bluuebunny/crossref_metadata_2025 huggingface dataset:
Annihilation of Frenkel Pairs in B.C.C. Metals (α‐Iron). I. The Case of the Unstressed Lattice (General Consideration)
Authors: Ratishvili I. G.
Published: July 2007

A model describing the Frenkel pair annihilation process is presented. There are postulated two factors governing the annihilation rate: the distribution function X(r), giving the initial relative spacing of components of a Frenkel pair, and the distribution function F(r), describing the field of potential barriers in the vicinity of a vacancy–interstitial pair. The analytical form of X(r) and F(r) functions is formulated and general expressions of the Frenkel pair annihilation rate and separation rate are obtained.
The Distribution of the Exchange Magnetic Fields in Spin Glasses. The Account of Local State Probabilities
Authors: Vladimir M. I. , Moskalenko V. A. , Skafaru V. V.
Published: July 2007

The distribution of the internal magnetic fields in spin glasses at non‐zero temperatures is obtained. The fact, that the spin glass phase has a huge number of local minima and that each minimum participates in the configurational averaging of the physical quantities with its own statistical weight, is taken into account. It is shown, that the probability distribution of the exchange fields in all sites does not factorize upon the sites because of the interferentional terms belonging to different sites. Detailed calculations are carried out for the homogeneous (white) averaging and for the averaging with the canonical weight multiplier exp {s/kβ}.
Atomic Particle Ionization in a Crystal in Random Orientation
Authors: Bazylev V. A. , Demura A. V.
Published: July 2007

A theory of the electron loss of an ion passing through a crystal in random orientation is developed for three mechanisms of ion–electron interaction with the crystal: 1) coherent atomic interaction with the crystal lattice without phonon production; 2) incoherent atomic interaction with crystal phonon energy changing; 3) electron–electron interaction with crystal electron energy changing. It is shown that under certain conditions any of the mechanisms considered can be dominant in the process of electron loss from the ion. It is also shown that for a multiply charged ion passing through the crystal an abnormal dependence of the ionization probability on the amount and direction of the ion velocity can occur.
The Mixing of Frenkel and Charge‐Transfer Excited States. II. Numerical Treatment of Non‐Symmetric Dimers
Authors: Schmid B. J. , Reineker P.
Published: July 2007

The mixing of Frenkel and charge‐transfer excitations is discussed for singlet excitions in a dimer consisting of inequivalent molecules. Depending on the parameter values of the system a more or less rapid crossover of the lowest eigenstate between a predominant Frenkel and a predominant charge‐transfer excitation is observed if one of the system parameters is varied. The case of singlet excitons in anthracene/TCNB is explicitly considered.
The Fundamental Absorption Edge Tail of Ferroelectric SbSI
Authors: Žičkus K. , Audzijonis A. , Batarunas J. , Šileika A.
Published: July 2007

The temperature dependence of the fundamental absorption edge of SbSI is studied in the range 320 to 5 K. In the paraelectric phase the edge is described by the Urbach's rule. The pertinent parameters of the ferroelectric phase are found to be temperature dependent. The influence of spontaneous polarisation on the absorption edge is discussed. The unusual Urbach behaviour in the ferroelectric phase is explained by the temperature dependence of the spontaneous polarisation. The results of SbSI absorption edge studies are found to be consistent with the microscopic model of Sumi‐Toyozawa.
Phase Transitions and Intervalley Jahn‐Teller Effect in the System (GeTe)1–x (AgSbTe2)x
Authors: Plachkova S. K. , Tersiev L. A.
Published: July 2007

The energy of intervalley Jahn‐Teller effect (IVJTE) accompanying the O–C phase transition in (GeTe)1–x(AgSbTe2)x solid solutions (x = 0.06) is calculated on the base of a band‐edge structure model of the group IV‐tellurides with T–L splitting in the rhombohedral phase. The heat effect of the transition is measured. It is shown that the contribution of the IVJTE energy in the whole energy balance of phase transition is ≈ 40%. This energy is used for the uniaxial deformation of a crystal.
Optical Determination of the Valence‐Band Parameters in CdTe
Authors: Milchberg G. , Saminadayar K. , Molva E. , Zelsmann H. R.
Published: July 2007

The set of valence‐band parameters μ, Δ, R0, introduced in the Baldereschi‐Lipari model allows the determination of several energy levels of shallow acceptors in a semiconductor. A critical examination of the methods of determining these parameters is presented. These values are calculated for CdTe using Lipari's analytical expressions for the electronic state energies and experimental data from luminescence and IR spectra of five acceptor impurities. The main conclusions are: 1) the restriction to transition energies (the only energies directly obtained from the experimental spectra) leads to more than one solution for μ, Δ, and R0; 2) when the energy levels of three “unperturbed” P states are known, the valence band‐parameters are unambiguously determined. For CdTe: μ = 0.69 ± 0.03, Δ = 0.12 ± 0.01, R0 = (30 ± 3) meV. Values of these parameters deduced directly from the experimental Luttinger parameters are generally too uncertain to be taken into account.
The Theory of X‐Ray Diffraction Analysis of Elastic‐Strain States in Epitaxial Films
Authors: Khapachev Yu. P. , Dyshekov A. A. , Kiselev D. S.
Published: July 2007

