Studies of Nonstoichiometry and Physical Properties of the Perovskite SrxHo1-xFeO3-y System

摘要

Perovskite type oxides of the SrxHo1-xFeO3-y system with compositions of x=0.00, 0.25, 0.50, 0.75, and 1.00 have been prepared at 1200 ∩ in air. X-ray powder diffraction assigns the compositions with x=0.00 and 0.25 to the orthorhombic crystal system and those with x=0.50, 0.75, and 1.00 to the cubic one. The unit cell volumes of solid solutions increase with x in the system. Nonstoichiometric chemical formulas were determined by Mohr salt titration. The mole ratio of Fe4+ ions to total iron ions and the concentration of oxygen ion vacancies increase with x. Mossbauer spectra for the compositions of x= 0.00, 0.25, and 0.50 show six lines indicating the presence of Fe3+ ions in the octahedral site. However, the presence of Fe4+ ions may also be detected in the spectra for the compositions with x=0.25 and x=0.50. In the compositions with x=0.75 and 1.00, single line patterns show also the mixed valence state of Fe3+ and Fe4+ ions. The electrical conductivity in the temperature range of -100 ∩ to 100 ∩ under atmospheric air pressure increases sharply with x but the activation energy decreases with the mole ratio of Fe4+ ion. The conduction mechanism of the perovskite system seems to be hopping of the conduction electrons between the mixed valence iron ions.