Determination of thermodynamic parameters in the Cu$_{1.95}$Ni$_{0.05}$S phase-transition regions

X-ray diffraction and differential thermal analysis data obtained in the Cu$_{1.95}$Ni$_{0.05}$S phase-transition region are analyzed. It is established that the low-temperature rhombic $\alpha$ phase in Cu$_{1.95}$Ni$_{0.05}$S transforms to the hexagonal $\beta$ phase at temperatures of 370–390 K and to the cubic $\gamma$ phase at temperatures of 740–765 K according to the scheme $\alpha\to\underset{370-390 K}{\alpha+\beta}\to\underset{740-765 K}{\beta+\gamma}\to\gamma$. It is determined (using the temperature dependence of differential thermal analysis) that the transition $\alpha\to\beta$ is accompanied by heat absorption while the transition $\beta\to\gamma$ is accompanied by heat release. It is found that both transitions are allowed and belong to the reconstructive type. Both transitions are found to occur in a fluctuation volume of $\sim$10$^{-20}$ cm$^3$ at temperature rates of 0.11 and 0.08 K$^{-1}$. It is demonstrated that the transition $\alpha\to\gamma$ is accompanied by alternation of the structures passing through the intermediate $\beta$ phase, which is incommensurate with respect to the $\alpha$ and $\gamma$ phases.