Relaxation processes in the incommensurate phase of a crystal with defects

The nature of the relaxation of the incommensurate superstructure of a ferroelectric to the equilibrium state is investigated experimentally. It is shown that near a phase transition the temperature dependence of the relaxation time of the incommensurate phase of the defective crystal is exponential. This law agrees qualitatively with the notion of domain wall motion in an inhomogeneous medium containing “random local phase-transition temperature” type defects. Fiz. Tverd. Tela (St. Petersburg) 41, 513–515 (March 1999)     

Relaxation processes in mesoscopic superconductors

We investigate the possibility of a novel kind of optical pump probe spectroscopy where the two laser pulses are focused on different areas of the sample. The response to the destruction of the superconducting state in a large part of a mesoscopic ring is studied numerically. We use the time dependent Ginzburg-Landau equations with periodic boundary conditions and external magnetic field. We evaluate the relaxation rates of the superconducting order parameter as well as the voltage induced by the charge imbalance. Computer simulations confirm that the perturbation of superconductivity on one part of the ring induces a voltage which decelerates the superconducting electrons on the other part of the ring. This deceleration results in the decrease of the superconducting current and the superfluid density. The relaxation times are of the order of the picosecond, the induced voltage of few millivolts and the variation of the superconducting gap of 10% which we believe to be suitable for time resolved femtosecond optical spectroscopy.     

Relaxation processes in non-Debye dielectrics

The specific features of the relaxation processes in non-Debye dielectrics have been investigated. The nature of the difference between the relaxation frequencies of the dielectric constant and dielectric loss (conductivity) has been explained. It has been shown that the average relaxation frequency of the conductivity is considerably (in some cases, by several orders of magnitude) higher than the relaxation frequency of the dielectric constant owing to an increase in the conductivity spectra of the statistical weight of the relaxation processes with short relaxation times.     

Relaxation and exchange in a nuclear cooling agent: NMR and EPR in single crystal PrNi5

NMR of Pr and ESR of Gd in single crystals of PrNi₅ are observed to exhibit a dramatic increase of the resonance linewidth with temperature in the range 1.2K ? T ? 10K. The observations are interpreted, within the framework of a crystal field spin Hamiltonian model calculation, in terms of low frequency fluctuations of the Pr ions induced by Pr-Pr exchange coupling. A fitting procedure of the theory to the experimental data enabled us to extract the various Pr-Pr and Pr-Gd exchange parameters. The former yield independent information concerning the lowest temperature that can be achieved in nuclear cooling experiments.     

锂原子光电离过程中的弛豫效应

利用基于多组态Dirac-Fock方法的程序包GRASP92和RATIP以及在此基础上最新发展的RERR06程序,计算了锂原子1s²nl(n=2,3; l=s, p) 的内壳层和外壳层的光电离截面. 计算中详细考虑了光电离过程中的弛豫效应. 结果表明：在锂原子内壳层电子的光电离过程中弛豫效应较强,而在外壳层电子的光电离过程中弛豫效应较弱. 另外,相应于不同态的内壳层光电离过程,其弛豫效应的影响也不同,对激发态的影响比对基态的影响大,对高激发态 关键词： 多组态Dirac-Fock方法 光电离截面 弛豫效应     

Dynamics of relaxation processes in a triglycine selenate single crystal in a ferroelectric phase

The deviation of the relaxation spectrum from the Debye type is studied experimentally and the presence of the non-Debye relaxation is shown, which is defined in different temperature ranges either by proton multiposition transitions below the Curie point T _c or relaxation domain and interphase boundaries in the vicinity of T _c. For triglycine selenate, the methods of analysis of dielectric non-Debye spectra are used.     

Phase transitions in SbSI

In ferroelectric SbSI the phase transitions are studied by means of precise birefringence measurement. It is observed that the transition from D^162h phase to C⁹_2v phase occurs at 15.70°C. At ? 36.61°C, the second order transition from C⁹_2v phase to C¹_s or C²_s phase is observed. From the behavior of birefringence near the second order transition point, the mechanism of the phase transition in SbSI is considered.     

Study on nitridation processes of β-Ga2O3 single crystal

Nitridated /3-Ga2Os (100) substrate was investigated as the substrate for CaN epitaxial growth.The effects of nitridation temperature and surface roughness of -Ga2O3 wafers on the formation of CaN were studied.     

Relaxation energy for single vacancy in Na

Using a new method, the qualitative corrections to the relaxation energies in the discrete lattice theory, including displacements of a limited number of neighbouring ions around single vacancy in Na, are calculated. The long-range effect of the relaxation is important and brings about the increase of the relaxation energy, i.e. the decrease of the formation energy.     

