In-situ spark plasma sintering behavior of La₂O₃–Y₂O₃ co-doped AlON ceramics: An attempt to prevent carbon contamination

Un-doped and La₂O₃–Y₂O₃ co-doped Aluminum oxynitride (AlON) ceramics were fabricated by reactive spark plasma sintering method (R–SPS) by using Al₂O₃ and AlN as starting powders with a composition of 70 mol% and 30 mol%, respectively. The effects of co-doping system on densification, microstructure, mechanical properties and optical transmittance of AlON ceramics were investigated. X-ray analysis confirmed the fully transformation of γ-AlON phase for all compositions prepared at 1650 °C in 30 min under 40 MPa under nitrogen. The results indicated that 0.02 wt% La₂O₃+0.08 wt% Y₂O₃ added composition had the optimal combination of sintering additives. In an attempt to reduce the graphite contamination, the powder mixture was encapsulated in a Nb-coated graphite foil before subjecting to SPS. Nb-coated graphite foil encapsulated sample was found to reduce carbon contamination leading to high densification (99.6 %) and high transmission (∼81 % at 2500 nm). This study demonstrated that optical transmittance of R-SPSed AlON ceramics is significantly improved without any post-heat treatment by using Nb-coated graphite foil during SPS processing.