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1.
The calculations of clusters modeling the fluorine-doping and oxygen deficiency of YBa2Cu3O2,have been performed by the method of all-electron ab initio Hartree-Fock with self-consistent crystal field Results show that in CuO planes electric charge significantly increases,the chemical valence of Cu decreases and the covalent bonding of Cu-O greatly weakens owing to oxygen deficiency,while the effect of F restores the local electronic structure of YBa2Cu3O7 The reported opinion that F occupied the oxygen vacancy in Cu-O chains seems disputable according to the calculated bonding characteristics. 相似文献
2.
Ansgar Schäfer Christian Huber Jürgen Gauss Reinhart Ahlrichs 《Theoretical chemistry accounts》1993,87(1-2):29-40
Summary Experimentally known copper selenium clusters show extraordinary geometrical features, especially short Cu-Cu distances. We report the first theoretical investigation of Cu2Se and Cu4Se2. Various quantum chemical methods (SCF, MP2, CPF, CCSD, CCSD(T), LDF) are applied to determine the importance of dynamic electron correlation. We find that inclusion of correlation does not essentially change the electronic structure of the clusters but has a strong influence on geometries. To reduce the computational effort we apply effective core potentials (ECPs) in combination with small, but carefully optimized basis sets. The applicability of simple modellings of correlation energies for approximate inclusion of correlation effects in SCF geometry optimizations is tested. 相似文献
3.
The conformational properties of methanesulfonyl peroxynitrate, CH3S(O)2OONO2 (MSPN), and its radical decomposition products CH3S(O)2OO· and CH3S(O)2O· were studied by ab initio and density functional methods. The dihedral angle around the S–O and the O–O single bond are calculated to be ?70.5° and ?97.8° (B3LYP/6‐311++G(3df,3pd)), respectively. The principal unimolecular dissociation pathways for MSPN were studied using complete basis set (CBS) methods. The reaction enthalpies for the channels CH3S(O)2OONO2→ CH3S(O)2OO·+NO2 and CH3S(O)2OONO2→CH3S(O)2O·+NO3 were computed to be 111.0 and 140.9 kJ/mol, respectively. The enthalpies of formation at 298 K for MSPN and CH3S(O)2OO radical were predicted to be ?358.2 and ?281.3 kJ/mol, respectively. 相似文献
4.
Shinobu Fujihara Hiromitsu Kozuka Toshinobu Yoko Sumio Sakka 《Journal of Sol-Gel Science and Technology》1994,1(2):133-140
It was shown that a single phase YBa2Cu4O8 (124-phase) could be formed from gels at 1 atm oxygen pressure, and the mechanism of its formation was elucidated. It was found that there are two key routes for the sol-gel formation of the 124-phase, one involving the tetragonal YBa2Cu3O
y
with a low concentration of oxygen defects (tetra-I phase) and the other involving the Ba2Cu3O5.9 as important intermediates of the 124-phase. The rapid formation of these intermediate compounds from the gel was attributed to the small particle size of the oxides and carbonates precipitating at the initial stage of heating. It was thought that the small particles characteristic of sol-gel processing lead to the rapid formation of the intermediate compounds and subsequent precipitation of the 124-phase. 相似文献
5.
Hui-Zhou Liu Zhen-Hua Xu Shi-Fu Weng Wei-Jin Zhou Hai Guo Ying-Zhang Lin Jia-Fu Wang Fuo-An Liu Duan-Fu Xu Jin-Guang Wu Guang-Xian Xu 《Mikrochimica acta》1988,95(1-6):369-372
An investigation of FT far IR spectra of YBa2Cu3Ox highT
c
superconductor and Ln-Ba-Cu-O systems were carried out at room and liquid nitrogen temperature, respectively. It indicated that the intensity of the IR bands reduces dramatically as the samples transform into superconductor. However, reliable spectra can be obtained from the sintered film samples directly. 相似文献
6.
Phase diagrams for cuprates of alkaline earth and rare earth elements are presented, covering binary to quintenary oxides and including selected solid solution series with other elements. Elementary crystal chemical data are included for identification of the occurring phases. Chemical stability is discussed with respect to the high-temperature reactions with Lewis acids like CO2, protons, etc. Particularly the occurrence of oxide carbonates is consistently pointed out as one of the possible reasons for contradictory results in phase diagrams which comprise oxides with high basicity. 相似文献
7.
Xing Liu 《Molecules (Basel, Switzerland)》2021,26(1)
Unlike the usual method of COx (x = 1, 2) hydrogenation using H2 directly, H2S and HSiSH (silicon-activated H2S) were selected as alternative hydrogen sources in this study for the COx hydrogenation reactions. Our results suggest that it is kinetically infeasible for hydrogen in the form of H2S to transfer to COx at low temperatures. However, when HSiSH is employed instead, the title reaction can be achieved. For this approach, the activation of CO2 is initiated by its interaction with the HSiSH molecule, a reactive species with both a hydridic Hδ− and protonic Hδ+. These active hydrogens are responsible for the successive C-end and O-end activations of CO2 and hence the final product (HCOOH). This finding represents a good example of an indirect hydrogen source used in CO2 hydrogenation through reactivity tuned by silicon incorporation, and thus the underlying mechanism will be valuable for the design of similar reactions. 相似文献
8.
