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Use of the Pearson type VII distribution in the neutron profile refinement of the structures of LiReO3 and Li2ReO3

1982; American Institute of Physics; Linguagem: Inglês

10.1063/1.33714

1935-0465

A. Santoro, R. J. Cava, D. W. Murphy, Robert Roth,

Inorganic Fluorides and Related Compounds

The crystal structures of the compounds LiReO3 and Li2ReO3 have been refined with the Rietveld method.1 Neutron powder diffraction data collected at room temperature were used in these calculations. Since the shapes of the diffraction lines for both materials could not be approximated by Gaussians with sufficient accuracy, the Pearson type VII function was used in all refinements.2,3 The value of m was assumed to be 2θ‐independent in these calculations. The best fits to the experimental observations were obtained with m=1.5 for LiReO3 and m=3 for Li2ReO3. These values indicate that the lines of the first compound are almost Lorentzians, while those of the second are close to the so‐called ‘‘modified Lorentzians.’’ The final R‐factors are RI =5.66, Rp =5.55, RW =7.04, and χ=1.41 for LiReO3 and RI =8.05, Rp =7.58, RW =9.77, and χ=1.27 for Li2ReO3. The non‐Gaussian peak shape cannot be attributed to instrumental factors since the instrumental function of the diffractometer used to collect the data is Gaussian to a very good approximation. Crystallite size effects could explain the observed intensity distributions, but other factors could also be present. Both compounds crystallize with the symmetry of space group R3c, and the lattice parameters (hexagonal axes) are a=5.0918(3), c=13.403(1) Å for LiReO3 and a=4.9711(4), c=14.788(1) Å for Li2ReO3.