Nucleation and growth of Si2N2O in Si3N4-materials employing different sintering additives

Si2N2O microcrystals from liquid-phase sintered Si3N4 materials exhibit small intragranular particles which were identified as α-Si3N4 through the combined approach of high-resolution and analytical TEM. They act as heterogeneous nucleation sites for Si2N2O being supported by topotacial orientation relationships between the constitutents. A possible orientation relationship between α-Si3N4 and Si2N2O proceeds from the boundary between α-Si3N4 and the newly formed SiO2-rich oxinitride liquid and is strongly viscosity-dependent. This mechanism was confirmed for different Si3N4 materials, independently of the nature of the sintering additive employed. (orig.)