共查询到20条相似文献,搜索用时 46 毫秒
1.
A. Gloter V. Serin Ch. Turquat C. Cesari Ch. Leroux G. Nihoul 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):179-186
The valency of vanadium, and thus indirectly the oxygen stoichiometry, of V-doped hafnia synthesized under different atmospheres
have been investigated on a nanometer scale by means of electron energy loss spectroscopy (EELS). The EELS V L2,3 spectra are compared with the results of crystal field multiplet calculations and experiments on reference vanadium oxides.
The EELS spectra indicate that V-doped hafnia prepared under reducing (H2) and neutral (Ar) atmosphere are unambiguously substituted with trivalent vanadium atoms leading to the creation of oxygen
vacancies in the structure. On the contrary, stoichiometric (Hf, V)O2 compound (i.e. V4+) is more likely to be stabilized under oxidative (air) atmospheres. We also show that the amount of hybridization alters
for the different compounds studied but may in part be analyzed by high spatially resolved EELS. The crystal field multiplet
calculations particularly indicate that a simple reduction of the Slater integrals gives a good account of the spectral modification
induced by hybridization for the case of tetravalent vanadium atoms.
Received 17 November 2000 and Received in final form 17 April 2001 相似文献
2.
Sun Guoya Xing D.Y. Shen R. Lin H.Q. 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):33-38
The Nambu spinor Green's function approach is applied to calculating the density of states (DOS) and superconducting order
parameter in normal-metal/insulator/ferromagnet/superconductor (NM/I/FM/SC) junctions. It is found that the s-wave superconductivity and ferromagnetism can coexist near the FM/SC interface, which is induced by proximity effect. On
the SC side, the spin-dependent DOS appears both within and without the energy gap. On the FM side, the superconducting order
parameter displays a damped oscillation and the DOS exhibits some superconducting behavior. The calculated result for the
DOS in FM for “0 state” and “π state” can reproduce recent tunneling spectra in Al/Al2O3/PdNi/Nb tunnel junctions.
Received 1st July 2002 Published online 19 November 2002 相似文献
3.
Oxidation of vanadium metal surfaces at room temperature by low-energy oxygen ion beams is investigated by X-ray photoelectron spectroscopy (XPS). It is observed that ion-beam irradiation of clean V results in formation of thin oxide layer containing vanadium in oxidation states corresponding to VO, V2O3, VO2 and V2O5 oxides. The composition of the products of ion-beam oxidation depends markedly on oxygen ion fluence. The results of angle-resolved XPS measurements are consistent with a structure of oxide film with the outermost part enriched in V2O5 and VO2 oxides and with V2O3 and VO oxides located in the inner region of the oxide layer. 相似文献
4.
X. Wu A.K. Ray 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):345-351
The electronic and geometric structures of bulk PuO2 and its (110) surface have been studied using a periodic model within the generalized gradient approximation (GGA) of density
functional theory (DFT). The sixty core electrons of the Pu atom have been represented by a relativistic effective core potential
and scalar relativistic effects have been incorporated on the valence orbitals. For bulk PuO2, we predict an equilibrium lattice constant of 10.10 a.u. and a cohesive energy of 17.28 eV, in good agreement with experimental
data. For the (110) surface, upon relaxation, the distance between the top layer and the next layer is found to decrease by
0.12 ?, i.e. 5.3% of the corresponding interlayer distance in the bulk. The distance between the two oxygen atoms on the top layer is
found to increase by 0.15 ?, i.e. 5.6% of the corresponding bulk value. The small surface relaxation energy of 0.268 eV per unit cell indicates the fair stability
of this surface. The effective charges on Pu and O atoms show that the chemical bonding in this system is not purely ionic.
Together with the metallic feature of the density of states (DOS) on the surface, the effective charge distribution provides
some basis for understanding surface reactivity and corresponding support for catalysis.
Received 16 June 2000 相似文献
5.
A. Ślebarski A. Jezierski M. Neumann S. Plogmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):519-523
The electronic structure of the Co2-xZrSn Heusler alloys has been studied by X-ray photoelectron spectroscopy (XPS). XPS valence band spectra can be compared with
ab initio electronic structure calculations using the linearized muffin-tin orbital (LMTO) method. The calculated magnetic moments
per Co atom agree well with the moments obtained from experiment. The LMTO calculations also show the energy shifts of the
Co, Zr and Sn valence electron states towards the Fermi level when the concentration of vacancies increases in these alloys.
