Network structure of multi-component sodium borosilicate glasses by neutron diffraction M. Fa ´bia ´n a , E. Sva ´b a, * , Gy. Me ´sza ´ros a , Zs. Re ´vay b , Th. Proffen c , E. Veress d a Research Institute for Solid State Physics and Optics, Department of Neutron Physics, Konkoly Thege Street 29-33, P.O. Box 49, H-1525 Budapest, Hungary b Institute of Isotopes, P.O. Box 77, H-1525 Budapest, Hungary c Los Alamos Natl. Lab., Lujan Neutron Scattering Ctr, Los Alamos, NM 87545, USA d Babes ß-Bolyai University, Faculty of Chemistry, 11 Arany Ja ´ nos Street., RO-3400 Cluj, Romania Available online 29 March 2007 Abstract Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the com- position of (65  x)SiO 2. Æ xB 2 O 3 Æ 25Na 2 O Æ 5BaO Æ 5ZrO 2 , x = 5–15 mol%. The maximum momentum transfer of the experimental structure factor was 30 A ˚ 1 , which made available to determine the distribution function with high r-space resolution. Reverse Monte Carlo modelling was applied to calculate several partial atomic pair correlation functions, nearest neighbor distances and coordination numbers have been revealed. The characteristic features of Si–O and Si–Si distributions are similar for all glassy samples, suggesting that the Si–O network consisting of tetrahedral SiO 4 units is highly stable even in the multi-component glasses. The B–O correlations proved to be fairly complex, two distinct first neighbor distances are present at 1.40 A ˚ and 1.60 A ˚ , the latter equals the Si–O distance. Coordi- nation number distribution analyzes has revealed 3 and four-coordinated boron atoms. The O–O distribution suggests a network con- figuration consisting of boron rich and silicon rich regions. Our findings are consistent with a structure model where the boron rich network contains mostly trigonal BO 3 units, and the silicon rich network is formed by a mixed continuous network of [4] Si–O–Si [4] with several different [4] B–O–Si [4] and [3] B–O–Si [4] linkages. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.12.Ld; 61.43.Bn; 61.43.Fs Keywords: Diffraction and scattering measurements; Neutron diffraction/scattering; Modeling and simulation; Monte Carlo simulations; Oxide glasses; Borosilicates; Structure; Short-range order 1. Introduction Multi-component alkali borosilicate glasses are gener- ally accepted as suitable materials for the immobilization of high-level atomic wastes [1]. Structural characterization of these host glasses is essential for understanding of glass durability. Although several methods, like neutron and X-ray diffraction [2–7], NMR [8,9], X-ray absorption near edge structure (XANES) [10], and Raman scattering [11] proved to be successful tools to obtain information on the network structure of glassy systems, our knowledge on the multi-component glasses is very limited, so far. Due to the high number of contributing elements and the overlapping distances, it is very difficult to derive adequate structural data from diffraction experiments. Here we present a systematic neutron diffraction study of sodium borosilicate host glasses in dependence of boron content: (65  x)SiO 2 Æ xB 2 O 3 Æ 25Na 2 O Æ 5BaO Æ 5ZrO 2 , x = 5, 10, 15 mol%. Glassy specimens of similar composi- tion, but containing fewer components are also studied: 70SiO 2 Æ 25Na 2 O Æ 5BaO, 70SiO 2 Æ 30Na 2 O and vitreous v-B 2 O 3 and v-SiO 2 . Neutron diffraction measurements 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.02.030 * Corresponding author. Tel.: +36 1 3922634; fax: +36 1 3959162. E-mail address: svab@szfki.hu (E. Sva ´b). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 2084–2089