Debye temperature and standard entropies and enthalpies of compound semiconductors of the type I-III-VI₂

Abstract

The heat capacities at constant pressure have been measured for CuInSe₂, CuInTe₂ and AgGaTe₂ in the temperature range 1K ≤T≤40K and for CuInS₂ and AgInTe₂ between 1 K and room temperature. From the low temperature data we derive the following Debye temperatures θ_D in the limit T → O K: θ_D(CuInS₂) = 273 K, θ_D(CuInSe₂) = 222 K, θ_D(CuInTe₂) = 191 K, θ_D(AgGaTe₂) = 182 K and θ_D(AgInTe₂) = 156 K. A plot of the average atomic heat capacity at constant volume C_v shows that the data scale to one general curve for all 5 compounds considered in this paper. This is, also, true for a plot C_v, i.e., all I-III-VI₂ compounds measured thus far deviate similarly from the Debye approximation. By integration of the general curves C_v(T/θ_D) and θ_D x C_v(T/θ_D) we derive tne standard entropies S ²⁹⁸₀ and energies E ²⁹⁸₀ -E ⁰₀ of 11 compounds of the type I-III-VI₂, for which the Debye temperatures are known. The difference between the energies E ²⁹⁸₀ -E ⁰₀ and enthalpies H ²⁹⁸₀ -H ⁰₀ is within the error limits of the experimental data (< 1%). The molar S ²⁹⁸₀ and H ²⁹⁸₀ -H ⁰₀ values for the I-III-VI₂ compounds are approximately twice the corresponding molar values for their II-VI isoelectronic analogs. The thermodynamic functions at standard state obtained by integration of the experimental data are all < 10% smaller than the corresponding values estimated on the basis of the Debye approximation.