Institut Lumière Matière, Université Lyon 1, CNRS, UMR 5306, F-69622 Villeurbanne Cedex, France.
J Chem Phys. 2013 Aug 14;139(6):064506. doi: 10.1063/1.4817778.
In glass, starting from a dependence of the Angell's fragility on the Poisson ratio [V. N. Novikov and A. P. Sokolov, Nature 431, 961 (2004)], and a dependence of the Poisson ratio on the atomic packing density [G. N. Greaves, A. L. Greer, R. S. Lakes, and T. Rouxel, Nature Mater. 10, 823 (2011)], we propose that the heterogeneities are predominantly density fluctuations in strong glasses (lower Poisson ratio) and shear elasticity fluctuations in fragile glasses (higher Poisson ratio). Because the excess of low-frequency vibration modes in comparison with the Debye regime (boson peak) is strongly connected to these fluctuations, we propose that they are breathing-like (with change of volume) in strong glasses and shear-like (without change of volume) in fragile glasses. As a verification, it is confirmed that the excess modes in the strong silica glass are predominantly breathing-like. Moreover, it is shown that the excess breathing-like modes in a strong polymeric glass are replaced by shear-like modes under hydrostatic pressure as the glass becomes more compact.
在玻璃中，我们从安杰尔（Angell）易碎性依赖泊松比[V. N. Novikov 和 A. P. Sokolov，《自然》431,961（2004）]和泊松比依赖于原子堆积密度[G. N. Greaves、A. L. Greer、R. S. Lakes 和 T. Rouxel，《自然材料》10,823（2011）]这两个事实出发，提出在强玻璃（较低泊松比）中，非均匀性主要是密度波动，而在脆性玻璃（较高泊松比）中，非均匀性主要是剪切弹性波动。由于与这些波动强烈相关的低频振动模式的过剩，我们提出它们在强玻璃中是呼吸式（体积变化）的，而在脆性玻璃中是剪切式（体积不变）的。作为验证，我们确认了强二氧化硅玻璃中的过剩模式主要是呼吸式的。此外，我们还表明，随着玻璃变得更加紧密，在强聚合物玻璃中，过剩的呼吸式模式在静水压力下被剪切式模式所取代。
