The crystal structure described by Ba4Nb2O9 crystallizes in the trigonal P-3m1 space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 6-coordinate geometry to six equivalent O(1) atoms. In the second Ba site, Ba(2) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(2)O12 cuboctahedra and faces with six equivalent Nb(1)O6 octahedra. In the third Ba site, Ba(3) is bonded in a distorted q6 geometry to three equivalent O(2) and six equivalent O(1) atoms. Nb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form NbO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra and faces with three equivalent Ba(2)O12 cuboctahedra. The corner-sharing octahedra are not tilted. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Ba(1), one Ba(2), two equivalent Ba(3), and one Nb(1) atom. In the second O site, O(2) is bonded to two equivalent Ba(2), two equivalent Ba(3), and two equivalent Nb(1) atoms to form a mixture of distorted corner and face-sharing OBa4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ba4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.027
_cell_length_b   6.027
_cell_length_c   8.508
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   267.650
_cell_formula_units_Z   1
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
  Ba  Ba0  1  0.000  0.000  0.500  1.0
  Ba  Ba1  1  0.000  0.000  0.000  1.0
  Ba  Ba2  1  0.333  0.667  0.755  1.0
  Ba  Ba3  1  0.667  0.333  0.245  1.0
  Nb  Nb4  1  0.333  0.667  0.164  1.0
  Nb  Nb5  1  0.667  0.333  0.836  1.0
  O  O6  1  0.174  0.826  0.274  1.0
  O  O7  1  0.826  0.174  0.726  1.0
  O  O8  1  0.174  0.348  0.274  1.0
  O  O9  1  0.826  0.652  0.726  1.0
  O  O10  1  0.652  0.826  0.274  1.0
  O  O11  1  0.348  0.174  0.726  1.0
  O  O12  1  0.500  0.000  0.000  1.0
  O  O13  1  0.000  0.500  0.000  1.0
  O  O14  1  0.500  0.500  0.000  1.0
[/CIF]
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The crystal structure described by Ba4Nb2O9 crystallizes in the trigonal P-3m1 space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 6-coordinate geometry to six equivalent O(1) atoms. In the second Ba site, Ba(2) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(2)O12 cuboctahedra and faces with six equivalent Nb(1)O6 octahedra. In the third Ba site, Ba(3) is bonded in a distorted q6 geometry to three equivalent O(2) and six equivalent O(1) atoms. Nb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form NbO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra and faces with three equivalent Ba(2)O12 cuboctahedra. The corner-sharing octahedra are not tilted. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Ba(1), one Ba(2), two equivalent Ba(3), and one Nb(1) atom. In the second O site, O(2) is bonded to two equivalent Ba(2), two equivalent Ba(3), and two equivalent Nb(1) atoms to form a mixture of distorted corner and face-sharing OBa4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ba4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.027
_cell_length_b   6.027
_cell_length_c   8.508
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   267.650
_cell_formula_units_Z   1
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
  Ba  Ba0  1  0.000  0.000  0.500  1.0
  Ba  Ba1  1  0.000  0.000  0.000  1.0
  Ba  Ba2  1  0.333  0.667  0.755  1.0
  Ba  Ba3  1  0.667  0.333  0.245  1.0
  Nb  Nb4  1  0.333  0.667  0.164  1.0
  Nb  Nb5  1  0.667  0.333  0.836  1.0
  O  O6  1  0.174  0.826  0.274  1.0
  O  O7  1  0.826  0.174  0.726  1.0
  O  O8  1  0.174  0.348  0.274  1.0
  O  O9  1  0.826  0.652  0.726  1.0
  O  O10  1  0.652  0.826  0.274  1.0
  O  O11  1  0.348  0.174  0.726  1.0
  O  O12  1  0.500  0.000  0.000  1.0
  O  O13  1  0.000  0.500  0.000  1.0
  O  O14  1  0.500  0.500  0.000  1.0
[/CIF]
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