The elastic Debye temperature is calculated for each of several tetragonal crystals using both rigorous and approximate methods. It is found that only the rigorous method can be relied upon to provide a value suitable for determining the contribution of acoustic lattice vibrations to the low-temperature heat capacity. This is especially important when the latter is being analyzed to search for extra excitations.

• Received 27 July 1981

DOI:https://doi.org/10.1103/PhysRevB.25.5230