Sr5Ta4O15 crystallizes in the trigonal P-3c1 space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 12-coordinate geometry to three equivalent O(1), three equivalent O(3), and six equivalent O(2) atoms. In the second Sr site, Sr(2) is bonded in a 6-coordinate geometry to six equivalent O(1) atoms. In the third Sr site, Sr(3) is bonded to six equivalent O(2) and six equivalent O(3) atoms to form distorted SrO12 cuboctahedra that share corners with six equivalent Sr(3)O12 cuboctahedra, faces with two equivalent Ta(2)O6 octahedra, and faces with six equivalent Ta(1)O6 octahedra. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form TaO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ta(2)O6 octahedra, and faces with three equivalent Sr(3)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 13-17°. In the second Ta site, Ta(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra and  a faceface with one Sr(3)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 17°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sr(1), two equivalent Sr(2), and one Ta(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sr(3), two equivalent Sr(1), one Ta(1), and one Ta(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Sr(1), two equivalent Sr(3), and two equivalent Ta(1) atoms.
Sr5Ta4O15 crystallizes in the trigonal P-3c1 space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 12-coordinate geometry to three equivalent O(1), three equivalent O(3), and six equivalent O(2) atoms. All Sr(1)-O(1) bond lengths are 2.56 Å. All Sr(1)-O(3) bond lengths are 3.03 Å. There are three shorter (2.61 Å) and three longer (3.11 Å) Sr(1)-O(2) bond lengths. In the second Sr site, Sr(2) is bonded in a 6-coordinate geometry to six equivalent O(1) atoms. There are three shorter (2.55 Å) and three longer (2.57 Å) Sr(2)-O(1) bond lengths. In the third Sr site, Sr(3) is bonded to six equivalent O(2) and six equivalent O(3) atoms to form distorted SrO12 cuboctahedra that share corners with six equivalent Sr(3)O12 cuboctahedra, faces with two equivalent Ta(2)O6 octahedra, and faces with six equivalent Ta(1)O6 octahedra. All Sr(3)-O(2) bond lengths are 2.75 Å. There are three shorter (2.60 Å) and three longer (3.07 Å) Sr(3)-O(3) bond lengths. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form TaO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ta(2)O6 octahedra, and faces with three equivalent Sr(3)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 13-17°. All Ta(1)-O(2) bond lengths are 1.95 Å. All Ta(1)-O(3) bond lengths are 2.04 Å. In the second Ta site, Ta(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra and  a faceface with one Sr(3)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 17°. All Ta(2)-O(1) bond lengths are 1.87 Å. All Ta(2)-O(2) bond lengths are 2.18 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sr(1), two equivalent Sr(2), and one Ta(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sr(3), two equivalent Sr(1), one Ta(1), and one Ta(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Sr(1), two equivalent Sr(3), and two equivalent Ta(1) atoms.