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) 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 K₀ = 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.