Elastic, vibration and thermodynamic properties of Cu1_xAgxlnTe2 (x=0,0.25, 0.5, 0.75 and 1) chalcopyrite compounds via first principles

CuInTe2 chalcopyrite compound is widely used in the fields of optoelectronics and pyroelectricity, and doping atoms can further improve the physical properties of the CuInTe2 compound. For all we know, this is the first time that the elastic behaviors and lattice dynamical properties of Ag-doped CuInTe2 compounds with the tetragonal system are determined theoretically. The elastic, lattice dynamical and thermal properties of Cu-1_xAgxInTe2 (x = 0, 0.25, 0.5, 0.75 and 1) compounds have been investigated by using density functional theory. The obtained elastic constants of Cu1-xAgxInTe2 compounds indicate that these compounds are mechanically stable and elastic anisotropic. The anisotropy of the {001} plane is more obvious than those of the {100} and {010} planes. Additionally, with increasing Ag doping concentrations, the bulk and shear moduli of Cu1-xAgxInTe2 compounds decrease and their toughness improves. The phonon spectra and density of states reveal that Cu (or Ag) atoms in Cu1-xAgxInTe2 compounds form chemical bonds with Te atoms, and Cu-Te bonds are gradually replaced by Ag-Te bonds with increasing Ag doping concentration. Vibration modes of Cu1-xAgxInTe2 compounds at the Lambda point in the Brillouin zone show that each Cu1-xAgxInTe2 (x = 0 and 1) crystal includes five irreducible representations (A(1), A(2), B-1, B-2 and E). As for Cu1-xAgxInTe2 (x = 0.25, 0.5 and 0.75) compounds, each crystal has three irreducible representations (A, B and E). The atomic displacements of several typical phonon modes in CuInTe2 crystals have been analyzed to deepen the understanding of lattice vibrations in Cu1-xAgxInTe2 compounds. With increasing Ag doping concentration, the Debye temperatures of Cu1-xAgxInTe2 compounds decrease, while their heat capacities increase.