View Publication | CEMHTI CNRS UPR3079 Orléans France

J.F.Brun, L.del Campo, D.De Sousa Meneses, P.Echegut, 'Infrared optical properties of alpha-alumina with the approach to melting: gamma-like tetrahedral structure and small polaron conduction', J. Appl. Phys. 114 223501 (2013) doi:10.1063/1.4846077

The normal spectral emittance of a-Al2O3 single crystal has been measured from room temperature up to the liquid state and from 20 cm-1 up to 10 000 cm-1, in two polarization configurations. The spectra were fitted with a semi-quantum dielectric function model. AlO4 structure units are revealed within the phonon spectral range more than a hundred degrees below the melting point when heating from the solid state. In parallel, the anomalous increase of emittance observed within the transparency spectral range with the approach to melting appears strongly correlated. Implications on the electronic structure are discussed: the existence of small polaron conduction is suggested which has never been mentioned before.