Lucas Pierre, Coleman Garrett J, Venkateswara Rao Manga, Edwards Angharad N, Devaadithya Chrishani, Wei Shuai, Alsayoud Abduljabar Q, Potter B G, Muralidharan Krishna, Deymier Pierre A
Department of Materials Science and Engineering, University of Arizona , Tucson, Arizona 85721, United States.
School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287, United States.
J Phys Chem B. 2017 Dec 14;121(49):11210-11218. doi: 10.1021/acs.jpcb.7b10857. Epub 2017 Dec 1.
The fraction of edge- and corner-sharing tetrahedra in liquid ZnCl is quantified as a function of temperature using Raman spectroscopy and ab initio molecular dynamic simulations. Two distinct regimes are found in the temperature dependence of the change in these structural units. This behavior is consistent with the existence of a fragile-to-strong transition in liquid ZnCl as suggested by calorimetric and viscosity measurements. The structural origin of this transition is rationalized in terms of a constraint counting formalism. It is suggested that the ratio of edge- to corner-sharing tetrahedra controls the configurational entropy and in turn the viscosity of the melt. The temperature dependence of this ratio above the melting point is also found to be qualitatively consistent with neutron diffraction data. The observation of a similar fragile-to-strong transition in the isostructural GeSe melt indicates that it may be a common feature of tetrahedral liquids.
利用拉曼光谱和从头算分子动力学模拟，对液态ZnCl中边共享和角共享四面体的比例作为温度的函数进行了量化。在这些结构单元变化的温度依赖性中发现了两种不同的状态。这种行为与量热法和粘度测量所表明的液态ZnCl中存在从脆性到强性的转变是一致的。根据约束计数形式对这种转变的结构起源进行了合理化解释。有人认为，边共享与角共享四面体的比例控制着构型熵，进而控制着熔体的粘度。还发现，熔点以上该比例的温度依赖性在定性上与中子衍射数据一致。在同结构的GeSe熔体中观察到类似的从脆性到强性的转变，表明这可能是四面体液体的一个共同特征。