Electronic polarization in SbSI near electrodes

An experimental study has been made of the residual-polarization charge [q] at various temperatures in darkness and with illumination. Illumination of the anode has the greatest effect on the q = f(E) dependence. The potential distribution in the sample and the q = f(T) dependences reveal a high electron density near the anode, giving rise to polarization charge of up to 10^-5 C/cm², in SbSI with In-Ga electrodes. The time dependence of the discharge current reveals three slow-relaxation components, with relaxation times of 1.4 · 10², 1.1·10³, and 2.1·10³ sec.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 45–49, December, 1969.The authors thank M. S. Kosman and V. A. Izvozchikov for discussion of these results.     

Relaxation processes in metals at high strain rates

Mathematical modeling is used for experiments involving the loading of plates by plane shock waves to study the relaxation of shear stresses during the high-rate deformation of metallic materials. It is established that the characteristic relaxation times vary broadly — from fractions of a nanosecond to several microseconds. Such variation is indicative of a change in the mechanism responsible for relaxation. As a result, there is a difference between the quasi-equilibrium shear stresses in the elastic precursor and the same stresses behind the shock front. Metallic materials remain capable of resisting plastic deformation behind the front. Structural irregularities created by high-rate deformation result in localization of plastic flow at the microscopic level, which in turn causes the parameters of the stress-strain state at this level to differ from the corresponding parameters on the macroscopic scale.Siberian Physico-Technical Institute, affiliated with Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 82–90, August, 1995.     

Relaxation processes in glasses of the Ge-As-S system

The internal friction in Ge _x As_{40 ? x} S₆₀ glasses is investigated in the temperature range 100 K-T _g at infralow frequencies (10^?3?10^?1 Hz). It is shown that the concentration dependence of the internal friction of these materials changes as a result of the transformation of the dominant kinetic unit in dissipative processes of the relaxation and nonrelaxation types. It is established tha the change in the mechanism of internal friction in the Ge _x As_{40 ? x} S₆₀ glasses leads to a jump in the activation energy of the α relaxation and to a local minimum in the frequency factor τ₀.     

Ferroelectric phase transition in SbSI type crystals

In this work Lorenz field coefficients F for SbSI type crystals are estimated. Also transverse and longitudinal frequencies (ω _T and ω _l) of optical vibrations are determined. From a study of these quantities it was concluded that a combination of F is an inadequate condition for ferroelectric phase transitions to take place. Taking the electronic structure, chemical bond model, electronic potential and condition ω _T—>0 into account, the phase transition in SbSI type crystals was investigated. The dependence of the electronic potential upon the composition of V-VI-VII crystals and mixed crystals has revealed the factors that change the phase transition temperature T _c and the dynamics of the soft mode.     

Relaxation of a single two-level system

A relaxation problem for a single two-level system coupled to a Bose field is investigated. The stationary state and relaxation time of the system is analysed. The correction to the unperturbed stationary state is derived in the fourth order of the interaction between the system and bosons. The criteria for an application of the perturbation calculation are discussed.Supported in part by the Polish Academy of Sciences under Contract No. MR I-9.The author would like to express his sincere thanks to the members of the Department of Theoretical Physics at the Silesian University for their comments and discussions.     

Relaxation polarizations: Strong and weak processes

It has been shown that the through conductivity can differently affect the frequency dependences of the dielectric loss tangent of dielectrics with relaxation polarization. According to this difference, the relaxations in dielectrics are divided into two types: strong and weak. In the case of strong relaxations, the frequency dependences of the imaginary part of the complex conductivity exhibit extrema. Strong and weak relaxations have been investigated in Debye and in non-Debye dielectrics in order to determine the boundary between these processes and explain the existence of relaxations of two types. It has been established that the relaxations in dielectrics can be separated because of the different ratios of the contributions to the polarization of dielectrics from the fast and relaxation polarizations. The corresponding data in the literature are reviewed and the data on the development of strong relaxations in heterogeneous dielectrics are reported.     

Relaxation processes in Mn-doped single-crystal and glassy lithium tetraborate

Dielectric relaxation in Mn-doped single-crystal and glassy Li₂B₄O₇ was studied. The effect of light Mn doping on the dielectric properties of Li₂B_rO₇ was revealed. The experimental results are analyzed in terms of the Debye model of dielectric relaxation. The energy characteristics of the relaxation processes and the ion hopping lengths are determined in the materials under study.     

Relaxation processes in self-assembling triads based on porphyrin Zn-heterodimers

The directional self-assembly of nanosized, structurally organized triads is implemented in methylcyclohexane at 295 K, which is based on the two-point extra coordination of nonsymmetric, covalently bound heterodimers of Zn porphyrins to bipyridyl-substituted porphyrin free-base extra ligands. Based on experimental data and theoretical calculations, the structural organization is determined and information on the energetics of electronic interactions of components is obtained and the rate constants of the directional energy transfer (k ^ET ∼ 10¹¹ s⁻¹) and photoinduced electron transfer (k ^PET ∼ 2.7 × 10⁹ s⁻¹) are determined. The effects of the orientation of interacting macrocycles, the intercenter distances and the solvent temperature on the efficiency of relaxation processes in the triad is investigated.