bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic Structure and Thermodynamic Properties of PdHx
Authors: Anagnostaras P. , Sikakana I. , Lowther J. E.
Published: July 2007

The cluster‐Bethe model developed for the electronic and cohesive properties of nonstoichiometric palladium hydride is now extended to compute thermodynamic properties. A plateau region in the computed isotherms is seen to emerge consistent with that suggested from observed hydride behaviour. The model is employed to give the critical concentration of hydrogen at which the gas will leave the metal. Results are presented for a range of different temperatures.
Temperature Variation of Optical Energy Gap and Deformation Potentials in AgInTe2
Authors: Quintero M. , Tovar R. , Bellabarba C. , Woolley J. C.
Published: July 2007

Values of the optical energy gap E0 of AgInTe2 as a function of temperature T in the range 10 to 300 K are obtained by optical absorption measurements. The variation of E0 with T is fitted well by a Manoogian‐Leclerc equation of the form E0(0) − E0(T) = UT + Vφ (coth φ/2T − 1). Values of (dE0/dT)1, the electron–phonon interaction contribution to the variation of the energy gap with temperature, and (dE0/dT)2, the lattice dilation contribution, are obtained from the Vφ and U terms, respectively. From these values of (dE0/dT)1 and (dE0/dT)2, values are determined for the acoustic deformation potentials of the conduction band Ce and the valence band Ch.
Spectroscopic Properties of Pr3+ and Nd3+ Ions in Zinc Tellurite Glasses
Authors: Kanoun A. , Alaya S. , Maaref H.
Published: July 2007

The optical absorption and emission of Pr3+ and Nd3+ ions in 1 ZnO, 2 TeO2 glasses are measured in the visible and near‐infrared region and an energy level scheme is established. The intensity parameters (Ω2, Ω4, Ω6) are calculated using the Judd‐Ofelt formulae. Using these parameters and the matrix element of Pr3+ and Nd3+ oscillator strengths, transition probabilities, and branching ratios are obtained.
Picosecond Photoconductivity Studies on Phenyl‐Substituted Poly (Phenylenevinylene) Derivatives
Authors: Li Haoliang , Rentsch S. , Yang Jiping , Lenzner M. , Bergner H.
Published: July 2007

Time resolved transient photoconductivity (PC) measurements are performed on phenyl‐substituted poly (phenylenevinylene) (P‐PPV) derivatives and one oligomer. The photogenerated carriers are assigned to be polarons and bipolarons, which are responsible for the picosecond and nanosecond PC components, respectively. By a deconvolution procedure the relaxation times are obtained for both components. The PC, the mobility, and the migration distance of carriers are obtained. Polymer and oligomer exhibit nearly the same value of electrical mobility. The hopping mechanism of carriers in the P‐PPV seems to be the dominating process for PC.
On the Critical State and Surface Barrier of a Type II Superconducting Long Cylinder
Authors: Saif A. G. , Refai T. F.
Published: July 2007

The creation and annihilation of the surface barrier in the frame of the general critical state theory of a type II superconducting long cylinder is studied. It is shown that the value of the superheating field is reduced when a transport current is allowed to flow along the cylinder's axis.
The Ising Antiferromagnet with Competing Interactions. Locating the Tricritical Point
Authors: Jäger I.
Published: July 2007

A thorough Monte Carlo investigation of the critical surface of the Ising antiferromagnet in the region of competing interactions is made with special respect to the location of the tricritical point. Results are that presumably the tricritical point is located at its Onsager value J2 = −0.4407kT not only for J1 = 0 but for all J1 (antiferro) and the tricritical field attains the value HT = 4J1 asymptotically. A drawing of the critical surface in the J1/kT−J2/kT−H/kT space is given.
EPR of a VO2+‐Doped Fe(NH4)2 (SO4)2 · 6H2O Single Crystal. VO2Fe2+ Exchange Interaction and Spin–Lattice Relaxation Time of Host Fe2+ Ions
Authors: Misra Sushil K. , Sun Jiansheng , Orhun U.
Published: July 2007

X‐band (≈9.5 GHz) electron paramagnetic resonance (EPR) studies of the VO2+ ion are carried out on a single crystal of the Tutton salt Fe(NH4)2(SO4)2 · 6H2O (FASH) at 295, 80, and 4.2 K. The data indicate two physically‐equivalent VO2+ sites in the unit cell, each consisting of three magneticallyinequivalent VO2+ ions. The principal values and direction cosines of the principal axes of the g2 and A2 tensors are evaluated, using a least‐squares‐fitting program. An impurity [VO(H2O)5]2+ complex model of the vanadyl ion is found to explain the data well. The V4+O2− bond directions for the VO2+ ions are deduced. The VO2+Fe2+ exchange‐interaction constant in FASH is estimated. The host‐ion (Fe2+) spin‐lattice relaxation time is estimated from VO2+ EPR linewidth.
Charge Distribution of Electrons at Intercalated Atoms in Layer Crystals
Authors: Lukiyanets B. A.
Published: July 2007

The charge distribution of electrons at intercalated atoms in a layer crystal is considered in the two‐impurity model of the Anderson type. The dependence of this distribution on the Coulomb interaction between intercalants and on the electron mixing of the intercalate–intercalant system is analyzed.
Theory of Germanium‐Related Defects in Vitreous Silicon Dioxide [GeO4]−‐Center
Authors: Dianov E. M. , Sokolov V. O. , Sulimov V. B.
Published: July 2007

