Structural Disorder and Heat Capacity of a Solid Solution between Cadmium and Strontium Fluorides

— The heat capacity C p ( T ) of cadmium fluoride, strontium fluoride, and the Cd 0.5 Sr 0.5 F 2 solid solution has been studied experimentally (2–300 K). We have detected deviations Δ C p ( T ) of the C p ( T ) data from additivity. The low-temperature (2–50 K), positive deviations Δ C p ( T ) have been tentatively attributed to the effect of two-level systems associated with the glasslike character of the low-temperature thermal properties of the solution due to disorder in the Cd–Sr sublattice. The high-temperature (100–300 K), negative deviations Δ C p ( T ) are caused by the effect of anharmonicity of lattice vibrations, whose increasing role is also associated with the disordered arrangement of atoms in the crystal lattice upon formation of the solution. The C p ( T ) data for the solution of the system studied have been analyzed in the Debye–Einstein model. We have determined model parameters: characteristic temperatures Θ i and the fractions of different contributions, a i , to total thermal characteristics of the substances studied.