PRETRANSITIONAL BEHAVIOR IN ZINCBLENDE HGTE UNDER HIGH-PRESSURE AND TEMPERATURE

The equation of state of mercury telluride, HgTe, has been measured un der pressure in its zincblende and cinnabar phases up to 800 K, by X-r ay diffraction under synchrotron radiation in a large volume Paris-Edi nburgh cell. Tile thermal expansion coefficient decreases to zero arou nd 1.1 GPa and then becomes negative up to the first-order phase trans ition to the high-pressure cinnabar phase, around 1.4 GPa. This behavi or is related to the increase with temperature of the nonlinearity in the pressure dependence of the bulk modulus. It indicates an overall s oftening of the phonon branches of zincblende HgTe prior to the phase transition which characterizes a second-order pretransitional behavior .