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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on K3NbAs2O9 by Materials Project

K3NbAs2O9 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to seven O2- atoms to form distorted KO7 hexagonal pyramids that share corners with two equivalent KO7 hexagonal pyramids, a cornercorner with one AsO4 tetrahedra, edges with three equivalent NbO6 octahedra, and edges with three AsO4 tetrahedra. There are a spread of K–O bond distances ranging from 2.74–2.86 Å. In the second K1+ site, K1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of K–O bond distances ranging from 2.76–3.41 Å. In the third K1+ site, K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.57–3.30 Å. Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with five AsO4 tetrahedra and edges with three equivalent KO7 hexagonal pyramids. There are a spread of Nb–O bond distances ranging from 1.77–2.42 Å. There are two inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with two equivalent NbO6 octahedra and an edgeedge with one KO7 hexagonal pyramid. The corner-sharing octahedral tilt angles are 32°. There are a spread of As–O bond distances ranging from 1.68–1.77 Å. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share a cornercorner with one KO7 hexagonal pyramid, corners with three equivalent NbO6 octahedra, and edges with two equivalent KO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 32–34°. There are a spread of As–O bond distances ranging from 1.69–1.75 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to four K1+ and one As5+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to three K1+ and one As5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to four K1+ and one As5+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to three K1+, one Nb5+, and one As5+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two K1+, one Nb5+, and one As5+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to four K1+ and one Nb5+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K6NbAs3O by Materials Project

K6NbAs3O crystallizes in the cubic P2_13 space group. The structure is three-dimensional. there are four inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a distorted single-bond geometry to one K1+, four equivalent As3-, and one O2- atom. The K–K bond length is 3.60 Å. There are a spread of K–As bond distances ranging from 3.34–3.65 Å. The K–O bond length is 2.71 Å. In the second K1+ site, K1+ is bonded in a 3-coordinate geometry to three equivalent K1+ and six equivalent As3- atoms. There are three shorter (3.80 Å) and three longer (3.89 Å) K–As bond lengths. In the third K1+ site, K1+ is bonded to three equivalent As3- and one O2- atom to form KAs3O trigonal pyramids that share corners with four equivalent NbAs3O tetrahedra. All K–As bond lengths are 3.21 Å. The K–O bond length is 2.94 Å. In the fourth K1+ site, K1+ is bonded in a distorted trigonal non-coplanar geometry to three equivalent As3- atoms. All K–As bond lengths are 3.46 Å. Nb5+ is bonded to three equivalent As3- and one O2- atom to form distorted NbAs3O tetrahedra that share corners with four equivalent KAs3O trigonal pyramids. All Nb–As bond lengths are 2.54 Å. The Nb–O bond length is 1.86 Å. As3- is bonded in a 1-coordinate geometry to eight K1+ and one Nb5+ atom. O2- is bonded in a 1-coordinate geometry to four K1+ and one Nb5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KNb4AsO13 by Materials Project

