Ultrasonic Measurement of the Temperature Dependence of the Nonlinearity Parameters of Copper

Abstract

The temperature dependence of the nonlinearity parameters of copper single crystals has been measured in the range 77 to 300°K. (Nonlinearity parameters are combinations of third-order elastic constants.) These measurements were made from a quantitative determination of the second-harmonic distortion of pulsed MHz ultrasonic waves propagating in the three principal crystallographic directions. By maintaining a constant detector gap of about five microns with a pneumatically controlled variable-gap capacitive detector, it was possible to measure the nonlinearity parameters relative to their room-temperature values, which were determined by absolute calibration. Typically, the nonlinearity parameters change linearly with temperature by about ten percent. Over this temperature range, the measured values of the nonlinearity parameters are consistent with the assumption that the primary contributor to the third-order elastic constants is the closed-shell repulsive interaction of nearest-neighbor atoms.