Ion-exchangeable, electronically conducting layered perovskite oxyfluorides

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 RbLaNb2O 7, KCa2Nb3O10, and NaYTiO 4 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 RbLaNb 2O6F reveal room-temperature conductivity (2-7 × 102 Ω·cm) via a variable-range hopping mechanism, which is not substantially changed after aqueous proton exchange to H 1-xRbxLaNb2O6F (x ≈ 0.2). © 2009 American Chemical Society.