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Title: A new theory for X-ray diffraction

By considering the scattering distributed throughout space, there is an intensity enhancement at the Bragg angle even when the Bragg condition is not satisfied. This leads to an alternative explanation for the diffraction from powders and small crystals. This article proposes a new theory of X-ray scattering that has particular relevance to powder diffraction. The underlying concept of this theory is that the scattering from a crystal or crystallite is distributed throughout space: this leads to the effect that enhanced scatter can be observed at the ‘Bragg position’ even if the ‘Bragg condition’ is not satisfied. The scatter from a single crystal or crystallite, in any fixed orientation, has the fascinating property of contributing simultaneously to many ‘Bragg positions’. It also explains why diffraction peaks are obtained from samples with very few crystallites, which cannot be explained with the conventional theory. The intensity ratios for an Si powder sample are predicted with greater accuracy and the temperature factors are more realistic. Another consequence is that this new theory predicts a reliability in the intensity measurements which agrees much more closely with experimental observations compared to conventional theory that is based on ‘Bragg-type’ scatter. The role of dynamical effects (extinction etc.)more » is discussed and how they are suppressed with diffuse scattering. An alternative explanation for the Lorentz factor is presented that is more general and based on the capture volume in diffraction space. This theory, when applied to the scattering from powders, will evaluate the full scattering profile, including peak widths and the ‘background’. The theory should provide an increased understanding of the reliability of powder diffraction measurements, and may also have wider implications for the analysis of powder diffraction data, by increasing the accuracy of intensities predicted from structural models.« less
Authors:
 [1]
  1. PANalytical Research Centre, Sussex Innovation Centre, Falmer, Brighton, East Sussex BN1 9SB (United Kingdom)
Publication Date:
OSTI Identifier:
22351155
Resource Type:
Journal Article
Resource Relation:
Journal Name: Acta crystallographica. Section A, Foundations and advances (Online); Journal Volume: 70; Journal Issue: Pt 3; Other Information: PMCID: PMC4011009; PMID: 24815975; PUBLISHER-ID: sc5066; OAI: oai:pubmedcentral.nih.gov:4011009; Copyright (c) Paul F. Fewster 2014; This is an open-access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United Kingdom
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ACCURACY; AUGMENTATION; BRAGG REFLECTION; CAPTURE; DIFFUSE SCATTERING; MONOCRYSTALS; ORIENTATION; PEAKS; POWDERS; RELIABILITY; STRUCTURAL MODELS; WIDTH; X-RAY DIFFRACTION