The material described by Bi2Ti2O7 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with four equivalent Ti(2)O6 octahedra,  a cornercorner with one Bi(1)O6 pentagonal pyramid, and  an edgeedge with one Bi(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 40-49°. In the second Ti site, Ti(2) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form TiO6 octahedra that share corners with two equivalent Ti(2)O6 octahedra, corners with four equivalent Ti(1)O6 octahedra,  a cornercorner with one Bi(1)O6 pentagonal pyramid, and edges with two equivalent Bi(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 40-49°. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(7) atoms to form distorted BiO6 pentagonal pyramids that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Ti(2)O6 octahedra, corners with two equivalent Bi(1)O6 pentagonal pyramids,  an edgeedge with one Ti(1)O6 octahedra, and edges with two equivalent Ti(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 62-67°. In the second Bi site, Bi(2) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), and two equivalent O(7) atoms. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Ti(2) and one Bi(1) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to two equivalent Ti(1) and one Bi(2) atom. In the third O site, O(7) is bonded to two equivalent Bi(1) and two equivalent Bi(2) atoms to form corner-sharing OBi4 tetrahedra. In the fourth O site, O(1) is bonded in a 3-coordinate geometry to one Ti(1), one Ti(2), and one Bi(1) atom. In the fifth O site, O(2) is bonded in a 3-coordinate geometry to one Ti(1), one Ti(2), and one Bi(1) atom. In the sixth O site, O(3) is bonded in a 4-coordinate geometry to one Ti(1), one Ti(2), one Bi(1), and one Bi(2) atom. In the seventh O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to one Ti(1), one Ti(2), and one Bi(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ti2Bi2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.360
_cell_length_b   7.417
_cell_length_c   10.397
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   567.494
_cell_formula_units_Z   4
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Ti  Ti0  1  0.005  0.005  0.009  1.0
  Ti  Ti1  1  0.995  0.505  0.991  1.0
  Ti  Ti2  1  0.495  0.505  0.509  1.0
  Ti  Ti3  1  0.505  0.005  0.491  1.0
  Ti  Ti4  1  0.244  0.246  0.740  1.0
  Ti  Ti5  1  0.756  0.746  0.260  1.0
  Ti  Ti6  1  0.256  0.746  0.240  1.0
  Ti  Ti7  1  0.744  0.246  0.760  1.0
  Bi  Bi8  1  0.027  0.976  0.469  1.0
  Bi  Bi9  1  0.973  0.476  0.531  1.0
  Bi  Bi10  1  0.473  0.476  0.969  1.0
  Bi  Bi11  1  0.527  0.976  0.031  1.0
  Bi  Bi12  1  0.275  0.295  0.262  1.0
  Bi  Bi13  1  0.725  0.795  0.738  1.0
  Bi  Bi14  1  0.225  0.795  0.762  1.0
  Bi  Bi15  1  0.775  0.295  0.238  1.0
  O  O16  1  0.193  0.431  0.879  1.0
  O  O17  1  0.807  0.931  0.121  1.0
  O  O18  1  0.307  0.931  0.379  1.0
  O  O19  1  0.693  0.431  0.621  1.0
  O  O20  1  0.703  0.931  0.384  1.0
  O  O21  1  0.297  0.431  0.616  1.0
  O  O22  1  0.797  0.431  0.884  1.0
  O  O23  1  0.203  0.931  0.116  1.0
  O  O24  1  0.794  0.045  0.875  1.0
  O  O25  1  0.206  0.545  0.125  1.0
  O  O26  1  0.706  0.545  0.375  1.0
  O  O27  1  0.294  0.045  0.625  1.0
  O  O28  1  0.325  0.551  0.365  1.0
  O  O29  1  0.675  0.051  0.635  1.0
  O  O30  1  0.175  0.051  0.865  1.0
  O  O31  1  0.825  0.551  0.135  1.0
  O  O32  1  0.991  0.261  0.684  1.0
  O  O33  1  0.009  0.761  0.316  1.0
  O  O34  1  0.509  0.761  0.184  1.0
  O  O35  1  0.491  0.261  0.816  1.0
  O  O36  1  0.505  0.742  0.573  1.0
  O  O37  1  0.495  0.242  0.427  1.0
  O  O38  1  0.995  0.242  0.073  1.0
  O  O39  1  0.005  0.742  0.927  1.0
  O  O40  1  0.986  0.767  0.621  1.0
  O  O41  1  0.014  0.267  0.379  1.0
  O  O42  1  0.514  0.267  0.121  1.0
  O  O43  1  0.486  0.767  0.879  1.0
[/CIF]
.
