Intermediate-range order and the liquid ↔ glass transformation

Various experiments suggest that intermediate-range order (IRO) is a constitutive property of disordered condensed matter. Here IRO designates the existence of a correlation of properties of the material (e.g. moduli and structure) over a spatial scale somewhere between roughtly 10 and 100 Angstrom. We focus on experimental evidence from the boson peak (BP) of inelastic scattering (light and neutrons). Here we address the functions which IRO may have, namely to couple low-energy modes strongly with each other in the glass, to offer a structural skeleton that allows both relaxations and vibrational excitations to occur (in the liquid and glass respectively including a continuous switch between them) and to stabilize the undercooled melt with respect to the crystal phase (thermodynamically and kinetically). Considering the vibrational and relaxational fluctuation amplitudes [x(2)] in the energy region of the BP, we are led to a scenario for the liquid <----> glass transformation based on coupling of modes which are (quasi)localized on the IRO scale.