α-Silicon nitride Si₃N₄

Unit cell

Lattice constants

a = 7.752 Å, b = 7.752 Å, c = 5.620 Å; α = 90°, β = 90°, γ = 120°

Cell volume

292.5 ų

Atoms in the cell

28 (N 16, Si 12)

Formula units Z

4

Calculated density

1.27 g cm⁻³

Shortest contact

1.685 Å

Coordination

N

CN 3 at 1.76 Å (3 Si)

Si

CN 4 at 1.70 Å (4 N)

About the structure

• Corner-sharing SiN₄ tetrahedra: every N is bonded to three Si in a nearly planar arrangement, every Si to four N, building a rigid three-dimensional network — the nitrogen analogue of a silicate.
• The α and β forms differ in the stacking of their Si–N layers; Si₃N₄ ceramics are used for turbine bearings and cutting tools because the network is strong to 1,500 °C.
• Coordinates from the Crystallography Open Database, entry 1001238 (open data); hydrogen and water sites with partial occupancy below 0.5 are left out.

Atom positions (fractional, one cell)

Z, coordination numbers, distances, density and packing on this page are computed from these coordinates.