Origin of the first sharp diffraction peak in glasses

Abstract

Although glasses have been largely used for a wide variety of technological applications, much of their underlying structure and dynamical properties remain puzzling. We present a detailed investigation of the intermediate-range structure of a series of alkaline borate glasses carried out by performing neutron diffraction measurements. We propose that the first sharp diffraction peak of glasses arises from the periodicity of the boundaries of voids in a random network and explain its compositional and pressure dependence. In this framework, the planar section of a void is an $n$-membered ring of all-side vertex sharing basic structural units. Furthermore, we suggest that thermally activated relaxations responsible for the ultrasonic absorption in borate glasses stem from transverse motions of atoms bridging structural units confining voids.