bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Cohesive and Anharmonic Properties of Alkaline Earth Fluoride Crystals
Authors: Singh R. K. , Rao Chandrika N.
Published: July 2007

The cohesive and anharmonic properties of alkaline earth fluoride crystals are described using the model parameters determined for the computer simulation study by de Leeuw using the two‐body interaction potential devised by Benson and Dempsey. It is found that this potential gives better prediction of these properties when the hardness parameters (ϱij, i,j = +, −) are taken different for different ion pairs. The results obtained from this potential on cohesive energy and second and third‐order elastic constants are in better agreement with their corresponding experimental data than those achieved by earlier workers from similar or other potentials.
Physisorption and Chemisorption Effects on Atom—Adsorbate van der Waals Potentials. Application to He and He* Scattering from Adsorbed CO
Authors: Lovrić D. , Gumhalter B.
Published: July 2007

The dynamical polarizability of an atomic or molecular species may undergo significant changes upon physical and chemical adsorption onto a metallic substrate. The physical effect derives from the presence of the polarizable substrate surface which gives rise to a modification of all the polarization induced or van der Waals potentials acting between the adsorbate and the nearby atoms or molecules in the gas phase. The chemical effect, viz. chemisorption, may give rise to the broadening of adsorbate valence orbitals into resonances which will be occupied up to the substrate Fermi level. Provided the electronic density of the localized resonance states at the Fermi level is non‐vanishing, chemisorption will open a new channel of intra‐adsorbate dynamic polarizability. Both effects (i.e. the physical and the chemical one) will enhance the total van der Waals potentials encountered in the thermal energy atom scattering and Penning spectroscopy of adsorbates. Calculations are made of these effects on the adsorbate—gas phase atom van der Waals potentials and their influence on the thermal energy atom scattering (TEAS) cross sections and the effective Penning deexcitation energies discussed for the case of He and He* collisions with adsorbed CO.
A Pseudopotential Band Structure Calculation of Bismuth, Antimony, and Their Alloys
Authors: Rose J. , Schuchardt R.
Published: July 2007

A semiempirical pseudopotential band structure calculation with account of spin—orbit‐interaction is performed for Bi, Sb, and Bi1−xSbx alloys considering the alloy potential in the framework of VCA. The parameter of Fermi surfaces are evaluated on the basis of the calculated energies. The resulting Fermi surfaces of the pure elements correspond better to experimental data than those of previous work. The composition dependences as well of gap and overlap as the Fermi surface dimensions agree qualitatively with the measured dependences.
Short‐Range Order and Superconductivity in Binary Alloys Containing V, Nb, and Ta
Authors: Khwaja Farid A. , Brouers F.
Published: July 2007

The problem of superconductivity in V, Nb, and Ta binary solid solutions is discussed in the light of interatomic pair interaction and density of states. Using a tight‐binding recursion method for degenerate d‐bands the superconducting transition temperatures are calculated for equiconcentration VNb, VTa, and NbTa alloys. The theoretical predictions about the existence of clustering of similar atoms in NbTa and ordering in VTa and VNb alloys is confirmed by measuring the values of Cowley's short‐range order parameter αi for these systems. The measured data show negative values of α1 on the first coordination sphere for VNb and VTa alloys and positive values for NbTa.
2D NMR Study near the Ferroelectric Phase Transition of TSCC
Authors: Engelke F. , Michel D. , Windsch W. , Petersson J.
Published: July 2007

Deuterium nuclear magnetic resonance (2D NMR) investigations are performed in order to get information about structural changes of the hydrogen bonds for deuterated crystals of trissarcosine calcium chloride (TSCC) near the ferroelectric phase transition at Tc = 130 K. The electric field gradient (efg) tensors at the deuterium sites in the hydrogen bonds are determined at room temperature by measuring the angular dependence of the spectra for rotations around the three crystallographic axes. Near the phase transition (Tc − T = 5 K) the positions of the 2D NMR lines change in an interval of about 10 kHz. These changes can be explained through a rotation of the efg tensor by an angle of about 4° at 125 K. The interpretation is in agreement with results from 1H ENDOR and 13C ENDOR measurements of TSCC crystals doped with Mn2+ according to which a static rotation of sarcosine molecules occurs at the phase transition giving rise also to the spontaneous polarization.
Short‐range order in multicomponent solid solutions
Authors: Dimitrov V. I. , Shteinberg A. S.
Published: July 2007

On the basis of the Ising model for multicomponent solid solutions generalized alloying potentials (or ordering energy parameters) are suggested and using them in the mean‐field approximation a short‐range order theory is presented.
Mn 3d states in photoelectron spectra from Cd1−xMnxTe
Authors: Mašek J. , Velický B.
Published: July 2007

A parametrized tight‐binding model is used to describe the electronic structure of semimagnetic Cd1–xMnxTe. The density of states and the spectral density are calculated by using the coherent potential approximation. The features connected with the presence of the Mn 3d states are identified and the controversial results of angle‐resolved and integrated photoemission from Cd1–xMnxTe are then explained.
Electronic structure of the Cd vacancy in CdTe
Authors: Meijer P. H. E. , Pecheur P. , Toussaint G.
Published: July 2007

By means of a tight binding parametrization of the band structure of cadmium telluride, in conjunction with the Green's function method the density of states of the perfect crystal is determined. Various parametrizations for this compound are compared. Next, the energy levels for the Cd vacancy are calculated taking into account the change in the wave functions around the missing atom as well as the various possibilities for the charged state at this site. Spin–orbit coupling is not taken into account, nor the possible neighbor relaxation around the vacancy.
“Dissolution” of 4f–4f transitions in phonon sidebands (ZnS:Tm3+)
Authors: Boyn R. , Zimmermann H.
Published: July 2007

