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Simultaneous refinement of powder diffraction data from parallel and focusing beam geometry

AppNote XRD-UIV_01: combined beam geometry Rietveld analysis

Background

Rietveld method or Whole Pattern Fitting structure refinement (invented by Hugo Rietveld) is now widely accepted as an exceptionally valuable method for structural analysis of nearly all classes of crystalline materials not available as single crystals. Rietveld method also gives effective quantitative phase analysis of simple-to-complex materials where the crystal structures are known, in addition to providing microstructural information, such as crystallite size, shape and hydrostatic strain. Before this advance, an accurate and standardless quantitative phase analysis of complex materials using powder diffraction was almost impossible. In conventional unit cell parameter determination, which utilizes data collected in BB para-focusing geometry, the systematic errors in peak positions—such as those resulting from zero point shift, sample displacement and sample transparency—are either compensated for, at least in part, by using an internal standard or by excluding such measurements from first-principles accuracy. Here we show Rietveld refinement results from X-ray powder diffraction data collected in PB and BB geometry on four SRMs, an acetaminophen (C₈H₉NO₂) tablet—a common pharmaceutical drug—and a rock sample (chunk) composed of six mineral phases; a typical geological material.

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