scholarly journals Characterization of Pressure-induced Phase Transition on [Co(bpy)3](NO3)2·3H2O

2014 ◽  
Vol 70 (a1) ◽  
pp. C57-C57
Author(s):  
Ya-Wen Lee ◽  
Yu-Chun Chuang ◽  
Jyh-Fu Lee ◽  
Chi-Rung Lee ◽  
Chih-Ming Lin ◽  
...  
Keyword(s):  
Phase Transition ◽  
Raman Spectroscopy ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Spin Transition ◽  
Xrd Analysis ◽  
External Pressure ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

The pressure-induced phase transition study of high-spin (HS) compound, [Co(bpy)3](NO3)2·3H2O (bpy = 2,2'-bipyridine), is characterized by powder x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), Raman spectroscopy, and theoretical calculations. The results indicate that the HS ground state t2g5eg2 on Co(II) is gradually transformed to low-spin (LS) state with configuration t2g6eg1 . This phase transition behavior is similar to the thermal-induced spin crossover phenomenon once it is incorporated into certain framework. In this study, we put the compound into diamond anvil cell and applied physical pressure to replace the framework effect. To analyze the x-ray absorption near edge structure (XANES) and Raman spectroscopy, the finite difference method for near-edge structure (FDMNES) and density functional theory (DFT) calculations are applied to illustrate the experimental spectroscopies, respectively. In XANES results, an intersection point around 7756.33 eV beyond 1.73 GPa is assigned as the critical point between HS and LS state. The extended x-ray absorption fine structure (EXAFS) analysis indicates that the averaged Co-N bond lengths is 2.127(7) Å at HS state and decreased to 1.950(4) Å at LS state. Based on XRD analysis, the external pressure reduces the hexagonal cell constants from a = 13.77(3) Å and c = 21.71(3) Å to a = 13.37(5) Å and c = 21.11(1) Å. According to those experimental results, the mechanism of such pressure-induce spin transition can be interpreted as the enhancement of intermolecular interaction by increasing the external pressure.

scholarly journals Local and electronic structure around Ga in CdTe: evidence of DX- and A-centers

2012 ◽  
Vol 20 (1) ◽  
pp. 166-171
Author(s):  
Vasil Koteski ◽  
Jelena Belošević-Čavor ◽  
Petro Fochuk ◽  
Heinz-Eberhard Mahnke
Keyword(s):  
Density Functional ◽  
Plane Waves ◽  
Lattice Relaxation ◽  
Defect Structures ◽  
Functional Theory ◽  
Edge Structure ◽  
X Ray ◽  
First Time ◽  
X Ray Absorption ◽  
Good Agreement

The lattice relaxation around Ga in CdTe is investigated by means of extended X-ray absorption spectroscopy (EXAFS) and density functional theory (DFT) calculations using the linear augmented plane waves plus local orbitals (LAPW+lo) method. In addition to the substitutional position, the calculations are performed for DX- and A-centers of Ga in CdTe. The results of the calculations are in good agreement with the experimental data, as obtained from EXAFS and X-ray absorption near-edge structure (XANES). They allow the experimental identification of several defect structures in CdTe. In particular, direct experimental evidence for the existence of DX-centers in CdTe is provided, and for the first time the local bond lengths of this defect are measured directly.

X-ray absorption spectroscopy and density functional analysis of the Fe3+ distribution profile on Al sites in a chrysoberyl crystal, BeAl2O4:Fe3+

2016 ◽  
Vol 49 (2) ◽  
pp. 385-388 ◽  
Author(s):  
Kanokwan Kanchiang ◽  
Atipong Bootchanont ◽  
Janyaporn Witthayarat ◽  
Sittichain Pramchu ◽  
Panjawan Thanasuthipitak ◽  
...  
Keyword(s):  
Optical Properties ◽  
Absorption Spectroscopy ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Distribution Profile ◽  
Laser Applications ◽  
Edge Structure ◽  
X Ray ◽  
Site Distribution ◽  
X Ray Absorption

Chrysoberyl is one of the most interesting minerals for laser applications, widely used for medical purposes, as it exhibits higher laser performance than other materials. Although its utilization has been vastly expanded, the location of transition metal impurities, especially the iron that is responsible for chrysoberyl's special optical properties, is not completely understood. The full understanding and control of these optical properties necessitates knowledge of the precise location of the transition metals inside the structure. Therefore, synchrotron X-ray absorption spectroscopy (XAS), a local structural probe sensitive to the different local geometries, was employed in this work to determine the site occupation of the Fe3+ cation in the chrysoberyl structure. An Fe K-edge X-ray absorption near-edge structure (XANES) simulation was performed in combination with density functional theory calculations of Fe3+ cations located at different locations in the chrysoberyl structure. The simulated spectra were then qualitatively compared with the measured XANES features. The comparison indicates that Fe3+ is substituted on the two different Al2+ octahedral sites with the proportion 60% on the inversion site and 40% on the reflection site. The accurate site distribution of Fe3+ obtained from this work provides useful information on the doping process for improving the efficiency of chrysoberyl as a solid-state laser material.