The properties of the anisotropic paramagnetic [GeO4]− center (tetrahedral coprdinated Ge substitutional atom with an electron trapped) in vitreous silicon dioxide are investigated in a cluster approach by means of the MNDO quantum‐chemical method taking the atomic relaxation into account.
On the Energy Transfer in the Thermally Annealed KCl: Pb2+, Eu2+ System
Authors: Muñoz‐Santiuste J. E. , García‐Solé J. , Manfredi M.
Published: July 2007

Pb → Eu energy transfer mechanisms in the thermally annealed KCl: Pb2+, Eu2+ system are examined by means of optical absorption, emission, and time decay spectra of the luminescence. The thermal annealing produced the formation of the Pb2+ Suzuki phase and the results show that the Eu2+ ions enter this phase by substituting for some Pb2+ ions. The Pb → Eu transfer is found to be a very efficient process, with a very short transfer time. The analysis of the time decay signals shows that the transfer is a single pair mechanism; no migration of the excitation energy is experimentally detected.
High‐Temperature Equilibrium between High‐Tc Oxide and Gas Phase
Authors: Tsidilkovskii V. I. , Leonidov I. A. , Lakhtin A. A. , Mezrin V. A.
Published: July 2007

The equilibrium between the high‐Tc oxide YBa2Cu3O7‐δ and the gas phase is studied for some models of the ioic and electroic (e.g., two‐band model) systems of the compound. The calculations show that the contribution of the electron‐hole system to this equilibrium is essential. The comparison of the theory with experiment allows to obtain such paramenters as binding energy of oxygen ions, their effective Einstein frequency Δ, the hole effective mass mp, etc., the Δ and Mp values being in agreement with those reported elsewhere. A number of relations, e.g. the electron and hole concentrations versus oxygen pressure Po2 and T, as well as the influence of doping (with donors of acceptors) on these relations and on the oxygen content ae predicted using the parameters obtained. The region of high Po2 is also studied.
Relativistic Wave U‐Equation of the Internal Q‐State of the Θ‐(Cu) Superconductor
Authors: Gangan N. A.
Published: July 2007

The coherent (“condensate”) pairing of “Kaino” electrons (those braced by the “nuclei”) in the “perovskite” Θ‐(Cu) superconductor (YBa)CuO3‐θ (θ small) is considered. The invariant definition of the physical S matrix and of the geodesic (on 𝔐) projective variables of the (“inertial”) relative (in the Cayley‐Beltrami metric) three‐variable movement of particles is given. The (Beltrami) W‐invariant (relativistic) three‐dimensional wave equation of the internal (“relative motion”) condensate Q‐state of the Theta;‐(Cu) superconductor is obtained.
Isochoric Thermal Conductivity and Thermal Pressure of Solid CCI4
Authors: Konstantinov V. A. , Manzhelii V. G. , Smirnov S. A.
Published: July 2007

Isochoric thermal conductivity and thermal pressure are studied of monoclinic and rhombohedral phases of solid CCl4 at different densities in the temperature range 210 to 300 K and up to the pressures of 200 MPa. It is found that at constant density the thermal conductivity increases with increasing temperature in both the phases. The experimental results are discussed on the basis of the conception of the minimum value of the thermal conductivity.
Antiferromagnetism and Anisotropic High‐Temperature Superconductivity A Further Macroscopic Study
Authors: Shehata L. N.
Published: July 2007

The macroscopic studies of the possible coexistence of antiferromagnetism (AF) with anisotropic high‐temperature superconductivity (SC) are reviewed. A modified Ginzburg‐Landau energy functional is presented. The temperature condition for such coexistence is estimated in terms of the GL coefficients for the uniform SC and AF. The derived equations with the appropriate boundary conditions are used to study the vortex structure and evaluate the first and second critical fields in the new materials. Applications and comparison with the available data are also presented.
A Theoretical Investigation about the “F” Centre in MeF2:A+ (MeCa, Sr; ALi, Na, K)
Authors: Amara A. , Cremer G. , Martin‐Brunetiere F. , Thuau M.
Published: July 2007

One of the most conspicuous colour centres in MeF2:A+ (Me=Ca, Sr; A=Li, Na, K) is the so‐called “Fe”. It is investigated whether this centre may really be composed of three neighbouring fluorine vacancies, along a [0, 0, 1] direction, decorated by two electrons, with an alkaline impurity A+ in the vicinity. This structure seems to be ruled out by a comparison of the experimental magnetic circular dichroǐsm data of other authors with the results of present Hartree‐Fock calculations of the energy levels of linear F centres in fluorite‐like lattices. For this calculation, an H hydrogen molecular ion model is used similar to the ones which have already proved efficient in several other colour centre problems.
Vibrational Spectroscopy of the Structural Phase Transition and Raman Evidence of Librational Fluctuations in Thallium Thiocyanate
Authors: Sathaiah S. , Bist H. D.
Published: July 2007

A detailed analysis of Raman and IR spectra of thallium thiocyanate (TINCS) in the temperature (T) range 293 to 438 K is carried out. The orthorhombic‐to‐tetragonal structural phase transition (SPT) near T ≈ 367 K (= Tc) is spectroscopically characterized as an order‐disorder transition exhibiting predominant second‐order features. Remarkably, consistent mean field type exponents:order parameter exponent β = 0.45 ± 0.04 and correlation length exponent v = 0.46 ± 0.04, and activation energy for the reorientational motion of NCS− ions U = (0.32 ± 0.02) eV, are extracted from characteristic spectral changes in the thermosensitive Raman modes. The appearance of side bands in each of the internal modes of the NCS− group in the Raman spectra are attributed to splittings due to an internal field in the ordered orthorhombic phase; the continuous growth in the relative intensities and decrease in splitting energies reveal the gradual diminution of the internal field as T approaches Tc.
Non‐Linear Elastic Behaviour and Third‐Order Elastic Constants of a Roller‐Bearing Steel and Some Standard Steels
Authors: Wasserbäch W.
Published: July 2007