J. Horn H. -Ch. Semmelhack H. Börner F. Schlenkrich 《Journal of Thermal Analysis and Calorimetry》1994,41(5):995-1005
We propose a reaction model for the synthesis of YBa2Cu4O8 under normal pressure conditions, which contains 4 partial reaction steps. In a first step bariumnitrate and copperoxide react to Ba2Cu3O5+δ. This substance will be formed for each mixtures Ba:Cu=2∶3...3∶2. The following two partial reaction steps are connected to Ba2Cu3O5+δ, which reacts with Y2O3 and CuO to YBa2Cu4O8 or decomposes to BaCuO2 and CuO. In a last step parts of BaCuO2 reacts with Y2O3 and CuO to YBa2Cu4O8. 相似文献
9.
Z. Hegedüs 《Journal of Thermal Analysis and Calorimetry》1995,43(2):461-468
Solid state reactions at 925°C between the high-T c ceramic superconductor YBa2Cu3O7?δ and La2O3 and SrCO3, respectively, mixed in various molar ratiosr=MeOn/YBa2Cu3O7?δ, were studied using X-ray powder diffraction and scanning electron microscopy. The reaction between YBa2Cu3O7?δ and La2O3 yielded (La1?xBax)2CuO4?δ, withx≈0.075?0.10. La2?xBa1+xCu2O6?δ, withx≈0.2?0.25 and La-doped (Y1?xLax)2BaCuO5, withx≈0.10?0.15. Forr=3.0, Y-doped La2BaCuO5 resulted also. The reaction between YBa2Cu3O7?δ and SrCO3 yielded (Sr1?zBaz)2CuO3, withz≈0.1, Y2(Ba1?zSrz)CuO5, withz=0.1?0.15, and a nonsuperconducting compound with an approximate composition of Y(Ba0.5Sr0.5)5Cu3.5O10±δ. At values ofr≤2.0, unsubstituted YBa2Cu3O7?delta was found in the reaction products. 相似文献
10.
Summary By use of an approximate band-structure treatment based on the EHMO approach, the energy band structures for the Zn-doped superconductor YBa2Cu3–x
Zn
x
O
y
were calculated in the present paper and the influence of partial substitution of zinc for copper on the electronic structures for orthorhombic YBa2Cu3Oy was studied. From analysis of the band structures and the densities of states for YBa2Cu3–x
Zn
x
O
y
, it was demonstrated that the 2D Cu-O planes in the Y-Ba-Cu-O superconducting system have a direct and dominant influence on superconductivity, whereas the role of the 1D Cu-O ribbons and the O(4) atoms is also of some importance. 相似文献
11.
用电泳法在厚度为5 mm×10 mm×0.5 mm的YBa2Cu3O7-δ上沉积厚约70 μm的 La0.8Te0.2MnO3 形成La0.8Te0.2MnO3/YBa2Cu3O7-δ (F/S)双层结构. 通过扫描电子显微镜观察双层结构剖面的形貌, 采用标准的四引线法测量YBa2Cu3O7-δ层的电阻特性. 在F/S双层结构中通入1 mA的注入电流, 无论电流从S层流入F层( Iinj), 或者电流从F层流入S层(-Iinj), 正常电阻均比未加注入电流时的电阻低; 超导转变温度均比未加注入电流的转变温度高. 相似文献
12.
Maria Ochsenkühn-Petropulu Petros Tarantilis John Tsarouchis Klaus Ochsenkühn George Parissakis 《Mikrochimica acta》1998,129(3-4):233-238
Large area coatings (>10cm2) of the high temperature superconductor YBa2Cu3O7–x (x = 0.1 – 0.2) (YBCO) have been prepared by scale up an electrophoretic deposition technique using silver sheets and Si-wafers coated with Ag or Au as substrates. Several parameters, like the kind of the solvent, the applied voltage, the distance between the electrodes, the initial concentration of the suspension and the temperature during the electrophoresis were investigated in order to attain high deposition rates, as well as uniform YBCO coatings with the proper stoichiometry. To obtain a strongly adherent and dense coating a subsequent appropriate sintering and annealing procedure has been developed. The coatings obtained were characterized for their stoichiometry and superconducting properties by X-ray diffraction (XRD), Raman spectroscopy and magnetic measurements. The homogeneity and thickness of the films and the average grain size of the deposited particles have been investigated by optical and scanning electron microscopy (SEM). 相似文献
13.