scholarly journals A High-Pressure Investigation of the Synthetic Analogue of Chalcomenite, CuSeO3∙2H2O

Crystals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 643 ◽  
Author(s):  
Javier Gonzalez-Platas ◽  
Placida Rodriguez-Hernandez ◽  
Alfonso Muñoz ◽  
U. R. Rodríguez-Mendoza ◽  
Gwilherm Nénert ◽  
...  
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
Raman Spectroscopy ◽  
Pressure Dependence ◽  
Density Functional ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Raman Modes

Synthetic chalcomenite-type cupric selenite CuSeO3∙2H2O has been studied at room temperature under compression up to pressures of 8 GPa by means of single-crystal X-ray diffraction, Raman spectroscopy, and density-functional theory. According to X-ray diffraction, the orthorhombic phase undergoes an isostructural phase transition at 4.0(5) GPa with the thermodynamic character being first-order. This conclusion is supported by Raman spectroscopy studies that have detected the phase transition at 4.5(2) GPa and by the first-principles computing simulations. The structure solution at different pressures has provided information on the change with pressure of unit–cell parameters as well as on the bond and polyhedral compressibility. A Birch–Murnaghan equation of state has been fitted to the unit–cell volume data. We found that chalcomenite is highly compressible with a bulk modulus of 42–49 GPa. The possible mechanism driving changes in the crystal structure is discussed, being the behavior of CuSeO3∙2H2O mainly dominated by the large compressibility of the coordination polyhedron of Cu. On top of that, an assignation of Raman modes is proposed based upon density-functional theory and the pressure dependence of Raman modes discussed. Finally, the pressure dependence of phonon frequencies experimentally determined is also reported.

Hydrogenation Effects of Ultrananocrystalline Diamond Detected by X-ray Absorption Near Edge Structure and Raman Spectroscopy

2012 ◽  
Vol 51 (9R) ◽  
pp. 095201 ◽  
Author(s):  
Sekhar C. Ray ◽  
Rudolph M. Erasmus ◽  
H. M. Tsai ◽  
C. W. Pao ◽  
I.-N. Lin ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Edge Structure ◽  
X Ray ◽  
Ultrananocrystalline Diamond ◽  
X Ray Absorption

scholarly journals A Deep Neural Network for the Rapid Prediction of X-ray Absorption Spectra

2020 ◽  
Author(s):  
Conor Rankine ◽  
Marwah Madkhali ◽  
Thomas Penfold
Keyword(s):  
Neural Network ◽  
Absorption Spectra ◽  
Deep Neural Network ◽  
Theoretical Calculations ◽  
End Users ◽  
Supervised Machine Learning ◽  
Strong Impact ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

<p>X-ray spectroscopy delivers strong impact across the physical and biological sciences by providing end-users with highly-detailed information about the electronic and geometric structure of matter. To decode this information in challenging cases, e.g. <i>in operando</i> catalysts, batteries, and temporally-evolving systems, advanced theoretical calculations are necessary. The complexity and resource requirements often render these out of reach for end-users, and therefore data are often not interpreted exhaustively, leaving a wealth of valuable information unexploited. In this paper, we introduce supervised machine learning of X-ray absorption spectra, by developing a deep neural network (DNN) that is able to estimate Fe K-edge X-ray absorption near-edge structure spectra in less </p><p>than a second with no input beyond geometric information about the local environment of the absorption site. We predict peak positions with sub-eV accuracy and peak intensities with errors over an order of magnitude smaller than the spectral variations that the model is engineered to capture. The performance of the DNN is promising, as illustrated by its application to the structural refinement of iron(II)tris(bipyridine) and nitrosylmyoglobin, but also highlights areas for which future developments should focus.</p>

The Structural Characterization of a Series of Uranium-containing Gadolinium Zirconates

2012 ◽  
Vol 1475 ◽  
Author(s):  
Daniel J. Gregg ◽  
Yingjie Zhang ◽  
Zhaoming Zhang ◽  
Inna Karatchevtseva ◽  
Mark G. Blackford ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Diffuse Reflectance ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
Edge Structure ◽  
Gadolinium Zirconate ◽  
X Ray ◽  
Host Materials ◽  
X Ray Absorption

