Ba3SrTa2O9 is Krennerite-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 Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 23°. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Sr(1)O6 octahedra and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 23°. 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 Ta(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 Ta(1) atom.
Ba3SrTa2O9 is Krennerite-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 2.78 Å. All Ba(1)-O(2) bond lengths are 3.02 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 2.86 Å. All Ba(2)-O(2) bond lengths are 2.69 Å. Sr(1) is bonded to six equivalent O(2) atoms to form SrO6 octahedra that share corners with six equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 23°. All Sr(1)-O(2) bond lengths are 2.44 Å. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Sr(1)O6 octahedra and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 23°. All Ta(1)-O(1) bond lengths are 2.14 Å. All Ta(1)-O(2) bond lengths are 1.89 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 Ta(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 Ta(1) atom.