Local atomic arrangement in Ge-As-chalcohalide glasses

Time of flight neutron diffraction measurements for (As2Se3)1-x(GeI4)x glasses with x=0 - 0.5 have been carried out to investigate details of structural units present in chalcohalide glasses, in which Ge and As coexist as cation atoms. The first sharp diffraction peak in the structure factor, S(Q), at Q=1.0 - 1.3 A-1 is clearly observed at any composition, which reveals the existence of connecting As-pyramidal and Ge-tetrahedral units in the glass. A shoulder at a larger r side of the first peak in the pair distribution function, g(r), suggests the formation of longer As-I and Ge-I bonds in the glass. These structural features correspond well to the result of Raman spectra in the present glasses. It has been made clear after the present investigation that I atoms are preferentially bonded to As atoms in the AsSe3/2 network matrix to form AsI3 molecular units, while, Ge atoms combine together with Se atoms in the matrix and remaining I atoms to form partially I-substituted GeSe4/2 tetrahedral units. (author)