Ultrasonic nonlinearity parameters and third-order elastic constants of germanium between 300 and 77 °K

The ultrasonic-harmonic-generation technique has been used to determine the nonlinearity parameters of germanium between 300 and 77 ^∘{}K. These results have been combined with pressure-derivative results to isolate a complete set of third-order elastic constants at room temperature. Comparison of these data with predictions of simplified models reveals that a central-force-nearest-neighbor model is less accurate for germanium than for copper. The discrepancy appears to increase as the temperature is lowered.