New fluoroindate glass compositions
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A. Soufiane and M. Poulain Centre d'Etude des Materiaux Avances, Av. General Leclerc, Universite de Rennes, Beaulieu, 35042, Rennes Cedex, France (Received 27 May 1992; accepted 14 December 1992)
The limits of glass formation of new fluoroindate glass compositions have been determined for the basic systems InF 3 -BaF 2 -GdF 3 -20ZnF 2 -20SrF 2 -2XF,, where X = Na, La and InF 3 -BaF 2 -20ZnF 2 -20SrF 2 -2GdF 3 -XF,,, where X = Ca and Y. The incorporation of small amounts of GaF3 and/or GdF 3 increases strongly the thermal glass stability. All the fluoroindate compositions studied are highly transparent in the mid-infrared range; their transmission edge is shifted beyond 7 fim and the theoretical attenuation coefficient, extrapolated at the CO laser wavelength emission, is typically a = 100 dB/km. Large bulks and preforms have been prepared allowing the drawing of optical fibers.
I. INTRODUCTION Among the many compositions tested to improve the physical properties of Heavy Metal Fluoride Glasses (HMFG), it was found recently that InF3-based systems allowed glasses with better forming ability and better optical properties to be prepared. 12 These new compositions are emerging as one of the major groups of the HMFG glass family. These glasses present a theoretical minimum value of the optical attenuation in the infrared region lower than that of the fluorozirconate compositions, and their absorption edge is shifted toward longer wavelength, beyond 7 fim. Therefore, they offer potential applications for the realization of optical fibers for the power delivery of CO laser which emits at ~ 5 fim. Various ternary, quaternary, and quinternary systems with indium fluoride as the main constituent have already been investigated. The most stable compositions were initially found in the InF 3 -ZnF 2 -BaF 2 -SrF 2 -CdF 2 system,2'3 which allows the casting of rather large samples. Although these glasses show enhanced thermal stability compared to the standard fluorozirconate [e.g., ZBLAN (ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF)], it was not possible till now to draw fibers due to crystallization of the preform during the process. Consequently, better InF3-based compositions with lower devitrification rates are necessary. Mitachi et al.A have studied the effect of small (up to 3%) GdF 3 addition to fluorozirconate standard compositions and found a drastic improvement of the stability and devitrification process for these glasses, making these compositions the best for fiber drawing. J. Mater. Res., Vol. 8, No. 4, Apr 1993 http://journals.cambridge.org
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Using a similar approach, we investigated the thermal stability and the optical properties of several InF 3 based compositions containing a small amount of GdF 3 . The glass stability has also been drastically improved and the crystallization rates reduced significantly. Some compositions are shown to be adequate for the fabrication of optical fibers.
II. EXPERIMENTAL The basic starting materials used for this study were ZnF 2 from Merck, BaF 2 and SrF2 from B.D
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