ACCURACY OF PAIR DISTRIBUTION FUNCTION-ANALYSIS APPLIED TO CRYSTALLINE AND NONCRYSTALLINE MATERIALS

Pair distribution function (PDF) analysis of neutron or X-ray powder diffraction data is a useful technique for analysis of short-range structure in both amorphous and crystalline materials. Errors in PDF determinations may arise from several sources: termination of the Fourier transform, lack of instrument resolution, counting statistics and inaccurate corrections for experimental artifacts. Estimates of the amount of error from termination and instrument resolution are computed using a model structure. A general method for estimating the expected contribution of statistical error to the PDF is introduced for the first time. The effect of termination varies with the type of material and with the amplitude of lattice vibrations but, in general, termination with Q > 30 angstrom produces minimal errors. Broadening of the diffraction pattern produces negligible effect for conventional instrumentation. With moderate data-collection times, the statistical errors can be reduced to reasonable levels. Pulsed-neutron diffraction can provide accurate and precise PDF measurements, as is demonstrated in this work by the agreement between model and experimental results for polycrystalline aluminium.