Physical and photoelectrochemical characterizations of Ba2SnO4-δ elaborated by chemical route

Abstract

Ba2SnO4 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 cm2 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 VSCE and electron density of 1.50 × 1018 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).