Abstract
A user-friendly program has been developed to analyze diffuse scattering from single crystals with the reverse Monte Carlo method. The approach allows for refinement of correlated disorder from atomistic supercells with magnetic or structural (occupational and/or displacive) disorder. The program is written in Python and optimized for performance and efficiency. Refinements of two user cases obtained with legacy neutron-scattering data demonstrate the effectiveness of the approach and the developed program. It is shown with bixbyite, a naturally occurring magnetic mineral, that the calculated three-dimensional spin-pair correlations are resolved with finer real-space resolution compared with the pair distribution function calculated directly from the reciprocal-space pattern. With the triangular lattice Ba3Co2O6(CO3)0.7, refinements of occupational and displacive disorder are combined to extract the one-dimensional intra-chain correlations of carbonate molecules that move toward neighboring vacant sites to accommodate strain induced by electrostatic interactions. The program is packaged with a graphical user interface and extensible to serve the needs of single-crystal diffractometer instruments that collect diffuse-scattering data.
Highlights
Crystalline materials with disorder giving rise to unusual properties can be studied with diffuse-scattering measurements (Frey, 1995)
The program addresses each of the three disorder types: occupational, displacive and magnetic
It is optimized for performance and is accompanied by a user-friendly graphical interface that allows a user to load in collected data, process
Summary
Crystalline materials with disorder giving rise to unusual properties can be studied with diffuse-scattering measurements (Frey, 1995). This autocorrelation function describing the deviations away from the average structure can be obtained for occupational/displacive disorder (Weber & Simonov, 2012) and magnetic disorder (Roth et al, 2018) through the Fourier transform. Changes are made by rotating moments, replacing atoms with vacancies and displacing atoms until the disordered supercell configuration agrees with experiment through the calculated diffraction intensity This relatively straightforward approach is a robust method for quantifying the disorder from experimental single-crystal diffraction data, allowing for direct calculation of threedimensional pair correlations.
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