Pressure-induced structural transitions in PbI(2): A high pressure Raman and optical absorption study.

The effect of pressure on the 2H and 4H polytype of PbI(2) has been investigated by Raman and optical absorption spectroscopy, using the diamond anvil cell. The 2H-polytype undergoes pressure- induced phase transitions at 5 kbar and near 30 kbar. The 4H-polytype exhibits phase transitions near 8 kbar and above 30 kbar. The Raman modes abruptly change at these pressures. The optical absorption edge shifts read at the rate of 15 +- 1 meV/kbar in the 2H-PbI(2) and at the rate of 7 meV/kbar in phase II. The latter phase is most likely to possess a 3d- structure and not a layer type. The possible structures for the high pressure phases are discussed.