The material described by Sr4Nb2O9 is Pb (Zr_0.50 Ti_0.48) O_3-like structured and crystallizes in the triclinic P1 space group. There are eight inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 10-coordinate geometry to one O(15), one O(16), one O(18), one O(3), one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms. In the second Sr site, Sr(2) is bonded in a 6-coordinate geometry to one O(1), one O(12), one O(2), one O(3), one O(5), and one O(6) atom. In the third Sr site, Sr(3) is bonded in a 5-coordinate geometry to one O(12), one O(13), one O(4), one O(7), and one O(8) atom. In the fourth Sr site, Sr(4) is bonded in a 8-coordinate geometry to one O(1), one O(12), one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. In the fifth Sr site, Sr(5) is bonded in a 12-coordinate geometry to one O(11), one O(13), one O(15), one O(16), one O(18), one O(9), two equivalent O(10), two equivalent O(14), and two equivalent O(17) atoms. In the sixth Sr site, Sr(6) is bonded to one O(11), one O(12), one O(13), one O(4), one O(7), one O(8), and one O(9) atom to form distorted SrO7 pentagonal bipyramids that share corners with three equivalent Nb(3)O6 octahedra, corners with two equivalent Nb(2)O6 pentagonal pyramids, and  an edgeedge with one Nb(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 17-33°. In the seventh Sr site, Sr(7) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(13), one O(14), one O(17), one O(8), and two equivalent O(9) atoms. In the eighth Sr site, Sr(8) is bonded in a 8-coordinate geometry to one O(1), one O(14), one O(15), one O(16), one O(17), one O(18), one O(2), and one O(6) atom. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(15), one O(16), one O(18), one O(2), and one O(6) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 16-17°. In the second Nb site, Nb(2) is bonded to one O(12), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form distorted NbO6 pentagonal pyramids that share corners with two equivalent Sr(6)O7 pentagonal bipyramids and  an edgeedge with one Sr(6)O7 pentagonal bipyramid. In the third Nb site, Nb(3) is bonded to one O(10), one O(11), one O(13), one O(14), one O(17), and one O(9) atom to form NbO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra and corners with three equivalent Sr(6)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 13-18°. In the fourth Nb site, Nb(4) is bonded to one O(10), one O(14), one O(15), one O(16), one O(17), and one O(18) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 13-18°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to one Sr(2), one Sr(4), one Sr(8), two equivalent Sr(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Sr(2), one Sr(4), one Sr(8), two equivalent Sr(1), and one Nb(1) atom. In the third O site, O(3) is bonded to one Sr(1), one Sr(2), one Sr(4), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom. In the fifth O site, O(5) is bonded to one Sr(1), one Sr(2), one Sr(4), and one Nb(2) atom to form a mixture of corner and edge-sharing OSr3Nb tetrahedra. In the sixth O site, O(6) is bonded in a 1-coordinate geometry to one Sr(1), one Sr(2), one Sr(4), one Sr(8), and one Nb(1) atom. In the seventh O site, O(7) is bonded to one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the eighth O site, O(8) is bonded to one Sr(3), one Sr(6), one Sr(7), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the ninth O site, O(9) is bonded in a 1-coordinate geometry to one Sr(5), one Sr(6), two equivalent Sr(7), and one Nb(3) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Sr(7), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one Sr(5), one Sr(6), one Sr(7), and one Nb(3) atom. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Sr(2), one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom. In the thirteenth O site, O(13) is bonded in a 1-coordinate geometry to one Sr(3), one Sr(5), one Sr(6), one Sr(7), and one Nb(3) atom. In the fourteenth O site, O(14) is bonded in a 2-coordinate geometry to one Sr(7), one Sr(8), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the fifteenth O site, O(15) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. In the sixteenth O site, O(16) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. In the seventeenth O site, O(17) is bonded in a 5-coordinate geometry to one Sr(7), one Sr(8), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the eighteenth O site, O(18) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. is represented by the CIF card [CIF]
