Physical and photoelectrochemical characterizations of Ba 2 SnO 4-δ elaborated by chemical route

Ba 2 SnO 4 is synthesized by nitrate route, and the physical and photoelectrochemical properties are investigated. The oxide crystallizes in the perovskite structure with a quadratic symmetry. UV-visible spectroscopy shows an optical transparency over the visible region with a direct transition of 3.18 eV. The magnetic susceptibility (~2.2 × 10 −5 emu cgs mol −1 ) is in conformity with collective electrons. The thermal variation of the conductivity indicates a conduction mechanism by adiabatic polaron hopping σ = σ o exp (1.5 meV kT −1 ) with an electron mobility ( μ 300K ) of 5.43 × 10 −4 cm 2 V −1 s −1 . The sign of hole-like small polarons is that of n -type carriers originating from oxygen off-stochiometry. The thermal variation of the thermo power indicates a finite density of state at the Fermi level. A pronounced dip, associated with a phonon drag contribution, is observed near 30 K. The nonlinear dependence of log σ vs. T −1 is due to the transition to variable range hopping at low temperature. The Mott-Schottky characteristic in KOH medium confirms the n -type conductivity and gives a flat band potential of −0.91 V SCE and electron density of 1.50 × 10 18 cm −3 . The Nyquist plot shows the contribution of both bulk and grain boundaries whereas the straight line at 45° at low frequencies corresponds to the Warburg diffusion. The data are modeled to an equivalent circuit with a constant phase element ( CPE ).