bluuebunny/crossref_metadata_2025_split huggingface dataset:
AC Properties of a Random Barrier Network
Authors: Sinkkonen J. 
Published: July 2007

AbstractThe ac properties of random barrier network are analyzed using the effective medium theory. At low frequencies σm ∼ ωs and at high frequencies it saturates to the value determined by the conductivity of the bulk material. Below the percolation threshold s ≈ 0.8, at the threshold s ≈ 0.4, and above the threshold s still decreases. The effective dielectric constant εm decreases with increasing frequency saturating to the bulk value at high frequencies. At the percolation threshold εm shows a pronounced maximum exceeding by several orders of magnitude the bulk value.
ENDOR Study of Cubic Fe3+ Centres in KMgF3
Authors: Duvarney R. C. , Niklas J. R. , Spaeth J. M. 
Published: July 2007

AbstractThe superhyperfine (shf) interactions of the Fe3+ impurity ion in KMgF3 with its nearest neighbour (n.n.) and next‐nearest neighbours (n.n.n.) F− ions are determined. Using ENDOR‐induced ESR it could be shown that the cubic field splitting parameter has the same (positive) sign as the n.n. neighbour shf interaction. Weak satellites in the ESR and ENDOR‐induced ESR spectra are tentatively assigned to a hf interaction with the 2.2% abundant 57Fe nucleus. The interpretation of the shf data in terms of a covalency and overlap model shows that the n.n.n. shf interaction can be explained as a transferred shf interaction via F−–F− ion core overlaps.
Study of Cohesion and Allied Properties of Silver Halide Crystals
Authors: Singh R. K. , Khare P. 
Published: July 2007

AbstractAn interionic potential model is developed by introducing modifications of the Hafemeister and Flygare (HF) potential to include the effects of three‐body and van der Waals interactions. This modified HF potential is applied to investigate the cohesion and associated physical properties of silver halides and found to give better descriptions than those obtained by earlier workers. The importance of the significant role of the three‐body and van der Waals interactions is also emphasised.
Density Excitation Spectrum of the One‐Dimensional Fermi Gas
Authors: Apostol M. , Corciovei A. , Stoica S. 
Published: July 2007

AbstractThe collective excitations of the particle‐density fluctuations are studied in the one‐dimensional Fermi gas by means of the generator coordinate method. The dispersion relation are obtained both, for the forward and backward scattering interaction. It is shown that for repulsive interaction a gap occurs in the frequency of the backscattering excitations at wavevectors equal to twice the Fermi momentum.
Induced Magnetism via Conduction Electron Exchange Application to PrAl2
Authors: Palermo L. , Da Silva X. A. 
Published: July 2007

AbstractThe magnetization, susceptibility, and magnetic specific heat of PrAl2 versus temperature are studied within a model where the onset of magnetism is due to the mutual magnetization of rareerth ions and conduction electrons, and the ionic magnetization process is van Vleck‐like. The crystal field, bandwidth, and exchange parameters of the model which fit the available experimental data are 2.5, 7000, and 341 meV, respectively.
Acceptor States in Zero‐Gap Semiconductors in Magnetic Field. Theory for Short‐Range Defect potential
Authors: Gortel Z. W. , Szymański J. , Świerkowski L. 
Published: July 2007

AbstractThe high magnetic field behaviour of resonance acceptor states in zero‐gap semiconductors produced by short‐range defect potential is studied in the actual structure of an inverted Γ8‐band. Results of numerical calculations for different zero‐field acceptor level energies are presented and optical selection rules for transitions between acceptor states and Γ6 and Γ8 Landau levels are given.
Spectre de photoémission de l'alliage ternaire Ga1−xAlxSb
Authors: Ance C. , Amamou A. 
Published: July 2007

AbstractLes mesures de photoémission UPS et XPS effectuées sur Ga1−xAlxSb montrent une modification des spectres de la bande de valence, en fonction de x, reliée directement aux structures de la bande de valence. L'évolution des énergies de liaison de Ga et Sb ne s'interprète pas directement par un transfert de charges, car la différence entre les énergies des niveaux internes de Ga et Sb reste inchangée quel que soit x. Ce résultat qui est en désaccord avec l'augmentation de l'ionicité, semble s'expliquer par une délocalisation de la charge transferrée vers l'anion.
Evaluation of the Fourth‐Order Elastic Constants of NaCl‐Structure Alkali Halide Crystals
Authors: Shanker J. , Singh J. P. , Gupta V. P. 
Published: July 2007

