Anomalous sound attenuation in the metal-nonmetal transition range of liquid mercury

Abstract

The sound velocity, v, and the sound attenuation coefficient, , of fluid mercury have been measured at 20 MHz in the temperature and pressure range up to 1600 °C and 200 MPa. To obtain the precise sound attenuation data under high temperature and pressure, we have derived the formula for estimating by taking into account the sound absorption in the buffer rods and the acoustic impedance mismatches between the buffer rods and the sample Hg. The measurements have been carried out with four different sample lengths, and the agreements among these measurements are fairly good in the common density range. Beside the critical attenuation of sound propagation, we have observed the secondary maximum in the density dependence of at a density near 9 g cm-3, where the metal-nonmetal (M-NM) transition occurs. In contrast to the critical attenuation, the height of the secondary maximum is almost independent of temperature. Assuming a Debye-type relaxation for the frequency-dependent adiabatic compressibility, we have estimated the relaxation time from the anomalous attenuation. We conclude that in expanded liquid Hg slow dynamics is generated by the sound pressure in the M-NM transition range.