High-pressure phase transition to the Gd(2)S(3) structure in Sc(2)O(3): a new trend in dense structures in sesquioxides.

In situ X-ray diffraction experiments using a laser-heated diamond anvil cell revealed a novel dense phase with the Gd(2)S(3) structure stabilizing in Sc(2)O(3) at pressures over 19 GPa. Although no phase transformation was induced during room-temperature compression up to 31 GPa, the C rare earth sesquioxide structure transformed into the B rare earth sesquioxide structure at 10 GPa after laser annealing and subsequently into the Gd(2)S(3) structure at 19 GPa. Neither the A rare earth sesquioxide structure nor the U(2)S(3) structure was found in Sc(2)O(3). Static density functional lattice energy calculations demonstrated that the C structure prefers Gd(2)S(3) over U(2)S(3) as the post phase. Sc(2)O(3) is the second sesquioxide, after In(2)O(3), to crystallize into a Gd(2)S(3) structure at high pressures and high temperatures.