A new Sillén – Aurivillius family of layered bismuth oxyhalides has been designed and successfully constructed on the basis of PbBiO 2 X (X = halogen) synthetic perites and γ-form of Bi 2 VO 5.5 solid electrolyte. This demonstrates, for the first time, the ability of the latter to serve as a building block in construction of mixed-layer structures. The parent compound PbBi 3 VO 7.5-δ Cl (δ ≤ 0.05) has been investigated by powder XRD, TEM, XPS methods and magnetic susceptibility measurements. An unexpected but important condition for the formation of the mixed-layer structure is partial (ca. 5%) reduction of V V into V IV which probably suppresses competitive formation of apatite-like Pb – Bi vanadates. This reduction also stabilizes the γ polymorphic form of Bi 2 VO 5.5 not only in the intergrowth structure, but in Bi 2 V 1-x M x O 5.5-y (M = Nb, Sb) solid solutions. [ABSTRACT FROM AUTHOR]