Über Ordnungs-Unordnungsphänomene bei Sauerstoff perowskiten vom Typ A2+3B2+M5+2O9 |
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Authors: | U Treiber S Kemmler-Sack |
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Institution: | Institut für Anorganische Chemie der Universität Tübingen, Auf der Morgenstelle 18, D-7400 Tübingen, West Germany |
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Abstract: | Perovskites of the type A2+3B2+M5+2O9, where A2+ = Ba, Sr; B2+ = Mn, Co, Ni, Zn; M5+ = Nb, Ta, show order-disorder phenomena. At lower temperatures a thermodynamically unstable disordered cubic perovskite is formed ( formula unit——in the cell), which transforms irreversibly into a 1: 2 ordered high-temperature form with 3L structure (sequence (c)3). For A2+ = Ba this lattice is hexagonal (space group ; one formula unit in the cell); with A2+ = Sr a triclinic distortion is observed. For Ba3CoNb2O9 a second transformation into a cubic disordered perovskite takes place at 1500°C. This transition is reversible and of the order-disorder type. The vibrational and diffuse reflectance spectra are discussed. |
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Keywords: | To whom inquiries should be addressed |
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