Specific heats and lattice dynamics of cuprous halides

The specific heats Cp(T) of CuCl, CuBr, and Cul were measured by the adiabatic calorimetric technique. The corresponding Debye temperature for each crystal is given and a comparison between the results is drawn. The room-temperature phonon dispersion relations for these cystals are fitted by a nine-parameter shell model which gives good fits to CuBr and Cul and a fair fit to CuCl. These model calculations are used to compute CV(T) for the three cuprous halides and the calculated results are compared with experiment. The agreement is good for the range of T > 30 °K and less so for T < 30 °K where discrepancies are to be expected due to anharmonicity that affects the theoretical results. For CuCl we also obtain the Griineisen parameter y(T) using thermal expansion data.