BaTi2O5 crystallizes in the monoclinic C2 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 12-coordinate geometry to one O(3), two equivalent O(4), two equivalent O(5), two equivalent O(6), two equivalent O(7), and three equivalent O(1) atoms. In the second Ba site, Ba(2) is bonded to two equivalent O(3), two equivalent O(6), four equivalent O(7), and four equivalent O(8) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ti(3)O6 octahedra, faces with two equivalent Ba(2)O12 cuboctahedra, and faces with four equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-43°. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(4), one O(5), one O(7), one O(8), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with three equivalent Ti(1)O6 octahedra,  an edgeedge with one Ti(3)O6 octahedra, and faces with two equivalent Ba(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 4-8°. In the second Ti site, Ti(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(7), one O(8), and two equivalent O(3) atoms. In the third Ti site, Ti(3) is bonded to one O(3), one O(4), one O(8), and three equivalent O(2) atoms to form TiO6 octahedra that share corners with three equivalent Ba(2)O12 cuboctahedra, corners with two equivalent Ti(3)O6 octahedra,  an edgeedge with one Ti(1)O6 octahedra, and edges with two equivalent Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles are 28°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to three equivalent Ba(1) and one Ti(2) atom. In the second O site, O(2) is bonded to one Ti(2) and three equivalent Ti(3) atoms to form a mixture of distorted corner and edge-sharing OTi4 trigonal pyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Ba(1), one Ba(2), one Ti(3), and two equivalent Ti(2) atoms. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Ba(1), one Ti(1), and one Ti(3) atom. In the fifth O site, O(5) is bonded in a distorted linear geometry to four equivalent Ba(1) and two equivalent Ti(1) atoms. In the sixth O site, O(6) is bonded in a distorted linear geometry to one Ba(2), two equivalent Ba(1), and two equivalent Ti(1) atoms. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), one Ti(1), and one Ti(2) atom. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to two equivalent Ba(2), one Ti(1), one Ti(2), and one Ti(3) atom.
BaTi2O5 crystallizes in the monoclinic C2 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 12-coordinate geometry to one O(3), two equivalent O(4), two equivalent O(5), two equivalent O(6), two equivalent O(7), and three equivalent O(1) atoms. The Ba(1)-O(3) bond length is 3.30 Å. There is one shorter (2.70 Å) and one longer (2.74 Å) Ba(1)-O(4) bond length. There is one shorter (2.97 Å) and one longer (3.03 Å) Ba(1)-O(5) bond length. There is one shorter (2.98 Å) and one longer (3.00 Å) Ba(1)-O(6) bond length. There is one shorter (3.23 Å) and one longer (3.28 Å) Ba(1)-O(7) bond length. There are two shorter (2.70 Å) and one longer (2.72 Å) Ba(1)-O(1) bond length. In the second Ba site, Ba(2) is bonded to two equivalent O(3), two equivalent O(6), four equivalent O(7), and four equivalent O(8) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ti(3)O6 octahedra, faces with two equivalent Ba(2)O12 cuboctahedra, and faces with four equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-43°. Both Ba(2)-O(3) bond lengths are 3.02 Å. Both Ba(2)-O(6) bond lengths are 2.95 Å. There are two shorter (2.80 Å) and two longer (2.85 Å) Ba(2)-O(7) bond lengths. There are two shorter (2.87 Å) and two longer (2.90 Å) Ba(2)-O(8) bond lengths. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(4), one O(5), one O(7), one O(8), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with three equivalent Ti(1)O6 octahedra,  an edgeedge with one Ti(3)O6 octahedra, and faces with two equivalent Ba(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 4-8°. The Ti(1)-O(4) bond length is 1.99 Å. The Ti(1)-O(5) bond length is 1.96 Å. The Ti(1)-O(7) bond length is 1.96 Å. The Ti(1)-O(8) bond length is 2.13 Å. There is one shorter (1.81 Å) and one longer (2.13 Å) Ti(1)-O(6) bond length. In the second Ti site, Ti(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(7), one O(8), and two equivalent O(3) atoms. The Ti(2)-O(1) bond length is 1.73 Å. The Ti(2)-O(2) bond length is 2.06 Å. The Ti(2)-O(7) bond length is 1.88 Å. The Ti(2)-O(8) bond length is 2.51 Å. Both Ti(2)-O(3) bond lengths are 2.00 Å. In the third Ti site, Ti(3) is bonded to one O(3), one O(4), one O(8), and three equivalent O(2) atoms to form TiO6 octahedra that share corners with three equivalent Ba(2)O12 cuboctahedra, corners with two equivalent Ti(3)O6 octahedra,  an edgeedge with one Ti(1)O6 octahedra, and edges with two equivalent Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles are 28°. The Ti(3)-O(3) bond length is 2.10 Å. The Ti(3)-O(4) bond length is 1.81 Å. The Ti(3)-O(8) bond length is 1.85 Å. There are a spread of Ti(3)-O(2) bond distances ranging from 2.02-2.16 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to three equivalent Ba(1) and one Ti(2) atom. In the second O site, O(2) is bonded to one Ti(2) and three equivalent Ti(3) atoms to form a mixture of distorted corner and edge-sharing OTi4 trigonal pyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Ba(1), one Ba(2), one Ti(3), and two equivalent Ti(2) atoms. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Ba(1), one Ti(1), and one Ti(3) atom. In the fifth O site, O(5) is bonded in a distorted linear geometry to four equivalent Ba(1) and two equivalent Ti(1) atoms. In the sixth O site, O(6) is bonded in a distorted linear geometry to one Ba(2), two equivalent Ba(1), and two equivalent Ti(1) atoms. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), one Ti(1), and one Ti(2) atom. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to two equivalent Ba(2), one Ti(1), one Ti(2), and one Ti(3) atom.