Ab-initio structure determination of LiSbWO6 by X-ray powder diffraction
TL;DR: In this article, the crystal structure of LiSbWO6 was solved from X-ray powder diffraction data and the structure was refined using Rietveld profile refinement principles.
About: This article is published in Materials Research Bulletin.The article was published on 1988-03-01. It has received 2325 citations till now. The article focuses on the topics: Rietveld refinement & Powder diffraction.
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TL;DR: In this article, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed and the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure is discussed.
Abstract: In spite of intrinsic limitations, neutron powder diffraction is, and will still be in the future, the primary and most straightforward technique for magnetic structure determination. In this paper some recent improvements in the analysis of magnetic neutron powder diffraction data are discussed. After an introduction to the subject, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed. Next, we discuss the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure. The simulated annealing approach for magnetic structure determination is briefly discussed and, finally, some features of the program FullProf concerning the magnetic structure refinement are presented and discussed. The different themes are illustrated with simple examples.
11,923 citations
TL;DR: Fityk is portable, open-source software for nonlinear curve fitting and data analysis that enables Pawley refinement of powder diffraction data and size–strain analysis.
Abstract: Fityk is portable, open-source software for nonlinear curve fitting and data analysis. It specializes in fitting a sum of bell-shaped functions to experimental data. In particular, it enables Pawley refinement of powder diffraction data and size–strain analysis.
2,083 citations
Cites methods from "Ab-initio structure determination o..."
...Popular methods of powder pattern analysis, such as Rietveld (1969), Pawley (1981) and Le Bail (Le Bail et al., 1988) whole profile refinement, are optimization procedures that serve for derivation of a set of parameters that provide the best fit of a mathematical function to the diffraction data....
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TL;DR: A set of general guidelines for structure refinement using the Rietveld (whole profile) method has been formulated by the International Union of Crystallography Commission on Powder Diffraction.
Abstract: A set of general guidelines for structure refinement using the Rietveld (whole-profile) method has been formulated by the International Union of Crystallography Commission on Powder Diffraction. The practical rather than the theoretical aspects of each step in a typical Rietveld refinement are discussed with a view to guiding newcomers in the field. The focus is on X-ray powder diffraction data collected on a laboratory instrument, but features specific to data from neutron (both constant-wavelength and time-of-flight) and synchrotron radiation sources are also addressed. The topics covered include (i) data collection, (ii) background contribution, (iii) peak-shape function, (iv) refinement of profile parameters, (v) Fourier analysis with powder diffraction data, (vi) refinement of structural parameters, (vii) use of geometric restraints, (viii) calculation of e.s.d.'s, (ix) interpretation of R values and (x) some common problems and possible solutions.
1,808 citations
TL;DR: In this article, the DICVOL04 algorithm was extended to include a tolerance to the presence of impurity (or inaccurately measured) diffraction lines, a refinement of the zero-point position, a reviewing of all input lines from the solution found from, generally, the first 20 lines, and a cell analysis, based on the concept of the reduced cell, to identify equivalent monoclinic and triclinic solutions.
Abstract: The efficiency of the successive dichotomy method for powder diffraction pattern indexing [Louer & Louer (1972). J. Appl. Cryst. 5, 271–275] has been proved over more than 30 years of usage. Features implemented in the new version of the computer program DICVOL04 include (i) a tolerance to the presence of impurity (or inaccurately measured) diffraction lines, (ii) a refinement of the `zero-point' position, (iii) a reviewing of all input lines from the solution found from, generally, the first 20 lines, (iv) a cell analysis, based on the concept of the reduced cell, to identify equivalent monoclinic and triclinic solutions, and (v) an optional analysis of input powder data to detect the presence of a significant `zero-point' offset. New search strategies have also been introduced, e.g. each crystal system is scanned separately, within the input volume limits, to limit the risk of missing a solution characterized by a metric lattice singularity. The default values in the input file have been extended to 25 A for the linear parameters and 2500 A3 for the cell volume. The search is carried out exhaustively within the input parameter limits and the absolute error on peak position measurements. Many tests with data from the literature and from powder data of pharmaceutical materials, collected with the capillary technique and laboratory monochromatic X-rays, have been performed with a high success rate, covering all crystal symmetries from cubic to triclinic. Some examples reported as `difficult' cases are also discussed. Additionally, a few recommendations for the correct practice of powder pattern indexing are reported.
