Sr4Nd3Ta2Al5O21 is (Cubic) Perovskite-derived structured and crystallizes in the trigonal R-3m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to three equivalent O(2) and nine equivalent O(1) atoms to form SrO12 cuboctahedra that share corners with three equivalent Sr(2)O12 cuboctahedra, corners with three equivalent Nd(1)O12 cuboctahedra, corners with six equivalent Sr(1)O12 cuboctahedra, faces with three equivalent Sr(1)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra,  a faceface with one Al(2)O6 octahedra, faces with three equivalent Al(1)O6 octahedra, and faces with four equivalent Ta(1)O6 octahedra. In the second Sr site, Sr(2) is bonded to three equivalent O(1), three equivalent O(3), and six equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with three equivalent Sr(1)O12 cuboctahedra, corners with three equivalent Nd(2)O12 cuboctahedra, corners with six equivalent Sr(2)O12 cuboctahedra, faces with three equivalent Sr(1)O12 cuboctahedra, faces with three equivalent Nd(1)O12 cuboctahedra,  a faceface with one Al(1)O6 octahedra,  a faceface with one Al(3)O6 octahedra, faces with three equivalent Ta(1)O6 octahedra, and faces with three equivalent Al(2)O6 octahedra. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to three equivalent O(2), three equivalent O(4), and six equivalent O(3) atoms to form NdO12 cuboctahedra that share corners with three equivalent Sr(1)O12 cuboctahedra, corners with nine equivalent Nd(1)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra, faces with three equivalent Nd(2)O12 cuboctahedra,  a faceface with one Ta(1)O6 octahedra, faces with three equivalent Al(2)O6 octahedra, and faces with four equivalent Al(3)O6 octahedra. In the second Nd site, Nd(2) is bonded to six equivalent O(3) and six equivalent O(4) atoms to form NdO12 cuboctahedra that share corners with six equivalent Sr(2)O12 cuboctahedra, corners with six equivalent Nd(2)O12 cuboctahedra, faces with six equivalent Nd(1)O12 cuboctahedra, faces with two equivalent Al(2)O6 octahedra, and faces with six equivalent Al(3)O6 octahedra. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form TaO6 octahedra that share corners with three equivalent Al(1)O6 octahedra, corners with three equivalent Al(2)O6 octahedra,  a faceface with one Nd(1)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra, and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-1°. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to six equivalent O(1) atoms to form AlO6 octahedra that share corners with six equivalent Ta(1)O6 octahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with six equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. In the second Al site, Al(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form AlO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Al(3)O6 octahedra,  a faceface with one Sr(1)O12 cuboctahedra,  a faceface with one Nd(2)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra, and faces with three equivalent Nd(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 1-3°. In the third Al site, Al(3) is bonded to three equivalent O(3) and three equivalent O(4) atoms to form AlO6 octahedra that share corners with three equivalent Al(2)O6 octahedra, corners with three equivalent Al(3)O6 octahedra,  a faceface with one Sr(2)O12 cuboctahedra, faces with three equivalent Nd(2)O12 cuboctahedra, and faces with four equivalent Nd(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-3°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Sr(2), three equivalent Sr(1), one Ta(1), and one Al(1) atom. In the second O site, O(2) is bonded in a distorted linear geometry to one Sr(1), two equivalent Sr(2), one Nd(1), one Ta(1), and one Al(2) atom. In the third O site, O(3) is bonded in a distorted linear geometry to one Sr(2), one Nd(2), two equivalent Nd(1), one Al(2), and one Al(3) atom. In the fourth O site, O(4) is bonded to two equivalent Nd(1), two equivalent Nd(2), and two equivalent Al(3) atoms to form a mixture of distorted corner and face-sharing ONd4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°.
