A COMPARISON OF THE MEDIUM-RANGE ORDER IN GLASSY GES2 AND SB2S3

In amorphous (a-) GeS2 there is only one medium-range order (MRO) dependent X-ray scattering feature, i.e., the 'first sharp diffraction peak' (FSDP), whereas in a-Sb2S3 all scattering features in the interval 1-2.4 angstrom-1 are in fact MRO-dependent. The basic element of MRO in a-GeS2 is a part of a chain of comer bound tetrahedra extracted from the high temperature form of c-GeS2; in a-Sb2S3 it is a part of a crystalline-like (Sb2S3)n band. Ordering of parts of these bands is characterized by a greater interband separation than in the crystal. By contrast with a-GeS2, the MRO-dependent medium-angle scattering features in a-Sb2S3 are less sensitive to fluctuations of the interband (intercluster) ordering distance.