Received 9 March 1999 and Received in final form 6 May 1999 相似文献
6.
Phase evolution of layered cobalt oxides versus varying corrugation of the cobalt-oxygen basal plane
A general spin-state model and a qualitative physical picture have been proposed for a class of lately synthesized layered
cobalt oxides (LCOs) by means of density functional calculations. As the plane corrugation of the cobalt-oxygen layer decreases,
the LCOs evolve from a high-spin (HS) superexchange-coupled antiferromagnetic (AFM) insulator to an almost-HS AFM/ferromagnetic
(FM) competing system where the FM coupling is mediated via the p-d exchange by an increasing amount of delocalized pdσ holes having mainly the planar O 2p character. It is tentatively suggested that the delocalized holes more than 0.3 per CoO2 basal square are likely necessary for the insulator-metal and/or AFM-FM transitions in the corrugation-weakened LCOs. A phase
control may be realized in LCOs by varying the plane corrugation (thus modifying the hole concentration) through an ionic-size
change of the neighboring layers on both sides of the cobalt-oxygen layer. In addition, a few experiments are suggested for
a check of the present model and picture.
Received 28 July 2002 / Received in final form 10 October 2002 Published online 31 December 2002 相似文献
7.
L. Bartosch P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):29-36
We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals
for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln2-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions
to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e
4 appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω
2 which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω
1)1/2exp(- Ω
1/|ω|) at T = 0, where Ω
1 is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance
that can be compared with experiments.
Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002 相似文献
8.
E. Caurier F. Nowacki A. Poves 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):145-150
Recent shell model calculations for the neutron-rich nuclei around the magic numbers N = 20, N = 28 and N = 40 are reviewed. We stress two points: i) The crucial role played by the monopole part of the effective interaction that
determines the evolution of the spherical mean field. In particular, the reduction in the quasiparticle gaps at the magic
numbers can erode or even erase the shell closures. ii) The rich variety of structures that can be found in these situations,
with coexisting deformed and spherical states, rapid changes of behaviour with N or Z, and the massive occurrence of intruder states as ground states.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: alfredo.poves@uam.es 相似文献
9.
B. Schmidt V. Yushankhai L. Siurakshina P. Thalmeier 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):43-47
A pronounced Curie-like upturn of the magnetic susceptibility χ(
T
) of the quasi one-dimensional spin chain compound Ba2V3O9 has been found recently [#!kaul:02!#]. Frequently this is taken as a signature for a staggered field mechanism due to the
presence of g-factor anisotropy and Dzyaloshinskii-Moriya interaction. We calculate this contribution within a realistic structure of vanadium
3
d- and oxygen 2
p-orbitals and conclude that this mechanism is far too small to explain experimental results. We propose that the Curie term
is rather due to a segmentation of spin chains caused by broken magnetic bonds which leads to uncompensated S
= ? spins of segments with odd numbers of spins. Using the finite-temperature Lanczos method we calculate their effective moment
and show that ∼ 1% of broken magnetic bonds is sufficient to reproduce the anomalous low-T behavior of χ(
T
) in Ba2V3O9.
Received 19 December 2002 / Received in final form 29 January 2003 Published online 14 March 2003 相似文献
10.
The present study pertains to a vanadium/titania-based catalyst for removing nitrogen oxides at a relatively low temperature window. More specially, the present study relates to a vanadium/titania-based catalyst containing VOx (x < 2.5) and having excellent ability to remove nitrogen oxides at a wide temperature window, particularly at a relatively low temperature window and a process for removing nitrogen oxides using the same. In this study, various TiO2 supports have been tested to determine the role of support. Raw TiO2 were examined a variety of physical properties. Also comparing with commercial V2O5/TiO2 catalyst, the activity of various VOx (x < 2.5)/TiO2 in this study have quite different values.To find the source of lattice oxygen in vanadium oxides, the effect of calcination conditions on the removal efficiency of nitrogen oxides was examined. When nitrogen instead of air was introduced as a balance gas in calcination step, the activity of catalysts in this study was not changed. That may indicate the source of lattice oxygen in vanadium oxides as that of TiO2. The results of X-ray photoelectron spectroscope (XPS) revealed that after vanadium oxides loaded the support, TiO2 was reduced to Ti2O3, etc. In the test of calcination temperature of a variety of vanadium/titania-based catalysts, it has been found that TiO2 supports affects the optimal calcination temperature, indicating that the difference of crystal structure, defect and binding energy in TiO2 may make inherent VOx (x < 2.5)/V2O5 molar ratios, respectively. Its ratio seems to be an index of activity. 相似文献
11.
