Theoretical Investigation of the Solid State Reaction of Silicon Nitride and Silicon Dioxide forming Silicon Oxynitride (Si₂N₂O) under Pressure

Abstract

Abstract The high‐pressure behavior of Si 2 N 2 O is studied for pressures up to 100 GPa using density functional theory calculations. The investigation of a manifold of hypothetical polymorphs leads us to propose two dense phases of Si 2 N 2 O, succeeding the orthorhombic ambient‐pressure polymorph at higher pressures:a defect spinel structure at moderate pressures and a corundum‐type structure at very high pressures. Taking into account the formation of silicon oxynitride from silicon dioxide and silicon nitride and its pressure dependence, we propose five pressure regions of interest for Si 2 N 2 O within the pseudo‐binary phase diagram SiO 2 ‐Si 3 N 4 : (i) stability of the orthorhombic ternary phase of Si 2 N 2 O up to 6 GPa, (ii) a phase assemblage of coesite, stishovite, and β ‐Si 3 N 4 between 6 and 11 GPa, (iii) a possible defect spinel modification of Si 2 N 2 O between 11 and 16 GPa, (iv) a phase assemblage of stishovite and γ ‐Si 3 N 4 above 40 GPa, and (v) a possible ternary Si 2 N 2 O phase with corundum‐type structure beyond 80 GPa. The existence of both ternary high‐pressure phases of Si 2 N 2 O, however, depends on the delicate influence of configurational entropy to the free energy of the solid state reaction.