The structural, elastic, electronic and optical properties of orthorhombic FeX2 (X=S, Se, Te)

Abstract

The structural, elastic, electronic and optical properties of FeX2 (X = S, Se, Te) with orthorhombic (space group Pnnm) structure have been investigated through the first-principles calculations. The calculated lattice constants, internal structure parameters and two kinds of Fe-X bond lengths agree reasonably with the experimental results. The corresponding single crystal elastic constants, polycrystalline elastic moduli, transverse, longitudinal, average elastic wave velocities, Debye temperature and minimum thermal conductivity decrease from FeS2 to FeTe2 while the elastic anisotropy index increases from FeS2 to FeTe2. All the three compounds show the brittle nature and covalent bonding. The orthorhombic FeX2 are non-magnetic semiconductors with indirect band gaps of 1.17eV, 0.64eV and 0.27eV, respectively. There have strong hybridizations between Fe-d orbitals and X-p orbitals. The real part and imaginary part of the dielectric function, refractive index and absorption coefficient are obtained and analyzed, the results show that the three compounds possess excellent absorption properties in ultraviolet and visible light regions. Both elastic properties and optical properties exhibit obvious anisotropy in the three compounds.