The material described by BaAl2Si2O8 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 9-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(7), one O(8), and two equivalent O(6) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with three equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(4), one O(7), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra and corners with three equivalent Al(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra and corners with three equivalent Al(2)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a 3-coordinate geometry to one Ba(1), one Al(2), and one Si(1) atom. In the second O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Al(1), and one Si(1) atom. In the third O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Al(2), and one Si(2) atom. In the fourth O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), one Al(1), and one Si(1) atom. In the fifth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Al(2), and one Si(2) atom. In the sixth O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Si(1) atom. In the seventh O site, O(4) is bonded in a bent 120 degrees geometry to one Ba(1), one Al(2), and one Si(2) atom. In the eighth O site, O(6) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Al(1), and one Si(2) atom. is represented by the CIF card [CIF]
data_BaAl2(SiO4)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.658
_cell_length_b   9.318
_cell_length_c   9.318
_cell_angle_alpha   88.972
_cell_angle_beta   82.173
_cell_angle_gamma   82.173
_symmetry_Int_Tables_number   1
_cell_volume   737.837
_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  0.718  0.564  0.064  1.0
  Ba  Ba1  1  0.782  0.936  0.436  1.0
  Ba  Ba2  1  0.282  0.436  0.936  1.0
  Ba  Ba3  1  0.218  0.064  0.564  1.0
  Al  Al4  1  0.109  0.066  0.200  1.0
  Al  Al5  1  0.391  0.800  0.934  1.0
  Al  Al6  1  0.609  0.200  0.066  1.0
  Al  Al7  1  0.891  0.934  0.800  1.0
  Al  Al8  1  0.034  0.551  0.296  1.0
  Al  Al9  1  0.466  0.704  0.449  1.0
  Al  Al10  1  0.966  0.449  0.704  1.0
  Al  Al11  1  0.534  0.296  0.551  1.0
  Si  Si12  1  0.525  0.059  0.789  1.0
  Si  Si13  1  0.475  0.941  0.211  1.0
  Si  Si14  1  0.598  0.573  0.710  1.0
  Si  Si15  1  0.975  0.211  0.941  1.0
  Si  Si16  1  0.402  0.427  0.290  1.0
  Si  Si17  1  0.098  0.710  0.573  1.0
  Si  Si18  1  0.902  0.290  0.427  1.0
  Si  Si19  1  0.025  0.789  0.059  1.0
  O  O20  1  0.989  0.082  0.824  1.0
  O  O21  1  0.511  0.176  0.918  1.0
  O  O22  1  0.011  0.918  0.176  1.0
  O  O23  1  0.489  0.824  0.082  1.0
  O  O24  1  0.489  0.564  0.325  1.0
  O  O25  1  0.011  0.675  0.436  1.0
  O  O26  1  0.511  0.436  0.675  1.0
  O  O27  1  0.989  0.325  0.564  1.0
  O  O28  1  0.897  0.818  0.947  1.0
  O  O29  1  0.603  0.053  0.182  1.0
  O  O30  1  0.103  0.182  0.053  1.0
  O  O31  1  0.397  0.947  0.818  1.0
  O  O32  1  0.402  0.316  0.424  1.0
  O  O33  1  0.098  0.576  0.684  1.0
  O  O34  1  0.598  0.684  0.576  1.0
  O  O35  1  0.902  0.424  0.316  1.0
  O  O36  1  0.704  0.979  0.752  1.0
  O  O37  1  0.796  0.248  0.021  1.0
  O  O38  1  0.296  0.021  0.248  1.0
  O  O39  1  0.204  0.752  0.979  1.0
  O  O40  1  0.003  0.139  0.362  1.0
  O  O41  1  0.497  0.638  0.861  1.0
  O  O42  1  0.997  0.861  0.638  1.0
  O  O43  1  0.503  0.362  0.139  1.0
  O  O44  1  0.478  0.143  0.643  1.0
  O  O45  1  0.022  0.357  0.857  1.0
  O  O46  1  0.522  0.857  0.357  1.0
  O  O47  1  0.978  0.643  0.143  1.0
  O  O48  1  0.727  0.248  0.474  1.0
  O  O49  1  0.773  0.526  0.752  1.0
  O  O50  1  0.273  0.752  0.526  1.0
  O  O51  1  0.227  0.474  0.248  1.0
[/CIF]
.
