Temperature variation of the longitudinal acoustic excitation dispersion curve in liquid Ge ₁₅ Te ₈₅ by high-resolution inelastic x-ray scattering

High-resolution inelastic x-ray scattering measurements of liquid Ge₁₅Te₈₅have been carried out to investigate the momentum transfer dependence of the longitudinal acoustic excitation energy. Liquid Ge₁₅Te₈₅undergoes the semiconductor-metal transition accompanying the transformation from tetrahedral to octahedral local orders with increasing temperature. The obtained longitudinal acoustic excitation dispersion curve exhibits a sinusoidal shape near the melting temperature, changing to a flat-topped one at high temperatures. These results indicate that the flat-topped dispersion curve is correlated with a distorted local structure. The present result seems consistent with the idea that a distorted structure results from an octahedral local order induced by a Peierls distortion in a liquid.