Pretransitional behavior in zincblende HgTe under high pressure and temperature

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