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

Stoichiometric Ge-poor (<50% GeS2) GeAsPS glasses, as well as GeAsPS glasses 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 properties and nuclear magnetic resonance (NMR) spectra of the stoichiometric glasses indicates that tetrahedral SPS3/2 groups constitute the dominant P species. 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 (As,P)4S3 species, respectively, whereas those of variable S glasses with S deficits ⩽15% show a high frequency band indicating the presence of tetrahedral SPS3/2 groups. NMR spectra of glasses with S deficits of 7–15% are dominated by a 31P resonance at about 117 ppm that is assigned to trigonal PS3/2 groups. NMR spectra of glasses with S deficits ⩾10% have a 31P 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 associate with As instead of Ge as next nearest neighbors.