Supertetrahedral Layers Based on GaAs or InAs

The solid-state compounds M15Tr22As32 and M3Ga6As8 (M = Sr, Eu; Tr = Ga, In) were synthesized by heating the elements, and their crystal structures were determined by single-crystal and powder X-ray diffraction (space group C2/c). The structures are hierarchical variants of the HgI2 type and consist of layers of polymeric T5 (M15Tr22As32) or T6 supertetrahedra (M3Ga6As8), separated by strontium or europium cations. These compounds constitute hitherto unknown GaAs- or InAs-based supertetrahedral structures and represent the first binary vacancy-free T5 and T6 supertetrahedra. Vacancies or mixed-metal strategies for charge compensation, as known from related chalcogenides, are not required for supertetrahedra based on charge-neutral GaAs or InAs. Optical band gap, resistivity, and Hall-effect measurements together with DFT calculations reveal that the supertetrahedral compounds are direct band gap semiconductors similar to binary GaAs or InAs. Magnetic susceptibility measurements confirm Eu2+ in Eu15Ga22As32, Eu15In22As32, and Eu3Ga6As8 and indicate antiferromagnetic ordering below 10 K.通过单质热合成法制备了固态化合物M15Tr22As32与M3Ga6As8（其中M代表Sr、Eu；Tr代表Ga、In），并借助单晶与粉末X射线衍射（空间群C2/c）解析了其晶体结构。该类结构属于HgI2型结构的层级变体，由聚合态T5（对应M15Tr22As32）或T6超四面体（supertetrahedra）层构成，层间通过锶或铕阳离子分隔。此类化合物为迄今未见报道的基于GaAs或InAs的超四面体结构，同时也是首例二元无空位T5与T6超四面体结构。对于基于电荷中性GaAs或InAs的超四面体结构而言，无需像相关硫族化合物那样采用空位或混合金属策略进行电荷补偿。通过光学带隙、电阻率与霍尔效应测试，结合密度泛函理论（Density Functional Theory, DFT）计算，结果表明该超四面体化合物为直接带隙半导体，其性质与二元GaAs或InAs相似。磁化率测试证实了Eu15Ga22As32、Eu15In22As32与Eu3Ga6As8中存在Eu²+，并表明其在10 K以下存在反铁磁有序行为。