STUDIES OF NONSTOICHIOMETRY AND MAGNETIC-PROPERTIES OF THE PEROVSKITE GD1-XSRXCOO3-Y SYSTEM

A series of samples in the Gd1-xSrxCoO3-y(x = 0.00, 0.25, 0.50, 0.75, and 1.00) system with perovskite-type oxide have been prepared at 1200°C under an atmosphere with and without oxygen gas flow. X-ray diffraction analysis of the solid solution assigns the structure of the compositions of x = 0.00, 0.25, and 1.00 to the orthorhombic system, x = 0.50 to the cubic system, and x = 0.75 to the tetragonal system. The reduced lattice volume of the system is increased as the x value gets higher. The amount of Co4+ ion or the mixed valence state between Co3+ and Co4+ ions is quantitatively analyzed by the iodometric titration method. The mole ratio of the Co4+ ion, the τ value, is maximized at the composition of x = 0.50 and the y value, the oxygen deficiency, increases as the x value increases. Nonstoichiometric chemical formulas are obtained with the x, τ, and y values. The electrical conductivity of the GdCoO3.00 sharply increases within the experimental temperature range; therefore, the activation energy of this compound is higher than those of the other compositions. The electrical conductivity measurement of the composition (x = 0.50) indicates a metallic property. The compounds of the compositions (x = 0.00 ∼ 0.75) show a paramagnetic property. The magnetic measurement shows that the paramagnetic Curie temperature (θp) is a positive value in the case of x = 0.50 with the maximum amount of the Co41 ion. The μeff-Co is decreased as the τ value gets higher. The SrCoO2.52 has the Néel temperature of 550 K. © 1993 Academic Press, Inc.