A three-dimensional extended Sb network in the metallic antimonides (M',Ti)5Sb8 (M' = Zr, Hf, Nb, Mo).
(M',Ti)5Sb8 was prepared from the melt by arc-melting suitable mixtures of Ti, TiSb2, and M'Sb2, respectively. This phase exists at least with M' = Zr, Hf, Nb, and Mo. A significant phase range for Zr delta Ti5 - delta Sb8 was found to be within 1.10(8) < or = delta < or = 3.9(3). All (M',Ti)5Sb8 representatives investigated occur in the same, yet hitherto unknown structure type, as determined by single-crystal analyses. E.g., the lattice dimensions of Zr delta Ti5 - delta Sb8 range from a = 654.49(3) pm, c = 2662.4(2) pm for delta = 1.10(8) to a = 671.06(6), c = 2679.7(4) pm for delta = 3.9(3) (space group I4(1)22, No. 98, Z = 4). The three chemically inequivalent metal sites are statistically occupied by different mixtures of the M atoms M' and Ti, included in a three-dimensional network of Sb atoms on 6- to 8-fold Sb coordinated positions. Sb-Sb bonds of intermediate lengths occur in addition to the predominating heteronuclear M-Sb bonds. Physical property measurements of (Zr,Ti)5Sb8 reveal these phases being metallic exhibiting specific resistances of several m omega.cm and a small Seebeck coefficient at room temperature, in agreement with the results of the electronic structure calculations on the LMTO and extended Hückel levels. The calculations indicate a possible change to semiconducting properties by heavy doping.
Kleinke
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Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. kleinke@uwaterloo.ca