The dislocation model of strain anisotropy in whole powder-pattern fitting: the case of an Li-Mn cubic spinel

Anisotropic strain broadening in X-ray or neutron powder diffraction can cause severe difficulties in whole powder-pattern fitting and Rietveld structure refinement. Several phenomenological models have been proposed to deal with this problem. These, however, lack physically sound bases. In the present work the dislocation-based model of strain anisotropy is applied in the Fourier formalism of profile fitting. It is shown that the anisotropic contrast of dislocations can fully account for strain anisotropy. A few physically sound parameters, namely the average dislocation density, the average coherent domain size, the dislocation arrangement parameter and the dislocation contrast factors, enable a perfect profile fitting to the powder pattern of a cubic Li-Mn spinel obtained at the Daresbury synchrotron storage ring.