Vibrational, single-particle-like, and diffusive dynamics in liquid Se, Te, and Te50Se50

Abstract

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.

Microscopic structure and dynamics of molten Se50Te50 alloys

“…34 Clearly the presence of Te atoms enhances the mobility with respect to the elemental Se, mainly by destabilization of the covalent chains responsible for the semiconducting character of molten Se. As to what extent our calculations reproduce the experimental values for the alloy, unfortunately, to our knowledge, the only experimental diffusion coefficient available 6 corresponds to 1100 K, namely, D = 6.1ϫ 10 −9 m/s 2 somewhat lower than our estimates. This might be connected with the fact, already commented above, that the ab initio calculations tends to overestimate bonding, in particular, SeTe bonds, at least when comparing RMC and MD structural results.…”

“…15 The sample was contained in a sealed cylindrical quartz tube with an outer diameter of 10 mm and wall thickness of 1 mm. The quartz tube was held by a thin vanadium tube in a furnace and measurements were performed at 700, 900, and 1100 K. This corresponds to the same points in the phase diagram measured by inelastic neutron scattering by Chiba et al 6 Background was subtracted and the data were normalized to a vanadium measurement. Corrections for absorption, extinction, and multiple scattering were performed with the GUDRUN package available at ISIS.…”

“…The latter has been checked against the inelastic neutron scattering results of Chiba et al 6 The rest of the paper is sketched as follows. In the next section we summarize the experimental details.…”

“…In particular, the fact that increasing temperature induces a semiconductor/metal transition has motivated numerous experimental and theoretical investigations. [1][2][3][4][5][6] In the case of alloys, this transition can also be tuned by changes in the composition, a feature that makes this system even more attractive from the technological point of view. However, despite the growing number of works concerned with the properties of elemental Se and Te, relatively few investigations have focused on the behavior of SeTe alloys.…”

“…Some 20 years ago, Bellisent published a rather complete neutron diffraction study 7 ͑in which, however, the different components of the structure factor could not be extracted͒ and some data for inelastic neutron scattering of SeTe glasses 8 have only very recently been complemented by more detailed studies of the dynamic structure factor of equimolar SeTe. 5,6 Additionally, Tsuchiya 9 presented a study of the thermodynamics of isostructural transitions in liquid SeTe alloys from a careful determination of sound velocities and isothermal compressibilities. Some ab initio computer simulation results have also been recently published by Lomba et al 10 focusing on the compositional dependence of the microscopic structure and dynamics.…”