Thursday, May 14, 2015

TOMORROW! Seminar: "Structure, Optical Properties, and Crystallization in Multicomponent Chalcogenide Glasses" by John McCloy 5.15.15/3:00-4:00pm/ CREOL RM 103

Seminar: "Structure, Optical Properties, and Crystallization in Multicomponent Chalcogenide Glasses" by John McCloy
Friday, May 15, 2015 3:00 PM to 4:00 PM
CREOL Room 103

Celebrating the International Year of Light 2015

John McCloy

The search for producible materials with simultaneous occurrence of superior thermo-mechanical properties and long-wave infrared (LWIR) transmission has been a longstanding problem in infrared ceramics engineering.  Recent research has suggested the possibility of using chalcogenide glass processing as a means to achieve breakthroughs in this area.  This talk will focus on three aspects of this problem.  1) vision and scoping experiments for fully ceramized LWIR glass ceramics based on sulfide glasses; 2) prediction methods of optical properties of multicomponent IR glasses; and 3) comparative topological effects on structural and optical properties of ternary Ge-based chalcogenide glasses. 

Long-wave Infrared Transmitting Glass-Ceramics
Three sulfide systems were explored including two with La2S3 in hopes of imparting strong bonds from this refractory sulfide, and two containing GeS2 in hopes of widening the glass-forming region. Attempts were made to produce glasses in the Ga2S3-La2S3-(ZnS,CaS) system, the GeS2-La2S3 system, and the GeS2-Ga2S3-CdS system. Microstructural and thermal analyses were used to explore nucleation and growth in these systems and infrared transmission and mechanical hardness showed potential for LWIR window use. The GeS2-Ga2S3-CdS system showed good LWIR transmission and pre-crystallized hardness superior to chemical vapor deposited ZnS. The Ga2S3-La2S3 glasses did not appear to be viable candidates at this time due to strong tendency for phase separation, a small temperature window between crystallization and glass transition temperatures, and problems with oxygen contamination in the La2S3 source. Glass formation in these materials is shown to be a strong function of quenching method and raw materials.  Suggestions are made for alternative methods for producing fully ceramized LWIR-transmitting glass ceramics. 
Optical Property Prediction in Infrared Glasses
It is often useful to obtain custom glasses that meet particular requirements of refractive index and dispersion for high-end optical design and applications.  In the case of infrared glasses, limited experimental data are available due to difficulties in processing of these glasses and also measuring refractive indices accurately.  Methods for estimating refractive index and dispersion as a function of composition for selected infrared-transmitting glasses are reviewed and evaluated, including Gladstone-Dale, Wemple-DiDomenico single oscillator, Optical basicity, and Lorentz-Lorenz total polarizability.  Various estimates for a set of PbO-Bi2O3-Ga2O3 (heavy metal oxide) and As-S (chalcogenide) glasses are compared with measured values of index and dispersion.  Problems associated with known glass topology changes and index prediction are discussed.      
Topological Effects on Properties of Ge-based Ternary Chalcogenide Glasses
Germanium based ternary chalcogenide glasses have been explored for over 50 years.  However, glass scientists are still discovering the complexities of these systems, particularly in relation to the continuum between random covalent network (RCN) and chemical ordered covalent network (COCN) structures. Recent understanding of crystal precipitation in these glass systems has aided in understanding of the medium range ordering.  In this final part of the talk, a comparison is made between the behavior of glass transition versus average coordination number for known compositions in Ge-Ga-Se, Ge-Ga-S, Ge-Sb-Se, and Ge-As-Se systems.

John McCloy, PhD, is an Associate Professor of Materials Science and Engineering at Washington State University (WSU) in the School of Mechanical and Materials Engineering
(MME). He hold degrees in Materials Science & Engineering from the Massachusetts Institute of Technology and the University of Arizona. From 2008-2013 he was a senior scientist at the Pacific Northwest National Laboratory (PNNL), for the last several years as Team Lead of Glass and Materials Science. From 2000-2008 he was with Raytheon Missile Systems working on infrared systems and materials. Dr. McCloy has held roles in line management, technology management, research and development, engineering, and manufacturing. He has worked in operations, test, and engineering organizations, and led multi-disciplinary project teams of >20 in both manufacturing and engineering research & development. His current research and teaching at WSU involves Nuclear, Optical, Magnetic, and Electronic materials, with particular focus on the effect of disordering on structure and functional properties.

For additional information:
Dr. Kathleen Richardson


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