H. Zheng Y. Wang G. Ma 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):61-69
The electronic structure of LaNi5 and its hydride LaNi5H7 are obtained using the self-consistent cluster-embedding calculation method. The Fermi level of LaNi5H7 is 5.172 eV higher than that of LaNi5. In both materials, the La 5d electrons locate nearby the Fermi levels, and make only a small contribution to the density of states (DOS) of the valence
bands. There is no significant charge transfer from La to Ni in LaNi5. But for LaNi5H7, there is a charge transfer of 1.16 electrons from La to H, and H atoms are combined mainly with Ni to form hybridized orbitals
in the energy regions far below the Fermi level. An explanation of hydrogenation of LaNi5 is proposed: It is easy for hydrogens to take off some localized La 5
d electrons near the Fermi level, and combine with Ni to form hybridized orbitals in lower energy regions. This process is
therefore in favor of energy, and forces a lattice expansion until the Fermi level rises to zero.
Received 13 July 2001 / Received in final form 10 December 2001 Published online 17 September 2002 相似文献
12.
13.
Semiclassical expansions derived in the framework of the Extended Thomas-Fermi approach for the kinetic energy density τ(
r) and the spin-orbit density
J(
r) as functions of the local density ρ(
r) are used to determine the central nuclear potentials V
n(
r) and V
p(
r) of the neutron and proton distribution for effective interactions of the Skyrme type. We demonstrate that the convergence
of the resulting semiclassical expansions for these potentials is fast and that they reproduce quite accurately the corresponding
Hartree-Fock average fields.
Received: 12 February 2000 / Accepted: 14 March 2002 相似文献
14.
C.M. Teodorescu F. Chevrier R. Brochier C. Richter V. Ilakovac O. Heckmann P. De Padova K. Hricovini 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):305-313
Interface reaction and magnetism of epitaxially-grown Fe on InAs(100) are studied by core-level photoemission (As 3d and In 4d) and Fe 2p X-ray magnetic circular dichroism using synchrotron radiation. The reactivity of Fe/InAs(100) is relatively low compared
to that of other interfaces involving deposition of 3d metals on III-V semiconductors. As a consequence, we observe a magnetic signal at Fe L2, 3 edges for the lowest thicknesses studied (1 ML). The atomic magnetic moment reaches a value close to that of the bulk α-Fe
(2.2 μ
B) for Fe coverages exceeding 5 ML. A ferromagnetic compound with approximate stoichiometry of FeAs is formed at the interface.
The orbital magnetism represents between 12 and 20% of the total momentum, due to 3d density of states depletion and to crystal-field modification of the electronic levels. These properties make the Fe/InAs(100)
interface very promising for spin-tunneling devices.
Received 4 April 2002 / Received in final form 13 May 2002 Published online 31 July 2002 相似文献
15.
B. Pilawa I. Keilhauer G. Fischer S. Knorr J. Rahmer A. Grupp 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):321-330
The magnetic properties of the cyclic compound [Fe6(bicine)6] LiClO4
. 2MeOH are reported. The cluster Fe6(bicine)6 forms an antiferromagnetically coupled ring structure of Fe III ions. The magnetic susceptibility is measured between 2 and 300 K and yields the exchange coupling of J/k
B = - 27.5±0.5 K. The field dependence of the magnetic moment is studied at 3 and 6 K in magnetic fields up to 5 T. The zero-field
splitting of the first excited spin states with S = 2 and 3 are determined by ESR at 94 GHz. The intra-molecular interactions of the Fe III ions are analyzed and the on-site anisotropy of the Fe III due to the ligand-configuration is determined to d /k
B = - 0.633±0.008K.
Received 28 October 2002 / Received in final form 22 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: bernd@piobelix.physik.uni-karlsruhe.de 相似文献
16.
