Valence changes of manganese and praseodymium in Pr1−xSrxMn1−yInyO3−δ perovskites upon cation substitution as determined with XANES and ELNES

Systematic valence changes in Pr1−xSrxMn1−yInyO3−δ upon cation substitution with Sr2+ and In3+ have been found using Mn K-edge and Pr L-edge X-ray absorption, and Mn LII,III and Pr MIV,V electron energy-loss spectroscopy. The average valence of the praseodymium ions is close to +3.0 and virtually constant over the sample set when the samples also contained manganese ions. Pr0.5Sr0.5InO3−δ showed a distinct increase in the praseodymium valence state. In contrast, the average valence of the manganese ions changed from the trivalent state to intermediate values between +3.0 and +4.0 and approached the tetravalent state depending on the level of substitution. The knowledge of the valence is required to understand the conduction mechanisms in the material due to the small polaron hopping (electronic conductivity) and motion of oxygen ions along the vacancies (ionic conductivity). Addition of strontium and indium led to the formation of oxygen vacancies. A previously assumed intermediate valence of praseodymium as causal factor for the higher oxygen catalytic activity cannot be confirmed with room temperature measurements.