A new IR excitation in semiconducting Ba1-xKxBiO3 single crystals

We report optical reflectivity measurements on Ba1-xKxBiO3 (x=0, 0.15) single crystals in the frequency range 70-30 000 cm-1 and at different temperatures in an attempt to understand the transport mechanism in the semiconducting state before it undergoes semiconductor-metal transition. For x=0.15, at 400 K, we find a hump in reflectivity at ∼1280 cm-1. Neff of total IR transition shifts towards low frequency as temperature increases above 300 K. We suggest the presence of new and thermally excited states in the Peierls band gap and the possible new IR excitations