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Общее количество найденных документов : 32
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1.
Инвентарный номер: нет.
   
   E 43


   
    Electronic Properties of New Ca(AlxSi1 – x)2 and Sr(GaxSi1 – x)2 Superconductors in Crystalline and Nanotubular States / I. R. Shein, V. V. Ivanovskaya, N. I. Medvedeva, A. L. Ivanovskii // JETP Letters. - 2002. - Vol. 76, № 3. - P. 189-193 : il. - Bibliogr. : p. 193 (19 ref.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
СВЕРХПРОВОДНИКИ -- НАНОТРУБКИ КАРБОНОВЫЕ -- SrGaSi -- CaAlSi
Аннотация: The band structure of new layered (AlB2 type) Ca(AlxSi1 – x)2 and Sr(GaxSi1 – x)2 superconductors is studied by the first-principle full-potential LMTO method. It has been shown that the superconducting properties of ternary silicides are due to the high density of (Ca,Sr)d states at the Fermi level, whereas the growth of TC in going from Sr(GaxSi1 – x)2 to Ca(AlxSi1 – x)2 is associated with the increase in phonon frequencies due to the decrease in atomic masses. Simulations are performed for the electronic properties of hypothetical (11,11) and (20,0) CaAlSi and SrGaSi nanotubes. In going from the crystalline to the nanotubular state, the silicide systems retain metal-like properties. The template and “film rolling” techniques can be used for obtaining silicide nanotubes

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2.
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   I-61


   
    Inhomogeneous State of the Electron System in BaPb1 – xSbxO3 Superconducting Perovskites: The 207Pb NMR Study / A. F. Sadykov, Yu. V. Piskunov, V. V. Ogloblichev, I. Yu. Arapova, A. P. Gerashchenko, A. L. Buzlukov, S. V. Verkhovskii, I. A. Leonidov // JETP Letters. - 2010. - Vol. 91, № 5. - P245-250 : il. - Bibliogr. : p. 249-250 (31 ref.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
ПЕРОВСКИТЫ -- СВИНЕЦ -- СВЕРХПРОВОДИМОСТЬ
Аннотация: Comprehensive measurements of the 207Pb NMR spectra, Knight shifts 207Ks, spin–lattice relaxation rate, and the Pb spin echo decay 207E(2t) in BaPb1 – xSbxO3 superconducting oxides (x ≤ 0.33) have been performed. A considerable increase in the shift distribution width when Sb is substituted for Pb indicates the formation of the inhomogeneous state of the electron system in the oxide conduction band. The shift magnitude proportional to the density of states near the Fermi energy, 207Ks ∝ N(EF), reaches its maximum in the compounds with x = 0.18–0.25 with the maximum temperatures Tc of the superconducting transition. In the BaPb1 – xSbxO3 compounds, the Korringa relation is met, indicating that all of the samples are in the metal phase. The data on the Pb spin echo decay and the relevant estimates of the indirect coupling constants of the nuclei of the nearest neighbor Pb atoms clearly demonstrate the development of the electron system state in the oxide metal phase, which is microscopically inhomogeneous over the crystal

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3.
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   M 45


   
    Mechanisms of hopping conductivity in weakly doped La1-xBaxMnO3 [Текст] / R. Laiho, K. G. Lisunov, E. Laehderanta, M. A. Shakhov, V. N. Stamov, V. S. Zakhvalinskii, V. L. Kozhevnikov, I. A. Leonidov, E. B. Mitberg, M. V. Patrakeev // Journal of Physics: Condensed Matter. - 2005. - Vol. 17, № 21. - С. 3429-3444. - Библиогр. : с. 3444 (35 назв.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
КЕРАМИКА -- МАНГАНИТЫ
Аннотация: The resistivity, ρ, of ceramic La1−xBaxMnO3 with x = 0.02–0.10 corresponding to the concentrations of holes c ≈ 0.15–0.17 displays an activated behaviour both above and below the paramagnetic to ferromagnetic transition temperature TC = 175–209 K, obtained from measurements of the magnetization. Above T~ 310–390 K ρ(T, x) is determined by nearest-neighbour hopping of small polarons with activation energy Ea = 0.20–0.22 eV. Below the onset temperature Tv = 250–280 K, depending on x, a Shklovskii–Efros-like variable-range hopping conductivity mechanism, governed by a soft temperature independent Coulomb gap, The resistivity, ρ, of ceramic La1−xBaxMnO3 with x = 0.02–0.10 corresponding to the concentrations of holes c ≈ 0.15–0.17 displays an activated behaviour both above and below the paramagnetic to ferromagnetic transition temperature TC = 175–209 K, obtained from measurements of the magnetization. Above T ~ 310–390 K ρ(T, x) is determined by nearest-neighbour hopping of small polarons with activation energy Ea = 0.20–0.22 eV. Below the onset temperature Tv = 250–280 K, depending on x, a Shklovskii–Efros-like variable-range hopping conductivity mechanism, governed by a soft temperature independent Coulomb gap, ≈ 0.44–0.46 eV, and a rigid gap, δ(T ), is found. For the range T ~ 50–120K, δ(T ) is connected to the formation of small lattice polarons in conditions of strong electron– phonon interaction and lattice disorder. The rigid gap obeys a law δ(T ) ~ T 1/2 within two temperature intervals above and below TC, exhibits an inflection at TC and reaches at Tv a value of δv ≈ 0.14–0.18 eV. Such behaviour suggests a spin dependent contribution to δ(T ). The localization radius of the charge carriers, a, has different constant values within the temperature intervals where δ(T ) ~ T 1/2. With further decrease of T , a increases according to the law expected for small lattice polarons ≈ 0.44–0.46 eV, and a rigid gap, δ(T ), is found. For the range T ~ 50–120K, δ(T ) is connected to the formation of small lattice polarons in conditions of strong electron– phonon interaction and lattice disorder. The rigid gap obeys a law δ(T ) ~ T 1/2 within two temperature intervals above and below TC, exhibits an inflection at TC and reaches at Tv a value of δv ≈ 0.14–0.18 eV. Such behaviour suggests a spin dependent contribution to δ(T ). The localization radius of the charge carriers, a, has different constant values within the temperature intervals where δ(T ) ~ T 1/2. With further decrease of T , a increases according to the law expected for small lattice polarons

