Structural behaviour of alkaline sulfides under compression: High-pressure experimental study on Cs2S

The high-pressure behaviour of cesium sulphide Cs2S has been studied up to 19 GPa at room temperature using angle-dispersive x-ray powder diffraction in a diamond-anvil cell. X-ray results show that the initial anticotunnite-type structure (S.G. Pnma) seems to undertake a continuous transformation to a distorted Ni2In-type structure (also with S.G. Pnma), starting below 1 GPa and being almost completed at 5 GPa. The profile of the x-ray diffraction patterns did not change noticeably from this pressure to 17 GPa. The observed structural changes in Cs2S are discussed in relation to the high-pressure behaviour of the rest of alkaline sulfides and their systematic trends are pointed out. Finally, we discuss the analogies between the structures of alkaline-metal chalcogenides and those of the cationic arrays of their corresponding oxides (sulfates, selenates, and tellurates) comparing the insertion of oxygen and the application of pressure.