AbstractAll the fourth‐order elastic constants are calculated for 16 alkali halide crystals with NaCl structure using Lundqvist's three‐body potential energy expression. In addition to long‐range Coulomb interactions the short‐range overlap repulsive interactions are considered between first‐and second‐nearest neighbours as well as the van der Waals dipole–dipole and dipole–quadrupole interactions. Values of the fourth‐order elastic constants calculated in the present study are used to deduce the first pressure derivatives of the third‐order elastic constants and second pressure derivatives of the second‐order elastic constants for the crystals under investigation. The results are discussed and compared with available experimental data.
Thermoluminescence of Ag+‐Doped CsBr Crystals
Authors: Chowdari B. V. R. , Selvasekarapandian S. 
Published: July 2007

AbstractThermoluminescence and thermoluminescence emission of pure and Ag+ doped CsBr crystals are studied and the results are correlated with optical absorption studies. Two glow peaks at 356 and 393 K are observed in pure CsBr crystals. These two peaks are attributed to the first two stages of F centres. Four glow peaks at 348, 356, 366, and 393 K are observed in Ag+ doped CsBr crystals. While the glow peaks at 356 and 393K could be attributed to thermal decay of F centres as in pure CsBr, the 348 and 366 K peaks may be attributed to Ag° and Ag2+, respectively. Pure CsBr crystals give three thermoluminescence emission bands at 425, 450, and 475 nm. The origin of these three bands is discussed.
Energy Structure of the Alkaline‐Earth Fluorides
Authors: Starostin N. V. , Shepilov M. P. , Alekseev A. B. 
Published: July 2007

AbstractThe density of valence states for fluorite‐type crystals is calculated on the basis of tight‐binding (TB) and OPW methods. More precisely energy values of valence bands determined by the TB method at high‐symmetry points Γ, X, L are reported. A comparison is made with other theoretical estimates and experimental data.
Transition Temperature of Superconducting Alloys with Random Transfer Integrals
Authors: Kolley E. , Kolley W. , Beckmann A. 
Published: July 2007

AbstractA formalism is developed to describe nonmagnetic weak‐coupling superconducting alloys in the presence of random transfer integrals of the additive type. The off‐diagonal disorder in the lattice space is treated within an extended version of the coherent potential approximation (ODCPA). Vertex corrections are performed by means of Ward‐type relations. The concentration dependence of the superconducting transition temperature Tc is determined. Numerical results are discussed in view of the sensitivity of Tc to different bandwidths of the components. A comparison with experimental Tc(x) data on TaxV1−x and TixV1−x is given.
Theory of the Free‐Carrier Absorption in Zincblende Narrow‐Gap Semiconductors
Authors: Sierańaski K. , Szatkowski J. 
Published: July 2007

AbstractFree‐carrier absorption due to chemical disorder as well as to introduced intentionally periodic fluctuations of composition, is calculated in mixed semiconductors with the zincblende structure and dispersion relation that is typical for III–V and II–VI compounds. It is found that for low electron concentration, absorption coefficients due to chemical disorder and to ionized impurities are of the same order. Intentionally introduced periodic fluctuations of molar composition give an additional contribution to the absorption. This contribution for narrow period of the fluctuation (≈ 100 Å) has the form of a well defined peak.
Electron Structure and the Nature of Co3Ti Phase Formation
Authors: Tukhfatullin A. A. , Panin V. E. , Simakov V. I. , Demidenko V. S. , Kalyanov A. P. 
Published: July 2007

AbstractA theoretical study of the electronic structure of the Co3Ti alloy is carried out in ordered and disordered states. The division of the ordered alloy energy spectrum into two band groups separated by an energy region of low state density is established. The genetic connection of the low and upper group of bands with atoms of different components and the character of wave functions in these bands are analyzed. On the basis of the calculation of the band energy the character of limited solubility of Ti in Co and the nature of the Co3Ti phase formation are analyzed for different alloy concentrations.
Padé Approximations for the Thermodynamic Functions of Weakly Interacting Coulombic Quantum Systems
Authors: Ebeling W. , Richert W. , Kraeft W. D. , Stolzmann W. 
Published: July 2007

