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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ta8Pb6O25 by Materials Project

Ta8Pb6O25 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are eight inequivalent Ta+4.75+ sites. In the first Ta+4.75+ site, Ta+4.75+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with four PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 36–43°. There are a spread of Ta–O bond distances ranging from 1.96–2.04 Å. In the second Ta+4.75+ site, Ta+4.75+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with two PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 37–44°. There are a spread of Ta–O bond distances ranging from 1.94–2.05 Å. In the third Ta+4.75+ site, Ta+4.75+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with four PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 36–43°. There are a spread of Ta–O bond distances ranging from 1.96–2.04 Å. In the fourth Ta+4.75+ site, Ta+4.75+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with two PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 34–44°. There are a spread of Ta–O bond distances ranging from 1.94–2.06 Å. In the fifth Ta+4.75+ site, Ta+4.75+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with four PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 36–42°. There are a spread of Ta–O bond distances ranging from 1.96–2.04 Å. In the sixth Ta+4.75+ site, Ta+4.75+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with four PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 36–42°. There are a spread of Ta–O bond distances ranging from 1.98–2.02 Å. In the seventh Ta+4.75+ site, Ta+4.75+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with two PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 37–44°. There are a spread of Ta–O bond distances ranging from 1.96–2.04 Å. In the eighth Ta+4.75+ site, Ta+4.75+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with two PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 34–44°. There are a spread of Ta–O bond distances ranging from 1.94–2.05 Å. There are six inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a hexagonal planar geometry to six O2- atoms. There are a spread of Pb–O bond distances ranging from 2.65–2.89 Å. In the second Pb2+ site, Pb2+ is bonded in a hexagonal planar geometry to six O2- atoms. There are a spread of Pb–O bond distances ranging from 2.68–2.85 Å. In the third Pb2+ site, Pb2+ is bonded to seven O2- atoms to form distorted PbO7 hexagonal pyramids that share a cornercorner with one PbO7 hexagonal pyramid, edges with three PbO7 hexagonal pyramids, and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.37–2.77 Å. In the fourth Pb2+ site, Pb2+ is bonded to seven O2- atoms to form distorted PbO7 hexagonal pyramids that share a cornercorner with one PbO7 hexagonal pyramid, edges with three PbO7 hexagonal pyramids, and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.36–2.74 Å. In the fifth Pb2+ site, Pb2+ is bonded to seven O2- atoms to form distorted PbO7 hexagonal pyramids that share a cornercorner with one PbO7 hexagonal pyramid, edges with three PbO7 hexagonal pyramids, and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.37–2.79 Å. In the sixth Pb2+ site, Pb2+ is bonded to seven O2- atoms to form distorted PbO7 hexagonal pyramids that share a cornercorner with one PbO7 hexagonal pyramid, edges with three PbO7 hexagonal pyramids, and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.37–2.78 Å. There are twenty-five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta+4.75+ and two Pb2+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta+4.75+ and two Pb2+ atoms. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and two Pb2+ atoms. In the seventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and two Pb2+ atoms. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta+4.75+ and two Pb2+ atoms. In the ninth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta+4.75+ and two Pb2+ atoms. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta+4.75+ and two Pb2+ atoms. In the eleventh O2- site, O2- is bonded in a tetrahedral geometry to four Pb2+ atoms. In the twelfth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and two Pb2+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the fourteenth O2- site, O2- is bonded in a bent 150 degrees geometry to two Ta+4.75+ atoms. In the fifteenth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta+4.75+ and two Pb2+ atoms. In the sixteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the seventeenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and two Pb2+ atoms. In the eighteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the nineteenth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta+4.75+ and two Pb2+ atoms. In the twentieth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and two Pb2+ atoms. In the twenty-first O2- site, O2- is bonded in a 2-coordinate geometry to two Ta+4.75+ and two Pb2+ atoms. In the twenty-second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the twenty-third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the twenty-fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom. In the twenty-fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.75+ and one Pb2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta6Pb4O19 by Materials Project

