The compound described by Sr2Nb2O7 is Pb (Zr_0.50 Ti_0.48) O_3-like structured and crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 7-coordinate geometry to one O(7), three equivalent O(3), and three equivalent O(4) atoms. In the second Sr site, Sr(2) is bonded to one O(7), two equivalent O(2), two equivalent O(6), three equivalent O(1), and four equivalent O(5) atoms to form distorted SrO12 cuboctahedra that share corners with six equivalent Sr(2)O12 cuboctahedra, faces with four equivalent Sr(2)O12 cuboctahedra, faces with two equivalent Nb(1)O6 octahedra, and faces with six equivalent Nb(2)O6 octahedra. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(2), one O(3), one O(4), one O(6), and two equivalent O(7) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, and faces with two equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 16-37°. In the second Nb site, Nb(2) is bonded to one O(2), one O(6), two equivalent O(1), and two equivalent O(5) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and faces with six equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 8-37°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to three equivalent Sr(2) and two equivalent Nb(2) atoms. In the second O site, O(2) is bonded to two equivalent Sr(2), one Nb(1), and one Nb(2) atom to form distorted OSr2Nb2 tetrahedra that share  a cornercorner with one O(4)Sr3Nb tetrahedra and corners with two equivalent O(2)Sr2Nb2 tetrahedra. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Sr(1) and one Nb(1) atom. In the fourth O site, O(4) is bonded to three equivalent Sr(1) and one Nb(1) atom to form OSr3Nb tetrahedra that share  a cornercorner with one O(2)Sr2Nb2 tetrahedra and corners with six equivalent O(4)Sr3Nb tetrahedra. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to four equivalent Sr(2) and two equivalent Nb(2) atoms. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to two equivalent Sr(2), one Nb(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), and two equivalent Nb(1) atoms. is represented by the CIF file [CIF]
data_Sr2Nb2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.648
_cell_length_b   13.648
_cell_length_c   5.766
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   163.181
_symmetry_Int_Tables_number   1
_cell_volume   310.746
_cell_formula_units_Z   2
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
  Sr  Sr0  1  0.292  0.708  0.038  1.0
  Sr  Sr1  1  0.708  0.292  0.538  1.0
  Sr  Sr2  1  0.449  0.551  0.471  1.0
  Sr  Sr3  1  0.551  0.449  0.971  1.0
  Nb  Nb4  1  0.838  0.162  0.503  1.0
  Nb  Nb5  1  0.162  0.838  0.003  1.0
  Nb  Nb6  1  0.058  0.942  0.471  1.0
  Nb  Nb7  1  0.942  0.058  0.971  1.0
  O  O8  1  0.452  0.548  0.943  1.0
  O  O9  1  0.548  0.452  0.443  1.0
  O  O10  1  0.908  0.092  0.663  1.0
  O  O11  1  0.092  0.908  0.163  1.0
  O  O12  1  0.800  0.200  0.768  1.0
  O  O13  1  0.200  0.800  0.268  1.0
  O  O14  1  0.215  0.785  0.791  1.0
  O  O15  1  0.785  0.215  0.291  1.0
  O  O16  1  0.992  0.008  0.223  1.0
  O  O17  1  0.008  0.992  0.723  1.0
  O  O18  1  0.888  0.112  0.173  1.0
  O  O19  1  0.112  0.888  0.673  1.0
  O  O20  1  0.349  0.651  0.467  1.0
  O  O21  1  0.651  0.349  0.967  1.0
[/CIF]
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The compound described by Sr2Nb2O7 is Pb (Zr_0.50 Ti_0.48) O_3-like structured and crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 7-coordinate geometry to one O(7), three equivalent O(3), and three equivalent O(4) atoms. In the second Sr site, Sr(2) is bonded to one O(7), two equivalent O(2), two equivalent O(6), three equivalent O(1), and four equivalent O(5) atoms to form distorted SrO12 cuboctahedra that share corners with six equivalent Sr(2)O12 cuboctahedra, faces with four equivalent Sr(2)O12 cuboctahedra, faces with two equivalent Nb(1)O6 octahedra, and faces with six equivalent Nb(2)O6 octahedra. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(2), one O(3), one O(4), one O(6), and two equivalent O(7) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, and faces with two equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 16-37°. In the second Nb site, Nb(2) is bonded to one O(2), one O(6), two equivalent O(1), and two equivalent O(5) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and faces with six equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 8-37°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to three equivalent Sr(2) and two equivalent Nb(2) atoms. In the second O site, O(2) is bonded to two equivalent Sr(2), one Nb(1), and one Nb(2) atom to form distorted OSr2Nb2 tetrahedra that share  a cornercorner with one O(4)Sr3Nb tetrahedra and corners with two equivalent O(2)Sr2Nb2 tetrahedra. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Sr(1) and one Nb(1) atom. In the fourth O site, O(4) is bonded to three equivalent Sr(1) and one Nb(1) atom to form OSr3Nb tetrahedra that share  a cornercorner with one O(2)Sr2Nb2 tetrahedra and corners with six equivalent O(4)Sr3Nb tetrahedra. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to four equivalent Sr(2) and two equivalent Nb(2) atoms. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to two equivalent Sr(2), one Nb(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), and two equivalent Nb(1) atoms. is represented by the CIF file [CIF]
data_Sr2Nb2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.648
_cell_length_b   13.648
_cell_length_c   5.766
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   163.181
_symmetry_Int_Tables_number   1
_cell_volume   310.746
_cell_formula_units_Z   2
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
  Sr  Sr0  1  0.292  0.708  0.038  1.0
  Sr  Sr1  1  0.708  0.292  0.538  1.0
  Sr  Sr2  1  0.449  0.551  0.471  1.0
  Sr  Sr3  1  0.551  0.449  0.971  1.0
  Nb  Nb4  1  0.838  0.162  0.503  1.0
  Nb  Nb5  1  0.162  0.838  0.003  1.0
  Nb  Nb6  1  0.058  0.942  0.471  1.0
  Nb  Nb7  1  0.942  0.058  0.971  1.0
  O  O8  1  0.452  0.548  0.943  1.0
  O  O9  1  0.548  0.452  0.443  1.0
  O  O10  1  0.908  0.092  0.663  1.0
  O  O11  1  0.092  0.908  0.163  1.0
  O  O12  1  0.800  0.200  0.768  1.0
  O  O13  1  0.200  0.800  0.268  1.0
  O  O14  1  0.215  0.785  0.791  1.0
  O  O15  1  0.785  0.215  0.291  1.0
  O  O16  1  0.992  0.008  0.223  1.0
  O  O17  1  0.008  0.992  0.723  1.0
  O  O18  1  0.888  0.112  0.173  1.0
  O  O19  1  0.112  0.888  0.673  1.0
  O  O20  1  0.349  0.651  0.467  1.0
  O  O21  1  0.651  0.349  0.967  1.0
[/CIF]
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