Kristallstrukturuntersuchungen an Verbindungen des Typs A3(M,Nb)8O21 (A Tl,Ba; M Fe,Ni) |
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Authors: | R. Brandt,Hk. Mü ller-Buschbaum |
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Abstract: | Crystal Structure Investigations of Compounds with the A3(M, Nb)8O21-Type (A ? Tl, Ba; M ? Fe, Ni) Tl3Fe0,5Nb7,5O21 (A), a hitherto unknown phase of the A3(M, Nb)8O21-type, and Ba3Fe2Nb6O21 (B), Ba3Ni1.33Nb6,66O21 (C) were prepared and investigated by single crystal X-ray technique. ((A): a = 9.145(1), c = 11.942(1) Å; (B): a = 9.118(2), c = 11.870(1) Å; (C) a = 9.173(3), c = 11.923(1) Å, space group D? P63/mcm, Z = 2). There is a statistic occupation of the M-positions by Nb5+ and Fe3+ or Nb5+ and Ni2+, respectively. An other compound Ba3Fe2Ta6O21 is partially ordered in respect to Ta5+ and Fe3+. Calculations of the Coulomb-part of lattice energy are discussed. |
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