The deviations from Hooke's law in the hardened roller bearing steel SAE 52100 (100Cr6) in cyclic stress—strain experiments are related to the third‐order elastic constants of standard steels and α‐iron. The comparison of the measured values of the non‐linear constant kM, with the values calculated from the third‐order elastic constants reveals a surprisingly good agreement, even for the case that kM, is calculated using the single‐crystal data of α‐iron.
On the Theory of Coupled Phonon—Plasmon Polariton Excitation on the Surface of Polar Semiconductors
Authors: Arakelian V. H. , Hovsepian N. M.
Published: July 2007

The problem of polariton formation on the surface of polar semiconductors is considered. Polaritons are excited by charged particles crossing the interface between vacuum and polar semiconductor. The part of particle energy expended on excitation of coupled phonon‐plasmon polaritons on the interface is calculated. Excitation frequency zones and intensities are found, as well as the loss‐energy dependence on the phase velocity of surface polaritons.
Interpolation of the One‐Electron Energies Using Theoretical‐Numerical Nets
Authors: Kanalin A. G. , Mokhracheva L. P.
Published: July 2007

The method of global Fourier‐series approximation of the one‐electron energies ϵ(k) in the Brillouin zone is considered. To calculate the Fourier series expansions of the ϵ(k)‐functions optimal for trigonometric polynomials theoretical‐numerical nets are used. Convergence and accuracy of the approximation is investigated using one‐ and two‐band models of the ϵ(k)‐dependence. It is shown that the method described is more accurate then piecewise linear interpolation in the volumes of elementary tetrahedra, generated in regular nets, and is comparable to piecewise quadratic interpolation.
Magnetic Field Dependence of Hydrogen Energy Levels in GaAsGa1−xAlxAs Quantum‐Well Structure
Authors: Shen Zhong‐Jun , Zhong Shu‐Au , Gu Shi‐Hei
Published: July 2007

A calculation is made of the binding energies of the hydrogenic donor ground state in a GaAsGa1−xAlxAs quantum well of finite barrier height in the presence of a magnetic field, which is taken to be parallel to the growth axis of the quantum‐well structure. Strong‐pertubation theory and pertubative‐variational approach are used. The results are given as a function of the size of the quantum well.
Dissipative Processes Due to Fluxoid Motion in Superconductive YBCO Specimens
Authors: Abbattista F. , Appino C. , Masoero A. , Mazzetti P. , Stepanescu A. , Vallino M.
Published: July 2007

Comparative measurements are made on the dissipative effects due to dc current flow and ac magnetization processes on the same YBCO superconducting specimen at 77.3 K. The material is brought into the Abrikosov mixed phase by a dc magnetic field H0. Different sets of data are reported concerning: (a) the dependence of the dc resistivity ϱ on H0 and on the current density J, (b) the dependence of H(t) on the frequency and on the value of H0 of the magnetic power loss generated by a very small (0.34 A/m) sinusoidal magnetic field H(t) superimposed to H0. By a numerical calculation it is shown that at high frequencies the magnetic power loss is very closely equal to the one expected for eddy current dissipation in a conducting material whose resistivity depends on the current density and has a value rather closely equal to the one measured on the YBCO specimen with a conventional four‐terminal technique. A second component of the magnetization power loss, which is closely proportional to the magnetization frequency and corresponds to the hysteretic loss, is also seen.
Magnetic Phase Diagram of (Ni1−xMgx)O Solid Solutions
Authors: Menshikov A. Z. , Dorofeev Yu. A. , Klimenko A. G. , Mironova N. A.
Published: July 2007

A magnetic phase diagram of the (Ni1−xMgx)O solid solutions is drawn by the results of elastic magnetic neutron scattering and magnetic measurements. The ranges of homogeneous antiferromagnetism (0 ≦ x ≦0.37), tricritical behaviour or frustrated antiferromagnetism (0.37 < x ≦ 0.6), cluster spin glass (0.6 < x ≦ 0.75) and paramagnetic behaviour of the Ni2+ spin moments in the ground state (x ≧ 0.8) are determined. It is shown that diamagnetic Mg2+ ions serve as a source of a random field inducing an extra diamagnetic moment of value 0.35μB.
Angular Dependence of the Ti K Edge in Rutile TiO2
Authors: Poumellec B. , Cortes R. , Tourillon G. , Berthon J.
Published: July 2007

The angular dependence is investigated of the X‐ray absorption spectrum of TiK edge in TiO2 recorded in the total electron yield mode. Despite the weak distortion of the octahedral coordination, the absorption spectra exhibit wide contrast which enables designation of the excited state orbitals involved in the strong transitions. The energy splittings between the degenerate transitions in perfect octahedral symmetry are much more pronounced than could be expected from a one‐electron ground state analysis. It is deduced that the first allowed transitions (i.e. 1s → 4p) seem to show sensitive dependence on the local symmetry. However, for the weak transitions before the edge, the analysis is not straightforward and is still in progress.
19F NMR study of the fluorite‐Type Ca1−xThxF2+2x solid solution
Authors: Suh Kyung‐Soo , Senegas J. , Reau J. M. , Hagenmuller P.
Published: July 2007

