Structures of lanthanum and yttrium aluminosilicate glasses determined by X-ray and neutron diffraction I. Pozdnyakova a, * , N. Sadiki b , L. Hennet a , V. Cristiglio c , A. Bytchkov d , G.J. Cuello c , J.P. Coutures b , D.L. Price a a CNRS-CRMHT, 1d avenue de la Recherche Scientifique, 45071 Orle ´ans cedex 2, France b PROMES, Rambla de la Thermodynamique, Tecnosud, 66100 Perpignan, France c ILL, 6 rue Jules Horowitz, BP 156, 38042 Grenoble cedex 9, France d ESRF, 6 rue Jules Horowitz, BP 220, 38043 Grenoble cedex, France Received 5 March 2007; received in revised form 17 November 2007 Available online 8 January 2008 Abstract We have measured the structures of lanthanum and yttrium aluminosilicate glasses by X-ray and neutron diffraction and determined the interatomic distances and nearest-neighbor coordination numbers. The results obtained with the two techniques are in good agree- ment with each other and with recent NMR studies. The Si–O and Al–O coordination numbers are found to be 4 and 4.5, respectively. All the glasses show pronounced intermediate-range order that exhibits a reduced length scale with increasing La or Y content. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.10.i; 61.12.q; 61.43.Fs Keywords: Neutron diffraction/scattering; Synchrotron radiation; X-ray diffraction; Aluminosilicates; Short-range order 1. Introduction Aluminosilicate glasses containing rare-earth element cations such as Y 3+ and La 3+ are interesting for a variety of technological applications, as well as for elucidating gen- eral principles of glass formation and structure. These glasses have unusually high glass transition temperatures (900 °C) [1–4], high hardness (8 GPa) and elastic mod- ulus (100 GPa) [5–8], and good chemical durability (nor- malized losses at high surface:volume ratio of Si, Al, and Ln 10 5 –10 7 g/m 2 J) [9–11]. Rare-earth aluminosilicate based glasses have been successfully used as a laser ion hosts, optical lenses, seals, and as in vivo radiation delivery vehicles [12]. Also these glasses, with or without small amounts of alkali modifiers, can be considered as model systems for the study of a potential matrix for the storage of long-lived actinides. The physical properties of a glass are closely related to its atomic structure. Despite their industrial importance, the information about the structure of Ln 3+ contained alu- minosilicate glasses is not complete. Generally an alumino- silicate glass is thought of as a more or less ordered network of corner-shared Si–O and Al–O tetrahedra. If no network-modifying cations (e.g.,K + , Na + , Ca 2+ , etc.) are added, then the tetrahedra are linked together by bridg- ing oxygens (BO) so that Al–O–Si chains are formed. The addition of cations leads to the formation of non-bridging oxygens (NBO) linking the Si–O and Al–O tetrahedra with ones based on cations [13]. The effect of the modifying cat- ion on the formation of NBO has been studied extensively in the case of alkali and alkali-earth modifiers ([14] and bib- liography therein). Furthermore, the coordination of the Al is questionable even for the simple SiO 2 –Al 2 O 3 system, 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.11.012 * Corresponding author. Tel.: +33 238257693; fax: +33 238638103. E-mail address: pozdnya@cnrs-orleans.fr (I. Pozdnyakova). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 354 (2008) 2038–2044