Light transmittance in α-SiAlON ceramics: Effects of composition, microstructure, and refractive index anisotropy

Translucent α-SiAlON ceramics were synthesized by hot pressing and spark plasma sintering. The in-line transmittance of the visible-infrared light through the α-SiAlON ceramics was discussed in correlation with the SiAlON compositions, rare earth dopant types, microstructures, and the refractive index anisotropy of the α-SiAlON grains. The results showed that the α-SiAlON ceramics had a refractive index about 2.17 and a refractive index anisotropy about 0.014. The birefringent losses due to the index anisotropy were the main reason for the severe transmission degradation in the visible light regions in the transmission curves. Accordingly, smaller grain sizes could be used to counteract the large birefringent losses to improve the in-line transmittance of the short wavelength light.