Structural aspects of Pr_1-xSr_xFeO_3-w

Structural aspects of the distorted perovskite ABO₃ phase Pr_1-xSr_xFeO_3-w,x=0.00-0.80,w=0.000-0.332, were studied by powder X-ray diffraction, powder neutron diffraction, ⁵⁷Fe Mössbauer spectroscopy, and Fe K-, Sr K-, and Pr L_III-edge EXAFS techniques. The diffraction data revealed no indications for ordering of Pr and Sr at the A site, nor for oxygen vacancy ordering at O sites for heavily reduced samples. Mössbauer spectroscopy showed octahedral, square pyramidal, and tetrahedral Fe coordinations with relative amounts closely following the predictions for a binomial distribution of oxygen vacancies. In addition to Fe³⁺ and Fe⁴⁺, also Fe⁵⁺ appears at 77 K for (G-type) antiferromagnetic samples with high average Fe valence. This suggests dynamic 2 Fe⁴⁺↔Fe³⁺+Fe⁵⁺ fluctuations. At 296 K, a mixed valence Fe⁽³⁺ⁿ⁾⁺ component significantly improved the fit of Mössbauer spectra for the most oxidized paramagnetic samples. The qualitative EXAFS study shows that the local environments for Fe, Pr, and Sr strongly depend on x and w. The local Pr- and Sr-site geometries differ significantly from the cubic average structure for Pr_0.50Sr_0.50FeO_2.746.