Structure of liquids and glasses in the Ge-Se binary system

A summary is given of the partial structure factors that have been measured for liquids and glasses in the Ge-Se binary system by using diffraction methods. Information is presented on the pair correlation functions describing the atomic species and use is made of the Bhatia-Thornton formalism to separate those pair correlation functions describing the system topology from those that describe the chemical ordering. The information made available by the measured Bhatia-Thornton partial structure factors on the thermodynamic properties of Ge-Se mixtures is briefly summarized. The properties of the network structures formed in liquid and glassy GeSe compounds are investigated as a function of composition, temperature and pressure. For GeSe, at ambient pressure it is shown that the so-called first sharp diffraction peak, which appears in the measured diffraction patterns at a small scattering wavevector value of approximate to angstrom(-1) and which is associated primarily with Ge-Ge correlations, does account for discernable features of the observed intermediate range order in both the liquid and glassy phase. The first sharp diffraction peak in the measured Ge-Ge partial structure factor for both phases is described by comparable parameters suggesting communality in the underlying intermediate range order which survives the glass transition. Homopolar bonds are found to be a feature in the structure of liquid GeSe and both liquid and glassy GeSe2 with Ge-Ge and Se-Se distances in the ranges 2.33(3)-2.42(2) and 2.30(2)-2.34(2) angstrom, respectively. (c) 2007 Elsevier B.V. All rights reserved.