Oxide and interface characteristics of oxidized silicon oxynitride ceramics - An investigation by electron microscopy

Hot-isostatically pressed silicon oxynitride (Si₂N₂O) ceramics free from sintering aids were oxidized in 1 atm dry oxygen at 1100 and 1300 °C. The structural and chemical characteristics of the oxide and the nature of the oxide-Si₂N₂O interface were determined using cross-sectional transmission electron microscopy in conjunction with small-probe energy dispersive X-ray analysis and selected-area electron diffraction. Oxidation of Si₂N₂O resulted in the formation of amorphous SiO₂. The oxide-Si₂N₂O interface was chemically abrupt. The interface was very flat when parallel to low-index, high atomic density Si₂N₂O crystal planes but became notably undulated if oriented to high index, low atomic density planes. About 6 vol % residual SiO₂ phase was present in the bulk of the Si₂N₂O ceramics. Current results have provided an important baseline for the understanding of the oxidation behaviour of Si₂N₂O.