THE OXYGEN DEFICIENT PEROVSKITES SRFE1-XCUXO2.5-X/2+DELTA, BAFE1-XCUXO2.5-X/2+DELTA EXHIBITING MIXED-VALENCE OF IRON AND COPPER IONS

Two new oxygen deficient perovskites AFe//1// minus //xCu//xO//2. 5 minus x/2 plus delta (A equals Sr, Ba) have been synthesized. The structural characteistics of these phases were established by X-ray and electron diffraction. Chemical analysis coupled with Mossbauer spectroscopy and magnetic susceptibility measurements allowed the different oxidation states of copper and iron to be determined. The agreement between the Mossbauer and the magnetic susceptibility measurements led to the consideration of a high spin-low spin transition for the Fe(IV) cations when the number of oxygen vacancies increased i. e. when the amount of copper increased. The electron transport properties, based on hole delocalization in a copper band, have shown the influence of the nature of the alkaline-earth on the hole mobility.