DOE OSTI2020
Bi7Ta3O18 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are six inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with three TaO6 octahedra, a cornercorner with one BiO6 pentagonal pyramid, and an edgeedge with one BiO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 15–33°. There are a spread of Ta–O bond distances ranging from 1.95–2.08 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with three TaO6 octahedra, a cornercorner with one BiO6 pentagonal pyramid, and an edgeedge with one BiO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 13–33°. There are a spread of Ta–O bond distances ranging from 1.89–2.15 Å. In the third Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent TaO6 octahedra, a cornercorner with one BiO7 pentagonal bipyramid, and edges with two BiO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 31–35°. There are a spread of Ta–O bond distances ranging from 1.97–2.03 Å. In the fourth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with three TaO6 octahedra, a cornercorner with one BiO7 pentagonal bipyramid, a cornercorner with one BiO6 pentagonal pyramid, and an edgeedge with one BiO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 15–34°. There are a spread of Ta–O bond distances ranging from 1.90–2.14 Å. In the fifth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent TaO6 octahedra, a cornercorner with one BiO7 pentagonal bipyramid, and edges with two BiO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 31–35°. There are a spread of Ta–O bond distances ranging from 1.91–2.13 Å. In the sixth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with three TaO6 octahedra, a cornercorner with one BiO7 pentagonal bipyramid, a cornercorner with one BiO6 pentagonal pyramid, and an edgeedge with one BiO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 13–34°. There are a spread of Ta–O bond distances ranging from 1.92–2.13 Å. There are fourteen inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Bi–O bond distances ranging from 2.28–2.96 Å. In the second Bi3+ site, Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.27–2.90 Å. In the third Bi3+ site, Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.25–2.95 Å. In the fourth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.26–2.67 Å. In the fifth Bi3+ site, Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.21–2.95 Å. In the sixth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.30–2.67 Å. In the seventh Bi3+ site, Bi3+ is bonded in a 8-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.35–2.88 Å. In the eighth Bi3+ site, Bi3+ is bonded to six O2- atoms to form distorted BiO6 pentagonal pyramids that share corners with two TaO6 octahedra and edges with two TaO6 octahedra. The corner-sharing octahedra tilt angles range from 29–30°. There are a spread of Bi–O bond distances ranging from 2.13–2.70 Å. In the ninth Bi3+ site, Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.21–2.96 Å. In the tenth Bi3+ site, Bi3+ is bonded to six O2- atoms to form distorted BiO6 pentagonal pyramids that share corners with two TaO6 octahedra, a cornercorner with one BiO7 pentagonal bipyramid, and edges with two TaO6 octahedra. The corner-sharing octahedral tilt angles are 47°. There are a spread of Bi–O bond distances ranging from 2.10–2.75 Å. In the eleventh Bi3+ site, Bi3+ is bonded to seven O2- atoms to form distorted BiO7 pentagonal bipyramids that share corners with two TaO6 octahedra and edges with two TaO6 octahedra. The corner-sharing octahedral tilt angles are 33°. There are a spread of Bi–O bond distances ranging from 2.22–2.78 Å. In the twelfth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.13–2.88 Å. In the thirteenth Bi3+ site, Bi3+ is bonded to seven O2- atoms to form distorted BiO7 pentagonal bipyramids that share corners with two TaO6 octahedra, a cornercorner with one BiO6 pentagonal pyramid, and edges with two TaO6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are a spread of Bi–O bond distances ranging from 2.29–2.79 Å. In the fourteenth Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.11–2.88 Å. There are thirty-six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and two Bi3+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the eighth O2- site, O2- is bonded in a 1-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the tenth O2- site, O2- is bonded in a linear geometry to two Ta5+ atoms. In the eleventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and two Bi3+ atoms. In the twelfth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the fourteenth O2- site, O2- is bonded in a bent 150 degrees geometry to two Ta5+ and one Bi3+ atom. In the fifteenth O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the sixteenth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra. In the seventeenth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra. In the eighteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and one Bi3+ atom. In the nineteenth O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the twentieth O2- site, O2- is bonded in a 3-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the twenty-first O2- site, O2- is bonded in a 4-coordinate geometry to four Bi3+ atoms. In the twenty-second O2- site, O2- is bonded in a 3-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the twenty-third O2- site, O2- is bonded in a bent 150 degrees geometry to two Ta5+ and two Bi3+ atoms. In the twenty-fourth O2- site, O2- is bonded to four Bi3+ atoms to form distorted corner-sharing OBi4 tetrahedra. In the twenty-fifth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of distorted edge and corner-sharing OBi4 tetrahedra. In the twenty-sixth O2- site, O2- is bonded in a 1-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the twenty-seventh O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the twenty-eighth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and two Bi3+ atoms. In the twenty-ninth O2- site, O2- is bonded in a 3-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the thirtieth O2- site, O2- is bonded in a 1-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the thirty-first O2- site, O2- is bonded in a 4-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the thirty-second O2- site, O2- is bonded in a 2-coordinate geometry to one Ta5+ and three Bi3+ atoms. In the thirty-third O2- site, O2- is bonded in a 1-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the thirty-fourth O2- site, O2- is bonded to four Bi3+ atoms to form corner-sharing OBi4 tetrahedra. In the thirty-fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Ta5+ and two Bi3+ atoms. In the thirty-sixth O2- site, O2- is bonded in a linear geometry to two Ta5+ atoms.