Aravindakshan Nikhil P, Johnson Keith E, East Allan L L
Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada.
J Chem Phys. 2019 Jul 21;151(3):034507. doi: 10.1063/1.5109138.
In a continuing effort to master the reasons for conductivity maxima vs temperature in semicovalent molten halides, the structure and some transport properties of molten zinc halide are examined with ab initio molecular dynamics. Molten zinc halides are a special class of molten salts, being extremely viscous near their melting point (with a glassy state below it) and low electrical conductivity, and since they are also known (ZnI) or predicted (ZnBr and ZnCl) to exhibit conductivity maxima, they would be useful additional cases to probe, in case the reasons for their maxima are unique. Strong attractive forces in ZnX result in tight tetrahedral coordination, and the known mixture of edge-sharing vs corner-sharing ZnX tetrahedra is observed. In the series zinc chloride → bromide → iodide, (i) the ratio of edge-sharing vs corner-sharing tetrahedra increases, (ii) the diffusion coefficient of Zn increases, and (iii) the diffusion coefficient of the anion stays roughly constant. A discussion of conductivity, with focus on the Walden product W = ηΛ, is presented. With predicted Haven ratios of 1-15 when heated toward their conductivity maxima, the physical chemistry behind molten zinc halide conductivity does not appear to be fundamentally different from other semicovalent molten halides.
为了持续深入探究半共价熔融卤化物中电导率最大值与温度之间的关系，我们采用从头算分子动力学方法研究了熔融卤化锌的结构和一些输运性质。熔融卤化锌是一类特殊的熔盐，在熔点附近具有极高的粘度（其下方存在玻璃态）且电导率较低，并且由于它们已知（碘化锌）或被预测（溴化锌和氯化锌）会出现电导率最大值，所以如果其最大值的原因是独特的，那么它们将是用于探究的有用的额外实例。卤化锌中的强吸引力导致紧密的四面体配位，并且观察到了已知的边共享与角共享卤化锌四面体的混合情况。在氯化锌→溴化锌→碘化锌系列中，（i）边共享与角共享四面体的比例增加，（ii）锌的扩散系数增加，（iii）阴离子的扩散系数大致保持恒定。本文围绕电导率展开了讨论，重点关注瓦尔登乘积W = ηΛ。当加热至电导率最大值时，卤化锌的预测黑文比率为1 - 15，熔融卤化锌电导率背后的物理化学性质似乎与其他半共价熔融卤化物并无根本差异。