KNb4AsO13 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of K–O bond distances ranging from 2.72–3.13 Å. In the second K1+ site, K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.76–3.37 Å. In the third K1+ site, K1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of K–O bond distances ranging from 2.75–3.02 Å. In the fourth K1+ site, K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.75–3.37 Å. There are sixteen inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–41°. There are a spread of Nb–O bond distances ranging from 1.87–2.16 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–41°. There are a spread of Nb–O bond distances ranging from 1.87–2.17 Å. In the third Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, corners with two AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 20–29°. There are a spread of Nb–O bond distances ranging from 1.83–2.29 Å. In the fourth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, corners with two AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 21–29°. There are a spread of Nb–O bond distances ranging from 1.84–2.29 Å. In the fifth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, corners with two AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 21–29°. There are a spread of Nb–O bond distances ranging from 1.84–2.29 Å. In the sixth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, corners with two AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 20–29°. There are a spread of Nb–O bond distances ranging from 1.84–2.29 Å. In the seventh Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–41°. There are a spread of Nb–O bond distances ranging from 1.87–2.17 Å. In the eighth Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–41°. There are a spread of Nb–O bond distances ranging from 1.87–2.17 Å. In the ninth Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–40°. There are a spread of Nb–O bond distances ranging from 1.86–2.17 Å. In the tenth Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–41°. There are a spread of Nb–O bond distances ranging from 1.87–2.16 Å. In the eleventh Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, corners with two AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 21–29°. There are a spread of Nb–O bond distances ranging from 1.84–2.29 Å. In the twelfth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, corners with two AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 21–29°. There are a spread of Nb–O bond distances ranging from 1.84–2.29 Å. In the thirteenth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, corners with two AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 20–28°. There are a spread of Nb–O bond distances ranging from 1.83–2.30 Å. In the fourteenth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, corners with two AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 21–29°. There are a spread of Nb–O bond distances ranging from 1.84–2.29 Å. In the fifteenth Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–40°. There are a spread of Nb–O bond distances ranging from 1.86–2.17 Å. In the sixteenth Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–41°. There are a spread of Nb–O bond distances ranging from 1.87–2.17 Å. There are four inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 45–55°. There is two shorter (1.70 Å) and two longer (1.74 Å) As–O bond length. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 45–55°. There is two shorter (1.70 Å) and two longer (1.74 Å) As–O bond length. In the third As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 45–55°. There is two shorter (1.70 Å) and two longer (1.74 Å) As–O bond length. In the fourth As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 45–55°. There is two shorter (1.70 Å) and two longer (1.74 Å) As–O bond length. There are fifty-two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the seventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two K1+ and two Nb5+ atoms. In the eighth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two Nb5+ atoms. In the ninth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the tenth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the eleventh O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the twelfth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two Nb5+ atoms. In the fourteenth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the fifteenth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the sixteenth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the seventeenth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the eighteenth O2- site, O2- is bonded in a 3-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the nineteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Nb5+ and one As5+ atom. In the twentieth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Nb5+ and one As5+ atom. In the twenty-first O2- site, O2- is bonded in a distorted trigonal planar geometry to two Nb5+ and one As5+ atom. In the twenty-second O2- site, O2- is bonded in a distorted trigonal planar geometry to two Nb5+ and one As5+ atom. In the twenty-third O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the twenty-fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the twenty-fifth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the twenty-sixth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the twenty-seventh O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the twenty-eighth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the twenty-ninth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the thirtieth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the thirty-first O2- site, O2- is bonded in a distorted trigonal planar geometry to two Nb5+ and one As5+ atom. In the thirty-second O2- site, O2- is bonded in a distorted trigonal planar geometry to two Nb5+ and one As5+ atom. In the thirty-third O2- site, O2- is bonded in a distorted trigonal planar geometry to two Nb5+ and one As5+ atom. In the thirty-fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Nb5+ and one As5+ atom. In the thirty-fifth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the thirty-sixth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the thirty-seventh O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the thirty-eighth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the thirty-ninth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the fortieth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the forty-first O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the forty-second O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the forty-third O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the forty-fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the forty-fifth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the forty-sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two K1+ and two Nb5+ atoms. In the forty-seventh O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the forty-eighth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the forty-ninth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2Nb2As2O11 by Materials Project

