Pressure-induced tetrahedral tilting and deformation in Ge₂N₂O

High-pressure time-of-flight neutron diffraction studies have been carried out on orthorhombic Ge₂N₂O to 25.4 × 10⁸ Pa and by X-ray diffraction to 49 × 10⁸ Pa. The zero-pressure axial compressibility coefficients are K_a = 33 (2), K_b = 41 (2), K_c = 28 (2), and volume K_v = 99 (5) × 10 ^-13 Pa^-1. The changes in bond angles and bond lengths at pressures from 10⁵ to 25.4 × 10⁸ Pa have been measured. The structure of Ge₂N₂O consists of GeN₃O tetrahedra linked along the a direction by Ge-O-Ge bonds and along the b and c directions by three coordinated Ge-N bonds. This structural framework adjusts to applied pressure by tetrahedra tilting in a cooperative fashion, the biggest change being observed in the Ge-O-Ge angle which decreases by 12.4°. The behavior of Ge₂N₂O is very similar to its isomorph Si₂N₂O, though the tetrahedra deform somewhat more for Ge₂N₂O. The pressure changes in the lattice parameters of Ge₂N₂O up to ~8 × 10⁸ Pa are very similar to those of Si₂N₂O up to ~24 × 10⁸ Pa, supporting the contention that germanates behave as high-pressure models for silicates.