AbstractA weakly interacting system of electrons (e) and ions (i) is considered. Based on analytical formulae in the limiting regions of both weak and strong degeneration of the e4‐contribution and a few computer calculated points in the intermediate region n Λ3 ≈ 1 (n electron density, Λ thermal wavelength, Λ2 = 2πβh2/me, β = (kBT)−1, me electron mass) Padé‐approximations for the thermodynamic functions are constructed which are valid in the entire temperature–density plane. The temperature dependence of the exchange and correlation contribution to the chemical potential is taken into account here for the first time. In the framework of an unsymmetrical electron–hole model of germanium, a phase transition occurs with a critical point at Tc = 8 K and nc = 1.0 × 1017 cm−3.
Two‐Phonon Absorption Spectra in ϵ‐GaSe
Authors: Riede V. , Neumann H. , Lévy F. , Sobotta H. 
Published: July 2007

AbstractPolarization‐dependent optical transmission spectra of ϵ‐GaSe are measured at room temperature in the wave number range from 180 to 600 cm−1. The absorption peaks observed can be interpreted in terms of two‐phonon combination modes including Γ, A, and M point phonons. The M point phonon frequencies derived from the two‐phonon absorption spectra are in good accordance with data previously published.
Volume Dependence of the Bulk Modulus in Alkali Metals
Authors: López J. M. , Alonso J. A. 
Published: July 2007

AbstractThe bulk modulus of alkali metals (calculated by the density functional method) is decomposed into a part due to the electronic gas, assumed homogeneous, and another part arising from the inhomogeneity of the electron density. The relative contributions of the two terms is studied as a function of volume and as a function of the ionic radius. The theoretical results for the bulk modulus and its variation with volume show very good agreement with the experiments.
Diagrammatic Perturbation Theory for a Spin–Phonon System
Authors: Barker G. C. , Tucker J. W. 
Published: July 2007

AbstractIn a diagrammatic expansion of the phonon Green function for a coupled spin–phonon system an essential quantity that enters the calculation is the polarisation matrix associated with the generalised spin susceptibility. Averages of time‐ordered products of spin operators that occur have been conveniently expressed in terms of semi‐invariants and are evaluated using a diagrammatic technique. Hitherto, only the zeroth‐ and second‐order contributions to the polarisation matrix are derived for a system of paramagnetic ions coupled to the phonons of the host lattice through an interaction that is linear in the strain. Near a spin resonance frequency, higherorder terms in the polarisation matrix become important. The complete expression for the fourthorder contribution to the polarisation matrix is reported. The result is valid for all temperatures and the concentration dependence of the paramagnetic ions is accounted for.
Internal Strains and Raman‐Active Optical Phonons
Authors: Anastassakis E. , Cardona M. 
Published: July 2007

AbstractThe connection between internal strains and Raman‐active optical phonons in crystals is discussed. In crystals with more than one atom per unit cell, there is usually a number of atomic position parameters which cannot be uniquely defined by crystal symmetry arguments. Within the present scheme, it is shown that those parameters correspond to the number of fully symmetric (Γ1, A1) optical phonons at q = 0. Besides lowering the symmetry of the crystal, an external stress can introduce new atomic position parameters (internal strains). The criteria are given for determining the type of internal strain which may be produced by an external stress. The internal strain is looked upon as a “frozen” Raman‐active phonon, both belonging to the same irreducible representation of the crystal point group. It is shown that the well‐known matrices of the Raman tensor can be used directly to determine the selection rules for the stress‐induced internal strains in all crystals, regardless of symmetry. Related unit cell crystal parameters can be determined with X‐ray diffraction techniques.
Energy of Magnetic Anisotropy and Reduction Symmetry of Crystals
Authors: Volkov V. M. , Kustov E. F. , Makietov T. K. , Steczko G. 
Published: July 2007

AbstractUsing the properties of reduction symmetry of the crsytals, the expressions for the energy of magnetic anisotropy (MA) for almost all symmetry groups are given. The newly introduced constants of the MA are calculated for some magnetic materials and the relationships between these constants and the constants generally used are given. The rules of behaviour of the new constants of MA in some crystals are analysed.
On the Kinetics of Phosphorescence and High‐Temperature Glow Peak in CaF2:Pr Single Crystals
Authors: Sinha R. K. , Mukherjee M. L. 
Published: July 2007

