Tkachev Sergey N, Zoller Charlie M, Kenney-Benson Curtis, Ahart Muhtar, Hemley Russell J, Novikov Vladimir N, Kojima Seiji
Center for Advanced Radiation Sources, <a href="https://ror.org/024mw5h28">University of Chicago</a>, Chicago, Illinois 60637, USA.
Department of Physics, <a href="https://ror.org/02mpq6x41">University of Illinois Chicago</a>, Chicago, Illinois 60607, USA.
Phys Rev E. 2024 Aug;110(2-1):024501. doi: 10.1103/PhysRevE.110.024501.
Amber is a unique example of a fragile glass that has been extensively aged below its glass transition temperature, thus reaching a state that is not accessible under normal experimental conditions. We studied the medium-range order of Baltic amber by x-ray diffraction (XRD) at high pressures. The pressure dependences of the low-angle XRD intensity between 0 and 5 Å^{-1} were measured from 0 to 7.3 GPa by the energy-dispersive XRD. The first diffraction peak at 1.1 Å^{-1} and ambient pressure has a doublet structure consisting of the first sharp diffraction peak (FSDP) at 1.05 Å^{-1} and the second feature at 1.40 Å^{-1}. The peak position and the width of the FSDP increase as the pressure increases, while the intensity of the FSDP decreases. Below P_{0}=2.4 GPa, the rapid increase of the FSDP peak position was observed, while above P_{0}, the gradual increase was observed. Below P_{0}, voids and holes in a relatively low-density state are suppressed, whereas above P_{0}, the suppression becomes mild. Such a change suggests the crossover from the low- to high-density state at P_{0}. There is a close correlation between the pressure dependence of XRD and previously reported sound velocity results. The correlation between the mean-square fluctuation of the shear modulus on the nanometer scale and fragility in amber and other glass formers is also discussed.
琥珀是一种独特的易碎玻璃，它在远低于其玻璃化转变温度的条件下经历了长时间老化，从而达到了在正常实验条件下无法实现的状态。我们通过高压X射线衍射（XRD）研究了波罗的海琥珀的中程有序结构。利用能量色散XRD在0至7.3 GPa范围内测量了0至5 Å⁻¹之间低角度XRD强度随压力的变化。在1.1 Å⁻¹和常压下的第一个衍射峰具有双峰结构，由1.05 Å⁻¹处的第一个尖锐衍射峰（FSDP）和1.40 Å⁻¹处的第二个特征峰组成。随着压力增加，FSDP的峰位和宽度增加，而FSDP的强度降低。在P₀ = 2.4 GPa以下，观察到FSDP峰位快速增加，而在P₀以上，则观察到逐渐增加。在P₀以下，相对低密度状态的空隙和孔洞受到抑制，而在P₀以上，抑制作用变弱。这种变化表明在P₀处从低密度状态到高密度状态的转变。XRD的压力依赖性与先前报道的声速结果之间存在密切关联。还讨论了纳米尺度上剪切模量的均方涨落与琥珀及其他玻璃形成体的脆性之间的相关性。
