Mikhaylushkin Arkady S, Nylén Johanna, Häussermann Ulrich
Inorganic Chemistry, Stockholm University, 10691 Stockholm, Sweden.
Chemistry. 2005 Aug 19;11(17):4912-20. doi: 10.1002/chem.200500020.
We investigated crystal structure relationships, phase stability and chemical bonding of the thermoelectric materials ZnSb, alpha-Zn4Sb3, and beta-Zn4Sb3 by means of first principles calculations. The structures of these materials are difficult to rationalise. This is especially true for beta-Zn4Sb3 because of the presence of vacancies and interstitial atoms. We recognised rhomboid rings Zn2Sb2 as central structural building units present in all materials. Importantly, these rings enable to establish a clear relationship between disordered beta-Zn4Sb3 and ordered low-temperature alpha-Zn4Sb3. Concerning the phase stability of Zn4Sb3 we identified a peculiar situation: alpha-Zn4Sb3 is metastable and beta-Zn4Sb3 can only be thermodynamically stable when its structural disorder accounts for a large entropy contribution to free energy. According to their electronic structure zinc antimonides represent heteroatomic framework structures with a modest polarity. The peculiar electronic structure of Zn/Sb systems can also be modelled by Al/Si systems. The high coordination numbers in the frameworks implies the presence of multicentre bonding. We developed a simple bonding picture for these frameworks where multicentre bonding is confined to rhomboid rings Zn2Sb2.
我们通过第一性原理计算研究了热电材料ZnSb、α-Zn4Sb3和β-Zn4Sb3的晶体结构关系、相稳定性和化学键合。这些材料的结构难以合理化。对于β-Zn4Sb3来说尤其如此，因为存在空位和间隙原子。我们认识到菱形环Zn2Sb2是所有材料中存在的核心结构构建单元。重要的是，这些环能够在无序的β-Zn4Sb3和有序的低温α-Zn4Sb3之间建立明确的关系。关于Zn4Sb3的相稳定性，我们发现了一种特殊情况：α-Zn4Sb3是亚稳的，而β-Zn4Sb3只有当其结构无序对自由能有很大的熵贡献时才在热力学上稳定。根据它们的电子结构，锌锑化物代表具有适度极性的异原子骨架结构。Zn/Sb系统的特殊电子结构也可以用Al/Si系统来模拟。框架中的高配位数意味着存在多中心键合。我们为这些框架开发了一个简单的键合图，其中多中心键合局限于菱形环Zn2Sb2。