For the example of the 1G4 → 3H6 emission spectra of two Tm3+ centers in ZnS crystals (measured by means of dye‐laser site‐selective excitation at helium temperature) it is shown that lines arising from transitions to higher Stark levels of a given manifold may “dissolve” in the phonon sideband of the transitions to lower Stark levels. This phenomenon, which involves a transfer of intensity from lines to sidebands, is discussed quantitatively by applying Fano's general theory of continuum–discrete level interaction, as formulated by Shibatani and Toyozawa, to this vibronic problem. On this basis the large sideband‐intensities observed may be understood for the present systems. Furthermore, the dissolution effect can, at least partly, explain the general observation that transitions to higher Stark levels tend to have smaller apparent intensities than those to the lowest Stark levels.
NMR powder spectrum simulation for nuclei with I > 1/2
Authors: Goc R. , Fiat D.
Published: July 2007

A program to calculate powder NMR spectra for nuclei with spin I > 1/2 is written. The spin Hamiltonian used includes Zeeman term, isotropic dipolar broadening, anisotropic chemical shift, and quadrupolar interaction with asymmetric field gradient treated up to second‐order term of perturbation theory. Two sites with different sets of parameters determining the shape of the spectrum can be included in calculation. The approach to the problem is entirely numerical without deriving analytical formulas for the lineshape.
Molecular dynamics in [(CH3)4N]2 CdI4. A proton magnetic relaxation study
Authors: Venu K. , Sastry V. S. S. , Ramakrishna J.
Published: July 2007

Proton spin–lattice relaxation experiments (at Larmor frequencies 10, 20, and 30 MHz), and second moment measurements are carried out on [(CH3)4N]2 CdI4 in the temperature range 77 to 400 K. The results are interpreted based on a molecular dynamical model of randomly reorienting methyl groups and isotropically tumbling tetramethyl ammonium group. The relaxation data show contributions from spin–rotation interaction at high temperatures and presence of inequivalent methyl groups. The correlation times and associated activation energies, connected with this model, are calculated from the data. The structure in the absorption line and in the free‐induction decay signal at 77 K indicates the possibility of tunnelling motion of the methyl groups.
Interference spectra of semiconducting slabs at excitonic resonances studied by Stahl's coherent wave approach to band gap electrodynamics
Authors: Czajkowski G. , Schillak P.
Published: July 2007

Interference structures observed in reflection and transmission spectra of thin semiconducting slabs in the excitonic region of the spectrum are investigated within the framework of Stahl's coherent wave theory of electrodynamic processes near the semiconductor band edge. The theoretical spectra agree well with those experimentally observed. An adjustable damping parameter is used. From the best fit the exciton collision time is determined.
Observation of an incommensurate structure by optical spectroscopy with a 5f ion as an internal probe. U4+–ThCl4 System
Authors: Krupa J. C. , Malek C. Khan , Delamoye P. , Moine B. , Pedrini C.
Published: July 2007

The second order phase transition in β‐ThCl4 (Tc = 70 K) leads to an incommensurate tetragonal structure modulated along the fourfold symmetry axis. This is due to the freezing of an optical soft mode which induces a modulation of the chlorine ion positions in a plan perpendicular to this axis. Consequently in neighbouring unit cells the crystal field strength acting on the U4+ ion is slightly different. Then the line shape in the optical spectra shows a continuous variation which reflects the shift of the energy as the symmetry changes. Selective excitation of the resulting different classes of sites, S4, D2, and various C2p ermits one to establish a correlation between absorption and emission profiles of U4+ ions. The green and the red observed fluorescences of U4+ in ThCl4 are assigned in the different symmetries and the energy level mapped out as a function of a phase angle φl related to the distortion according to the Delamoye and Currat model.
Pair‐correlation functions of liquid noble metals through Born‐Green‐Yvonne theory
Authors: Bhattacharya T. , Ghosh A. K.
Published: July 2007

Born‐Green‐Yvonne (BGY) equation is numerically solved to calculate pair‐correlation functions for liquid Cu, Ag, and Au utilizing the resonant model potential of Lam et al., and an experimental potential for Cu given by Rautioaho. A comparison of results with the earlier calculations of the authors based on the Percus‐Yevick (PY) equation helps to conclude that the BGY equation is at least as good as the PY equation as far as calculation of pair‐correlation functions of liquid noble metals is concerned.
Calculating the energy parameters for the CV and OPF methods
Authors: Gusev A. I. , Rempel A. A.
Published: July 2007

A method is proposed for calculating the energies ε (with ε being the energy of the m‐configuration of a type s figure), which are parameters of the cluster variation (CV) method and the order parameter functional (OPF) method. An analytic expression is derived which describes the energy ε in terms of power series expansion coefficients of the formation enthalpy of a disordered crystal. It is shown that a necessary condition for ordering is the presence of a nonlinear composition dependence of the formation enthalpy of a disordered crystal.
Lifetime studies on excited (F2+)* and M centers in NaF doped with magnesium
Authors: Bosi L. , Nimis M.
Published: July 2007

