Structure,Magnetic Properties and Electromagnetic Response of Y-Type Hexaferrites and Hexaferrite-Based Composite Materials

Russian Physics Journal - The paper presents a study of the phase composition, morphology, magnetic and electromagnetic properties both of Y-type hexaferrites Ba2Ni2–xCuxFe12O22 (x = 0.4,...     

New Vanadium Germanium Garnets

New vanadatogermanates Ca_3–xMe_{2 + x}V₂GeO₁₂, Ca₃Mе₂VGe₂O₁₂, and Ca₃Me₂Ge₃O₁₂, where Me = Mg, Mn, Co, Ni, Fe, Zn, and x = 0–1, have been synthesized through coupled substitutions of cations in the initial garnets Ca_2.5Mn₂V₃O₁₂ or Ca₃Fe₂Ge₃O₁₂. The unit cell parameters of the synthesized samples have been determined. Probability analysis of the cation distribution in the octahedral positions of the crystal lattice as a function of crystallographic radii has been performed taking into account the spin state of the cations.     

Correlation between the equilibrium and relaxation dielectric properties of 1,2-ethanediol

The data on the dispersion of the permittivity ?*(ω) of 1,2-ethanediol over the temperature range 161–453 K and the frequency range 0.1 Hz–150 GHz were analyzed using the Dissado-Hill cluster model. The relaxation frequency ω_p = τ _DH ^?1 and intra-(n _DH) and intercluster (m _DH) correlation parameters were calculated. The energy barrier to the libration of molecular axes in clusters was found to be B _DH = 2.96 kJ/mol. The apparent enthalpy of activation was determined; it increased from ΔH _{DH exp} ^# = 22.18 kJ/mol to ΔH _{DH exp} ^# = 129.19 kJ/mol close to the glass transition temperature. The mean dipole moments $ \bar \mu _c The data on the dispersion of the permittivity ɛ*(ω) of 1,2-ethanediol over the temperature range 161–453 K and the frequency range 0.1 Hz–150 GHz were analyzed using the Dissado-Hill cluster model. The relaxation frequency ω_p = τ_DH⁻¹ and intra-(n _DH) and intercluster (m _DH) correlation parameters were calculated. The energy barrier to the libration of molecular axes in clusters was found to be B _DH = 2.96 kJ/mol. The apparent enthalpy of activation was determined; it increased from ΔH _{DH exp}^# = 22.18 kJ/mol to ΔH _{DH exp}^# = 129.19 kJ/mol close to the glass transition temperature. The mean dipole moments of 1,2-ethanediol clusters were calculated; they decreased from 162920 to 18.08 D as the temperature increased from 161 to 453 K. According to approximate estimates, the number of 1,2-ethanediol molecules in a cluster /μ_v decreased from 72405 at 161 K to 8.04 at 453 K (μ_v is the dipole moment of the molecule in the vacuum), which substantiated the suggestion of the existence of a spatial structure close to the boiling point. Original Russian Text ? N.V. Lifanova, T.M. Usacheva, V.I. Zhuravlev, V.K. Matveev, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 10, pp. 1973–1981.     

Structural disordering in Cr-doped Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> spinels

The processes of lithium redistribution in the structure of cubic Li₄Ti₅O₁₂ spinel, caused by both chromium doping and thermal activation, have been investigated by nuclear magnetic resonance. It is shown that Li ions migrate from tetra- to octahedral crystallographic positions with an increase in temperature. This process becomes more pronounced at temperatures above 400 K. In contrast, the fraction of tetrahedrally coordinated Li increases as a result of doping with chromium.     

Turbulence of incompressible liquid flow near local equilibrium and the principle of secondary maximum of entropy

The variational principle of maximum entropy is used to describe the dynamics of weakly nonequilibrium turbulence using the theory of Reynolds stresses for viscous incompressible liquid flow. From this principle, equations closing the theory of Reynolds stresses and also equations describing mean flow-turbulence interaction for 3D turbulent flows are derived. The theory is reduced to 2D flows and weak turbulence. Thermodynamic analogues and an example of Couette flow are considered.     

Special features of electromagnetic wave propagation in a two-layered cylindric waveguide with right- and left-handed media

Results of modeling of the coefficients of waveguide mode propagation in a two-layered circular waveguide filled with media having positive and negative refractive indices called Right- and Left-Handed Media (LHM and RHM, respectively) are presented that allow us to conclude that complex waves and waves with significant slowing down of the phase velocity exist in these waveguides.     

Luminescent characteristics of tetraphenylporphyrin and its derivatives with lutetium

The spectral and luminescent characteristics of new tetraphenylporphyrin derivatives that contain the lutetium atom in their structure are studied in comparison with the most completely studied unsubstituted tetraphenylporphyrin and its complex with zinc. The luminescence quantum yields in liquid and frozen solutions are measured. The specific features of luminescent characteristics of these compounds and their possible applications are discussed.     

Parametric excitation of temperature oscillations in a high-Q dielectric microwave resonator in liquid helium vapor

We study the threshold conditions of the parametric excitation of temperature oscillations using pulsed microwave pumping in three-mode regime for high-Q ferroelectric cryogenic resonators made of SrTiO₃ and KTaO₃. Comparative analysis is performed for the threshold power of the excitation of temperature oscillations and the threshold power of the ponderomotive parametric excitation of acoustic oscillations in the resonator. It is shown that in three-mode regime, temperature oscillations can develop under a rather moderate pump power of about 0.1–8 μW, depending on the combination of interacting temperature and electromagnetic modes. The calculated low threshold powers allow one to apply resonators in practice as high-sensitivity infrared sensors, resonant bolometers, and parametric amplifiers. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 2, pp. 172–180, February 2009.     

Hydration and proton transport in solid solutions based on Ba<Subscript>2</Subscript>CaWO<Subscript>6</Subscript>

Hydrated alkaline-earth metal tungstates Ba₄Ca_{2 + x} W_{2 ? x} O_{12 ? 2x} with perovskite structure were studied by the thermogravimetry, ¹H NMR, IR, and Raman spectroscopy methods. Electrical conductivity and transfer numbers were measured with varying T, \(p_{O_2 } \) and \(p_{H_2 O} \). The solid solutions are capable of reversibly intercalating water and can exhibit high-temperature proton transport. The localization of protons on oxygen results in the appearance of energetically nonequivalent OH groups; a small fraction of protons are present in the form of H₂O and H₃O⁺.