The elastic behaviour of indium under pressure and with temperature up to the melting point

The ultrasonic pulse-echo overlap technique has been used to measure pressure and temperature dependences of elastic wave propagation velocities along various crystallographic directions in single-crystal indium. The results provide a complete set of the pressure derivatives of the elastic constants of indium between room temperature and the melting point (429·7 K). This in turn has allowed the long-wavelength acoustic mode Grüneisen parameters to be determined over that temperature range. The values obtained for acoustic mode Grüneisen parameters show that there is a significant increase in vibrational anharmonicity as the melting temperature is approached. To allow determination of the thermal Grüneisen parameters γth up to the melting point, the thermal expansion tensor components α11 and α33 have also been measured. The mean zone-centre acoustic mode Grüneisen parameter γe1 is found to be larger than γth owing mainly to the contributions from the more anharmonic slow shear modes (k[110], e[110] and k[101], e[Φ]).