Short range structure in the amorphous As–S–Br system

Abstract The short-range structure in the amorphous As–S–Br system has been investigated through Raman spectroscopy, EXAFS, X-ray diffraction and neutron diffraction measurements using (As2S3)1−xBrx and As0.4−xS0.6Brx alloys. Raman bands relating to AsBr3 molecular units, which have not been observed in the amorphous As–Se–Br system, appear in the present As–S–Br alloys. The intensity of the Raman bands assigned to S8-ring clusters increases at larger x in amorphous (As2S3)1−xBrx alloys, reflecting that, owing to the preferential formation of the As–Br bonding, extra S atoms in the amorphous AsS3/2 network matrix associate with each other to form S8-ring clusters. Interatomic distances of As–S, As–Br and S–S pairs involved in the nearest neighbor shell in the present As–S–Br alloys are estimated to be 2.26, 2.36 and 2.05 A, respectively, by least squares fitting of observed EXAFS, and X-ray diffraction and neutron diffraction data. Further, total coordination numbers of constituent atoms in the system remain unchanged at any x and are computed to be three for As, two for S and unity for Br, respectively.