The lifetime and the decay properties of the relaxed excited state (RES) of the (F2+)* center in NaF:Mg are investigated: similarities with the F2+ center RES in pure NaF are once more evidenced. Nevertheless, two strange new effects are found: a) the radiative quantum yield is an increasing function of temperature up to 300 K; b) the (F2+)* luminescence can be induced by light excitation in the M center absorption band, in spite of the apparent absence of (F2+)* levels which can absorb in this spectral range. Furthermore, an absence of perturbative effects by magnesium ions on the decay properties of the M centers is ascertained.
Lattice thermal conductivity of solid helium crystals
Authors: Pal S. K. , Kumar A.
Published: July 2007

Vacancy like excitations are suggested for solid helium which can be scattered due to the vacancy–phonon interaction processes. The phonon conductivity of solid helium is analysed by modifying Callaway's expression for high frequency phonons and for Poiseuille's flow of phonons. An excellent agreement between theory and experiment is obtained when the combination of static and dynamic dislocation scattering processes is considered as an effective dislocation scattering of phonons.
Frequencies of a general damped coupled nonlinear oscillator system
Authors: Bose S. K. , Dubey U. B.
Published: July 2007

A system of 2m damped coupled nonlinear oscillators is considered when the nonlinear and coupling terms are of homogeneous even power 4p in position variables. Using a convenient canonical transformation to remove the damping term from the equation of motion and action and angle variables in Hamilton‐Jacobi theory, first order corrected frequencies are obtained. The expression for the corrected frequencies bears all the characteristic features of a damped coupled nonlinear oscillator system.
Electron–phonon interaction in dielectric interface systems
Authors: Jin‐Sheng Pan
Published: July 2007

The integral and differential equations for the polarization eigenmodes of the dielectric interface systems are given by making use of the macroscopic electric field caused by the bulk and interface polarization charges. It is shown that the polarization eigenmodes should be normalized according to the ortho‐normalized relation interpreted in the text. It is also shown that the interaction of the charged particles with SO phonons can be described by Fröhlich‐like coupling constant αSO characterizing the interface system.
The role of supersonic davydov solitons for energy exchange between two joined molecular chains
Authors: Ivić Z. , Satarić M. , Shemsedini Z. , Žakula R.
Published: July 2007

The statistical treatment of the energy transfer from one molecular chain to the other by the mechanism of supersonic Davydov solitons is presented. Two one dimensional molecular chains are considered which have the junction point enabling energy exchange between the chains. The supersonic solitons have the contribution to the energy transfer between joined chains. This contribution is inversely proportional to the soliton velocity.
Estimation of plasmon dispersion‐coefficient and evaluation of the effective mass of electrons in metals
Authors: Misra L. K. , Tripathy D. N.
Published: July 2007

Using an improved version of the Bohm‐Pines effective Hamiltonian for the electron–plasmon system, the correct value is reproduced of the critical wave‐vector, kc, for the plasmons in the random phase approximation (RPA) by minimizing the total energy of the system. The calculated values for the effective mass m* of the electron show a close agreement with the experimental result for sodium and potassium. By introducing an adjustable mass‐parameter, meff, in the theory not only a very good fit of the plasmon frequencies with the experimental data is obtained but also reproduced the observed value of the plasmon dispersion coefficient, α, for metals like Al, In, Na, and K. Further, an explanation for the two branch behaviour of the volume plasmon in Al and In is given. Finally, a qualitative argument is put forth to explain the difference between the calculated values of m* and those of meff.
Tunneling in k‐space. Application to degenerate valence band in the infinite spin–orbit interaction limit
Authors: Dargys A. , Rudolph A. F.
Published: July 2007

Hole tunneling between light and heavy mass bands in a homogeneous semiconductor due to a strong electric field is analyzed in the framework of spherical and at k = 0 degenerate bands when the spin–orbit interaction is infinite. Nonperturbative techniques are used to solve the problem. As in the case of zero spin–orbit interaction it is found that intervalence band tunneling takes place in a ring‐shaped volume whose symmetry axis is parallel to the electric field.
Influence of hydrogenation on the hyperfine interactions in (Y0.97Hf0.03)Fe2
Authors: Budzyński M. , Kochetov O. I. , Subotowicz M. , Niezgoda H. , Spustek H. , Tańska‐Krupa W.
Published: July 2007

Measurements of the parameters of the hyperfine interactions in (Y0.97Hf0.03)Fe2 before and after hydrogenation are performed by means of the time differential perturbed angular correlations (TDPAC) and Mössbauer effect (ME) methods. After hydrogenation of the intermetallic alloys superparamagnetic clusters are formed; they have equal anisotropy fields but their axes of easy magnetization are distributed randomly.
Quantum Theory of Channeling in Deformed Crystals
Authors: Kirilyuk A. P.
Published: July 2007

A description of charged particle channeling in crystals with smooth strain fields of arbitrary nature and form is built within the framework of quantum mechanical approach based on the dynamical diffraction theory. General features of the solution obtained are discussed, and its particular applications to the studies of beam deflection by bent crystals and dechanneling on extended distortions are outlined, special attention is given to the influence of channel curvature variations. The effect of bulk retrapping into the channel is predicted and shown to play an important role for the case of alternating bending.
Stochastic Forces in Anharmonic Crystals and on Their Surfaces
Authors: Wiatrowski G.
Published: July 2007

The phonon theory for inhomogeneous thin films with fluctuation of equilibrium position is developed in the anharmonic approximation. The analytical relations describing the stochastic forces as a term of the system memory with fluctuating parameter, δ, the quasi‐exponential autocorrelation functions, and the asymptotic behaviour of the system at low temperatures are obtained. The present results concern the surface as well as the bulk, so that the spatial distribution of phonon excitations in the system with and without fluctuations, in dependence of the initial conditions, can be discussed. Moreover, some conclusions on the local and global melting points in thin films are presented.
Temperature Dependence of Second‐ and Third‐Order Elastic Constants of Rare Gas Solids
Authors: Lehri S. , Shanker J.
Published: July 2007

