Zeitz S, Boyko M, Ponou S, Hlukhyy V, Fässler T F
School of Natural Science, Technical University of Munich, Chair of Inorganic Chemistry with Focus on Novel Materials, Lichtenbergstraße 4, D-85747, Garching, Germany.
Chemistry. 2025 Jan 22;31(5):e202403592. doi: 10.1002/chem.202403592. Epub 2024 Nov 27.
The large variety of structures of Zintl phases are generally well understood since their anionic substructures follow bonding rules according to the valence concept. But there are also exceptions, which make the semiconductors especially interesting in terms of structure-property relationships. Although several Na-Sn-Pnictides with a variety of structural motives are known, up to this point no ternary compound in the Na-Sn-Bi system has been described. In this paper we present the Zintl-phase NaSnBi comprising a complex, open-framework structure of Sn atoms, with one mixed Sn/Bi site, hosting Na atoms. An additional Bi atom is loosely connected with only weak contacts to the framework filling a larger cavity within the network. According to band structure calculations of the two ordered variants with either full occupation of the mixed site with Sn or Bi, resulting in NaSnBi and NaSnBi, respectively, both compounds are semiconductors with band gaps of 0.5 eV. A comparison of the band structures with the structurally related binary compounds NaSn and NaSn shows that only the perfectly charge balanced NaSn is a semiconductor whereas NaSn is metallic. The rather specific electronic situation in the ternary compound is traced back to the loosely bound Bi atom, which acts as a guest atom according to Bi@NaSnBi, with x=1 and y=0.27, capable to change its oxidation state and thus to uptake additional electrons allowing the system to be a semiconductor. Therefore, NaSnBi can be understood as a rare example of an open framework structure of Sn atoms comprising Bi atoms in the cavities.
由于其阴离子亚结构遵循价态概念的成键规则，所以一般来说对津特耳相的多种结构有很好的理解。但也有例外情况，这使得这些半导体在结构 - 性能关系方面特别有趣。虽然已知几种具有多种结构模式的钠 - 锡 - 磷族化合物，但截至目前，尚未描述钠 - 锡 - 铋体系中的任何三元化合物。在本文中，我们展示了津特耳相NaSnBi，它包含一个由锡原子构成的复杂开放框架结构，有一个混合的锡/铋位点，容纳钠原子。另一个铋原子仅通过弱相互作用与框架松散相连，填充网络内一个较大的空腔。根据对两种有序变体的能带结构计算，混合位点分别被锡或铋完全占据，分别得到NaSnBi和NaSnBi，这两种化合物都是带隙为0.5 eV的半导体。将其能带结构与结构相关的二元化合物NaSn和NaSn进行比较表明，只有电荷完美平衡的NaSn是半导体，而NaSn是金属。三元化合物中相当特殊的电子情况可追溯到松散结合的铋原子，根据Bi@NaSnBi，其中x = 1且y = 0.27，它作为客体原子，能够改变其氧化态，从而吸收额外的电子，使体系成为半导体。因此，NaSnBi可以被理解为一种罕见的例子，即由锡原子构成的开放框架结构，其空腔中包含铋原子。
