The intermediate phase: Fact or fiction?
Fluids and Materials Seminar
17th May 2018, 2:00 pm – 3:00 pm
Main Maths Building, SM2
Constraint counting theory can be used to predict macroscopic properties of glasses such as their hardness or fragility. It predicts a transition from floppy (under-constrained) to rigid (over-constrained) in the GexSe1-x (0 <= x <= 0.42) system at x = 0.2 (the composition where the material is “perfectly constrained”).
At the end of the last century a group in Cincinnati discovered by using modulated differential scanning calorimetry (MDSC) and Raman spectroscopy that there is not just one composition where the glass is perfectly constrained, but instead there is a whole range of compositions, the so-called intermediate phase, where the atoms are believed to re-organise to avoid stressed rigidity. A large number of publications followed and text books were written.
However, after the initial excitement doubts were cast as to the existence (or not) of this intermediate phase where e.g. people claim that “the intermediate phase only exists in Cincinnati”. The debate is still ongoing with heated discussions during conferences.
We have studied the GexSe1-x (0 <= x <= 0.42) in detail, using both neutron and x-ray diffraction, and MDSC. We also collated information of density, viscosity of the liquid and other properties to get a full picture of this fundamental glass forming material. The outcome will be presented in this talk.