Thursday, April 9, 2015

Seminar: "Tailoring crystallization in oxide glasses: Application to transparent polycrystalline ceramics and nanostructured glass-ceramics" by: Mathieu Allix 5.15.15/11:00am-12:00pm/ CREOL RM 103

Seminar: "Tailoring crystallization in oxide glasses: Application to transparent polycrystalline ceramics and nanostructured glass-ceramics" by: Mathieu Allix
Friday, May 15, 2015 11:00 AM to 12:00 PM
CREOL Room 103

Celebrating the International Year of Light 2015

Crystallization from glass can be a powerful process to elaborate innovating transparent materials for optical and photonic applications if nucleation and crystal growth steps can be precisely controlled. This talk will focus on two main applications: transparent polycrystalline ceramics elaborated by full and congruent crystallization from glass and nanostructured glass-ceramics designed from nanoscale phase separated glasses.
Transparent polycrystalline ceramics elaborated by full crystallization from glass
Transparent polycrystalline ceramics are an emerging class of photonic quality materials competing with single crystal technology for a diverse range of applications including high-energy lasers, scintillating devices, optical lenses, and transparent armor. Polycrystalline ceramics offer several advantages, particularly in the fabrication of complex shapes and large-scale industrial production, and enable greater and more homogenous doping of optically active ions than is possible in single crystals. However, up to date, only a limited number of such materials has been reported. These are either cubic or nanocrystalline transparent polycrystalline ceramics which require complex, time-consuming and so expensive synthetic approaches.
Our recent work shows the possibility to obtain transparent polycrystalline ceramics by full and congruent crystallization from glass. Transparency is observed despite micrometer scale crystals and a non cubic symmetry (no structural isotropy) of the crystalline phase. Interestingly, crystallization from glass can give access to new crystalline phases given the relatively low crystallization temperature compared to classic solid state elaboration temperature. This is demonstrated in the case of a new composition, BaAl4O7, showing the existence of two orthorhombic polymorphs both showing high transparency in the visible and infra-red ranges [1,2]. The crystallographic structures of these polymorphs have been determined ab initio from powder diffraction data. From these structural models, the optical birefringence has been obtained by DFT calculations of the dielectric function. These results enable to discuss the transparency property of these materials as a function of the determined crystalline structures and the observed microstructures. Remarkably, these materials show promising scintillation properties when doped by europium [3]. The same elaboration process has been applied to cubic compositions, Sr3Al2O6 and Sr3Ga2O6, allowing very high transparencies to be attained [4]. Lastly, we have focused our work on strontium aluminosilicate compositions, the addition of silica enabling large scale glass samples to be obtained. The full and congruent crystallization of Sr1+x/2Al2+xSi2-xO8 compositions leads to new transparent polycrystalline ceramics forming a crystalline solid solution exhibiting hexagonal symmetry. These materials show an impressive transmittance higher than 90%, which sets a transparency record for oxide ceramics. A crystallographic study coupled to NMR experiments and DFT calculations of the birefringence allowed us to evidence the role of structural disorder (Al/Si substitution and presence of vacancies on strontium sites) in the origin of the optical isotropy observed in these structurally anisotropic materials. These results propose an innovative concept, the addition of a controlled structural disorder within crystalline structures, in order to lower the birefringence and to elaborate new transparent ceramics [5].

New nanostructured gallogermanate- and gallosilicate-based glass materials exhibiting high transparency in the visible range have been fabricated by conventional melt-quenching. These materials can accommodate wide oxide compositions and present nanoscale phase separation. The size of the nanostructuring can be tailored depending on the nominal composition. A single heat treatment then allows selective crystallization of the phase separated glass, resulting in glass-ceramic materials exhibiting nanostructures and transparency similar to the parent glass.[6,7]
The wide possibilities of designing new nanostructured glass-ceramics with tunable optical properties will be illustrated in the case of a highly transparent ZnGa2O4 glass-ceramic exhibiting 50 wt% of nanocrystals with homogeneous and tunable sizes. High resolution scanning transmission electron microscopy analysis coupled with in situ high temperature X-ray diffraction and optical measurements led to a detailed description of the crystallization process. Remarkably, red long-lasting luminescence arising from the entire sample volume is observed in this Cr3+ doped material, opening the route to a wider range of performing applications for this famous zinc gallate persistent phosphor.[8,9]

