Phase and structural study of self-doped La1-x-yCaxOyMnO3+delta


To understand the combined effect of divalent ion and A-site vacancy (circle divide) self-doping, beyond the binary La1-xMnO3 system, polycrystalline La(1-x-y)Ca(x)circle divide(y)MnO(3+delta) samples were studied. Samples with Ca substitution and excess Mn in the range x < 0.33 and y < 0.45, respectively, were prepared by standard solid-state reactions. Structural and phase analysis of the samples were done by X-ray diffraction and transmission electron microscopy. The manganite structure in this composition range includes rhombic and orthorhombic phases. Most samples contain the hausmanite phase (Mn3O4) coexisting with the manganite phase. A small amount of perovskite related AMn(7)O(12) (A = La, Ca) structure near the hausmanite-manganite boundary is also found in samples treated in oxygen atmosphere. The calculated vacancy content accommodated in the manganite phase can be higher than 1/8, the reported limit for La1-xMnO3, which is confirmed in our x = 0 sample. For the compositions studied, a ferromagnetic metallic behavior below T-C is found, confirming the stability of the Mn sublattice, and near the optimum stoichiometric ((x = 0.33, y = 0) system, a net A-site vacancy content (up to y = 0.2) does not degrade the magnetic and electric properties.



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Figueiras, F; Araujo, JP; Amaral, VS; Tavares, PB; Lopes, AB; Vieira, JM

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