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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Petrakovskii G. A., Aleksandrov K. S., Aplesnin S. S., Roessli B., Semadeni F., Amato A., Baines C., Bartolome J., Evangelisti M.
Заглавие : Spin-glass state in CuGa2O4
Место публикации : Phys. Rev. B. - 2001. - Vol. 63, Is. 18. - Ст.184425. - ISSN 0163-1829, DOI 10.1103/PhysRevB.63.184425
Примечания : Cited References: 28
Предметные рубрики: TRANSITION
Ключевые слова (''Своб.индексиров.''): copper--gallium--glass--oxygen--acceleration--article--magnetism--measurement--molecular dynamics--phase transition
Аннотация: Magnetic susceptibility, magnetization, specific-heat, and positive muon spin relaxation (?SR) measurements have been used to characterize the magnetic ground state of the spinel compound CuGa2O4. We observe a spin-glass transition of the S = 1/2 Cu2+ spins below Tf = 2.5 K characterized by a cusp in the susceptibility curve which is suppressed when a magnetic field is applied. We show that the magnetization of CuGa2O4 depends on the magnetic history of the sample. Well below Tf, the muon signal resembles the dynamical Kubo-Toyabe expression reflecting that the spin freezing process in CuGa2O4 results in a Gaussian distribution of the magnetic moments. By means of Monte Carlo simulations, we obtain the relevant exchange integrals between the Cu2+ spins in this compound.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Nasluzov V. A., Rivanenkov V. V., Gordienko A. B., Neyman K. M., Birkenheuer U., Rosch N.
Заглавие : Cluster embedding in an elastic polarizable environment: Density functional study of Pd atoms adsorbed at oxygen vacancies of MgO(001)
Место публикации : J. Chem. Phys.: AMER INST PHYSICS, 2001. - Vol. 115, Is. 17. - P8157-8171. - ISSN 0021-9606, DOI 10.1063/1.1407001
Примечания : Cited References: 88
Предметные рубрики: TRANSITION-METAL ATOMS
AB-INITIO
OXIDE SURFACES
ELECTRONIC-PROPERTIES
ENERGY CALCULATIONS
MOLECULAR-DYNAMICS
MOTT-LITTLETON
MADELUNG FIELD
IONIC-CRYSTAL
MGO
Ключевые слова (''Своб.индексиров.''): atoms--binding energy--computer simulation--electron energy levels--electronic structure--magnesia--oxygen--palladium--polarization--probability density function--quantum theory--relaxation processes--charged defects--cluster embedding--elastic polarizable environment--electron affinity--oxygen vacancies--adsorption
Аннотация: Adsorption complexes of palladium atoms on F-s, F-s(+), F-s(2+), and O2- centers of MgO(001) surface have been investigated with a gradient-corrected (Becke-Perdew) density functional method applied to embedded cluster models. This study presents the first application of a self-consistent hybrid quantum mechanical/molecular mechanical embedding approach where the defect-induced distortions are treated variationally and the environment is allowed to react on perturbations of a reference configuration describing the regular surface. The cluster models are embedded in an elastic polarizable environment which is described at the atomistic level using a shell model treatment of ionic polarizabilities. The frontier region that separates the quantum mechanical cluster and the classical environment is represented by pseudopotential centers without basis functions. Accounting in this way for the relaxation of the electronic structure of the adsorption complex results in energy corrections of 1.9 and 5.3 eV for electron affinities of the charged defects F-s(+) and F-s(2+), respectively, as compared to models with a bulk-terminated geometry. The relaxation increases the stability of the adsorption complex Pd/F-s by 0.4 eV and decreases the stability of the complex Pd/F-s(2+) by 1.0 eV, but it only weakly affects the binding energy of Pd/F-s(+). The calculations provide no indication that the metal species is oxidized, not even for the most electron deficient complex Pd/F-s(2+). The binding energy of the complex Pd/O2- is calculated at -1.4 eV, that of the complex Pd/F-s(2+) at -1.3 eV. The complexes Pd/F-s and Pd/F-s(+) exhibit notably higher binding energies, -2.5 and -4.0 eV, respectively; in these complexes, a covalent polar adsorption bond is formed, accompanied by donation of electronic density to the Pd 5s orbital. (C) 2001 American Institute of Physics.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Janowitz C., Seidel U., Unger RST, Krapf A., Manzke R., Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Strong spin triplet contribution of the first removal state in the insulating regime of Bi2Sr2Ca1-xYxCu2O8+delta
Разночтения заглавия :авие SCOPUS: Strong spin triplet contribution of the first removal state in the insulating regime of Bi2Sr2Ca1-xY xCu2O8+δ
Место публикации : JETP Letters. - 2004. - Vol. 80, Is. 11. - P.692-696. - ISSN 0021-3640, DOI 10.1134/1.1862796
Примечания : Cited References: 18
Предметные рубрики: ELECTRONIC-STRUCTURE
APICAL OXYGEN
MODEL
SUPERCONDUCTIVITY
ONSET
Аннотация: The experimental dispersion of the first removal state in the insulating Bi2Sr2Ca1 - xYxCu2O8 + delta regime is found to differ significantly from that of other parent materials: oxyclorides and La2CuO4. For Y contents of 0.92 greater than or equal to x greater than or equal to 0.55 due to nonstoichiometric effects in the Bi-O layers, the hole concentration in the CuO2 layers is almost constant and, on the contrary, the crystal lattice parameters a, b, c change very strongly. This (a, b) parameter increase and c parameter decrease results in an unconventional three peak structure at (0, 0), (pi/2, pi/2), (pi, pi) for x = 0.92. We can describe the experimental data only beyond the framework of the three-band p-d-model involving the representations of a new triplet counterpart for the Zhang-Rice singlet state. (C) 2004 MAIK "Nauka/Interperiodica".
