The elastic constants of sodium from 20 to 95°C

We report ultrasonic pulse echo measurements of the elastic constants of sodium in the high temperature region. At room temperature the results agree with those of earlier work. No pronounced effects of anharmonicity are found contrary to theoretical predictions. The behaviour of the elastic constants is further analysed in terms of compressibilities, of Grüneisen parameters and of effects caused by lattice defects. The quantity?lnω_i(q)/?T]_v is calculated from the temperature and pressure variation of the elastic constants.