W0089

Colossal magnetoresistance in perovskite-type manganese oxides has stimulated research on this type of oxides. Many mixed oxides of general formula R_xA_1-xMnO₃ (R: trivalent rare earth, A: alkaline-earth), belong to the group of orthorhombic distorted perovskites. The mixture of divalent and trivalent cations and the simultaneous occurrence of Mn⁺³ and Mn⁺⁴ ions, introduce mismatch in the original orthorhombic crystal structure. The phase diagram of these families is non-symmetric and hole or electron doping cause dissimilar effects. Usually a complex phase diagram results. In a previous study of the Y_1-xCa_xMnO₃ system¹, no solid solution was obtained in the whole range of composition. To explain this result we examined the effect of cadmium doping for all range of x concentration. The conditions to obtain the orthorhombic perovskite structure were investigated and the different phases were characterized. The samples were synthesized by solid-state reaction (SSR) and Liquid-Mix (LM) methods. X-ray Powder Diffraction (XRD) from 20K to 300 K, scanning electron microscopy and thermogravimetric analysis were used to characterize the samples. Structural parameters were determined using the Rietveld method. Some points of the structural phase diagram were determined. Using the SSR method the perovskite like phase appears at 1100^o C for x ~ 0.5, with a small quantity of segregated phases. A single orthorhombic phase (Y-Cd)MnO₃ is obtained in the range 0.15 ≤ x ≤ 0.25 at 700^o C using LM synthesis in oxygen atmosphere . Outside of this range the samples also contain other crystalline phases and amorphous components. At 800^o C the pure Ytrium perovskite (x = 0) YMnO₃ is obtained. Low temperature XRD (20 -300K) for all samples show a slight change in the cell parameters without any structural change.