SURFACE SEGREGATION STUDIES OF SOFC CATHODES: COMBINING SOFT X-RAYS AND ELECTROCHEMICAL IMPEDENCE SPECTROSCOPY

AbstractA system to grow heteroepitaxial thin-films of solid oxide fuel cell (SOFC) cathodes on single crystal substrates was developed. The cathode composition investigated was 20% strontium-doped lanthanum manganite (LSM) grown by pulsed laser deposition (PLD) on single crystal (111) yttria-stabilized zirconia (YSZ) substrates. By combining electrochemical impedance spectroscopy (EIS) with x-ray photoemission spectroscopy (XPS) and x-ray absorption spectroscopy XAS measurements, we conclude that electrically driven cation migration away from the two-phase gas-cathode interface results in improved electrochemical performance. Our results provide support to the premise that the removal of surface passivating phases containing Sr2+ and Mn2+, which readily form at elevated temperatures even in O2 atmospheric pressures, is responsible for the improved cathodic performance upon application of a bias.

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A single crystal, linearly polarized Fe 2p X-ray absorption study of gillespite

Mineralogical Magazine ◽

10.1180/002646198547477 ◽

1998 ◽

Vol 62 (1) ◽

pp. 65-75 ◽

Cited By ~ 7

Author(s):

P. F. Schofield ◽

G. van der Laan ◽

C. M. B. Henderson ◽

G. Cressey

Keyword(s):

Single Crystal ◽

Ground State ◽

Branching Ratio ◽

Linear Dichroism ◽

Electronic Charge ◽

Magic Angle ◽

X Rays ◽

X Ray ◽

Peak Structure ◽

X Ray Absorption

AbstractThe Fe 2p X-ray absorption spectra of single crystal gillespite, BaFeSi4O10, show a strong linear dichroism, i.e. a large difference in the absorption when measured with the polarization of the X-rays either parallel or perpendicular to the plane of the FeO4 group. The isotropic spectrum, obtained from measurement at the ‘magic angle’, and the polarization dependent spectra have been compared to atomic multiplet calculations and show an excellent agreement with theory. Analysis of the branching ratio, the linear dichroism, and the detailed peak structure confirms that the 5A1 level is the ground state at room temperature and pressure. The 5B2 level is sufficiently low in energy that a distortion of the electronic charge density, induced by increased pressure, may result in a 5B2 ground state.

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Diffraction of X-rays by crystals at elevated temperatures

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1939.0094 ◽

1939 ◽

Vol 172 (948) ◽

pp. 116-126 ◽

Cited By ~ 30

Keyword(s):

Single Crystal ◽

Theoretical Investigation ◽

Elevated Temperatures ◽

Chemical Change ◽

Age Hardening ◽

Effect Of Temperature ◽

Pure Aluminium ◽

X Rays ◽

X Ray

During an investigation of age-hardening of an alloy of aluminium with 4% copper, a large number of Laue photographs was taken and attention was directed to certain anomalous streaks on these photographs which altered as the process of hardening took place (Preston 1938). In addition to these streaks, which were associated with the chemical change in the crystal, there were others which did not seem to change with the hardness and which were also present on photographs of aluminium. A further investigation showed that when a single crystal of the alloy or of pure aluminium was photographed at a temperature of about 550° C, the intensity of these streaks was greatly increased. The purpose of the present paper is to give a description of this effect which has now also been observed in crystals of rocksalt, periclase, diamond and zinc. The presence of streaks running through the normal reflexions is a commonplace on Laue photographs; they were observed 25 years ago by Friedrich (1913) in photographs of KCl and NaCl. Ten years later Faxén (1923), in a theoretical investigation of the effect of temperature on the intensity of X-ray reflexion, referred to Friedrich’s observations and suggested that an attempt should be made to correlate these streaks with the temperature of the crystal. So far as I am aware this suggestion has never been carried out. The experiments described below show that Faxén was correct in his surmise that the streaks are connected with the temperature of the crystal.

