Ion-exchangeable, electronically conducting layered perovskite oxyfluorides

Year: 2009 DOI: 10.1021/ja9040829

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Yoji Kobayashi, Mingliang Tian, Miharu Eguchi, Thomas E. Mallouk.   Journal of the American Chemical Society, 2009, 131, 9849-9855.


Cation-exchangeable d0 layered perovskites are amenable to intercalation, exfoliation, and a variety of topochemical reactions, but they lack the interesting electronic and magnetic functionalities of mixed-valent perovskites. Conversely, electronically and magnetically interesting layered perovskites lack scope in terms of interlayer chemistry. To bridge this gap, the insulating, cation-exchangeable layered perovskites RbLaNb2O7, KCa2Nb3O10, and NaYTiO4 were reacted with poly(tetrafluoroethylene) under inert atmosphere conditions to yield layer perovskites in which some of the oxygen is substituted by fluorine. In the fluorinated materials, the B-site cations are reduced to a mixed-valent state without introducing oxygen vacancies into the anion sublattice. The resulting electronically conducting solids can be exposed to air and water and even ion-exchanged in acid without oxidation of the B-site cations. Electronic transport measurements on the air-stable RbLaNb2O6F reveal room-temperature conductivity (2-7 x 102 ohms x cm) via a variable-range hopping mechanism, which is not substantially changed after aqueous proton exchange to H1-xRbxLaNb2O6F (x approximately = 0.2).