Materials Data on K3Ta8O21 by Materials Project
K3Ta8O21 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. K1+ is bonded in a 6-coordinate geometry to twelve O2- atoms. There are a spread of K–O bond distances ranging from 2.91–3.28 Å. There are two inequivalent Ta+4.88+ sites. In the first Ta+4.88+ site, Ta+4.88+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 21–41°. There are three shorter (1.93 Å) and three longer (2.11 Å) Ta–O bond lengths. In the second Ta+4.88+ site, Ta+4.88+ is bonded to six equivalent O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles are 37°. 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 one K1+ and three equivalent Ta+4.88+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent K1+ and two equivalent Ta+4.88+ atoms. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent K1+ and two Ta+4.88+ atoms.