Anharmonicity of lattice vibrations and the thermal properties of Сd$_{1-x}$Sr$_{x}$F$_{2}$ solid solutions

The temperature changes in the crystal lattice parameters $a(T)$ of cadmium and strontium fluorides and also of their mutual Сd$_{1-x}$Sr$_{x}$F$_{2}$ ($x$ = 0.23, 0.50) solid solutions has been studied experimentally at temperatures 5–300 K. The temperature dependences of the unit cell volume of these fluorides are analyzed in the Debye–Einstein model. The lattice vibration anharmonicity of the solutions is found to substantially influence their thermal properties due to a disordering of their crystal structure. The model parameters and the characteristics of the anharmonic contribution have been determined. The results are used to calculate the concentration dependence of the thermal conductivity of the Сd$_{1-x}$Sr$_{x}$F$_{2}$ solid solutions at $T$ = 300 K in the Callaway model, and the calculation results are compared to the available experimental data. It is shown that the thermal conductivity of the single-crystal solid solution of the system under study can be estimated on the base of the data on the thermal properties of the solution components obtained from powder samples.