Tb2Ti2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 8-coordinate geometry to one O(10), one O(13), one O(2), one O(3), one O(6), one O(7), and two equivalent O(5) atoms. In the second Tb site, Tb(2) is bonded in a 8-coordinate geometry to one O(1), one O(14), one O(2), one O(3), one O(4), one O(6), one O(8), and one O(9) atom. In the third Tb site, Tb(3) is bonded in a 7-coordinate geometry to one O(11), one O(5), one O(7), two equivalent O(10), and two equivalent O(13) atoms. In the fourth Tb site, Tb(4) is bonded in a 8-coordinate geometry to one O(12), one O(14), one O(4), one O(8), two equivalent O(1), and two equivalent O(9) atoms. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(11), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 30-49°. In the second Ti site, Ti(2) is bonded to one O(12), one O(3), one O(4), one O(8), and two equivalent O(9) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 26-49°. In the third Ti site, Ti(3) is bonded to one O(12), one O(14), one O(2), one O(8), and two equivalent O(1) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 26-45°. In the fourth Ti site, Ti(4) is bonded to one O(10), one O(11), one O(13), one O(14), one O(2), and one O(6) atom to form corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 30-45°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Tb(2), two equivalent Tb(4), and two equivalent Ti(3) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(2), one Ti(3), and one Ti(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(2), one Ti(1), and one Ti(2) atom. In the fourth O site, O(4) is bonded to one Tb(2), one Tb(4), one Ti(1), and one Ti(2) atom to form distorted OTb2Ti2 tetrahedra that share  a cornercorner with one O(8)Tb2Ti2 tetrahedra,  a cornercorner with one O(5)Tb3Ti tetrahedra, corners with two equivalent O(14)Tb2Ti2 tetrahedra, and  an edgeedge with one O(8)Tb2Ti2 tetrahedra. In the fifth O site, O(5) is bonded to one Tb(3), two equivalent Tb(1), and one Ti(1) atom to form distorted OTb3Ti tetrahedra that share  a cornercorner with one O(4)Tb2Ti2 tetrahedra, corners with two equivalent O(13)Tb3Ti tetrahedra, corners with two equivalent O(5)Tb3Ti tetrahedra, corners with four equivalent O(10)Tb3Ti tetrahedra, and  an edgeedge with one O(13)Tb3Ti tetrahedra. In the sixth O site, O(6) is bonded in a distorted see-saw-like geometry to one Tb(1), one Tb(2), one Ti(1), and one Ti(4) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(3), and one Ti(1) atom. In the eighth O site, O(8) is bonded to one Tb(2), one Tb(4), one Ti(2), and one Ti(3) atom to form a mixture of distorted corner and edge-sharing OTb2Ti2 tetrahedra. In the ninth O site, O(9) is bonded in a 5-coordinate geometry to one Tb(2), two equivalent Tb(4), and two equivalent Ti(2) atoms. In the tenth O site, O(10) is bonded to one Tb(1), two equivalent Tb(3), and one Ti(4) atom to form distorted OTb3Ti tetrahedra that share  a cornercorner with one O(14)Tb2Ti2 tetrahedra, corners with two equivalent O(10)Tb3Ti tetrahedra, corners with four equivalent O(5)Tb3Ti tetrahedra, and edges with three equivalent O(13)Tb3Ti tetrahedra. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Tb(3), one Ti(1), and one Ti(4) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Tb(4), one Ti(2), and one Ti(3) atom. In the thirteenth O site, O(13) is bonded to one Tb(1), two equivalent Tb(3), and one Ti(4) atom to form distorted OTb3Ti tetrahedra that share  a cornercorner with one O(14)Tb2Ti2 tetrahedra, corners with two equivalent O(13)Tb3Ti tetrahedra, corners with two equivalent O(5)Tb3Ti tetrahedra,  an edgeedge with one O(5)Tb3Ti tetrahedra, and edges with three equivalent O(10)Tb3Ti tetrahedra. In the fourteenth O site, O(14) is bonded to one Tb(2), one Tb(4), one Ti(3), and one Ti(4) atom to form distorted OTb2Ti2 tetrahedra that share  a cornercorner with one O(8)Tb2Ti2 tetrahedra,  a cornercorner with one O(10)Tb3Ti tetrahedra,  a cornercorner with one O(13)Tb3Ti tetrahedra, corners with two equivalent O(4)Tb2Ti2 tetrahedra, and  an edgeedge with one O(8)Tb2Ti2 tetrahedra.
Tb2Ti2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 8-coordinate geometry to one O(10), one O(13), one O(2), one O(3), one O(6), one O(7), and two equivalent O(5) atoms. The Tb(1)-O(10) bond length is 2.36 Å. The Tb(1)-O(13) bond length is 2.45 Å. The Tb(1)-O(2) bond length is 2.61 Å. The Tb(1)-O(3) bond length is 2.52 Å. The Tb(1)-O(6) bond length is 2.40 Å. The Tb(1)-O(7) bond length is 2.32 Å. There is one shorter (2.41 Å) and one longer (2.45 Å) Tb(1)-O(5) bond length. In the second Tb site, Tb(2) is bonded in a 8-coordinate geometry to one O(1), one O(14), one O(2), one O(3), one O(4), one O(6), one O(8), and one O(9) atom. The Tb(2)-O(1) bond length is 2.33 Å. The Tb(2)-O(14) bond length is 2.45 Å. The Tb(2)-O(2) bond length is 2.45 Å. The Tb(2)-O(3) bond length is 2.44 Å. The Tb(2)-O(4) bond length is 2.40 Å. The Tb(2)-O(6) bond length is 2.35 Å. The Tb(2)-O(8) bond length is 2.25 Å. The Tb(2)-O(9) bond length is 2.31 Å. In the third Tb site, Tb(3) is bonded in a 7-coordinate geometry to one O(11), one O(5), one O(7), two equivalent O(10), and two equivalent O(13) atoms. The Tb(3)-O(11) bond length is 2.32 Å. The Tb(3)-O(5) bond length is 2.40 Å. The Tb(3)-O(7) bond length is 2.22 Å. There is one shorter (2.33 Å) and one longer (2.39 Å) Tb(3)-O(10) bond length. There is one shorter (2.32 Å) and one longer (2.33 Å) Tb(3)-O(13) bond length. In the fourth Tb site, Tb(4) is bonded in a 8-coordinate geometry to one O(12), one O(14), one O(4), one O(8), two equivalent O(1), and two equivalent O(9) atoms. The Tb(4)-O(12) bond length is 2.32 Å. The Tb(4)-O(14) bond length is 2.28 Å. The Tb(4)-O(4) bond length is 2.25 Å. The Tb(4)-O(8) bond length is 2.27 Å. There is one shorter (2.47 Å) and one longer (2.68 Å) Tb(4)-O(1) bond length. There is one shorter (2.45 Å) and one longer (2.65 Å) Tb(4)-O(9) bond length. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(11), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 30-49°. The Ti(1)-O(11) bond length is 1.93 Å. The Ti(1)-O(3) bond length is 2.24 Å. The Ti(1)-O(4) bond length is 2.07 Å. The Ti(1)-O(5) bond length is 1.91 Å. The Ti(1)-O(6) bond length is 2.00 Å. The Ti(1)-O(7) bond length is 1.78 Å. In the second Ti site, Ti(2) is bonded to one O(12), one O(3), one O(4), one O(8), and two equivalent O(9) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 26-49°. The Ti(2)-O(12) bond length is 1.93 Å. The Ti(2)-O(3) bond length is 1.82 Å. The Ti(2)-O(4) bond length is 1.92 Å. The Ti(2)-O(8) bond length is 2.00 Å. There is one shorter (1.97 Å) and one longer (2.33 Å) Ti(2)-O(9) bond length. In the third Ti site, Ti(3) is bonded to one O(12), one O(14), one O(2), one O(8), and two equivalent O(1) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 26-45°. The Ti(3)-O(12) bond