An investigation is made by 19F NMR of the disordered fluorite‐related solid solution Ca1−xThxF2+2x (0 ≦ x ≦ 0.18). The existence is shown of different fluoride sublattices at low temperatures and the setting‐up of partial exchanges between them at increasing temperature. The identity of these sublattices with those identified by neutron diffraction is discussed. The NMR study allows to confirm the formation of clusters of 1:0:3 type in Ca1−xThxF2+2x. The results obtained are so in good agreement with the composition dependence of the ionic conductivity properties and are satisfying with respect to the model of the processes of clustering proposed for the anion excess CaF2‐type solid solutions: indeed, within Ca1−xThxF2+2x, the F‴ interstitial fluoride ions seem to play the main role in the long‐range motions.
The influence of surface states on the photovoltage of real silicon surface
Authors: Schulz J. , Würfel P. , Ruppel W.
Published: July 2007

The surface photovoltage caused by band‐to‐band generation within the semiconductor depends on light intensity. This dependence differs significantly in two limiting cases. When recombination via fast surface states is negligible, the slope of the photovoltage versus the logarithm of intensity is always less than kT/e and depends on the amount of semiconductor band bending in the dark. When recombination via fast surface states becomes strong, this slope is kT/e, independent of the band bending. These differences are experimentally observed using a structure with ferroelectric NaNO2 deposited on a real silicon surface. The switching of the direction of the spontaneous polarization of the ferroelectric results in significant changes of the semiconductor band bending in the dark. The charge exchange with slow surface states results in a continuous change of the band bending in the dark. The measurements reveal a pronounced minimum of the density of fast surface states near mid‐gap. The results compare well to those from measurements on a field effect transistor structure with NaNO2 as gate insulator.
MT effective medium approximation in R‐representation for the electron structure of 3d metals
Authors: Ya. Asanovich V. , Miklashevich I. A.
Published: July 2007

A continuum model for the electron structure of 3d melted metals in coordinative submission is proposed. The electron state density n(E) is defined by site scattering matrix tj, Green functions, and derivatives from these figures. The nearest — neighbour order is evaluated with the help of radial distribution scatterers g(r). The d‐bond of Fe is filled in partly, and its width is about 0.2 Ry. This figure is a little bit more then in cluster models. The peak width is connected with a more correct calculation of the nearest — neighbour order.
Electron‐energy‐loss spectroscopy of a n—i—p—i semiconductor superlattice
Authors: Albuquerque E. L. , Farias G. A. , Auto M. M.
Published: July 2007

A semi‐infinite superlattice structure consisting of a periodical array of n‐ and p‐doped semiconductors layers intercalated by an insulator is considered and it is examined how the electron‐energy‐loss spectroscopy can be used to probe the spectra of surface plasmon modes which propagate in these structures. A backscattering geometry is used for the scattered electron and a semiclassical theoretical approach for interpreting the electron‐energy‐loss spectra.
Self‐consistent states of a flow of quasi‐particles and immobile deformation in one‐dimensional systems
Authors: Ermakov V. N. , Ponezha E. A. , Tkach V. I.
Published: July 2007

New solutions are obtained of a set of two‐component nonlinear equations that correspond to a self‐consistent state of moving quasi‐particles and immovable deformation. The deformation is a periodic structure that consists of potential wells. It is shown that in the case considered the effective mass of carriers is determined by the probability of tunneling and may rise appreciably.
Static Skin Effect at High Current Densities
Authors: Oyamada K. , Peschanskii V. G. , Stepanenko D. I.
Published: July 2007

The nonlinear effects in the conductivity of metals and intrinsic semiconductors placed into a homogeneous magnetic field H0 are investigated under the conditions of the static skin effect. The electric current distribution and the intrinsic magnetic field of the current Hj in the sample are obtained by the asymptotic solution of the system of Maxwell and kinetic equations in the case of a slowly changing total magnetic field over a distance of the order of the electron Larmor radius. It is shown that by varying H0 one can study separately the dynamic nonlinear effect associated with the Hj influence on the ballistics of conduction electrons, and the deviation from Ohm's law due to charge carrier heating by electric current.
On the Possibility of Exchange Induced Pairing Mechanism in Model Heavy Fermion Superconducting Systems
Authors: Ghosh S. C. , Ghosh N. K. , Sarkar R. L.
Published: July 2007

The periodic Anderson model extended by exchange induced non‐phononic pairing interaction between f‐ and d‐electrons is investigated in the context of singlet like superconductivity. d–d, f–f, and f–d pair density functions are calculated and the stability of different pairing due to various interactions are studied. f–d cross‐over effect is observed and the exchange interaction is found to have the effect of stabilising the pairing; low temperature specific heat is calculated and explained.
Thermal Quenching of the Eu2+ Photoluminescence in KCl and NaCl Crystals
Authors: Sokólska I. , Mugeński E.
Published: July 2007

The photoluminescence spectra, lifetimes, and intensity of emission of Eu2+ are examined for KCl:Eu2+ and NaCl:Eu2+ crystals within the range of 15 to 800K. The quantum yield of emission related to the dipoles and aggregation products formed up to 400 K is found to be temperature independent. Thermal quenching of the emission related to the aggregation products formed at 425 to 525 K is explained by the two‐channel nonradiative de‐activation of excited t2g(4f65d) levels.
X‐Ray K‐Absorption Edge Shift of Copper in Some of Its Compounds and Organo‐Metallic Complexes
Authors: Pandey S. K. , Chetal A. R.
Published: July 2007