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4.
Инвентарный номер: нет.
   
   N 52


   
    New Superconductor with a Layered Crystal Structure: Nickel Oxybismuthide LaO1-deltaNiBi / V. L. Kozhevnikov, O. N. Leonidova, A. L. Ivanovskii, I. R. Shein, B. N. Goshchitskii, A. E. Kar'kin // JETP Letters. - 2008. - Vol. 87, № 11. - P649-651 : il. - Bibliogr. : p. 651 (18 ref.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
ОКСИВИСМУТИД НИКЕЛЯ -- ОКСИВИСМУТИДЫ МЕТАЛЛОВ -- СВЕРХПРОВОДНИКИ
Аннотация: The results of synthesizing a new layered phase—nickel oxybismuthide LaO 1 –δNiBi in a series of superconducting oxypnictides—and its properties in the superconducting and normal states are reported. Although the temperature of the transition of this phase to the superconducting state, Tc~ 4 K, is much lower than the value Tc= 55 K reached at present in oxyarsenide SmO1 –δ FeAs, the similarity of the crystal structures and ρ(T) dependencies indicates that the mechanism responsible for the appearance of the semiconducting state is the same in lanthane oxybismuthide and samarium oxyarsenide

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5.
Инвентарный номер: нет.
   
   P 56


   
    Nickel Alloy Substrates with a Sharp Cube Texture for High-Tc Superconducting TapesTexture [Text] / V. M. Schastlivtsev [et al.] // Doklady Physics. - 2004. - Vol. 49, № 3. - P. 167-170. - Библиогр. : с.170 (11 назв.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
СПЛАВЫ НИКЕЛЯ -- СВЕРХПРОВОДИМОСТЬ -- ПЕРЕХОДНЫЕ МЕТАЛЛЫ

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6.
Инвентарный номер: нет.
   
   S 53


    Shein, I. R.
    Ab initio probing of the electronic band structure and Fermi surface of fluorine-doped WO3 as a novel low-TC superconductor / I. R. Shein, A. L. Ivanovskii // Письма в Журнал экспериментальной и теоретической физики. - 2012. - Т. 95, № 1-2. - С.72-75 : рис., табл., граф. - Библиогр.: с. 75 (20 назв.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
ПОВЕРХНОСТЬ ФЕРМИ -- ДОПИРОВАНИЕ -- ФТОР -- СВЕРХПРОВОДНИКИ НИЗКОТЕМПЕРАТУРНЫЕ -- ОКСИФТОРИД ВОЛЬФРАМА
Аннотация: First-principles calculations were performed to investigate the electronic structure and the Fermi surface of the newly discovered low-temperature superconductor: fluorine-doped WO3. We find that F doping provides the transition of the insulating tungsten trioxide into a metallic-like phase WO3-xFx, where the near-Fermi states are formed mainly from W 5d with admixture of O 2p-orbitals. The cooperative effect of fluorine additives in WO3 consists in change of electronic concentration as well as the lattice constant. At probing their influence on the near-Fermi states separately, the dominant role of the electronic factor for the transition of tungsten oxyfluoride into superconducting state was established. The volume of the Fermi surface gradually increases with the increase of the doping. In the sequence WO3> WO2.5F0.5 the effective atomic charges of W and O ions decrease, but much less, than it is predicted within the idealized ionic model - owing to presence of the covalent interactions W-O and W-F

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7.
Инвентарный номер: нет.
   
