The material described by Si3N4 crystallizes in the trigonal P31c space group. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one N(3), one N(4), and two equivalent N(1) atoms to form corner-sharing SiN4 tetrahedra. In the second Si site, Si(2) is bonded to one N(1), one N(2), and two equivalent N(3) atoms to form corner-sharing SiN4 tetrahedra. There are four inequivalent N sites. In the first N site, N(1) is bonded in a trigonal planar geometry to one Si(2) and two equivalent Si(1) atoms. In the second N site, N(2) is bonded in a trigonal planar geometry to three equivalent Si(2) atoms. In the third N site, N(3) is bonded in a trigonal planar geometry to one Si(1) and two equivalent Si(2) atoms. In the fourth N site, N(4) is bonded in a trigonal planar geometry to three equivalent Si(1) atoms. is represented by the CIF file [CIF]
data_Si3N4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.752
_cell_length_b   7.752
_cell_length_c   5.619
_cell_angle_alpha   90.001
_cell_angle_beta   90.000
_cell_angle_gamma   120.003
_symmetry_Int_Tables_number   1
_cell_volume   292.429
_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
  Si  Si0  1  0.082  0.570  0.196  1.0
  Si  Si1  1  0.488  0.918  0.196  1.0
  Si  Si2  1  0.914  0.167  0.988  1.0
  Si  Si3  1  0.570  0.082  0.696  1.0
  Si  Si4  1  0.086  0.253  0.488  1.0
  Si  Si5  1  0.167  0.914  0.488  1.0
  Si  Si6  1  0.430  0.512  0.196  1.0
  Si  Si7  1  0.747  0.833  0.488  1.0
  Si  Si8  1  0.918  0.488  0.696  1.0
  Si  Si9  1  0.512  0.430  0.696  1.0
  Si  Si10  1  0.833  0.747  0.988  1.0
  Si  Si11  1  0.253  0.086  0.988  1.0
  N  N12  1  0.345  0.390  0.469  1.0
  N  N13  1  0.046  0.655  0.469  1.0
  N  N14  1  0.390  0.345  0.969  1.0
  N  N15  1  0.610  0.954  0.469  1.0
  N  N16  1  0.000  0.000  0.989  1.0
  N  N17  1  0.996  0.315  0.735  1.0
  N  N18  1  0.000  0.000  0.489  1.0
  N  N19  1  0.667  0.333  0.641  1.0
  N  N20  1  0.682  0.685  0.235  1.0
  N  N21  1  0.655  0.046  0.969  1.0
  N  N22  1  0.954  0.610  0.969  1.0
  N  N23  1  0.333  0.667  0.141  1.0
  N  N24  1  0.004  0.318  0.235  1.0
  N  N25  1  0.318  0.004  0.735  1.0
  N  N26  1  0.685  0.682  0.735  1.0
  N  N27  1  0.315  0.996  0.235  1.0
[/CIF]
.
The material described by Si3N4 crystallizes in the trigonal P31c space group. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one N(3), one N(4), and two equivalent N(1) atoms to form corner-sharing SiN4 tetrahedra. In the second Si site, Si(2) is bonded to one N(1), one N(2), and two equivalent N(3) atoms to form corner-sharing SiN4 tetrahedra. There are four inequivalent N sites. In the first N site, N(1) is bonded in a trigonal planar geometry to one Si(2) and two equivalent Si(1) atoms. In the second N site, N(2) is bonded in a trigonal planar geometry to three equivalent Si(2) atoms. In the third N site, N(3) is bonded in a trigonal planar geometry to one Si(1) and two equivalent Si(2) atoms. In the fourth N site, N(4) is bonded in a trigonal planar geometry to three equivalent Si(1) atoms. is represented by the CIF file [CIF]
data_Si3N4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.752
_cell_length_b   7.752
_cell_length_c   5.619
_cell_angle_alpha   90.001
_cell_angle_beta   90.000
_cell_angle_gamma   120.003
_symmetry_Int_Tables_number   1
_cell_volume   292.429
_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
  Si  Si0  1  0.082  0.570  0.196  1.0
  Si  Si1  1  0.488  0.918  0.196  1.0
  Si  Si2  1  0.914  0.167  0.988  1.0
  Si  Si3  1  0.570  0.082  0.696  1.0
  Si  Si4  1  0.086  0.253  0.488  1.0
  Si  Si5  1  0.167  0.914  0.488  1.0
  Si  Si6  1  0.430  0.512  0.196  1.0
  Si  Si7  1  0.747  0.833  0.488  1.0
  Si  Si8  1  0.918  0.488  0.696  1.0
  Si  Si9  1  0.512  0.430  0.696  1.0
  Si  Si10  1  0.833  0.747  0.988  1.0
  Si  Si11  1  0.253  0.086  0.988  1.0
  N  N12  1  0.345  0.390  0.469  1.0
  N  N13  1  0.046  0.655  0.469  1.0
  N  N14  1  0.390  0.345  0.969  1.0
  N  N15  1  0.610  0.954  0.469  1.0
  N  N16  1  0.000  0.000  0.989  1.0
  N  N17  1  0.996  0.315  0.735  1.0
  N  N18  1  0.000  0.000  0.489  1.0
  N  N19  1  0.667  0.333  0.641  1.0
  N  N20  1  0.682  0.685  0.235  1.0
  N  N21  1  0.655  0.046  0.969  1.0
  N  N22  1  0.954  0.610  0.969  1.0
  N  N23  1  0.333  0.667  0.141  1.0
  N  N24  1  0.004  0.318  0.235  1.0
  N  N25  1  0.318  0.004  0.735  1.0
  N  N26  1  0.685  0.682  0.735  1.0
  N  N27  1  0.315  0.996  0.235  1.0
[/CIF]
.