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

Abstract

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 Ge–Se compounds are investigated as a function of composition, temperature and pressure. For GeSe2 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 ≈1Å−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)Å, respectively.