DOI: 10.17188/1263293
title: Materials Data on NaTa4O8 by Materials Project

description: NaTa4O8 crystallizes in the orthorhombic Pmmn space group. The structure is three-dimensional. there are three inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.40–2.62 Å. In the second Na1+ site, Na1+ is bonded to eight O2- atoms to form distorted NaO8 hexagonal bipyramids that share edges with four equivalent TaO6 octahedra and edges with four equivalent TaO6 pentagonal pyramids. There are a spread of Na–O bond distances ranging from 2.39–2.61 Å. In the third Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.28–2.63 Å. There are six inequivalent Ta+3.75+ sites. In the first Ta+3.75+ site, Ta+3.75+ is bonded in a rectangular see-saw-like geometry to four equivalent O2- atoms. All Ta–O bond lengths are 2.02 Å. In the second Ta+3.75+ site, Ta+3.75+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Ta–O bond lengths are 2.03 Å. In the third Ta+3.75+ site, Ta+3.75+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Ta–O bond lengths are 2.03 Å. In the fourth Ta+3.75+ site, Ta+3.75+ is bonded to six O2- atoms to form distorted TaO6 pentagonal pyramids that share corners with two equivalent TaO6 pentagonal pyramids, an edgeedge with one NaO8 hexagonal bipyramid, an edgeedge with one TaO6 octahedra, and an edgeedge with one TaO6 pentagonal pyramid. There are a spread of Ta–O bond distances ranging from 1.98–2.20 Å. In the fifth Ta+3.75+ site, Ta+3.75+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Ta–O bond lengths are 2.02 Å. In the sixth Ta+3.75+ site, Ta+3.75+ is bonded to six O2- atoms to form distorted TaO6 octahedra that share corners with two equivalent TaO6 octahedra, an edgeedge with one NaO8 hexagonal bipyramid, an edgeedge with one TaO6 octahedra, and an edgeedge with one TaO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 32–65°. There are a spread of Ta–O bond distances ranging from 1.96–2.17 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ta+3.75+ atoms. In the second O2- site, O2- is bonded in a distorted T-shaped geometry to one Na1+ and two equivalent Ta+3.75+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one Na1+ and three Ta+3.75+ atoms. In the fourth O2- site, O2- is bonded to two Na1+ and two equivalent Ta+3.75+ atoms to form a mixture of distorted edge and corner-sharing ONa2Ta2 tetrahedra. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to one Na1+ and three Ta+3.75+ atoms. In the sixth O2- site, O2- is bonded to two Na1+ and two equivalent Ta+3.75+ atoms to form a mixture of distorted edge and corner-sharing ONa2Ta2 trigonal pyramids. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to one Na1+ and three Ta+3.75+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Na1+ and two equivalent Ta+3.75+ atoms.