The material described by Ta3O8 crystallizes in the orthorhombic Pmma space group. There are four inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms to form TaO7 pentagonal bipyramids that share corners with two equivalent Ta(1)O7 pentagonal bipyramids,  an edgeedge with one Ta(4)O6 octahedra, edges with two equivalent Ta(2)O6 octahedra, and edges with two equivalent Ta(3)O6 octahedra. In the second Ta site, Ta(2) is bonded to one O(1), one O(2), one O(4), one O(6), and two equivalent O(7) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(4)O6 octahedra, corners with two equivalent Ta(3)O6 octahedra, corners with three equivalent Ta(2)O6 octahedra, and  an edgeedge with one Ta(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 5-36°. In the third Ta site, Ta(3) is bonded to one O(2), one O(3), one O(6), one O(8), and two equivalent O(9) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(4)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, corners with three equivalent Ta(3)O6 octahedra, and  an edgeedge with one Ta(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 0-36°. In the fourth Ta site, Ta(4) is bonded to two equivalent O(10), two equivalent O(3), and two equivalent O(4) atoms to form TaO6 octahedra that share corners with two equivalent Ta(2)O6 octahedra, corners with two equivalent Ta(3)O6 octahedra, corners with two equivalent Ta(4)O6 octahedra, and  an edgeedge with one Ta(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 4-36°. There are ten inequivalent O sites. In the first O site, O(7) is bonded in a linear geometry to two equivalent Ta(2) atoms. In the second O site, O(8) is bonded in a linear geometry to two equivalent Ta(3) atoms. In the third O site, O(9) is bonded in a linear geometry to two equivalent Ta(3) atoms. In the fourth O site, O(10) is bonded in a linear geometry to two equivalent Ta(4) atoms. In the fifth O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Ta(1) and two equivalent Ta(2) atoms. In the sixth O site, O(2) is bonded in a distorted trigonal planar geometry to one Ta(1), one Ta(2), and one Ta(3) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Ta(1), one Ta(3), and one Ta(4) atom. In the eighth O site, O(4) is bonded in a bent 150 degrees geometry to one Ta(2) and one Ta(4) atom. In the ninth O site, O(5) is bonded in a linear geometry to two equivalent Ta(1) atoms. In the tenth O site, O(6) is bonded in a bent 150 degrees geometry to one Ta(2) and one Ta(3) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ta3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.923
_cell_length_b   9.109
_cell_length_c   17.024
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   608.271
_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
  Ta  Ta0  1  0.000  0.689  0.250  1.0
  Ta  Ta1  1  0.000  0.311  0.750  1.0
  Ta  Ta2  1  0.000  0.399  0.370  1.0
  Ta  Ta3  1  0.000  0.601  0.630  1.0
  Ta  Ta4  1  0.000  0.399  0.130  1.0
  Ta  Ta5  1  0.000  0.601  0.870  1.0
  Ta  Ta6  1  0.000  0.815  0.441  1.0
  Ta  Ta7  1  0.000  0.185  0.559  1.0
  Ta  Ta8  1  0.000  0.815  0.059  1.0
  Ta  Ta9  1  0.000  0.185  0.941  1.0
  Ta  Ta10  1  0.000  0.057  0.250  1.0
  Ta  Ta11  1  0.000  0.943  0.750  1.0
  O  O12  1  0.000  0.461  0.250  1.0
  O  O13  1  0.000  0.539  0.750  1.0
  O  O14  1  0.000  0.623  0.368  1.0
  O  O15  1  0.000  0.377  0.632  1.0
  O  O16  1  0.000  0.623  0.132  1.0
  O  O17  1  0.000  0.377  0.868  1.0
  O  O18  1  0.000  0.878  0.325  1.0
  O  O19  1  0.000  0.122  0.675  1.0
  O  O20  1  0.000  0.878  0.175  1.0
  O  O21  1  0.000  0.122  0.825  1.0
  O  O22  1  0.000  0.199  0.333  1.0
  O  O23  1  0.000  0.801  0.667  1.0
  O  O24  1  0.000  0.199  0.167  1.0
  O  O25  1  0.000  0.801  0.833  1.0
  O  O26  1  0.500  0.694  0.250  1.0
  O  O27  1  0.500  0.306  0.750  1.0
  O  O28  1  0.000  0.332  0.478  1.0
  O  O29  1  0.000  0.668  0.522  1.0
  O  O30  1  0.000  0.332  0.022  1.0
  O  O31  1  0.000  0.668  0.978  1.0
  O  O32  1  0.500  0.407  0.372  1.0
  O  O33  1  0.500  0.593  0.628  1.0
  O  O34  1  0.500  0.407  0.128  1.0
  O  O35  1  0.500  0.593  0.872  1.0
  O  O36  1  0.000  0.000  0.500  1.0
  O  O37  1  0.000  0.000  0.000  1.0
  O  O38  1  0.500  0.822  0.438  1.0
  O  O39  1  0.500  0.178  0.562  1.0
  O  O40  1  0.500  0.822  0.062  1.0
  O  O41  1  0.500  0.178  0.938  1.0
  O  O42  1  0.500  0.049  0.250  1.0
  O  O43  1  0.500  0.951  0.750  1.0
[/CIF]
.
