Anisotropic Sample Broadening Faulting

X ray powder pattern (Cu K ) of a commercial talc sample showing the complex coexistence of narrow peaks, broad ones, and very broad asymmetrical bands related to turbostratic effects (strongly disoriented layers). An excellent fitting of such a pattern with a complete physical description of the distortions is far beyond our current capabilities. 

Part of the neutron powder pattern (A =1.909 A) of cubic double perovskite HNbOs, showing very different profile shapes and widths. No excellent fit of that pattern has ever been produced from a realistic model, though the most probable faulting inside of the sample is a simple three dimensional antiphase effect due to [Nb06] octahedra inversion of the tilting angles of connection. 

Attempts to consider a hkl dependence of the broadening in the Rietveld method were made by using different approaches involving ellipsoid, quartic and quadratic forms, either representing the modulation of the average sizes M /,fc/and Mi / /and microstrain T hki, or used for a purely phenomenological qualitative fit without trying to extract any physical parameters. 

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An improved modelling of the average structure of ice Ic includes linear combination of stacking-probability driven structure models and anisotropic size broadening. It allows for a quantitative modelling of neutron diffraction data of different ice Ic samples. It will serve as well for the description of ice Ih samples with stacking faults. 

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