Evolution of core-rim structures and phase transformations in infra-red transmitting Y-α-SiAlON ceramics

Core-rim structures were observed as common features in Y-alpha-SiAlON ceramics hot-pressed between 1550-1950 degrees C. We found most dopants were taken into alpha'-rims, and a transition layer grown first on alpha-cores from liquid-phase over-saturated with metal solutes. Elongated p'-grain were formed as minor phase with ce- or AlN-cores thus only after the alpha' matrix had consumed up all Y solutes, revealing that the alpha' -> beta' transformation is controlled by the transient liquid-phase and similar defects and dangling bonds could be detected in both SiA1ON phases by cathodoluminescence. Quantitative assessment of Y-m/3Si12-(m+n)Alm+nOnN16-n demonstrates the multiphase evolution, initiated by over-saturation of Y solutes at low temperatures thus retaining alpha-phase as cores to lower the infra-red transmittance, dictated by homogenization of Al solutes at higher temperature. The elimination of those phase boundaries leads to better dopant and sintering design for achieving transparent and high-performance SiAlON ceramics.

Automated summary

Core-rim structures were observed in Y-alpha-SiAlON ceramics hot-pressed between 1550-1950 degrees C. Doping mainly occurred in the alpha'-rims, with a transition layer grown first on the alpha-cores. The presence of elongated p'-grain was observed as a minor phase with ce- or AlN-cores. The alpha' -> beta' transformation was found to be controlled by the transient liquid-phase.