Structural analysis of perovskite LaCr1 − x Ni x O3 by Rietveld refinement of X-ray powder diffraction data

The crystal structure of perovskite LaCr(1 - x)Ni(x)O(3) (0 < or = x < or = 1.0) has been systematically investigated by analyzing X-ray powder-diffraction data taken at room temperature. Rietveld refinement has confirmed the structural evolution from the orthorhombic phase (Pbnm, Z = 4) to the two-phase (the orthorhombic and the rhombohedral phases) region around x = 0.7, then to the rhombohedral (R 3c, Z = 2) phase for 0.8 < or = x < or = 1.0. The lattice parameters are also obtained in the refinement process. The results are discussed in terms of reduced Cr/Ni-O bond length with increasing Ni-doping level, leading to an increased tolerance factor caused by the substitution of smaller Ni(3+) (R(Ni3+) = 0.60 A, six-coordinate) ions for larger Cr(3+) (R(Cr3+) = 0.615 A, six-coordinate) ions.