In situ study of amorphization and changes in coordination in Si2N2O at high pressure

Silicon oxynitride was investigated by x-ray powder diffraction and infrared absorption spectroscopy at pressures close to 50 GPa. Gradual amorphization was found to occur above 25 GPa. This process is associated with the disappearance of the strong B-1 Si-O stretching mode of the SiN3O tetrahedra at close to 1130 cm(-1) and the appearance of additional modes at lower frequencies with respect to the Si-O stretching modes. This is evidence of an increase in the coordination of Si. Whereas the silicon atom appears to revert to a fourfold coordination below 7 GPa, the material remains amorphous.