High pressure transition in cadmium selenide

Abstract

The wurtzite--rock salt phase boundary of a single crystal of cadmium selenide was investigated experimentally over the P, T range up to 25kb and 700℃ by observing the electrical resistance behavior is a cubic compact anvil device. In single crystal samples the room temperature transition pressure is found to be 24.7±1.6kb. At the transition the electrical resistance decreases by several orders of magnitude. The transition pressure is lowered with increasing temperature. The wurtzite--rock salt phase boundary has a slope of -0.012kb/deg. The heat of transition at room temperature calculated from the Clapeyron equation is 5.0×10^2cal/mole. The change in entropy is found to be 1.7 e. u. Both the atmospheric wurtzite phase and the high-pressure rock salt phase are semiconductors. From the measurements of electrical resistance as a function of temperature it is found that the energy gap of CdSe of the wurtzite phase is about 1.6eV. For the CdSe of the rock salt phase the energy gap obtained is about 0.6eV.