K2Nb2As2O11 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are four inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of K–O bond distances ranging from 2.90–3.20 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of K–O bond distances ranging from 2.92–3.22 Å. In the third K1+ site, K1+ is bonded to eight O2- atoms to form distorted KO8 hexagonal bipyramids that share corners with two NbO6 octahedra, corners with two AsO4 tetrahedra, and edges with four NbO6 octahedra. The corner-sharing octahedral tilt angles are 61°. There are a spread of K–O bond distances ranging from 2.88–3.03 Å. In the fourth K1+ site, K1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of K–O bond distances ranging from 2.74–3.21 Å. There are four inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share a cornercorner with one NbO6 octahedra, corners with four AsO4 tetrahedra, and an edgeedge with one KO8 hexagonal bipyramid. The corner-sharing octahedral tilt angles are 27°. There are a spread of Nb–O bond distances ranging from 1.77–2.31 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share a cornercorner with one NbO6 octahedra, corners with four AsO4 tetrahedra, and an edgeedge with one KO8 hexagonal bipyramid. The corner-sharing octahedral tilt angles are 26°. There are a spread of Nb–O bond distances ranging from 1.77–2.34 Å. In the third Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share a cornercorner with one KO8 hexagonal bipyramid, a cornercorner with one NbO6 octahedra, corners with four AsO4 tetrahedra, and an edgeedge with one KO8 hexagonal bipyramid. The corner-sharing octahedral tilt angles are 27°. There are a spread of Nb–O bond distances ranging from 1.79–2.26 Å. In the fourth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share a cornercorner with one KO8 hexagonal bipyramid, a cornercorner with one NbO6 octahedra, corners with four AsO4 tetrahedra, and an edgeedge with one KO8 hexagonal bipyramid. The corner-sharing octahedral tilt angles are 26°. There are a spread of Nb–O bond distances ranging from 1.79–2.26 Å. There are four inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with four NbO6 octahedra. The corner-sharing octahedra tilt angles range from 46–54°. There are a spread of As–O bond distances ranging from 1.70–1.76 Å. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with four NbO6 octahedra. The corner-sharing octahedra tilt angles range from 46–54°. There are a spread of As–O bond distances ranging from 1.69–1.76 Å. In the third As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share a cornercorner with one KO8 hexagonal bipyramid and corners with four NbO6 octahedra. The corner-sharing octahedra tilt angles range from 52–56°. All As–O bond lengths are 1.72 Å. In the fourth As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share a cornercorner with one KO8 hexagonal bipyramid and corners with four NbO6 octahedra. The corner-sharing octahedra tilt angles range from 52–56°. All As–O bond lengths are 1.72 Å. There are twenty-two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two Nb5+ atoms. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two Nb5+ atoms. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two K1+ and one Nb5+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to two K1+ and one Nb5+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Nb5+ and one As5+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the ninth O2- site, O2- is bonded in a bent 120 degrees geometry to one Nb5+ and one As5+ atom. In the tenth O2- site, O2- is bonded in a bent 120 degrees geometry to one Nb5+ and one As5+ atom. In the eleventh O2- site, O2- is bonded in a distorted single-bond geometry to three K1+ and one Nb5+ atom. In the twelfth O2- site, O2- is bonded in a distorted single-bond geometry to three K1+ and one Nb5+ atom. In the thirteenth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the fourteenth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the fifteenth O2- site, O2- is bonded in a 1-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the sixteenth O2- site, O2- is bonded in a 1-coordinate geometry to two K1+, one Nb5+, and one As5+ atom. In the seventeenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one K1+, one Nb5+, and one As5+ atom. In the eighteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one K1+, one Nb5+, and one As5+ atom. In the nineteenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one Nb5+, and one As5+ atom. In the twentieth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one Nb5+, and one As5+ atom. In the twenty-first O2- site, O2- is bonded in a 3-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the twenty-second O2- site, O2- is bonded in a 3-coordinate geometry to one K1+, one Nb5+, and one As5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KNb4AsO13 by Materials Project

KNb4AsO13 crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.81–3.33 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with five NbO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–42°. There are a spread of Nb–O bond distances ranging from 1.87–2.17 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four equivalent NbO6 octahedra, corners with two equivalent AsO4 tetrahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 20–28°. There are a spread of Nb–O bond distances ranging from 1.84–2.28 Å. As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 45–54°. There are a spread of As–O bond distances ranging from 1.71–1.74 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Nb5+ and one As5+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Nb5+ and one As5+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two Nb5+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two equivalent Nb5+ atoms. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+ and two Nb5+ atoms.

36 MATERIALS SCIENCE↗