The possibility to determine five components of the strain tensor of an expitaxial film is demonstrated. The general expressions are given for the values of the discrepancy of periods of the film and the substrate, and for the components of the stress tensor in cubic heterostructures. Special emphasis is given to the definition of stresses in the layers of a superlattice.
XANES and EXAFS Study of the Compound CoAsSe
Authors: Chattopadhyay S. , Mande C.
Published: July 2007

The X‐ray absorption near edge fine structure (XANES) and the extended X‐ray absorption fine structure (EXAFS) associated with the CoK absorption discontinuity are investigated in the pure metal, in the compound CoAsSe and in two other similar trivalent compounds. The analysis of the results obtained enables to obtain the average bond length (Co‐ligand distance) in CoAsSe for which the value is not known from crystallographic work.
A Disorder Model of Melting II. Alkali Halides
Authors: Vaid B. A. , Sharma K. C. , Syal V. K.
Published: July 2007

The disorder model of melting recently proposed, is generalized to include alkali halides. The thermodynamic ‘defects’ are identified with the (ion‐)vacancy pairs existing in molten halides. The agreement of the calculated values of thermodynamic properties viz. thermal expansion coefficient, heat capacity, and compressibility, with the experimental data is found to be quite reasonable.
On Laser‐Induced Lattice Heating in a Polar Semiconductor
Authors: Vasconcellos A. R. , Luzzi R.
Published: July 2007

Nonlinear transport phenomena and relaxation processes in highly photoexcited polar direct‐gap semiconductors are considered. The rates of energy transfer between subsystems are calculated and it is shown that for ultra‐short laser pulses lattice heating is unimportant. However, for cw laser‐light illumination a pronounced enhancement of the lattice temperature is expected when laser power approaches, or surpasses, a critical value, leading the system to melting conditions.
Compressibility of Rare‐Gas Solids under the Effect of High Pressure
Authors: Narain J. , Agrawal G. G. , Shanker J.
Published: July 2007

An interionic potential model is formulated for rare‐gas solids by considering the effect of three‐body interactions, zero‐point energy, and thermal contributions. The model is applied to evaluate compression curves for Ne, Ar, Kr, and Xe, up to a pressure of about 20 kbar at their triple‐point temperatures. The calculated and experimental results are found in good agreement with each other.
Charge Transfer and Concentration Dependence of Magnetization in Amorphous FeB Alloys
Authors: Maksymowicz A. Z. , Stobiecki T. , Jarocki E. , Karaś W.
Published: July 2007

Measurements are reported of the magnetic moment μFe of Fe atoms in amorphous Fe1−xBx alloys. The observed concentration dependence of μFe can be explained qualitatively in terms of a simple rigid‐band model assuming a transfer of v electrons per B atom to the Fe d‐band. The rigid band is assumed as described by the density of states of densely packed structures. The best agreement is obtained for the charge transfer of about 1.5 electrons per boron atom yielding the observed critical concentration x = 0.60 at which magnetism disappears. Details of the density of states and the assumed number of electrons for pure Fe do not change the characteristic features of the μFe versus x dependence.
Free‐Carrier Optical Absorption Induced by Dislocation Scattering Mechanisms in III‐V Compounds
Authors: Vignaud D. , Farvacque J. L.
Published: July 2007

The influence of dislocations on the free carrier absorption in the case of III‐V compounds are determined theoretically taking into account the piezoelectric scattering potential associated with dislocations and the eventual existence of a deep flat band. Then the possibility to observe such effects is discussed and these calculations are illustrated by experimental results obtained on InSb.
Spectroscopic Study of the Crystal Field Splittings in TbPO4
Authors: Böhm W. , Kahle H. G. , Wüchner W.
Published: July 2007

The optical absorption and emission spectra of Tb3+ in TbPO4 in its tetragonal structure above 2.3 K are studied to obtain the energies, symmetry types, and wave functions of mainly the lowest crystal field components of the ground term 7F6. Crystal field parameters are evaluated and used to calculate the anisotropy of the single‐ion energy in a semi‐classical way. This gives interesting indications for the types of magnetic structures and Jahn‐Teller distortion which occur in this substance below 2.3 K.
On the Theory of Crystal Excitation by Electric Discharges
Authors: Voitikov S. V. , Gribkovskii V. P.
Published: July 2007

The problem is considered of semiconductor excitation by the streamer discharge electric field front in the case where the carrier generation processes do not reduce to the quasiclassical Zener tunneling because of high discharge velocities V and a steep front of the field. The streamerexcited interband transitions, unlike previously known ones, are shown to be indirect even in the first‐order processes taking place without phonon assistance. The first‐order transition slope is equal to h V. The calculated interband transition probabilities ωcv and the carrier concentrations Ne, Nh directly depend on the velocity of discharge, the form of its electric field, and the polarity: ωcv, Ne, and Nh are the greater, the higher the discharge velocity, the thinner the field front, and the faster the field intensity drop outside the discharge.
Electronic Theory of Atomic Short‐Range Order for Ternary Alloys Using the Pseudopotential Approximation and Its Comparison with Experiments
Authors: Mekhrabov Amdulla O. O. , Doyama M.
Published: July 2007

An analysis of the electronic theory of atomic short‐range ordering for ternary alloys in the pseudopotential approximation is made. The partial ordering energies and short‐range order parameters are calculated for ternary NiReMo, Ni3,(Fe0.10, Cr0.15), and Ni3(Fe0.20, Mn0.05) alloys using the model pseudopotential of Animalu. The comparison of the results between calculated and measured shows a good agreement for all the chosen systems.
Heat of Solution of Hydrogen in Aluminum
Authors: Mahajan S. , Prakash S.
Published: July 2007

