95Mo and 17O NMR studies of aqueous molybdate solutions

Aqueous molybdate solutions with molybdenum concentrations of [Mo]=1, 0.4, and 0.2 M have been studied by NMR at pH 7-1 and in 0.3-6 M HClO4. The 95Mo NMR spectrum of isopolyanion (IPA) Mo7O24(6-) (I) at pH=5 consists of a signal at 210 ppm and two overlapping peaks at 32 and approximately 15 ppm with the intensity ratio approximately 1:4:2, and that of beta-Mo8O26(4-) (II) consists of two signals at approximately 100 and 10 ppm with the intensity ratio approximately 1:3. A broad 95Mo NMR line at around 0 ppm was observed in the pH range of IPA Mo36O112(8-) (III), and a signal of cationic oxospecies including MoO2(2+) (IV) was observed from -62 to -69 ppm. Two protonation sites of IPA I have been identified from 17O NMR spectra, which suggests binding of up to two protons. The distribution diagram, derived from the 95Mo NMR spectra, is given for [Mo]=0.4 M. The 95Mo NMR signals shift to lower frequencies with increasing number and strength of the Mo-O terminal bonds.     

Mechanics and optics of rotating particles and drops in gas flows

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 103–110, September–October, 1989.     

Atomic structure of Sr0.75Ba0.25Nb2O6 single crystal and composition-structure-property relationin (Sr,Ba)Nb2O6 solid solutions

The structure of the Sr_0.75Ba_0.25Nb₂O₆ single crystal has been investigated by x-ray diffraction. The occupancies of the Ba and Sr sites in two structural channels are determined. It is found that these sites are split in the large (pentagonal) channel. A qualitative correlation is revealed between the smearing of the phase transition and the displacement of the Sr atom from the m symmetry plane in the pentagonal channel at different [Sr]/[Ba] ratios. The degree of acentricity of the NbO₆ octahedra is analyzed as a function of the [Sr]/[Ba] ratio.     

Magnetic phase transitions in nanoclusters and nanostructures

Four nanosystems possessing the first order magnetic phase transitions (FOMPT) are considered: (1) isolated iron oxide nanoclusters, (2) iron oxide nanostructures in the beginning of sintering, (3) nanostructures induced by shear stress under high-pressure action, (4) ordered iron oxide nanostructures. The thermodynamic models for FOMPT appearance and cluster critical size are proposed. The role of surface tension, defect density and nanocluster organization are discussed.     

Comments on the implementation of the state standard “The pH scale of aqueous solutions”

The newly implemented State Standard Gost 8.134-98 is commented on, and the tabulated data on pH of standard solutions contained in this document are given.     

Transfer coefficients of cations and anions upon glow discharge-induced nonequilibrium vaporization of solutions of alkaline earth metal salts

Firing of atmospheric-pressure, electrolytic-cathode glow discharge leads to an effect that is similar to well-known cathode sputtering. This process can be called nonequilibrium vaporization of the solution. Unlike quasi-equilibrium vaporization, the nonequilibrium process entails the transfer of nonvolatile components of the solution to the gas phase. Previously, studying glow discharge with calcium and barium chloride solutions as the cathode, we have shown that the transfer of cations and anions via the nonequilibrium vaporization of the nonvolatile solutes is not necessarily stoichiometric [1].     

Two-band BCS mechanism of superconductivity in a Ba(Fe0.9Co0.1)2As2 high-temperature superconductor

Terahertz and infrared spectra of the conductivity, σ(ν), and dielectric constant, ?(ν), of a Ba(Fe_0.9Co_0.1)₂As₂ film (T _c = 20 K) have been analyzed together with previous specific-heat and angular resolved photoelectron spectroscopy data. It has been shown that the spectra σ(ν) and ?(ν) of Ba(Fe_0.9Co_0.1)₂As₂ in the superconducting phase at T = 5 K, as well as the magnetic field penetration depth, can be described well using the standard Bardeen-Cooper-Schrieffer (BCS) model with an additive contribution of electron and hole bands. It has been found that the measured temperature dependence of the magnetic field penetration depth in a wide temperature range 5 K < T < T _c can be described only with the introduction of interband pairing interaction. The coupling constant of electron and hole bands, λ_{1, 2} = 0.1, as well as the temperature dependences of superconducting gaps in the electron and hole subsystems, has been determined using the model of two-band superconductivity developed earlier for MgB₂.     

Propagation of a short pulse in a medium with a resonance relaxation: The exact solution

A new analytical representation is obtained for the fundamental solution (Green’s function) to the problem of the propagation of a short pulse in an arbitrary medium with a single resonance relaxation process. The analytical representation is based on the generalized function of the local response of a linear medium [1] and includes the well-known Debye and Lorentz relaxation models as particular cases. The representation is used to determine the complete set of possible types of behavior for a short pulse propagating in the medium.