Pressure Derivatives of the Elastic Constants of Copper, Silver, and Gold to 10 000 Bars

The pressure derivatives of the elastic constants of the homologous series of metals, copper, silver, and gold have been measured over the pressure range from 0 to 10 000 bars, using a modified ultrasonic pulse-echo method. Means have been devised to measure the change of elastic constant with pressure as directly as possible. The values found for the pressure derivatives of the elastic constants are as follows: The notation $C=C_{44}$, $C^{\prime }=\frac{(C_{11}-C_{12})}{2}$, and $B_s=\frac{{(C_{11}+2\mathrm{}{C}_{12})}_s}{3}$ has been used. The data for each metal, of the three elastic constants and their pressure derivatives, have been interpreted in terms of conventional theory. The theoretical contributions of long-range interactions have been subtracted off and the remainder attributed to short-range nearest-neighbor interaction. The analysis indicates that these must be non-central, many-body interactions in order to account for the shear constants and especially their pressure derivatives. The many-body character of the interactions is of rapidly increasing importance in the sequence copper, silver, and gold.