The compound described by Er3TaO7 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to two equivalent O(1) and four equivalent O(4) atoms. In the second Er site, Er(2) is bonded to one O(3), two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted ErO7 pentagonal bipyramids that share corners with two equivalent Ta(1)O6 octahedra, corners with three equivalent Er(2)O7 pentagonal bipyramids, edges with two equivalent Ta(1)O6 octahedra, and edges with two equivalent Er(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 35-45°. Ta(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with four equivalent Er(2)O7 pentagonal bipyramids, and edges with four equivalent Er(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 38°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Er(1), two equivalent Er(2), and one Ta(1) atom to form distorted OEr3Ta tetrahedra that share corners with four equivalent O(4)Er4 tetrahedra, edges with two equivalent O(1)Er3Ta tetrahedra, and edges with two equivalent O(4)Er4 tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Er(2) and one Ta(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Er(2) and two equivalent Ta(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Er(1) and two equivalent Er(2) atoms to form OEr4 tetrahedra that share corners with four equivalent O(1)Er3Ta tetrahedra, corners with six equivalent O(4)Er4 tetrahedra,  an edgeedge with one O(4)Er4 tetrahedra, and edges with two equivalent O(1)Er3Ta tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Er3TaO7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.429
_cell_length_b   7.508
_cell_length_c   10.526
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   587.046
_cell_formula_units_Z   4
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
  Er  Er0  1  0.012  0.795  0.250  1.0
  Er  Er1  1  0.252  0.968  0.520  1.0
  Er  Er2  1  0.252  0.968  0.980  1.0
  Er  Er3  1  0.248  0.468  0.020  1.0
  Er  Er4  1  0.248  0.468  0.480  1.0
  Er  Er5  1  0.488  0.295  0.750  1.0
  Er  Er6  1  0.512  0.705  0.250  1.0
  Er  Er7  1  0.752  0.532  0.520  1.0
  Er  Er8  1  0.752  0.532  0.980  1.0
  Er  Er9  1  0.748  0.032  0.020  1.0
  Er  Er10  1  0.748  0.032  0.480  1.0
  Er  Er11  1  0.988  0.205  0.750  1.0
  Ta  Ta12  1  0.999  0.748  0.750  1.0
  Ta  Ta13  1  0.501  0.248  0.250  1.0
  Ta  Ta14  1  0.499  0.752  0.750  1.0
  Ta  Ta15  1  0.001  0.252  0.250  1.0
  O  O16  1  0.036  0.046  0.124  1.0
  O  O17  1  0.036  0.046  0.376  1.0
  O  O18  1  0.040  0.582  0.612  1.0
  O  O19  1  0.040  0.582  0.888  1.0
  O  O20  1  0.248  0.336  0.250  1.0
  O  O21  1  0.255  0.731  0.116  1.0
  O  O22  1  0.255  0.731  0.384  1.0
  O  O23  1  0.245  0.231  0.616  1.0
  O  O24  1  0.245  0.231  0.884  1.0
  O  O25  1  0.252  0.836  0.750  1.0
  O  O26  1  0.460  0.082  0.112  1.0
  O  O27  1  0.460  0.082  0.388  1.0
  O  O28  1  0.464  0.546  0.624  1.0
  O  O29  1  0.464  0.546  0.876  1.0
  O  O30  1  0.536  0.454  0.124  1.0
  O  O31  1  0.536  0.454  0.376  1.0
  O  O32  1  0.540  0.918  0.612  1.0
  O  O33  1  0.540  0.918  0.888  1.0
  O  O34  1  0.748  0.164  0.250  1.0
  O  O35  1  0.755  0.769  0.116  1.0
  O  O36  1  0.755  0.769  0.384  1.0
  O  O37  1  0.745  0.269  0.616  1.0
  O  O38  1  0.745  0.269  0.884  1.0
  O  O39  1  0.752  0.664  0.750  1.0
  O  O40  1  0.960  0.418  0.112  1.0
  O  O41  1  0.960  0.418  0.388  1.0
  O  O42  1  0.964  0.954  0.624  1.0
  O  O43  1  0.964  0.954  0.876  1.0
[/CIF]
.
