New Stable Iodide Glasses in the Cd-As-I and Cd-As-Ge-I Systems
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NEW STABLE IODIDE GLASSES IN THE Cd-As-I AND Cd-As-Ge-I SYSTEMS JONG HEO AND GEORGE H. SIGEL, Jr. Fiber Optic Materials Research Program, Rutgers, The State University of New Jersey, Piscataway, NJ 08855 ABSTRACT Iodide glasses presently being investigated suffer from their poor glass forming abilities, thermal instabilities and general lack of chemical durability. Glasses in the Cd-As-I and Cd-AsGe-I systems are investigated in this study for the purpose of developing water-resistant, thermally stable iodide glasses and optical fibers. Differential scanning calorimetry(DSC) showed that glasses in these systems have glass transition temperature(Tg) values above 300*C. Devitrification of glasses during cooling and reheating can be suppressed by incorporating small amount of Ge atoms into ternary Cd-As-I glasses. They are transparent up to 141trm in the infrared region with excellent durability against liquid water at 90°C. INTRODUCTION Recently there has been considerable interest in the development of new halide glasses for the optical fiber materials which operate at the mid-infrared region. Most of the research activities has been focused on the ZrF4-based glasses[l] due to their practical implications for long-distance, repeaterless fiber optic communications. However, fluoride glasses are composed of light elements and their vibrational absorption becomes so high that infrared light is strongly absorbed beyond 7gm. Thus, for the applications requiring high transparency in the far-infrared region (8-14gm), non-fluoride halide glasses such as chloride, bromide and iodide glasses seem to offer greater potential. ZnC12 was the first chloride glass discovered over 50 years ago[2] and since then, a large number of glass-forming systems have been reported on various combinations of halides. Shultz[31 reported several binary glasses based on ZnBr2 containing KCI, KBr or KI as the second component. Hu et al.[4] observed that ZnBr2 glass is transparent up to 204m but with poor chemical and thermal durability. A class of various chloride glasses based on BiC13 has been described by Angell and Ziegler[5]. Glasses in the BiC13-KC1, BiCI3-KCI-PbC12 have
glass transition temperature(Tg) values in the range of 25"C to 57"C. Several glass-forming iodide systems have also been reported by Nasu et al.[6], Cooper and Angell[7] and Nishii et al.[8] over the last several years. For instance, Cooper and Angell[7] proved that CdI2-based glasses exhibit high far-IR transmittance with much improved moisture resistance compared to chloride glasses but with low Tg values in the range of 10"C - 35"C. A comprehensive review on the glass-forming systems and properties of non-fluoride halide glasses can be found elsewhere[9]. In general, none of these previous glasses have been attractive for practical applications as optical materials. Most of them exhibit very low Tg values ranging from 120*C down to below room temperature. In addition, they are extremely sensitive to the moisture and do not last any
longer than a few days in the ambient
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