Infrared properties of β-sialon as a function of composition

The infrared properties of beta-sialons, Si6-zAlzOzN8-z, prepared by hot, isostatic pressing for nine z-values, as well as a corresponding set of samples containing 1 wt% of yttria have been studied. The samples all have densities over 99% of their theoretical value and were found to be single-phased for z < 3.8. Polished and cleaned sialon samples and one fully dense beta-Si3N4 sample were used for infrared reflectance measurements. The lattice bands in the infrared reflectance spectra were analyzed for the different compositions. Numerical fits, using the parameters for a maximum of five classical Lorentz oscillators as free variables, were carried out. A strong Si-N resonance at 900 cm(-1) was identified, the oscillator strength of which scaled linearly with z. The IR reflectance bands represent a potential for selectively low emittance applications on radomes in the 8-12 mu m atmospheric window. The evaluation of the appropriate average window emittance showed a close to linear increase from about 0.5 to 0.9 for 0.35 < z < 4.5. (C) 1998 Elsevier Science B.V.