data_Sr4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.877
_cell_length_b   5.882
_cell_length_c   14.678
_cell_angle_alpha   89.612
_cell_angle_beta   89.328
_cell_angle_gamma   60.707
_symmetry_Int_Tables_number   1
_cell_volume   442.460
_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  0.736  0.631  0.919  1.0
  Sr  Sr1  1  0.395  0.349  0.806  1.0
  Sr  Sr2  1  0.304  0.375  0.561  1.0
  Sr  Sr3  1  0.044  0.010  0.763  1.0
  Sr  Sr4  1  0.028  0.982  0.251  1.0
  Sr  Sr5  1  0.982  0.035  0.525  1.0
  Sr  Sr6  1  0.669  0.674  0.394  1.0
  Sr  Sr7  1  0.385  0.307  0.071  1.0
  Nb  Nb8  1  0.054  0.977  0.997  1.0
  Nb  Nb9  1  0.708  0.637  0.668  1.0
  Nb  Nb10  1  0.366  0.311  0.330  1.0
  Nb  Nb11  1  0.704  0.650  0.162  1.0
  O  O12  1  0.739  0.175  0.928  1.0
  O  O13  1  0.261  0.096  0.938  1.0
  O  O14  1  0.485  0.738  0.783  1.0
  O  O15  1  0.393  0.947  0.616  1.0
  O  O16  1  0.974  0.438  0.772  1.0
  O  O17  1  0.158  0.659  0.934  1.0
  O  O18  1  0.973  0.752  0.649  1.0
  O  O19  1  0.837  0.494  0.537  1.0
  O  O20  1  0.200  0.153  0.395  1.0
  O  O21  1  0.015  0.534  0.250  1.0
  O  O22  1  0.697  0.097  0.389  1.0
  O  O23  1  0.655  0.322  0.664  1.0
  O  O24  1  0.263  0.611  0.406  1.0
  O  O25  1  0.573  0.444  0.240  1.0
  O  O26  1  0.839  0.860  0.093  1.0
  O  O27  1  0.392  0.757  0.084  1.0
  O  O28  1  0.482  0.982  0.234  1.0
  O  O29  1  0.921  0.323  0.088  1.0
[/CIF]
.
The material described by Sr4Nb2O9 is Pb (Zr_0.50 Ti_0.48) O_3-like structured and crystallizes in the triclinic P1 space group. There are eight inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 10-coordinate geometry to one O(15), one O(16), one O(18), one O(3), one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms. In the second Sr site, Sr(2) is bonded in a 6-coordinate geometry to one O(1), one O(12), one O(2), one O(3), one O(5), and one O(6) atom. In the third Sr site, Sr(3) is bonded in a 5-coordinate geometry to one O(12), one O(13), one O(4), one O(7), and one O(8) atom. In the fourth Sr site, Sr(4) is bonded in a 8-coordinate geometry to one O(1), one O(12), one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. In the fifth Sr site, Sr(5) is bonded in a 12-coordinate geometry to one O(11), one O(13), one O(15), one O(16), one O(18), one O(9), two equivalent O(10), two equivalent O(14), and two equivalent O(17) atoms. In the sixth Sr site, Sr(6) is bonded to one O(11), one O(12), one O(13), one O(4), one O(7), one O(8), and one O(9) atom to form distorted SrO7 pentagonal bipyramids that share corners with three equivalent Nb(3)O6 octahedra, corners with two equivalent Nb(2)O6 pentagonal pyramids, and  an edgeedge with one Nb(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 17-33°. In the seventh Sr site, Sr(7) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(13), one O(14), one O(17), one O(8), and two equivalent O(9) atoms. In the eighth Sr site, Sr(8) is bonded in a 8-coordinate geometry to one O(1), one O(14), one O(15), one O(16), one O(17), one O(18), one O(2), and one O(6) atom. