High precision X-ray diffraction studies of polycrystalline materials on synchrotron radiation

Abstract

The review is devoted to application of synchrotron radiation (SR) for studying the structure of polycrystalline materials. The main emphasis is made on the equipment and techniques for acquiring high precision structural information -high angular resolution powder diffractometry and the use of anomalous scattering effect in structural studies. Various schemes of recording the high resolution X-ray patterns are presented, diffractometers operating in the world's leading synchrotron radiation centers are described, and examples of particular applications are reported. S134 space, simplicity and reliability of such X-ray radiation source provided its wide use. X-ray tubes with Ti, Cr, Fe, Co, Ni, Cu, Mo and Ag anodes are intensively employed in modern lab-scale diffractometers.The radiation intensity of X-ray tube is limited by the efficiency of heat removal from the anode. At the average anode current of 100 mA and voltage of 100 kV, a 10 kW power is released at the ∼1 mm 2 anode area. In the process, no more than 3% of the power is re-emitted in the X-ray range. Such mode of operation can be provided only by the tubes with a rotating anode, where the released power is distributed over a large surface area of the anode. At the same time, intensity of the radiation source determines numerous parameters of an X-ray diffractometer -the acquisition time of X-ray pattern, angular resolution, sensitivity of X-ray diffraction analysis, accuracy of experimental data, etc. Improvement of the source would open a way to radically new possibilities of X-ray diffraction studies.In the middle of the last century, the development of elementary particle physics resulted in creating the cyclic accelerators and then the storage rings, where charged high-energy particles follow the closed trajectories and collide at a site where beams meet to generate fluxes of particles -products of the interaction. Such experimental scheme provides a double gain in energy as compared to the case when accelerated particles are directed to a stationary heavy target. The particle flux density in counter beams is much lower than density of the target, so the probability of particles collision is also much lower. Nevertheless, the multiple -several million times a second -repetition of beam collisions gives an acceptable statistics for reasonable times. If the colliding particles have equal weights and opposite charges, counter beams can be stored in a single ring chamber, dimensions of the setup being halved at the retained energy of the particles. Cyclic colliders are very productive devices for elementary particle physics; however, a serious problem arose at the early stage of their applicationlosses of particle energy for radiation [4].Motion of a charged particle along a curved trajectory is accompanied by emission of electromagnetic radiation, the so-called magnetodeceleration or synchrotron radiation. Designers of cyclic accelerators tried to minimize the radiation losses, which resulted mainly in an increased size of setups; these losses were c...

Operando characterization and DFT modelling of nanospinels: Some examples showing the relationship with catalytic activity

“…Different investigations have already been dedicated to heterogeneous catalysis [127][128][129][130], AWAXS experiments being a more easy way to consider such structural parameters [131][132][133][134][135][136][137][138]. This technique is based on the energy dependence of the atomic scattering factor, f(k,E), near an absorption edge.…”

“…The complete set of data collected on this catalytic system seems to describe a defective spinel structure in Zn 2+ and O 2around the zinc atoms and underline the importance of vacancies. Now, thanks to the increase ability of beamtime on different synchrotron centres as well as the technical developments of optics and detection, such approach which combines XAS and AWAXS has been used to investigate different catalytic systems[132][133][134][135][136][137][138]145].…”