Nonstoichiometry and physical properties of the SrSn1-xFexO3-y system

Perovskite-type compounds in the SrSn1-xFexO3-y series (x = 0.00, 0.25, 0.5 0, 0.75, and 1.00) system have been prepared by the ceramic method, XRD pat terns of the samples assign all the composition to cubic symmetry in which Sn and Fe ions are randomly distributed over 6-coordinate B site, Mohr salt analysis shows that the ratio of Fe4+ ions(tau) and the y value increase w ith the x value and nonstoichiometric chemical formulas of the system can b e formulated from the x, tau, and y values, The Mossbauer spectra also show that Fe ions have a mixed valence state between Fe3+ and Fe4+ with high sp in states that are randomly distributed over the Sn matrix. The electrical conductivity of the compounds, except the insulator SrSnO3, results from el ectron transfer from Fe3+ (t(2g)(3)e(g)(2)) ions to Fe4+ (t(2g)(3)e(g)(1)) ions through the Fe-O-Fe bond with the e(g) electron hole as an acceptor, S ince the diamagnetic Sn matrix acts as a wall between domains with superexc hange interaction of Fe-O-Fe and forms a conduction barrier, the electrical conductivities of the SrSn1-xFexO3-y system increase with the x value. In the case of the compounds with x = 0.25 and 0.50, the field-cooled magnetiz ation data show hysteresis while zero-field-cooled data show paramagnetic b ehavior at 5 K, There is ferromagnetic Fe3+-O2--Fe4+ coupling within small domains over the diamagnetic Sn4+ matrix, The small magnetic domains are fr ozen with magnetization vectors aligned along the direction of the external magnetic field for the BC. Therefore, the compounds with x = 0.25 and 0.50 show divergence between the FC and ZFC magnetic susceptibility curves. (C) 1999 Academic Press.