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Temperature dependence of the optical absorption edge of pyrite FeS2 thin films

Optical absorption edge measurements of pyrite thin films prepared by flash evaporation have been made at different temperatures in the range 10-300 K. Absorption edge values vary from 1.05 to 0.99 eV in that temperature interval. Experimental data have been fitted to the Varshni formula and to an expression proportional to the statistical Bose-Einstein factor used previously by other workers. The main phonon energy calculated from the fitting of the experimental points to the Bose-Einstein expression is in good agreement with the average energy of the active optical phonons as determined by Raman spectroscopy carried out on the same pyrite thin film.