The heat of solution of hydrogen in aluminum is investigated accounting for both, the lattice dilation and its relaxation. The lattice contribution is evaluated using a linearly screened local model potential for the ions. The non‐linear screening in the density functional formalism along with the exchange and correlation corrections in the jellium model is used to evaluate the proton contribution. The dilation enhances the lattice contribution by about 12% and decreases the protonic contribution by about 5%. The relaxation energy is reduced by about 40% for the dilated lattice. Adding all the contributions, the heat of solution is found to be 20% larger for the dilated lattice than that for the undilated lattice. The calculated heat of solution is found in good agreement with the experimental value. Comparing the results with the calculations of Perrot and Rasolt, the spherical solid model correction is estimated and it is found that it further improves the results.
The Photoexcited Flow of Nonequilibrium Phonons along a Crystal Surface
Authors: Blokh M. D. , Entin M. V.
Published: July 2007

It is shown, that for a light beam of oblique incidence to the crystal surface, a nonequilibrium phonon flux along the surface can exist. The transverse acoustic phonons of the lower branch of spectrum whose free path length is large at low temperatures give the main contribution to the flow. Such phonons arise either immediately at infrared absorption or as the result of the decay of optical and longitudinal acoustic phonons. The phonon energy flux is calculated and shown to be of the same order of magnitude as the incident light flux. The phonon‐electron drag current in the metal film bordering the unexposed surface of the dielectric is considered.
Angular Dependence of Spin‐Wave Resonance in Thin Films with Asymmetrical Boundary Conditions. Analytical Treatment
Authors: Jirsa M. , Kamberský V.
Published: July 2007

The boundary problem is solved for an isotropic homogeneous infinite insulator film with spins pinned asymmetrically by a uniaxial surface anisotropy. An arbitrarily oriented external magnetic field is assumed. Formally a simple condition for the values of the resonant wave‐vector k1 is obtained. The analytical expressions for the standing spin‐wave resonance (SSWR) mode linewidths and intensities are derived and discussed. The second part of the paper is devoted to the SSWR in thin metallic films with thicknesses 2d ≪ δ (the skin depth). The influence of conductivity on the mode positions, linewidths, and intensities is investigated analytically with the help of the spin‐wave approximation.
Temperature Dependence of the Electronic Energy Bands of NaNO2Crystal from 20 to 245 °C
Authors: El‐Dib A. M. , Hassan H. F.
Published: July 2007

The electronic band structure of NaNO2 crystals is calculated. The band structure is studied in the temperature range from 20 to 245 °C in the principal directions as well as at the high symmetry points inside the Brillouin zone. The temperature dependence of the minimum energy gap is also investigated. The calculations are carried out using a semiempirical LCAO method. The general features of the electronic energy bands at various temperatures are similar to that at 20 °C. The optical energy gap calculated at 20 °C equals to 3.24 eV which is in good agreement with experimental results.
Simulation fo Dynamical Bond Charge Transfer Properties in Elemental Semiconductors by Means of a Simple Quantum‐Mechanical Model
Authors: Pietsch U.
Published: July 2007

A simple model is presented, that constructs the valence charge density of monoatomic semiconductors by linear superposition of appropriate diatomic molecules including the bond charges between next neighbour atoms. By means of this model the study of dynamical density properties is possible being in general calculated by full self‐consistent pseudopotential schemes. An essential feature of that density variation is the bond charge transfer, which will be analyzed with respect to the variation of the next neighbour distance and the bond angle. During stretching or compressing of the next neighbour distance the variation in the |s〉 portion of the valence orbitals has to be taken into account. Using the results for silicon, which are fitted to the self‐consistent outcome and to experimental data, an estimation of the transfer constants of other group‐IV elemental crystals is given. The model can be applied to the interpretation of dynamical bond charge transfer influenced experiments, like pressure and temperature dependence of the “forbidden” X‐ray reflection power.
Electrical Resistivity of Liquid Noble Metal Alloys
Authors: Alam M. A. , Tomak M.
Published: July 2007

Calculations of the dependence of the electrical resistivity in liquid AgAu, CuAg, CuAu binary alloys on composition are reported. The structure of the binary alloy is described as a hard‐sphere system. A one‐parameter local pseudopotential, which incorporates s‐d hybridization effects phenomenologically, is employed in the resistivity calculation. A reasonable agreement with experimental trends is observed in cases where experimental information is available.
Derivation of Some Equations of State for Solids. A New Approach
Authors: Dass N. , Kumari M.
Published: July 2007

It is shown that the pressure‐independence of the product of the thermal coefficient of volume expansion, α, and the isothermal bulk modulus, BT, can give rise to the equation of state for solids as given by (i) Birch, (ii) Murnaghan, (iii) Tait, and others which are extensively used to fit the compression data. Moreover, some new equations of state are also developed. Further, as an example, the values of V(P, T)/V(0, T) are computed at 300 K for the case of sodium chloride and the results so obtained are compared with the data available in the literature. Overall, the conclusion is drawn that Murnaghan's equation of state is the best of all the equations of state available so far from the utility and practical point of view.
One‐Phonon Resonance Raman Scattering
Authors: Giner C. Trallero , Costa O. Sotolongo
Published: July 2007