1,284 citations
Cites methods from "Ab-initio structure determination o..."
...…another useful complementary check of cell validity is the use of a pattern-matching approach (combined with a zoom facility), e.g. the iterative Le Bail algorithm (Le Bail et al., 1988), in which a full pattern ®tting is carried out using peak positions constrained by the found cell parameters....
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TL;DR: In this paper, a model of the multi-dimensional distribution of lattice metrics within a powder sample is developed, leading naturally to a few parameters which can be varied to achieve optimal line-shape fits.
Abstract: Anisotropic line-shape broadening (peak width which is not a smooth function of d-spacing) is frequently observed in powder diffraction patterns, and can be a source of considerable difficulty for whole-pattern fitting or Rietveld analysis. A model of the multi-dimensional distribution of lattice metrics within a powder sample is developed, leading naturally to a few parameters which can be varied to achieve optimal line-shape fits. Conditions on these parameters are derived for all crystal systems, and the method is illustrated with two examples: sodium p-hydroxybenzoate and rubidium fulleride.
1,121 citations
Additional excerpts
...A rather large number of line-shape parameters are required to accurately describe the data set in a Le Bail ®t (Le Bail et al., 1988) of the pro®le....
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References
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TL;DR: In this paper, a structure refinement method was described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram.
Abstract: A structure refinement method is described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram. Nuclear as well as magnetic structures can be refined, the latter only when their magnetic unit cell is equal to, or a multiple of, the nuclear cell. The least-squares refinement procedure allows, with a simple code, the introduction of linear or quadratic constraints between the parameters.
14,360 citations
TL;DR: In this paper, the authors established some criteria for the choice of collimators for a crystal spectrometer for neutron diffraction in order to achieve a good compromise between luminosity and resolution.
988 citations
TL;DR: In this paper, a trial-and-error method is described for facilitating the indexing of X-ray powder patterns with the help of a computer based on the variation of parameters by dichotomy, i.e. successive division of available phase space.
Abstract: A trial-and-error method is described for facilitating the indexing of X-ray powder patterns with the help of a computer. It is based on the variation of parameters by dichotomy, i.e. successive division of available phase space. The observational errors are rigorously treated. The program, written in Fortran IV, presupposes orthorhombic or higher symmetry. The principles used are illustrated with several X-ray powder patterns.
229 citations
TL;DR: In this article, the powder indexing method based on successive dichotomies is considered in terms of partition of volume space, and two approaches are described; if density and molecular weight are introduced, the calculations are accelerated.
Abstract: The powder indexing method based on successive dichotomies is considered in terms of partition of volume space. With this strategy, the smaller and more probable solutions are found first. Two approaches are described; if density and molecular weight are introduced, the calculations are accelerated. Extension of the method to the monoclinic case is described, and can be useful for unit cells with not too large volumes. A program, DICVOL, has been written in Fortran which allows a search for systems down to monoclinic.
132 citations
TL;DR: In this article, the lattice constants from the experimental work are refined by least-squares methods; reflections are assigned hkl indices consistent with space group extinctions, and relative intensities, calculated densities, literature references, and other relevant data are included.
Abstract: Patterns useful for identification are obtained by automated diffractometer methods. The lattice constants from the experimental work are refined by least-squares methods; reflections are assigned hkl indices consistent with space group extinctions. Relative intensities, calculated densities, literature references, and other relevant data are included.
126 citations