Sr3Zr2Nb2O12 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), three equivalent O(3), and six equivalent O(1) atoms to form SrO12 cuboctahedra that share corners with twelve equivalent Sr(1)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra, faces with four equivalent Zr(1)O6 octahedra, and faces with four equivalent Nb(1)O6 octahedra. In the second Sr site, Sr(2) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(2)O12 cuboctahedra, faces with six equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Nb(1)O6 octahedra, and faces with six equivalent Zr(1)O6 octahedra. Zr(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form ZrO6 octahedra that share corners with three equivalent Zr(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, 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 0-6°. Nb(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form NbO6 octahedra that share corners with three equivalent Zr(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra,  a faceface with one Sr(2)O12 cuboctahedra, and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-6°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Sr(2), two equivalent Sr(1), one Zr(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a distorted linear geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Zr(1) atoms. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Sr(1) and two equivalent Nb(1) atoms.
Sr3Zr2Nb2O12 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), three equivalent O(3), and six equivalent O(1) atoms to form SrO12 cuboctahedra that share corners with twelve equivalent Sr(1)O12 cuboctahedra, faces with three equivalent Sr(2)O12 cuboctahedra, faces with four equivalent Zr(1)O6 octahedra, and faces with four equivalent Nb(1)O6 octahedra. All Sr(1)-O(2) bond lengths are 2.92 Å. All Sr(1)-O(3) bond lengths are 2.86 Å. All Sr(1)-O(1) bond lengths are 2.92 Å. In the second Sr site, Sr(2) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(2)O12 cuboctahedra, faces with six equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Nb(1)O6 octahedra, and faces with six equivalent Zr(1)O6 octahedra. All Sr(2)-O(1) bond lengths are 2.83 Å. All Sr(2)-O(2) bond lengths are 2.92 Å. Zr(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form ZrO6 octahedra that share corners with three equivalent Zr(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, 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 0-6°. All Zr(1)-O(1) bond lengths are 2.10 Å. All Zr(1)-O(2) bond lengths are 2.10 Å. Nb(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form NbO6 octahedra that share corners with three equivalent Zr(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra,  a faceface with one Sr(2)O12 cuboctahedra, and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-6°. All Nb(1)-O(1) bond lengths are 2.01 Å. All Nb(1)-O(3) bond lengths are 2.03 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Sr(2), two equivalent Sr(1), one Zr(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a distorted linear geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Zr(1) atoms. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Sr(1) and two equivalent Nb(1) atoms.