Chemical shift, ΔE, of the X‐ray K‐absorption edge is measured in some compounds and organometallic complexes of copper possessing formal oxidation states 1+ and 2+. The best fit correlation between the chemical shift, ΔE, and the effective charge, q, using the least‐squares regression analysis procedure is found to be a non‐linear equation ΔE = Aq + Bq2 + Cq3, where A, B and C are constants. In the light of statistical treatment it is shown that the effective charge, q, is a significant explanatory factor of the variation in the X‐ray absorption chemical shift, ΔE. Interpretations to the variations in X‐ray absorption chemical shift are also given on the basis of electronegativity, oxidation state, the valence d‐orbital electrons, atomic number, crystal structure, etc.
Raman Spectra of [N(CH3)4]2ZnCl4 Single Crystals I. Raman Spectra of the Parent Phase
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Rabkin L. M. , Durnev Yu. I. , Latush L. T.
Published: July 2007

Polarized Raman spectra of [N(CH3)4]2ZnCl4 crystals are studied in phase I in the frequency range between 10 and 3500 cm−1. An assignment of the lines observed to motion types is carried out. The sublattice of the TMA ions is found to behave as a quasi‐liquid. The distorsion of the ZnCl tetrahedra is insignificant. A considerable orientational disorder is shown to occur in this phase.
Helical Nature of Collective Excitations in α‐Helical Protein
Authors: Ichinose S.
Published: July 2007

Collective excitations in long α‐helical proteins are investigated, including two types of peptide groups displacements provided by changes of the helix pitch and its radius. It is shown that the motion of asymmetric excitations along the protein molecule have a helical nature. For these excitations there occurs an exchange of excitations between chains as a result of the resonance interaction between peptide groups belonging to different chains.
Vortex Nucleation in Thin Film of an Uniaxial Anisotropic Superconductor
Authors: Krzysztoń T.
Published: July 2007

In the framework of London theory the problem of vortex nucleation in a thin film of an anisotropic superconductor is studied. The Gibbs free energy of a vortex as a function of its distance from the surface of the film is calculated. This energy is considered as a surface barrier opposing penetration of the vortices into the film. The barrier disappears when a certain value of external magnetic field – the field of first penetration – is applied. The strength of this field is calculated as a function of an angle between the anisotropy axis and the direction of external magnetic field.
Phonon‐Polaritons in Isotropic Ferromagnets I. The Influence of the Magnetization on Surface Phonon‐Polaritons
Authors: Dimitriev O. P. , Lozovskii V. Z. , Getsko O. M.
Published: July 2007

In the frame of a phenomenological approach the propagation of phonon surface polaritons (SP) on an isotropic isolator having non‐zero magnetization is considered. Dispersion relations of SP are presented for following orientations of the magnetization: 1) magnetization in the surface plane and perpendicular to the wave vector of SP; 2) magnetization parallel to the wave vector of SP; 3) magnetization perpendicular to the surface plane It is shown that for the two last geometries new SP arise which are not TM‐waves, and their properties are dependent on the values of medium magnetization and applied magnetic fields.
Temperature Dependence of the Structure Factor of Liquid Alkali Metals
Authors: Nigam S. K. , Khanna K. N.
Published: July 2007

The temperature dependence of the structure factor, S(q), of liquid alkali metals is studied using a Percus‐Yevick‐tail reference system including a Cummings potential in a random phase approximation. The Cummings potential parameters, determined at the melting temperature for each metal are also used at higher temperatures and are found to be related to the atomic number of the metal.
Self‐Diffusion in Crystals
Authors: Buchbinder G. L.
Published: July 2007

The mobility of a vacancy in the lattice is considered. The jump of the vacancy is interpreted as a transition of the system from some quantum state with localized vacancy into another one in which the vacancy is localized at a neighbouring site. The expression for the jump rate W is obtained. At high temperatures the temperature dependence of W describes an activation process with an activation energy defined by the second moment of the frequency distribution function of the defective crystal. At low temperatures the influence of resonant modes on mobility of the vacancy is considered.
Disclinations in Heterogeneous Small Particles
Authors: Gryaznov V. G. , Kaprelov A. M. , Polonskii I. A. , Romanov A. E.
Published: July 2007

Elastic effects in elastically inhomogeneous pentagonal small particles are analyzed. Two continual elastic models are applied and considered in detail: a wedge Frank disclination in an infinite elastic cylinder consisting of two coaxial layers of different phases and a Marks‐Yoffe disclination in an elastic sphere consisting of two concentrical layers of different phases. The corresponding boundary problems are solved. It is shown on the basis of these solutions that the disclination–interface elastic interaction stimulates interface migration and hence may either promote or retard phase transformation processes. Disclination elastic fields may initiate dislocation generation at the interface and cause a point‐defect diffusion flux resulting in an inhomogeneous distribution of impurities in the particle.
Existence of Two‐Phonon Bound States in Deuterated Naphthalene
Authors: Bhandari R. , Jindal V. K.
Published: July 2007

A numerical calculation is performed to search for the existence of two‐phonon bound states in deuterated naphthalene crystals. The quartic anharmonic force constant needed for the calculation of the poles in the two‐phonon Green's function is approximated by using Peierls approximation and already calculated results of the explicit anharmonic shifts to the phonon frequencies. The results indicate that the existence of two‐phonon bound states is possible in a deuterated naphthalene crystal at various temperatures.
Approximation of Local‐Field Effects in the Dielectric Formalism of Lattice Dynamics
Authors: Falter C. , Klenner M. , Ludwig W.
Published: July 2007

