ELLIPSOMETRIC STUDIES OF Ag7+x(P1-xGex)S6 SINGLE CRYSTALLINE SOLID SOLUTIONS

The present work is aimed to the study of the physical characteristics of single crystal samples of Ag7+x(P1-xGex)S6 solid solutions (x = 0, 0.1, 0.25, 0.33, 0.5, 0.75, 1). Single crystals of Ag7+x(P1-xGex)S6 solid solutions were grown by the method of directional crystallization from the melt. Specially prepared samples of the grown single crystals of Ag7+x(P1-xGex)S6 solid solutions were studied by spectral ellipsometry method. The spectral dependences of the refractive index are characterized by nonlinearity with a maximum in the spectral range ~645-820 nm. It has been found that cationic substitution in P5+→Ge4+ solid solutions lead to a monotonic nonlinear increase in the refractive index n from 2.58 (x = 0) to 2.75 (x = 1). The obtained values of the refractive index were used to describe the optical parameters using the Wemple-DiDomenico equation. It was found that parameters of Wemple-DiDomenico model – the energy of a single oscillator, the dispersion energy are characterized by a tendency to monotonous decrease in the process of heterovalent cationic P5+→Ge4+ substitution. The established values of the optical band gap Eg suggest that single crystal samples of Ag7+x(P1-xGex)S6 solid solutions can be used as promising materials for solar energy.