Lattice dynamics and thermodynamical study of yttrium monochalcogenides

In this work we have investigated the structural, mechanical, electronic, phonon and thermodynamical properties of yttrium monochalcogenides (YX: X = S, Se and Te) in the rocksalt phase using state-of-the-art first principles density functional theory. The calculated results of optimized lattice parameters, elastic constants, and bulk modulus agree well with the available experimental and other theoretical values. The electronic band structure of the yttrium monochalcogenides reveals the metallic character of these compounds. The shear modulus, Young’s modulus, Poisson’s ratio and Lame’s constants are calculated and discussed in detail. The calculated mechanical properties indicate that the considered yttrium monochalcogenides are brittle in nature. The Debye temperature of yttrium compounds is also calculated. The first time reported phonon dispersion curves and phonon density of states for YS, YSe and YTe calculated using ab initio first principles calculations shows that the B1 phase of YS, YSe and YTe is lattice dynamically stable at ambient conditions. The temperature dependence of thermodynamical properties on temperature is also calculated by using the quasi harmonic approximation and discussed. The variation of constant volume lattice-specific heat with temperature obeys the classical Dulong–Petit’s law at high temperature, while at low-temperature it obeys the Debye’s T3 law.