Third-Order Elastic ConstantC111in NaCl and KCl

The third-order elastic constant ${\mathrm{C}}_{111}$ has been measured for NaCl and KCl single crystals by ultrasonic-pulse techniques. A capacitance microphone was used to measure the absolute amplitudes of the fundamental and second harmonic of longitudinal waves propagated in the crystals. Measurements were made without static stress on the samples. The measured results for ${\mathrm{C}}_{111}$ in NaCl and KCl are (-8.3±0.8) × ${10}^{12}$ and (-7.1±0.7) × ${10}^{12}$ dyn/${\mathrm{cm}}^2$, respectively.