Direct Evidence for Intrinsically Broken Chemical Ordering in Melt-Quenched Glasses

Rigidity Transition in Chalcogenide Glasses

“…These atoms usually take on a 2-fold coordination with a pair of electrons forming a non-bonding lone pair. Te as a dopant in selenide and sulfide glasses or crystals can replace the lighter chalcogen atoms in the backbone, and serve as a probe of their local bonding chemistry, as elegantly illustrated 7,28 by Mössbauer emission spectroscopy using parent as a dopant through nuclear quadrupole interactions 28 . The covalent radius of Te (1.36Å) is 17% larger than that of Se (1.16Å).…”

“…These include absorption spectroscopy as a vibrational probe 39 of Ge (cation sites) and emission spectroscopy as a chemical probe 7,28 of Se (anion sites) of the network backbone. We comment on the results of these experiments separately.…”

“…The former site is identified with an iodine species to a Ge nearest neighbor (nn), while the latter site to an I to a Se nn. In a Se glass only B-type of a local environment is expected while in a chemically ordered network only A-type of a local environment is expected as discussed elsewhere 7,28 . The Mössbauer site intensity ratio variation deduced from the experiments appears in Fig.…”

“…Some of these anomalies are elastic in origin, some vibrational in character, others structure related 7,28 . While still others 23 29 such as the activation energy for stress relaxation , non-radiactive decay rates of guest molecules and the semiconductor to metal transition pressures 10 , collectively point towards an unusual morphological state of matter in the transition region.…”

“…I spectra of bulk glasses can be deconvoluted 7,28 into two chemically inequivalent local environments, labelled as sites A and B. The former site is identified with an iodine species to a Ge nearest neighbor (nn), while the latter site to an I to a Se nn.…”