Upper bound of fragility from spatial fluctuations of shear modulus and boson peak in glasses

It is shown that the normalized rms fluctuation of the shear modulus on the medium-range order scale in glasses correlates with fragility: the higher fragility, the smaller the fluctuation amplitude. The latter is calculated within the heterogeneous elasticity theory using the data on the boson peak in glasses. On a smaller scale corresponding to cooperative structural relaxation, the normalized rms fluctuation of the infinite-frequency shear modulus was estimated using the data on the decoupling of viscosity and diffusion in supercooled liquids. These fluctuations are much smaller in amplitude, and, in contrast, they increase with increasing fragility. Extrapolation predicts intersection of both rms fluctuations and disappearing of the boson peak at the upper limit to fragility asymptotic to 180.

Automated summary

Research shows that normalized rms fluctuation of shear modulus in glasses correlates with fragility, with higher fragility leading to smaller fluctuations on a medium range scale, while on a smaller scale, fluctuations are much smaller in amplitude and may either increase or decrease with increasing fragility. Extrapolation predicts the disappearance of the boson peak at an upper limit to fragility asymptotic to 180.