Abstract
Pressure- and temperature-dependent mechanical, elastic, and thermodynamical properties of rock salt to CsCl structures in semiconducting SrX (X = O, S, Se, and Te) chalcogenides are presented based on model interatomic interaction potential with emphasis on charge transfer interactions, covalency effect, and zero point energy effects apart from long-range Coulomb, short-range overlap repulsion extended and van der Waals interactions. The developed potential with non-central forces validates the Cauchy discrepancy among elastic constants. The volume collapse (V P/V 0) in terms of compressions in SrX at higher pressure indicates the mechanical stiffening of lattice. The expansion of SrX lattice is inferred from steep increase in V T/V 0 and is attributed to thermal softening of SrX lattice. We also present the results for the temperature-dependent behaviors of hardness, heat capacity, and thermal expansion coefficient. From the Pugh’s ratio (ϕ = B T /G H), the Poisson’s ratio (ν) and the Cauchy’s pressure (C 12–C 44), we classify SrO as ductile but SrS, SrSe, and SrTe are brittle material. To our knowledge these are the first quantitative theoretical prediction of the pressure and temperature dependence of mechanical stiffening, thermally softening, and brittle nature of SrX (X = O, S, Se, and Te) and still await experimental confirmations.
Highlights
Strontium chalcogenides SrX (X = O, S, Se, and Te) witnesses a pressure-induced phase transition from the six folds coordinated rock salt structure (B1) to the eightfold coordinated CsCl structure (B2) [1]
The volume collapse (VP/V0) in terms of compressions in SrX at higher pressure indicates the mechanical stiffening of lattice
The understanding of pressure-dependent structural properties as first-order structural phase transition, associated volume collapse; elastic properties as ductility, mechanical stiffening, thermal softening, anisotropy in elastic constants, Shear (Young’s) modulus, hardness, Lame’s constant, Kleinman’s parameter, shear and longitudinal elastic wave velocity as well thermodynamics properties viz Debye temperature, melting temperature, heat capacity and thermal expansion coefficient of SrX needs the formulation of an effective interatomic potential
Summary
The understanding of pressure-dependent structural properties as first-order structural phase transition, associated volume collapse; elastic properties as ductility, mechanical stiffening, thermal softening, anisotropy in elastic constants, Shear (Young’s) modulus, hardness, Lame’s constant, Kleinman’s parameter, shear and longitudinal elastic wave velocity as well thermodynamics properties viz Debye temperature, melting temperature, heat capacity and thermal expansion coefficient of SrX needs the formulation of an effective interatomic potential. The thermodynamically stable phase at a given pressure P is the one with lowest entropy, and the thermo dynamical potential is the Helmholtz free energy (H). After determining the stable phase we compute the higher order elastic constants, their pressure derivatives and anisotropy With these understanding of interatomic potential in SrX, we have four material parameters, namely, modified ionic charge; hardness, range, force parameter [Zm, b, q, f(r)]. Values of them can be deduced from equilibrium conditions [32,33,34,35,36,37]
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