AbstractPhosphorescence decay at room temperature (RT) and thermoluminescence (TL) are studied in CaF2:Pr single crystals following X‐irradiation at RT. With the increase of the doping concentration the TL increases initially, reaches a maximum, and then decreases slowly as the concentration is further increased. The order of kinetics is estimated for the phosphorescence at RT and the TL peak at 530 K. Corresponding values of trap depth (E) and frequency factor (S) are calculated by various methods. The trap depth for the phosphorescence decay and the TL glow peak is found to be 1.04 and 1.68 eV, respectively. The frequency factors estimated by several methods compare well and the average value of 1014 s−1 tallies with the result reported earlier.
Simple Non‐Local Calculation of Jellium Metal Surface Properties
Authors: Kiejna A. 
Published: July 2007

AbstractThe gradient expansion for the kinetic, exchange, and correlation energy contributions to the surface energy and work function of jellium metals is investigated. For the gradient correction of the exchange‐correlation the coefficient given by Geldart and Rasolt and the first gradient coefficient of Gupta and Singwi are used. The surface energy is determined from the variational principle for the energy, using parametrized trial functions for the electron density. The calculated surface energies are in agreement with some other nonlocal calculations. The work functions are calculated both, from the classical expression of Lang and Kohn and from less density‐profile‐sensitive expression. The calculated values of the work functions are in excellent agreement with the results of Lang and Kohn.
The Application of Kramers‐Kronig Relations to the Analysis of the Resonance Lines of Metallic Samples in ESR Spectroscopy
Authors: Jarosz J. 
Published: July 2007

AbstractThe application of Kramers‐Kronig (K‐K) relations is employed to the analysis of the shape of asymmetrical resonance lines observed for metallic samples, using ESR spectrometers. Intermetallic Gd1−xHoxAl2 compounds with x equal to 0, 0.01, 0.02, 0.03, and 0.04 are investigated, taking advantage of this method. For x equal to 0 and 0.02 samples are investigated, with particle sizes changing from 5 × 10−6 to 2.5 × 10−3 m. Agreement is found between the obtained results and those predicted by Dyson and Bloembergen. Using the pure absorption line separated from the observed resonance line, the g factor and the linewidth DH are calculated. Good agreement is achieved with the g and DH values calculated according to the method described by Peter et al.
Study of Anharmonic Properties of Alkaline Earth Oxides
Authors: Sanyal S. P. , Singh R. K. 
Published: July 2007

AbstractThe third order elastic constants, pressure derivatives of second order elastic constants, Anderson‐Grüneisen parameters, and second Grüneisen constants are calculated for alkaline earth oxides with the help of a new interionic potential. The potential consists of Hafemeister and Zarht (HZ) type short‐range overlap repulsion, effective up to second neighbours, van der Waals (vDW), and three‐body interaction (TBI) effects. The vDWI coefficients are calculated from the Slater‐Kirkwood variational method. The results obtained are in good agreement with experimental data.
Influence of the Interatomic Potential and the Elastic Scattering Cross‐Section Approximation on the Spatial Distribution of Implanted Ions
Authors: Burenkov A. F. , Komarov F. F. , Temkin M. M. 
Published: July 2007

AbstractThe elastic scattering cross‐sections are calculated both in the framework of Lindhard wide‐angle extrapolation method and on the basis of an exact solution of the classical equation of motion of a particle in a central‐force potential. Using a direct method for the numerical solution of integro‐differential equations governing the ion implantation spatial distribution parameters, the projected ranges, projected and lateral stragglings, and skewnesses are calculated in a wide interval of reduced energies. It is shown that for incident energies ε < 0.1 all these parameters are affected by the choice of both the interatomic potential and elastic scattering cross‐section approximation.
Thermoremanent Magnetization in Bi2O3 · Fe2O3 System
Authors: Banerjee B. , Sharma J. , Lahiry S. 
Published: July 2007

AbstractAll samples of Bi2O3 · Fe2O3 or BiFeO3, prepared by different methods, exhibit when recooled from 700 K in presence of a residual magnetic field (≈ 20 Oe) an unusual increase in susceptibility or magnetization near their Néel temperatures (≈ 540 to 600 K), and this behaviour is characterized as thermoremanent magnetization (TRM). Salient characteristics of TRM as documented by Néel are observed. Different possible mechanisms on the origin of TRM in these samples including the formation of fine lamellae of α‐Fe2O3 in Bi2O3 · Fe2O3 are discussed.
Lattice Dynamics of KCN and NaCN in the Anti‐Ferroelectric Phase
Authors: Anderson A. , Gash P. , Lüty F. 
Published: July 2007

