Mathieu Rozé

Structural Investigations of Glass Ceramics in the Ga2S3―GeS2―CsCl System

Transparent glass ceramics have been prepared in the Ga(2)S(3)-GeS(2)-CsCl pseudoternary system using appropriate heat treatment time and temperature. In situ X-ray diffraction at the heat treatment temperature and (133)Cs and (71)Ga solid-state nuclear magnetic resonance have been performed in function of annealing time to understand the crystallization process. Both techniques have evidenced the nucleating agent role played by gallium with the formation of Ga(2)S(3) nanocrystals. On the other hand, cesium is incorporated very much later into the crystallites during the ceramization. Moreover, the addition of CsCl, which is readily integrated into the glassy network, permits us to shift the optical band gap toward shorter wavelength. Thus, new glass ceramics transmitting in the whole visible range up to 11.5 mum have been successfully synthesized from the (Ga(2)S(3))(35)-(GeS(2))(25)-CsCl(40) base glass composition.

Similar behaviors of sulfide and selenide-based chalcogenide glasses to form glass ceramics

In this paper, the strong influence of alkali halide in chalcogenide glasses is reminded, leading for the first time to highly transparent glasses from the visible range up to 11μm. The behavior of crystallization has been demonstrated to be similar in sulfide and selenide glasses containing gallium as well. The structural evolution of several glass compositions from the Ge-Ga-S or Ge-Ga-Se systems leading to reproducible glass ceramics has been studied by XRD, NMR and thermal analysis. Whatever the composition, gallium plays a fundamental role as nanosized domains appear by phase separation between Ge rich regions and Ga rich regions. The determination of the appropriate crystallization time and temperature has permitted to obtain new passive and active glass-ceramics with a broadened transmittance region thanks to the incorporation of various alkali halides. In the first case, the controllable generation of nanocrystals leads to an increase of the main thermo-mechanical properties. In the second case, the incorporation of rare-earth ions inside the glass ceramics has exacerbated their photoluminescence properties. The possibility to combine the ceramization process with the shaping has also been demonstrated.