The physical properties of oxygen-deficient perovskite SrPbO3-δ

The transport properties of oxygen-deficient perovskite SrPbO3-δ with mixed lead valency were investigated down to 4.2 K. The small δ-value (0.059), determined from iodometry, is due to the inert lone pair Pb2+ that does not enjoy regular octahedral coordination in spite of collective electron behaviour. The oxide exhibits a temperature-independent magnetic susceptibility consistent with itinerant electrons. The sign of carriers like polarons is that of n-type conductivity coming from the balance charge via oxygen extraction. The thermal variation of conductivity and thermopower reveal the existence of an energy gap. The conduction mechanism occurs by polaron hopping in conformity with small activation energy. The metal-insulating transition seems to be of Anderson type, resulting from the disorder of oxygen vacancies. At low temperature, the conductivity was fitted to a variable range hopping ln (1/ ρ) ∝ T-4. A comparison with SrSnO3 will be reported. The covalency of Sn-O raises the antibonding conduction state of 5s parentage and increases the forbidden gap from 1.78 to 3.30 eV