The material described by BaAl2Si2O8 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 9-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(7), one O(8), and two equivalent O(6) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with three equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(4), one O(7), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra and corners with three equivalent Al(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra and corners with three equivalent Al(2)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a 3-coordinate geometry to one Ba(1), one Al(2), and one Si(1) atom. In the second O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Al(1), and one Si(1) atom. In the third O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Al(2), and one Si(2) atom. In the fourth O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), one Al(1), and one Si(1) atom. In the fifth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Al(2), and one Si(2) atom. In the sixth O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Al(1), and one Si(1) atom. In the seventh O site, O(4) is bonded in a bent 120 degrees geometry to one Ba(1), one Al(2), and one Si(2) atom. In the eighth O site, O(6) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Al(1), and one Si(2) atom. is represented by the CIF card [CIF]
data_BaAl2(SiO4)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.658
_cell_length_b   9.318
_cell_length_c   9.318
_cell_angle_alpha   88.972
_cell_angle_beta   82.173
_cell_angle_gamma   82.173
_symmetry_Int_Tables_number   1
_cell_volume   737.837
_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  0.718  0.564  0.064  1.0
  Ba  Ba1  1  0.782  0.936  0.436  1.0
  Ba  Ba2  1  0.282  0.436  0.936  1.0
  Ba  Ba3  1  0.218  0.064  0.564  1.0
  Al  Al4  1  0.109  0.066  0.200  1.0
  Al  Al5  1  0.391  0.800  0.934  1.0
  Al  Al6  1  0.609  0.200  0.066  1.0
  Al  Al7  1  0.891  0.934  0.800  1.0
  Al  Al8  1  0.034  0.551  0.296  1.0
  Al  Al9  1  0.466  0.704  0.449  1.0
  Al  Al10  1  0.966  0.449  0.704  1.0
  Al  Al11  1  0.534  0.296  0.551  1.0
  Si  Si12  1  0.525  0.059  0.789  1.0
  Si  Si13  1  0.475  0.941  0.211  1.0
  Si  Si14  1  0.598  0.573  0.710  1.0
  Si  Si15  1  0.975  0.211  0.941  1.0
  Si  Si16  1  0.402  0.427  0.290  1.0
  Si  Si17  1  0.098  0.710  0.573  1.0
  Si  Si18  1  0.902  0.290  0.427  1.0
  Si  Si19  1  0.025  0.789  0.059  1.0
  O  O20  1  0.989  0.082  0.824  1.0
  O  O21  1  0.511  0.176  0.918  1.0
  O  O22  1  0.011  0.918  0.176  1.0
  O  O23  1  0.489  0.824  0.082  1.0
  O  O24  1  0.489  0.564  0.325  1.0
  O  O25  1  0.011  0.675  0.436  1.0
  O  O26  1  0.511  0.436  0.675  1.0
  O  O27  1  0.989  0.325  0.564  1.0
  O  O28  1  0.897  0.818  0.947  1.0
  O  O29  1  0.603  0.053  0.182  1.0
  O  O30  1  0.103  0.182  0.053  1.0
  O  O31  1  0.397  0.947  0.818  1.0
  O  O32  1  0.402  0.316  0.424  1.0
  O  O33  1  0.098  0.576  0.684  1.0
  O  O34  1  0.598  0.684  0.576  1.0
  O  O35  1  0.902  0.424  0.316  1.0
  O  O36  1  0.704  0.979  0.752  1.0
  O  O37  1  0.796  0.248  0.021  1.0
  O  O38  1  0.296  0.021  0.248  1.0
  O  O39  1  0.204  0.752  0.979  1.0
  O  O40  1  0.003  0.139  0.362  1.0
  O  O41  1  0.497  0.638  0.861  1.0
  O  O42  1  0.997  0.861  0.638  1.0
  O  O43  1  0.503  0.362  0.139  1.0
  O  O44  1  0.478  0.143  0.643  1.0
  O  O45  1  0.022  0.357  0.857  1.0
  O  O46  1  0.522  0.857  0.357  1.0
  O  O47  1  0.978  0.643  0.143  1.0
  O  O48  1  0.727  0.248  0.474  1.0
  O  O49  1  0.773  0.526  0.752  1.0
  O  O50  1  0.273  0.752  0.526  1.0
  O  O51  1  0.227  0.474  0.248  1.0
[/CIF]
.