Structure and Bonding of Zinc Antimonides: Complex Frameworks and Narrow Band Gaps

We investigated crystal structure relationships, phase stability and chemical bonding of the thermoelectric materials ZnSb, α‐Zn 4 Sb 3 , and β‐Zn 4 Sb 3 by means of first principles calculations. The structures of these materials are difficult to rationalise. This is especially true for β‐Zn 4 Sb 3 because of the presence of vacancies and interstitial atoms. We recognised rhomboid rings Zn 2 Sb 2 as central structural building units present in all materials. Importantly, these rings enable to establish a clear relationship between disordered β‐Zn 4 Sb 3 and ordered low‐temperature α‐Zn 4 Sb 3 . Concerning the phase stability of Zn 4 Sb 3 we identified a peculiar situation: α‐Zn 4 Sb 3 is metastable and β‐Zn 4 Sb 3 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 Zn 2 Sb 2 .