Effect of pressure on the electric transport properties of carbon-doped EuB6

We report about the influence of external pressure on the electrical resistivity of EuB_5.99C_0.01, the compound believed to be intrinsically inhomogeneous due to fluctuations of carbon content. Our results show that the low-temperature resistivity maximum shifts to a lower temperature with applied pressure, opposite to the behavior reported for stoichiometric EuB₆. The origin of such a qualitative difference we associate with the increasing volume fraction of the phase that is not compatible with ferromagnetic ordering (originating in regions with relatively higher carbon concentration) with increasing pressure. Our results support a recent proposition of Batkova et al. (2008) [12] that carbon-rich regions strongly influence magnetotransport properties of carbon-doped EuB₆, such as they play a role of “spacers”, which prevent the percolation of a ferromagnetic phase.     

Anomalies of the specific heat near the quantum critical point in Tm<Subscript>0.74</Subscript>Yb<Subscript>0.26</Subscript>B<Subscript>12</Subscript>

The behavior of the specific heat near the quantum critical point x ∼ 0.3 in the Tm_{1 − x} Yb _x B₁₂ system has been studied. Detailed measurements have been performed on high-quality single-crystalline Tm_0.74Yb_0.26B₁₂ samples within a wide temperature range of 1.9–300 K in a magnetic field up to 9 T. The temperature dependence of the magnetic contribution to the specific heat has a logarithmic divergence of the form C/T ∼ lnT at T < 4 K, which can be attributed to the quantum critical behavior regime suppressed by the external magnetic field. The Schottky anomaly of the magnetic contribution to the specific heat in Tm_0.74Yb_0.26B₁₂ has been analyzed.     

Hall Effect in the Antiferromagnetic State of Ho0.8Lu0.2B12

JETP Letters - Detailed measurements of the Hall effect in the Ho0.8Lu0.2B12 antiferromagnetic compound (Néel temperature TN = 5.75 K) in magnetic fields up to 80 kOe oriented in the (110)...     

Tensor A yy and vector A y analyzing powers in the 1H(d, d′)X and 12C(d, d′)X reactions at initial deuteron momenta of 9 GeV/c in the region of baryonic resonance excitation

The angular dependence of the tensor A _yy and vector A _y analyzing powers in the inelastic scattering of deuterons with a momentum of 9.0 GeV/c on hydrogen and carbon has been measured. The range of measurements corresponds to the baryonic resonance excitation with masses of ∼2.2–2.6 GeV/c ². The A _yy data, being in good agreement with the previous results, demonstrate an approximate t scaling up to −1.5 (GeV/c)². The large values of A _y show a significant role of the spin-dependent part of the elementary amplitude of the NN → NN* reaction. The results of the experiment are compared with model predictions of the plane-wave impulse approximation. The text was submitted by the authors in English.     

Anisotropic disk dielectric resonator with conducting end faces

Electrodynamic analysis of a disk dielectric resonator with finite-conductivity end faces that is excited at the whispering-gallery mode is carried out. The inverse problem of determining the components of the permittivity tensor of the anisotropic uniaxial crystal, loss tangent of the dielectric material, and surface resistance of the conductor is formulated and solved. The frequency spectra and energy characteristics of a Teflon disk resonator with copper-covered end faces are studied in the 8-mm wave range.     

Antiferromagnetic instability and the metal-insulator transition in Tm1 − x Yb x B12 rare earth dodecaborides

The magnetic and transport characteristics of substitutional solid solutions of the Tm_1?x Yb _x B₁₂ rare earth dodecaborides have been investigated. The measurements performed in the wide temperature range 1.8?300 K on the high-quality single-crystalline samples make it possible to conclude that as x increases, antiferromagnetic instability develops with the quantum critical point (T _N = 0) near x = 0.3 and relevant dielectrization of the electron structure in the range 0 ≤ x ≤ 0.8 takes place. With the results of the thermoelectric measurements in Tm_1?x Yb _x B₁₂, the activation energy values and their dependence on x have been determined.     

The directional crystallization of W-B-C-d-transition metal alloys

Crystallization from the melt during arc melting and directional solidification during induction zone melting of pseudo-alloys tungsten carbide (WC)-MeB₂ (Me—Ti, Zr, Cr) and a number of alloys of the W-B-C system (WB_0.12C_0.74; WB_0.25C_0.75; WB_0.34C_0.32; WB_0.49C_0.76; WB_0.59C_0.76; WB_0.89C_0.75; (WC)_0.9B_0.1) has been studied. It was shown that the alloys WC—80 mass%-ZrB₂—20 mass% and WC—72 mass%-WB—28 mass% are the closest ones to eutectic compositions. Investigation of the microstructure of eutectic alloys in the WC-WB system by thin foil method has revealed that both matrix and reinforcing phases are single crystalline.Hardness tests by indentation of the eutectic structure area (P=10.3 N) do not result in radial crack formation, which is evidence of the essential plasticity of the obtained composite material. It is established that new ceramic-ceramic eutectic composite materials based on WC with transition metal diborides and with a boride phase of tungsten may be created. Such materials can be successfully applied in contemporary high-temperature techniques.     

Kinetic models of CO oxidation on Pd-containing catalysts (with and without SO2)

The effect of reactants and experimental conditions on the Pd/C catalyzed oxidation of DS at 110–150°C and 0.3–1.0 MPa in alkaline aqueous solution is described with emphasis on the maximal reaction rate, yield of DGA and catalyst deactivation. Oxygen causes practically irreversible deactivation of catalyst.

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DS Pd/C 110–150°C 0.3–1.0 . , DGA . .

     

CO oxidation over CuCr/Al2O3 catalysts in presence of SO2

Poisoning of variously prepared CuCr/Al₂O₃ catalysts having different compositions by sulfur dioxide has been studied. Comparative values for a decrease in the catalyst activities have been obtained.

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CO .

     

Anisotropic Spherical Cavity Resonator I. Azimuthally Homogeneous Oscillations

Resonant oscillations are considered in the spherical cavity with the uniform crystal medium and bounded by a non-perfect conductor. The Maxwell equations are reduced to the couple of wave equations each describing the TE and TH modes. We show that the crystal anisotropy affects only the TM modes. The solution of the wave equations satisfies the boundary conditions on the spherical surface that define the spherical characteristics of the resonant oscillations. New types if TM modes appear caused by the anisotropy of the medium. The analytical solution of the dispersion equation is considered in the form of continued fraction. Numerical results are presented demonstrating of natural frequencies of higher mode numbers.