The material described by Bi2Ti2O7 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with four equivalent Ti(2)O6 octahedra,  a cornercorner with one Bi(1)O6 pentagonal pyramid, and  an edgeedge with one Bi(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 40-49°. In the second Ti site, Ti(2) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form TiO6 octahedra that share corners with two equivalent Ti(2)O6 octahedra, corners with four equivalent Ti(1)O6 octahedra,  a cornercorner with one Bi(1)O6 pentagonal pyramid, and edges with two equivalent Bi(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 40-49°. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(7) atoms to form distorted BiO6 pentagonal pyramids that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Ti(2)O6 octahedra, corners with two equivalent Bi(1)O6 pentagonal pyramids,  an edgeedge with one Ti(1)O6 octahedra, and edges with two equivalent Ti(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 62-67°. In the second Bi site, Bi(2) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), and two equivalent O(7) atoms. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Ti(2) and one Bi(1) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to two equivalent Ti(1) and one Bi(2) atom. In the third O site, O(7) is bonded to two equivalent Bi(1) and two equivalent Bi(2) atoms to form corner-sharing OBi4 tetrahedra. In the fourth O site, O(1) is bonded in a 3-coordinate geometry to one Ti(1), one Ti(2), and one Bi(1) atom. In the fifth O site, O(2) is bonded in a 3-coordinate geometry to one Ti(1), one Ti(2), and one Bi(1) atom. In the sixth O site, O(3) is bonded in a 4-coordinate geometry to one Ti(1), one Ti(2), one Bi(1), and one Bi(2) atom. In the seventh O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to one Ti(1), one Ti(2), and one Bi(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ti2Bi2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.360
_cell_length_b   7.417
_cell_length_c   10.397
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   567.494
_cell_formula_units_Z   4
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Ti  Ti0  1  0.005  0.005  0.009  1.0
  Ti  Ti1  1  0.995  0.505  0.991  1.0
  Ti  Ti2  1  0.495  0.505  0.509  1.0
  Ti  Ti3  1  0.505  0.005  0.491  1.0
  Ti  Ti4  1  0.244  0.246  0.740  1.0
  Ti  Ti5  1  0.756  0.746  0.260  1.0
  Ti  Ti6  1  0.256  0.746  0.240  1.0
  Ti  Ti7  1  0.744  0.246  0.760  1.0
  Bi  Bi8  1  0.027  0.976  0.469  1.0
  Bi  Bi9  1  0.973  0.476  0.531  1.0
  Bi  Bi10  1  0.473  0.476  0.969  1.0
  Bi  Bi11  1  0.527  0.976  0.031  1.0
  Bi  Bi12  1  0.275  0.295  0.262  1.0
  Bi  Bi13  1  0.725  0.795  0.738  1.0
  Bi  Bi14  1  0.225  0.795  0.762  1.0
  Bi  Bi15  1  0.775  0.295  0.238  1.0
  O  O16  1  0.193  0.431  0.879  1.0
  O  O17  1  0.807  0.931  0.121  1.0
  O  O18  1  0.307  0.931  0.379  1.0
  O  O19  1  0.693  0.431  0.621  1.0
  O  O20  1  0.703  0.931  0.384  1.0
  O  O21  1  0.297  0.431  0.616  1.0
  O  O22  1  0.797  0.431  0.884  1.0
  O  O23  1  0.203  0.931  0.116  1.0
  O  O24  1  0.794  0.045  0.875  1.0
  O  O25  1  0.206  0.545  0.125  1.0
  O  O26  1  0.706  0.545  0.375  1.0
  O  O27  1  0.294  0.045  0.625  1.0
  O  O28  1  0.325  0.551  0.365  1.0
  O  O29  1  0.675  0.051  0.635  1.0
  O  O30  1  0.175  0.051  0.865  1.0
  O  O31  1  0.825  0.551  0.135  1.0
  O  O32  1  0.991  0.261  0.684  1.0
  O  O33  1  0.009  0.761  0.316  1.0
  O  O34  1  0.509  0.761  0.184  1.0
  O  O35  1  0.491  0.261  0.816  1.0
  O  O36  1  0.505  0.742  0.573  1.0
  O  O37  1  0.495  0.242  0.427  1.0
  O  O38  1  0.995  0.242  0.073  1.0
  O  O39  1  0.005  0.742  0.927  1.0
  O  O40  1  0.986  0.767  0.621  1.0
  O  O41  1  0.014  0.267  0.379  1.0
  O  O42  1  0.514  0.267  0.121  1.0
  O  O43  1  0.486  0.767  0.879  1.0
[/CIF]
.