length is 1.93 Å. The Ti(3)-O(14) bond length is 1.93 Å. The Ti(3)-O(2) bond length is 1.83 Å. The Ti(3)-O(8) bond length is 2.00 Å. There is one shorter (1.96 Å) and one longer (2.26 Å) Ti(3)-O(1) bond length. In the fourth Ti site, Ti(4) is bonded to one O(10), one O(11), one O(13), one O(14), one O(2), and one O(6) atom to form corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 30-45°. The Ti(4)-O(10) bond length is 1.86 Å. The Ti(4)-O(11) bond length is 1.91 Å. The Ti(4)-O(13) bond length is 1.87 Å. The Ti(4)-O(14) bond length is 2.01 Å. The Ti(4)-O(2) bond length is 2.17 Å. The Ti(4)-O(6) bond length is 2.01 Å. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Tb(2), two equivalent Tb(4), and two equivalent Ti(3) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(2), one Ti(3), and one Ti(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(2), one Ti(1), and one Ti(2) atom. In the fourth O site, O(4) is bonded to one Tb(2), one Tb(4), one Ti(1), and one Ti(2) atom to form distorted OTb2Ti2 tetrahedra that share  a cornercorner with one O(8)Tb2Ti2 tetrahedra,  a cornercorner with one O(5)Tb3Ti tetrahedra, corners with two equivalent O(14)Tb2Ti2 tetrahedra, and  an edgeedge with one O(8)Tb2Ti2 tetrahedra. In the fifth O site, O(5) is bonded to one Tb(3), two equivalent Tb(1), and one Ti(1) atom to form distorted OTb3Ti tetrahedra that share  a cornercorner with one O(4)Tb2Ti2 tetrahedra, corners with two equivalent O(13)Tb3Ti tetrahedra, corners with two equivalent O(5)Tb3Ti tetrahedra, corners with four equivalent O(10)Tb3Ti tetrahedra, and  an edgeedge with one O(13)Tb3Ti tetrahedra. In the sixth O site, O(6) is bonded in a distorted see-saw-like geometry to one Tb(1), one Tb(2), one Ti(1), and one Ti(4) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(3), and one Ti(1) atom. In the eighth O site, O(8) is bonded to one Tb(2), one Tb(4), one Ti(2), and one Ti(3) atom to form a mixture of distorted corner and edge-sharing OTb2Ti2 tetrahedra. In the ninth O site, O(9) is bonded in a 5-coordinate geometry to one Tb(2), two equivalent Tb(4), and two equivalent Ti(2) atoms. In the tenth O site, O(10) is bonded to one Tb(1), two equivalent Tb(3), and one Ti(4) atom to form distorted OTb3Ti tetrahedra that share  a cornercorner with one O(14)Tb2Ti2 tetrahedra, corners with two equivalent O(10)Tb3Ti tetrahedra, corners with four equivalent O(5)Tb3Ti tetrahedra, and edges with three equivalent O(13)Tb3Ti tetrahedra. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Tb(3), one Ti(1), and one Ti(4) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Tb(4), one Ti(2), and one Ti(3) atom. In the thirteenth O site, O(13) is bonded to one Tb(1), two equivalent Tb(3), and one Ti(4) atom to form distorted OTb3Ti tetrahedra that share  a cornercorner with one O(14)Tb2Ti2 tetrahedra, corners with two equivalent O(13)Tb3Ti tetrahedra, corners with two equivalent O(5)Tb3Ti tetrahedra,  an edgeedge with one O(5)Tb3Ti tetrahedra, and edges with three equivalent O(10)Tb3Ti tetrahedra. In the fourteenth O site, O(14) is bonded to one Tb(2), one Tb(4), one Ti(3), and one Ti(4) atom to form distorted OTb2Ti2 tetrahedra that share  a cornercorner with one O(8)Tb2Ti2 tetrahedra,  a cornercorner with one O(10)Tb3Ti tetrahedra,  a cornercorner with one O(13)Tb3Ti tetrahedra, corners with two equivalent O(4)Tb2Ti2 tetrahedra, and  an edgeedge with one O(8)Tb2Ti2 tetrahedra.