J. C. Park A. Wattiaux J.-C. Grenier K. Frhlich P. Dordor M. Pouchard P. Hagenmuller 《无机化学与普通化学杂志》1992,608(2):153-158
An appropriate treatment called “Vacuum-Oxygen Cycle” (V.O.C.) has been carried out in order to obtain highly densified YBa2Cu3O7-δceramics. The obtained materials exhibit a homogeneous oxygen distribution and their feature have been characterized using relevant physical measurements. Preliminary electrochemical experiments have been performed and this treatment seems to improve their superconducting properties. 相似文献
14.
《Comptes Rendus Chimie》2015,18(9):935-944
Peracetylated d-glucopyranose has a high solubility in CO2 and can be a promising phase-change physical solvent or absorbent for CO2, as reported recently. However, peracetylated d-glucopyranose is unstable under acidic atmospheres, especially in sulfur-containing waste gases, and the possibly major decomposition products are 2,3,4,6-tetra-O-acetyl-d-glucopyranose, 1-thiol-d-glucopyranose tetraacetate, and 1-mercaptoethyl-d-glucopyranose tetraacetate. Therefore, it is highly interesting to investigate the interaction between CO2 and these three compounds using ab initio calculations, including geometry optimizations with HF/3-21G, B3LYP/6-31+G** and single-point energy calibration with MP2/aug-cc-pVDZ. The results indicate that the electrostatic interactions between the substrates and CO2 are mainly influenced by the interaction distance and the numbers of negative charge donors or the interacting pairs involved in the complex. It is furthermore found that ΔE increases significantly if S and O atoms could interact with CO2 simultaneously. The binding energy is irrelevant if one considers the chemical environment of the O atom (i.e. OAc, OE or OS) or the S atom (i.e. SEt or SH), and the electronegativity difference between the S and O atoms. The three substrates studied are still excellent CO2-philes, although their average ΔE (–20 kJ/mol) is slightly lower than that of peracetylated d-glucose (–22 kJ/mol), which has one more O atom that can interact with CO2. Therefore, the applications of carbohydrates can be expanded to include adsorbents for CO2, SO2 or both, and the functional groups attached to the carbohydrate can vary from those to the acetyl groups. 相似文献
15.
Ju Guan-zhi Feng Da-cheng Cai Zheng-ting Deng Chong-hao 《Theoretical chemistry accounts》1988,74(5):403-414
The dynamics of elementary rate processes for H+O2 collisions on an ab initio potential energy surface have been simulated by quasiclassical trajectory theory (QCT). For H+O2 (v=0,j=1), we have obtained the reaction probabilityP
r
(E,b) as a function of collision energy E and impact parameterb, the reaction cross sectionS
r
as a function ofE, and the average values
of the product quantum numbers of OH.For H+02 (v=2,j=1, 20, 40, 60, 80, 100;v=1, 3, 4, 5,j=1) atE=0.3 eV, we have found thatb
max is about 4.5a
0 and the impact parameter at whichP
r
is maximum decreases asj increases. The reaction cross section increases asj andv become large. For inelastic collisions, whenb is small andj is large, the
and
are both small. For reactive collisions,
almost equals zero, but the probability of
being larger than zero increases with increasingj; and¯v
OH even shows population inversion forj=100. Additional details of the dynamics are shown in figures of interparticle distance and stereographs. 相似文献
16.
Based on the EHMO approach, the energy band structures for superconductors YBa2Cu3–x
Sn
x
O
y
(y>7) and YBa2Cu3–x
Ni
x
Oy (y<7) were calulated in the present paper. The influence of the cation doping at the Cu site in the unit cell and the oxygen content on their electronic structures was studied. The results showed that the cation doping at the Cu site resulted in the great decreases in the bandwidths of the broad anisotropic Cu-O bands and the densities of states. In YBa2Cu3–x
Sn
x
O
y
, however, these decreases are compensated by the increase in the oxygen content caused by the Sn-doping, which results in a small change in the total densities of states. For YBa2Cu3–x
Ni
x
O
y
, the effect of the doping on its electronic structures in dominant. The Ni-doping, therefore, results in a great change in the electronic structures. In addition, the study on the projected densities of states of the Ni-doped system revealed that the 2D Cu-O planes in the Y-Ba-Cu-O system played a dominant role in superconductivity. 相似文献
17.
18.
19.
20.
Ab initio caculations with RHF/6-31G and MP2/6-31G have been used to study the isomerization of 3-amino-2-pyridone in gas-phase and in water. The results obtained show that 3-amino-2-pyridone is isomerized into 3-amino-2-hydroxy pyridine via a four-center cyclic transition state in the gas-phase, and via a six-center cyclic transition state in water. The activation energies of this reaction are 226.3336(RHF/6-31G) and 171.2269(MP2/6-31G) in gas-phase, and 81.6398(RHF/6-31G) and 59.8668(MP2/6-31G) kJ mol−1 under the condition of a single water molecule as the catalyst, respectively. 相似文献