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Gavrichkov V. A., Ovchinnikov S. G., Nekrasov I. A., Pchelkina Z. V., Anisimov V. I.
Заглавие : Hybrid LDA and generalized tight-binding method for electronic structure calculations of strongly correlated electron systems
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2005. - Vol. 72, Is. 16. - Ст.165104. - ISSN 1098-0121, DOI 10.1103/PhysRevB.72.165104
Примечания : Cited References: 82
Предметные рубрики: T-J MODEL
DENSITY-FUNCTIONAL CALCULATION
NARROW ENERGY BANDS
MEAN-FIELD THEORY
COULOMB INTERACTIONS
FERMION SYSTEMS
COPPER OXIDES
SUPERCONDUCTORS
LA2-XSRXCUO4
OXYGEN
Аннотация: A hybrid scheme for the electronic structure calculations of strongly correlated electron systems is proposed. The ab initio local density approximation calculation is used to construct the Wannier functions and obtain single electron and Coulomb parameters of the multiband Hubbard-type model. In strong correlation regime the electronic structure within multiband Hubbard model is calculated by the generalized tight-binding method, which combines the exact diagonalization of the model Hamiltonian for a small cluster (unit cell) with perturbation treatment of the intercluster hopping and interactions. For undoped La2CuO4 and Nd2CuO4 this scheme results in charge transfer insulators with correct values of gaps and dispersions of bands in agreement with the angle-resolved photoemission data.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Boehm M., Roessli B., Schefer J., Ouladdiaf B., Kulda J., Petrakovskii G. A.
Заглавие : Coexisting 1D and 3D magnetic interactions in the insulating copper-oxygen compound CuB2O4
Разночтения заглавия :авие SCOPUS: Coexisting 1D and 3D magnetic interactions in the insulating copper-oxygen compound CuB2 O4
Место публикации : Physica B: ELSEVIER SCIENCE BV, 2006. - Vol. 378-80: International Conference on Strongly Correlated Electron Systems (SECES 05) (JUL 26-30, 2005, Vienna, AUSTRIA). - P1128-1129. - ISSN 0921-4526, DOI 10.1016/j.physb.2006.01.540
Примечания : Cited References: 8
Предметные рубрики: SPIN-WAVE SPECTRUM
PHASE 10 K
METABORATE
Ключевые слова (''Своб.индексиров.''): cuprates--magnetic soliton lattice--heisenberg exchange--low-dimensional excitations--cuprates--heisenberg exchange--low-dimensional excitations--magnetic soliton lattice--dispersions--insulating materials--magnetic properties--neutron scattering--positive ions--cuprates--heisenberg exchange--low-dimensional excitations--magnetic soliton lattice--copper compounds
Аннотация: We performed inelastic neutron scattering measurements on CuB2O4 with a magnetic field applied in the tetragonal basal plane. The spin dynamics in this cuprate is determined by the interplay of two magnetic Cu2+ subsystems, the magnetic cage with predominant 3d Heisenberg exchange and quasi Id zig-zag chains. The comparison of the dispersion spectra along the chain direction in zero field and under applied field suggests a decoupling of the two magnetic sublattices under field. (c) 2006 Elsevier B.V. All rights reserved.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Di Valentin C., Neyman K. M., Risse T., Sterrer M., Fischbach E., Freund H. J., Nasluzov V. A., Pacchioni G., Rosch N.
