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71.
72.
A. I. Karelin N. S. Tkacheva S. E. Nadkhina L. S. Leonova A. M. Kolesnikova L. S. Usacheva A. V. Levchenko Yu. A. Dobrovol’skii 《Russian Journal of Inorganic Chemistry》2016,61(9):1144-1152
The effect of antimony doping of tin dioxide at Sb/Sn = 0.2–2.5 on the physical properties and structure of air-dry samples of hydrous tin dioxide, SnO2 ? nH2O (HTD), was studied by IR and Raman spectroscopy, powder X-ray diffraction, impedance measurements, TGA, and electron microscopy. The doped materials retained the structure of undoped HTD materials if the Sb/Sn ratio did not exceed the threshold value of 1.0. When Sb/Sn > 1, crystalline antimony oxide admixture appeared. The data of IR spectroscopy attested to the presence of two types of water in HTD-Sb, namely, physisorbed and chemisorbed water. The major part of water of the former type can be removed by evacuation at room temperature. Chemisorption occurs upon coordination of water molecules by metal ions through the formation of metal–oxygen bonds. Water molecules of the latter type are retained in evacuated samples at room temperature and on heating above the boiling point of liquid water. By impedance spectroscopy, HTD-Sb samples were shown to possess fairly high proton conductivity at high humidity; however, the conductivity decreased by two orders of magnitude after partial removal of water molecules of the former type. This attests to the destruction of the loosely bound hydrogen bond network, across which proton transfer takes place. It was also found that under conditions of constant humidity, the proton conductivity successively decreases with increasing antimony concentration. This is attributable to the fact that Sb(III) ions polarize the local environment to a lesser extent than Sn(IV) ions. 相似文献
73.
Alexander V. Evteev Elena V. Levchenko Leila Momenzadeh Irina V. Belova Graeme E. Murch 《哲学杂志》2016,96(6):596-619
Using results of equilibrium molecular dynamics simulation in conjunction with the Green–Kubo formalism, we present a general treatment of thermal impedance of a crystal lattice with a monatomic unit cell. The treatment is based on an analytical expression for the heat current autocorrelation function which reveals, in a monatomic lattice, an energy gap between the origin of the phonon states and the beginning of the energy spectrum of the so-called acoustic short-range phonon modes. Although, we consider here the f.c.c. Al model as a case example, the analytical expression is shown to be consistent for different models of elemental f.c.c. crystals over a wide temperature range. Furthermore, we predict a frequency ‘window’ where the thermal waves can be generated in a monatomic lattice by an external periodic temperature perturbation. 相似文献
74.
A phenomenological theory of the magnetic-field penetration-depth (λ
iα
) anisotropy in high-temperature superconductors is constructed taking account of the magnetic susceptibility (χ
ik
) anisotropy of the surface layer. The factor of 1.9 change in the anisotropy λ
c
/λ
ab
with 4% substitution of Co for Cu ions in YBa2Cu3O7 is virtually completely due to the increase in the magnetic susceptibility anisotropy. For Cu-Zn substitutions the change
in λ
c
/λ
ab
is characterized primarily by a change in the anisotropy of the tensor of the reciprocal effective masses of the charge carriers
(pairs).
Fiz. Tverd. Tela (St. Petersburg) 41, 1552–1555 (September 1999) 相似文献
75.
