Reflectivity Spectra and Optical Constants of Pyrites (FeS₂, CoS₂ and NiS₂) between 0.2 and 4.4 eV

Abstract

Near-normal incidence reflectivity spectra of pyrite type compounds (FeS₂, CoS₂ and NiS₂) have been measured for photon energies between 0.2 and 4.4 eV. By using Kramers-Kronig relations, optical constants (n and k) and absorption coefficient have been calculated. Absorption spectra of FeS₂ and CoS₂ thus obtained are in good agreement with those directly measured on thin films. Absorption edge of NiS₂ is located around 0.3 eV, which is very close to 0.37 eV obtained from the absorption spectrum of a bulk crystal. Absorption spectra of FeS₂ and CoS₂ in the energy region of the measurements are interpreted in terms of the band to band transition from the occupied t_2g states to the unoccupied e_g states derived from the transition metal ions of these compounds.