Synthesis of AFeO2.5+x(0

The low-temperature formation of Sr and Ca ferrates by thermal oxidative decomposition of tetrahydrates of Sr and Ca nitroprussides (pentacyanonitrosilferrates(II)) is reported. IR spectroscopy, X-ray diffraction (including Rietveld analysis), and thermal analysis were used to follow the process. The amount of active oxygen (concentration of Fe(IV)) in the products was chemically determined. For the Sr compound, the final product was an oxygen-deficient perovskite that could be produced with a very low content of carbonate in the temperature range 750–850°C. For the calcium compound, only Ca2Fe2O5with the brownmillerite type structure was obtained.