Structure of the Intermediate Phase Glasses GeSe3 and GeSe4: The Deployment of Neutron Diffraction With Isotope Substitution

What is it about?

We employ neutron diffraction with isotope substitution to measure, for the first time, the full set of partial pair-correlation functions for two prototypical chalcogenide glasses, GeSe3 and GeSe4. Benchmark results are presented for guiding in the development of realistic structural models for exploring the network rigidity and other structure-related properties of the glass.

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Photo by Mihály Köles on Unsplash

Photo by Mihály Köles on Unsplash

Why is it important?

Many of the properties of glassy materials are related to the topology of their network structures. According to the mean field constraint counting theory, these network structures should undergo an abrupt transformation from an elastically floppy to a stressed-rigid phase when the mean number of bonding constraints per atom is equal to number of degrees of freedom per atom. Here, the glassy GexSe1-x system (0 < x < 1) is a testbed for exploring the structure-property relationships in network glass-forming materials, and the transformation is predicted to occur at x = 0.2 where the mean coordination number n = 2.4. More recently, temperature modulated differential scanning calorimetry experiments have been interpreted in terms of the existence of a third “intermediate" phase, i.e., a range of compositions that separate the floppy and stressed rigid regimes. The new diffraction results provide maximal information on the structure for two glass compositions that delimit the intermediate phase. They do not, however, reveal a structural origin.

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