1. M.Allix, S.Alahrache, F.Fayon, M.Suchomel, F.Porcher, T.Cardinal, G.Matzen, Highly Transparent BaAl4O7 Polycrystalline Ceramic Obtained by Full Crystallization from GlassAdvanced Materials, 24 5570-5575 (2012)
2. "Transparent aluminate glass, glass-ceramics and ceramics", International patent deposited 1/12/2011, published 6/6/2013, WO2013079707 A1, PCT international extension PCT/EP2012/074171, US20140336032 13/11/2014.
3. G.Patton, F.Moretti, A.Belsky, K.Al Saghir, S.Chenu, G.Matzen, M.Allix, and C.Dujardin, Light yield sensitization by X-ray irradiation in BaAl4O7 : Eu2+ ceramic scintillator obtained by full crystallization from glassPhysical Chemistry Chemical Physics., 16 24824 (2014)
4. S.Alahraché, K.Al Saghir, S.Chenu, E.Véron, D.De Sousa Meneses, A.I.Becerro, M.Ocaña, F.Moretti, G.Patton, C.Dujardin, F.Cussó, J-P.Guin, M.Nivard, J-C.Sangleboeuf, G.Matzen, M.Allix, Perfectly transparent Sr3Al2O6 polycristalline ceramic elaborated from glass crystallizationChemistry of Materials, 25 4017-4024 (2013)
5. K.Al Saghir, S.Chenu, E.Veron, F.Fayon*, M.Suchomel, C.Genevois, F.Porcher, G.Matzen, D.Massiot and M.Allix*, Transparency through Structural Disorder: A New Concept for Innovative Transparent CeramicsChemistry of Materials, 27 508-514 (2015)
6. "Nanostructured glass and glass-ceramics transparent in the visible and infrared ranges"International patent deposited 28/02/2014, published 4/9/2014, WO2014131881 A1, PCT in progress, PCT/EP2014/053932.
7. S.Chenu, E.Véron, C.Genevois, G.Matzen, T.Cardinal, A.Etienne, D.Massiot, M.Allix, Tuneable Nanostructuring of Highly Transparent Zinc Gallogermanate Glasses and Glass-CeramicsAdvanced Optical Materials, 2 364 (2014)
8. S. Chenu, E. Veron, C. Genevois, A. Garcia, G. Matzen, M. Allix, Long-lasting luminescent ZnGa2O4:Cr3+ transparent glass-ceramics,Journal of Materials Chemistry C, 2 10002-10010 (2014)
9. M.Allix, S.Chenu, E.Véron, T.Poumeyrol, E.A.Kouadri-Boudjelthia, S.Alahraché, F.Porcher, D.Massiot, F.Fayon, Considerable improvement of long-persistent luminescence in germanium and tin substituted ZnGa2O4Chemistry of Materials, 25 1600–1606 (2013)
Keywords: Glass crystallization, transparent polycrystalline ceramics, transparent glass-ceramics, phase separation, structure determination from powder diffraction, long lasting luminescence, scintillation, Transmission electron

Dr. Mathieu Allix is a CNRS researcher in material chemistry in Orléans, France. He received his PhD from the University of Caen in 2004 and eventually moved to a 3 years postdoctoral position in Liverpool, UK under the supervision of Matt Rosseinsky. His research focuses on crystallization in oxide glasses with an application to transparent polycrystalline ceramics elaborated by full and congruent crystallization from glass and nanostructured glass-ceramics designed from nanoscale phase separated glasses. He is author of over 70 publications and recently received the CNRS bronze medal award.

For additional information:
Dr. Kathleen Richardson

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