The compound described by Sr2Ta2O7 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one O(3), two equivalent O(2), two equivalent O(6), three equivalent O(4), and four equivalent O(5) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Ta(2)O6 octahedra, and faces with six equivalent Ta(1)O6 octahedra. In the second Sr site, Sr(2) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(7) atoms. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(2), one O(6), two equivalent O(4), and two equivalent O(5) atoms to form TaO6 octahedra that share corners with two equivalent Ta(2)O6 octahedra, corners with four equivalent Ta(1)O6 octahedra, and faces with six equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 3-15°. In the second Ta site, Ta(2) is bonded to one O(1), one O(2), one O(6), one O(7), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, and faces with two equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 6-16°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Sr(2) and one Ta(2) atom to form a mixture of distorted corner and edge-sharing OSr3Ta tetrahedra. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Sr(1), one Ta(1), and one Ta(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Sr(1) and two equivalent Ta(2) atoms. In the fourth O site, O(4) is bonded to three equivalent Sr(1) and two equivalent Ta(1) atoms to form a mixture of distorted corner and edge-sharing OSr3Ta2 square pyramids. In the fifth O site, O(5) is bonded in a distorted linear geometry to four equivalent Sr(1) and two equivalent Ta(1) atoms. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Sr(1), one Ta(1), and one Ta(2) atom. In the seventh O site, O(7) is bonded to three equivalent Sr(2) and one Ta(2) atom to form a mixture of distorted corner and edge-sharing OSr3Ta tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Sr2Ta2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.820
_cell_length_b   13.820
_cell_length_c   5.711
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   163.519
_symmetry_Int_Tables_number   1
_cell_volume   309.441
_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  0.447  0.553  0.237  1.0
  Sr  Sr1  1  0.553  0.447  0.737  1.0
  Sr  Sr2  1  0.286  0.714  0.750  1.0
  Sr  Sr3  1  0.714  0.286  0.250  1.0
  Ta  Ta4  1  0.945  0.055  0.739  1.0
  Ta  Ta5  1  0.055  0.945  0.239  1.0
  Ta  Ta6  1  0.841  0.159  0.244  1.0
  Ta  Ta7  1  0.159  0.841  0.744  1.0
  O  O8  1  0.208  0.792  0.511  1.0
  O  O9  1  0.792  0.208  0.011  1.0
  O  O10  1  0.101  0.899  0.488  1.0
  O  O11  1  0.899  0.101  0.988  1.0
  O  O12  1  0.649  0.351  0.739  1.0
  O  O13  1  0.351  0.649  0.239  1.0
  O  O14  1  0.547  0.453  0.237  1.0
  O  O15  1  0.453  0.547  0.737  1.0
  O  O16  1  0.002  0.998  0.495  1.0
  O  O17  1  0.998  0.002  0.995  1.0
  O  O18  1  0.903  0.097  0.472  1.0
  O  O19  1  0.097  0.903  0.972  1.0
  O  O20  1  0.795  0.205  0.488  1.0
  O  O21  1  0.205  0.795  0.988  1.0
[/CIF]
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The compound described by Sr2Ta2O7 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one O(3), two equivalent O(2), two equivalent O(6), three equivalent O(4), and four equivalent O(5) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Ta(2)O6 octahedra, and faces with six equivalent Ta(1)O6 octahedra. In the second Sr site, Sr(2) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(7) atoms. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(2), one O(6), two equivalent O(4), and two equivalent O(5) atoms to form TaO6 octahedra that share corners with two equivalent Ta(2)O6 octahedra, corners with four equivalent Ta(1)O6 octahedra, and faces with six equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 3-15°. In the second Ta site, Ta(2) is bonded to one O(1), one O(2), one O(6), one O(7), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, and faces with two equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 6-16°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Sr(2) and one Ta(2) atom to form a mixture of distorted corner and edge-sharing OSr3Ta tetrahedra. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Sr(1), one Ta(1), and one Ta(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Sr(1) and two equivalent Ta(2) atoms. In the fourth O site, O(4) is bonded to three equivalent Sr(1) and two equivalent Ta(1) atoms to form a mixture of distorted corner and edge-sharing OSr3Ta2 square pyramids. In the fifth O site, O(5) is bonded in a distorted linear geometry to four equivalent Sr(1) and two equivalent Ta(1) atoms. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Sr(1), one Ta(1), and one Ta(2) atom. In the seventh O site, O(7) is bonded to three equivalent Sr(2) and one Ta(2) atom to form a mixture of distorted corner and edge-sharing OSr3Ta tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Sr2Ta2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.820
_cell_length_b   13.820
_cell_length_c   5.711
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   163.519
_symmetry_Int_Tables_number   1
_cell_volume   309.441
_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  0.447  0.553  0.237  1.0
  Sr  Sr1  1  0.553  0.447  0.737  1.0
  Sr  Sr2  1  0.286  0.714  0.750  1.0
  Sr  Sr3  1  0.714  0.286  0.250  1.0
  Ta  Ta4  1  0.945  0.055  0.739  1.0
  Ta  Ta5  1  0.055  0.945  0.239  1.0
  Ta  Ta6  1  0.841  0.159  0.244  1.0
  Ta  Ta7  1  0.159  0.841  0.744  1.0
  O  O8  1  0.208  0.792  0.511  1.0
  O  O9  1  0.792  0.208  0.011  1.0
  O  O10  1  0.101  0.899  0.488  1.0
  O  O11  1  0.899  0.101  0.988  1.0
  O  O12  1  0.649  0.351  0.739  1.0
  O  O13  1  0.351  0.649  0.239  1.0
  O  O14  1  0.547  0.453  0.237  1.0
  O  O15  1  0.453  0.547  0.737  1.0
  O  O16  1  0.002  0.998  0.495  1.0
  O  O17  1  0.998  0.002  0.995  1.0
  O  O18  1  0.903  0.097  0.472  1.0
  O  O19  1  0.097  0.903  0.972  1.0
  O  O20  1  0.795  0.205  0.488  1.0
  O  O21  1  0.205  0.795  0.988  1.0
[/CIF]
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