Department of Physics, Washington University in St. Louis, St. Louis, Missouri 63130, USA.
J Chem Phys. 2018 May 28;148(20):204509. doi: 10.1063/1.5032319.
Previous studies reported a number of anomalies when estimates of linear thermal expansion coefficients of metallic liquids and glasses from x-ray scattering experiments were compared with direct measurements of volume/length changes with temperature. In most cases, the first peak of the pair correlation function showed a contraction, while the structure factor showed an expansion, but both at rates much different from those expected from the direct volume measurements. In addition, the relationship between atomic volume and the characteristic lengths obtained from the structure factor from scattering experiments was found to have a fractional exponent instead of one equal to three, as expected from the Ehrenfest relation. This has led to the speculation that the atomic packing in liquids and glasses follow a fractal behavior. These issues are revisited in this study using more in-depth analysis of recent higher resolution data and some new ideas suggested in the literature. The main conclusion is that for metallic alloys, at least to a large extent, most of these anomalies arise from complicated interplays of the temperature dependences of the various partial structure factors, which contribute to the total intensities of the scattering peaks.
先前的研究报告指出，当将金属液体和玻璃的线性热膨胀系数的估计值从 X 射线散射实验与直接测量的温度下的体积/长度变化进行比较时，存在许多异常情况。在大多数情况下，对关联函数的第一个峰值显示收缩，而结构因子显示膨胀，但两者的速率与直接体积测量所预期的速率有很大不同。此外，从散射实验的结构因子获得的原子体积与特征长度之间的关系被发现具有分数指数，而不是预期的 Ehrenfest 关系中的三分之一。这导致了这样的推测，即液体和玻璃中的原子堆积遵循分形行为。本研究使用最近更高分辨率数据的更深入分析以及文献中提出的一些新思想重新探讨了这些问题。主要结论是，对于金属合金，至少在很大程度上，这些异常主要来自各种部分结构因子的温度依赖性的复杂相互作用，这导致了散射峰的总强度。