Pb4Ta6O19 crystallizes in the monoclinic C2/m 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 six TaO6 octahedra, edges with two equivalent PbO8 hexagonal bipyramids, and edges with two equivalent PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 34–42°. There are a spread of Ta–O bond distances ranging from 1.89–2.13 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra, edges with two PbO8 hexagonal bipyramids, and edges with two equivalent PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 36–42°. There are a spread of Ta–O bond distances ranging from 1.98–2.02 Å. In the third Ta5+ site, Ta5+ is bonded to six O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 40–43°. 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 corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 34–42°. There are a spread of Ta–O bond distances ranging from 1.94–2.03 Å. In the fifth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with six PbO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 41–42°. 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 corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 36–40°. There are two shorter (1.99 Å) and four longer (2.02 Å) Ta–O bond lengths. There are five inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a hexagonal planar geometry to six O2- atoms. There are a spread of Pb–O bond distances ranging from 2.60–2.75 Å. In the second Pb2+ site, Pb2+ is bonded in a hexagonal planar geometry to six O2- atoms. There are four shorter (2.68 Å) and two longer (2.70 Å) Pb–O bond lengths. In the third Pb2+ site, Pb2+ is bonded to seven O2- atoms to form distorted PbO7 hexagonal pyramids that share edges with three PbO8 hexagonal bipyramids and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.14–2.83 Å. In the fourth Pb2+ site, Pb2+ is bonded to eight O2- atoms to form distorted PbO8 hexagonal bipyramids that share edges with four equivalent PbO8 hexagonal bipyramids, edges with two equivalent PbO7 hexagonal pyramids, and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.43–2.80 Å. In the fifth Pb2+ site, Pb2+ is bonded to eight O2- atoms to form PbO8 hexagonal bipyramids that share edges with four PbO8 hexagonal bipyramids, edges with two equivalent PbO7 hexagonal pyramids, and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.44–2.74 Å. There are thirteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two Ta5+ atoms. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and one Pb2+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and one Pb2+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ta5+ and two Pb2+ atoms. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and one Pb2+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and one Pb2+ atom. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to two Ta5+ atoms. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ta5+ and two Pb2+ atoms. In the ninth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta5+ and two Pb2+ atoms. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta5+ and two equivalent Pb2+ atoms. In the eleventh O2- site, O2- is bonded to four Pb2+ atoms to form distorted corner-sharing OPb4 tetrahedra. In the twelfth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta5+ and two Pb2+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ta5+ and two Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta2Pb2O7 by Materials Project

Pb2Ta2O7 crystallizes in the orthorhombic Cmc2_1 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 corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 2–19°. There are a spread of Ta–O bond distances ranging from 1.88–2.23 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form distorted corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 2–19°. There are a spread of Ta–O bond distances ranging from 1.85–2.35 Å. There are two inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Pb–O bond distances ranging from 2.49–2.59 Å. In the second Pb2+ site, Pb2+ is bonded in a 11-coordinate geometry to eleven O2- atoms. There are a spread of Pb–O bond distances ranging from 2.55–3.09 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two Ta5+ and two equivalent Pb2+ atoms. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Ta5+ and four equivalent Pb2+ atoms. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one Ta5+ and three equivalent Pb2+ atoms. In the fourth O2- site, O2- is bonded in a distorted linear geometry to two Ta5+ and two equivalent Pb2+ atoms. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to one Ta5+ and three equivalent Pb2+ atoms. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ta5+ and one Pb2+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ta5+ and two equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta2Pb2O7 by Materials Project

Pb2Ta2O7 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Ta5+ is bonded to six equivalent O2- atoms to form TaO6 octahedra that share corners with six equivalent TaO6 octahedra and edges with six equivalent PbO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. All Ta–O bond lengths are 2.02 Å. Pb2+ is bonded to eight O2- atoms to form distorted PbO8 hexagonal bipyramids that share edges with six equivalent PbO8 hexagonal bipyramids and edges with six equivalent TaO6 octahedra. There are two shorter (2.34 Å) and six longer (2.82 Å) Pb–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Pb2+ atoms to form corner-sharing OPb4 tetrahedra. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ta5+ and two equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta5Pb11O26 by Materials Project

