title: Structure and bonding of zinc antimonides: complex frameworks and narrow band gaps.
abstract: 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.
authors.affiliation: Inorganic Chemistry, Stockholm University, 10691 Stockholm, Sweden.
authors.forename: Arkady S
authors.initials: AS
authors.lastname: Mikhaylushkin
authors.forename: Johanna
authors.initials: J
authors.lastname: Nylén
authors.forename: Ulrich
authors.initials: U
authors.lastname: Häussermann