Ba3SrNb2O9 is Orthorhombic Perovskite-derived structured and crystallizes in the hexagonal P6_3/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to three equivalent O(1) and six equivalent O(2) atoms. In the second Ba site, Ba(2) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(2) atoms. Sr(1) is bonded to six equivalent O(2) atoms to form SrO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. Nb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted NbO6 octahedra that share corners with three equivalent Sr(1)O6 octahedra and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Ba(1), two equivalent Ba(2), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ba(1), one Ba(2), one Sr(1), and one Nb(1) atom.
Ba3SrNb2O9 is Orthorhombic Perovskite-derived structured and crystallizes in the hexagonal P6_3/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to three equivalent O(1) and six equivalent O(2) atoms. All Ba(1)-O(1) bond lengths are 2.80 Å. All Ba(1)-O(2) bond lengths are 3.06 Å. In the second Ba site, Ba(2) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(2) atoms. All Ba(2)-O(1) bond lengths are 2.84 Å. All Ba(2)-O(2) bond lengths are 2.72 Å. Sr(1) is bonded to six equivalent O(2) atoms to form SrO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. All Sr(1)-O(2) bond lengths are 2.47 Å. Nb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted NbO6 octahedra that share corners with three equivalent Sr(1)O6 octahedra and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. All Nb(1)-O(1) bond lengths are 2.19 Å. All Nb(1)-O(2) bond lengths are 1.92 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Ba(1), two equivalent Ba(2), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ba(1), one Ba(2), one Sr(1), and one Nb(1) atom.