Nanophase separation and effects on properties of Ge–As–Se chalcogenide glasses Fang Xia a,b , S. Baccaro b , Wei Wang a , L. Pilloni c , Xianghua Zhang a , Huidan Zeng a , Guorong Chen a, * a Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China b ENEA-FIM-FIS/ION, Via Anguillarese 301, 00060 Rome, Italy c ENEA-MAT/TEC, Via Anguillarese 301, 00060 Rome, Italy Available online 19 November 2007 Abstract Nanophase separation in the bulk Ge–As–Se chalcogenide glasses was observed by SEM and supported by XRD and IR measure- ments. Effects of nanophase separation on glass transition temperature (T g ), microhardness (H v ), optical band gap (E opt ) and thermal expansion coefficient (a) were investigated in terms of glass rigidity transitions. According to the correlations between the properties and average coordination number Z, it is established that nanophase separation becomes more intensive when Z is larger than 2.64. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.10.Nz; 64.75.+g; 78.30.Hv; 81.05.Kf Keywords: Infrared glasses; Chalcogenides; Microstructure; Nano-clusters 1. Introduction Phase separation in oxide glass systems could take place under certain conditions and has been applied to prepare porous glasses, anisotropic glasses, hollow fiber mem- branes and nonlinear optic glasses, etc. [1–7]. On the other hand, non-oxide chalcogenide glasses have been intensively studied due to their unique infrared transmitting and semi- conducting properties. Particularly, microscaled phase sep- aration in multicomponent chalcogenide glasses has been of general interest in glass science and has been studied in the past decades. Applications of such studies include producing chalcogenide glass ceramics and nanocrystalline thin films etc. [8,9]. Comparatively, little attention was paid to nanophase separation in chalcogenide glasses which in fact could not only induce pronounced effects on some physical properties of glasses but also influence their per- formance for different applications. Also, nanophase sepa- rated chalcogenide glasses can find their application in producing nanocrystalline glass ceramics that can be used in nonlinear optical components and infrared transmission lenses. Such lenses would have excellent mechanical perfor- mance with uninfluenced optical transmission in the appli- cation windows (3–12 lm) [3,9–13]. Thus a good understanding of nanophase separation phenomenon in chalcogenide glasses, as well as the involved mechanism and its effects on properties is essential. So far as chalcogenide glasses are concerned, many sys- tems have been developed up to now among which Ge–As– Se glasses have attracted even greater attention due to their large glass forming region, good mechanical and thermal properties and widespread applications [13–15]. The pres- ent study focuses on nanophase separation in this system as well as effects induced thereout on properties including glass transition temperature, T g , Vickers microhardness, H v , thermal expansion coefficient, a, and optical band gap, E opt . 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.11.029 * Corresponding author. Tel.: +86 21 64252647; fax: +86 21 64253395. E-mail address: grchen@ecust.edu.cn (G. Chen). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 354 (2008) 1137–1141