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Interlayer switching of reduction in layered oxide, Bi4V2O(11-δ) (0 ≤ δ ≤ 1).

In contrast to the rich oxygen nonstoichiometry in vanadium oxides, we report here an interesting Bi4V2O(11-δ) oxide system whose vanadate layer allows only a narrow oxygen deficiency range. Beyond δ = 0.4, reduction of Bi4V2O(11-δ) does not proceed in the V-O layer, but instead suddenly switches to the Bi-O layer by precipitation of metallic bismuth. A new structure is realized for 0.4 ≤ δ ≤ 1, and its ordered V(4+) cation forms a rigid V(4+)/V(5+) = 2/3 pair giving rise to one-dimensional magnetism that can be understood in terms of an S = 1/2 antiferromagnetic Heisenberg chain model. In situ X-ray diffraction measurement yielded the first phase diagram for the system of current study and revealed the unusual phase relation as a function of oxygen nonstoichiometry. It is suggested that at higher temperatures than 570 °C all compositions would be unified into an oxygen disordered tetragonal phase, whose implication for oxide ion mobility could have significant impact on our understanding of ionic conduction.