Differences in behaviour of adsorbed water in kaolinites and montmorillonites in temperature range from -90°C to +140°C by dielectric spectroscopy

Two different types of natural layer aluminosilicates (clay minerals), montmorillonite with the exchangeable K+ and Ni2+ cations and kaolinite with the exchangeable K+ and Ba2+ cations, were investigated by dielectric spectroscopy. The different effects of water adsorption in montmorillonites and kaolinites on the dielectric response were observed in wide temperature (-90°C ÷ +140°C) and frequency (1 Hz ÷ 1 MHz) ranges. The influence of the nature of the hydration centers on adsorbed water dynamics and influence of ions nature on the activation energy values of the relaxation processes were discussed

Two types of adsorbed water in natural montmorillonites at low temperatures by dielectric spectroscopy

Dielectric spectroscopy was applied to natural clay mineral - montmorillonite with the exchangeable K+ and Ni2+ cations where the effect of water adsorption in the samples on the dielectric response was examined in the temperature from -115°C to -75°C and frequency from 1 Hz to 1 MHz ranges. Two relaxation processes (1 and 2) were revealed. The process 1 was related to the adsorbed ordered water structures formed on the interior surface of interlayer channels while the relaxation process 2 was attributed to the disordered water structures built between two surface water monolayers

The percolation phenomenon and fractal dimension of natural silicates

© (2015) Trans Tech Publications, Switzerland. Many physical effects, such as dc conductivity and percolation, depend on the morphology of the silicate structure and its relationship to adsorbed water. These effects play an important role in numerous technological applications, in geology, oil-extracting industry, and other practical fields. In this study, all the samples: natural montmorillonite, kaolinite, and ?linoptilolite with different exchangeable cations in their structures, - were stored in ambient air humidity. The investigation was carried by using two separate techniques, namely Dielectric Spectroscopy and a fractal analysis of electron micrographs. The aims of this work were to analyze the complex relaxation behavior of the relaxation process in temperature range -70°C ÷ 70°C and to determine the fractal dimensions of silicates from the dielectric response at percolation. Dielectric measurements in the frequency range of 1 Hz ÷ 1 MHz were performed using a BDS 80 Dielectric Spectrometer based on an Alpha Impedance Analyzer (Novocontrol). The micrographs were analyzed using a special Matlab based program. The analysis of aspects of the dielectric relaxation spectra related to percolation was used for the determination of the numerical characteristics of geometric heterogeneity of natural silicates. The percolation temperatures of the studied samples were determined. The percolation phenomenon in the silicates is related to the transfer of the electric excitation within the developed network of open pores due to the migration of protons and ions along the surface of connected pores on the outer surfaces of the granules. The analysis of these processes allows one to extract the fractal dimensions associated with the migration of charge carriers within the porous medium. Fractal dimensions of the silicates calculated in two ways: from dielectric spectroscopy study and from fractal analysis of the micrographs, - are in good agreement with each other. It was demonstrated that conventional method of the spatial fractal dimension determination using fractal analysis of electron micrographs leads to overestimation in the case of spatial fractal bounded by a surface fractal. The dielectric spectroscopy method is free from such overestimation

Anomalous state of a 2DEG in vicinal Si MOSFET in high magnetic fields

We report the observation of an anomalous state of a 2D electron gas near a vicinal surface of a silicon MOSFET in high magnetic fields. It is characterised by unusual behaviour of the conductivities $\sigma_{xx}$ and $\sigma_{xy}$, which can be described as a collapse of the Zeeman spin splitting accompanied by a large peak in $\sigma_{xx}$ and an anomalous peak in $\sigma_{xy}$. It occurs at densities corresponding to the position of the Fermi level above the onset of the superlattice mini-gap inherent to the vicinal system. The range of fields and densities where this effect exists has been determined, and it has been shown that it is suppressed by parallel magnetic fields

Considerable enhancement of the critical current in a superconducting film by magnetized magnetic strip

We show that a magnetic strip on top of a superconducting strip magnetized in a specified direction may considerably enhance the critical current in the sample. At fixed magnetization of the magnet we observed diode effect - the value of the critical current depends on the direction of the transport current. We explain these effects by a influence of the nonuniform magnetic field induced by the magnet on the current distribution in the superconducting strip. The experiment on a hybrid Nb/Co structure confirmed the predicted variation of the critical current with a changing value of magnetization and direction of the transport current.Comment: 6 pages, 7 figure

Three-Nucleon Continuum by means of the Hyperspherical Adiabatic Method

This paper investigates the possible use of the Hyperspherical Adiabatic basis in the description of scattering states of a three-body system. In particular, we analyze a 1+2 collision process below the three-body breakup. The convergence patterns for the observables of interest are analyzed by comparison to a unitary equivalent Hyperspherical Harmonic expansion. Furthermore, we compare and discuss two different possible choices for describing the asymptotic configurations of the system, related to the use of Jacobi or hyperspherical coordinates. In order to illustrate the difficulties and advantages of the approach two simple numerical applications are shown in the case of neutron-deuteron scattering at low energies using s-wave interactions. We found that the optimization driven by the Hyperspherical Adiabatic basis is not as efficient for scattering states as in bound state applications.Comment: 29 pages, 5 figures, accepted for publication in Few-Body Systems (in press

Dielectric spectroscopy of amino alcohols at low temperatures

© 2016 Pleiades Publishing, Ltd. The dielectric properties of three vicinal amino alcohols are studied at temperatures in the range of -140-70°C and the frequency interval of 0.1 Hz to 1 MHz. The temperature dependences of the observed relaxation processes indicate both glass transition and melting processes. The relatively high conductivity of the samples was considered from the viewpoint of proton conductivity through a network of hydrogen bonds of amino alcohol molecules

The variety of states of adsorbed water in heterogeneous materials and their dielectric response

Whenever water interacts with another dipolar or charged entity, there exists a broadening of its dielectric relaxation peak. Often this broadening can be described by the phenomenological Cole-Cole (CC) spectral function. A new approach has been recently presented (A. Puzenko, P. Ben Ishai, and Y. Feldman, Phys. Rev. Letters 105, 037601-4 (2010)), which is based on the fractal nature of the time set of the interaction of the relaxing water dipoles with their encompassing matrix. It demonstrates a fundamental connection between the relaxation time, τ, the broadening parameter, α, and the Kirkwood-Froehlich correlation function B. The parameters B, τ and α were chosen as the coordinates of the new 3D space, wherein the evolution of the relaxation process, as a result of the variation of external macroscopic parameters (temperature, pressure etc.), will depict a trajectory. This trajectory is a result of the connection between the kinetic and the structural properties of water in the complex system. © 2013 American Institute of Physics