Molecular Phase Separation and Cluster Size in Germanium-Selenide Glass.

The chalcogen site in bulk glasses of GeSe(,2) has been probed by nuclear quadrupole interactions in ('129)I emission and ('125)Te absorption Mossbauer spectroscopy and by the local vibrational modes in Raman spectroscopy. Two distinct types of chalcogen (Te) sites (A and B) are observed. These B-sites, which are found even in the stoichiometric GeSe(,2) glass, are identified as homopolar bonds which break the chemical order of the glass network. The compositional dependence of the Mossbauer site intensity ratio I(,B)/I(,A)(x) and the Raman scattering strength ratio A(,1)('c)/A(,1)(x) reveal a power-law variation which requires that the homopolar bonds are not randomly distributed in the network but are located at the edges of characteristic clusters. The cluster morphology is based on the raft-like fragments of the layered structure of crystalline (beta)-GeSe(,2). The characteristic size of these clusters is found to be 50 to 75 A.