PREPARATION OF LAFEO3 PARTICLES BY SOL-GEL TECHNOLOGY

The study of submicroscopic particles in already known systems has res ulted in a renewed interest due to the large differences found in thei r properties when the particle size is reduced, and because of possibl e new technological applications. In this work we report the preparati on of LaFeO3 particles by the sol-gel route, starting from a solution of the corresponding metallic nitrates and using urea as gelificant ag ent. Gels were decomposed at 200 degrees C and calcined 3 h at several temperatures, T, in the range 250-1000 degrees C. The samples were st ructurally characterized by x-ray diffraction (XRD) showing that the o rthoferrite crystallizes at T as low as 315 degrees C. From the x-ray diffraction peak broadening, the particle size was determined. The siz e increases from 60 to 300 nm as the calcination T increases. Infrared spectroscopy was used to characterize gels and calcined samples. From these studies a mechanism for the gel formation is proposed. Study of the magnetic properties of LaFeO3 particles shows the presence of a f erromagnetic component which diminishes as the calcination temperature increases, vanishing at T = 1000 degrees C.