Vibrational spectroscopy at high pressures. Part 50. A Raman scattering study of MSCN (M = K,Rb, Cs,NH4) at high pressures

The phase behaviour of the title compounds was studied at high pressures using Raman spectroscopy. The isostructural materials KSCN and RbSCN show two phase changes (12.5 and 45.5 kbar; 10.5 and 37.5 kbar, respectively) which appear to be second order in type. Structures and transition mechanisms are proposed for each phase. CsSCN has a different orthorhombic structure and shows only one phase change in the range studied, at 23.5 ± 1.5 kbar, which also seems to be second order. The known phase transition in NH₄SCN at 2 kbar has been confirmed, and a new one found at 10 kbar. A monoclinic cell is proposed for the new phase.