Structural and optical properties of AgIn5S8

Abstract

Compounds of the chalcogenide family Ag–In–VI (VI = S, Se, Te) are interesting materials due to their stoichiometric stability and potential application in nonlinear optics and solar cells. A polycrystalline ingot of AgIn5S8, an ordered vacancy semiconductor, was prepared by direct fusion of the stoichiometric mixture of the elements in an evacuated quartz ampoule. The presence of a single phase with cubic structure was confirmed by X-ray powder diffraction at room temperature. The lattice parameter, [Formula: see text], was calculated, giving 10.821750 Å. Samples in evacuated quartz ampoules were used to perform Differential Thermal Analysis measurements, showing congruent melting at 1110[Formula: see text]C. Transmittance and reflectivity measurements were used to calculate the absorption coefficient [Formula: see text]. From the plot of ([Formula: see text])2 versus [Formula: see text], two direct transitions are observed at 1.25 eV and 1.88 eV. While the higher energy direct transition has been observed by other authors, the direct nature of the lower energy transition was confirmed from the fitting of the plot of the reflectivity versus 1/[Formula: see text] between 0.53 eV[Formula: see text] (1.89 eV) and 0.55 eV[Formula: see text] (1.82 eV), obtaining a value of 1.29 eV. The real refractive index [Formula: see text] and the high-frequency dielectric constant [Formula: see text] were also obtained from the fit of the reflectivity, resulting to be 2.68 and 7.2, respectively.