Single phase, cubic perovskites of composition La 0.2 Sr 0.8 Fe 0.8 B 0.2 O 3−δ , B = Al, Ga, Cr, Ti, Ta and Nb, were prepared by spray pyrolysis from aqueous precursor solutions. The effect of B-site substitution on the stability in a H 2 containing atmosphere was investigated using temperature programmed reduction (TPR). High temperature X-ray diffraction (HT-XRD) was performed under conditions similar to those in the TPR experiments. La 0.2 Sr 0.8 FeO 3−δ forms a brownmillerite-type anion-deficient ordered perovskite upon reduction at T ≈ 500• C. B-site substitution suppresses oxygen vacancy ordering, maintaining a perovskite structure under the above reducing conditions up to T ≈ 700• C. Trends in the kinetics of decomposition of B-site substituted La 0.2 Sr 0.8 FeO 3−δ are discussed.

The oxygen non-stoichiometry was determined by coulometric titration for the perovskite oxides La 0.2 Sr 0.8 FeO 3−δ and La 0.2 Sr 0.8 Fe 0.8 B 0.2 O 3−δ (B = Al 3+ , Ti 4+ and Ta 5+ ) in the temperature range 600• C and the oxygen partial pressure range: 1 · 10 −15 ≤ p O 2 ≤ 0.209 atm. The non-stoichiometry (δ) is observed to decrease with B-site substitution of Fe. The data can be well fitted with simple defect chemistry models. At low oxygen non-stoichiometry all compositions show a deviation from a localized electrons defect model. The standard and partial molar thermodynamic quantities were obtained and a gradual transition from localized to itinerant electrons with decreasing non-stoichiometry is proposed from the δ-dependency of the configurational entropy. The absolute value of the enthalpy of oxidation decreases upon B-site substitution of Fe proposing a decreased thermodynamic stability for the substituted materials. The electrical conductivity was measured at T = 900• C in the oxygen partial pressure range: 1 · 10 −17 ≤ p O 2 ≤ 0.209 atm. The electrical conductivity and charge carrier mobility decrease upon 20% substitution of Fe roughly by a factor of 2, but do not show a significant dependence on the nature of the B-site dopant.