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Neutron Powder Diffraction Investigation of Crystal Structures

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Neutron Powder Diffraction Investigation of Crystal Structures P AUL SCHERRER INSTITUT Technology Transfer R&D Services Neutron Powder Diffraction Investigation of crystal structures Introduction Figure 2: HRPT: Powder diffractometer. X-rays vs. Neutrons For many decades X-ray powder diffraction (XRD) has been an established and versatile tool for manifold applications in material science and engineering. It is well known as a rapid analytical method, used for both routine examination and scientific charac- terization of crystalline materials. Neutron powder diffraction in terms of its principles of operation is similar to X-ray diffraction. Contrary to X-rays, however, which interact primarily with the electron cloud surrounding each atom of a given The extracted information is in many Physical properties gained material, most scattering of neutrons occurs cases unique compared to that obtained at the atom nuclei, thus providing comple- from conventional X-ray diffraction tech- The most common information typically mentary information not accessible with niques, because neutrons are sensitive to extracted from a neutron powder diffraction X-rays. low atomic number materials, such as Hy- experiment includes the symmetry of crys- The neutron furthermore carries a mag- drogen and Boron, and capable of distin- tal lattices, the dimensions of the unit cells netic moment, which makes it an excellent guishing between elements with adjacent of the crystal structures and the elemental probe for the determination of magnetic atomic numbers, such as Iron and Cobalt, composition thereof. Additionally, the frac- properties of matter. Isotopes of the same element, or element tional coordinates and occupation factors In the majority of cases, diffraction is groups whose atomic numbers are wide of the atoms within the unit cell are ex- the main mechanism of the interaction of apart, such as Palladium and Hydrogen tracted with typically very high precision, the neutron with matter. This is why powder (Deuterium). For these materials systems providing reliable information on the in- diffraction experiments are perhaps the ,neutron powder diffraction is ideally suited teratomic bond distances, angles and ther- most straightforward among all neutron to addressing the shortcomings of conven- mal displacements of atoms. scattering techniques. tional XRD methods. Finally, microstructure parameters charac- terizing the grain size distributions and microstresses in the crystal lattice may also be determined. Applications Figure 1: Structual determination of Neutron powder diffraction is most widely orthorhombic RbFeO – 2 used in the fields of crystallography, min- Rietveld refinement plot eralogy, geochemistry, solid-state physics, of the HRPT data collected at T=1.5K: both crystal chemistry, material science & engineering and magnetic structure and biology. Some materials systems, spe- refinement. cifically accessible and predestined to be analyzed with this technique, are high- lighted below: • Metallic alloys • Powdered minerals • Ceramics • Isotope-substituted materials • Low atomic number materials • Hydrogen storage materials • Antiferromagnetic and ferromagnetic materials Neutron powder diffractometers at SINQ Neutron diffraction experiments are carried out using sophisticated modern instru- ments located at powerful neutron sources, such as nuclear reactors or spallation (ac- celerator-type) sources. Among other large- scale facilities, PSI operates the Swiss spal- Figure 3: The DMC powder diffractometer is also appropriate for the investigation of magnetic 1 lation neutron source SINQ , which phenomena. encompasses an up-to-date park of neutron scattering instruments. Among these, two neutron powder dif- The table below details the key operational Please feel free to ask us for further details. fractometers, DMC2 and HRPT3, are high- characteristics of the DMC and HRPT instru- lighted below: ments. Individual sample environment set- ups are possible on demand. 1 http://sinq.web.psi.ch/ DMC 2 http://sinq.web.psi.ch/dmc The high-intensity diffractometer DMC is Properties DMC HRPT 3 http://sinq.web.psi.ch/hrpt mainly designed for studies of phase tran- Wavelength 2.3 – 6.0 Å 0.94 – 2.41 Å 4 https://duo.psi.ch/duo/, sitions and the detection of weak or fast Scattering range 80° (400 160° (1600 http://sinq.web.psi.ch/sinq/sinq_call.html processes. DMC provides: channels) channels) • high intensity for weak scattering Best resolution ≥ 0.006 ≥ 0.0009 materials or small samples ∆d/d • access to low scattering angles, needed Temperature 110mK–1400 K range, sample (–273 °C …1127 °C) for magnetic structure determination Contact Magnetic field, ≤ 4 T (vertical), ≤ 2 T sample (horizontal) Dr. Denis Sheptyakov, HRPT 3 Dr. Lukas Keller Complementary to DMC, the diffractometer Hydrostatic pres- 1.5 GPa (few cm ), sure, sample 10 GPa (few 10 mm3) Laboratory for Neutron Scattering, HRPT is designed for high-resolution neu- Beam size Up to 5 cm (h) x 1 cm (w) ETHZ & PSI tron powder diffraction studies with thermal neutrons. Tel. +41 (0)56 310 30 70 Tel. +41 (0)56 310 40 07 HRPT provides: Example Email: [email protected] • very high resolution over a large A typical HRPT diffraction pattern and the re- Email: [email protected] scattering angle range sulting crystal structure are shown in figure 1. Technology Transfer PSI • high suitability for advanced structural Tel. +41 (0)56 310 27 22 determination Contact us [email protected] The broad range of research topics investi- Both, the HRPT and DMC diffractometers Paul Scherrer Institute gated at DMC and HRPT is complemented are open to users from the world-wide sci- 5232 Villigen PSI, Switzerland by a large collection of sample environ- entific community through the user-access Tel. +41 (0)56 310 21 11 ments, covering an extremely wide range program4, as well as for scientific coopera- www.psi.ch of pressures and temperatures. tion with industry. NUM-F08-D-10, 9.3.2010.
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