STRUCTURE OF LAYERED PEROVSKITE-TYPE NA2CA2NB4O13 SINGLE-CRYSTALS

Single crystals of Na2Ca2Nb4O13 were grown by the flux technique and t he structure was investigated by the single crystal X-ray diffraction technique with final R/wR factors of 0.052/0.022 for observed 699 refl ections assuming the space group Immm with cell dimensions a = 3.885(3 ), b = 3.884(3), and c = 36.15(3) Angstrom. Layers with formula [(Ca2N a)Nb4O13](-) are concatenated by Na+ cations near the interlayer. The Na+ cations also reside in the intralayer, substituting part of twelve -fold coordinated Ca2+ cations in the perovskite-type unit. The stacki ng vector of the perovskite-type layer is parallel to the body-diagona l direction, making a clear contrast to that along the face-diagonal d irection in the Dion-Jacobson phase with K+ cations residing near the interlayer. A detailed crystallographic study is being in progress, co nsidering a slight structural distortion into base-centred structure. (C) 1998 Elsevier Science B.V. All rights reserved.