Published papers

Dynamic structures of liquid Te 70 Se 30 and Te 50 Se 50 were investigated by inelastic neutron scattering experiments in the semiconductor-to-metal transition range. The bond-stretching modes for the both liquid mixtures were found to clearly soften when the transition occurs. We discuss the change of static and dynamic structures that accompany the transition.

We carried out inelastic neutron scattering measurements to study the dynamic structure of liquid Se and Te50Se50. The bond-stretching modes for both liquids were found to lie in higher energies than those forming a trigonal phase, showing that the chainlike molecules are more isolated than in the troigonal phase. The Q-dependence of the intensity of the dynamic structure factor was examined at the region of the stretching modes, and found to be explained by a simple model where we assumed completely out-of-phase motions of two atoms. The result shows the possibilities of extracting short-range structural information from such Q-dependences for these kinds of basically isolated molecules.

Neutron scattering measurements were carried out for liquid Se, liquid Te, and liquid Te50Se50. The results are discussed in the context of semiconductor-to-metal transition. As to liquid Te50Se50, the vibrational modes show a remarkable change when the semiconductor-to-metal transition occurs by temperature increase. A soft stretching mode was observed for the metallic phase and it shows the structural change; the appearance of long bonds in the metallic phase. The vibrational modes for liquid Se and liquid Te were obtained and agreed well with former works. The crossover from collective to single-particle-like regime was also observed for all liquid samples and the transition ranges (Q = 4.5–8 Å–1) are presented. The diffusive features in the low-Q region and single-particle-like properties in the high-Q region are discussed and are shown to be consistent with the results for the vibrational modes.

We have carried out neutron scattering experiments for liquid Te50Se50 at 700 K (semiconducting regime), 900 K (transition regime) and 1100 K (metallic regime). The quasielastic scattering peak is comparatively narrow at the peak positions of S(Q). A remarkable increase in the peak width is observed near the first minimum of S(Q), when the semiconductor-to-metal transition occurs. Since the first peak of S(Q) in this system proves to mainly reflect the inter-chain correlation and the second peak to the intra-chain correlation, the observed broadening may suggest frequent bond-switching between the chains in the metallic regime.

We measured the vibrational spectra of liquid Se2Cl2 and Se2Br2 by neutron and Raman scattering. The spectra measured by each technique show roughly good agreements with earlier Raman works. A partial disagreement was observed for the neutron scattering data at the bond-bending mode of liquid Se2Br2. It is suggested that the disagreement might be attributed to the slightly dispersive behaviour of the mode. The generalized vibrational density of states, G(Q,E), for Se2Br2 obtained by neutron scatterings is reported to show the observed vibrational modes in the energy-momentum space.