Theory of the Anomalous Temperature Dependence of C12 in NaCl‐Like Structure Solids Direct Observation of Phonon—Lattice Interactions

The basic quantum theory is presented for the temperature dependence of the elastic constants of solids. The phonon—lattice interaction is invoked to explain the anomalous temperature dependence of C12 in NaCl‐like structure alkali halides. The calculated values of dC12/dT for lithium and sodium halides are negative and dC12/dT for potassium and rubidium halides (except KF) are positive (showing an anomalous temperature dependence of C12). These results are in excellent agreement with available experimental data.