A5Sn2As6 (A = Sr, Eu). Synthesis, Crystal and Electronic Structure, and Thermoelectric Properties

Two new ternary Zintl phases, Sr5Sn2As6 and Eu5Sn2As6, have been synthesized, and their structures have been accurately determined through single-crystal X-ray diffraction. Both compounds crystallize in orthorhombic space group Pbam (No. 55, Z = 2) with cell parameters of a = 12.482(3)/12.281(5) Å, b = 14.137(3)/13.941(5) Å, and c = 4.2440(10)/4.2029(16) Å for Sr5Sn2As6 (R1 = 0.0341; wR2 = 0.0628) and Eu5Sn2As6 (R1 = 0.0324; wR2 = 0.0766), respectively. Their structure belongs to the Sr5Sn2P6 type, which can be closely related to the Ca5Ga2As6 type. Electronic band structure calculations based on the density functional theory reveal an interesting electronic effect in the structure formation of these two types of Zintl phases, which substantially affect their corresponding electronic band structure. Related studies on the thermal stability, magnetism, and thermoelectric properties of Eu5Sn2As6 are presented as well.

两种新型三元Zintl相（Zintl phase）：Sr₅Sn₂As₆与Eu₅Sn₂As₆已被成功合成，其晶体结构通过单晶X射线衍射技术得以精准解析。两种化合物均结晶于正交晶系Pbam空间群（第55号空间群，Z=2）；其中Sr₅Sn₂As₆的晶胞参数为a=12.482(3) Å、b=14.137(3) Å、c=4.2440(10) Å，残差因子R1=0.0341、wR2=0.0628；Eu₅Sn₂As₆的晶胞参数为a=12.281(5) Å、b=13.941(5) Å、c=4.2029(16) Å，残差因子R1=0.0324、wR2=0.0766。二者的晶体结构均属于Sr₅Sn₂P₆结构类型，且与Ca₅Ga₂As₆结构类型具有密切的结构关联性。基于密度泛函理论（density functional theory）的电子能带结构计算表明，这两类Zintl相的结构形成过程中存在一种独特的电子效应，该效应对其电子能带结构具有显著影响。此外本文还报道了关于Eu₅Sn₂As₆的热稳定性、磁学性能及热电性能的相关研究工作。