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The fluorite-like [Bi2O2]2+ layer is a fundamental building unit in a great variety of layered compounds. Here in this contribution, we presented a comprehensive study on an unusual Aurivillius phase Bi3.6V2O10 with respect to its defect chemistry and polymorphism control as well as implications for fast oxide ion transport at lower temperatures. The bismuth oxide layer in Bi4V2O11 is found to tolerate a large number of Bi vacancies without breaking the high temperature prototype I4/mmm structure (γ-phase). On cooling, an orthorhombic distortion occurs to the γ-phase, giving rise to a different type of phase (B-phase) in the intermediate temperature region. Cooling to room temperature causes a further transition to an oxygen-vacancy ordered A-phase, which is accompanied by the charge ordering of V4+ and V5+ cations, providing magnetic (d¹) and nonmagnetic (d0) chains along the a axis. This is a novel charge ordering transition in terms of the concomitant change of oxygen coordination. Interestingly, upon quenching, both the γ- and B-phase can be kinetically trapped, enabling the structural probing of the two phases at ambient temperature. Driven by the thermodynamic forces, the oxide anion in the γ-phase undergoes an interlayer diffusion process to reshuffle the compositions of both Bi-O and V-O layers. [ABSTRACT FROM AUTHOR]

In contrast to the rich oxygen nonstoichiometry in vanadium oxides, we report here an interesting Bi4V2O11-delta; oxide system whose vanadate layer allows only a narrow oxygen deficiency range. Beyond δ = 0.4, reduction of Bi4V2O11-delta; 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 V4+ cation forms a rigid V4+/V5+ = 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. [ABSTRACT FROM AUTHOR]