A Layered Double Perovskite Ca₂FeMnO₆ with Unusually High Valence Fe⁴⁺ Obtained by Low-Temperature Topotactic Oxidation

Abstract

A new double perovskite Ca 2 FeMnO 6 with a layered arrangement of Mn 4+ and the unusually high valence Fe 4+ was obtained by oxidizing the brownmillerite Ca 2 FeMnO 5 with ozone at 200 °C. The low-temperature topotactic reaction kept the layered cation arrangement of the brownmillerite but oxidized Mn 3+ to Mn 4+ and Fe 3+ to Fe 4+. The crystal structure with a P2 1 /c space group was analyzed with the synchrotron X-ray diffraction data. The changes in the valence states of Fe and Mn were confirmed by bond valence sum calculations, X-ray absorption spectroscopy, and Mössbauer spectra measurements.