CRYSTAL-STRUCTURE REFINEMENT AND STABILITY OF LAFEXNI1-XO3 SOLID-SOLUTIONS

The crystal structure refinement of LaFexNi1-xO3 (0 less than or equal to x less than or equal to 1) solid solutions was determined and anal yzed by means of Rietveld refinement from X-ray powder diffraction dat a. The solid solutions with 0 less than or equal to x < 0.5 are isostr uctural with LaNiO3 and crystallize in the rhombohedral system, space group R3c, while those with composition 0.5 < x less than or equal to 1 are isoestructural with LaFeO3 and crystallize in the orthorhombic s ystem, space group Pnma. All of the solutions are single phase except that with the intermediate composition (x = 0.5), where both phases ar e observed. The cell volume increases with the iron content. This can be ascribed to the larger ionic radius of Fe3+ (HS) compared to Ni3+ ( LS). LaFe0.25Ni0.75O3 was found to be single phase when prepared at te mperatures as high as 1000 degrees C, indicating an increase in the st ability of the perovskite phase at high temperatures when a relatively small amount of iron is substituted for Ni in LaNiO3. (C) 1997 Academ ic Press.