Property-Composition Relationship of Chalcogenide Glasses Containing Germanium
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PROPERTY-COMPOSITION RELATIONSHIP OF CHALCOGENIDE GLASSES CONTAINING GERMANIUM JAY J.L. YI* and PETER R.STRUTT The University of Connecticut, Institute of Materials Science, Storrs, CT 06269, U.S.A. *now with Circon ACMI Corp., Stamford, CT 06904. ABSTRACT In-depth studies of property-composition relationship in chalcogenide glasses have revealed some interesting structural features. For example, specific discoveries in the Ge-Se-Sb and meta-stable phase separation for similar systems were of (i) glasses with a high Se or S content ( >70 at.% ), and (ii) abnormal behavior of some structure-sensitive properties ( e.g. optical band-gap energy ) for glasses with Se or S in the range of 60-70 at.%. In carefully studying the Ge-Se system, the liquidus curve ( reported by H.Ipser et al, 1982 ).was reexamined ; this was found to have an S-shape at the phase-separation region. Another interesting finding was the dependence of the band-gap energy on composition in (l-x)GeSe2 xSb2Se3 glasses; this was not a linear relation but a curve with a maximum band-gap energy at 9 at.% Sb. INTRODUCTION Chalcogenide glasses have been researched to assess their suitability as passive optical components and fiber optic waveguides in the mid-infrared range, because of their good transparency in 8-12gm region, and their relatively good thermal, mechanical and chemical properties. Germanium is often introduced into these glasses, because GeS2 and GeSe2 are themselves glass-formers, and the glasses containing germanium have improved technological properties. The present work was performed to obtained some property-compositionstructure relationships of these chalcogenide glasses. The Ge-Se-Sb glass system has been selected as an example due to its importance to practical use. Fig.l is the Ge-Se-Sb phase diagram [E], in which the composition region of glass formation is indicated. Glasses with Se content >70 at.% show a tendency to meta-stable phase separation [2]; while glass melts with Se content less than 60 at.% devitrify readily during cooling. Glasses of practical interest are those with Se content 60-70 at.%. Sb2Se 3 itself does not form glass; the compositions most favourable to glass-formation are those within the GeSe2 crystalline field and near to the boundary line with Sb2Se 3 phase. The experiment work consists chiefly of two parts. For glasses with high Se or S content, the meta-stable phase separation was examined; and for glasses with 60-70 at.% S or Se, some properties sensitive to glass structure were studied. META-STABLE PHASE SEPARATION In the authors' previous work [2], the phase separation phenomenon of Ge-Se glasses was examined directly under scanning electron microscope [2]. It was found that the morphology of the micro-phase components changes with decreasing Se-content:
Mat. Res. Soc. Symp. Proc. Vol. 172. @1990 Materials Research Society
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so Fig.1 Glass formation region in Ge-Se-Sb phase diagram
GoSe crystalline
immiscibdity Gap
T00 T('.)
(a)
600
400
(b)
200
100 Fig.2
SEM micrograph of Ge20Se8O glass
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