Si3N4 is Hausmannite-like structured and crystallizes in the orthorhombic Pnma space group. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one N(1), one N(3), and two equivalent N(2) atoms to form a mixture of corner and edge-sharing SiN4 tetrahedra. The corner-sharing octahedral tilt angles range from 62-66°. In the second Si site, Si(2) is bonded to one N(1), one N(3), and four equivalent N(2) atoms to form SiN6 octahedra that share corners with four equivalent Si(2)N6 octahedra, corners with four equivalent Si(3)N6 octahedra, corners with four equivalent Si(1)N4 tetrahedra, edges with two equivalent Si(3)N6 octahedra, and  an edgeedge with one Si(1)N4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-54°. In the third Si site, Si(3) is bonded to two equivalent N(1), two equivalent N(2), and two equivalent N(3) atoms to form SiN6 octahedra that share corners with four equivalent Si(2)N6 octahedra, corners with two equivalent Si(1)N4 tetrahedra, edges with two equivalent Si(2)N6 octahedra, edges with two equivalent Si(3)N6 octahedra, and edges with two equivalent Si(1)N4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-54°. There are three inequivalent N sites. In the first N site, N(1) is bonded to one Si(1), one Si(2), and two equivalent Si(3) atoms to form corner-sharing NSi4 tetrahedra. In the second N site, N(2) is bonded in a rectangular see-saw-like geometry to one Si(1), one Si(3), and two equivalent Si(2) atoms. In the third N site, N(3) is bonded in a rectangular see-saw-like geometry to one Si(1), one Si(2), and two equivalent Si(3) atoms.
Si3N4 is Hausmannite-like structured and crystallizes in the orthorhombic Pnma space group. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one N(1), one N(3), and two equivalent N(2) atoms to form a mixture of corner and edge-sharing SiN4 tetrahedra. The corner-sharing octahedral tilt angles range from 62-66°. The Si(1)-N(1) bond length is 1.71 Å. The Si(1)-N(3) bond length is 1.77 Å. Both Si(1)-N(2) bond lengths are 1.74 Å. In the second Si site, Si(2) is bonded to one N(1), one N(3), and four equivalent N(2) atoms to form SiN6 octahedra that share corners with four equivalent Si(2)N6 octahedra, corners with four equivalent Si(3)N6 octahedra, corners with four equivalent Si(1)N4 tetrahedra, edges with two equivalent Si(3)N6 octahedra, and  an edgeedge with one Si(1)N4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-54°. The Si(2)-N(1) bond length is 1.92 Å. The Si(2)-N(3) bond length is 1.87 Å. There are two shorter (1.88 Å) and two longer (2.12 Å) Si(2)-N(2) bond lengths. In the third Si site, Si(3) is bonded to two equivalent N(1), two equivalent N(2), and two equivalent N(3) atoms to form SiN6 octahedra that share corners with four equivalent Si(2)N6 octahedra, corners with two equivalent Si(1)N4 tetrahedra, edges with two equivalent Si(2)N6 octahedra, edges with two equivalent Si(3)N6 octahedra, and edges with two equivalent Si(1)N4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-54°. Both Si(3)-N(1) bond lengths are 1.86 Å. Both Si(3)-N(2) bond lengths are 1.95 Å. Both Si(3)-N(3) bond lengths are 1.95 Å. There are three inequivalent N sites. In the first N site, N(1) is bonded to one Si(1), one Si(2), and two equivalent Si(3) atoms to form corner-sharing NSi4 tetrahedra. In the second N site, N(2) is bonded in a rectangular see-saw-like geometry to one Si(1), one Si(3), and two equivalent Si(2) atoms. In the third N site, N(3) is bonded in a rectangular see-saw-like geometry to one Si(1), one Si(2), and two equivalent Si(3) atoms.