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(15), one O(16), one O(18), one O(2), and one O(6) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 16-17°. In the second Nb site, Nb(2) is bonded to one O(12), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form distorted NbO6 pentagonal pyramids that share corners with two equivalent Sr(6)O7 pentagonal bipyramids and  an edgeedge with one Sr(6)O7 pentagonal bipyramid. In the third Nb site, Nb(3) is bonded to one O(10), one O(11), one O(13), one O(14), one O(17), and one O(9) atom to form NbO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra and corners with three equivalent Sr(6)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 13-18°. In the fourth Nb site, Nb(4) is bonded to one O(10), one O(14), one O(15), one O(16), one O(17), and one O(18) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 13-18°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to one Sr(2), one Sr(4), one Sr(8), two equivalent Sr(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Sr(2), one Sr(4), one Sr(8), two equivalent Sr(1), and one Nb(1) atom. In the third O site, O(3) is bonded to one Sr(1), one Sr(2), one Sr(4), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom. In the fifth O site, O(5) is bonded to one Sr(1), one Sr(2), one Sr(4), and one Nb(2) atom to form a mixture of corner and edge-sharing OSr3Nb tetrahedra. In the sixth O site, O(6) is bonded in a 1-coordinate geometry to one Sr(1), one Sr(2), one Sr(4), one Sr(8), and one Nb(1) atom. In the seventh O site, O(7) is bonded to one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the eighth O site, O(8) is bonded to one Sr(3), one Sr(6), one Sr(7), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the ninth O site, O(9) is bonded in a 1-coordinate geometry to one Sr(5), one Sr(6), two equivalent Sr(7), and one Nb(3) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Sr(7), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one Sr(5), one Sr(6), one Sr(7), and one Nb(3) atom. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Sr(2), one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom. In the thirteenth O site, O(13) is bonded in a 1-coordinate geometry to one Sr(3), one Sr(5), one Sr(6), one Sr(7), and one Nb(3) atom. In the fourteenth O site, O(14) is bonded in a 2-coordinate geometry to one Sr(7), one Sr(8), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the fifteenth O site, O(15) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. In the sixteenth O site, O(16) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. In the seventeenth O site, O(17) is bonded in a 5-coordinate geometry to one Sr(7), one Sr(8), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the eighteenth O site, O(18) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. is represented by the CIF card [CIF]
data_Sr4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.877
_cell_length_b   5.882
_cell_length_c   14.678
_cell_angle_alpha   89.612
_cell_angle_beta   89.328
_cell_angle_gamma   60.707
_symmetry_Int_Tables_number   1
_cell_volume   442.460
_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  0.736  0.631  0.919  1.0
  Sr  Sr1  1  0.395  0.349  0.806  1.0
  Sr  Sr2  1  0.304  0.375  0.561  1.0
  Sr  Sr3  1  0.044  0.010  0.763  1.0
  Sr  Sr4  1  0.028  0.982  0.251  1.0
  Sr  Sr5  1  0.982  0.035  0.525  1.0
  Sr  Sr6  1  0.669  0.674  0.394  1.0
  Sr  Sr7  1  0.385  0.307  0.071  1.0
  Nb  Nb8  1  0.054  0.977  0.997  1.0
  Nb  Nb9  1  0.708  0.637  0.668  1.0
  Nb  Nb10  1  0.366  0.311  0.330  1.0
  Nb  Nb11  1  0.704  0.650  0.162  1.0
  O  O12  1  0.739  0.175  0.928  1.0
  O  O13  1  0.261  0.096  0.938  1.0
  O  O14  1  0.485  0.738  0.783  1.0
  O  O15  1  0.393  0.947  0.616  1.0
  O  O16  1  0.974  0.438  0.772  1.0
  O  O17  1  0.158  0.659  0.934  1.0
  O  O18  1  0.973  0.752  0.649  1.0
  O  O19  1  0.837  0.494  0.537  1.0
  O  O20  1  0.200  0.153  0.395  1.0
  O  O21  1  0.015  0.534  0.250  1.0
  O  O22  1  0.697  0.097  0.389  1.0
  O  O23  1  0.655  0.322  0.664  1.0
  O  O24  1  0.263  0.611  0.406  1.0
  O  O25  1  0.573  0.444  0.240  1.0
  O  O26  1  0.839  0.860  0.093  1.0
  O  O27  1  0.392  0.757  0.084  1.0
  O  O28  1  0.482  0.982  0.234  1.0
  O  O29  1  0.921  0.323  0.088  1.0
[/CIF]
.