HIGH-PRESSURE PHASE-TRANSITION STUDIES OF CSSNCL3

The phase transitions of CsSnCl3 have been investigated by Raman scatt ering and optical observations under high pressure up to 60 kbar in a diamond anvil cell. Two new high pressure phases have been discovered. The first phase transition II/III is first order and occurs at 3.3 kb ar. It is marked by the softening of the nu1 mode of the SnCl3- ion an d dramatic spectral changes for all the Raman bands. The second transi tion III/IV is also first order and occurs at 25.3 kbar. This phase tr ansition is manifested by the disappearance of all the Raman peaks in phase IV. In this phase, the molecules are more closely packed than in the monoclinic phase II. The nu1 mode which is at 296 cm-1 for the fr ee SnCl3- ion appears as a strong Raman peak at 167 cm-1 for CsSnCl3 i n phase II.