Static and dynamical inhomogeneity at liquid - liquid phase transition of Se-Te mixtures

Abstract

We have carried out x-ray transmission and small-angle x-ray scattering (SAXS) measurements of liquid Se70-Te30 mixture up to 1000 °C and 100MPa and inelastic x-ray scattering (IXS) measurement of liquid Se50-Te50 mixture at SPring-8 in Japan. In this paper, we report the preliminary results. In liquid Se70Te30 at 6MPa, with increasing temperature from 400 °C, the density first normaly decreases but anomalously increases from 650 °C. This anomalous density behaviour can be interpreted that the sample exhibits continuous transition from low-density phase to high-density one in this temperature region. As a proof of that, the zero-wavenumber-limit of SAXS intensity I(0) increases and shows maximum in this region, which means that the static density inhomogeneity arises due to phase transition. When the pressure is elevated, the density and I(0) curves shift to lower temperature side. The velocity of acoustic mode in Se50-Te50 estimated by IXS data is much higher than the ultrasonic sound velocity (so-called "fast sound" state) and the temperature dependences of the two velocities are totally different. But the ratio of the two velocities, the strength of "fast sound", seems to increase with approaching to the transition region and thus it seems to be a good sign of dynamical inhomogeneity.