Indirect creation and annihilation probabilities for a Wannier‐Mott exciton with arbitrary kinetic energy and interacting with longitudinal optical (LO) phonons are obtained as a function of temperature. These results are applied to the calculation of the one‐phonon (Stokes and anti‐Stokes) resonance Raman scattering (RRS) cross‐section in the case when the intermediate states are considered to be hot excitons, interacting with the LO‐phonons. The scattering cross‐section of these processes in CdS at 77, 150, and 300 K are presented as a function of the incident radiation frequency. It is shown that the cross‐section calculated for high temperatures and for incident radiation energies larger than the energy gap is dominant with respect to the cross‐section corresponding to processes in which only one phonon participates (no indirect transition).
Photostimulated Transformations of Complex Colour Centres in Lithium Hydride Single Crystals
Authors: Pilipenko G. I. , Oparin D. V. , Tyutyunnik O. I. , Gavrilov F. F.
Published: July 2007

Optical absorption, luminescence, and EPR are applied to study the nature of complex aggregate colour centres which arise in nonstoichiometric lithium hydride single crystals. Electron‐anionic disorder induced by the lack of hydrogen is found to create F‐centres which interact with the lattice through electron‐phonon coupling. Photostimulated transformation of F‐centres into F3‐centres is studied. The vibronic structure of the F‐centres absorption spectra is due to the interaction of the electronic transition with acoustic phonons TA(X), TA(L), LA(X), LA(X) + TA(X) and to the excitement of a quasilocal mode; the structure of F3‐centres spectra is due to the interaction of the electronic transition with acoustic TA(X), TA(L), LA(X), LA(X) + TA(W), and optical TO(L) phonons. The considerable deviation from the stoichiometry is shown to give rise to the formation of metallic lithium colloids.
On SCCF Theory of Falicov‐Ramirez‐Kimball Transitions in 1D Binary Alloys
Authors: Slechta J.
Published: July 2007

Self‐consistent continued‐fraction (SCCF) theory of the Falicov‐Ramirez‐Kimball (F‐R‐K) metalnonmetal transitions in 1D binary alloys, both with statistical short‐range order and purely random, is presented. Results for sets of critical parameters, and those of interest, are then given and shown that the F‐R‐K transitions depend, sensitively, upon the higher spatial correlations (HSC) in these alloys.
On the Possibility of Anomalous Bulk Photovoltaic Effect and of Induced Absorption in the Nominal Transparency Region of a Noncentrosymmetric Crystal in a Magnetic Field
Authors: Kristoffel N.
Published: July 2007

The possibility is shown of the appearance of photovoltaic current in the first order spectral transparency region for a noncentrosymmetric crystal in the magnetic field. This phenomenon must be accompanied by an unusual absorption induced by the electric field of the exciting light wave.
Cluster Structure of a Two‐Dimensional Lattice Gas Model
Authors: Esin V. O. , Danilyuk V. I.
Published: July 2007

Using the Monte Carlo method the cluster structure of a two‐dimensional lattice gas model is investigated. The ratios Γs and Γε of the perimeter S and boundary energy ε of a cluster to its size are studied over a wide temperature interval. For all temperatures, beyond some characteristic temperature‐dependent cluster size l0, ΓS and Γε are found to be independent of l. The temperature dependences of the ratios of the perimeter and energy of a cluster to its size, of the mean size of clusters, and of the vacant‐site concentration of occupied‐site clusters in a two‐dimensional system are studied.
Low‐Frequency Lattice Dynamics of NaNO2 Crystals
Authors: Kozlov G. V. , Kryukova E. B. , Wyncke B. , Brehat F. , Sherif M. E.
Published: July 2007

Submillimeter monochromatic BWT spectroscopy (3 to 33 cm−1) and far infrared reflection spectroscopy (40 to 600 cm−1) are used to investigate the low‐frequency dynamics of the classical ferroelectric NaNO2 of the order‐disorder type in the temperature interval 20 to 210 °C in the ferro‐ and paraelectric phase. In the submillimeter dielectric spectra ε★(v, T) of the NaNO2 crystal, together with the previously observed radiofrequency mode and the optical phonon 180 cm−1, low‐frequency anharmonic excitation subsidiary to the soft mode is recorded at the intermediate frequency 33 cm−1, Analysing the temperature behaviour of the parameters of this apparently relaxation excitation it is possible to assume that it is directly associated with the process of ferroactive crystal subsystem disordering at the ferroelectric phase transition.
Photo‐ and Thermochemical Reactions with Participation of Br− Centres in X‐Rayed KBr
Authors: Akilbekov A. , Dauletbekova A. , Elango A.
Published: July 2007

The photodissociation of Br centres (H′, V4, V2, D3 centres) at 4.2 K, created by X‐ray in pure and doped KBr at 4.2 to 300 K, and the thermorestoration of Br centres from their photodestruction products are investigated by the absorption method. It is shown that VF and H centres are created as a result of photodissociation of the high‐temperature Br centres (V4, V2, D3), but only H centres arise during the photodissociation of low‐temperature H′ centres. It is concluded that at temperatures above 80 K the Br ion occupies regular cation and anion sites, i.e. X‐radiation creates both cation and anion vacancies. At temperatures below 80 K the Br ion has an interstitial bent configuration, indicating that cation vacancies are not created.
On the Measurement of Solid State Compton Profiles by Inelastic Fast‐Ion‐Atom Collisions under Channeling Conditions. A Case Study
Authors: Bell F.
Published: July 2007

