The method of long-wave spectroscopy made it possible to study the IR reflection spectra of layered single crystals β-Tl1-xCuxInS2 (0≤X≤0.015) in in the frequency range of 40-500 cm−1 and the temperature range of 84 ¸ 300 K. It was shown that partial substitution of thallium atoms with copper atoms leads to a decrease in the frequencies of the corresponding oscillations in the frequency range of 40-500 cm−1 and does not lead (at these concentrations) to local oscillations. It was found that solid solutions β-Tl1-xCuxInS2 (X=0 ÷ 0.015) exhibit the characteristic single-mode behavior. It was shown that partial substitution of thallium atoms with copper atoms in single crystals β-Tl1-xCuxInS2 (X = 0.005; 0.010; 0.015) weakens the ionic bond in Tl–S, as a result of which the frequencies of “internal” oscillations shift towards low temperatures.

The anisotropy of the refractive index and the electro-optical effect in Tl1-xCuxGaSe2(0≤X≤0/02) crystals were studied. Refractive indices were shown to rise as they approach their own absorption band. The electro-optical effect in TlGaSe2 crystals was studied. It was shown that the EO effect in the case where the light and external electric field are directed along the “C” axis within the studied electric fields (up to 5 kV / cm) is quadratic. The quadratic EO effect for TlGaSe2 equals 1.3 · 10−9 CGS units. It was found that when the electric field is directed perpendicular to the “C” axis and the light is directed along the “C” axis the EO effect is linear. The results of the EO measurements are consistent with the fact that the TlGaSe2 compounds crystallize in a monoclinic lattice, with the space group Cc, but at the same time the TlGaSe2 crystals have higher symmetry than Cc.

Phase formation during contact melting, including in the presence of electric transfer, in the system indium-zinc and stannic-zinc with the introduction of a small admixture of strontium was studied. The formation of two-component intermetallic compounds has been established. An attempt has been made to explain the obtained results.