1,013 research outputs found
Angular dependence of core hole screening in LiCoO2: A DFT+U calculation of the oxygen and cobalt K-edge x-ray absorption spectra
Angular dependent core-hole screening effects have been found in the cobalt
K-edge x-ray absorption spectrum of LiCoO2, using high-resolution data and
parameter-free GGA+U calculations. The Co 1s core-hole on the absorber causes
strong local attraction. The core-hole screening on the nearest neighbours
cobalt induces a 2 eV shift in the density of states with respect to the
on-site 1s-3d transitions, as detected in the Co K pre-edge spectrum. Our DFT+U
calculations reveal that the off-site screening is different in the
out-of-plane direction, where a 3 eV shift is visible in both calculations and
experiment. The detailed analysis of the inclusion of the core-hole potential
and the Hubbard parameter U shows that the core-hole is essential for the
off-site screening, while U improves the description of the angular dependent
screening effects. In the case of oxygen K-edge, both the core-hole potential
and the Hubbard parameter improve the relative positions of the spectral
features
Стан збереження та проблеми охорони культурної спадщини на Путивльщині
In a 2010 paper Aziz, Chergui and colleagues observe fluorescence yield (FY) detected X-ray absorption spectra that are concentration-dependent and show both dips and peaks. In this comment I will show that all observed spectral features are a consequence of the relative ratio of background and edge emission, combined with energy-dependent X-ray emission decay channels
Atomic and itinerant effects at the transition metal x-ray absorption K-pre-edge exemplified in the case of VO
X-ray absorption spectroscopy is a well established tool for obtaining
information about orbital and spin degrees of freedom in transition metal- and
rare earth-compounds. For this purpose usually the dipole transitions of the L-
(2p to 3d) and M- (3d to 4f) edges are employed, whereas higher order
transitions such as quadrupolar 1s to 3d in the K-edge are rarely studied in
that respect. This is due to the fact that usually such quadrupolar transitions
are overshadowed by dipole allowed 1s to 4p transitions and, hence, are visible
only as minor features in the pre-edge region. Nonetheless, these features
carry a lot of valuable information, similar to the dipole L-edge transition,
which is not accessible in experiments under pressure due to the absorption of
the diamond anvil pressurecell. We recently performed a theoretical and
experimental analysis of such a situation for the metal insulator transition of
(V(1-x)Crx)2O3. Since the importance of the orbital degrees of freedom in this
transition is widely accepted, a thorough understanding of quadrupole
transitions of the vanadium K-pre-edge provides crucial information about the
underlying physics. Moreover, the lack of inversion symetry at the vanadium
site leads to onsite mixing of vanadium 3d- and 4p- states and related quantum
mechanical interferences between dipole and quadrupole transitions. Here we
present a theoretical analysis of experimental high resolution x-ray absorption
spectroscopy at the V pre-K edge measured in partial fluorescence yield mode
for single crystals. We carried out density functional as well as configuration
interaction calculations in order to capture effects coming from both,
itinerant and atomic limits
Origin of the high Seebeck coefficient of the misfit [CaCoO][CoO] cobaltate from site-specific valency and spin-state determinations
Layered misfit cobaltate [CaCoO][CoO], which emerged as
an important thermoelectric material~[A. C. Masset et al. Phys. Rev. B, 62, 166
(2000)], has been explored extensively in the last decade for the exact
mechanism behind its high Seebeck coefficient. Its complex crystal and
electronic structures have inhibited consensus among such investigations. This
situation has arisen mainly due to difficulties in accurate identification of
the chemical state, spin state, and site symmetries in its two subsystems
(rocksalt [CaCoO] and triangular [CoO]). By employing resonant
photoemission spectroscopy and x-ray absorption spectroscopy along with charge
transfer multiplet simulations (at the Co ions), we have successfully
identified the site symmetries, valencies and spin states of the Co in both
layers. Our site-symmetry observations explain the experimental value of the
high Seebeck coefficient and also confirm that the carriers hop within the
rocksalt layer, which is in contrast to earlier reports where hopping within
triangular CoO layer has been held responsible for the large Seebeck
coefficient.Comment: 5 pages, 4 figures and 1 supplementary with 3 figure
Сучасний університет в умовах викликів глобалізованого світу
In this work, three industrially relevant zeolites with framework topologies of MOR, FAU and FER have been explored on their ability to form an AlPO4 phase by reaction of a phosphate precursor with expelled framework aluminum. A detailed study was performed on zeolite H-mordenite, using in situ STXM and soft X-ray absorption tomography, complemented with 27Al and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, XRD, FT-IR spectroscopy, and N2 physisorption. Extraframework aluminum was extracted from steam-dealuminated H-mordenite and shown to dominantly consist of amorphous AlO(OH). It was found that phosphoric acid readily reacts with the AlO(OH) phase in dealuminated H-mordenite and forms an extraframework amorphous AlPO4 phase. It was found that while AlPO4 crystallizes outside of the zeolitic channel system forming AlPO4 islands, AlPO4 that remains inside tends to stay more amorphous. In the case of ultrastable zeolite Y the FAU framework collapsed during phosphatation, due to extraction of framework aluminum from the lattice. However, using milder phosphatation conditions an extraframework AlPO4 α-cristobalite/tridymite phase could also be produced within the FAU framework. Finally, in steamed zeolite ferrierite with FER topology the extraframework aluminum species were trapped and therefore not accessible for phosphoric acid; hence, no AlPO4 phase could be formed within the structure. Therefore, the parameters to be taken into account in AlPO4 synthesis are the framework Si/Al ratio, stability of framework aluminum, pore dimensionality and accessibility of extraframework aluminum species
Теоретичні та практичні аспекти приватизації в Україні
Цели статьи заключаются в изучении спроса покупателей на объекты приватизации и анализе финансового состояния предприятий к принятию решения
об их приватизации (на основе данных за I квартал 2006 года), раскрытии основных критериев целесообразности принятия решения о приватизации объектов ведения хозяйства.Цілі статті полягають у вивченні попиту покупців на об'єкти приватизації та
аналізі фінансового стану підприємств до прийняття рішення про їх приватизацію (на основі даних за I квартал 2006 року), розкритті основних критеріїв
доцільності прийняття рішення про приватизацію об'єктів господарювання
Регіональні аспекти удосконалення системи управління персоналом на державній службі
У статті розкривається суть регіональних вимірів удосконалення системи управління персоналом на державній службі та висвітлюється досвід Управління державної служби Головдержслужби України в Миколаївській області на шляху до прозорості влади і залучення громадськості до державотворення.The article reveals the essence of regional measurements of improvement the HR Management system in the civil service and reports the experience of the Office of Civil Service of The Main Department of Civil Service of Ukraine in the Mykolaiv region towards transparency in government and public involvement in the nation
- …