Solid state Compton profiles can be obtained by inelastic ion‐atom scattering. The energy distribution of ejected electrons within the region of the binary encounter peak is connected with the Compton profile of the target atom. The question is discussed whether the core contribution to the total Compton profile can be suppressed under channeling conditions.
Theoretical Description of the Stopping Power of Light Ions in the Intermediate Energy Range
Authors: Kührt E. , Wedell R. , Semrad D. , Bauer P.
Published: July 2007

A modified version of the binary encounter approximation by Kührt and Wedell is presented, where the motion of the target electrons is described in a more rigorous way. Moreover, the use of an alternative energy transfer cut‐off now makes it possible to describe the contribution of the outer electrons to the stopping cross section better. The very good agreement of this theory with experimental data is shown for a variety of target elements of different electronic structure (insulators, semiconductors, and metals).
Kinetic Properties of the Two‐Level Systems in Glasses with Account of Tunneling
Authors: Fushman D. A.
Published: July 2007

The kinetics of two‐level systems in glasses at low temperatures is studied with account of a distribution of their tunneling parameter values. Integral equations describing the process of spectral diffusion in a glass are obtained by the methods of the continuous time random walk theory. The long‐time asymptotics of the process is a superposition of individual and ‘collective’ relaxations, the latter one is characterized by the single relaxation rate. Manifestation of the results in echo saturation recovery experiments in glasses is discussed.
Dispersion of Magnon‐Polaritons in Uniaxial Ferrites
Authors: Voss R. , Kotzott R. , Merten L.
Published: July 2007

General dispersion equations of magnon‐polaritons in uniaxial ferrites are derived from Maxwell's equations. From these relations the dispersion curves for a simple artificial uniaxial ferrimagnetic crystal are calculated for different angles of wave propagation against the optical axis. The principal differences between the dispersion of ferrimagnetic and antiferromagnetic magnon‐polaritons are pointed out.
Magnetic Excitons in a Spin‐Cluster System
Authors: Meisen A. , Heber G.
Published: July 2007

Magnetic properties are calculated in the effective‐field approximation for a four‐level (singlet‐triplet) spin‐cluster system. Furthermore the spectrum of magnetic excitons propagating in this interacting system having in zero order discrete energy levels is studied. For the treatment of the magnetic spin‐cluster crystal the standard‐basis operator (SBO) formalism is applied. The model Hamiltonian used by Heber, Nara, and Freudenhammer is transformed in terms of the SBO's; and the eigen‐values are determined. The thermodynamic properties are obtained from the SBO Green's function equations of motion developing in the random‐phase approximation (RPA). A formula for the magnetization and susceptibility is derived.
Theory for the Magnetic Circular Polarization of the F‐Center Luminescence
Authors: Iwahana K.
Published: July 2007

A simple theoretical model is developed for the magnetic circular polarization (MCP) of the F‐center luminescence on the basis of a vibronic theory. In this model new rate equations for the optical pumping cycle are proposed to describe the unthermalized spin systems at low temperatures. It is shown that the model can consistently explain the unusual dependences of the MCP upon the magnetic field and temperature which are observed in the low temperature region. From the analysis of the temperature dependence of the MCP, ΔMCP(T), in the high temperature region, it is found that one must have Δ > 2 as far as V4 ≦ 0.6 to account for the nearly temperature independent behaviour of ΔMCP(T) in KCl in contrast to Δ < 2 given previously from the analysis of the temperature dependence of the radiative lifetime. It is pointed out that the discrepancy may be reconciled if assuming that the contribution to ΔMCP(T) of the field‐induced level splitting in the adjacent excited states is negligibly small.
Trap‐Limited Hopping in One‐Dimensional and Quasi‐One‐Dimensional Systems
Authors: Prigodin V. N. , Seidel Ch. , Nakhmedov A. P.
Published: July 2007

Trap‐controled hopping in 1D systems is studied by means of the Berezinsky technique. In the case of a discrete trap niveau exact time and field dependences are given of the relaxation current produced by injected carriers. In an initial time interval any kind of traps acts as deep species and one obtains the same current kinetics as formerly found for the randomly broken bond model, i.e., some exponential dependences. At large times the traps acting as shallow species give rise to a diminished stationary current. The effect of spatial disorder in the hopping sites is discussed. Taking into account a small transverse hopping rate the 1D results are generalized to quasi‐1D systems.
Optical Properties of the Quaternary II–VI Mixed Crystals in the Far Infrared Region
Authors: Burlakov V. M. , Litvinchuk A. P. , Pyrkov V. N. , Tarasov G. G. , Vitrikhovskii N. I.
Published: July 2007

The optical properties of mixed crystals CdTe1−x−ySexSy and ZnTe1−x−;ySexSy are investigated by methods of far infrared spectroscopy. Different types of transformation of the vibrational spectra of these solid solutions with composition are found. The longitudinal and transverse optical vibration frequencies are calculated theoretically by means of a unit cell version of the random element isodisplacement model. The calculations are in satisfactory agreement with the experimental results. The reflection spectra peculiarities with mixed crystal disordering are discussed.
Phonon Dispersion in Platinum and Palladium
Authors: Rajput A.
Published: July 2007

