X-Ray Diffraction Methods
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For X-ray diffraction characterisation of solid materials, we hold two STOE STADI-P powder-X-ray diffractometers. Collected pattern are processed with the GSAS-software for Rietveld refinement.
For the crystallographic orientation of single crystals we use a Laue-diffractometer.
X-Ray Powder Diffractometer (XRD)
The determination of angles and intensities produced by diffraction of X-Ray radiation by mineral lattices provides information, which is characteristic for their crystalline structures. X-Ray powder diffraction is used by for identification, quantitative phase analysis and structure refinement of phases in synthesized powders. Most diffraction data is processed by the Rietveld method using the GSAS software package. The lab includes two STOE Stadi P diffractometer equipped with a curved Germanium (111) primary monochromator yielding a convergent primary beam of Kα1 radiation and a high resolution MYTHEN-detector. The typical sample size we use is around 1 mg.
Contact: Dr. Bernd Wunder, Hans-Peter Nabein
Laue X-ray diffraction crystal orientation system
The precise characterization of the non-isotropic physical properties of crystalline geomaterials requires a precise knowledge of the orientation of samples used to perform experimental studies. The orientation of individual crystals can be obtained by Laue X-ray diffraction, a well-established technique that allows a precise determination of the orientation matrix of the crystal under investigation. The X-ray diffraction lab hosts a vertical Laue backscattering X-ray diffraction orientation system (by Photonic Science) that allows to determine the orientation of crystals down to sizes of the order of 200 microns. Our system uses a white beam with an energy range between 5 and 50 keV. The beam is focused to 200 microns beam spot, a CCD detector with wide active area (155 x 105 mm²) and high resolution (2500 x 1650 pixels). The sample positioning system is a completely automated XYZ stage. The system has also a dedicated analysis software to refine crystal orientation. The system allows to refine orientations with a resolution better than 0.1 degrees and accuracy of 0.1 degrees (tested on standard materials).
Contact: Dr. Sergio Speziale
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Single Crystal X-Ray Diffractometer
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X-Ray Powder Diffractometer
An x-ray powder diffractometer is primarily used for the identification of phases in powder form. An x-ray beam of known wavelength is focused on a powdered sample and x-ray diffraction peaks are measured using a germanium detector; the d-spacing of the observed diffraction peaks is calculated using Bragg's Law [n*lamda = 2dsin(theta)]. The Scintag Pad V automated powder diffractometer uses a Cu x-ray tube with variable filters, a four-sample changer, and a low-noise, high efficiency, liquid-nitrogen cooled germanium detector. The goniometer is automated and software packages are run from a PC running Windows NT 4. A number of Scintag software packages are available for routine powder diffraction data acquisition, background correction and peak identification. Unknowns can be matched to JCPDS cards in an on-line database. Other software is available for quantitative analysis of powder mixtures, unit cell refinement, Rietveld analysis, and GSAS structural analysis. Samples sho uld be prepared as powders with a grain size of 10 um (approximately), and typically about 100 milligrams of sample is required. Additional information available at "http://www.gps.caltech.edu/facilities/analytical/xrd.html" [Summary provided by Caltech] (Source: Global Change Master Directory (GCMD). 2023. GCMD Keywords, Version 16.3. Greenbelt, MD: Earth Science Data and Information System, Earth Science Projects pision, Goddard Space Flight Center (GSFC) National Aeronautics and Space Administration (NASA). URL (GCMD Keyword Forum Page): https://forum.earthdata.nasa.gov/app.php/tag/GCMD+Keywords)