Precise sound velocity measurement for liquid Se50Te50 under high pressure

We have measured the sound velocity in liquid Se50Te50 at 19.5, 32.6, 45.6, and 58.2 MHz simultaneously by means of an ultrasonic pulse transmission/echo method. By using a phase-sensitive-detection technique the relative error was reduced to less than 0.1%. The temperature dependence of sound velocity at 100 MPa exhibits a minimum at 600 oC and a maximum at 1035 oC, which are related to the large structural change accompanied by the semiconductor-metal (S-M) transition. In addition, sound dispersion has been observed at temperatures from 500 °C to 900 °C for the first time, where anomalous sound attenuation was previously reported. This result implies that a structural relaxation on nanosecond timescale takes place in the S-M transition region.