The Surface Substructural Effects on Reststrahlen Bands in Reflectance of Alumina Ceramics with Different Sized Grains

Abstract

Directional hemispherical reflectance (DHSR) of alumina ceramics was measured in the reststrahlen band (500-1000cm^-1). Three different samples with different grain sizes of 3-5μm, 11-13μm, and 28-34μm were used. Comparing the measured DHSR to the calculated reflectance using published optical constants of α-Al₂O₃ single crystal, we observed some difference between these reflectance data. The origin of this difference was identified as the surface substructure on the grains after some calculations based on the effective medium approximation. The distribution of the probability of the effective polarization factor of the surface substructure was determined by the fitting of the calculated reflectance by taking account its effect. The obtained in homogeneity well corresponds to the surface morphology observed by SEM and AFM.