Synthesis, physical and photo electrochemical characterization of La-doped SrSnO3

The transport properties of Sr0.98La0.02SnO3−δ in the system Sr1−xLaxSnO3−δ, after which the pyrochlore La2Sn2O7 appears, were investigated over the temperature range 4.2–300 K. The oxide was found to be n-type semiconductor with concomitant reduction of Sn4+ into Sn2+. 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 mo. 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 Sn4+/2+. The linear increase of thermo-power with temperature yields an electron mobility μ300 K (2×10−4 cm2 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 VSCE in KOH (1 M). The Mott–Schottky plot C−2–V shows a linear behavior from which the flat band potential Vfb=+0.01 VSCE at pH 7 and the doping density ND=1.04×1021 cm−3 were determined.