Oxygen nonstoichiometry, Mössbauer spectra and mixed conductivity of Pr 0.5Sr 0.5FeO 3−δ

Abstract

The oxygen deficiency of perovskite-type Pr 0.5Sr 0.5FeO 3− δ , studied by coulometric titration, thermogravimetry and Mössbauer spectroscopy, is significantly higher than that in La 0.5Sr 0.5FeO 3− δ at 973–1223 K. The variations of hole mobility and Seebeck coefficient in oxidizing atmospheres, where the total conductivity of praseodymium-strontium ferrite is predominantly p-type electronic, suggest progressive delocalization of the p-type charge carriers on increasing oxygen chemical potential. As for other perovskite-type ferrites, reduction leads to the co-existence of vacancy-ordered and disordered domains. The n-type electronic conductivity of Pr 0.5Sr 0.5FeO 3− δ at reduced p(O 2) and the hole transport under oxidizing conditions are both lower compared to the La-containing analogue. Analogous conclusion was drawn for the ionic conductivity, calculated from the steady-state oxygen permeation data under oxidizing conditions and from the p(O 2)-dependencies of total conductivity in the vicinity of electron-hole equilibrium points where the average iron oxidation state is 3+. The similar activation energies for partial ionic and electronic conductivities in Ln 0.5Sr 0.5FeO 3− δ (Ln=La, Pr) indicate that the presence of praseodymium does not alter any of the conduction mechanisms but decreases the charge-carrier mobility due to the smaller radius of Pr 3+ cations stabilized in the perovskite lattice.