Concentration Fluctuations Induced by Structural Changes in the Liquid Se–Te Alloy

Abstract

New thermodynamic relations are applied to the liquid Se-Te system to investigate the concentration fluctuations induced by the structural change. The excess Darken stability caused by the structural change has been quantitatively evaluated with experimentally available data. It is definitely negative, and the absolute magnitude of which takes a peak in the compositiontemperature region where the structural change occurs. The results provide the thermodynamic basis of the segregation tendency in a microscopic scale developed with increasing temperature, which was found with high resolution neutron diffraction experiments nearly two decades ago. Discussion has been made in relation to the intrinsic instability of chain structure of VIb chalcogenide elements which plays a key role to makes the effective interaction between Se-Te pair dependent on composition and temperature.

Peculiar temperature dependence of dynamical sound speed in liquid Se50Te50 by inelastic x-ray scattering

“…The fluctuations at a Q → 0 limit are expressed by summing the density-density S nn (0), concentration-concentration S cc (0) and density-concentration S nc (0) correlations in the partial structure factors of the Bhatia-Thornton form [53]. Tsuchiya [30] could estimate these values in liquid Se-Te mixtures using the thermodynamic quantities and relations as briefly described in supplementary data. Figure 8 shows S nn (0), (S cc (0) + S nc (0)) and these sum S(0) as a function of T. Here S(0), S nn (0) and (S cc (0) + S nc (0)) are scaled using the atomic form factors of Se and Te for x-ray.…”

“…The electronic properties in liquid Se-Te mixtures were gradually transformed into metallic ones with increasing T. T dependence of density [26] and US speed [27] in liquid Se-Te mixtures were investigated in detail. Using these results, new relations between thermodynamic quantities were proposed [28] based on the inhomogeneous liquid model [29], and applied to liquid Se-Te mixtures [30]. Although the results obtained in [30] seemed reasonable, the model had weakness of no experimental evidences of structural inhomogeneities in liquid Se-Te mixtures and prior discussion of the electronic structure in disordered materials based on microscopic inhomogeneities [31] was strongly criticized by Mott [32] .…”