High-pressure experimental study on Rb₂S: antifluorite to Ni₂In-type phase transitions

Acta Cryst. (2011). B67, 109-115 (doi.org/10.1107/S010876811005370X)

The crystal structures of anticotunnite Rb₂S (Pnma) at 0.7 GPa (top) and Rb₂SO₄ at room conditions (Pnam) (bottom), showing the similarities of both Rb₂S arrays. Colour key: Rb-grey, S-yellow, O-tiny-red. [SO₄] tetrahedra are olive coloured.

The crystal structures of two new high-pressure phases of Rb₂S are reported. Antifluorite Rb₂S firstly transforms into an anticotunnite structure below 0.7 GPa and, subsequently, into an Ni₂In-type structure at 2.6 GPa. Interestingly, the structures of these phases are identical to the cationic arrays of the two existing polymorphs of the corresponding sulfate, Rb₂SO₄. Once more, cations do not seem to be 'isolated entities' but they recognize themselves in spite of being surrounded by oxygen atoms.