Synthesis, physical and photo electrochemical characterization of La-doped SrSnO 3

Abstract

The transport properties of Sr 0.98La 0.02SnO 3− δ in the system Sr 1− x La x SnO 3− δ , after which the pyrochlore La 2Sn 2O 7 appears, were investigated over the temperature range 4.2–300 K. The oxide was found to be n-type semiconductor with concomitant reduction of Sn 4+ into Sn 2+. The magnetic susceptibility was measured down to 4.2 K and is less than 3×10 −5 emu cgs mol −1 consistent with itinerant electron behavior. The electron is believed to travel in a narrow band of Sn:5s character with an effective mass ∼4 m o. The highest band gap is 4.32 eV and the optical transition is directly allowed. A further indirect transition occurs at 4.04 eV. The electrical conductivity follows an Arrhenius-type law with a thermal activation of 40 meV and occurs by small polaron hopping between nominal states Sn 4+/2+. The linear increase of thermo-power with temperature yields an electron mobility μ 300 K (2×10 −4 cm 2 V −1 s −1) thermally activated. The insulating-metal transition seems to be of Anderson type resulting from random positions of lanthanum sites and oxygen vacancies. At low temperatures, the conduction mechanism changes to a variable range hopping with a linear plot Ln ρ −1 vs. T −4. The photo electrochemical (PEC) measurements confirm the n-type conductivity and give an onset potential of −0.46 V SCE in KOH (1 M). The Mott–Schottky plot C −2– V shows a linear behavior from which the flat band potential V fb=+0.01 V SCE at pH 7 and the doping density N D=1.04×10 21 cm −3 were determined.