Small polaron of β-FeSi2 obtained from optical measurements

Beta-iron disilicide β-FeSi2 polycrystals were synthesized by the horizontal gradient freeze method, and β-FeSi2 single crystals were grown by the chemical vapor transport method using polycrystals as the starting material and iodine as a transport agent. The β-FeSi2 polycrystals and single crystals were characterized by optical measurements. The Raman and infrared active optical phonons were observed by Raman scattering and optical reflection measurements, respectively. The dielectric constants were calculated by Kramers–Kronig transformation of the optical reflection spectrum. The small polaron reflecting LO phonon of β-FeSi2 was discussed by Fröhlich's model using the obtained dielectric constants.