G.-P. Zhang S.-J. Xiong 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):491-495
We show that the electronic states in a one-dimensional (1D) Anderson model of diagonal disorder with long-range correlation
proposed by de Moura and Lyra exhibit localization-delocalization phase transition in varying the energy of electrons. Using
transfer matrix method, we calculate the average resistivity and investigate how it changes with the size of the system N. For given value of α (> 2) we find critical energies Ec1 and Ec2 such that the resistivity decreases with N as a power law ∝ N
- γ for electron energies within the range of [E
c1, E
c2], and exponentially grows with N outside this range. Such behaviors persist in approaching the transition points and the exponent γ is in the range from 0.92
to 0.96. The origin of the delocalization in this 1D model is discussed.
Received 18 December 2001 / Received in final form 2 May 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: sjxiong@nju.edu.cn 相似文献
17.
J. Ding L. Wang A. Roy J. Ghose 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):49-54
A compensation temperature of 138 K was observed in the temperature-dependent magnetization curves of MoFe2O4. Relatively slow magnetization relaxation characterized the transitions between different spin states (compensated and uncompensated).
Large magnetic after effect was found in time-dependent magnetization curves after heating or cooling from different characteristic
temperatures for different spin states. The magnetic relaxation was nearly independent on magnetic field, supporting the presence
of spin states and no involvement of domain structure. For the Ti substituted Mo0.6Ti0.4Fe2O4 sample, there were a compensation at ∼ 100 K and a maximum of magnetization at ∼ 175 K. Similar results of anomalous magnetic
relaxation was observed in Ti substituted Mo-ferrite (Mo0.6Ti0.4Fe2O4). If the Mo0.6Ti0.4Fe2O4 sample was heated from 100 K to 235 K, the time-dependent magnetization curve could be considered as a combination of two
magnetic relaxation processes. However, if the sample was heated from 100 K to 295 K, the time- dependent magnetization curve
became complex.
Received 30 October 2001 and Received in final form 21 January 2002 相似文献
18.
T. Mazet J. Tobola B. Malaman 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):183-191
The electronic structure of the RFe
6
Ge
6
compounds ( R
=
Sc, Lu, Ti, Zr, Hf and Nb) of HfFe
6
Ge
6
-type structure has been studied using the muffin-tin Korringa-Kohn-Rostoker method in a non-relativistic approach. The chemical
bonding is analyzed based on the l-decomposed site projected densities of states. Spin-dependent changes in the R nd- Fe 3d covalent bond are shown to be responsible for the experimentally observed rise in the Fe moment and hyperfine field upon
increasing the R valency. The limited quantitative agreement between theoretical and experimental values is interpreted as
being due to a non-negligible orbital moment and to a significant asphericity in the spin density at the iron site. The theoretical
results also forecast a strong increase of the Ge(2e) transferred hyperfine field with the R valency.
Received 20 December 2002 Published online 4 June 2003
RID="a"
ID="a"e-mail: Thomas.Mazet@lcsm.uhp-nancy.fr
RID="b"
ID="b"Associé au CNRS (UMR 7555) 相似文献
19.
V.A. Pashchenko A. Sulpice F. Mila P. Millet A. Stepanov P. Wyder 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):473-476
We report on the magnetic susceptibility and electron spin resonance measurements on polycrystalline samples of the vanadium
oxide VOSb2O4, a quasi-one-dimensional S
= 1/2 Heisenberg system. The susceptibility vanishes at zero temperature, but there is no cusp at the onset of the susceptibility
drop, and the ESR linewidth exhibits an increase characteristic of a phase transition at a much lower temperature. We show
that this behaviour is consistent with the formation of a pseudo-gap in a spin-Peierls system in the adiabatic limit.
Received 7 February 2001 and Received in final form 24 April 2001 相似文献
20.
G. Savona D.V. Livanov A.A. Varlamov 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):415-420
We study the fluctuation-induced magnetotransport of a two-dimensional superconductor in the quasiballistic regime, where
ξ
GL(T) ≪ ℓ (ℓ is the electron mean free path and ξ
GL(T) is the Ginzburg-Landau coherence length). The magnetoconductivity is evaluated in the nonlocal fluctuation regime thereby
extending the existing theory valid in the local limit. We show that the Maki-Thompson (MT) and density-of-states (DOS) contributions
strongly compensate each other and their sum is negligible in comparison with the Aslamazov-Larkin (AL) term. The hierarchy
of the fluctuation contributions to the magnetoconductivity in the high-field limit is also qualitatively discussed.
Received 10 July 2002 / Received in final form 21 November 2002 Published online 7 May 2003 相似文献