DOE OSTI2020
Na4SrTa5O15 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are five inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to twelve O2- atoms to form distorted NaO12 cuboctahedra that share corners with four equivalent SrO12 cuboctahedra, corners with eight NaO12 cuboctahedra, a faceface with one SrO12 cuboctahedra, faces with five NaO12 cuboctahedra, and faces with eight TaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.62–3.04 Å. In the second Na1+ site, Na1+ is bonded to twelve O2- atoms to form distorted NaO12 cuboctahedra that share corners with three equivalent SrO12 cuboctahedra, corners with nine NaO12 cuboctahedra, faces with two equivalent SrO12 cuboctahedra, faces with four NaO12 cuboctahedra, and faces with eight TaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.62–3.05 Å. In the third Na1+ site, Na1+ is bonded to twelve O2- atoms to form distorted NaO12 cuboctahedra that share corners with two equivalent SrO12 cuboctahedra, corners with ten NaO12 cuboctahedra, faces with two equivalent SrO12 cuboctahedra, faces with four NaO12 cuboctahedra, and faces with eight TaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.62–3.04 Å. In the fourth Na1+ site, Na1+ is bonded to twelve O2- atoms to form distorted NaO12 cuboctahedra that share corners with two equivalent SrO12 cuboctahedra, corners with ten NaO12 cuboctahedra, a faceface with one SrO12 cuboctahedra, faces with five NaO12 cuboctahedra, and faces with eight TaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.62–3.03 Å. In the fifth Na1+ site, Na1+ is bonded to twelve O2- atoms to form distorted NaO12 cuboctahedra that share corners with two equivalent SrO12 cuboctahedra, corners with ten NaO12 cuboctahedra, faces with two equivalent SrO12 cuboctahedra, faces with four NaO12 cuboctahedra, and faces with eight TaO6 octahedra. There are a spread of Na–O bond distances ranging from 2.62–3.03 Å. Sr2+ is bonded to twelve O2- atoms to form distorted SrO12 cuboctahedra that share a cornercorner with one SrO12 cuboctahedra, corners with eleven NaO12 cuboctahedra, faces with six NaO12 cuboctahedra, and faces with eight TaO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.61–3.01 Å. There are six 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 six TaO6 octahedra, faces with two equivalent SrO12 cuboctahedra, and faces with six NaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 2–18°. There are four shorter (2.00 Å) and two longer (2.01 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 six TaO6 octahedra, faces with two equivalent SrO12 cuboctahedra, and faces with six NaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 2–18°. 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 six TaO6 octahedra, a faceface with one SrO12 cuboctahedra, and faces with seven NaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–18°. There are three shorter (1.99 Å) and three longer (2.02 Å) Ta–O bond lengths. In the fourth Ta+4.80+ site, Ta+4.80+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra, faces with two equivalent SrO12 cuboctahedra, and faces with six NaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 2–18°. There are two shorter (2.00 Å) and four longer (2.01 Å) Ta–O bond lengths. In the fifth Ta+4.80+ site, Ta+4.80+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra, faces with two equivalent SrO12 cuboctahedra, and faces with six NaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–18°. There are a spread of Ta–O bond distances ranging from 1.98–2.04 Å. In the sixth Ta+4.80+ site, Ta+4.80+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six TaO6 octahedra, a faceface with one SrO12 cuboctahedra, and faces with seven NaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 1–18°. There are a spread of Ta–O bond distances ranging from 1.98–2.02 Å. There are sixteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to four Na1+ and two Ta+4.80+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the ninth O2- site, O2- is bonded in a 2-coordinate geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to four Na1+ and two Ta+4.80+ atoms. In the eleventh O2- site, O2- is bonded in a distorted linear geometry to four Na1+ and two equivalent Ta+4.80+ atoms. In the twelfth O2- site, O2- is bonded in a distorted linear geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted linear geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the fourteenth O2- site, O2- is bonded in a distorted linear geometry to three Na1+, one Sr2+, and two Ta+4.80+ atoms. In the fifteenth O2- site, O2- is bonded in a distorted linear geometry to four Na1+ and two Ta+4.80+ atoms. In the sixteenth O2- site, O2- is bonded in a distorted linear geometry to two equivalent Na1+, two equivalent Sr2+, and two equivalent Ta+4.80+ atoms.