LOCAL ATOMIC ARRANGEMENT IN GE-TE AND GE-S-TE GLASSES

X-ray diffraction and Raman spectroscopic studies have been made on Ge xTe1-x (x = 0.16-0.20) and Ge(S1-xTex)(2) (x = 0-0.75) glasses. The po sition and width of the first peak in g(r) in Te-enriched Ge-Te glasse s vary with composition, suggesting that the nearest neighbor shell in the glass contains more than one atomic correlation, namely Ge-Te and Te-Te. It was indicated by a least squares analysis of intensity func tions that each Ge atom is surrounded by four Te atoms, implying that the chemically ordered 4-2 coordination model is favored in Ge-Te glas ses. Results of both the Raman spectrum and diffraction intensity anal ysis on Ge(S1-xTex)(2) glasses show that basic structural units in the glasses are anion-mixed tetrahedra, Ge(S-(4-n)/Te-2(n/2)) type where it = 0 similar to 4, with a Ge atom in the central site. The results a gree with the case in Ge(S1-xSex)(2) glasses. However, S-enriched anio n-mixed units, for example, n = 1 or 2 type, are not formed in the pre sent telluride glass, due to a considerable difference in atomic size between S and Te.