DOE OSTI2020
Mn4Ta2O9 is Ilmenite-like structured and crystallizes in the monoclinic Cc space group. The structure is three-dimensional. there are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with three equivalent TaO6 octahedra, corners with three equivalent MnO6 octahedra, corners with two equivalent MnO6 pentagonal pyramids, and a faceface with one MnO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 38–46°. There are a spread of Ta–O bond distances ranging from 1.90–2.25 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with three equivalent TaO6 octahedra, corners with three equivalent MnO6 octahedra, a cornercorner with one MnO6 pentagonal pyramid, and an edgeedge with one MnO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 38–42°. There are a spread of Ta–O bond distances ranging from 1.90–2.21 Å. There are four inequivalent Mn2+ sites. In the first Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with six TaO6 octahedra and edges with two equivalent MnO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 38–46°. There are a spread of Mn–O bond distances ranging from 2.13–2.29 Å. In the second Mn2+ site, Mn2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mn–O bond distances ranging from 2.11–2.46 Å. In the third Mn2+ site, Mn2+ is bonded to six O2- atoms to form distorted MnO6 pentagonal pyramids that share corners with three TaO6 octahedra, an edgeedge with one TaO6 octahedra, edges with two equivalent MnO6 octahedra, and a faceface with one TaO6 octahedra. The corner-sharing octahedra tilt angles range from 59–65°. There are a spread of Mn–O bond distances ranging from 2.15–2.38 Å. In the fourth Mn2+ site, Mn2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mn–O bond distances ranging from 2.14–2.43 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded to one Ta5+ and three Mn2+ atoms to form a mixture of distorted corner and edge-sharing OTaMn3 trigonal pyramids. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Mn2+ atoms. In the third O2- site, O2- is bonded to one Ta5+ and three Mn2+ atoms to form distorted corner-sharing OTaMn3 trigonal pyramids. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to two Ta5+ and two Mn2+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to two Ta5+ and two Mn2+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Mn2+ atoms. In the seventh O2- site, O2- is bonded in a distorted see-saw-like geometry to one Ta5+ and three Mn2+ atoms. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to two Ta5+ and two Mn2+ atoms. In the ninth O2- site, O2- is bonded to one Ta5+ and three Mn2+ atoms to form a mixture of distorted corner and edge-sharing OTaMn3 trigonal pyramids.