Debye–Einstein model and anomalies of heat capacity temperature dependences of solid solutions at low temperatures

Abstract

An approach is proposed for analysing the deviations of the heat capacity Cp(T) of solid solutions from the Kopp–Neumann rule (KNR) ΔC(T) = Cp(T) − CKNR(T). Temperature dependences of the heat capacity Cp(T) of selected compositions of systems (InP)x (InAs)1−x and (GaAs)x (InAs)1−x at temperatures of 5–300 K are analysed in the Debye–Einstein approximation. It was established that in the case of substitution of atoms in the cation subsystem (Ga3+ ↔ In3+) with the same subsystem of anions (As3−), the positive values of ΔC(T) at T 100 K are the result of a decrease in the fraction of the Debye contribution without changing the upper limit of the oscillation frequency. In the case of substitution in the cation subsystem (P3− ↔ As3−) with the invariant cation subsystem (In3+) to the low-temperature positive contribution of the additional low-frequency Einstein mode, a positive part is added from the modified Debye mode having the characteristic temperature θD below the additive value θDKNR. The adequacy of this model is confirmed by Raman scattering data.