A phenomenological model that takes into account both, two‐ and three‐body interactions is developed for the calculation of the phonon frequency spectra of a homogeneously strained facecentred cubic (f.c.c.) crystal. The model is tested by applying it to the calculation of phonon dispersion curves and lattice heat capacity of the transition metals platinum and palladium. The theoretical results are found to agree well with the corresponding experimental data.
Static and Dynamical Valence Charge and Bond Charge Properties of Zincblende Structure Compounds
Authors: Pietsch U.
Published: July 2007

By means of a simple quantummechanical model of the linear superposition of “two‐electron‐molecules” both, the valence charge density and the bond charge density of zinc blende structure compounds are constructed. This scheme makes use of the results calculated for elemental semiconductors. Further it is extended by the self‐consistent determination of the effective charge and by an approximation describing the dehybridization of valence orbitals for increasing ionicity. The estimated valence charge densities are in rather good agreement with those published till now from band structure calculations. The model permits us to explain some known empirical properties concerning the ionicity dependence of the bond charge amount, the effective charge, the value 2e/ε0 defined by the dielectric theory, and the charge dependence of ionic radii. Due to the variation in both, the next neighbour distance and the co‐ordination angles the bond charge amount has to vary for a disturbed lattice. The bond charge transfer constants are calculated for thermal displacement and for hydrostatic pressure.
The Influence of Impurities on the Range of 28 MeV α‐Particles in NaCl Single Crystals
Authors: Basu A. M. , Choudhury A. , Chaudhuri S. , Mukhopadhyay P. , Baliga B. B.
Published: July 2007

Pure and impurity‐doped NaCl crystals are irradiated with 28 MeV α‐particles at room temperature. The beam current is 2 nA and the irradiation is continued for one minute in each case. Due to irradiation, F‐centers are produced uniformly in the crystals. The beam divergence is estimated from the observed area of the colored circular spot on the crystal. The optical absorption band of the colored samples are recorded. The efficiency of coloration (F‐center) is determined and is found to be independent of orientation and concentration of impurities in the crystal. The range of α‐particles is measured, which is found to be shorter in impurity‐doped crystals than in pure crystals. The results are explained in terms of recent observations.
Specific Heat and Magnetocaloric Effects in TbPO4. II. Mean Field Theory
Authors: Kasten A. , Üffinger G.
Published: July 2007

The magnetic phases and crystal distortions occurring in TbPO4 at low temperatures are described in mean field theory taking into account the influence of exchange and dipole interaction, Jahn‐Teller coupling, and the external field. The calculations are compared with the results of specific heat and magneto‐caloric measurements. The theory reflects the qualitative behaviour but there are still considerable differences. In an extended model, a magnetisation‐dependent exchange interaction is introduced leading to a better agreement in low fields.
The Classical and Generalized Moment Problem in the Theory of Relaxation
Authors: Giannozzi P. , Grosso G. , Parravicini G. Pastori
Published: July 2007

The classical moment problem for continued fraction expansion of relaxation functions is surveyed. The theory is then extended to the moment problem associated to relaxation operators or super‐operators. Numerical aspects and sensitivity of algorithms to round‐off errors are also examined. A new convenient approach is developed exploiting a product‐difference recursive scheme, within the memory function formalism.
Spectroscopic Investigation and Polarized Luminescence of Silver Pair Centers in Sodium Chloride
Authors: Atoussi B. , Pedrini C. , Moine B. , Madej C.
Published: July 2007

Absorption, emission, and excitation spectra of heavily Ag+ doped NaCl single crystals are investigated at various temperatures. Besides the ultra‐violet emission due to Ag+ single ions and the violet emission already observed, the crystal displays a new green fluorescence. It is shown that the fundamental emitters in the visible range are (Ag+)2 pair centers. The polarization properties of luminescence of dimers are carefully analyzed. The measurement of the magnitude of the degree of polarization of fluorescence and its azimuthal dependence suggest that the two (Ag+)2 luminescent centers are oriented along the C4 axes of the crystal. Models for the paired (Ag+)2 centers are proposed and some of their spectral properties discussed.
Annihilation of Frenkel Pairs in B.C.C. Metals (α‐Iron). II. The Case of the Unstressed Lattice (Numerical Results)
Authors: Ratishvili I. G.
Published: July 2007

A model describing the Frenkel pair annihilation process is presented. The annihilation rate is assumed to be governed by two factors: the distribution function X(r), giving the initial relative spacing of the components of a Frenkel pair, and the distribution function F(r), describing the potential barriers in the vicinity of a vacancy‐interstitial pair. Numerical calculations are performed for the case of the b.c.c. lattice of α‐iron and the results are compared with the experimental data. In the proposed scheme of description the existence of a number of substages at the first annealing stage is explained easily.
Chemical Activity of Noble Gases in Diamond
Authors: Tkachev V. D. , Zaitsev A. M. , Tkachev V. V.
Published: July 2007

The matrix distortion influence on the noble gas atoms He and Ne introduced into diamond by ion implantation is discovered and explained. Consequences of the effect mentioned are the chemical activity of the noble gas atoms in diamond lattice and the formation of stable impurity‐defect complexes, as it follows from the investigation of Mössbauer‐type luminescence spectra.
Indirect Magnetoelastic Interaction and Magnetostriction of Dilute Rare‐Earth Alloys
Authors: Kozarzewski B. , Kurzyk J. , Deniszczyk J.
Published: July 2007

