The structure described by BaCaO2 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded to three equivalent O(1) and four equivalent O(2) atoms to form distorted BaO7 pentagonal bipyramids that share corners with four equivalent Ba(1)O7 pentagonal bipyramids, corners with three equivalent Ca(1)O5 trigonal bipyramids, edges with four equivalent Ba(1)O7 pentagonal bipyramids, edges with seven equivalent Ca(1)O5 trigonal bipyramids, and faces with two equivalent Ba(1)O7 pentagonal bipyramids. Ca(1) is bonded to two equivalent O(2) and three equivalent O(1) atoms to form CaO5 trigonal bipyramids that share corners with three equivalent Ba(1)O7 pentagonal bipyramids, corners with four equivalent Ca(1)O5 trigonal bipyramids, edges with seven equivalent Ba(1)O7 pentagonal bipyramids, and edges with two equivalent Ca(1)O5 trigonal bipyramids. There are two inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ba(1) and three equivalent Ca(1) atoms to form distorted OBa3Ca3 octahedra that share corners with nine equivalent O(2)Ba4Ca2 octahedra, edges with three equivalent O(2)Ba4Ca2 octahedra, edges with six equivalent O(1)Ba3Ca3 octahedra, and  a faceface with one O(2)Ba4Ca2 octahedra. The corner-sharing octahedral tilt angles range from 8-60°. In the second O site, O(2) is bonded to four equivalent Ba(1) and two equivalent Ca(1) atoms to form OBa4Ca2 octahedra that share corners with four equivalent O(2)Ba4Ca2 octahedra, corners with nine equivalent O(1)Ba3Ca3 octahedra, edges with two equivalent O(2)Ba4Ca2 octahedra, edges with three equivalent O(1)Ba3Ca3 octahedra,  a faceface with one O(1)Ba3Ca3 octahedra, and faces with two equivalent O(2)Ba4Ca2 octahedra. The corner-sharing octahedral tilt angles range from 8-60°. is represented by the CIF file [CIF]
data_BaCaO2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.764
_cell_length_b   6.324
_cell_length_c   12.262
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   291.902
_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
  Ba  Ba0  1  0.250  0.594  0.642  1.0
  Ba  Ba1  1  0.250  0.094  0.858  1.0
  Ba  Ba2  1  0.750  0.406  0.358  1.0
  Ba  Ba3  1  0.750  0.906  0.142  1.0
  Ca  Ca4  1  0.250  0.909  0.393  1.0
  Ca  Ca5  1  0.250  0.409  0.107  1.0
  Ca  Ca6  1  0.750  0.591  0.893  1.0
  Ca  Ca7  1  0.750  0.091  0.607  1.0
  O  O8  1  0.250  0.216  0.518  1.0
  O  O9  1  0.250  0.716  0.982  1.0
  O  O10  1  0.250  0.651  0.252  1.0
  O  O11  1  0.250  0.151  0.248  1.0
  O  O12  1  0.750  0.849  0.752  1.0
  O  O13  1  0.750  0.349  0.748  1.0
  O  O14  1  0.750  0.784  0.482  1.0
  O  O15  1  0.750  0.284  0.018  1.0
[/CIF]
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The structure described by BaCaO2 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded to three equivalent O(1) and four equivalent O(2) atoms to form distorted BaO7 pentagonal bipyramids that share corners with four equivalent Ba(1)O7 pentagonal bipyramids, corners with three equivalent Ca(1)O5 trigonal bipyramids, edges with four equivalent Ba(1)O7 pentagonal bipyramids, edges with seven equivalent Ca(1)O5 trigonal bipyramids, and faces with two equivalent Ba(1)O7 pentagonal bipyramids. Ca(1) is bonded to two equivalent O(2) and three equivalent O(1) atoms to form CaO5 trigonal bipyramids that share corners with three equivalent Ba(1)O7 pentagonal bipyramids, corners with four equivalent Ca(1)O5 trigonal bipyramids, edges with seven equivalent Ba(1)O7 pentagonal bipyramids, and edges with two equivalent Ca(1)O5 trigonal bipyramids. There are two inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ba(1) and three equivalent Ca(1) atoms to form distorted OBa3Ca3 octahedra that share corners with nine equivalent O(2)Ba4Ca2 octahedra, edges with three equivalent O(2)Ba4Ca2 octahedra, edges with six equivalent O(1)Ba3Ca3 octahedra, and  a faceface with one O(2)Ba4Ca2 octahedra. The corner-sharing octahedral tilt angles range from 8-60°. In the second O site, O(2) is bonded to four equivalent Ba(1) and two equivalent Ca(1) atoms to form OBa4Ca2 octahedra that share corners with four equivalent O(2)Ba4Ca2 octahedra, corners with nine equivalent O(1)Ba3Ca3 octahedra, edges with two equivalent O(2)Ba4Ca2 octahedra, edges with three equivalent O(1)Ba3Ca3 octahedra,  a faceface with one O(1)Ba3Ca3 octahedra, and faces with two equivalent O(2)Ba4Ca2 octahedra. The corner-sharing octahedral tilt angles range from 8-60°. is represented by the CIF file [CIF]
data_BaCaO2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.764
_cell_length_b   6.324
_cell_length_c   12.262
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   291.902
_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
  Ba  Ba0  1  0.250  0.594  0.642  1.0
  Ba  Ba1  1  0.250  0.094  0.858  1.0
  Ba  Ba2  1  0.750  0.406  0.358  1.0
  Ba  Ba3  1  0.750  0.906  0.142  1.0
  Ca  Ca4  1  0.250  0.909  0.393  1.0
  Ca  Ca5  1  0.250  0.409  0.107  1.0
  Ca  Ca6  1  0.750  0.591  0.893  1.0
  Ca  Ca7  1  0.750  0.091  0.607  1.0
  O  O8  1  0.250  0.216  0.518  1.0
  O  O9  1  0.250  0.716  0.982  1.0
  O  O10  1  0.250  0.651  0.252  1.0
  O  O11  1  0.250  0.151  0.248  1.0
  O  O12  1  0.750  0.849  0.752  1.0
  O  O13  1  0.750  0.349  0.748  1.0
  O  O14  1  0.750  0.784  0.482  1.0
  O  O15  1  0.750  0.284  0.018  1.0
[/CIF]
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