The three‐body interaction model recently developed by Lehri and Verma for rare gas solids is extended to include the effect of thermal contributions and zero‐point energy. The generalized expressions for second‐and third‐order elastic constants which are valid at any temperature are reported. These expressions are applied for evaluating the temperature dependence of second‐ and third‐order elastic contants for Ne, Ar, Kr, and Xe.
Quantum Interference in a Series of Metallic Rings in a Magnetic Field
Authors: Bulka B. R.
Published: July 2007

The role of quantum interference of free electrons in a one‐dimensional normal metal ring in a magnetic field is considered. Calculations of the transmission between two perfect wires connected to the ring through ideal splitters are presented. The transmission of the single ring is a symmetric function of the enclosed magnetic flux and oscillates with the basic period hc/e. However, in an infinite series of rings the interference conditions vary from ring to ring which leads to averaging of the transmission. The localization length shows oscillations with the period hc/2e. Recent resistance measurements on small metallic systems in a magnetic field are discussed in the framework of this model.
Quadrupole Scattering in PrNi5
Authors: Lippold B. , Müller H. , Mahmoud S.
Published: July 2007

The influence of the dipolar and quadrupolar scattering due to the 4f electrons on the temperature dependence of the electrical resistivity in PrNi5 is investigated. Using the experimental values of polycrystalline PrNi5 and the isostructural LaNi5 as well as the crystalline electric field splitting scheme it is found that the quadrupole scattering is the dominating one.
Stimulated Brillouin Scattering of EM Wave Propagating Obliquely in a Magnetoactive Solid State Plasma
Authors: Maheshwari K. P. , Tarey G.
Published: July 2007

An investigation is made of stimulated Brillouin scattering of an electromagnetic wave propagating obliquely with the external magnetic field in n‐InSb. As the pump wave propagates in the semiconductor, the electrons acquire oscillatory drift velocity. The oscillatory drift velocity and the magnetic field of the pump interact with low frequency acoustic perturbation to produce high frequency side band which further interact with the pump to produce low frequency ponderomotive force responsible for driving the original density perturbation. The nonlinear dispersion relation is obtained for the coupled mode. The results show that the growth rate for SBS increases with the obliquity of the pump. The growth rate is found to decrease with the angle of scattering. In the weak magnetic field regime (0 ⪅ ωc/ωa ⪅ 0.7) the growth rate decreases with the magnetic field whereas in the strong magnetic field regime (0.7 ⪅ ωc/ωa ⪅ 0.9) the growth rate increases with the magnetic field.
Etude par RMN de la mobilité de l'ion flour au sein de la solution solide Pb1−xBixOxF2−x
Authors: Laborde P. , Villeneuve G. , Reau J. M.
Published: July 2007

L'étude par RMN de 19F de la solution solide Pb1−x, BixOxF2−x (0 ≦ x ≦ 0,67) a montré que les anions oxygéne se placent préférentiellement dans les sites normanx (et relaxés), ronfirmant ainsi les hypothbses émises lors de l'étude de Pb1−xBixOxF2−x par diffraction de neutrons. Les mouvements des ions fluor détectés par RMN peuvent être considérés comme non‐diffusifs.
Measurement of Oscillator Strengths of “F2A” Centres in MeF2:A+ (Me = Ca, Sr; A+ = Li+, Na+, K+)
Authors: Hamaïdia A. , Margerie J.
Published: July 2007

From combined EPR and optical measurements, the oscillator strengths f are determined of absorption bands of “F2A” centres in CaF2,:Li+ CaF2:Na+ SrF2:Na+ and SrF2:K+. The results are compared with f‐values obtained from the observed lifetimes of the first excited level of the same centres.
On the Interband Absorption in Size‐Quantized Bi Films
Authors: Zalużny M. , Okulski W.
Published: July 2007

The influence of the size‐quantization on the interband absorption spectrum of Bi films with normal along the trigonal or binary axis is investigated. The optical conductivity is evaluated on the basis of the two‐band model, taking into account the k‐dependence of optical matrix elements.
Photostimulated Reorientations of PO2− Centers in Alkali Halides
Authors: Lohmeier F. J.
Published: July 2007

Reorientations of molecular PO2− centers following an electronic transition are investigated in different alkali halides. Photoinduced reorientations which occur during the vibrational relaxation, as well as thermal reorientations are studied. The results are compared with an earlier study of the isoelectronic AsO2− center.
Reorientation of Hole Centers in CaWO4 Monitored by EPR and Optical Absorption
Authors: Herget M. , Hofstaetter A. , Nickel T. , Scharmann A.
Published: July 2007

In CaWO4 intrinsic hole centers are created by X‐irradiation and localized at one oxygen of the WO4 tetrahedron at temperatures below 150 K. More information about this trapping mechanism can be obtained by EPR measurements with applied uniaxial pressure and by optical absorption measurements. The results point to a Jahn‐Teller instability as the main part of this mechanism leading to a trigonal distortion of the tetrahedron.
Detailed Study of IR Absorption Spectra of Manganese–Zinc Ferrites
Authors: Katsnelson E. Z. , Karoza A. G. , Meleshchenko L. A. , Pankov V. V. , Khavkin B. G.
Published: July 2007