The theory of indirect magnetoelastic interaction in dilute rare‐earth alloys is rederived in more general form. Expressions are obtained for conduction electron contribution to the crystal field parameters and magnetoelastic coupling constants. They appear to depend on Slater integrals, electron‐phonon interaction, and band structure of the alloy. The particular case of an alloy of the cubic symmetry is discussed as an example. Magnetoelastic coupling constants of some AgRE alloys are calculated within the nearly free electron approximation for the Ag band states.
A Discussion about the N‐Pole Approximation to the Continued‐Fraction Expansion
Authors: Pires A. S. T.
Published: July 2007

The conditions are studied to be satisfied in order to use a N‐pole truncation to the continued‐fraction expansion. The correct way is shown to do the cut off and the result are applied to analyse experimental data for the unidimensional antiferromagnetic TMMC at low temperatures.
Light Scattering by Surface Ripples in a Spatially Dispersive Medium
Authors: Albuquerque E. L. , Almeida N. S. , Oliveros M. C.
Published: July 2007

A theory is presented of the scattering of light by acoustic surface‐ripple in a medium which shows spatial dispersion for any polarization of the incident light. The exciton‐photon interaction, leading to the exciton‐polariton, is described in a purely phenomenological way, as in the early description of the phonon‐polariton. Some numerical results of the scattering cross section due to surface waves of the Rayleigh type are also presented and their features discussed.
Integration over the Two‐Dimensional Brillouin Zone
Authors: Kurganskii S. I. , Dubrovskii O. I. , Domashevskaya E. P.
Published: July 2007

A new method is proposed for the calculation of integrals over the two‐dimensional Brillouin zone (BZ) such as the density of states. The BZ is subdivided into triangles, in which quadratic interpolation over six points for the integrands in wave vector is used, and further subdivision of the BZ into smaller triangles appears to be possible. In each of the “small” triangles obtained the integrals are taken in analytical form on the supposition of linear dependence of integrands on wave vector. Tests of the calculation of the free electron density of states shows quite a high efficiency of the hybrid triangle method.
Calculation of the Thermoelectric Power of Ga, Ni, Rh, and Pd Impurities in Copper
Authors: Mertig I. , Mrosan E. , Zeller R. , Dederichs P. H. , Ziesche P.
Published: July 2007

Starting from the Mott formula the thermoelectric power for Ga, Ni, Rh, and Pd impurities in a copper host is calculated taking into account the full anisotropic electronic band structure of the host. The necessary Fermi surface integrations are performed numerically using the tetrahedron method. The calculation of the scattering properties of the impurities is based on density functional theory in the local density approximation and on the KKR Green function method. The muffin tin potentials of the impurity are calculated self consistently. Theoretical results for the thermoelectric power and also for the residual resistivity are discussed in relation to recently measured values.
Charge Carrier Mobility Caused by Scattering from Hybrid Plasmon–Phonon Modes
Authors: Kasiyan A. I. , Russu P. I.
Published: July 2007

A polar semiconductor containing one‐component electron plasma of free charge carriers is studied. The carrier density is assumed to vary over a wide range from a non‐degenerate state to a high degenerate plasma state. The interaction between the L O phonons and charge carrier plasma modes leads to hybrid plasmon‐phonon branches in the spectrum. The spectrum of renormalized plasmon‐phonon modes is calculated for PbTe and GaAs crystals. The electron mobility as a function of carrier density is investigated considering electron scattering by renormalized plasmon‐phonon modes both, in non‐degenerate and degenerate specimens of these crystals.
A Pseudopotential Approach to the Structural and Thermodynamical Properties of III–V Ternary Semiconductor Alloys
Authors: Ito T.
Published: July 2007

The structural and thermodynamical properties of III–V ternary semiconductor alloys (AlGaAs, AlGaSb, AlInAs, AlInSb, GaInAs, and GaInSb) are investigated using a pseudopotential perturbation treatment. A simple calculation method is proposed to estimate the disorder contribution to the total crystal energy of III–V ternary semiconductor alloys. The calculated results of compositional lattice parameter are in good agreement with the previously reported experimental data. Phase diagram calculations of III–V pseudobinary systems are also successfully achieved.
Mössbauer Diffraction in the Superionic Conductor RbAg4I5
Authors: Zolotoyabko E. V. , Ovanesyan N. S.
Published: July 2007

The problem of Mössbauer diffraction on crystals with intensive diffusion is analysed for the case of the superionic conductor RbAg4I5. An expression for the Mössbauer spectra of the diffracted beam is given for different diffusional model. The experimental temperature dependence of the coherent scattering of Mössbauer radiation in this sample is interpreted on the basis of developed theoretical assumptions.
Optical Anisotropy and Dichroism of A‐Centres in NaCl and KCl Single Crystals Irradiated with X‐Rays under DC Fields
Authors: Chaudhary R. K. , Rao A. V. Krishna , Rao K. V.
Published: July 2007

The optical absorption characteristics of the Petroff A‐band reported in our earlier work on NaCl and KCl single crystals X‐ray irradiated under dc fields, are studied in greater detail using polarized light. The results seem to indicate that the A‐centres exhibit anisotropic and dichroic behaviour. A possible explanation of the results is attempted.
Active Representations in Crystals of Cubic Symmetry
Authors: Hatch D. M. , Stokes H. T.
Published: July 2007

