Crystal Structure and High Hardness Mechanism of Orthorhomic Si₂N₂O

A quasi-single-phase orthorombic Si₂N₂O compound is obtained by hot-pressing sintering using homogeneous precursors as raw materials under nitrogen atmosphere. The bulk hardness of orthorombic Si₂N₂O (o-Si₂N₂O) is investigated by a nanoindenter experiment; the results show that o-Si₂N₂O with maximal value about 19GPa has a high hardness covalent crystal besides β-Si₃N₄. It is discovered that the high hardness is mainly attributed to the unique crystal structure. The bridging O atoms in the o-Si₂N₂O are responsible for decreasing hardness. It is found that the Si-O bonds in the open tetrahedral crystal structure are more easily broken and tilted than other bonds.