A new six-layer perovskite-related structure Ba6Na2Nb2M2O17 (M = P, V), which

consists of cubic (c) BaO3 layers and oxygen-deficient pseudocubic (c') BaO2

layers stacked in the sequence c'ccccc, was presented. In Ba6Na2Nb2M2O17, twodimensional

slabs of the well-known 2:1 octahedral cation-ordered perovskite

motif were isolated between layers of tetrahedral units formed by anion vacancy

ordering: two consecutive NbO6 octahedral layers were sandwiched by two single

NaO6 octahedral layers, which, in turn, connect with two isolated MO4 tetrahedral

layers. Both oxides were derived from the 2:1 ordered perovskite structure (e.g.,

Ba3ZnTa2O9) by ordered removal of O atoms in every sixth BaO3 layer.

Isolation of Two-Dimensional 2:1 Cation-Ordered Perovskite Units by Anion

Vacancy Ordering in Ba6Na2Nb2P2O17. X.Kuang, J.B.Claridge, T.Price,

D.M.Iddles, M.J.Rosseinsky: Inorganic Chemistry, 2008, 47[19], 8444-50