New Members of the Homologous Series A<i>_m</i>[M₆Se₈]<i>_m</i>[M₅₊<i>_n</i>Se₉₊<i>_n</i>]: The Quaternary Phases A₁_-<i>_x</i>M‘₃_-<i>_x</i>Bi₁₁₊<i>_x</i>Se₂₀ and A₁₊<i>_x</i>M‘₃_-₂<i>_x</i>Bi₇₊<i>_x</i>Se₁₄ (A = K, Rb, Cs; M‘ = Sn, Pb)

The compounds A1+xM‘3-2xBi7+xSe14 and A1-xM‘3-xBi11+xSe20 (A = K, Rb, Cs; M‘ = Sn, Pb) were discovered from reactions involving A2Se, Bi2Se3, M‘, and Se at 760 °C. The single-crystal structures reveal that A1+xM‘3-2xBi7+xSe14 are isostructural to K2.5Bi8.5Se14 whereas A1-xM‘3-xBi11+xSe20 adopt a new structure type. Both compound types belong to the homologous series Am[M6Se8]m[M5+nSe9+n] (M = di- and trivalent metal), whose characteristics are three-dimensional anionic frameworks with tunnels filled with alkali ions. The building units are derived from different sections of the NaCl lattice, perpendicular to the [111] (NaCl111-type) and [100] (NaCl100-type) directions, respectively, with dimensions and shapes defined by m and n. The structures of A1+xM‘3-2xBi7+xSe14 (m = 2, n = 3) and A1-xM‘3-xBi11+xSe20 (m = 1, n = 3) exhibit the same type of step-shaped NaCl111-type layer but differ in the size of the NaCl100-type unit. In both structures, the Bi and Sn (Pb) atoms are extensively disordered over the metal sites of the chalcogenide network. The physicochemical and charge transport properties of A1+xM‘3-2xBi7+xSe14 and A1-xM‘3-xBi11+xSe20 (A = K, Rb, Cs; M‘ = Sn, Pb) are reported.本研究通过以A₂Se、Bi₂Se₃、M‘及单质硒为反应物，在760 ℃下的合成反应中，首次得到化合物A₁₊ₓM‘₃₋₂ₓBi₇₊ₓSe₁₄与A₁₋ₓM‘₃₋ₓBi₁₁₊ₓSe₂₀（其中A代表K、Rb、Cs，M‘代表Sn、Pb）。单晶结构解析显示，A₁₊ₓM‘₃₋₂ₓBi₇₊ₓSe₁₄与K₂.₅Bi₈.₅Se₁₄为同构结构，而A₁₋ₓM‘₃₋ₓBi₁₁₊ₓSe₂₀则属于全新的结构类型。两类化合物均隶属于同系列Aₘ[M₆Se₈]ₘ[M₅₊ₙSe₉₊ₙ]（其中M为二价及三价金属），该同系列的结构特征为具备内嵌碱金属离子隧道的三维阴离子骨架。其结构基元分别源自氯化钠（NaCl）晶格沿[111]（NaCl111型）与[100]（NaCl100型）方向截取的不同片段，基元的尺寸与形态由参数m和n共同确定。对于A₁₊ₓM‘₃₋₂ₓBi₇₊ₓSe₁₄（m=2，n=3）与A₁₋ₓM‘₃₋ₓBi₁₁₊ₓSe₂₀（m=1，n=3）而言，二者均呈现阶梯状NaCl111型层状结构，但NaCl100型结构单元的尺寸存在差异。在两类化合物的结构中，铋（Bi）与锡（Sn）、铅（Pb）原子在硫属化物骨架的金属位点上存在广泛的无序分布。本文同时报道了A=K、Rb、Cs，M‘=Sn、Pb的A₁₊ₓM‘₃₋₂ₓBi₇₊ₓSe₁₄与A₁₋ₓM‘₃₋ₓBi₁₁₊ₓSe₂₀两类化合物的物理化学性质与电荷输运性能。