The effects of Ca and Mn excess co-doping in CMR manganites solid solution structures


A comprehensive study of CMR manganite related phases, particularly those that develop under the effects of Ca and Mn-excess co-doping is undertaken. The relationships between phase composition, processing and observed crystalline structure are investigated for co-precipitated powders of composition La1-xCaxMn1+zO3+delta, thermally treated at 800 and 1000 degrees C in air for Ca contents of x-0.10 and x=0.15 and Mn content from z=0 up to z=0.88. A relevant structural transition from orthorhombic to rhombohedric symmetry is observed as a function of Mn excess near 25% A site vacancies. This solid solution is in equilibrium with the conjugated phases, either LaMn7O12 at 800 degrees C, or Mn3O4 at 1000 degrees C, respectively. Results suggest that at the polymorphic phase transition the solid solution is stable enough to slow down Mn diffusion into the perovskite cell. Ca-doping introduces stability in the perovskite structure and broadens the domain for phase formation reaction. The solid solution limit of the Ca-manganite solid solution is set above 50% Mn excess.




Materials Science


Figueiras, F; Vieira, JM; Guzik, ME; Legendziewicz, J; Tavares, PB; Amaral, VS

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