Faculty of Pharmacy, Niigata University of Pharmacy and Applied Life Sciences, 265-1 Higashijima, Akiha-ku, Niigata 956-8603, Japan.
J Phys Condens Matter. 2011 Jun 15;23(23):235102. doi: 10.1088/0953-8984/23/23/235102. Epub 2011 May 25.
High-energy x-ray diffraction measurements on molten Ag(2)Se were performed. Partial structure factors and radial distribution functions were deduced by reverse Monte Carlo (RMC) structural modelling on the basis of our new x-ray and earlier published neutron diffraction data. These partial functions were compared with those of molten AgI. Both AgI and Ag(2)Se have a superionic solid phase prior to melting. New RMC structural modelling for molten AgI was performed to revise our previous model with a bond-angle restriction to reduce the number of unphysical Ag triangles. The refined model of molten AgI revealed that isolated unbranched chains formed by Ag ions are the cause of the medium-range order of Ag. In contrast with molten AgI, molten Ag(2)Se has 'cage-like' structures with approximately seven Ag ions surrounding a Se ion. Connectivity analysis revealed that most of the Ag ions in molten Ag(2)Se are located within 2.9 Å of each other and only small voids are found, which is in contrast to the wide distribution of Ag-void radii in molten AgI. It is conjectured that the collective motion of Ag ions through small voids is required to realize the well-known fast diffusion of Ag ions in molten Ag(2)Se, which is comparable to that in molten AgI.
对熔融 Ag(2)Se 进行了高能 X 射线衍射测量。基于我们新的 X 射线和早期发表的中子衍射数据，通过反向蒙特卡罗（RMC）结构建模推导出部分结构因子和径向分布函数。将这些部分函数与熔融 AgI 的部分函数进行了比较。AgI 和 Ag(2)Se 在熔融之前都具有超离子固体相。对熔融 AgI 进行了新的 RMC 结构建模，以修正我们之前具有键角限制的模型，以减少不合理的 Ag 三角形数量。改进后的熔融 AgI 模型表明，由 Ag 离子形成的孤立无分支链是 Ag 中程有序的原因。与熔融 AgI 不同，熔融 Ag(2)Se 具有“笼状”结构，大约有七个 Ag 离子围绕一个 Se 离子。连通性分析表明，熔融 Ag(2)Se 中的大多数 Ag 离子彼此之间的距离都在 2.9Å 以内，只有很小的空隙，这与熔融 AgI 中 Ag-空隙半径的广泛分布形成对比。据推测，Ag 离子通过小空隙的集体运动是实现众所周知的熔融 Ag(2)Se 中 Ag 离子快速扩散的必要条件，这与熔融 AgI 中的扩散速度相当。
