Structural phase transition and elastic properties of mercury chalcogenides

Pressure induced structural transition and elastic properties of ZnS-type (B3) to NaCl-type (B1) structure in mercury chalcogenides (HgX; X = S, Se and Te) are presented. An effective interionic interaction potential (EIOP) with long-range Coulomb, as well charge transfer interactions, Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbor ions and van der Waals interactions are considered. Emphasis is on the evaluation of the pressure dependent Poisson's ratio ν, the ratio RBT/G of B (bulk modulus) over G (shear modulus), anisotropy parameter, Shear and Young's modulus, Lame constant, Kleinman parameter, elastic wave velocity and thermodynamical property as Debye temperature. The Poisson's ratio behavior infers that Mercury chalcogenides are brittle in nature. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of elastic and thermodynamical properties explicitly the ductile (brittle) nature of HgX and still awaits experimental confirmations.

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► Vast volume discontinuity in phase diagram infers transition from ZnS to NaCl structure.
► The shear elastic constant C44 is nonzero confirms the mechanical stability.
► Pressure dependence of θD infers the softening of lattice with increasing pressure.
► Estimated bulk, shear and tetragonal moduli satisfied elastic stability criteria.
► In both B3 and B1 phases, C11 and C12 increase linearly with pressure.