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X-Ray absorption edge elemental imaging of B. thuringienis

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153038 ◽

1989 ◽

Vol 47 ◽

pp. 212-213

Author(s):

R. L. Stears

Keyword(s):

Absorption Edge ◽

Elemental Distribution ◽

X Rays ◽

Differential Absorption ◽

Synchrotron Source ◽

High Brightness ◽

X Ray ◽

Elemental Imaging ◽

Cellular Integrity ◽

X Ray Absorption

Because of the nature of the bacterial endospore, little work has been done on analyzing their elemental distribution and composition in the intact, living, hydrated state. The majority of the qualitative analysis entailed intensive disruption and processing of the endospores, which effects their cellular integrity and composition.Absorption edge imaging permits elemental analysis of hydrated, unstained specimens at high resolution. By taking advantage of differential absorption of x-ray photons in regions of varying elemental composition, and using a high brightness, tuneable synchrotron source to obtain monochromatic x-rays, contact x-ray micrographs can be made of unfixed, intact endospores that reveal sites of elemental localization. This study presents new data demonstrating the application of x-ray absorption edge imaging to produce elemental information about nitrogen (N) and calcium (Ca) localization using Bacillus thuringiensis as the test specimen.

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Al-driven peculiarities of local coordination and magnetic properties in single-phase Alx-CrFeCoNi high-entropy alloys

Nano Research ◽

10.1007/s12274-021-3704-5 ◽

2021 ◽

Author(s):

Alevtina Smekhova ◽

Alexei Kuzmin ◽

Konrad Siemensmeyer ◽

Chen Luo ◽

Kai Chen ◽

...

Keyword(s):

Magnetic Properties ◽

Single Phase ◽

Magnetic Circular Dichroism ◽

Surface Region ◽

Face Centered Cubic ◽

X Rays ◽

X Ray ◽

High Entropy ◽

X Ray Absorption ◽

Absorption Edges

AbstractModern design of superior multi-functional alloys composed of several principal components requires in-depth studies of their local structure for developing desired macroscopic properties. Herein, peculiarities of atomic arrangements on the local scale and electronic states of constituent elements in the single-phase face-centered cubic (fcc)- and body-centered cubic (bcc)-structured high-entropy Alx-CrFeCoNi alloys (x = 0.3 and 3, respectively) are explored by element-specific X-ray absorption spectroscopy in hard and soft X-ray energy ranges. Simulations based on the reverse Monte Carlo approach allow to perform a simultaneous fit of extended X-ray absorption fine structure spectra recorded at K absorption edges of each 3d constituent and to reconstruct the local environment within the first coordination shells of absorbers with high precision. The revealed unimodal and bimodal distributions of all five elements are in agreement with structure-dependent magnetic properties of studied alloys probed by magnetometry. A degree of surface atoms oxidation uncovered by soft X-rays suggests different kinetics of oxide formation for each type of constituents and has to be taken into account. X-ray magnetic circular dichroism technique employed at L2.3 absorption edges of transition metals demonstrates reduced magnetic moments of 3d metal constituents in the sub-surface region of in situ cleaned fcc-structured Al0.3-CrFeCoNi compared to their bulk values. Extended to nanostructured versions of multicomponent alloys, such studies would bring new insights related to effects of high entropy mixing on low dimensions.

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Synchrotron X-ray induced acoustic imaging

Scientific Reports ◽

10.1038/s41598-021-83604-3 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Seongwook Choi ◽

Eun-Yeong Park ◽

Sinyoung Park ◽

Jong Hyun Kim ◽

Chulhong Kim

Keyword(s):

Acoustic Imaging ◽

Signal Frequency ◽

X Rays ◽

Repetition Period ◽

Linear Accelerators ◽

X Ray ◽

X Ray Computed ◽

Medical Linear Accelerators ◽

Ionizing Radiation Exposure ◽

X Ray Absorption

AbstractX-ray induced acoustic imaging (XAI) is an emerging biomedical imaging technique that can visualize X-ray absorption contrast at ultrasound resolution with less ionizing radiation exposure than conventional X-ray computed tomography. So far, medical linear accelerators or industrial portable X-ray tubes have been explored as X-ray excitation sources for XAI. Here, we demonstrate the first feasible synchrotron XAI (sXAI). The synchrotron generates X-rays, with a dominant energy of 4 to 30 keV, a pulse-width of 30 ps, a pulse-repetition period of 2 ns, and a bunch-repetition period of 940 ns. The X-ray induced acoustic (XA) signals are processed in the Fourier domain by matching the signal frequency with the bunch-repetition frequency. We successfully obtained two-dimensional XA images of various lead targets. This novel sXAI tool could complement conventional synchrotron applications.