IR absorption spectra of the Mn1−xZnxFe2O4 ferrite‐spinel system are investigated in the frequency range ν = 800 to 40 cm−1. The spectra of the second derivative d2T/dν2 are obtained from the computer processed experimental transmission spectra (T). On their basis the two complex bands ν1 and ν2 of the IR spectra are resolved into three and four components, respectively (for zinc ferrite — into three) and for the band ν3 — into two components. From the concentration dependences of the bands νm(n) (m, n = 1, 2, 3, 4) it is concluded that the vibrations, the frequencies of which are independent of zinc ferrite concentration in certain ranges x, correspond to those of separate bonds MnO, ZnO, FeO i.e. they are characteristic with respect to frequency. The spectra of the spinels investigated are analyzed in accord with the irreducible representations of the point group F43 m(Td2). Small tetrahedral structure distortions due to higher covalency of the ZnO bonds and the availability of the Jahn‐Teller ions are considered.
Temperature Dependence of the Static Structure Factor for Liquid Bi, Ga, Sb, and Sn
Authors: Zou Xian‐Wu , Jin Zhun‐Zhi , Tang Sheng‐Qun
Published: July 2007

A simple approach is presented to calculate the temperature dependence of the static structure factor for non‐simple liquid metals, based on the hard sphere cluster model and considering the temperature dependence of the hard sphere diameters and atomic percentage of the second type of clusters. The structure factors of liquid metals are calculated for Bi (T = 300, 500, 550, 800, and 950 °C), Ga (T = 50, 200, 550, 800, and 1000 °C), Sb (T = 660 and 800 °C), and Sn (T = 250, 300, 700, 900, and 1100 °C). The calculated results are in good agreement with experiments.
Group‐Theoretical Analysis of the Symmetry Changes in R2MX4 Compounds
Authors: Abdi S. , Mlik Y. , Ben Ghozlen M. H.
Published: July 2007

Commensurate subgroups of Pnma are obtained by a group‐theoretical method started from the Landau theory of continuous phase transitions. The investigated high symmetry points are Γ, X, Y, Z, R, T, S, U, Σ, Δ, and A. These points belonging to the first Brillouin zone, are the most involved ones according to literature experimental data. The selected order parameter is defined in the basis associated with the corresponding irreducible representation of Pnma, so it may represent any physical property. The results are given in table form together with some useful information concerning the low symmetry structure. A particular interest is devoted to R2MX4 compounds (R = organic cation; M = Cu, Cd, Hg, Zn,…; X = Cl, Br) where the parent structure has Pnma symmetry.
Lattice Vibrations in Mixed Alkali Halide Crystals
Authors: Gupta B. R. K.
Published: July 2007

The phonon dispersion curves of two mixed alkali crystals KCl0.5Br0.5 and K0.5Rb0.5Cl are calculated using the extended three‐body force shell model (ETSM). The ETSM developed in the present study consists of two short‐range overlap potential parameters (A, B), two long‐range three‐body interaction parameters (f0, r0f′0), two distortion polarizabilities (d1, d2), and two modified shell charge parameters (Y1, Y2). The results on phonon dispersion curves are found to agree reasonably well with the experimental curves of Beg and Kobbelt.
Mode Grüneisen Parameters and Pressure‐Induced Phase Transition of Tetrahedral Compounds
Authors: Kagaya H.‐Matsuo , Soma T.
Published: July 2007

The pressure effect on the phonon frequency, i.e. the mode Grüneisen parameter of AIP, AlAs, and AlSb is studied from the electronic theory of solids. Then, a linear correlation by Weinstein between the TA‐mode Grüneisen parameter γ at the point X and the phase transition pressure Pt, is not necessarily satisfied for all of tetrahedral covalent crystals.
Effective‐Atom Fluctuations and the Representative Effective Atom in Liquid Nickel. A Cluster Study within the Muffin‐Tin Concept
Authors: Solbrig H.
Published: July 2007

Superposition potentials are calculated for 50 atomic spheres in a big relaxed cluster. Two conclusions can be drawn: (i) Effective‐atom fluctuations contribute less than 10% to the observed d‐band broadening. (ii) There are two straightforward approaches to a representative effective atom. The first one attempts approximating highly probable cases whereas the second one accounts for fluctuations, too.
LO‐Phonon Modes Bound to Neutral Impurities in Polar Semiconductors. II. Special Cases and Experimental Results
Authors: Monecke J. , Cordts W. , Irmer G. , Bairamov B. H. , Toporov V. V.
Published: July 2007

In a previous paper the Fröhlich interaction between charge carriers bound at impurities and LO‐phonons in polar semiconductors is considered within second‐order perturbation theory. Here special cases including the possibilities of degenerate electronic ground and excited states are discussed. Jahn‐Teller like splittings of degenerate ground states as well as Lamb‐Retherford like splittings of degenerate excited states are obtained. Besides renormalized electronic excitations the solution of the eigenvalue problem yields phonons bound to neutral imuprities (dielectric modes). Results of Raman spectroscopic determinations of these modes in GaP:S, Te, Si, and Sn are presented and their experimental binding energies are compared with theoretical results.
On the Radiation Process in Incompressible Elastic Media
Authors: Szczepański A.
Published: July 2007

The radiation of equivoluminal waves by an accelerated inner point defect in an incompressible elastic medium is shown to possess a remarkable globality property, which renders it different from the radiation processes known in classical mechanis and standard classical electrodynamics.
Auger Neutralization of Fast Ions at Surfaces
Authors: Taute Elke
Published: July 2007

