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.

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