Temperature and pressure dependence of the single-crystal elastic constants ofLi6and natural lithium

The single-crystal elastic constants and their pressure derivatives were measured for ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and lithium of natural isotopic composition. The temperature dependence of the elastic constants was measured between 90 and 300°K. The pressure derivatives of the three independent elastic constants were measured at 300 and 195°K. The measurements show that the elastic constants, the temperature derivative of the elastic constants, and the pressure derivatives of the elastic constants are the same for the two isotopes. The ratio of the ultrasonic velocities for a given mode are found to vary as the square root of the inverse ionic mass ratio. These results are discussed and interpreted in terms of a simple model. The implications of this model for other thermophysical properties are also discussed.