Ba3La2Ti2Nb2O15 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 12-coordinate geometry to three equivalent O(2) and nine equivalent O(1) atoms. In the second Ba site, Ba(2) is bonded to six equivalent O(2) and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(2)O12 cuboctahedra, faces with six equivalent La(1)O12 cuboctahedra, faces with two equivalent Nb(1)O6 octahedra, and faces with six equivalent Ti(1)O6 octahedra. La(1) is bonded to three equivalent O(1), three equivalent O(3), and six equivalent O(2) atoms to form distorted LaO12 cuboctahedra that share corners with nine equivalent La(1)O12 cuboctahedra, faces with three equivalent Ba(2)O12 cuboctahedra, faces with three equivalent Nb(1)O6 octahedra, and faces with four equivalent Ti(1)O6 octahedra. Ti(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form TiO6 octahedra that share corners with three equivalent Ti(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, faces with three equivalent Ba(2)O12 cuboctahedra, and faces with four equivalent La(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-4°. Nb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form NbO6 octahedra that share corners with three equivalent Ti(1)O6 octahedra,  a faceface with one Ba(2)O12 cuboctahedra, and faces with three equivalent La(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 4°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to three equivalent Ba(1), one La(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), one Ba(2), two equivalent La(1), one Ti(1), and one Nb(1) atom. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Ba(2), two equivalent La(1), and two equivalent Ti(1) atoms.
Ba3La2Ti2Nb2O15 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 12-coordinate geometry to three equivalent O(2) and nine equivalent O(1) atoms. All Ba(1)-O(2) bond lengths are 3.18 Å. There are three shorter (2.82 Å) and six longer (2.91 Å) Ba(1)-O(1) bond lengths. In the second Ba site, Ba(2) is bonded to six equivalent O(2) and six equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(2)O12 cuboctahedra, faces with six equivalent La(1)O12 cuboctahedra, faces with two equivalent Nb(1)O6 octahedra, and faces with six equivalent Ti(1)O6 octahedra. All Ba(2)-O(2) bond lengths are 2.81 Å. All Ba(2)-O(3) bond lengths are 2.86 Å. La(1) is bonded to three equivalent O(1), three equivalent O(3), and six equivalent O(2) atoms to form distorted LaO12 cuboctahedra that share corners with nine equivalent La(1)O12 cuboctahedra, faces with three equivalent Ba(2)O12 cuboctahedra, faces with three equivalent Nb(1)O6 octahedra, and faces with four equivalent Ti(1)O6 octahedra. All La(1)-O(1) bond lengths are 2.52 Å. All La(1)-O(3) bond lengths are 3.00 Å. All La(1)-O(2) bond lengths are 2.87 Å. Ti(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form TiO6 octahedra that share corners with three equivalent Ti(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, faces with three equivalent Ba(2)O12 cuboctahedra, and faces with four equivalent La(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-4°. All Ti(1)-O(2) bond lengths are 1.97 Å. All Ti(1)-O(3) bond lengths are 2.01 Å. Nb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form NbO6 octahedra that share corners with three equivalent Ti(1)O6 octahedra,  a faceface with one Ba(2)O12 cuboctahedra, and faces with three equivalent La(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 4°. All Nb(1)-O(1) bond lengths are 1.91 Å. All Nb(1)-O(2) bond lengths are 2.15 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to three equivalent Ba(1), one La(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), one Ba(2), two equivalent La(1), one Ti(1), and one Nb(1) atom. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Ba(2), two equivalent La(1), and two equivalent Ti(1) atoms.