPa using a Birch–Murnaghan equation of state with K p fixed at 4. Refining K p resulted in K 0 = 72 ( 3 ) GPa and K p = 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 β a = 3.6 ( 1 ) × 1 0 − 3 GPa − 1 , β b = 3.7 ( 2 ) × 1 0 − 3 GPa − 1 , β c = 2.0 ( 1 ) × 1 0 − 3 GPa − 1 by straight line fits to the lattice constants over the range 0–6.2 GPa.