Small-angle X-ray scattering and Rayleigh scattering studies of the microstructure of some optical glasses F. Geotti Bianchini a , P. Riello b , A. Benedetti b, * a Stazione Sperimentale del Vetro, 30141 Murano-Venezia, Italy b Dipartimento di Chimica Fisica, Univ. di Venezia, Calle Larga S. Marta 2137, 30123 Venezia, Italy Received 24 June 1998; received in revised form 30 March 1999 Abstract Several optical glass samples were studied by small-angle X-ray Scattering (SAXS) in order to verify the presence of inhomogeneity in the range (1–100 nm). The results were compared with Rayleigh scattering measurements in order to verify a possible correlation between microstructure and scattering losses. For most glasses investigated, the presence of phase separation was excluded and the Rayleigh scattering intensities were attributed to refractive index fluctuations. For glasses ZKN7 and SK11 evidence of phase separation, with size of about 8 nm and less than 2 nm respectively, was obtained using SAXS. The particle size was insensitive to annealing treatments in the case of SK11 and showed a continuous growth with annealing time at 610°C in the case of ZKN7. For these two glasses the overall Rayleigh scattering intensity includes a contribution due to the presence of phase separated particles. Ó 1999 Elsevier Science B.V. All rights reserved. 1. Introduction Rayleigh scattering in optical glasses should be minimized to limit intensity losses. The Rayleigh (elastic) scattering originates at each wavelength in media with fluctuations of the refractive index in microscopically small volumes. The equations de- scribing the intensity of scattered light contain the relative refractive index n  n p =n m (i.e. the ratio between the refractive index of the scattering particle n p and of the matrix n m [1]). Theories to describe the Rayleigh scattering vary according to the ratio between particle size and the wavelength of light [1]. The overall light scattering intensity at each wavelength is the sum of all the intensities caused independently by each event. According to M orixbauer and Steinert et al. [2,3] the intensity of Rayleigh scattering in optical glasses varies in a broad range. In principle such scattering can be caused by various glass features with refractive index fluctuations including: (a) density and concentration fluctuations [4]; (b) metastable phase separation associated with amorphous particles generally in the range 1– 100 nm [5]; (c) technological inhomogeneities (melting rem- nants caused by refractory and metal (Pt) parti- cles and microbubbles, generally in the micrometer range) [6]. Each of these events is associated with some type of deviation from the ideal (fully random and homogeneous) liquid structure and gives rise to Journal of Non-Crystalline Solids 258 (1999) 198–206 www.elsevier.com/locate/jnoncrysol * Corresponding author. Tel.: +39-041 257 8544; fax: +39-041 257 8594; e-mail: benedett@unive.it 0022-3093/99/$ - see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 9 9 ) 0 0 5 4 3 - 8