Physical characterization of the semiconducting deficient perovskite BaSnO3−δ

The semiconducting stannate BaSnO3−δ, prepared in evacuated silica ampoule, crystallizes in a cubic perovskite structure. The magnetic susceptibility (less than 2×10−5 emu cgs mol−1) is due to itinerant electrons. The conductivity obeys to an exponential law σo exp (−Ea/kT) with activation energy of 3 meV and electrons hopping between mixed valences Sn2+/4+. A variable range hopping is predicted from the non linear behavior of the plot ln (σ) versus T−1. At high temperatures, the conductivity follows a thermally activated hopping of lattice polaron with activation energy of 0.17 eV. The plot deviates from the linear behavior due to the oxidation of BaSnO3−δ; the fully oxidized specimen is restored at 578 K in air. The thermal variation of the thermopower suggests a finite density of states at the Fermi level. The semiconducting properties are elucidated from the photo-electrochemical characterization. The Mott–Schottky plot in alkaline medium shows a straight line from which an electron density of 3.07×1021 cm−3, a flat band potential of −0.375 VSCE and a space charge region of 2.3 Å have been determined.