¹Uzhhorod National University, 46, Pidgirna str., 88000 Uzhhorod, Ukraine
²Ferenc Rákóczi II Transcarpathian Hungarian Institute, Kossuth Sq. 6, 90200 Beregovo, Ukraine
³Comenius University, Mlynska dolina, Bratislava 84248, Slovakia
⁴University of Presov, 17th November 1, Presov 08116, Slovakia
*Corresponding author e-mail: artempogodin88@gmail.com

Abstract. Ag8SiS6 single crystal was grown by directional crystallization from melt. A crystal sample was investigated by optical ellipsometry and spectroscopy. This sample had nonlinear spectral dependences of the refractive index n and the extinction coefficient k. The presence of a sharp maximum in the spectral dependence of the refractive index and a rather sharp decrease in the values of the extinction coefficient k at the wavelength of 780 nm were found. The behavior of the optical absorption edge of the Ag8SiS6 single crystal in the temperature range of 77…300 K was studied. An exponential dependence of the absorption coefficient α obeying the Urbach rule was observed at all the investigated temperatures. The optical pseudo-gap Eg* and the Urbach energy EU were calculated from the obtained experimental data. An increase in temperature of the Ag8SiS6 crystal was found to lead to a monotonic, almost linear decrease in Eg* (1.853…1.615 eV) and a monotonic nonlinear increase in EU (44.32…55.01 meV). The contributions of the temperature-independent (EU)X,C and temperature-dependent (EU)T components to the total Urbach energy EU for Ag8SiS6 were evaluated within the Einstein model.

Keywords: argyrodite, single crystal, optical absorption edge, Urbach’s rule.

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