Neutron Scattering - JUWEL - Forschungszentrum Jülich

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POWDER DIFFRACTOMETER SPODI 13 4. Evaluation of Powder Diffraction Data The methods of data treatment can be classified in analysis of phase composition or phase transformation, structure solution and structure refinement. Qualitative phase analysis is based on the determination of d-values and relative intensities (in particular intensities of strong reflections have to be considered). The phase identification is supported by crystallographic data bases (ICDD, ISCD), literature data and information from other methods (for instance, analysis of the chemical composition). Such kind of phase analysis is however typically carried out with X-ray diffraction. The majority of neutron powder diffraction studies is based on experiments at various temperatures to investigate phase transformation behaviour as a function of temperature. There is an increasing demand for parametric studies, i.e. diffraction studies under various environmental conditions (temperature, electric or magnetic field, mechanical stress, gas atmosphere...) with particular attention to reaction pathways/reaction kinetics. This kind of investigations require in general high-intensity powder diffraction. Powder diffracton data can be used either for phase identification or for the refinement of structural parameters, such as lattice parameters, fractional atomic coordinates, atomic occupancies and atomic displacement parameters by the full profile Rietveld analysis. In the Rietveld method, the full diffraction pattern is calculated by a structure model, taking into account the above mentioned structural parameters, as well as reflection profile parameters, instrumental parameters and background parameters. Using least-squares method, the experimental data can be fitted to the model in a stepwise refinement of the parameters. The complexity of the structures is directly dependent on the instrument specification, in particular, high-resolution powder diffractometers are designed for structure refinements on complex systems. Besides structure refinement, also structure solution can be done based on powder diffraction patterns by various methods.
14 POWDER DIFFRACTOMETER SPODI neutron counts 60000 46 % Ti Iobs Icalc 50000 difference plot Bragg positions 40000 30000 20000 10000 -10000 0 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 2� neutron counts 6000 5000 4000 3000 2000 1000 1/2 (311) c Cm 0 36 37 38 39 40 Figure 7: Data treatment of a measurement on the ferroelectric Pb0.99La0.01Zr0.54Ti0.46O3, carried out at 5 K at diffractometer SPODI (FRM II): Diffraction pattern including experimental data, calculated data by Rietveld fit, Bragg reflection positions of the phases (space groups CC and Cm) and difference plot (between experimental and calculated data). - zoom into the diffraction pattern, hightlighting a superlattice reflection of the CC phase. - structure model of the CC phase, view in the [001]c direction - structure model of the CC phase, view in the [010]c direction. In particular, the superstructure in the tiltings of oxygen octahedra can be seen. 2� (111) c Cc
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Page 78 and 79: SPHERES Backscattering spectrometer
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SPHERES 7 While the primary spectro
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SPHERES 9 neutron is scattered, it
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SPHERES 11 The stationary equilibri
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SPHERES 13 4. Summarize the tempera
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________________________ DNS Neutro
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DNS 3 1 Introduction Polarized neut
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DNS 5 Monochromator horizontal- and
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DNS 7 3 Preparatory Exercises The p
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DNS 9 important and always necessar
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DNS 11 Contact �� Phone:
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________________________ KWS-3 Very
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KWS-3 3 1 Introduction Ultra small
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KWS-3 5 2. The standard Q-range of
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KWS-3 7 Table 2. Samples for practi
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KWS-3 9 References [1] Eskilden, M.
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________________________ RESEDA Res
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RESEDA 3 1 Introduction Neutrons ar
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RESEDA 5 various length values l ac
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RESEDA 7 In this expression, a norm
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RESEDA 9 spin flip from up to down
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RESEDA 11 The neutrons are counted
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RESEDA 13 Contact ��
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2 S. Mattauch and U. Rücker Conten
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Neutron Scattering - JUWEL - Forschungszentrum Jülich

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