The phonon dispersion is investigated of a crystal where local field effects are taken into account using a first‐order perturbation expansion with respect to the off‐diagonal of the dielectric matrix. Such an expansion is used in other applications in the literature. It is shown that a straightforward application of this approach is not sufficient for a proper description of acoustic phonons in semiconductors and insulators in the limit of long wavelength because the acoustic sum rule is violated. A general expression for the correction term being of second order is given. Furthermore, the relations are illustrated with the phonon dispersion and certain phonon induced polarization charge densities in Si using a suitable model for the dielectric function.
The Time‐Dependent Ising Model on the 2D Penrose Lattice
Authors: Doroba A. , Sokalski K.
Published: July 2007

The kinetics of the Ising model on the 2D quasicrystal (Penrose) lattice is investigated. On the base of the Glauber method the system of the differential equations describing the temporal evolution of the expectation values of the averages of spins occupying the vertices of the Penrose “kite and dart” lattice is constructed. The mean field approximation, modified for the case of the nonperiodic system is applied. The stationary solution and their stability are discussed. The time‐dependent solutions of the problem in the case of the ferromagnetic and antiferromagnetic couplings between spins are found. The qualitative changes of the attractors under the changes of the external parameters are analysed. The limitations of applying the mean field approximation for the problems of the kinetics are discussed.
Scattering of Laser Light by an Acoustic Wave in Magnetoactive Noncentrosymmetric Semiconducting Crystals
Authors: Jat K. L. , Ghosh S.
Published: July 2007

Considering that the origin of nonlinear interaction lies in the second order optical susceptibility arising from the nonlinear induced current density and using the coupled mode theory, an analytical investigation of scattering of laser by acoustic wave and the consequent amplification of scattered modes and acoustic wave is carried out in a transversely magnetised semiconductor of noncentrosymmetric nature. The influence of carrier density is also considered. The threshold value of the pump electric field is obtained. Eoth is found to decrease with increasing magnetic field and decreasing scattering angle. The steady state growth rates for piezoelectric (gp) and deformation potential (gd) scattering and both (gb) ones are also obtained. The numerical estimations are made for n‐InSb crystals at 77 K. The gain constants are found to be higher in the presence of a strong magnetic field when the cyclotron frequency is near to the pump frequency. The doping level is also found to have a significant influence on the gain constant.
Bi2 Te3 Crystals Heavily Doped with Tin Atoms
Authors: Horák J. , Lošťak P. , Geurts J.
Published: July 2007

The values of transport coefficients (Hall constant and Seebeck coefficient) of Bi2Te3 crystals strongly doped with Sn atoms are determined at room temperature. From reflectivity measurements in the IR region, the plasma resonance frequency ωp, relaxation time τ, and high frequency permittivity are found. The interpretation of the results obtained in the concentration interval, 0 < x < 3 × 1020 Sn atoms per cm3, leads to the conclusion that one part of the Sn atoms incorporated enters into the bismuth sublattice giving rise to negatively charged substitutional defects Sn'Bi, the other part forms uncharged defects. The formation of uncharged defects produced by the incorporation of Sn‐atoms into the Bi2Te3 crystal lattice is explained in the following way: Sn‐atoms form seven‐layer‐lamellae of the composition Te‐Bi‐Te‐Sn‐Te‐Bi‐Te which corresponds to the structure of the SnBi2Te4 compound; this seven‐layer‐lamella is uncharged. The formation of such a seven‐layer‐lamella can easily explain the experimental results: Sn‐atoms incorporated into the seven‐layer‐lamella are electrically inactive.
Energy‐Dependent Connection Rules of Envelope Functions at Heterointerfaces
Authors: Paasch G. , Nguyen P. H. , Gobsch G.
Published: July 2007

It is shown that the energy‐dependent connection rule of Bastard can be derived in a simple manner. The method can be generalized to more general ones than the Kane band structure. Moreover, starting from a complete two‐band model a classification of different former approaches of connection rules is presented and that one of Ishibashi et al. is derived with less restrictions and in a simple way. It is shown that the use of the two‐band model modifies the tunneling probability as it is usually calculated from a one‐component description.
The Biexciton Influence on Bose‐Einstein Condensation of Orthoexcitons in Cu2O
Authors: Bobrysheva A. I. , Moskalenko S. A. , Russu S. S.
Published: July 2007

The influence of the biexcitons formed from two orthoexcitons on the Bose‐Einstein condensation (BEC) of orthoexcitons and the possibility of the BEC of biexcitons is studied theoretically. It is shown that the existence of biexcitons in Cu2O crystal leads to a considerable difficulty for the observation of the BEC of orthoexcitons. The lineshape of the net gain of biexciton transition in Cu2O crystal is calculated. The obtained line is characterized by a strongly marked asymmetric form with a gentle sloping long‐wave tail and a sharp peak which is peculiar to BEC of biexcitons.
Electronic Structure of Point Defects in Semiconductor Alloys
Authors: Das A. , Barbero C. J. , Singh V. A. , Corbett J. W.
Published: July 2007

A simplified tight‐binding approach based on the coherent potential approximation (CPA) formalism is presented for the host electronic structure of semiconductor alloys (e.g. Ga1−xAlxAs). Several schemes to locate the gap level due to point defects are discussed. In particular, a novel scheme is introduced: the deep level approximation (DLA). It is pointed out that the vacancy results in the CPA are identical to the simpler virtual crystal approximation (VCA). In addition, the electronic band structure of SixGe1−x alloys is presented using a non‐orthogonal tight‐binding approach, namely the extended Hückel theory (EHT). Preliminary calculations of the dependence of the band gap on concentration are also presented.
Molecular‐Field Theory Analysis of Rare‐Earth Ternary Carbides Derived from R2Fe17 Compounds
Authors: Qiao W. H. , Wang Q. , Zhong X. P. , Luo H. L.
Published: July 2007