The material described by Ta3O8 crystallizes in the orthorhombic Pmma space group. There are four inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms to form TaO7 pentagonal bipyramids that share corners with two equivalent Ta(1)O7 pentagonal bipyramids,  an edgeedge with one Ta(4)O6 octahedra, edges with two equivalent Ta(2)O6 octahedra, and edges with two equivalent Ta(3)O6 octahedra. In the second Ta site, Ta(2) is bonded to one O(1), one O(2), one O(4), one O(6), and two equivalent O(7) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(4)O6 octahedra, corners with two equivalent Ta(3)O6 octahedra, corners with three equivalent Ta(2)O6 octahedra, and  an edgeedge with one Ta(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 5-36°. In the third Ta site, Ta(3) is bonded to one O(2), one O(3), one O(6), one O(8), and two equivalent O(9) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(4)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, corners with three equivalent Ta(3)O6 octahedra, and  an edgeedge with one Ta(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 0-36°. In the fourth Ta site, Ta(4) is bonded to two equivalent O(10), two equivalent O(3), and two equivalent O(4) atoms to form TaO6 octahedra that share corners with two equivalent Ta(2)O6 octahedra, corners with two equivalent Ta(3)O6 octahedra, corners with two equivalent Ta(4)O6 octahedra, and  an edgeedge with one Ta(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 4-36°. There are ten inequivalent O sites. In the first O site, O(7) is bonded in a linear geometry to two equivalent Ta(2) atoms. In the second O site, O(8) is bonded in a linear geometry to two equivalent Ta(3) atoms. In the third O site, O(9) is bonded in a linear geometry to two equivalent Ta(3) atoms. In the fourth O site, O(10) is bonded in a linear geometry to two equivalent Ta(4) atoms. In the fifth O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Ta(1) and two equivalent Ta(2) atoms. In the sixth O site, O(2) is bonded in a distorted trigonal planar geometry to one Ta(1), one Ta(2), and one Ta(3) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Ta(1), one Ta(3), and one Ta(4) atom. In the eighth O site, O(4) is bonded in a bent 150 degrees geometry to one Ta(2) and one Ta(4) atom. In the ninth O site, O(5) is bonded in a linear geometry to two equivalent Ta(1) atoms. In the tenth O site, O(6) is bonded in a bent 150 degrees geometry to one Ta(2) and one Ta(3) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ta3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.923
_cell_length_b   9.109
_cell_length_c   17.024
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   608.271
_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
  Ta  Ta0  1  0.000  0.689  0.250  1.0
  Ta  Ta1  1  0.000  0.311  0.750  1.0
  Ta  Ta2  1  0.000  0.399  0.370  1.0
  Ta  Ta3  1  0.000  0.601  0.630  1.0
  Ta  Ta4  1  0.000  0.399  0.130  1.0
  Ta  Ta5  1  0.000  0.601  0.870  1.0
  Ta  Ta6  1  0.000  0.815  0.441  1.0
  Ta  Ta7  1  0.000  0.185  0.559  1.0
  Ta  Ta8  1  0.000  0.815  0.059  1.0
  Ta  Ta9  1  0.000  0.185  0.941  1.0
  Ta  Ta10  1  0.000  0.057  0.250  1.0
  Ta  Ta11  1  0.000  0.943  0.750  1.0
  O  O12  1  0.000  0.461  0.250  1.0
  O  O13  1  0.000  0.539  0.750  1.0
  O  O14  1  0.000  0.623  0.368  1.0
  O  O15  1  0.000  0.377  0.632  1.0
  O  O16  1  0.000  0.623  0.132  1.0
  O  O17  1  0.000  0.377  0.868  1.0
  O  O18  1  0.000  0.878  0.325  1.0
  O  O19  1  0.000  0.122  0.675  1.0
  O  O20  1  0.000  0.878  0.175  1.0
  O  O21  1  0.000  0.122  0.825  1.0
  O  O22  1  0.000  0.199  0.333  1.0
  O  O23  1  0.000  0.801  0.667  1.0
  O  O24  1  0.000  0.199  0.167  1.0
  O  O25  1  0.000  0.801  0.833  1.0
  O  O26  1  0.500  0.694  0.250  1.0
  O  O27  1  0.500  0.306  0.750  1.0
  O  O28  1  0.000  0.332  0.478  1.0
  O  O29  1  0.000  0.668  0.522  1.0
  O  O30  1  0.000  0.332  0.022  1.0
  O  O31  1  0.000  0.668  0.978  1.0
  O  O32  1  0.500  0.407  0.372  1.0
  O  O33  1  0.500  0.593  0.628  1.0
  O  O34  1  0.500  0.407  0.128  1.0
  O  O35  1  0.500  0.593  0.872  1.0
  O  O36  1  0.000  0.000  0.500  1.0
  O  O37  1  0.000  0.000  0.000  1.0
  O  O38  1  0.500  0.822  0.438  1.0
  O  O39  1  0.500  0.178  0.562  1.0
  O  O40  1  0.500  0.822  0.062  1.0
  O  O41  1  0.500  0.178  0.938  1.0
  O  O42  1  0.500  0.049  0.250  1.0
  O  O43  1  0.500  0.951  0.750  1.0
[/CIF]
.