The structure described by Ba4Ta2O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 6-coordinate geometry to six equivalent O(2) atoms. In the second Ba site, Ba(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted BaO6 pentagonal pyramids that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ba(2)O6 pentagonal pyramids, and edges with three equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Ba(2)O6 pentagonal pyramids, edges with three equivalent Ba(2)O6 pentagonal pyramids, and  a faceface with one Ta(1)O6 octahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(2) and two equivalent Ta(1) atoms to form a mixture of distorted edge and corner-sharing OBa2Ta2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ba(2), two equivalent Ba(1), and one Ta(1) atom. is represented by the CIF file [CIF]
data_Ba4Ta2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.265
_cell_length_b   6.265
_cell_length_c   15.931
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   541.498
_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
  Ba  Ba0  1  0.333  0.667  0.532  1.0
  Ba  Ba1  1  0.333  0.667  0.795  1.0
  Ba  Ba2  1  0.333  0.667  0.295  1.0
  Ba  Ba3  1  0.333  0.667  0.032  1.0
  Ba  Ba4  1  0.667  0.333  0.705  1.0
  Ba  Ba5  1  0.667  0.333  0.205  1.0
  Ba  Ba6  1  0.667  0.333  0.968  1.0
  Ba  Ba7  1  0.667  0.333  0.468  1.0
  Ta  Ta8  1  0.000  0.000  0.653  1.0
  Ta  Ta9  1  0.000  0.000  0.847  1.0
  Ta  Ta10  1  0.000  0.000  0.153  1.0
  Ta  Ta11  1  0.000  0.000  0.347  1.0
  O  O12  1  0.000  0.765  0.250  1.0
  O  O13  1  0.036  0.742  0.902  1.0
  O  O14  1  0.258  0.964  0.402  1.0
  O  O15  1  0.036  0.294  0.402  1.0
  O  O16  1  0.000  0.235  0.750  1.0
  O  O17  1  0.235  0.235  0.250  1.0
  O  O18  1  0.258  0.294  0.902  1.0
  O  O19  1  0.706  0.964  0.902  1.0
  O  O20  1  0.294  0.258  0.598  1.0
  O  O21  1  0.235  0.000  0.750  1.0
  O  O22  1  0.706  0.742  0.402  1.0
  O  O23  1  0.294  0.036  0.098  1.0
  O  O24  1  0.742  0.706  0.098  1.0
  O  O25  1  0.765  0.765  0.750  1.0
  O  O26  1  0.964  0.706  0.598  1.0
  O  O27  1  0.742  0.036  0.598  1.0
  O  O28  1  0.765  0.000  0.250  1.0
  O  O29  1  0.964  0.258  0.098  1.0
[/CIF]
.
The structure described by Ba4Ta2O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 6-coordinate geometry to six equivalent O(2) atoms. In the second Ba site, Ba(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted BaO6 pentagonal pyramids that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ba(2)O6 pentagonal pyramids, and edges with three equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Ba(2)O6 pentagonal pyramids, edges with three equivalent Ba(2)O6 pentagonal pyramids, and  a faceface with one Ta(1)O6 octahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(2) and two equivalent Ta(1) atoms to form a mixture of distorted edge and corner-sharing OBa2Ta2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ba(2), two equivalent Ba(1), and one Ta(1) atom. is represented by the CIF file [CIF]
data_Ba4Ta2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.265
_cell_length_b   6.265
_cell_length_c   15.931
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   541.498
_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
  Ba  Ba0  1  0.333  0.667  0.532  1.0
  Ba  Ba1  1  0.333  0.667  0.795  1.0
  Ba  Ba2  1  0.333  0.667  0.295  1.0
  Ba  Ba3  1  0.333  0.667  0.032  1.0
  Ba  Ba4  1  0.667  0.333  0.705  1.0
  Ba  Ba5  1  0.667  0.333  0.205  1.0
  Ba  Ba6  1  0.667  0.333  0.968  1.0
  Ba  Ba7  1  0.667  0.333  0.468  1.0
  Ta  Ta8  1  0.000  0.000  0.653  1.0
  Ta  Ta9  1  0.000  0.000  0.847  1.0
  Ta  Ta10  1  0.000  0.000  0.153  1.0
  Ta  Ta11  1  0.000  0.000  0.347  1.0
  O  O12  1  0.000  0.765  0.250  1.0
  O  O13  1  0.036  0.742  0.902  1.0
  O  O14  1  0.258  0.964  0.402  1.0
  O  O15  1  0.036  0.294  0.402  1.0
  O  O16  1  0.000  0.235  0.750  1.0
  O  O17  1  0.235  0.235  0.250  1.0
  O  O18  1  0.258  0.294  0.902  1.0
  O  O19  1  0.706  0.964  0.902  1.0
  O  O20  1  0.294  0.258  0.598  1.0
  O  O21  1  0.235  0.000  0.750  1.0
  O  O22  1  0.706  0.742  0.402  1.0
  O  O23  1  0.294  0.036  0.098  1.0
  O  O24  1  0.742  0.706  0.098  1.0
  O  O25  1  0.765  0.765  0.750  1.0
  O  O26  1  0.964  0.706  0.598  1.0
  O  O27  1  0.742  0.036  0.598  1.0
  O  O28  1  0.765  0.000  0.250  1.0
  O  O29  1  0.964  0.258  0.098  1.0
[/CIF]
.