Phase transformation in pure selenium

Abstract

Pure selenium transforms upon cooling from the hexagonal close packed to the diamond cubic phase. The lattice parameters of the hexagonal close packed phase are a=4. 3615A and c=4. 9633A. The lattice parameter of the diamond cubic phase is a=5. 0672A. The enthalpy of phase transformation on cooling associated with this phase transformation is 77 cal/mole. There is an indication that the hexagonal close packed phase can be stabilized upon annealing at elevated temperatures. The habit plane of transformation is close to the O11 plane of the cubic phase.