The effect of phosphorus on the properties and structure of GeAsS glasses

Stoichiometric Ge-poor (< 50% GeS2) GeAsPS glasses, as well as GeAsPS glass es with a fixed Ge:As:P ratio of 5:1:1 and S contents ranging from 56%, to 74%, were synthesized. The compositional dependence of the physical propert ies and nuclear magnetic resonance (NMR) spectra of the stoichiometric glas ses indicates that tetrahedral S = PS3/2 groups constitute the dominant P s pecies. On reducing the S content, the absorption edge of variable S GeAsPS glasses remains constant until S deficits of about 25% are attained. Raman spectra of stoichiometric and S-deficient glasses show bands attributed to As2P2S8 and (As1P)(4)S-3 species, respectively, whereas those of variable S glasses with S deficits less than or equal to 15% show a high frequency b and indicating the presence of tetrahedral S = PS3 .2 groups. NMR spectra o f glasses with S deficits of 7-15'% are dominated by a P-31 resonance at ab out 117 ppm that is assigned to trigonal PS3/2 groups. NMR spectra of glass es with S deficits greater than or equal to 10% have a P-31 resonance near -100 ppm, indicating that tetrahedral S = PS3/2 and trigonal PS3 .2 groups are replaced by species containing P-P and, ultimately, P-(Ge, As) bonds as the S content of these glasses decreases. Comparison of these results with those for GeAsS glasses demonstrates that P-P bonds form preferentially to metal-metal bonds containing either Ge or As, and that P tends to associat e with As instead of Ge as next nearest neighbors. (C) 2001 Elsevier Scienc e B.V. All rights reserved.