NaCa_1.5(NbO)₂O₂(AsO₄)₂

The structure of the title compound, sodium calcium niobate oxide arsenate, NaCa_1.5(NbO)₂O₂(AsO₄)₂, is built up from chains of NbO₆ octahedra, parallel to the c axis, corner-sharing with AsO₄. There are two types of AsO₄ tetrahedron; one is connected to three different NbO₆ octahedra, whereas the other is linked to two NbO₆ octahedra only. The non-bonded O atoms point towards the inter-layer space where the sodium and calcium ions are located. A relationship between the structure of the title compound and the related Na₃SbO(PO₄)₂ (one-dimensional), Na₂NbO₂AsO₄(two-dimensional) and NaVOAsO₄ and SbOPO₄ (three-dimensional) structures is discussed.