engleski

Lattice dynamics Calculations of the High-pressure Phase Transition in CdTe

The study of pressure induced phase transitions has been rapidly expanding field of research during the past few decades. It was discovered that many semiconductors have a rich phase diagram, as a function of pressure and temperature, with a number of phases, which were not known before. The understanding of the mechanism of high pressure phase transitions at microscopic level is far from complete and more theoretical models are required. We investigated the stability of the metallic rocksalt structure with respect to the high pressure Cmcm structure for II-VI semiconductor CdTe. The lattice dynamics calculations, based on density functional perturbation theory (DFPT), reveal that the rocksalt structure is unstable with respect to transversal acoustic mode at the Brillouin zone boundary. The phase transition is of the second order (zero volume change), associated with cell doubling in the high pressure Cmcm phase with frozen in deformation. The present calculation gives the transition pressure more accurately then classical common tangent method. Since the volume change at the transition is very small or zero, the transition was estimated from the pressure at which the frequency of zone boundary transversal acoustic mode goes to zero. The observed pressure of the phase transition in structural measurements was reproduced more accurately then in previous calculations and the difference between observed and calculated transition pressure is well below 10%.

lattice dynamics ; DFPT ; phase transition ; metals

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