Low-temperature phases of the solid electrolyte RbAg 4 I 5
Low-temperature phases of the solid electrolyte RbAg 4 I 5
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DOI：
10.1103/physrevb.14.4345
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发表时间：
1976-11
影响因子：
3.7
通讯作者：
S. Geller
中科院分区：
文献类型：
--
作者：
S. Geller
${\mathrm{RbAg}}_{4}$${\mathrm{I}}_{5}$ 的两个低温相的重要结构特征（按温度降低的顺序指定为 $\ensuremath{\beta}$、$\ensuremath{\gamma}$）已确定，尽管 $\ensuremath{\gamma}$ 相的精确结构由于大量的结构参数和可用材料的限制而无法获得数据。在 130 K 时，$\ensuremath{\beta}$ 相为菱面体，空间群 $R32({D}_{3}^{7})$，其中 $a=11.17\ifmmode\pm\else\textpm\fi{}0.01$ \AA{}， $\ensuremath{\alpha}=90.1\ifmmode^\circ\else\text Degree\fi{}\ifmmode\pm\else\textpm\fi{}0.05\ifmmode^\circ\else\text Degree\fi{}$。大多数离子和平衡 ${\mathrm{Ag}}^{+}$ 离子位点相对于 $\ensuremath{\alpha}$ 相的位移都很小，最大为 0.3 \AA{}，即两个 ${\mathrm{Ag}}^{+}$ 离子位点的位移。 ${\mathrm{I}}^{\ensuremath{-}}$ 离子的最大位移为 0.1 \AA{}。 $\ensuremath{\alpha}$ 和 $\ensuremath{\beta}$ 相之间最显着的区别是 ${\mathrm{Ag}}^{+}$ 离子的优先分布，在后者中，相对于以前晶体学上等效的位点集。然而，与类似位点相比，分布变化不大：在 $\ensuremath{\alpha}\ensuremath{-}\mathrm{Rb}{\mathrm{Ag}}_{4}{\mathrm{I}}_{5}$ 中，分布为 0.9、9.4 和 5.5 ${\mathrm{Ag}}^{+}$ 离子$\mathrm{Ag}\ensuremath{-}c$、Ag-II 和 Ag-III 位点分别，而 $\ensuremath{\beta}\ensuremath{-}\mathrm{Rb}{\mathrm{Ag}}_{4}{\mathrm{I}}_{5}$ 中的类似值分别为 1.3、10.5 和 4.2。 （误差限度可能与 $\ensuremath{\alpha}$ 阶段大致相同。） $\ensuremath{\alpha}$- 和 $\ensuremath{\beta}\ensuremath{-}\mathrm{Rb}{\mathrm{Ag}}_{4}{\mathrm{I}}_{5}$ 都无法排序，因此 209-K 转变是“无序-无序”转变。 $\ensuremath{\gamma}\ensuremath{-}\mathrm{Rb}{\mathrm{Ag}}_{4}{\mathrm{I}}_{5}$ 是三角最可能空间群 $P321 ({D}_{3}^{2})$，其中 $a=15.776\ifmmode\pm\else\textpm\fi{}0.005$ \AA{} 和 $c=19.320\ifmmode\pm\else\textpm\fi{}0.005$ \AA{} 在 90 K 时。晶胞的体积是菱面体晶胞的三倍，因此包含 12 个 ${\mathrm{RbAg}}_{4}$${\mathrm{I}}_{5}$。 $\ensuremath{\gamma}$ 相的结构与 $\ensuremath{\beta}$ 相的结构密切相关，可以通过首先将菱面体结构转换为三元原始六角形单元，然后允许离子和 ${\mathrm{Ag}}^{+}$ 离子位点相对于它们在 $\ensuremath{\beta}$ 相中的位置进一步位移，从而产生原始单元。结果表明，有 146 种可能的排序方案（假设 30 个 ${\mathrm{Ag}}^{+}$ 离子填充 Ag-II 型位点），并且对这些方案的研究得出了 $\ensuremath{\beta}$ 相中可能的 ${\mathrm{Ag}}^{+}$ 离子分布方案。这实际上有助于获得 $\ensuremath{\beta}$ 阶段的分布。 $\ensuremath{\gamma}$ 相在 90 K 时似乎不是有序的，但有序 $\ensuremath{\gamma}$ 相的单个最可能的排列是从 $\ensuremath{\beta}$ 相中的 ${\mathrm{Ag}}^{+}$ 离子分布推导出来的。
Important structural features of the two low-temperature phases of ${\mathrm{RbAg}}_{4}$${\mathrm{I}}_{5}$, designated $\ensuremath{\beta}$,$\ensuremath{\gamma}$ in order of decreasing temperature, have been determined, even though the precise structure of the $\ensuremath{\gamma}$ phase is unattainable because of the large number of structural parameters and the limitations on available data. At 130 K, the $\ensuremath{\beta}$ phase is rhombohedral, space group $R32({D}_{3}^{7})$, with $a=11.17\ifmmode\pm\else\textpm\fi{}0.01$ \AA{}, $\ensuremath{\alpha}=90.1\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}0.05\ifmmode^\circ\else\textdegree\fi{}$. Most of the displacements of ions and equilibrium ${\mathrm{Ag}}^{+}$ ion sites, relative to the $\ensuremath{\alpha}$ phase, are small, the largest, 0.3 \AA{}, being those for two ${\mathrm{Ag}}^{+}$ ion sites. The largest displacement of an ${\mathrm{I}}^{\ensuremath{-}}$ ion is 0.1 \AA{}. The most significant difference between the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ phases is the preferential distribution of ${\mathrm{Ag}}^{+}$ ions, in the latter, over sets of sites formerly crystallographically equivalent. However, the distribution does not change very much over analogous sites: In $\ensuremath{\alpha}\ensuremath{-}\mathrm{Rb}{\mathrm{Ag}}_{4}{\mathrm{I}}_{5}$ the distribution is 0.9, 9.4, and 5.5 ${\mathrm{Ag}}^{+}$ ions in the $\mathrm{Ag}\ensuremath{-}c$, Ag-II, and Ag-III sites, respectively, while the analogous values in $\ensuremath{\beta}\ensuremath{-}\mathrm{Rb}{\mathrm{Ag}}_{4}{\mathrm{I}}_{5}$ are 1.3, 10.5, and 4.2. (The limits of error are probably about the same as in the $\ensuremath{\alpha}$ phase.) Neither $\ensuremath{\alpha}$- nor $\ensuremath{\beta}\ensuremath{-}\mathrm{Rb}{\mathrm{Ag}}_{4}{\mathrm{I}}_{5}$ can be ordered and therefore the 209-K transition is a "disorder-disorder" transition. The $\ensuremath{\gamma}\ensuremath{-}\mathrm{Rb}{\mathrm{Ag}}_{4}{\mathrm{I}}_{5}$ is trigonal, most probable space group $P321 ({D}_{3}^{2})$, with $a=15.776\ifmmode\pm\else\textpm\fi{}0.005$ \AA{} and $c=19.320\ifmmode\pm\else\textpm\fi{}0.005$ \AA{} at 90 K. The unit cell has three times the volume of the rhombohedral cell and therefore contains 12 ${\mathrm{RbAg}}_{4}$${\mathrm{I}}_{5}$. The structure of the $\ensuremath{\gamma}$ phase is closely related to that of the $\ensuremath{\beta}$ phase and can be derived from it by first transforming the rhombohedral structure to a triply primitive hexagonal cell and then permitting further displacement of ions and ${\mathrm{Ag}}^{+}$ ion sites with respect to their positions in the $\ensuremath{\beta}$ phase, thus resulting in a primitive cell. It is shown that there are 146 possible ordering schemes (under the assumption that 30 ${\mathrm{Ag}}^{+}$ ions fill Ag-II type sites) and that a study of these leads to the probable ${\mathrm{Ag}}^{+}$ ion distribution schemes in the $\ensuremath{\beta}$ phase. This was actually instrumental in attaining the distributions in the $\ensuremath{\beta}$ phase. The $\ensuremath{\gamma}$ phase does not appear to be ordered at 90 K, but the single most probable arrangement for an ordered $\ensuremath{\gamma}$ phase is deduced from the ${\mathrm{Ag}}^{+}$ ion distribution in the $\ensuremath{\beta}$ phase.