Ta5Pb11O26 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Ta+4.80+ sites. In the first Ta+4.80+ site, Ta+4.80+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent PbO6 octahedra, corners with four equivalent TaO6 octahedra, and edges with two equivalent PbO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 35–48°. There are two shorter (2.00 Å) and four longer (2.02 Å) Ta–O bond lengths. In the second Ta+4.80+ site, Ta+4.80+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent PbO6 octahedra, corners with four TaO6 octahedra, and edges with two equivalent PbO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 35–50°. There are two shorter (2.00 Å) and four longer (2.01 Å) Ta–O bond lengths. In the third Ta+4.80+ site, Ta+4.80+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent TaO6 octahedra and corners with four PbO6 octahedra. The corner-sharing octahedra tilt angles range from 30–48°. There are a spread of Ta–O bond distances ranging from 1.99–2.01 Å. There are six inequivalent Pb+2.55+ sites. In the first Pb+2.55+ site, Pb+2.55+ is bonded to eight O2- atoms to form PbO8 hexagonal bipyramids that share edges with six TaO6 octahedra. There are two shorter (2.52 Å) and six longer (2.79 Å) Pb–O bond lengths. In the second Pb+2.55+ site, Pb+2.55+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Pb–O bond distances ranging from 2.33–3.03 Å. In the third Pb+2.55+ site, Pb+2.55+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Pb–O bond distances ranging from 2.30–3.06 Å. In the fourth Pb+2.55+ site, Pb+2.55+ is bonded in a hexagonal planar geometry to six O2- atoms. There are four shorter (2.62 Å) and two longer (2.93 Å) Pb–O bond lengths. In the fifth Pb+2.55+ site, Pb+2.55+ is bonded to six O2- atoms to form PbO6 octahedra that share corners with two equivalent PbO6 octahedra and corners with four equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 48–55°. There are two shorter (2.18 Å) and four longer (2.19 Å) Pb–O bond lengths. In the sixth Pb+2.55+ site, Pb+2.55+ is bonded to six O2- atoms to form PbO6 octahedra that share a cornercorner with one PbO6 octahedra and corners with five TaO6 octahedra. The corner-sharing octahedra tilt angles range from 44–55°. There are a spread of Pb–O bond distances ranging from 2.17–2.22 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ta+4.80+ and two Pb+2.55+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one Ta+4.80+ and three Pb+2.55+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one Ta+4.80+ and three Pb+2.55+ atoms. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta+4.80+ and two Pb+2.55+ atoms. In the fifth O2- site, O2- is bonded to four Pb+2.55+ atoms to form a mixture of edge and corner-sharing OPb4 tetrahedra. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Ta+4.80+ and two Pb+2.55+ atoms. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to one Ta+4.80+ and three Pb+2.55+ atoms. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to one Ta+4.80+ and three Pb+2.55+ atoms. In the ninth O2- site, O2- is bonded to four Pb+2.55+ atoms to form a mixture of distorted edge and corner-sharing OPb4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta2PbO6 by Materials Project

PbTa2O6 crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Ta5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ta–O bond distances ranging from 1.82–2.46 Å. Pb2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Pb–O bond distances ranging from 2.53–2.58 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one Ta5+ and two equivalent Pb2+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ta5+ and one Pb2+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to three equivalent Ta5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta2PbO6 by Materials Project

PbTa2O6 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ta5+ 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 22–37°. There are a spread of Ta–O bond distances ranging from 1.93–2.13 Å. Pb2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Pb–O bond distances ranging from 2.60–2.77 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ta5+ and two equivalent Pb2+ atoms. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ta5+ and one Pb2+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ta5+ and one Pb2+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ta5+ and one Pb2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta6Pb4O19 by Materials Project

Pb4Ta6O19 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. there are four inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra, edges with two equivalent PbO8 hexagonal bipyramids, and edges with two equivalent PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 34–44°. There are a spread of Ta–O bond distances ranging from 1.92–2.06 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedra tilt angles range from 34–41°. There is two shorter (1.98 Å) and four longer (2.01 Å) Ta–O bond length. In the third Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra, an edgeedge with one PbO8 hexagonal bipyramid, and edges with two equivalent PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 41–42°. There are a spread of Ta–O bond distances ranging from 1.98–2.01 Å. In the fourth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra and edges with four equivalent PbO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 38–40°. There is four shorter (1.99 Å) and two longer (2.00 Å) Ta–O bond length. There are three inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded to seven O2- atoms to form distorted PbO7 hexagonal pyramids that share edges with two equivalent PbO8 hexagonal bipyramids, an edgeedge with one PbO7 hexagonal pyramid, and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.22–2.88 Å. In the second Pb2+ site, Pb2+ is bonded in a hexagonal planar geometry to six O2- atoms. There are four shorter (2.67 Å) and two longer (2.69 Å) Pb–O bond lengths. In the third Pb2+ site, Pb2+ is bonded to eight O2- atoms to form PbO8 hexagonal bipyramids that share edges with two equivalent PbO8 hexagonal bipyramids, edges with four equivalent PbO7 hexagonal pyramids, and edges with six TaO6 octahedra. There are a spread of Pb–O bond distances ranging from 2.52–2.72 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ta5+ and two equivalent Pb2+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ta5+ and two equivalent Pb2+ atoms. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and one Pb2+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two Ta5+ atoms. In the fifth O2- site, O2- is bonded to four Pb2+ atoms to form corner-sharing OPb4 tetrahedra. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to two Ta5+ and two Pb2+ atoms. In the seventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ta5+ and two Pb2+ atoms. In the eighth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ta5+ and one Pb2+ atom.

36 MATERIALS SCIENCE↗