Crystallographic characterization of silicon nitride ceramics sintered with Y2O3–Al2O3 or E2O3–Al2O3 additions

Silicon nitride ceramics were sintered using Y2O3–Al2O3 or E2O3–Al2O3 (E2O3 denotes a mixed oxide of Y2O3 and rare-earth oxides) as sintering additives. The intergranular phases formed after sintering was investigated using high-resolution X-ray diffraction (HRXRD). The use of synchrotron radiation enabled high angular resolution and a high signal to background ratio. Besides the appearance of β-Si3N4 phase the intergranular phases Y3Al5O12 (YAG) and Y2SiO5 were identified in both samples. The refinement of the structural parameters by the Rietveld method indicated similar crystalline structure of β-Si3N4 for both systems used as sintering additive. On the other hand, the intergranular phases Y3Al5O12 and Y2SiO5 shown a decrease of the lattice parameters, when E2O3 was used as additive, indicating the formation of solid solutions of E3Al5O12 and E2SiO5, respectively.