The structural, electronic, elastic and optical properties of AlCu(Se1−xTex)2 compounds from first-principle calculations

The structural, electronic structure, elastic and optical properties of the AlCu(Se1−xTex)2 compounds have been investigated by using a first-principles method based on density functional theory. The lattice constants of the quaternary compounds AlCu(Se1−xTex)2 increase with the increasing of Te composition. The calculated lattice constants for the ternary compounds i.e. AlCuSe2 and AlCuTe2 are in good agreement with the experimental data. The band structures show that the compounds have direct band gap and the band gaps are found to vary nonlinearly with composition. The total and part density of states of the quaternary AlCu(Se1−xTex)2 compounds are discussed. The calculated elastic constants indicate that all of the AlCu(Se1−xTex)2 compounds are mechanically stable. The bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν can be obtained by using the Voigt–Reuss–Hill averaging scheme. The B/G ratios of the AlCu(Se1−xTex)2 compounds indicate that AlCu(Se0.8Te0.2)2 is ductile and the others are brittle. The Debye temperature of the AlCu(Se1−xTex)2 compounds decreases a little with increasing Te content except the compound with x = 0.4. The dielectric functions, refractive index, extinction coefficient, absorption spectrums and energy-loss function of the AlCuSe2 and AlCuTe2 are also calculated and discussed in this work.

► The lattice constants of AlCu(Se1−xTex)2 increase with increasing Te composition.
► The AlCu(Se1−xTex)2 compounds have direct band gap with increasing trend of composition dependence of band-gap energy.
► The AlCu(Se1−xTex)2 compounds are mechanically stable.
► AlCu(Se0.8Te0.2)2 is ductile and the others are brittle.
► The Debye temperature decreases a little with increasing Te content.