Far infrared properties of sintered NiO

Far infrared reflection spectra of NiO polycrystals sintered at 1100 °C for various times (30–240 min) were measured at room temperature using a FTIR Spectrometer—Brucker 113V. The measured spectra depended on the sintering time due to differences in the microstructural morphology of the material and were compared with the NiO single crystal reflectivity diagram. Numerical analyses of the experimental spectra were performed using Kramers-Kronig analysis, a four-parameter model of coupled oscillators and the effective medium modeling theory. In the three-component effective medium model based on Bruggeman's theory we assumed the presence of pores, intergranular material and crystalline grains. The intergranular material and crystalline grains were defined as single and coupled ionic oscillators.