A STRUCTURAL STUDY OF GLASSES IN THE AS2S3-SB2S3-TL2S SYSTEM

The local structure around As for glasses in the system As2S3-Sb2S3-Tl 2S has been studied by measuring the extended X-ray absorption fine st ructure (EXAFS) at the As K edge and by differential scanning calorime try. The variation of the EXAFS parameters and of the glass transition temperature as a function of the Sb2S3 concentration has been analyze d for three systems containing 0, 20 and 40 mol% Tl2S. For all the gla sses, As is found to be surrounded by 3 +/- 0.2 sulfur atoms. The main trends in the variation of the average As-S interatomic distance and the Debye-Waller factor are explained in terms of a simple structural model involving AsS3 and SbS3 pyramidal units. The pyramids are linked by the S atoms (bridging sulfur atoms) or are not linked (non-bridgin g sulfur atoms) depending on the Tl2S content. The effect of the addit ion of Tl2S has been confirmed by a study of glasses in the As2S3-Tl2S system.