MICROSTRUCTURE AND THERMAL-STABILITY OF AMORPHOUS MATERIALS IN THE GES2-LA2S3 SYSTEM

GeS2 is known to be a good chalcogenide glass former with a transmission cutoff at 11-mu-m and has been studied for fiber optic application in the mid infrared region. The rare earth sulfides, oxysulfides, and oxides (La-Er) form reasonably good and stable glasses when mixed with chalcogenides such as Ga2S3. In this work, glass formation was studied in the GeS2-La2S3 system. Two compositions containing 60 mol % and 92.5 mol % GeS2, respectively, were analyzed, and the effects of composition on the microstructure and thermal stability of these glasses were investigated. Microstructural studies were conducted on the as-prepared and heat-treated glasses using TEM and SEM/EDXA. Glasses rich in GeS2 exhibited primary (6-88 nm) and secondary (3-13 nm) phase separation at the molecular level. Differential thermal analysis performed on these glasses indicated glass transition temperatures (T(g)) of 510-degrees-C and 420-degrees-C for the two compositions studied. The glasses were stable and the (T(g)) was observed to decrease with increasing contents of GeS2 in these glasses.