On the basis of a two‐sublattice model, the temperature dependent magnetic properties of the intermetallic compounds R2Fe17C (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Lu) are analyzed using the molecular‐field theory. The results of the analysis show that the molecular‐field coefficients nRF are rather sensitive to the kind of the rare earth spin, but the spin‐exchange parameters ARF hardly change. The intersublattic molecular (ISM) field H and the spin‐exchange field H are calculated, the results are compared with other ones and discussed.
The Continuous Background of SERS from Ag Colloids in Alkali Halide Crystals
Authors: Abel H.‐B. , Fischer F.
Published: July 2007

The continuum background of the SERS spectrum from thermally or photochemically prepared Ag colloids in alkali halide crystals is studied from − 5000 to + 1400 cm−1 and for counting rates covering three decades. The Stokes side consists of three contributions extending to about − 1500, − 3800, and beyond − 5000 cm−1 for 488 nm exciting light. As long as there is no evidence for hot luminescence it may be interpreted as SERS caused by charge‐transfer from the Fermi sea of the silver to mobility states and band‐tail states of the host and to localized surface states of the colloid. The anti‐Stokes intensity of the continuum background is found to follow a Boltzmann law between room temperature and 80 K.
Dipole Tensors and Volume Changes of Point Defects in H.C.P. Lattices
Authors: Monti A. M.
Published: July 2007

By computer simulation techniques dipole tensors and relaxation volumes of point defects in h.c.p. lattices are calculated for the fully relaxed lattice. Short‐range pair interatomic potentials to represent Mg and α‐Zr are used. Calculations for the vacancy at its equilibrium and activated states are reported. Quantitative differences due to the material elastic properties are found. For self interstitials, dipole tensor symmetries and volume‐change values are analyzed taking into account the defect‐lattice symmetries.
Generation of LO‐Phonons in a Time‐Dependent Electric Field at the Surface of III – V Materials
Authors: Scholz R. , Stahl A.
Published: July 2007

Recent experiments with ultrashort light pulses have shown that in the semiconductor samples under study the surface field is screened so quickly that it can generate coherent LO‐phonons. A theoretical description of this effect necessitates the simultaneous consideration of a number of interacting quantities: the exciting light field, the time dependent distributions of electrons and holes evolving towards equilibrium, the LO‐phonon amplitude, and the electric field self‐consistent with monopolar and dipolar charges. It turns out that the wave‐like nature of electronic distributions plays a decisive role via quantum mechanical boundary conditions. In the theory presented here this is accounted for by the use of a real space density matrix description.
The Role of the Electron‐Hole System in the Thermodynamics of YBa2Cu3O7−δGas Equilibrium
Authors: Tsidilkovskii V. I. , Leonidov I. A. , Lakhtin A. A. , Mezrin V. A.
Published: July 2007

The YBa2Cu3O7−δ‐gas equilibrium is studied theoretically in terms of the approach proposed earlier by the authors. The contribution of the electron‐hole system of the HTSC oxide to the equilibrium thermodynamics is studied for several models of the electronic structure. Oxygen—oxygen interactions in the basal plane are taken into account to calculate the chemical potential of oxygen ions in the oxide, distinct from the previous paper where these interactions are disregarded. It is shown that the equilibrium is well described for a sufficiently broad (much broader than kT) valence band with a hole effective mass mp ≈ 3 to 5 free electron masses.
Non‐Linear Temperature—Band Gap Variation in Small‐Gap Semiconductors and Semimetals
Authors: Fau C. , Charar S. , Averous M.
Published: July 2007

A model is proposed to determine the high‐temperature band gap for small‐gap or semimetal II–VI compounds as Hg1‐xCdxTe or Hgi1‐xCdxSe, from an analysis of Hall data. It is shown that there exists a non‐linear band gap‐temperature dependence for a given Cd concentration. A variation law valid for 0 < x < 1 is proposed. This law is checked for a lot of samples, and it is demonstrated that there exists a very good agreement with experimental results even near the semimetal‐semiconductor transition.
A Study of a Stable AlCuFe Quasicrystal in Solid and Liquid State
Authors: Chen Lifan , Chen Xishen
Published: July 2007

A stable Al65Cu20Fe15 quasicrystal with an icosahedral structure is studied in solid and liquid state. It is found that the icosahedral phase in Al65Cu20Fe15 alloy does not grow directly from the pure liquid state, but rather forms between monoclinic Al13Fe4 and residual liquid state at 865 °C. The melting point of the Al65Cu20Fe15 icosahedral quasicrystal occurs at 865 °C and that of the Al65Cu20Fe15 alloy occurs at 1008 °C. Moreover, the monoclinic Al13Fe4 is transformed into the icosahedral phase easily at the temperature of 845 °C. The icosahedral quasicrystal in Al65Cu20Fe15 alloy has a high thermal stability even at 950 °C. Above 950 °C, the icosahedral structure tends to an amorphous structure.
Energy Gap Structure in Semiconducting Bi1−xSbx Alloys
Authors: Kirakozova L. A. , Krapf A. , Kraak W. , Lavrenyuk M. Yu. , Minina N. Ya.
Published: July 2007