A. V. Pashchenko V. P. Pashchenko V. K. Prokopenko V. A. Turchenko Yu. F. Revenko A. S. Mazur V. Ya. Sycheva N. A. Liedienov V. G. Pitsyuga G. G. Levchenko 《Journal of Experimental and Theoretical Physics》2017,124(1):100-113
The structure, the structure imperfection, and the magnetoresistance, magnetotransport, and microstructure properties of rare-earth perovskite La0.3Ln0.3Sr0.3Mn1.1O3–δ manganites are studied by X-ray diffraction, thermogravimetry, electrical resistivity measurement, magnetic, 55Mn NMR, magnetoresistance measurement, and scanning electron microscopy. It is found that the structure imperfection increases, and the symmetry of a rhombohedrally distorted R3?c perovskite structure changes into its pseudocubic type during isovalent substitution for Ln = La3+, Pr3+, Nd3+, Sm3+, or Eu3+ when the ionic radius of an A cation decreases. Defect molar formulas are determined for a real perovskite structure, which contains anion and cation vacancies. The decrease in the temperatures of the metal–semiconductor (T ms) and ferromagnet–paramagnet (T C) phase transitions and the increase in electrical resistivity ρ and activation energy E a with increasing serial number of Ln are caused by an increase in the concentration of vacancy point defects, which weaken the double exchange 3d 4(Mn3+)–2p 6(O2–)–3d 3(Mn4+)–V (a)–3d 4(Mn3+). The crystal structure of the compositions with Ln = La contains nanostructured planar clusters, which induce an anomalous magnetic hysteresis at T = 77 K. Broad and asymmetric 55Mn NMR spectra support the high-frequency electronic double exchange Mn3+(3d 4) ? O2–(2p 6) ? Mn4+(3d 3) and indicate a heterogeneous surrounding of manganese by other ions and vacancies. A correlation is revealed between the tunneling magnetoresistance effect and the crystallite size. A composition–structure imperfection–property experimental phase diagram is plotted. This diagram supports the conclusion about a strong influence of structure imperfection on the formation of the magnetic, magnetotransport, and magnetoresistance properties of rare-earth perovskite manganites. 相似文献
76.
This paper reports on the use of a local order measure to quantify the spatial ordering of a quantum dot array (QDA). By means of electron ground state energy analysis in a quantum dot pair, it is demonstrated that the length scale required for such a measure to characterize the opto-electronic properties of a QDA is of the order of a few QD radii. Therefore, as local order is the primary factor that affects the opto-electronic properties of an array of quantum dots of homogeneous size, this order was quantified through using the standard deviation of the nearest neighbor distances of the quantum dot ensemble. The local order measure is successfully applied to quantify spatial order in a range of experimentally synthesized and numerically generated arrays of nanoparticles. This measure is not limited to QDAs and has wide ranging applications in characterizing order in dense arrays of nanostructures. 相似文献
77.
A. V. Pashchenko V. P. Pashchenko V. K. Prokopenko Yu. F. Revenko N. G. Kisel V. I. Kamenev A. G. Sil’cheva N. A. Ledenev V. V. Burkhovetskii G. G. Levchenko 《Physics of the Solid State》2014,56(5):955-966
The structure, lattice imperfection, and properties of ceramic samples La0.6 ? x Nd x Sr0.3Mn1.1O3-δ (x = 0–0.4) have been investigated using the X-ray diffraction, resistive, magnetic (χac, 55Mn NMR), magnetoresistive and microscopic methods. It has been shown that there is a satisfactory agreement between the concentration decrease in the lattice parameters a of the rhombohedral (x = 0, 0.1, 0.2) and cubic (x = 0.3, 0.4) perovskite structures and the average ionic radii $\bar R$ for the lattice containing anion vacancies, cation vacancies, and nanostructured clusters with Mn2+ ions in A-positions. With an increase in the neodymium concentration x, the vacancy-type imperfection increases, the cluster-type imperfection decreases, the temperatures of metal-semiconductor phase transition T ms and ferromagnetic-paramagnetic phase transition T C decrease, and the content of the ferromagnetic phase decreases. The anomalous hysteresis is associated with the appearance of unidirectional exchange anisotropy induced in a clustered perovskite structure consisting of a ferromagnetic matrix and a planar antiferromagnetic cluster coherently coupled with it. An analysis of the asymmetrically broadened 55Mn NMR spectra has revealed a high-frequency electronic double exchange (Mn3+-O2?-Mn4+) ? (Mn4+-O2?-Mn3+) and an inhomogeneity of the magnetic and charge states of manganese due to the heterogeneous environment of the manganese ions by other ions and defects. The observed changes in the resonant frequency and width of the resonance curve are caused by changes in the ratio Mn3+/Mn4+ and magnetic inhomogeneity. An increase in the neodymium concentration x leads to a decrease in the ferromagnetic phase content determined from the dependences 4πNχac(T) and the 55Mn NMR curves. The phase diagram characterizes an interrelation between the composition, the imperfection of the structure, and the transport, magnetic, and magnetoresistive properties of lanthanum neodymium manganite perovskites. It has been found that there is a correlation between the imperfection, magnetic inhomogeneity, coercive force, and magnetoresistance effect exhibited by the perovskite structure. 相似文献
78.
