Single crystals of (FeIn$_{2}$S$_{4}$)$_{x}$ $\cdot$ (CuIn$_{5}$S$_{8}$)$_{1-x}$ alloys: Crystal structure, nuclear gamma resonance spectra, and thermal expansion

FeIn$_{2}$S$_{4}$ and CuIn$_{5}$S$_{8}$ compounds and (FeIn$_{2}$S$_{4}$)$_{x}$ $\cdot$ (CuIn$_{5}$S$_{8}$)$_{1-x}$ alloy single crystals are grown by planar crystallization. It is shown that both of the initial FeIn$_{2}$S$_{4}$ and CuIn$_{5}$S$_{8}$ compounds and alloys on their basis crystallize with the formation of the cubic spinel structure. It is established that the unit-cell parameter $a$ linearly varies with the composition parameter $x$. By means of nuclear gamma resonance spectroscopy in the transmission mode of measurements, the local states of iron ions in the alloys are studied. For the single crystals grown in the study, thermal expansion is explored using the dilatometry technique, the thermal-expansion coefficients are determined, and the Debye temperature and rms (root-mean-square) dynamic displacements are calculated.