Reductive Intercalation of Vanadyl Layered Perovskites
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Reductive Intercalation of Vanadyl Layered Perovskites Doinita Neiner,1,2 Ray L. Sweany,1 Vladimir Golub2 and John B. Wiley1,2 Department of Chemistry and 2Advanced Materials Research Institute University of New Orleans New Orleans, LA 70148-2820, USA
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ABSTRACT A new series of triple layered Ruddlesden-Popper compounds of the general formula (LixVO)La2Ti3O10, where x = 0.83, 0.93, 1.4 and 1.8, have been prepared. Lithium is intercalated into the layered perovskite in a reductive manner to produce new mixed valence compounds. The structure of the parent, (VO)La2Ti3O10, is maintained upon intercalation. Above a certain lithium content, the magnetic behavior of (LixVO)La2Ti3O10 changes from paramagnetic, for x = 0.83, 0.93, 1.4, to a magnetically ordered material for (Li1.8VO)La2Ti3O10. INTRODUCTION Layered materials with perovskite-related structures can exhibit a range of interesting properties such as catalytic activity, superconductivity, and magnetoresistivity. While traditionally these materials are prepared by high temperature ceramic methods, low temperature routes (T < 500°C), such as ion exchange and intercalation, offer the potential for making new compounds with tunable properties as a function of chemical composition. This work focuses on such low temperature synthetic methods for obtaining new materials. These routes allow the maintenance of the basic crystal structure of the parent phase and provide access to a wide variety of phases that cannot be formed by traditional solid-state reactions. The host material, a triple layered Ruddlesden-Popper compound, K2La2Ti3O10, consists of [La2Ti3O10]2- perovskite layers interleaved with two K+ strata. Many researchers have studied the ion exchange properties of these materials, with monovalent and divalent cations including (VO)2+.[1, 2, 3] Herein we use a combination of ion exchange and intercalation reactions to produce a new series of mixed valence titanates. This paper describes the synthesis and characterization of (LixVO)La2Ti3O10 (x = 0.83, 0.93, 1.4, 1.8) series. EXPERIMENTAL Synthesis K2La2Ti3O10 was prepared by a solid state reaction from K2CO3 (Alfa Aesar 99.997%), La2O3 (Alfa Aesar 99.99%), and TiO2 (Alfa Aesar 99.995%) mixed in stoichiometric amounts. [2] A 30% excess of K2CO3 was used to compensate for the loss due to volatilization. The reactants were ground, pelletized and heated for 12 hours at 550° C and for 6 hours at 1050° C in air. After the reaction, the product was washed with distilled water and dried at 150°C overnight. Phase purity for K2La2Ti3O10 was confirmed by X-ray powder diffraction (XRD). The powder pattern was indexed in a tetragonal unit cell a = 3.876(1) Å and c = 29.824(1) Å, which is in agreement with the values reported in the literature. [4]
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Ion exchange was used to substitute the K+ ions in K2La2Ti3O10 with vanadyl ions, (VO)2+. [1] The source of the vanadyl unit was vanadyl sulfate hydrate (VOSO4·nH2O, Alfa Aesar, 99.99%). K2La2Ti3O10 was mixed in a 1:2 molar ratio with VOSO4 in 100 ml water. The so
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