Journal
POWDER DIFFRACTION
Volume 24, Issue 4, Pages 315-326Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1154/1.3257906
Keywords
preferred orientation; texture; neutron powder diffraction; March model; generalized spherical harmonics; molybdite; calcite; Ti50.70Ni49.30 shape memory alloy
Funding
- National Institute of Standards and Technology
- U.S. Department of Commerce
- Basic Energy Sciences, Office of Science
- U.S. Department of Energy
- NSF Cooperative Agreement [EAR 01-35554]
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Preferred orientation or texture is a common feature of experimental powder patterns. The mathematics of two commonly used models for preferred orientation-the March-Dollase and the generalized spherical-harmonic models-is reviewed. Both models were applied individually to neutron powder data from uniaxially pressed molybdite (MoO3) and calcite (CaCO3) powders in Rietveld analyses, as well as the as-received powders. The structural refinement results are compared to single-crystal structures. The results indicate that reasonable refinement of crystal structures can be obtained using either the March model or generalized spherical-harmonic description. However, the generalized spherical-harmonic description provided better Rietveld fits than the March model for the molybdite and calcite. Therefore, the generalized spherical-harmonic description is recommended for correction of preferred orientation in neutron diffraction analysis for both crystal structure refinement and phase composition analysis. Subsequently, the generalized spherical-harmonic description is extended to crystal structure refinement of annealed and the aged polycrystalline Ni-rich Ni50.7Ti49.30 shape memory alloys. (C) 2009 International Centre for Diffraction Data. [DOI: 10.1154/1.3257906]
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