Заглавие : Density-functional model cluster studies of EPR g tensors of F-s(+) centers on the surface of MgO
Разночтения заглавия :авие SCOPUS: Density-functional model cluster studies of EPR g tensors of F s + centers on the surface of MgO
Место публикации : J. Chem. Phys.: AMER INST PHYSICS, 2006. - Vol. 124, Is. 4. - Ст.44708. - ISSN 0021-9606, DOI 10.1063/1.2161190
Примечания : Cited References: 37
Предметные рубрики: ELECTRONIC G-TENSORS
CORRELATION-ENERGY
MGO(001) SURFACE
OXYGEN VACANCIES
SPIN-ORBIT
G-VALUES
ATOMS
APPROXIMATION
COMPLEXES
MOLECULES
Ключевые слова (''Своб.индексиров.''): density-functional model cluster--single-crystalline thin films--spin-orbit interaction--anisotropy--paramagnetic resonance--single crystals--tensors--thin films--magnesium compounds
Аннотация: We report g tensors of surface color centers, so-called F-s(+) centers, of MgO calculated with two density-functional approaches using accurately embedded cluster models. In line with recent UHV measurements on single-crystalline MgO film, we determined only small g-tensor anisotropies and negative shifts Delta g equivalent to g-g(e) for all F-s(+) sites considered, namely, (001)-terrace, step, edge, and corner sites. The g values are very sensitive to the local structure of the defect: relaxation reverses the sign of Delta g. However, accounting for the spin-orbit interaction either self-consistently or perturbatively yields very similar results. In addition to the values of the tensor components, their direction with respect to the surface was determined. In contrast to edges, significant deviations from ideal C-2v symmetry were found for F-s(+) centers at steps. Recent data on single-crystalline thin films are reevaluated in the light of these results. (c) 2006 American Institute of Physics.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Zamkova N. G., Maksimov E. G., Sofronova S. N.
Заглавие : Lattice dynamics and ferroelectric instability in ordered and disordered PbSc1/2Ta1/2O3 and PbSc1/2Nb1/2O3 solid solutions
Разночтения заглавия :авие SCOPUS: Lattice dynamics and ferroelectric instability in ordered and disordered PbSc1/2Ta1/2O3 and PbSc1/2Nb 1/2O3 solid solutions
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 105, Is. 3. - P617-625. - ISSN 1063-7761, DOI 10.1134/S1063776107090191
Примечания : Cited References: 23
Предметные рубрики: RELAXOR FERROELECTRICS
PHASE-TRANSITION
LOCAL-STRUCTURE
PB(SC1/2NB1/2)O-3
PEROVSKITE
CRYSTALS
Ключевые слова (''Своб.индексиров.''): dipole moment--lattice vibrations--negative ions--phonons--positive ions--solid solutions--dynamic born charges--ferroelectric instabilities--frequency spectra--gordon-kim models--oxygen anions--phonon spectra--ferroelectricity
Аннотация: The dynamic Born charges and the frequency spectra of lattice oscillations in the crystals of ordered and disordered PbSc1/2Ta1/2O3 (PST) and PbSc1/2Nb1/2O3 (PSN) solid solutions have been calculated within the framework of the generalized Gordon-Kim model with allowance for the dipole and quadrupole polarizabilities. The phonon spectra of both compounds contain ferroelectric soft modes. The influence of various interactions on the magnitude of dynamic charges and ferroelectric instability in PSN and PST solid solutions has been studied and it is shown that both these charges and the ferroelectric instability are determined by the competition between long-range dipole-dipole interactions and short-range dipole-charge interactions, the determining role played by the interaction of Nb (Ta) cations and oxygen anions in the Nb-O (Ta-O) bond direction.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Gavriliuk A. G., Ovchinnikov S. G., Lyubutin I. S., Edel'man I. S., Rudenko V. V.
Заглавие : Evolution of the optical absorption spectra and electronic structure of the VBO3 crystal under high pressures
Коллективы : Russian Foundation for Basic Research [07-02-00490a, 08-02-00897a, 08-02-90708 mob_st, 09-02-00171a, 07-02-00226]; Federal Agency for Science and Innovation [MK-4278.2008.2, 01.164.12.HB11]; Russian Academy of Sciences
Место публикации : J. Exp. Theor. Phys. - 2009. - Vol. 109, Is. 3. - P.455-465. - ISSN 1063-7761, DOI 10.1134/S1063776109090118
Примечания : Cited References: 27. - We would like to thank A. D. Vasil'ev for performing the X-ray diffraction investigations.This study was supported by the Russian Foundation for Basic Research (project nos. 07-02-00490a, 08-02-00897a, 08-02-90708 mob_st, 09-02-00171a, and 07-02-00226), the Federal Agency for Science and Innovation (Rosnauka) (project no. MK-4278.2008.2, contract no. 01.164.12.HB11), and the Branch of Physical Sciences of the Russian Academy of Sciences within the framework of the program "Strongly Correlated Electrons."