Auger neutralization of fast He++ moving parallel to a solid surface at constant distance s is discussed. Results for the transition rate as a function of s and the impact energy of the ions are presented. The orientation for the He+2p‐states is also calculated leading to the conclusion that orientation effects due to Auger neutralization cannot be neglected a priori compared to those due to charge exchange.
Cluster Identities for the Ising Model as a Basis for Simple Effective Field Approximations Discerning between Various Lattices with the Same Coordination Number
Authors: Tomczak P. , Sarmento E. F. , Siqueira A. F. , Ferchmin A. R.
Published: July 2007

Identities are proposed for clusters of N interacting Ising spins. For a single spin they reduce to Callen identity, for a spin pair to that of Bobák and Jaščur. It is shown that effective field approximations for spin correlations lead to different Curie temperatures for lattices of the same coordination number but different dimension.
Magnetic Field Dependences of Two Kinds of Structural Transition Temperatures of CeAg1−xInx
Authors: Kurisu M. , Kadomatsu H. , Fujiwara H.
Published: July 2007

The magnetic field H dependence of the cubic‐tetragonal transition temperature, TM1, of the CeAg and TM2 of the CeAg1−xInx system with x = 0.01 and 0.02, are determined from resistivity measurements. TM1 is increased with H, while TM2 is decreased with H. These differences between the magnetic field dependences of TM1 and TM2 are attributed to their origins: 4f quadrupole ordering for TM1 and d‐band Jahn‐Teller effect for TM2, respectively.
On Some Optical Properties of NaF Single Crystals X‐Ray Irradiated under DC Fields
Authors: Veeraiah N.
Published: July 2007

Results of the following measurements on NaF single crystals X‐ray irradiated at room temperature under different de fields (0 to 20 kV/cm) are reported: (i) growth of absorption bands (F‐ and M‐bands) with de field, (ii) thermal bleaching characteristics of the absorption bands, (iii) thermo‐luminescence in the temperature range 30 to 300 °C, and (iv) the optical absorption of NaF samples X‐ray irradiated at elevated temperatures (100 and 190 °C) under de fields. These results are explained as due to the generation of negative ion vacancies near the dislocations by the de field and the formation of F‐centres on X‐ray irradiation. From these results it is also possible to establish a correlation between colour centre destruction and thermoluminescence peaks.
On the Screening Length of Disclinations in Amorphous Structures
Authors: Richter A. , Romanov A. E. , Pompe W. , Vladimirov V. I.
Published: July 2007

Disclinations represent the main defects beside dislocations in topologically disordered structures. The stress field and the energy of a disclination depend strongly on the boundary conditions, mostly the presence of a free surface. Stress field, self‐energy, and pair interactions of disclinations in a finite cylinder are calculated pointing out the relevance of additional interactions of disclinations with the surface, if the disclination is not positioned in the center of the cylinder. The energy of the model system is always diminished by such surface effects. Numerical calculations of the screening length in a disclination network for an amorphous structure show that a cut‐off radius only exists because of the interaction between defects. The screening length is about three times larger than the average distance between disclinations and depends on the disclination density. The cut‐off radius corresponds to the creation of internal surfaces resulting in an additional screening of defects.
Self‐Consistent Calculations of the Melting Criterion Based on Lattice Instability
Authors: Malinowska‐Adamska C.
Published: July 2007

Melting criterion as a function of the external pressure for cubic crystals is examined using Plakida and Siklòs's model for the lattice dynamics of crystals by computing the ratio, xm, of the rootmean‐square relative displacement of neighbouring atoms and the interatomic spacing at the instability temperature for a number of cubic metals belonging to different groups of the periodic table. This ratio has nearly the same value for elements of one particular group but exhibits wide variation from one group to another. The variation is in accordance with the nature of binding in metals.
Invariant Harmonic Oscillator Functions. IV. The Thirty Two Point Groups
Authors: Schöpp J. , Wöhlecke M. , Scherz U.
Published: July 2007

A method is given to calculate symmetry adapted harmonic oscillator functions for all 32 point groups. Due to reduction theorems between the various groups all functions can be found from those of the cubic groups and D4. The cubic groups are dealt with in the foregoing papers and here explicitely the oscillator functions for the group D4 are given.
Thermal Conductivity and Thermoelectric Figure of Merit of Bi1−xSbx Films With 0 < x ≦ 0.3
Authors: Völklein F. , Kessler E.
Published: July 2007

The thermal conductivity λ and thermoelectric figure of merit z of Bi1−xSbx films with 0 < x ≦ 0.3 and thicknesses from 30 to 400 nm are measured in the temperature range 80 to 400 K. The lattice thermal conductivity λϱ is determined from the measured total thermal conductivity λ and the calculated charge carrier contribution λe. The results are discussed in the framework of earlier proposed models for the charge carrier and phonon heat transport in polycrystalline films. The Sb‐concentrations for maximum z‐values of the films are established.
Collective Excitations in the Extended Hubbard Model with Intrasite Attraction
Authors: Kostyrko T.
Published: July 2007

Collective excitations in the superconducting state of an extended Hubbard model with an intrasite attraction are investigated using the random phase approximation method. The results for the energy of gapless excitations are consistent with the well known result of Anderson in the limit of weak attraction and the result of the perturbation theory (with respect to the band term) in the limit of strong attraction. Investigating the dependence of the excitation energy on the density of electrons in the band conditions are found of instability of the singlet superconducting state with respect to the disordered state (for attractive intersite interactions) and to the charge ordered superconducting state (for intersite repulsion).
Mixed Valence Properties of CeM2Si2 (M  Mn, Fe, Co, Ni, Cu)
Authors: Ammarguellat C. , Escorne M. , Mauger A. , Beaurepaire E. , Ravet M. F. , Krill G. , Lapierre F. , Haen P. , Godart C.
Published: July 2007

