Changes in optical behaviour of iron pyritohedron upon microwave treatment

We have utilized the volumetric heating of materials by microwave energy absorption for investigating the changes in the optical behavior of a well characterized natural crystal of iron pyritohedron (FeS2). For microwave treatment virgin central core pieces of the FeS2 crystal were ground to fine powder and then heated in a microwave oven for half an hour. Powder XRD measurements confirmed that the microwave treatment on FeS2 does not affect the face centered cubic structure of FeS2. The UV-Visible optical spectrum of the microwave treated FeS2 display a narrow optical absorption peak at ∼315 nm, on the other hand in the UV-Vis spectrum of pure FeS2 a broad absorption band with a maximum centered ∼310-330 nm was observed. The band gap energies for pure and microwave treated FeS2 are estimated to be 1.09 eV and 1.35 eV respectively. This study clearly indicates that microwave treatment results in a blue shift in the absorption edge and enhancement in the band gap energy.