Abstract
Phase transition, elastic, vibrational and thermal properties of KCuSe and KCuTe are investigated via performing ab-initio calculations combined with quasi-harmonic Debye model. Our results show that these two compounds undergo two first order phase transitions. The calculated equilibrium structural parameters with the modified generalized gradient approximation (PBEsol) agree closely with available experimental values. The mechanical stability is investigated using the calculated elastic constants for all phases. The tetragonal structure of KCuSe is not mechanically stable beyond 8.04 GPa. For KCuTe, C66−P is negative below 7.76 GPa. The mechanical parameters for polycrystalline materials are determined within the framework of the Voigt–Reuss–Hill approximation. From the Poisson’s ratio and the B/G relationship both compounds are brittle in the P63/mmc, while they are ductile in the other phases. The variation of the static and electronic elements of the dielectric tensor with pressure in the different phases is investigated. They show strong anisotropy and discontinuity at the transition pressure. The phonon spectra are also computed along high symmetry lines for both compounds in their different possible phases. The effect of pressure and temperature on the thermal expansion coefficient, bulk modulus, heat capacity and the Debye temperature is analyzed in detail.
Published Version
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