STUDIES OF NONSTOICHIOMETRY AND PHYSICAL-PROPERTIES OF THE PEROVSKITESM1-XSRXCOO3-Y SYSTEM

A series of samples in the Sm1-xSrxCoO3-y (x=0.00, 0.25, 0.50, 0.75 an d 1.00) system has been prepared at 1200 degrees C under ambient atmos phere. The X-ray diffraction patterns of the samples with x=0.00 and 0 .25 are indexed with orthorhombic symmetry like GdFeO3 and x=0.50 appe ars to be perfectly cubic. In the tetragonal system (x=0.75), the stru cture is similar to that of SrCoO2.80. The composition of x=1.00, SrCo O2.52, shows the brownmillerite-type structure. The reduced lattice vo lume is increased with x value in this system. The chemical analysis s hows the tau value (the amount of the Co4+ ions in the system) is maxi mized at the composition of x=0.50. Nonstoichiometric chemical formula s are determined by the x, tau and y values. The electrical conductivi ty has been measured in the temperature range of 78 to 1000 K. The act ivation energy is minimum for those of x=0.25 and x=0.50 with metallic behavior. First-order semiconductor-to-metal transition of SmCoO3 is not observed. Instead, a broad, high-order semiconductor-to-metal tran sition is observed. In general, the effective magnetic moment is incre ased with increasing tau values at low temperature. At high temperatur e, the magnetic moment is maximum for that of x=0.00. The 3d-electrons are collective and give ferromagnetism in x=0.50.