The compound described by Er3TaO7 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to two equivalent O(1) and four equivalent O(4) atoms. In the second Er site, Er(2) is bonded to one O(3), two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted ErO7 pentagonal bipyramids that share corners with two equivalent Ta(1)O6 octahedra, corners with three equivalent Er(2)O7 pentagonal bipyramids, edges with two equivalent Ta(1)O6 octahedra, and edges with two equivalent Er(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 35-45°. Ta(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with four equivalent Er(2)O7 pentagonal bipyramids, and edges with four equivalent Er(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 38°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Er(1), two equivalent Er(2), and one Ta(1) atom to form distorted OEr3Ta tetrahedra that share corners with four equivalent O(4)Er4 tetrahedra, edges with two equivalent O(1)Er3Ta tetrahedra, and edges with two equivalent O(4)Er4 tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Er(2) and one Ta(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Er(2) and two equivalent Ta(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Er(1) and two equivalent Er(2) atoms to form OEr4 tetrahedra that share corners with four equivalent O(1)Er3Ta tetrahedra, corners with six equivalent O(4)Er4 tetrahedra,  an edgeedge with one O(4)Er4 tetrahedra, and edges with two equivalent O(1)Er3Ta tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Er3TaO7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.429
_cell_length_b   7.508
_cell_length_c   10.526
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   587.046
_cell_formula_units_Z   4
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
  Er  Er0  1  0.012  0.795  0.250  1.0
  Er  Er1  1  0.252  0.968  0.520  1.0
  Er  Er2  1  0.252  0.968  0.980  1.0
  Er  Er3  1  0.248  0.468  0.020  1.0
  Er  Er4  1  0.248  0.468  0.480  1.0
  Er  Er5  1  0.488  0.295  0.750  1.0
  Er  Er6  1  0.512  0.705  0.250  1.0
  Er  Er7  1  0.752  0.532  0.520  1.0
  Er  Er8  1  0.752  0.532  0.980  1.0
  Er  Er9  1  0.748  0.032  0.020  1.0
  Er  Er10  1  0.748  0.032  0.480  1.0
  Er  Er11  1  0.988  0.205  0.750  1.0
  Ta  Ta12  1  0.999  0.748  0.750  1.0
  Ta  Ta13  1  0.501  0.248  0.250  1.0
  Ta  Ta14  1  0.499  0.752  0.750  1.0
  Ta  Ta15  1  0.001  0.252  0.250  1.0
  O  O16  1  0.036  0.046  0.124  1.0
  O  O17  1  0.036  0.046  0.376  1.0
  O  O18  1  0.040  0.582  0.612  1.0
  O  O19  1  0.040  0.582  0.888  1.0
  O  O20  1  0.248  0.336  0.250  1.0
  O  O21  1  0.255  0.731  0.116  1.0
  O  O22  1  0.255  0.731  0.384  1.0
  O  O23  1  0.245  0.231  0.616  1.0
  O  O24  1  0.245  0.231  0.884  1.0
  O  O25  1  0.252  0.836  0.750  1.0
  O  O26  1  0.460  0.082  0.112  1.0
  O  O27  1  0.460  0.082  0.388  1.0
  O  O28  1  0.464  0.546  0.624  1.0
  O  O29  1  0.464  0.546  0.876  1.0
  O  O30  1  0.536  0.454  0.124  1.0
  O  O31  1  0.536  0.454  0.376  1.0
  O  O32  1  0.540  0.918  0.612  1.0
  O  O33  1  0.540  0.918  0.888  1.0
  O  O34  1  0.748  0.164  0.250  1.0
  O  O35  1  0.755  0.769  0.116  1.0
  O  O36  1  0.755  0.769  0.384  1.0
  O  O37  1  0.745  0.269  0.616  1.0
  O  O38  1  0.745  0.269  0.884  1.0
  O  O39  1  0.752  0.664  0.750  1.0
  O  O40  1  0.960  0.418  0.112  1.0
  O  O41  1  0.960  0.418  0.388  1.0
  O  O42  1  0.964  0.954  0.624  1.0
  O  O43  1  0.964  0.954  0.876  1.0
[/CIF]
.