High-pressure neutron diffraction study of Si₂N₂O

The lattice parameters, bond lengths and bond angles of Si2N2O have been determined at pressures up to 23 kbar by time-of-flight neutron diffraction. The average compressibility coefficients of the orthorhombic structure are Ka = 21 (2), Kb = 34 (2), Kc = 25 (2) and Kν = 79 (4) x 10−5 kbar−1, though the anisotropy is more pronounced at lower pressures with Ka (at zero pressure) estimated to be 10 (8) × 10–5 kbar−1. The major contribution to the compression is a cooperative rotation of adjacent SiN3O tetrahedra brought about by a decrease in the Si–O–Si bond angle. The shortening of one Si–N bond within each tetrahedron further enhances the compression, especially along the b direction.