The Variation of the Adiabatic Elastic Constants of KCl, NaCl, CuZn, Cu, and Al with Pressure to 10,000 Bars

The adiabatic velocities of sound for longitudinal and transverse waves in single crystal specimens of five cubic solids have been measured as a function of pressure to 10,000 bars, using a pulse technique. The elastic constants calculated from these data in general agree well with previous measurements obtained for zero pressure elastic constants and compressibilities. With increasing pressure the anisotropy increases in crystals which are not closest-packed, but decreases in closest-packed structures. Consideration of the exchange force between nearest neighbors gives a qualitative explanation for this effect. Comparison of the present measurements with previous measurements of the variation of elastic constants with temperature indicates that the elastic moduli cannot be considered functions of volume alone but must also depend explicitly on the temperature.