The Fermi surface, Dingle temperature, and galvanomagnetic characteristics in semiconducting Bi1−xSbx (0.1 < x < 0.16) alloys under strong uniaxial compression along binary and bisectric axes are investigated. Uniaxial deformations up to 0.3% give a possibility for the Fermi level to pass through the energy gap in particular energy extrema. The totality of experimental data does not confirm the presence of the deep donor level with high density of impurity states in the energy gap of these alloys assumed in some recent papers. It is observed that a specific microscopic inhomogeneity of “cluster type” about 10 to 20 μm in size does not reveal itself in oscillation properties, but determines the anomalous behavior of resistivity in the strain interval when the Fermi level passes through the energy gap.
Polaron Pairing in Multi‐Layer Structures I. Bipolaron States in Multi‐Layer Structures with Quantum Wells
Authors: Pokatilov E. P. , Beril S. I. , Fomin V. M. , Ryabukhin G. Yu.
Published: July 2007

Interaction of two electrons with each other and with polar vibrations in a system consisting of a non‐polar layer bordered from two sides by polar media is examined. The electrons are considered to be in the layer. It is shown that under suitable selection of system parameters (dielectrical constants, effective masses, layer thickness, etc.), the conditions can be given under which the bipolaron is formed in the layer. The bipolaron coupling energy in that case is calculated and cited. It is shown that in favourable cases it can reach hundreds of Kelvins. Maximum coupling takes place in the case when l → 0 and with l‐growth it quickly decreases, in the case when l/Rs ≧ 1 (where l — nonpolar layer thickness, Rs is radius of the three‐dimensional polaron) it comes to zero. Thus, for the existence of strongly coupled bipolarons it is necessary to have the following condition: l ≦ Rs.
Molecular‐Dynamics Computer Simulation of Aluminum Clusters (Aln; n = 3 to 55). Empirical Many‐Body Potential Energy Function Calculation
Authors: El‐Bayyari Z. , Erkoç Ş.
Published: July 2007

The structural stability and energetics of Aln (n = 3 to 55) clusters are investigated by using a recently developed empirical many‐body potential energy function which contains two‐ and three‐body atomic interactions. Molecular‐dynamics technique is employed in the simulation. It is found that the energetically most stable structures of aluminum clusters are in compact distorted buckled form.
The Effect of the Electronic Density of States on the Stability of Dilute Cu‐Based Alloys with 3d‐Metals
Authors: Stepanyuk V. S. , Szasz A. , Katsnelson A. A. , Kozlov A. V. , Hendry A.
Published: July 2007

The electronic properties of dilute Cu‐based alloys are calculated by the method of linear augmented plane waves. The results are correlating with the stability of these alloys, and giving possibility to approximate the solubility of the alloying elements in Cu. A successful comparison with the experiments is given.
Phase Diagrams of a Spin‐One Ising Model with a Random Crystal Field in the Correlated Effective‐Field Treatment
Authors: Kaneyoshi T.
Published: July 2007

The phase diagram of the spin‐one Ising model with a random crystal field Di on a square lattice is investigated by the use of the correlated effective‐field theory, when the random crystal field is distributed according to the law P(Di) = pδ (Di − D) + (1 − p) δ (Di). A number of characteristic phenomena are obtained, such as the p‐dependence of the tricritical point and the reentrant phenomenon due to the disorder of the crystal field.
Magnetic Properties of Monolayers with Modified Gaussian Distribution of Exchange Integrals
Authors: Balcerzak T. , Mielnicki J. , Wojtczak L. , Wiatrowski G. , Reinhold J.
Published: July 2007

Magnetic properties of a monolayer with a Gaussian‐type distribution of exchange integrals are investigated within the Ising model. The Gaussian distribution is modified in order to omit the range of negative exchange interactions as well as extreme positive values. The obtained results concern phase diagrams, magnetization, and correlation functions. A comparison with analogous results obtained for an ordinary Gaussian distribution is also made.
87Rb NMR Study of the Low Temperature Phase of Rb2ZnCl4
Authors: Apih T. , Blinc R. , Dolinŝek J. , Milia F. , Ailion D. C.
Published: July 2007

The 87Rb 1/2 → − 1/2 NMR spectra and spin‐lattice relaxation rates T−11 are studied in the high temperature paraelectric phase, the incommensurate phase, the ferroelectric commensurate phase, and the low temperature commensurate phase of Rb2ZnCl4 between 325 and 6 K. The changes in the 87Rb NMR spectra on going into the low temperature commensurate phase are compatible with the proposed crystal structure of this phase, whereas the observed T1 anomaly reflects the condensation of the soft mode inducing this transition.
Studies on Some Ground State Properties and Specific Heat of Mixed‐Valence Systems
Authors: Ghosh N. K. , Ghosh S. C. , Sarkar R. L.
Published: July 2007

A simple two‐site model with spin is considered for which the exact solution is admissible. The phenomenon of valence transition is investigated. Finite temperature specific heat and magnetic intersite spin correlations are also studied. It is shown that strong f‐d Coulomb interaction makes the first‐order transition possible. It is also shown that the magnetic intersite spin correlations are sensitive to f‐d Coulomb interaction and hopping interaction. The results are compared with previous works.
Magnetic Susceptibilities of Low‐Dimensional Organic Donor–Acceptor Salts
Authors: Schulte J. , Böhm M. C.
Published: July 2007

The magnetic susceptibility χ of the low‐dimensional organic charge‐transfer salts TTF‐TCNQ, (TMTSF)2PF6 and (2,5‐CH3DCNQI)2Ag is studied by a theoretical model which takes into account the χ‐enhancement due to electronic correlations as well as volume effects of the lattice as a function of temperature. Experimental data are reproduced both under constant pressure and constant volume conditions. The suggested approach reproduces the absolute values of χ and the corresponding temperature gradient. The theoretical expressions are valid for any band filling and correlation strength.