Basic network structure of SiO2–B2O3–Na2O glasses from diffraction and reverse Monte Carlo simulation

Abstract

Neutron- and high-energy synchrotron x-ray diffraction experiments have been performed on the (75−x)SiO2–xB2O3–25Na2O x = 5, 10, 15 and 20 mol% glasses. The structure factor has been measured over a broad momentum transfer range, between 0.4 and 22 Å−1. For data analyses and modelling the Fourier transformation and the reverse Monte Carlo simulation techniques have been applied. The partial atomic pair correlation functions, the nearest neighbour distances, coordination number distributions and average coordination number values and three-particle bond angle distributions have been revealed. The Si–O network proved to be highly stable consisting of SiO4 tetrahedral units with characteristic distances at rSi–O = 1.60 Å and rSi–Si = 3.0(5) Å. The behaviour of network forming boron atoms proved to be more complex. The first neighbour B–O distances show two distinct values at 1.30 Å and a characteristic peak at 1.5(5) Å and, both trigonal BO3 and tetrahedral BO4 units are present. The relative abundance of BO4 and BO3 units depend on the boron content, and with increasing boron content the number of BO4 is decreasing, while BO3 is increasing.