New stable fluoroindate glasses
Introduction
Heavy metal fluoride glasses are promising materials with potential applications for infrared transmission [1], [2], [3], active devices such as fiber lasers and optical amplifiers [4] and for ionic conduction [5]. Main development focusses on fluorozirconate glasses that have been extensively studied [6] and may be drawn into low loss fibres. In some cases, there are some advantages in using glasses exhibiting low phonon energies, especially for laser transitions that are sensitive to the host vibrational energy. This is the case for the 1.3-μm emission of the Pr3+ [7] ion. Fluoroindates, which are transparent in the infrared at longer wavelengths than fluorozirconates, also have lower phonon energy: 510 cm−1 for fluoroindate glasses compared to 580 cm−1 for the standard ZBLAN glass based on the fluorides of Zr, Ba, La, Al and Na. In recent years, fluoroindate glasses have attracted much interest for this reason [7]. Since they were first reported [8], glass-forming regions have been studied in various fluoride systems based on InF3 [9], [10], [11].
The aim of this work is to define the glass compositions stable enough to give thick samples, preforms, and hopefully, optical fibers. For this purpose, new fluorides have been incorporated into glass composition and the evolution of the glass stability with respect to composition has been studied. A special emphasis was put on the substitution of gallium for indium. The influence of the GaF3 content on some physical properties is reported.
Section snippets
Experimental
Several samples were prepared by the conventional method described in Ref. [7]. Starting materials were In2O3 (99.9%), Y2O3 (99.9%), Ga2O3 (99.9%), BaF2 (>99%), SrF2 (>97%), NaF (>97%) and ZnF2 (>99%). The batches (about 6 g) were melted in a platinum crucible after weighing and mixing the various components. After a clear melt was obtained, liquid was poured into brass moulds held at a temperature 10 to 20 K below the glass transition temperature Tg—typically 280 °C. Finally, the samples were
Results
In order to identify the optimum compositions, we look for the maximum values of the thermal stability range ΔT and the stability criterion S. The starting composition for this study, expressed in mol%, is a quinternary glass [14]: 45InF3-5YF3-35BaF2-5SrF2-10NaF for which ΔT=84 K and S=1.2 K.
The glass-forming ability increases when InF3 is replaced by ZnF2 and GaF3, which also have a glass-forming ability. In the first step, 5% and 10% ZnF2 were incorporated in the base glass. Corresponding
Discussion
The methodology used in this work is based on the confusion principle. This principle expresses that glass stability increases as the number of the glass components increases. As an example, a binary glass may be prone to devitrification while composition adjustments in a ternary system will lead to a more stable glass. The starting point of this study was the ternary InF3–YF3–BaF2 system [14]. Then, additional fluorides were incorporated into glass composition according to the sequence:In Y Ba In Y
Conclusion
In this work, we have optimized the composition of the InF3-based glasses to enhance thermal stability. The stability parameter S is larger than in the starting glass and the thermal stability range Tx−Tg of this new glass is 109 K. This work confirms that increasing the number of components may enhance glass-forming ability. Glass samples as thick as 8 mm may be prepared in these multicomponent systems. For some applications such as optical fibers or bulk optics, glass stability should be
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