An Inhomogeneous Grain Boundary Composition in Silicon Nitride Ceramics as Revealed by 300 kV Field Emission Analytical Electron Microscopy

Abstract

The chemical compositions of the grain boundary phases of silicon nitride (Si3N4) ceramics containing additives of 1 mole% and 10 mole% of an equi-molar mixture of Y2O3 and Nd2O3 have been studied by 300 kV field emission analytical electron microscopy. The energy dispersive x-ray spectra (EDS) are obtained from both two-grains and triple-grain junctions, where an electron beam of about 0.5 nm in diameter is focused. The thickness of the intergranular thin film is found to be about 1 nm, whose value is almost the same between two samples. The sintering additives are highly enriched at the triple-grain junctions, while they are less concentrated at the two-grain junctions. It is also shown that the additives are distributed inhomogeneously within the triple-grain junctions. Based on the composition analysis among the grain boundaries, an inhomogeneous grain boundary composition model for the Si3N4 ceramics is proposed.