MOSSBAUER CHARACTERISTICS OF THE SR2COFEO6 PEROVSKITE OBTAINED BY ELECTROCHEMICAL OXIDATION

The Sr2CoFeO6 cubic perovskite was prepared using electrochemical oxid ation of the Sr2CoFeO5 brownmillerite - type compound. The starting ma terial was prepared by quenching in liquid nitrogen from 1473 K. This preparation method produces stoichiometric Sr2CoFeO5 with random distr ibution of Fe and Co cations in both crystallographic sites. The start ing material was characterized by powder X-ray diffraction and Fe-57 M ossbauer resonance spectroscopy. The electrochemical oxidation was car ried out in the galvanostatic mode (I = 250 muA), at room temperature, using a three electrode system with a solution of 1M NaOH in equilibr ium with air. The material obtained after this oxidation, Sr2CoFeO6, s howed a cubic structure (a = 383.7 pm) and its Mossbauer resonance spe ctra revealed the presence of Fe(IV) only. The temperature dependence of the spectra between 293 and 341 K characterizes the coexistence of magnetically ordered and paramagnetic phases up to 325 K, which corrob orates the ferromagnetic behaviour found at 325 K from magnetization m easurements.