AbstractA simple force constant model is described which allows the zone‐center normal mode frequencies of potassium cyanide and sodium cyanide in their ordered anti‐ferroelectric phase to be calculated. The degree of translational—librational coupling is deduced from the eigenvectors, and relative Raman and infrared intensities are estimated. Results are compared with available experimental data, and good agreement is obtained for KCN. The simple model is, however, unable to fully explain the observed Raman intensity distribution in NaCN, and possible additional contributing mechanisms are briefly discussed.
Cooperative Jahn‐Teller Effect and Spin—Orbit Coupling In d‐Systems
Authors: Mironov V. S. , Ionova G. V. , Lubimov V. S. , Groznov I. N. , Ionov S. P. 
Published: July 2007

AbstractThe mutual influence of the Jahn‐Teller effect and spin—orbit coupling on the ground state of octahedral d‐complexes is studied. Jahn‐Teller ordering is found in island systems with KOsF6‐type structure.
Thermodynamic and Transport Properties of Crystals in Anharmonic Approximation
Authors: Malinowska‐Adamska C. 
Published: July 2007

AbstractThe thermodynamic and transport properties of the three‐dimensional body‐centred cubic lattice are investigated on the basis of the dynamical theory of anharmonic crystals. It is shown that the anharmonic effects of lattice vibrations are not negligible in calculations concerning the high‐temperature region. A comparison with experimental data is given for potassium theoretically described by various potential functions.
Van der Waals Theory of the Phase Transition in Quasi‐Two‐Dimensional Electron Gas in Magnetic Semiconductors
Authors: Baru V. G. , Grekov E. V. 
Published: July 2007

AbstractA “liquid—gas” phase transition is investigated in a quasi‐two‐dimensional (quasi‐2D) electron gas in magnetic semiconductors. The quasi‐2D gas is produced by an external electric field in a metal—insulator—semiconductor system. The transition is due to s—f exchange interaction, which gives rise to a strong electron—electron attraction and, under certain conditions, makes the electron gas compression at the surface energetically favorable. The quantitative consideration is based on the analysis of the free energy functional obtained in the effective field approximation. Van der Waals isotherms and the phase diagram of the transition are plotted. The dimensions of electron liquid drops occuring for a given number of quasi‐2D electrons are estimated. Experiments for the detection of the phase transition are suggested.
Thermoluminescence of Heavy Metal Ion Doped Cesium Halides X‐Irradiated at Low Temperature
Authors: Chowdari B. V. R. , Selvasekarapandian S. 
Published: July 2007

AbstractTL studies of CsBr, CsBr:Ag+, CsBr:Cu+, CsCl:Ag+, and CsCl:Cu+ crystals X‐irradiated at liquid nitrogen temperature are made. Both, undoped and impurity‐doped CsBr crystals exhibit two main glow peaks at 116 and 159 K. CsBr:Ag+ crystal exhibits three additional glow peaks (weak) at 133, 176, and 192 K. The main glow peaks in these crystals are attributed to the double migration of thermally activated Vk centers followed by a radiative recombination with trapped electrons. The formation and decay of these centers is supported by optical absorption studies. The formation of Ag0 and Cu0 and the enhancement of Vk centers is also discussed. Similar studies are made on CsCl:Ag+ and CsCl:Cu+ crystals. Two main glow peaks observed at 204 and 246 K in these crystals are attributed to Vk center as in the case of CsBr crystals. The glow peaks are analysed and the TL parameters are evaluated.
Range of Magnetic Interactions in Some Anhydrous Sulphates of the 3d Transition Metals
Authors: Wegener W. , Hautecler S. , Will G. 
Published: July 2007

AbstractSeveral three‐parameter analyses are performed on β‐FeSO4, α‐FeSO4, α‐NiSO4, and α‐MnSOsb4 by selecting the exchange interactions among the set (J1, J2, J3, J4). These compounds disclose different spin configurations. As input data the experimental values for TN,χ(TN) are used and the second moments of the energy distributions of neutrons scattered by polycrystalline samples in their paramagnetic state. It is possible to determine the significant parameters. It is concluded that, in this series of compounds, the interactions extend up to the fourth neighbours, although the relative importance of the various parameters depends strongly on the ordering type.