Compositional changes of the first sharp diffraction peak ͑FSDP͒ in the measured structure factor have been studied for several binary selenide glasses using pulsed-neutron and high-energy x-ray diffraction techniques. The observed variations in the FSDP ͑factor of 10 in the amplitude and Ϸ0.5 Å −1 in the peak position͒ reflect multiple aspects in the glass network on both the short-and intermediate-range scales and are also correlated with macroscopic properties. An empirical relation has been discovered relating the compositional dependence of the FSDP position to the local coordination number of the guest atom.

No abstract

Liquid tellurium has been studied by density-functional/molecular-dynamics simulations at 560, 625, 722, and 970 K and by high-energy x-ray diffraction ͑HEXRD͒ at 763 K and 973 K. The HEXRD measurements agree very well with earlier neutron-scattering data of Menelle et al. The density maximum near the melting point ͑722 K͒ reflects the competition between twofold and threefold local coordination, which results in chain formation and changed ring statistics at lower T, and the variation with T of the volume of cavities ͑26-35 % of the total͒. A higher-order gradient expansion of the exchange-correlation functional is needed to describe structural details. Changes in the electronic properties ͑band gap and dc conductivity͒ upon cooling are consistent with a transition from a high-temperature metal to a semiconductor.

No abstract

For the first time, the Raman spectra of bulk SexTe1‐x glasses, 0.5 ≤ x ≤ 1.0, have been measured over the entire glass‐forming range. The spectra exhibit three broad spectral features between 150 and 300 cm−1, attributed to Te–Te, Se–Te, and Se–Se stretching modes according to DFT simulations. The observed weak chemical ordering in the glasses is discussed on the basis of heteropolar and homopolar bond fractions derived from integrated intensity of the Raman modes and DFT cross‐sections. The underlying structural model of the glasses suggests a random distribution of the Se–Se, Se–Te, and Te–Te chemical bonds with some preference for heteropolar bonding within Se–Te–Se structural units.

No abstract

No abstract

In contrast to the well-established structure of glassy GeS2, consisting of corner- and edge-sharing GeS(4/2) tetrahedra, the structural features of Ge-rich sulfide alloys remain essentially unknown. Two contrasting points of view: (1) a tetrahedral model, and (2) a distorted NaCl approach were neither confirmed nor excluded mostly because of missing advanced structural studies. Using high-energy X-ray scattering and neutron diffraction, we show the complexity of the short and intermediate range order in Ge(x)S(1-x) glasses, ⅓ ≤ x ≤ 0.47, formed by corner- and edge-sharing tetrahedra with two-fold coordinated sulfur species and a variable number of Ge-Ge bonds, and Ge-S units with three-fold coordinated sulfur at x ≥ 0.36.