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Structure-function relations of novel materials studied at neutron powder diffractometer SPODI

Markus Hoelzel 1,2Anatoliy Senyshyn 1,2Norbert Juenke 3Hans H. Boysen 4Wolfgang W. Schmahl 4Helmut Ehrenberg 5Hartmut Fuess 1

1. Technische Universität Darmstadt, Institute of Materials Science, Petersenstr. 23, Darmstadt 64287, Germany
2. Technischen Universität München, Forschungsneutronenquelle FRM-II (FRM2), Garching 85747, Germany
3. Universitaet Goettingen, Institut fuer Physikalische Chemie, Tammanstrasse 6, Goettingen 37077, Germany
4. LMU, Department of Earth and Environmental Sciences, Crystallography, Theresienstr. 41, München 81539, Germany
5. Institute for Complex Materials, IFW Dresden, Helmholtzstrasse 20, Dresden 01069, Germany


In this contribution selected experimental examples are presented which demonstrate some specific advantages of neutron powder diffraction for the investigation of crystal and micro-structures and their impact on the properties of technologically important materials. All experiments have been carried out at the neutron powder diffractometer SPODI (FRMII/Garching, Germany), offering possibilities for high resolution in-situ characterisation under various environmental conditions. The instrument is equipped with 80 position-sensitive 3He detectors of 300 mm active height covering an angular range of 160°. The two-dimensional raw data are treated by a sophisticated data evaluation procedure to obtain diffraction patterns with excellent profile shape. Furthermore, they allow to detect deviations from homogeneous powder particle distributions, in particular preferred orientation effects. Sample environment for in-situ methods include a tensile rig, an apparatus for gas charging over a broad temperature range, a cell for charging/discharging of Li-batteries, etc. The tensile rig (maximum force 100 kN) was used to investigate stress-induced lattice deformations, texture evolution and phase transformations in Ni-Ti shape memory alloys and superelastic alloys. Applying hysteresis loops on Ni-Ti shape memory alloys the texture development and the stress-induced formation of the rhombohedral “R-phase” was studied. The reflection intensity variations at different strain levels could be related to the corresponding twinning/detwinning processes.
Measurements on hydrogen storage materials, especially on sodium alanates (NaAlD4 ) with different doping elements, have been performed for structure refinement and phase analysis. The studies revealed the effects of the deuterium absorption/desorption cycles on the phase composition. Recently, an apparatus for deuterium loading has been set into operation to follow phase transformations in-situ. Studies on the lithium battery material LixCoPO4 (0 < x < 1) revealed the structural changes as a function of the Li-content. The stepwise analysis of the different compositions allowed to determine nuclear as well as magnetic contributions of the appearing phases. In particular, phase compositions, Li occupation numbers and magnetic moments were derived. Recently, first experiments on a lithium battery in operation were carried out successfully. The data are currently analysed.


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Related papers

Presentation: Oral at 11th European Powder Diffraction Conference, Microsymposium 9, by Markus Hoelzel
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-04-26 15:09
Revised:   2009-06-07 00:48