Lattice parameter measurements in the temperature range 12 to 300 K and LIII edge measurements in the range 4.2 to 300 K are performed on the compounds CeM2Si2 (M  Mn, Fe, Co, Ni, Cu) to study the valence changes. Magnetic measurements (1.6 to 600 K) for fields up to 1 T confirm antiferromagnetism of CeMn2Si2 (TN ≈ 370 K) and show enhanced Pauli paramagnetism of mixed valence compounds with M  Fe, Co, Ni with spin fluctuation temperatures around 150 K with Co, Ni. Transport properties measurements show that the compounds with M  Co, Ni, Fe do not become superconducting down at 18 mK and that a Fermi liquid behaviour exists in the range 40 to 70 K.
On the Effective Mass of Pekar's Polaron
Authors: Davydov A. S. , Enolskii V. Z.
Published: July 2007

The polaron motion in Pecar's model is shown to be possible only in ionic crystals with positive dispersion Ω2(κ)  Ω + νκ2, at the velocity ν ≦ ν0. The expression for the polaron effective mass up to v20 is obtained.
Selfconsistent Discrete Equations for Nonlinear Defects in Peierls Systems with Broken Electron–Hole Symmetry
Authors: Drechsler S. L. , Heiner E. , Malek J.
Published: July 2007

The SSH‐Hamiltonian extended by long‐range hopping parameters and long‐range interatomic elastic forces is investigated. A discrete system of electron eigenvalue equations together with self‐consistency conditions for atomic displacements is derived and numerically solved for soliton states in polyacetylene. As a novel feature it is found that (1) the soliton level is slightly shifted from the exact midgap position and (2) a weak internal charge structure appears for neutral solitons and antisolitons and gives rise to a long‐range repulsive interaction between them.
Helicon Waves in a Sinusoidal Periodic Structure
Authors: Achar B. N. Narahari
Published: July 2007

Helicon wave propagation in a sinusoidally modulated periodic structure in the local limit is governed by Mathieu's equation. The dispersion relation obtained numerically using continued fractions does not show strong band gap effects.
Non‐Stationary Stimulated Acousto‐Optical Interactions in Solid Dielectrics
Authors: Bukowski R. , Kleszczewski Z.
Published: July 2007

A theoretical analysis of non‐stationary interactions of intensive laser light and a bulk acoustic wave in dielectric crystals is made. The time dependence of the source of both, light waves and acoustic wave is considered. All fundamentals kinds of acousto‐optics interactions, viz. Stokes and anti‐Stokes processes, as well as the generation of acoustic waves by “mixing” two light beams are discussed.
The Memory Effect in Empirical Descriptions of Dielectric Relaxation
Authors: De La Fuente M. R. , Jubindo M. A. Pérez , Solier J. D. , Tello M. J.
Published: July 2007

An analysis of the memory effect in some empirical descriptions which account for the dynamical dielectric response of a great number of real systems is presented. The study is carried out considering the relaxations as stochastic processes. The involved time‐dependent transition rates are directly related with the memory effect. A comparison among underlying dipolar dynamics for the most usual empirical descriptions is made.
Self‐Consistent Description of the Effect of Point Defects on Spectrum and Dynamic Deceleration of Dislocations
Authors: Malashenko V. V. , Sobolev V. L. , Khudik B. I.
Published: July 2007

A self‐consistent equation of dislocation motion in elastic fields created by defects is obtained. The deceleration force value is calculated due to defect collisions and it is shown to have a quasiviscous character under low velocities.
The Bihole in Quantum Well Structures
Authors: Bobrysheva A. I. , Russu S. S. , Zaloj V. A.
Published: July 2007

In GaAs–Ga1−xAlxAsmany quantum well structures or superlattices the top valence subband VB1 of size quantization is heavy‐hole‐like HH1 and the effective mass m1 is positive. The second valence subband VB2 has a heavy‐hole – HH2 or light‐hole –LH1 character in dependence on the barrier and well layer thicknesses and the composition x. The effective mass m2 in VB2 is negative and the condition for bihole formation m1 > ‖m2| is fulfilled. The binding energy of the bihole is calculated. The bihole formation due to light absorption is studied. The oscillator strengths in the cases of inter‐ and intrasubband transitions of holes succeeded by bihole formation are obtained.
Anomalies in the Phonon Spectra and the Fermi Surface of the Random Substitutional Alloy Cu0.9Ni0.1
Authors: Rumyantsev A. Yu. , Mitrofanov N. L. , Ivanov A. S. , Chernoplekov N. A. , Weiss L. , Eschrig H. , Richter R.
Published: July 2007

With a full self‐consistent LCAO‐CPA‐calculation of the Bloch spectral function (representing the electronic bandstructure) of the random substitutional alloy Cu0.9Ni0.1, statements regarding the existence and the shape of the Fermi surface are given. The relation of the Fermi surface with various kinds of anomalies in the phonon dispersion curves as pointed out in previous papers is used to compare such anomalies as measured by neutron spectroscopy in the (110)‐plane of this alloy with the calculations. The experimental results show that the Fermi surface intersecting this plane is somewhat less extended than coming out from this calculation.
High‐Order Perturbation Formulae of the Spin‐Hamiltonian Parameters for the Ground State 3A2(F) of d8 Ions in Rhombic Symmetry
Authors: Chen Jia‐Jun , Zhao Min‐Guang
Published: July 2007

