Optical and mechanical properties of far infrared transmitting glass–ceramics Shizhen Zhu a , Hongli Ma a , Laurent Calvez a , Xianghua Zhang a, * , Jacques Lucas a , Jean-Luc Adam a , Haixia Shang b , Tanguy Rouxel b a UMR CNRS 6512 ‘Verres et Ce ´ramiques’, Universite ´ de Rennes I, Campus de Beaulieu, 35042 Rennes cedex, France b LARMAUR, FRE-CNRS 2717, Universite ´ de Rennes I, Campus de Beaulieu, 35042 Rennes cedex, France Available online 26 March 2007 Abstract We have studied the mechanical properties of a new family of infrared transmitting glass–ceramics based on the GeS 2 –Sb 2 S 3 –CsCl system. Cs-based crystals have been generated inside the glass matrix and the crystal size is controlled to be less than 100 nm in order to keep the transparency of the composite materials. The presence of crystals leads to significant increase of the fracture toughness and the critical load for crack initiation. The increases depend on the type and on the size of crystals. Other mechanical properties such as Young’s modulus, Shear modulus are much less sensitive to these crystals. Ó 2007 Elsevier B.V. All rights reserved. PACS: 42.70.Km; 81.05.P; 82.40 Keywords: Nanocrystals; Chalcogenides; Indentation; Microindentation; Scanning electron microscopy; FTIR measurements; Infrared properties 1. Introduction Chalcogenide glasses are glass based on sulphur or/and selenium or/and tellurium, mostly associated with germa- nium, arsenic or antimony. They are widely studied for dif- ferent applications such as infrared laser power delivery, thermal imaging and chemical sensing. The most interest- ing property of these materials is their wide transmission from visible to far infrared region. This large optical win- dow is unfortunately associated with the relatively weak chemical bond, leading to weaker materials compared to oxide glasses for example. One possible way to improve the mechanical perfor- mance of glasses is to fabricate composite materials such as glass–ceramics which are currently largely used in vari- ous applications such as telescope mirror and cooking tops. Glass–ceramics are defined here as glasses containing crys- tals and are generally made by controlled nucleation and crystallisation [1–5] of the parent glass. Oxide based glass–ceramics are generally studied for their excellent ther- mal and mechanical properties. Optical properties of glass– ceramics have been largely ignored for a long time because of the notion that glass–ceramics will never be transparent enough for application. For making transparent glass– ceramics, it is essential to control the size for crystal in order to minimize the optical losses due to scattering induced by the presence of crystals [6,7]. More recently, many studies on oxyfluoride glass– ceramics have been performed [8–11]. The idea is to benefit from the excellent chemical, thermal and mechanical prop- erties of oxide glasses, and also from the low phonon energy crystalline environment for rare earth doping, lead- ing to high quantum efficiency. The crystallisation of chalcogenide glasses have been intensively studied [12–14]. It is however not possible to control the crystal growth inside these glasses and big crys- tals are generally obtained, leading to completely opaque materials. It is difficult to make reproducible glass–ceram- ics from pure chalcogenide glasses. 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.10.075 * Corresponding author. Tel.: +33 223236937; fax: +33 223235611. E-mail address: xzhang@univ-rennes1.fr (X. Zhang). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 1298–1301