High‐pressure neutron diffraction study of Si 2 N 2 O

The lattice parameters, bond lengths and bond angles of Si 2 N 2 O have been determined at pressures up to 23 kbar by time‐of‐flight neutron diffraction. The average compressibility coefficients of the orthorhombic structure are K a = 21 (2), K b = 34 (2), K c = 25 (2) and K ν = 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 SiN 3 O 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.