High‐order perturbation formulae of the spin‐Hamiltonian parameters D and E and the g‐factor for the ground state 3A2(F) of d8 ions are obtained in the strong‐field coupling scheme. In the derivation, not only spin triplet states but also spin singlet states are considered. According to Zhao's μkα‐correlation ligand field model for the Ni2+−6X−(F−, Cl−, Br−, I−) complexes, the relationships between the spin‐Hamiltonian parameters and the crystalline ones of the Ni2+−6X− cluster are established and applied to ZnF2:Ni2+ and NiF2. In the calculation, no adjustable parameter is introduced. The results agree well with the experimental findings, indicating that the given relationships are reasonable.
On the Theory of Double Gamma Electronic Magnetic Resonance in Paramagnetic Systems
Authors: Sadykov E. K. , Skvortsov A. I.
Published: July 2007

The theoretical analysis is continued of the double gamma electronic magnetic resonance (DGEMR) phenomenon described previously. The possibility of essential modification of the hyperfine magnetic structure (HMS) in the nuclear gamma resonance (NGR) spectrum under coherent excitation of the electron spin system of the paramagnetic atom is demonstrated. The influence of the r.f. amplitude on the DGEMR spectrum form is considered. The nature of the r.f. collapse of the HMS taking place in these conditions is defined. For small values of r.f. amplitude the DGEMR spectrum form in presence of the inhomogeneous broadening of ESR line and optimal experimental conditions defined by this matter are investigated.
Optical Absorption of the Soliton Lattice
Authors: Puff H. , Streitwolf H. W.
Published: July 2007

The optical conductivity for the soliton‐lattice solution of the continuum approximation to the Su‐Schrieffer‐Heeger model of doped polyacetylene is calculated for different excess electron densities. The optical sum rule is verified in each case. The resulting shifts of the absorption maxima are compared with experiment. Implications of the finiteness of Δ0/W (gap/bandwidth) on the nature of the phase transition and the absorption are discussed.
Gauge Theory of Defect Systems and Equivalence Principle
Authors: Holz A.
Published: July 2007

A gauge theory of solid and liquid systems is developed based on sets of point like particles using simplicial and differential geometric methods. The proper use of the equivalence principle in the context of describing defect systems by means of gauge theory is worked out. The break‐down of the equivalence principle in the liquid state or highly defected state as a consequence of change of local order is discussed and alternatives are pointed out. Some applications of the theory to two‐dimensional systems using complex function theory are given and simple extensions of such defect structures to three dimensions are compared to space‐time structures in 2 + 1‐dimensional gravitation.
The Kink Energy in Anisotropic Media
Authors: Schoeck G. , Püschl W.
Published: July 2007

The energy of a kink pair is calculated by approximating the configuration by piecewise straight segments and minimizing the total energy with respect to the geometrical parameters. The elastic energy and the core energy contribute both to the total energy by nearly the same amount. The expression for the elastic energy includes all interaction terms between the different segments and takes fully account of anisotropy. The increase in core energy corresponding to the Peierls energy enters as an open parameter which can be calculated realistically only by atomistic considerations but which may be determined experimentally from the results.
Die unterschiedliche Löslichkeit der Wasserstoffisotope Protium, Deuterium und Tritium in Vanadium
Authors: Bleichert H. , Wenzl H.
Published: July 2007

Aus Löslichkeitsmessungen im Temperaturbereich 40 ≦ T ≦ 800°C und Druckbereich 10−4 ≦ p ≦ 2 × 105 Pa wird die partielle Lösungsenthalpie ΔHH und ΔS Lösungsentropie (Nicht‐Konfigurationsanteil) der Wasserstoffisotopen Protium (P), Deuterium (D) und Tritium (T) bei der Einlagerung von Wasserstoff (H) aus der Gasphase in verdünnte VHr‐Legierungen (0,003 ≦ r ≦ 0,045) bestimmt. Bei 200°C ergeben sich folgende Werte (r → O): ΔH = 29,2 kJ mol−1, ΔS = 68,1 JK−1 mol−1, ΔH = 31,1 kJ mol−1, ΔS = 71,9 JK−1 mol−1, ΔH = 34,5 kJ mol−1, ΔS = 77,9 JK−1 mol−1. Bei T < 400°C steigt bei gleichem Gasdruck die Löslichkeit mit steigender Isotopenmasse, bei T > 400°C sinkt sie mit steigender Isotopenmasse. Die Isotopieabhängigkeit in der Löslichkeit läßt sich durch ein harmonisches Oszillatormodell für die lokalisierten Schwingungen des Wasserstoffs auf Tetraederplätzen beschreiben, wobei die charakteristischen Anregungsenergien von Protium E1 = 120 meV und E2 = 180 meV (2‐fach entartet) betragen. Die Anregungsenergien der anderen Isotope ergeben sich durch Herabskalieren mit √2 für D und √3 für T.
The Surface Superconductivity of Layered Metals
Authors: Shapiro B. Ya. , Efimova L. V.
Published: July 2007

An investigation of the surface influence on superconducting parameters (critical temperature and upper critical magnetic field) of the metallic superlattices is made. The dependence of the critical temperature on superlattice parameters (distance L between the layers with better superconducting properties and distance D between the former from these layers and surface) is obtained. The temperature dependence of the upper critical field parallel and perpendicular to the superlattice surface is found for different ratio between L and D. The dependence of the critical parameters on number n of the layers of the superlattice is calculated. It is shown that the surface of the metallic superlattice induced superconducting state contrary to that of homogeneous superconductors.