The structure described by TbTa3O9 crystallizes in the monoclinic C2/m space group. Tb(1) is bonded to one O(1), two equivalent O(2), two equivalent O(7), three equivalent O(4), and four equivalent O(3) atoms to form TbO12 cuboctahedra that share corners with three equivalent Tb(1)O12 cuboctahedra, faces with two equivalent Tb(1)O12 cuboctahedra, faces with two equivalent Ta(2)O6 octahedra, faces with three equivalent Ta(1)O6 octahedra, and faces with three equivalent Ta(3)O6 octahedra. There are three inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(4), one O(5), two equivalent O(3), and two equivalent O(7) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, corners with three equivalent Ta(3)O6 octahedra, and faces with three equivalent Tb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-18°. In the second Ta site, Ta(2) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(7) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(2)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, corners with three equivalent Ta(3)O6 octahedra, and faces with two equivalent Tb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-15°. In the third Ta site, Ta(3) is bonded to one O(4), one O(6), two equivalent O(2), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ta(2)O6 octahedra, and faces with three equivalent Tb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 3-18°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Tb(1) and two equivalent Ta(2) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Tb(1), one Ta(2), and one Ta(3) atom. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Tb(1), one Ta(1), and one Ta(3) atom. In the fourth O site, O(4) is bonded to three equivalent Tb(1), one Ta(1), and one Ta(3) atom to form a mixture of distorted corner and edge-sharing OTb3Ta2 square pyramids. In the fifth O site, O(5) is bonded in a linear geometry to two equivalent Ta(1) atoms. In the sixth O site, O(6) is bonded in a linear geometry to one Ta(2) and one Ta(3) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Tb(1), one Ta(1), and one Ta(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_TbTa3O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.804
_cell_length_b   8.804
_cell_length_c   9.676
_cell_angle_alpha   56.947
_cell_angle_beta   56.947
_cell_angle_gamma   36.898
_symmetry_Int_Tables_number   1
_cell_volume   368.403
_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
  Tb  Tb0  1  0.326  0.326  0.001  1.0
  Tb  Tb1  1  0.674  0.674  0.999  1.0
  Ta  Ta2  1  0.077  0.077  0.257  1.0
  Ta  Ta3  1  0.583  0.583  0.751  1.0
  Ta  Ta4  1  0.750  0.750  0.262  1.0
  Ta  Ta5  1  0.250  0.250  0.738  1.0
  Ta  Ta6  1  0.923  0.923  0.743  1.0
  Ta  Ta7  1  0.417  0.417  0.249  1.0
  O  O8  1  0.500  0.500  0.000  1.0
  O  O9  1  0.573  0.098  0.227  1.0
  O  O10  1  0.098  0.573  0.227  1.0
  O  O11  1  0.927  0.428  0.218  1.0
  O  O12  1  0.176  0.176  1.000  1.0
  O  O13  1  0.824  0.824  0.000  1.0
  O  O14  1  0.000  0.000  0.500  1.0
  O  O15  1  0.665  0.665  0.503  1.0
  O  O16  1  0.725  0.250  0.773  1.0
  O  O17  1  0.572  0.073  0.782  1.0
  O  O18  1  0.428  0.927  0.218  1.0
  O  O19  1  0.250  0.725  0.773  1.0
  O  O20  1  0.750  0.275  0.227  1.0
  O  O21  1  0.275  0.750  0.227  1.0
  O  O22  1  0.335  0.335  0.497  1.0
  O  O23  1  0.073  0.572  0.782  1.0
  O  O24  1  0.902  0.427  0.773  1.0
  O  O25  1  0.427  0.902  0.773  1.0
[/CIF]
.
The structure described by TbTa3O9 crystallizes in the monoclinic C2/m space group. Tb(1) is bonded to one O(1), two equivalent O(2), two equivalent O(7), three equivalent O(4), and four equivalent O(3) atoms to form TbO12 cuboctahedra that share corners with three equivalent Tb(1)O12 cuboctahedra, faces with two equivalent Tb(1)O12 cuboctahedra, faces with two equivalent Ta(2)O6 octahedra, faces with three equivalent Ta(1)O6 octahedra, and faces with three equivalent Ta(3)O6 octahedra. There are three inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(4), one O(5), two equivalent O(3), and two equivalent O(7) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, corners with three equivalent Ta(3)O6 octahedra, and faces with three equivalent Tb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-18°. In the second Ta site, Ta(2) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(7) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(2)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, corners with three equivalent Ta(3)O6 octahedra, and faces with two equivalent Tb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-15°. In the third Ta site, Ta(3) is bonded to one O(4), one O(6), two equivalent O(2), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ta(2)O6 octahedra, and faces with three equivalent Tb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 3-18°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Tb(1) and two equivalent Ta(2) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Tb(1), one Ta(2), and one Ta(3) atom. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Tb(1), one Ta(1), and one Ta(3) atom. In the fourth O site, O(4) is bonded to three equivalent Tb(1), one Ta(1), and one Ta(3) atom to form a mixture of distorted corner and edge-sharing OTb3Ta2 square pyramids. In the fifth O site, O(5) is bonded in a linear geometry to two equivalent Ta(1) atoms. In the sixth O site, O(6) is bonded in a linear geometry to one Ta(2) and one Ta(3) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Tb(1), one Ta(1), and one Ta(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_TbTa3O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.804
_cell_length_b   8.804
_cell_length_c   9.676
_cell_angle_alpha   56.947
_cell_angle_beta   56.947
_cell_angle_gamma   36.898
_symmetry_Int_Tables_number   1
_cell_volume   368.403
_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
  Tb  Tb0  1  0.326  0.326  0.001  1.0
  Tb  Tb1  1  0.674  0.674  0.999  1.0
  Ta  Ta2  1  0.077  0.077  0.257  1.0
  Ta  Ta3  1  0.583  0.583  0.751  1.0
  Ta  Ta4  1  0.750  0.750  0.262  1.0
  Ta  Ta5  1  0.250  0.250  0.738  1.0
  Ta  Ta6  1  0.923  0.923  0.743  1.0
  Ta  Ta7  1  0.417  0.417  0.249  1.0
  O  O8  1  0.500  0.500  0.000  1.0
  O  O9  1  0.573  0.098  0.227  1.0
  O  O10  1  0.098  0.573  0.227  1.0
  O  O11  1  0.927  0.428  0.218  1.0
  O  O12  1  0.176  0.176  1.000  1.0
  O  O13  1  0.824  0.824  0.000  1.0
  O  O14  1  0.000  0.000  0.500  1.0
  O  O15  1  0.665  0.665  0.503  1.0
  O  O16  1  0.725  0.250  0.773  1.0
  O  O17  1  0.572  0.073  0.782  1.0
  O  O18  1  0.428  0.927  0.218  1.0
  O  O19  1  0.250  0.725  0.773  1.0
  O  O20  1  0.750  0.275  0.227  1.0
  O  O21  1  0.275  0.750  0.227  1.0
  O  O22  1  0.335  0.335  0.497  1.0
  O  O23  1  0.073  0.572  0.782  1.0
  O  O24  1  0.902  0.427  0.773  1.0
  O  O25  1  0.427  0.902  0.773  1.0
[/CIF]
.