AUTHOR=Zeidler Anita , Salmon Philip S. , Whittaker Dean A. J. , Pizzey Keiron J. , Hannon Alex C. 

TITLE=Topological Ordering and Viscosity in the Glass-Forming Ge–Se System: The Search for a Structural or Dynamical Signature of the Intermediate Phase

JOURNAL=Frontiers in Materials

VOLUME=4

YEAR=2017

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2017.00032

DOI=10.3389/fmats.2017.00032

ISSN=2296-8016

ABSTRACT=<p>The topological ordering of the network structure in vitreous Ge<italic><sub>x</sub></italic>Se<sub>1−</sub><italic><sub>x</sub></italic> was investigated across most of the glass-forming region (0 ≤ <italic>x</italic> ≤ 0.4) by using high-resolution neutron diffraction to measure the Bhatia-Thornton number-number partial structure factor. This approach gives access to the composition dependence of the mean coordination number <inline-formula><mml:math id="M70" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mi>n</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:math></inline-formula> and correlation lengths associated with the network ordering. The thermal properties of the samples were also measured by using temperature-modulated differential scanning calorimetry. The results do not point to a structural origin of the so-called intermediate phase, which in our work is indicated for the composition range 0.175(8) ≤ <italic>x</italic> ≤ 0.235(8) by a vanishingly small non-reversing enthalpy near the glass transition. The midpoint of this range coincides with the mean-field expectation of a floppy-to-rigid transition at <italic>x</italic> = 0.20. The composition dependence of the liquid viscosity, as taken from the literature, was also investigated to look for a dynamical origin of the intermediate phase, using the Mauro-Yue-Ellison-Gupta-Allan (MYEGA) model to estimate the viscosity at the liquidus temperature. The evidence points to a maximum in the viscosity at the liquidus temperature, and a minimum in the fragility index, for the range 0.20 ≤ <italic>x</italic> ≤ 0.22. The utility of the intermediate phase as a predictor of the material properties in network glass-forming systems is discussed.</p>