Anomalous sound attenuation in liquid Te₅₀Se₅₀mixture under high pressure

Abstract

The sound velocity, v, and the sound attenuation coefficient, α, have been measured for liquid Te50Se50 mixture at 20, 32 and 43 MHz in the temperature and pressure range up to 1000 °C and 150 MPa. Near the melting point α decreases with increasing temperature, as is expected from the temperature variation of shear viscosity. In addition to the normal behaviour, we have found two peaks of α in the temperature range where the semiconductor-to-metal transition is observed. One is the high temperature peak, which appears around 850 °C irrespective of the frequency, and the other is the low temperature peak, whose position depends strongly on the frequency. The peaks become more prominent with increasing pressure, indicating the importance of the inter-chain couplings. Assuming a Debye-type relaxation for the frequency-dependent adiabatic compressibility, we have estimated the relaxation time to be about 7 ns from the high temperature peak.

Meso-scale fluctuations in liquid chalcogens near the metal-nonmetal transition

“…From this analysis, the relaxation times are estimated to be τ fast ∼ 0.1nsec and τ slow ≥ 10nsec in the Q-range of the observation. This value of τ slow nearly coincides with the relaxation time obtained from the sound attenuation measurements, τ 15 ± 3nsec [2,3]. The slow component becomes dominant in the low-Q region, and this process may be related to the anomalous sound attenuation.…”

“…This transition is accompanied by anomalies in thermodynamic properties such as the thermal expansion coefficient and compressibility. Recently, sound attenuation measurements for liquid Te-Se mixtures revealed that there occur dynamic anomalies in the M-NM transition region [2,3]. From the frequency dependence of the sound attenuation coefficient α, their relaxation time is estimated to be of the order of nano-seconds.…”

Precise sound velocity measurement for liquid Se50Te50 under high pressure

“…The sound velocity was measured by an ultrasonic pulse transmission/echo method [7], which is useful under high temperature and high pressure conditions. The measurements were made at temperatures up to 1100°C at nearly constant pressure.…”

“…The measurements were made at temperatures up to 1100°C at nearly constant pressure. We used a sample cell similar to that described in the previous paper [7]. Two fused quartz buffer rods were inserted into a fused quartz tube, and a liquid sample exists in the gap between the rods.…”

“…Recently, we measured the sound attenuation, a, in liquid Se-Te alloys under high pressures [7][8][9]. Near the melting point, a decreases rapidly with increasing temperature; this can be assigned to conformational changes within the chain molecules.…”