Crystal and magnetic structures in Perovskite-related image (x=0.2, 0.33) Original Research Article

Using sol–gel synthesis, single phase perovskite-related compounds in the family La1−xCaxFeO3−δLa1−xCaxFeO3−δ have been formed for x =0.2 and x =0.33, but not for x =0.5. The x =0.2 and x =0.33 compounds are isostructural with LaFeO3LaFeO3 (Pnma). The magnetic structure of La0.8Ca0.2FeO3−δLa0.8Ca0.2FeO3−δ has been studied through Mössbauer spectroscopy and neutron powder diffraction. La0.8Ca0.2FeO3−δLa0.8Ca0.2FeO3−δ is a G-type antiferromagnet with a magnetic moment magnitude of 3.0±0.2μB3.0±0.2μB at room temperature. The reduction in the magnitude of the antiferromagnetic moment compared to that published for LaFeO3LaFeO3 is explained by the measurement being taken at room temperature rather than 4 K and by the presence of Fe4+Fe4+ ions which have weaker exchange interactions than Fe3+Fe3+, causing a strong reduction in TN. Room temperature Mössbauer shows a broad magnetic hyperfine field distribution on the Fe sites in both La0.8Ca0.2FeO3−δLa0.8Ca0.2FeO3−δ and La0.67Ca0.33FeO3−δLa0.67Ca0.33FeO3−δ. On cooling, disproportionation of Fe4+Fe4+ into Fe3+Fe3+ and Fe5+ is apparent, and the resulting Fe5+ sextet measured at low temperature gives a reliable measure of the Fe4+Fe4+ fraction. This in turn shows that creation of high-oxidation-state Fe is the dominant charge balance mechanism on doping Ca2+Ca2+ into the Ln3+Ln3+ site indicating a disordered distribution of Fe3+Fe3+ and Fe4+Fe4+. The lack of broadening of the Fe5+ sextet suggests that there may be ordering in the distribution of Fe5+.