Sr4Nd3Ta2Al5O21 is (Cubic) Perovskite-derived structured and crystallizes in the trigonal R-3m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to three equivalent O(2) and nine equivalent O(1) atoms to form SrO12 cuboctahedra that share corners with three equivalent Sr(2)O12 cuboctahedra, corners with three equivalent Nd(1)O12 cuboctahedra, corners with six equivalent Sr(1)O12 cuboctahedra, faces with three equivalent Sr(1)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra,  a faceface with one Al(2)O6 octahedra, faces with three equivalent Al(1)O6 octahedra, and faces with four equivalent Ta(1)O6 octahedra. All Sr(1)-O(2) bond lengths are 2.80 Å. There are six shorter (2.73 Å) and three longer (2.76 Å) Sr(1)-O(1) bond lengths. In the second Sr site, Sr(2) is bonded to three equivalent O(1), three equivalent O(3), and six equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with three equivalent Sr(1)O12 cuboctahedra, corners with three equivalent Nd(2)O12 cuboctahedra, corners with six equivalent Sr(2)O12 cuboctahedra, faces with three equivalent Sr(1)O12 cuboctahedra, faces with three equivalent Nd(1)O12 cuboctahedra,  a faceface with one Al(1)O6 octahedra,  a faceface with one Al(3)O6 octahedra, faces with three equivalent Ta(1)O6 octahedra, and faces with three equivalent Al(2)O6 octahedra. All Sr(2)-O(1) bond lengths are 2.85 Å. All Sr(2)-O(3) bond lengths are 2.71 Å. All Sr(2)-O(2) bond lengths are 2.73 Å. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to three equivalent O(2), three equivalent O(4), and six equivalent O(3) atoms to form NdO12 cuboctahedra that share corners with three equivalent Sr(1)O12 cuboctahedra, corners with nine equivalent Nd(1)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra, faces with three equivalent Nd(2)O12 cuboctahedra,  a faceface with one Ta(1)O6 octahedra, faces with three equivalent Al(2)O6 octahedra, and faces with four equivalent Al(3)O6 octahedra. All Nd(1)-O(2) bond lengths are 2.81 Å. All Nd(1)-O(4) bond lengths are 2.59 Å. All Nd(1)-O(3) bond lengths are 2.73 Å. In the second Nd site, Nd(2) is bonded to six equivalent O(3) and six equivalent O(4) atoms to form NdO12 cuboctahedra that share corners with six equivalent Sr(2)O12 cuboctahedra, corners with six equivalent Nd(2)O12 cuboctahedra, faces with six equivalent Nd(1)O12 cuboctahedra, faces with two equivalent Al(2)O6 octahedra, and faces with six equivalent Al(3)O6 octahedra. All Nd(2)-O(3) bond lengths are 2.65 Å. All Nd(2)-O(4) bond lengths are 2.73 Å. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form TaO6 octahedra that share corners with three equivalent Al(1)O6 octahedra, corners with three equivalent Al(2)O6 octahedra,  a faceface with one Nd(1)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra, and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-1°. All Ta(1)-O(1) bond lengths are 1.98 Å. All Ta(1)-O(2) bond lengths are 1.99 Å. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to six equivalent O(1) atoms to form AlO6 octahedra that share corners with six equivalent Ta(1)O6 octahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with six equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. All Al(1)-O(1) bond lengths are 1.91 Å. In the second Al site, Al(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form AlO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Al(3)O6 octahedra,  a faceface with one Sr(1)O12 cuboctahedra,  a faceface with one Nd(2)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra, and faces with three equivalent Nd(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 1-3°. All Al(2)-O(2) bond lengths are 1.92 Å. All Al(2)-O(3) bond lengths are 1.90 Å. In the third Al site, Al(3) is bonded to three equivalent O(3) and three equivalent O(4) atoms to form AlO6 octahedra that share corners with three equivalent Al(2)O6 octahedra, corners with three equivalent Al(3)O6 octahedra,  a faceface with one Sr(2)O12 cuboctahedra, faces with three equivalent Nd(2)O12 cuboctahedra, and faces with four equivalent Nd(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-3°. All Al(3)-O(3) bond lengths are 1.90 Å. All Al(3)-O(4) bond lengths are 1.94 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Sr(2), three equivalent Sr(1), one Ta(1), and one Al(1) atom. In the second O site, O(2) is bonded in a distorted linear geometry to one Sr(1), two equivalent Sr(2), one Nd(1), one Ta(1), and one Al(2) atom. In the third O site, O(3) is bonded in a distorted linear geometry to one Sr(2), one Nd(2), two equivalent Nd(1), one Al(2), and one Al(3) atom. In the fourth O site, O(4) is bonded to two equivalent Nd(1), two equivalent Nd(2), and two equivalent Al(3) atoms to form a mixture of distorted corner and face-sharing ONd4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°.