Non-markovian properties of dielectric relaxation in liquids

Statistical molecular memory is investigated in dielectric relaxation in a liquid medium. A new method of closing the infinite chain of kinetic equations for the time correlation function is proposed, and used to obtain an equation permitting the calculation of the smallest-order memory functions. The spectrum of the non-Markovian parameter obtained indicates that dielectric relaxation in liquid CH₃I is a significantly non-Markovian process.Kazan' State Pedagogical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 27–31, October, 1995.     

Computer simulation of the non-local dielectric function of polar liquids: boundary conditions revisited

For the calculation of ε(k) via the correlation function of the bound charge density fluctuations or the ratio of the bound charge density to an external charge density, a generalized form of the fluctuation dissipation theorem is derived which accounts for different types of boundary conditions through a modified Green's function. It is demonstrated for the case of an interaction site model of water that it is possible to obtain consistent results for the non-local dielectric function with different types of boundary conditions. This is shown by calculating ε(k) both from the correlation function 〈ρ_b(k)ρ_b(-k)〉 and from the dielectric response to an external electric field.     

脉冲激光烧蚀中电声弛豫时间的确定

为了提高脉冲激光制备薄膜的质量,准确掌握电声弛豫时间是关键,它对脉冲激光脉宽和能量密度的选取起着决定性的作用. 文中以铝靶材为例,利用经典的双温方程通过时域有限差分法(FDTD)得到电子、离子亚系统的温度随时间和位置演化的图像,进而得到电声弛豫时间的准确值. 这样便能准确划分热烧蚀和非平衡烧蚀,从而更好地控制激光的烧蚀过程. 同时找出了电声弛豫时间随激光脉宽以及能量密度变化的规律. 关键词： 飞秒激光 电声弛豫时间 双温方程 激光能量密度     

Mechanism of structural dielectric relaxation in associated liquids

A mechanism of structural dielectric relaxation is proposed, and on this basis the kinetic equations taking into account tunneling of protons from the clusters are written and investigated. The solution, together with the results of dielectric measurements, is used to determine the structural parameters of low-concentration aqueous solutions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 16–19, November, 1979.     

Numerical computer calculation of distribution of similar point charges at the dielectric surface

Results of numerical calculation of the distribution of similar point charges over a uniformly charged dielectric plane are presented for different surface charge densities and surface temperatures. It is shown that, in the case of the surface charge density ranging from 2 × 10⁻⁶ to 7 × 10⁻⁵ C/m² and temperatures ranging from 300 to 800 K, the Lindemann criterion is fulfilled for the average deviation of the point charge from the equilibrium position, and the collection of point charges at the dielectric surface can be regarded as a 2D Coulomb crystal.     

Molecular relaxation behaviour of mixtures of some polar non-associative liquids

Molecular relaxation studies have been made on rigid polar solutes dibenzofuran and s-trioxane and their mixtures with benzophenone, ortho- and meta-dichlorobenzenes in the microwave region over a range of temperatures in dilute benzene solutions. The relaxation times and the thermodynamic parameters for the activated state have been determined using the measured dielectric data. The results obtained have been discussed in terms of the molecular motion of the system and are consistent with those of other rigid molecules studied previously. The results are also compared with the computed values obtained by employing a relation proposed by us earlier.     

Formation of associates of solvated cations in salt solutions in polar dielectric liquids

Experimental results are presented on excitation of oscillations of polarization charges of solvated ions in an aqueous solution of a mixture of cerium and lead nitrates under an external asymmetric electric field and the directed motion of solvated cerium and lead cations, caused by this process. The applicability of the approximation of the existence of a self-consistent electric field in the solution volume to explain the observed frequency ranges of the manifestation of the effect of electroinduced selective drift of solvated cations is demonstrated. The results of a theoretical analysis of the possibility of forming associates from solvated ions are presented.     

An analytical study of the dielectric relaxation mechanism in crystals with polar molecules

The kinetic equations for motion of polar vacancies, the dipole moments of which are numerically equal to the moment of a molecule in an electric field, are derived and studied. The polarization process is explained through orientation of the polar vacancies. A formula for the dielectric loss angle as a function of the frequency spectrum of external fields and temperature is derived, and using this formula calculations are performed for crystals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp. 51–58, March, 1972.     

Anisotropic dielectric function in polar nanoregions of relaxor ferroelectrics

The Letter suggests treating the infrared reflectivity spectra of single crystal perovskite relaxors as fine-grained ferroelectric ceramics: locally frozen polarization makes the dielectric function strongly anisotropic in the phonon frequency range and the random orientation of the polarization at nanoscopic scale requires taking into account the inhomogeneous depolarization field. Employing a simple effective medium approximation (the Bruggeman symmetrical formula) turns out to be sufficient for reproducing all principal features of room temperature reflectivity of Pb(Mg(1/3)Nb(2/3))O3. One of the reflectivity bands is identified as a geometrical resonance entirely related to the nanoscale polarization inhomogeneity. The approach provides a general guide for systematic determination of the polar mode frequencies split by the inhomogeneous polarization at the nanometer scale.     

