DOI: 10.17188/1279979
title: Materials Data on Ca2Ta2O7 by Materials Project

description: Ca2Ta2O7 crystallizes in the orthorhombic C222_1 space group. The structure is three-dimensional. there are nine inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.43–2.84 Å. In the second Ca2+ site, Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.19–3.01 Å. In the third Ca2+ site, Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.36–3.07 Å. In the fourth Ca2+ site, Ca2+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.45–2.78 Å. In the fifth Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share a cornercorner with one TaO6 octahedra, edges with three CaO8 hexagonal bipyramids, and edges with six TaO6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are a spread of Ca–O bond distances ranging from 2.33–2.86 Å. In the sixth Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.29–2.73 Å. In the seventh Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share a cornercorner with one CaO8 hexagonal bipyramid, a cornercorner with one TaO6 octahedra, edges with two equivalent CaO8 hexagonal bipyramids, and edges with six TaO6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are a spread of Ca–O bond distances ranging from 2.32–2.84 Å. In the eighth Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent CaO8 hexagonal bipyramids, corners with two equivalent TaO6 octahedra, edges with two equivalent CaO8 hexagonal bipyramids, and edges with six TaO6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are a spread of Ca–O bond distances ranging from 2.18–2.92 Å. In the ninth Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent TaO6 octahedra and edges with six TaO6 octahedra. The corner-sharing octahedral tilt angles are 57°. There are a spread of Ca–O bond distances ranging from 2.19–2.81 Å. There are nine inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with five TaO6 octahedra and edges with two equivalent CaO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 34–45°. There are a spread of Ta–O bond distances ranging from 1.95–2.07 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share a cornercorner with one CaO8 hexagonal bipyramid and corners with four TaO6 octahedra. The corner-sharing octahedra tilt angles range from 35–46°. There are a spread of Ta–O bond distances ranging from 1.93–2.11 Å. In the third Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share a cornercorner with one CaO8 hexagonal bipyramid, corners with four TaO6 octahedra, and an edgeedge with one CaO8 hexagonal bipyramid. The corner-sharing octahedra tilt angles range from 40–44°. There are a spread of Ta–O bond distances ranging from 1.99–2.02 Å. In the fourth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share a cornercorner with one CaO8 hexagonal bipyramid, corners with four TaO6 octahedra, and edges with four CaO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 38–47°. There are a spread of Ta–O bond distances ranging from 1.93–2.13 Å. In the fifth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent CaO8 hexagonal bipyramids, corners with four equivalent TaO6 octahedra, and edges with four CaO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. There are two shorter (2.00 Å) and four longer (2.01 Å) Ta–O bond lengths. In the sixth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with two CaO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 40–44°. There are a spread of Ta–O bond distances ranging from 1.97–2.01 Å. In the seventh Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with five CaO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 38–45°. There are a spread of Ta–O bond distances ranging from 1.97–2.02 Å. In the eighth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with two equivalent CaO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 39–46°. There are a spread of Ta–O bond distances ranging from 1.97–2.01 Å. In the ninth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and an edgeedge with one CaO8 hexagonal bipyramid. The corner-sharing octahedra tilt angles range from 35–47°. There are a spread of Ta–O bond distances ranging from 1.97–2.00 Å. There are twenty-nine inequivalent O2- sites. In the first O2- site, O2- is bonded to three Ca2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ca2+ and two equivalent Ta5+ atoms. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+ and two equivalent Ta5+ atoms. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the tenth O2- site, O2- is bonded to three Ca2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. In the eleventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ca2+ and two Ta5+ atoms. In the twelfth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the thirteenth O2- site, O2- is bonded to three Ca2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. In the fourteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the fifteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the sixteenth O2- site, O2- is bonded to three Ca2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. In the seventeenth O2- site, O2- is bonded in a 2-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the eighteenth O2- site, O2- is bonded in a 2-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the nineteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the twentieth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the twenty-first O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the twenty-second O2- site, O2- is bonded to three Ca2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. In the twenty-third O2- site, O2- is bonded to three Ca2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. In the twenty-fourth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the twenty-fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ca2+ and two equivalent Ta5+ atoms. In the twenty-sixth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the twenty-seventh O2- site, O2- is bonded to three Ca2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. In the twenty-eighth O2- site, O2- is bonded in a 2-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the twenty-ninth O2- site, O2- is bonded to three Ca2+ and one Ta5+ atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra.