A layered double perovskite Ca2FeMnO6 with unusually high valence Fe4+ obtained by low-temperature topotactic oxidation

Abstract

A new double perovskite Ca2FeMnO6 with a layered arrangement of Mn4+ and the unusually high valence Fe4+ was obtained by oxidizing the brownmillerite Ca2FeMnO5 with ozone at 200 °C. The low-temperature topotactic reaction kept the layered cation arrangement of the brownmillerite but oxidized Mn3+ to Mn4+ and Fe3+ to Fe4+. The crystal structure with a P21/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.