N. E. Sluchanko A. N. Azarevich A. V. Bogach V. V. Glushkov S. V. Demishev M. A. Anisimov A. V. Levchenko V. B. Filipov N. Yu. Shitsevalova 《Journal of Experimental and Theoretical Physics》2012,115(3):509-526
The angular, temperature, and magnetic field dependences of the resistance recorded in the Hall effect geometry are studied for the rare-earth dodecaboride Tm1 ? x Yb x B12 solid solutions where the metal-insulator and antiferromagnetic-paramagnetic phase transitions are observed in the vicinity of the quantum critical point x c ?? 0.3. The measurements performed on high-quality single crystals in the temperature range 1.9?C300 K for the first time have revealed the appearance of the second harmonic contribution, a transverse even effect in these fcc compounds near the quantum critical point. This contribution a is found to increase drastically both under the Tm-to-ytterbium substitution in the range x > x c and with an increase in the external magnetic field. Moreover, as the Yb concentration x increases, a negative peak of a significant amplitude appears on the temperature dependences of the Hall coefficient R H(T) for the Tm1 ? x Yb x B12 compounds, in contrast to the invariable behavior R H(T) ?? const found for TmB12. The complicated activation-type behavior of the Hall coefficient is observed at intermediate temperatures for x ?? 0.5 with activation energies E g /k B ?? 200 K and E a/k B = 55?C75 K, and the sign inversion of R H(T) is detected at liquid-helium temperatures in the coherent regime. Renormalization effects in the electron density of states induced by variation of the Yb concentration are analyzed. The anomalies of the charge transport in Tm1 ? x Yb x B12 solid solutions in various regimes (charge gap formation, intra-gap many-body resonance, and coherent regime) are discussed in detail and the results are interpreted in terms of the electron phase separation effects in combination with the formation of nanosize clusters of rare earth ions in the cage-glass state of the studied dodecaborides. The data obtained allow concluding that the emergence of Yb-Yb dimers in the Tm1 ? x Yb x B12 cage-glass matrix is the origin of the metal-insulator transition observed in the achetypal strongly correlated electron system of YbB12. 相似文献
79.
D.?V.?Kulagin G.?G.?Levchenko A.?S.?Savchenko A.?S.?Tarasenko S.?V.?TarasenkoEmail author V.?G.?Shavrov 《Journal of Experimental and Theoretical Physics》2012,114(3):474-495
The features of refraction (including the Goos-Hánchen effect) of a TM or TE bulk electromagnetic wave incident from outside
on the surface of a chiral magnetoelectric with the homogeneous antisymmetric magnetoelectric interaction has been analytically
studied on an example of the two-sublattice model of a multiferroic. In particular, it has been shown that the requirement
that the diagonal components of the permeability and permittivity tensors are simultaneously negative is not necessary for
the implementation of the properties of a left-handed medium. The results have been generalized to the case of an easy-axis
antiferromagnet with an antisymmetry center with the 4
z
±2
x
+
I
− structure in the static external magnetic field perpendicular to the easy axis of magnetization. Some results of this work
were preliminarily reported in D.V. Kulagin, G.G. Levchenko, A.S. Savchenko, A.S. Tarasenko, and S.V. Tarasenko, JETP Lett.
92, 511 (2010). 相似文献
80.
Magnetoelectroelastic shear body waves in periodically layered metalized ferrite–piezoelectric media
A method of deriving the dispersion equations for magnetoelectroelastic shear waves in periodically layered media is proposed.
The media are formed by uniting identical metalized laminates, each consisting of two dissimilar piezoelectric layers separated
by a layer with the properties of ferrite. A numerical analysis is carried out and the propagation of body waves in different
structures consisting of ZnO and GaYtC layers is described within wide ranges of frequencies and wave numbers. The influence
of the physical, mechanical, and geometrical parameters of the layers on the structure of the transmission and suppression
zones and the effect of the piezoelectric effect of the position of transmission edges are examined 相似文献