ABSTRACTA series of uranium-containing gadolinium zirconate samples have been fabricated at 1723 K in air. X-ray diffraction and Raman spectroscopy have confirmed pyrochlore or defect fluorite structures, while diffuse reflectance, X-ray absorption near edge structure and X-ray photoelectron spectroscopies indicate a predominantly U6+ oxidation state, even when Ca2+ was added to charge balance for U4+. The results demonstrate the potential of gadolinium zirconates as host materials for actinides.

scholarly journals Oxygen vacancies induced photoluminescence in $$\hbox {SrZnO}_2$$ nanophosphors probed by theoretical and experimental analysis

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Manju ◽  
Megha Jain ◽  
Saibabu Madas ◽  
Pargam Vashishtha ◽  
Parasmani Rajput ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Band Structure ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Defect States ◽  
Functional Theory ◽  
Edge Structure ◽  
X Ray ◽  
New Energy ◽  
X Ray Absorption

Abstract We report, for the first time, the influence of oxygen vacancies on band structure and local electronic structure of $$\hbox {SrZnO}_2$$ SrZnO 2 (SZO) nanophosphors by combined first principle calculations based on density functional theory and full multiple scattering theory, correlated with experimental results obtained from X-ray absorption and photoluminescence spectroscopies. The band structure analysis from density functional theory revealed the formation of new energy states in the forbidden gap due to introduction of oxygen vacancies in the system, thereby causing disruption in intrinsic symmetry and altering bond lengths in SZO system. These defect states are anticipated as origin of observed photoluminescence in SZO nanophosphors. The experimental X-ray absorption near edge structure (XANES) at Zn and Sr K-edges were successfully imitated by simulated XANES obtained after removing oxygen atoms around Zn and Sr cores, which affirmed the presence and signature of oxygen vacancies on near edge structure.

Soft X-ray excited colour-centre luminescence and XANES studies of calcium oxide

2007 ◽  
Vol 85 (10) ◽  
pp. 853-858 ◽  
Author(s):  
JY Peter Ko ◽  
Franziskus Heigl ◽  
Yun Mui Yiu ◽  
Xing-Tai Zhou ◽  
Tom Regier ◽  
...  
Keyword(s):  
Calcium Oxide ◽  
Density Functional ◽  
X Rays ◽  
Colour Centre ◽  
Time Resolved ◽  
Edge Structure ◽  
Colour Centres ◽  
X Ray ◽  
Optical Luminescence ◽  
X Ray Absorption

In this study, we show that colour centres can be produced by irradiating calcium oxide with soft X-rays from a synchrotron radiation source. Using the X-ray excited optical luminescence (XEOL) technique, two colour centres, F-centre, and F+-centre can be identified. These colour centres emit photons at characteristic wavelengths. In addition, by performing time-resolved XEOL (TRXEOL), we are able to reveal timing and decay characteristics of the colour centres. We also present X-ray absorption near-edge structure (XANES) spectra collected across oxygen K-edge, calcium L3,2-edge, and calcium K-edge. Experimental results are compared with density functional theory (DFT) calculations.Key words: calcium oxide, colour centre, synchrotron, X-ray excited optical luminescence, X-ray absorption near-edge structure.

scholarly journals The Role of Structural Representation in the Performance of a Deep Neural Network for X-ray Spectroscopy

Molecules ◽  
2020 ◽  
Vol 25 (11) ◽  
pp. 2715
Author(s):  
Marwah M.M. Madkhali ◽  
Conor D. Rankine ◽  
Thomas J. Penfold
Keyword(s):  
Neural Network ◽  
Deep Neural Network ◽  
Mean Squared Error ◽  
Chemical Space ◽  
Theoretical Calculations ◽  
Local Environment ◽  
Structural Representation ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

An important consideration when developing a deep neural network (DNN) for the prediction of molecular properties is the representation of the chemical space. Herein we explore the effect of the representation on the performance of our DNN engineered to predict Fe K-edge X-ray absorption near-edge structure (XANES) spectra, and address the question: How important is the choice of representation for the local environment around an arbitrary Fe absorption site? Using two popular representations of chemical space—the Coulomb matrix (CM) and pair-distribution/radial distribution curve (RDC)—we investigate the effect that the choice of representation has on the performance of our DNN. While CM and RDC featurisation are demonstrably robust descriptors, it is possible to obtain a smaller mean squared error (MSE) between the target and estimated XANES spectra when using RDC featurisation, and converge to this state a) faster and b) using fewer data samples. This is advantageous for future extension of our DNN to other X-ray absorption edges, and for reoptimisation of our DNN to reproduce results from higher levels of theory. In the latter case, dataset sizes will be limited more strongly by the resource-intensive nature of the underlying theoretical calculations.

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