Calculation of the dielectric function for highly excited polar semiconductors

The optical dielectric function of an electron-hole plasma in highly excited polar semiconductors with a direct band gap is calculated by solving a Bethe-Salpeter equation for the polarization function. The screening of the Coulomb potential is treated in a damped phonon-plasmon-pole approximation. We include the complex dynamical self-energy corrections as well as electron-hole correlations.Project of the Sonderforschungsbereich Frankfurt/Darmstadt, financed by special funds of the Deutsche Forschungsgemeinschaft     

Influence of inertia on the dielectric properties of polar liquids. Application to deoxyhemoglobin S

In this paper, we have derived oscillator relations, including inertial effects, which are an extension of the Debye relations, and have shown their interest together with their limits of application. These relations may be applied as soon as the dimensionless damping parameter γ is less than 10, and yield a lot of information on the molecular structure of the medium. We have used them in the study of an abnormal hemoglobin, termed deoxyhemoglobin S, from experimental data of dielectric constants obtained by Delalic et al. Our calculation is based upon the Kramers-Kronig method. By means of a best-fit procedure of the dispersion plots together with the Cole-Cole plots, the presence of a monomeric phase and of three main aggregates which are well characterized, is found. So, we get several stereotypes of the medium, and its time evolution is interpreted in terms of molecular parameters. We calculate the moment of inertia of these aggregates and we give the evolution of the friction coefficient ξ. We remark that the decrease of γ corresponds to an ordered array of the medium and that its limiting value equal to 1.6 is related to a gel state, in full agreement with the theoretical estimate obtained by Coffey.     

The flexoelectric effect and the low-temperature limit of dielectric relaxation time

A polaron model of the quantum process of low-temperature relaxation in flexonanostructures is elaborated. The model enables us to deal with features of the electron spectrum and local strain, which are important in considering the size effects in structures with giant piezoelectricity.     

Theory of polar liquids

Two recent contributions to the statistical theory of polar fluids, namely the perturbation theory of Stell, Rasaiah and Narang (SRN) and the meanspherical-approximation (MSA) results of Wertheim, and of Nienhuis and Deutch, are compared and contrasted for the conceptually simple model of hard spheres, diameter R, with central point dipoles, of strength μ (dipolar hard spheres). It is shown that the MSA approach replaces correlation functions which enter correctly into the SRN theory by their low-density limits : to this extent it is unsatisfactory. On the other hand the MSA work does suggest reasons why the naive Padé approximant featuring in SRN theory may be expected to do reasonable justice to the physics of the problem. Numerical comparisons of the excess free-energy (as compared with non-polar hard spheres) as a function of reduced density, ρ* = ρR ³, are given at two temperatures, T* = 2 and T* = 0·25, where T* = kTR ³/μ². Similar curves, for T* = 1 and T* = 0·5, are available from the authors. The gas-liquid (T*, ρ*)-phase boundary is located, near the critical point, on both theories, as are the vapour pressure curves. These are calculated using the Carnahan-Starling equation of state for hard spheres ; and critical comment is made in justification of employing this in the context of MSA results for the excess quantities. The two theories are found to have appreciably different numerical consequences.     

Williams-watts dielectric relaxation: A fractal time stochastic process

Dielectric relaxation in amorphous materials is treated in a defect-diffusion model where relaxation occurs when a mobile defect, such as a vacancy, reaches a frozen-in dipole. The random motion of the defect is assumed to be governed by a fractal time stochastic process where the mean duration between defect movements is infinite. When there are many more defects than dipoles, the Williams-Watts decaying fractional exponential relaxation law is derived. The argument of the exponential is related to the number of distinct sites visited by the random walk of the defect. For the same reaction dynamics but with more traps than walkers, an algebraically decaying relaxation is found.     

Microwave hall field inertia due to dielectric relaxation time

The magnetoresistive e.m.f. caused by microwave was measured as a function of _m in wide (3 cm – 4mm) range wave length. It has been found that Maxwell relaxation time does not influence the microwave Hall field lag in semiconductors. The discussion of these results is presented.     

Non-equilibrium distribution function in polar direct gap semiconductors

Electron distribution function (EDF) for non-equilibrium configurations in polar direct gap semiconductors is obtained in the temperature range k_BT? ? ω_Lo. The sample is assumed to be free of impurities and crystal defects. Electron-phonon coupling is the main relaxation mechanism. Master equation is solved approximately and analitycal expressions for EDF are obtained. Average electron energy as a function of temperature is discussed.