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Semi-automated protein crystal mounting device for the sulfur single-wavelength anomalous diffraction method

Journal of Applied Crystallography ◽

10.1107/s0021889809054272 ◽

2010 ◽

Vol 43 (2) ◽

pp. 341-346 ◽

Cited By ~ 14

Author(s):

Yu Kitago ◽

Nobuhisa Watanabe ◽

Isao Tanaka

Keyword(s):

Diffraction Method ◽

Systematic Errors ◽

Protein Crystal ◽

X Rays ◽

Anomalous Diffraction ◽

X Ray ◽

Frozen Solution ◽

Custom Made ◽

Protein Molecules ◽

X Ray Absorption

Use of longer-wavelength X-rays has advantages for the detection of small anomalous signals from light atoms, such as sulfur, in protein molecules. However, the accuracy of the measured diffraction data decreases at longer wavelengths because of the greater X-ray absorption. The capillary-top mounting method (formerly the loopless mounting method) makes it possible to eliminate frozen solution around the protein crystal and reduces systematic errors in the evaluation of small anomalous differences. However, use of this method requires custom-made tools and a large amount of skill. Here, the development of a device that can freeze the protein crystal semi-automatically using the capillary-top mounting method is described. This device can pick up the protein crystal from the crystallization drop using a micro-manipulator, and further procedures, such as withdrawal of the solution around the crystal by suction and subsequent flash freezing of the protein crystal, are carried out automatically. This device makes it easy for structural biologists to use the capillary-top mounting method for sulfur single-wavelength anomalous diffraction phasing using longer-wavelength X-rays.

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Lower resolution Laue neutron data yield correct nanocluster formulations

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s205327331409812x ◽

2014 ◽

Vol 70 (a1) ◽

pp. C187-C187

Author(s):

Alison Edwards

Keyword(s):

Neutron Diffraction ◽

Single Crystal ◽

Diffraction Pattern ◽

Precise Determination ◽

Data Sets ◽

X Rays ◽

Low Resolution ◽

Neutron Data ◽

X Ray ◽

Product Formulation

"The renaissance in Laue studies - at neutron sources - provides us with access to single crystal neutron diffraction data for synthetic compounds without requiring synthesis of prohibitively large amounts of compound or improbably large crystals. Such neutron diffraction studies provide vital data where proof of the presence or absence of hydrogen in particular locations is required and which cannot validly be proved by X-ray studies. Since the commissioning of KOALA at OPAL in 2009[1] we have obtained numerous data sets which demonstrate the vital importance of measuring data even where the extent of the diffraction pattern is at relatively low resolution - especially when compared to that obtainable for the same compound with X-rays. In the Laue experiment performed with a fixed radius detector, data reduction is only feasible for crystals in the ""goldilocks"" zone – where the unit cell is relatively large for the detector, a correspondingly low resolution diffraction pattern in which adjacent spots are less affected by overlap will yield more data against which a structure can be refined than a pattern of higher resolution – one where neighbouring spots overlap rendering both unusable (in our current methodology). Analogous application of powder neutron diffraction in such determinations is also considered. Single crystal neutron diffraction studies of several important compounds (up to 5KDa see figure below)[2] in which precise determination of hydride content by neutron diffraction was pivotal to the final formulation will be presented. The neutron data sets typically possess 20% or fewer unique data at substantially "lower resolution" than the corresponding X-ray data sets. Careful refinement clearly reveals chemical detail which is typically unexplored in related X-ray diffraction studies reporting high profile chemistry despite the synthetic route being one which hydride ought to be considered/excluded in product formulation."

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Anisotropy of X-ray Absorption Cross Section in CeCoGe3 Single Crystal

Crystals ◽

10.3390/cryst11050544 ◽

2021 ◽

Vol 11 (5) ◽

pp. 544

Author(s):

Andrei Rogalev ◽

Fabrice Wilhelm ◽

Elena Ovchinnikova ◽

Aydar Enikeev ◽

Roman Bakonin ◽

...

Keyword(s):

Cross Section ◽

Absorption Cross Section ◽

Linear Dichroism ◽

X Rays ◽

Absorption Cross ◽

X Ray ◽

Measured Absorption ◽

Linearly Polarized ◽

X Ray Absorption ◽

Absorption Edges

Absorption spectra of two orthogonal linearly polarized x-rays in a single CeCoGe3 crystal were measured at the ID12 beamline of the ESRF for the energies near the K-edges of Ge, Co and near the L23 edges of Ce. The X-ray natural linear dichroism (XNLD) was revealed in the vicinity of all the absorption edges, which indicates a splitting of electronic states in a crystalline field. Mathematical modelling in comparison with experimental data allowed the isotropic and anisotropic parts of atomic absorption cross section in CeCoGe3 to be determined near all measured absorption edges. The calculations also show that the “average” anisotropy of the cross section close to the Ge K-edge revealed in the experiment is less than the partial anisotropic contributions corresponding to Ge atoms in two different Wyckoff positions.

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