New Ultra High CIS Polybutadiene Through a Novel Neodymium Catalyst

2002 ◽  
Vol 75 (5) ◽  
pp. 907-922 ◽  
Author(s):  
Gwanghoon Kwag ◽  
Aju Kim ◽  
Seunghwon Lee ◽  
Youngchan Jang ◽  
Pillsung Kim ◽  
...  
Keyword(s):  
Density Functional ◽  
Density Functional Method ◽  
Physical And Mechanical Properties ◽  
Functional Method ◽  
Edge Structure ◽  
X Ray ◽  
Butadiene Polymerization ◽  
Monomeric Structure ◽  
Ultra High Cis Polybutadiene ◽  
X Ray Absorption

Abstract A significant improvement in the catalytic activity of Nd-based catalyst for 1,3-butadiene polymerization has been achieved using a novel neodymium compound, NdH(neodecanoate)4 (Nd( neodecanoate)3 (neodecanoic acid)). The neodymium compound was characterized with a matrix assisted laser desorption ionization (MALDI) mass spectroscopy, with a synchrotron X-ray absorption spectroscopy (XAS), and with computer simulations. A distinguished molecular ion peak (m/z=838.7, [M]) and a pronounced absorption edge are observed in the mass and in the Nd-LIII XANES(X-ray absorption near edge structure) spectra of NdH(neodecanoate)4, respectively, which evidence its monomeric structure. An active-center of the monomeric Nd-catalyst is fully optimized by density functional method (B3LYP/CEP-31G), in which neodymium(III) is coordinated with carboxylate, allylic active end, penultimate double bond, and chloride. The bond distances are Nd-C1 2.586 A˚, Nd-C4 2.741 A˚, Nd-C5 2.738 A˚, Nd-Cl 2.651 A˚, and Nd-O1 2.167 A˚, respectively. The Nd-catalyst shows a high activity (1.6×106 g/Nd md·h) and produces polybutadiene with 99% cis content. The ultra high cis polybutadiene produced by the Nd-catalyst exhibits excellent physical and mechanical properties such as high abrasion resistance, rebound, tensile properties and remarkably low heat build-up, which will greatly improve tire performance.

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 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.

Theoretical and Experimental Studies of Structural Defects in CeO2 Nanoparticles

2020 ◽  
Vol 312 ◽  
pp. 68-73
Author(s):  
Maxim A. Pugachevskii ◽  
Andrey N. Chibisov ◽  
A.P. Kuzmenko ◽  
Aleksandr S. Fedorov
Keyword(s):  
Density Functional ◽  
Oxygen Vacancies ◽  
Cell Parameter ◽  
Density Functional Method ◽  
Experimental Studies ◽  
Functional Method ◽  
Structural Defects ◽  
X Ray ◽  
Transmission Electron ◽  
Electron Energy Loss

The atomic structure and morphology of cerium oxide nanoparticles obtained by laser ablation are experimentally and theoretically investigated. Using transmission electron microscopy, X-ray diffractometry, and electron energy loss spectroscopy, it has been shown that particles are enriched in oxygen vacancies that stabilize their internal structure. The density functional method was used to study the dependence of the unit cell parameter of CeO2 nanoparticles on their size. An analysis of the charge density distribution shows a different structural distribution of Ce3+ and Ce4+ atoms in nanoparticles.

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.

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