The reality, Landau, and Lifshitz conditions are reviewed within the formalism of the Landau theory of continuous phase transitions in crystals. It is shown that an incorrect use of these conditions in the literature has led to an omission of the W‐ and P‐point representations in the Oh crystal class. A detailed example for the W‐point is considered and the correct results obtained. The correct listing is given of the reality, Landau, and Lifshitz conditions for the entire cubic system (i.e., the classes T, Th, O, Td, and Oh).
Molecular Dynamics Study of Thermodynamics and Structure of Liquid Sodium under Pressure
Authors: Polukhin V. A. , Bratkovskii A. M. , Vaks V. G.
Published: July 2007

By the molecular dynamics method using 864 atoms the structural and thermodynamic properties of liquid Na are calculated for two states on the melting curve, which correspond to compressions u = 0 and u ≈︁ 20%. The radial distribution function g(r), structure factor S(k), energy U, and pressure p are found. Both, g(r) and S(k) are similar in the two states and differ mainly in a simple compression of all the scales. This similarity is in agreement with the hypothesis of the existence of the “crystallization criterion”, the universality of the short‐range order on the melting curves for simple liquids. A comparison with the Pereus‐Yevick (PY) approximation for S(k) shows that at u = 0 SPY(k) is close to SMD(k) and to the experiment, while at u ≈︁ 0.2 SPY(k) and SMD(k) diverge sharply, which is, apparently, due to the decreasing of the accuracy of the PY approximation at considerable values of u.
Random‐Field Correlations and Quantum Critical Phenomena
Authors: Uzunov D. I. , Korutcheva E. R. , Millev Y. T.
Published: July 2007

The effect of quenched random fields on the zero‐temperature critical behaviour is studied by the means of the Wilson‐Fisher renormalisation‐group recursion relations to first order in the ϵ‐expansion. A number of quantum models is considered. The simultaneous influence of both, the random‐field and the classical‐to‐quantum dimensional crossover phenomena on the quantum critical behaviour is investigated. A special attention is paid to the properties of some reasonable particular forms of Gaussian random correlations which might be of relevance to the description of natural systems.
XPS Study on a‐GeOx (1.3 < x < 2) Films Prepared from GeO2
Authors: Takano Y. , Tandoh Y. , Ozaki H. , Mori N.
Published: July 2007

An XPS study is made on a‐GeOx films prepared by deoxidizing GeO2 in Ar—H plasma. The XPS spectra of Ge 3d electrons are decomposed to five components, whose chemical shifts are estimated by taking into account the remote inductive effect and using the modified Sanderson method. The results are well explained by the model for the atomic configuration in the region of 1.3 < < x < 2.
Resonant Raman Scattering in Ga1—xInxP Solid Solutions
Authors: Bedel E. , Carles R. , Zwick A. , Renucci M. A. , Renucci J. B.
Published: July 2007

Resonant Raman scattering is investigated around the fundamental edge E0 in Ga1—xInxP solid solutions. The strong enhancements of the “forbidden” LO‐like modes are explained by a Fröhlich intraband interaction and lead to replica of the first‐order spectra. The non‐homogeneous activation of the one‐phonon density of states and the unusual sharp enhancements of LA‐like modes are interpreted as due to structural disorder effects. Local chalcopyrite arrangements are suggested.
Laser Induced Defects in GaAs Layers
Authors: Wesch W. , Wendler E. , Götz G. , Unger K. , Röppischer H. , Resagk Chr.
Published: July 2007

Annealing of ion implanted GaAs layers as well as irradiation of unimplanted samples with nanosecond laser pulses is connected with the formation of exponential absorption tails near the fundamental absorption edge with the dependenceK˜ exp [ħω(E)−1] on the photon energy. Identical behaviour is found in weakly damaged ion implanted layers. The observed high near edge absorption is connected with almost no refractive index change. The characteristic energyEis independent on the implanted ion species and increases with the nuclear deposited energy density and the laser energy density from about ≈ 0.1 eV up to a maximum value of 0.52 eV. The defects responsible for this behaviour act as compensating centers for free carriers. The experimental findings and the missing pronounced absorption tail in irradiated silicon supports the conclusion that defects typical for compound semiconductors are produced. Assuming high concentrations of vacancies and anti‐site defects the experimentally found values forEcan be explained from theoretical calculations.
The Effect of a Cu Overlayer on the Magnetization of an Fe Film
Authors: Schröder K.
Published: July 2007

The effect of a Cu overlayer on the magnetization of an Fe film is measured at room temperature in a high‐vacuum system. The deposition of Cu leads to an increase of the magnetic moment. If one associates this with the magnetic moment in the top monolayer of the copper film, then the measurements suggest that the magnetic moment of the copper film surface is equivalent to the magnetic moment of an iron film 0.16 nm thick.
Photoionization Cross‐Section for δ‐Shell Deep Levels
Authors: Masut R. , Penchina C. M.
Published: July 2007

A δ‐shell model is presented of deep impurities in semiconductors as a simple but effective extension of the well‐known δ‐function model of Lucovsky, in order to address the problem of fairly sharp photo‐ionization spectra. Whereas Lucovsky treated only the photo‐ionization of electrons from s‐like impurity states to the conduction band (forbidden transitions), this paper considers also the photo‐ionization of holes to the valence band (allowed transitions). The new δ‐shell model gives an improved fit to experimental photo‐ionization data. It can be used to determine the range of the deep impurity potential as well as the binding energy, and can help to determine the nature of the photoionized charge (electron/hole).