Bi6Fe2Ti3O18 crystallizes in the monoclinic Cm space group. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(11), one O(8), and four equivalent O(4) atoms to form distorted TiO6 octahedra that share  a cornercorner with one Ti(3)O6 octahedra,  a cornercorner with one Fe(1)O6 octahedra, and corners with four equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 14-19°. In the second Ti site, Ti(2) is bonded in a 6-coordinate geometry to one O(5), one O(7), and four equivalent O(1) atoms. In the third Ti site, Ti(3) is bonded to one O(6), one O(8), and four equivalent O(2) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 19-21°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(10), one O(11), and four equivalent O(12) atoms to form FeO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra, and corners with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 14-17°. In the second Fe site, Fe(2) is bonded to one O(10), one O(7), and four equivalent O(3) atoms to form corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 14-15°. There are six inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 3-coordinate geometry to one O(11), two equivalent O(12), and two equivalent O(4) atoms. In the second Bi site, Bi(2) is bonded in a 3-coordinate geometry to one O(10) and two equivalent O(3) atoms. In the third Bi site, Bi(3) is bonded in a distorted pentagonal planar geometry to one O(6) and four equivalent O(9) atoms. In the fourth Bi site, Bi(4) is bonded in a distorted pentagonal planar geometry to one O(5) and four equivalent O(9) atoms. In the fifth Bi site, Bi(5) is bonded in a 5-coordinate geometry to one O(8), two equivalent O(2), and two equivalent O(4) atoms. In the sixth Bi site, Bi(6) is bonded in a 3-coordinate geometry to one O(7) and two equivalent O(1) atoms. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ti(2) and one Bi(6) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Ti(3) and one Bi(5) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Fe(2) and one Bi(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ti(1), one Bi(1), and one Bi(5) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ti(2) and one Bi(4) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ti(3) and one Bi(3) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Ti(2), one Fe(2), and one Bi(6) atom. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to one Ti(1), one Ti(3), and one Bi(5) atom. In the ninth O site, O(9) is bonded to two equivalent Bi(3) and two equivalent Bi(4) atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra. In the tenth O site, O(10) is bonded in a distorted T-shaped geometry to one Fe(1), one Fe(2), and one Bi(2) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Ti(1), one Fe(1), and one Bi(1) atom. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to two equivalent Fe(1) and one Bi(1) atom.
Bi6Fe2Ti3O18 crystallizes in the monoclinic Cm space group. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(11), one O(8), and four equivalent O(4) atoms to form distorted TiO6 octahedra that share  a cornercorner with one Ti(3)O6 octahedra,  a cornercorner with one Fe(1)O6 octahedra, and corners with four equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 14-19°. The Ti(1)-O(11) bond length is 1.96 Å. The Ti(1)-O(8) bond length is 1.98 Å. There are two shorter (1.83 Å) and two longer (2.20 Å) Ti(1)-O(4) bond lengths. In the second Ti site, Ti(2) is bonded in a 6-coordinate geometry to one O(5), one O(7), and four equivalent O(1) atoms. The Ti(2)-O(5) bond length is 1.77 Å. The Ti(2)-O(7) bond length is 2.24 Å. There are two shorter (1.92 Å) and two longer (2.16 Å) Ti(2)-O(1) bond lengths. In the third Ti site, Ti(3) is bonded to one O(6), one O(8), and four equivalent O(2) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 19-21°. The Ti(3)-O(6) bond length is 1.80 Å. The Ti(3)-O(8) bond length is 2.18 Å. There are two shorter (1.90 Å) and two longer (2.17 Å) Ti(3)-O(2) bond lengths. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(10), one O(11), and four equivalent O(12) atoms to form FeO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra, and corners with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 14-17°. The Fe(1)-O(10) bond length is 1.99 Å. The Fe(1)-O(11) bond length is 2.12 Å. There are two shorter (1.94 Å) and two longer (2.10 Å) Fe(1)-O(12) bond lengths. In the second Fe site, Fe(2) is bonded to one O(10), one O(7), and four equivalent O(3) atoms to form corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 14-15°. The Fe(2)-O(10) bond length is 2.13 Å. The Fe(2)-O(7) bond length is 1.97 Å. There are two shorter (1.94 Å) and two longer (2.10 Å) Fe(2)-O(3) bond lengths. There are six inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 3-coordinate geometry to one O(11), two equivalent O(12), and two equivalent O(4) atoms. The Bi(1)-O(11) bond length is 2.22 Å. Both Bi(1)-O(12) bond lengths are 2.26 Å. Both Bi(1)-O(4) bond lengths are 2.75 Å. In the second Bi site, Bi(2) is bonded in a 3-coordinate geometry to one O(10) and two equivalent O(3) atoms. The Bi(2)-O(10) bond length is 2.20 Å. Both Bi(2)-O(3) bond lengths are 2.24 Å. In the third Bi site, Bi(3) is bonded in a distorted pentagonal planar geometry to one O(6) and four equivalent O(9) atoms. The Bi(3)-O(6) bond length is 2.32 Å. There are two shorter (2.20 Å) and two longer (2.60 Å) Bi(3)-O(9) bond lengths. In the fourth Bi site, Bi(4) is bonded in a distorted pentagonal planar geometry to one O(5) and four equivalent O(9) atoms. The Bi(4)-O(5) bond length is 2.40 Å. There are two shorter (2.19 Å) and two longer (2.51 Å) Bi(4)-O(9) bond lengths. In the fifth Bi site, Bi(5) is bonded in a 5-coordinate geometry to one O(8), two equivalent O(2), and two equivalent O(4) atoms. The Bi(5)-O(8) bond length is 2.20 Å. Both Bi(5)-O(2) bond lengths are 2.31 Å. Both Bi(5)-O(4) bond lengths are 2.62 Å. In the sixth Bi site, Bi(6) is bonded in a 3-coordinate geometry to one O(7) and two equivalent O(1) atoms. The Bi(6)-O(7) bond length is 2.19 Å. Both Bi(6)-O(1) bond lengths are 2.25 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ti(2) and one Bi(6) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Ti(3) and one Bi(5) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Fe(2) and one Bi(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ti(1), one Bi(1), and one Bi(5) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ti(2) and one Bi(4) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ti(3) and one Bi(3) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Ti(2), one Fe(2), and one Bi(6) atom. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to one Ti(1), one Ti(3), and one Bi(5) atom. In the ninth O site, O(9) is bonded to two equivalent Bi(3) and two equivalent Bi(4) atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra. In the tenth O site, O(10) is bonded in a distorted T-shaped geometry to one Fe(1), one Fe(2), and one Bi(2) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Ti(1), one Fe(1), and one Bi(1) atom. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to two equivalent Fe(1) and one Bi(1) atom.