Предметные рубрики: BAND-STRUCTURE
PHASE-TRANSITION
FEBO3
FE1-XVXBO3
STATE
MODEL
Ключевые слова (''Своб.индексиров.''): charge-transfer excitations--d-d transitions--ferromagnetic semiconductor--fundamental absorption edge--high pressure--optical absorption spectrum--absorption--boron--boron compounds--electronic properties--electronic structure--optical materials--oxygen--vanadium--light absorption
Аннотация: The evolution of optical absorption spectra of the ferromagnetic semiconductor VBO3 under high pressures up to 70 GPa has been investigated. It has been revealed that, below the fundamental absorption edge (E (g1) = 3.02 eV), the spectra exhibit a series of bands V1 (2.87 eV), V2 (2.45 eV), V3 (1.72 eV), and V4(1.21 eV) due to the d-d transitions in the V3+ ion and charge-transfer excitations. A model of the electronic structure of the VBO3 semiconductor has been constructed. This model combines the one-electron description of the s and p states of boron and oxygen and the many-electron description of the vanadium d states.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Rasch JCE, Boehm M., Ritter C., Mutka H., Schefer J., Keller L., Abramova G. M., Cervellino A., Loffler J. F.
Заглавие : Magnetoelastic coupling in the triangular lattice antiferromagnet CuCrS2
Коллективы : Russian Academy of Science (RAS), Siberian Branch [06-1000013-9002]
Место публикации : Phys. Rev. B. - 2009. - Vol. 80, Is. 10. - Ст.104431. - ISSN 1098-0121, DOI 10.1103/PhysRevB.80.104431
Примечания : Cited References: 30. - We are grateful for support and allocated beam time at the Institut Laue-Langevin (D1A, IN3),Grenoble, France, the spallation neutron source SINQ (TriCS, DMC) and the SLS-MS beamline, both Paul Scherrer Insitut, Villigen, Switzerland. This work was supported by INTAS Grant No. 06-1000013-9002 of the Russian Academy of Science (RAS), Siberian Branch.
Предметные рубрики: NEUTRON POWDER DIFFRACTION
MAGNETIC-STRUCTURE
STRUCTURAL-PROPERTIES
PHASE-TRANSITION
SOLID OXYGEN
ALPHA-PHASES
BETA-PHASES
SELENIDES
SULFIDES
Аннотация: CuCrS2 is a triangular lattice Heisenberg antiferromagnet with a rhombohedral crystal structure. We report on neutron and synchrotron powder diffraction results which reveal a monoclinic lattice distortion at the magnetic transition and verify a magnetoelastic coupling. CuCrS2 is therefore an interesting material to study the influence of magnetism on the relief of geometrical frustration.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Atuchin V. V., Gavrilova T. A., Kesler V. G., Molokeev M. S., Aleksandrov K. S.
Заглавие : Low-temperature synthesis and structural properties of ferroelectric K 3WO3F3 elpasolite
Место публикации : Chem. Phys. Lett. - 2010. - Vol. 493, Is. 1-3. - P.83-86. - ISSN 0009-2614, DOI 10.1016/j.cplett.2010.05.023
Примечания : Cited References: 37
Предметные рубрики: PEROVSKITE-LIKE OXYFLUORIDES
CORE-LEVEL SPECTROSCOPY
PHASE-TRANSITIONS
SOLID-STATE
ELECTRON-DIFFRACTION
DIFFUSE-SCATTERING
RHEED ANALYSIS
POLAR
BEHAVIOR
(NH4)(3)TIOF5
Ключевые слова (''Своб.индексиров.''): chemical synthesis--elpasolite--ferroelectric phase transition--fluorine atoms--low temperature synthesis--low temperatures--oxyfluorides--partial ordering--room temperature--sem--space groups--structure parameter--xrd--chemical properties--ferroelectric materials--ferroelectricity--fluorine--oxygen--phase transitions--rietveld method--single crystals--synthesis (chemical)--x ray photoelectron spectroscopy--x ray powder diffraction--scanning electron microscopy
Аннотация: Low-temperature ferroelectric G2 polymorph of K3WO 3F3 has been prepared by chemical synthesis. Structural and chemical properties of the final product have been evaluated with X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Structure parameters of G2-K 3WO3F3 are refined by the Rietveld method from XRD data measured at room temperature (space group Cm, Z = 2, a = 8.7350(3), b = 8.6808(5), c = 6.1581(3), ? = 135.124(3), V = 329.46(3) 3; RB = 2.47%). Partial ordering of oxygen and fluorine atoms has been found over anion positions. Mechanism of ferroelectric phase transition in A2BMO3F3 oxyfluorides is discussed. В© 2010 Elsevier B.V. All rights reserved.
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