   S 53


    Shein, I. R.
    Electronic properties of the novel 18-K superconducting Y2C3 ascompared with 4-K YC2 from first principles calculations / I. R. Shein, A. L. Ivanovskii // Solid State Communications. - 2004. - Vol. 131. - P. 223-227 : il. - Bibliogr. : p. 226-227 (18 ref.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
СВЕРХПРОВОДНИКИ -- РАСЧЕТЫ ПЕРВОПРИНЦИПНЫЕ -- КАРБИД ИТТРИЯ
Аннотация: The electronic band structure and ground state properties of the recently discovered 18-K superconducting Y2C3 material Akimitsu et al., 2004) have been examined by the full-potential linear muffin-tin method–generalized gradient approximation method and compared with those of the 4-K superconductor YC2. The calculations show that the growth of TC for the yttrium sesquicarbide as compared with 4-K YC2 may be due to the electronic factor: the near-Fermi DOS for Y2C3 was found to be about 36.7% higher that for YC2. The Fermi level of the "ideal" Y2C3 is located near the local DOS minimum, and thesuperconductivity of Y2C3-based materials will be very sensitive to synthesis conditions (for example, pressure and annealing effects) and the presence of various impurities and lattice vacancies. Probably these factors may be used to vary the superconductivity of the Y2C3 phase over a wide range

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8.
Инвентарный номер: нет.
   
   S 53


    Shein, I. R.
    First-principles calculations of elastic and electronic properties of tetragonal Th2NiC2 as a parent phase for new superconductors / I. R. Shein, A. L. Ivanovskii // Journal of Alloys and Compounds. - 2013. - Vol. 551. - P338-342 : il. - Bibliogr. : p. 341-342 (36 ref.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
Th2NiC2 -- ELASTIC PROPERTIES -- AB INITIO CALCULATIONS -- INTER-ATOMIC BONDING -- ELECTRONIC PROPERTIES
Аннотация: This work reports on the elastic, electronic properties and inter-atomic bonding of the newly discovered superconductor Th2NiC2 as obtained within ab initio calculations. We found that Th2NiC2 is mechanically stable and it will behave as a ductile material exhibiting enhanced elastic anisotropy in shear and a rather low hardness. The inter-atomic bonding in Th2NiC2 is described as an anisotropic mixture of covalent and ionic contributions, where inside [Th2C2] blocks covalent Th–C bonds emerge, and these blocks are bonded with the Ni atomic sheets through directional Ni–C bonds. Additionally, some inter-atomic ionic Th–C interactions occur owing to charge transfer Th → C. Our data reveal that for Th2NiC2 the Fermi level is located in a deep DOS minimum and the experimentally observed increase in TC in the sequence Th2NiC2 → Th1.8Sc0.2NiC2 may be explained by the growth of N(EF). We also speculate that an increase in N(EF) (and, probably, in TC) for Th2NiC2-based materials may be also achieved by an alternative way: by electron doping – for example, by partial substitution of V for Th or Cu for Ni, as well as by partial substitution of N for C with the formation of Th–Ni carbonitrides like Th2NiC2−xNx

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9.
Инвентарный номер: нет.
   
   S 53


    Shein, I. R.
    The Band Structures of Superconducting MgB2 and the Isostructural Compounds CaGa2, AgB2, AuB2, ZrBe2, and HfBe2 / I. R. Shein, N. I. Medvedeva, A. L. Ivanovskii // Physics of the Solid State. - 2001. - Vol. 43, № 12. - P2213-2218 : il. - Bibliogr. : p. 2218 (30 ref.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
СВЕРХПРОВОДНИКИ -- БОРИДЫ -- ДИБОРИД МАГНИЯ
Аннотация: This paper reports on a self-consistent, full-potential LMTO calculation of the band structure of the medium-Tc superconductor MgB2 and of the isostructural hexagonal phases of CaGa2, ZrBe2, HfBe2, AgB2, and AuB2. The factors responsible for the superconducting properties of magnesium diboride are considered. The results obtained are compared with previous calculations and available experimental dat

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10.
Инвентарный номер: нет.
   
   S 93


   
    Superconducting Properties of the Atomically Disordered MgB2 Compound / A. E. Kar'kin, V. I. Voronin, T. V. D'yachkova, N. I. Kadyrova, A. P. Tyutyunnik, V. G. Zubkov, Yu. G. Zainulin, M. V. Sadovskii, B. N. Goshchitskii // JETP Letters. - 2001. - Vol. 73, № 10. - P. 570-572 : il. - Bibliogr. : p. 572 (10 ref.)
ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
СВЕРХПРОВОДИМОСТЬ -- ДИБОРИД МАГНИЯ
Аннотация: The effect of disorder induced by neutron irradiation in a nuclear reactor (thermal neutron fluence 1x 10(19) cm–2) on the superconducting transition temperature Tc and the upper critical field Hc2 of polycrystalline MgB2 samples was investigated. Despite the appreciable radiation-induced distortions (more than ten displacements per atom), the initial crystal structure (C32) was retained. The temperature Tc decreased from 38 to 5 K upon irradiation and was practically completely restored after the subsequent annealing at a temperature of 700°C. A weak change in the dHc2/dT derivative upon irradiation is explained by the fact that the irradiated samples are described by the “pure” limit of the theory of disordered superconductors. The suppression of Tc upon disordering may be due to the isotropization of the originally anisotropic (or multicomponent) superconducting gap or to a decrease in the density of electronic states at the Fermi level

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