Dynamic Powder Crystallography With Synchrotron X-Ray Sources

Abstract

The increased brightness, tunability, low divergence and low emittance of X-ray beams available at synchrotron X-ray sources facilitate a variety of powder-diffraction experiments not practical using conventional in-house sources. Furthermore, the increased availability of fast position-sensitive detectors, along with implementation of improved software, make possible new classes of experiments. These include time-resolved powder-diffraction of phase transitions, precipitation, recrystallization and ion-exchange reactions. Examples of time-resolved studies that highlight some of these developments include: (1) observations of the phases forming during reaction under controlled hydrothermal conditions (e.g., FeS); (2) full Rietveld structure refinement using time-resolved data to determine the mechanism of ion exchange in zeolites. The advent of area detectors, commonly coupled with focusing optics at synchrotrons, will further increase the time resolution at the synchrotron, possibly leading to a data glut. Solutions are available now, and developments in the near term will allow semi-automatic decisions on which datasets to analyze amongst the thousands collected.Keywords: synchrotron radiation, crystallography, time-resolved studies, diffraction, scattering, high pressure, element partitioning, phase diagrams, ion-exchange reactions, energy-dispersive diffraction. SOMMAIRELa luminance accrue, la possibilité de syntoniser, la faible divergence et le faible pouvoir émissif des faisceaux de rayons X disponibles aux sources synchrotron permettent une série d'expériences en diffraction X sur poudres qui ne sont pas du tout pratiques avec les sources conventionnelles. De plus, la disponibilité accrue de détecteurs efficaces sensibles à la position et de logiciels améliorés rend possible de nouvelles sortes d'expériences. Par exemple, il est maintenant possible d'étudier par diffraction X sur poudres le progrès dans le temps d'une transition de phases, une précipitation, une recristallisation, et une réaction d'échange ionique. Nous décrivons les exemples suivants pour souligner certains de ces développements: (1) observations des phases apparaissant au cours d'une réaction hydrothermale sous conditions controlées, impliquant par exemple FeS; (2) affinement complet d'une structure par la méthode de Rietveld en utilisant des données échelonnées dans le temps pour étudier le mécanisme d'échange ionique dans les zéolites. L'installation de détecteurs à aire, couplée en général avec une focalisation optique dans le circuit d'un synchrotron, augmenteront surement la résolution temporelle dans de telles expériences, menant nécessairement à un surplus de données. Nous avons déjà des solutions à ce problème, et des développements dans un futur rapproché permettront des décisions semi-automatiques à propos de quels prélèvements de données sont à retenir pour analyse, parmi les milliers qui sont enregistrés.(Traduit par la Rédaction)Mots-clés: rayonnement synchrotron, cristallographie, résolution temporelle, diffractio...

Crystal Structures and Topological Aspects of the High‐Temperature Phases and Decomposition Products of the Alkali‐Metal Oxalates M2[C2O4] (M=K, Rb, Cs)

“…The samples were contained in sealed quartz capillaries with diameters between 0.3 and 0.5 mm loaded in a sapphire tube of 0.8 mm diameter attached to a flowreaction cell. [26,27] The temperature was monitored and controlled by a 0.01 in thermocouple (Omega) which was inserted straight into the sapphire tube adjacent to, and in contact with, the sample capillary. The sample was aligned such that the sample closest to the thermocouple was in the X-ray beam path.…”

Study of Ion-Exchanged Microporous Lithosilicate Na–RUB-29 Using Synchrotron X-Ray Single-Crystal Diffraction and 6Li MAS NMR Spectroscopy

“…The ease with which ion-exchange occurs at these sites may depend on their locations, with cations located on larger, more accessible sites being more readily exchanged than those on smaller sites. Details of the crystal structure during the ionexchange process can help rationalize which sites are available for exchange and the mechanism by which exchange occurs (3)(4)(5)(6).…”

“…Recent studies of Li-bearing zeolitic materials (9,10) suggest that the location of different Li sites can be probed and the population determined quantitatively by using 6 Li and 7 Li MAS NMR spectroscopy. In particular, the location of the Li cations impacts directly on nitrogen absorption properties of the materials due to a strong interaction between Li cations and nitrogen molecules (11 SiO 4 and estimated their exchange rate with increasing temperature using high-resolution 6 Li MAS NMR techniques. Feuerstein and Lobo investigated zeolite LiLSX (Li-exchanged low-silica X) using 6 Li and 7 Li MAS NMR in combination with neutron diffraction analysis (13).…”

“…In particular, the location of the Li cations impacts directly on nitrogen absorption properties of the materials due to a strong interaction between Li cations and nitrogen molecules (11 SiO 4 and estimated their exchange rate with increasing temperature using high-resolution 6 Li MAS NMR techniques. Feuerstein and Lobo investigated zeolite LiLSX (Li-exchanged low-silica X) using 6 Li and 7 Li MAS NMR in combination with neutron diffraction analysis (13). The three resolved 7 Li resonances of the dehydrated form of the material were assigned to three Li cation sites (SI 0 , SII, and SIII) located at different channel positions.…”

“…While NMR is a sensitive tool for the determination of Li mobility and site population, all attempts to distinguish non-framework and framework Li cation sites in microporous lithosilicates by 6 Li-and 7 Li NMR spectroscopy to date were unsuccessful (1,15,16). The 6 Li-and 7 Li spectra displayed only one resonance at around 0 ppm and a series of low-temperature experiments with dehydrated microporous lithosilicate samples (from 01C to À1501C) did not improve the resolution, even when oxygen was loaded into samples (16).…”