Materials Data on Na2Ta4O11 by Materials Project
Na2Ta4O11 crystallizes in the trigonal R-3c space group. The structure is three-dimensional. Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.48–2.75 Å. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to seven O2- atoms to form distorted TaO7 pentagonal bipyramids that share corners with two equivalent TaO6 octahedra, corners with two equivalent TaO7 pentagonal bipyramids, and edges with four equivalent TaO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 45°. There are a spread of Ta–O bond distances ranging from 1.98–2.45 Å. In the second Ta5+ site, Ta5+ is bonded to six equivalent O2- atoms to form corner-sharing TaO6 octahedra. All Ta–O bond lengths are 2.00 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Na1+ and two Ta5+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to three equivalent Ta5+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one Na1+ and three equivalent Ta5+ atoms.