bluuebunny/crossref_metadata_2025_split huggingface dataset:
On Determination of the Double‐Force Tensor of Point Defects in Cubic Crystals by Diffuse X‐Ray Scattering
Authors: Trinkaus H. 
Published: July 2007

AbstractA systematic method is described for determining the double‐force tensor of point defects in cubic crystals by analysing diffuse X‐ray scattering in the immediate vicinity of Bragg reflections (Huang‐scattering). Around a given reciprocal lattice point there may occur three types of isointensity surfaces depending on the symmetry of the defects: the “double‐drop” type (“lemniscatoidal” with two sheets), the “apple‐shaped” type (“lemniscatoidal” with one sheet) and the “single‐bubble” type (“ellipsoidal”). The double‐force tensor of point defects can be determined uniquely from Huang scattering if the defects are all equal and parallel. If the orientations of the defects are randomly distributed over equivalent directions of the lattice, information obtained from scattering intensity allows several double‐force tensors. In this case even three selected points of the reciprocal lattice are sufficient to present all of the information which Huang scattering can give about the structure of the defects.
Some Comments on Kubo and Obata' Treatment of the Orbital Susceptibility of Electrons in Metals
Authors: Hebborn J. E. , Place C. M. 
Published: July 2007

AbstractThe approximate treatment of the orbital susceptibility of a metal due to Kubo and Obata is discussed in relation to the more complete, but more complicated, calculations of Hebborn and Sondheimer and Hebborn et al. A physical interpretation of Kubo and Obata's result is presented and its connection with the more complete expressions established.
Conduction in Narrow Energy Bands
Authors: Monecke J. 
Published: July 2007

AbstractIt is proved that the conductivity in a s‐type band exhibits free acceleration behaviour even in the case of strong electronic correlations. A possible metal–insulator transition can occur as a jump in the mean effective mass and can be calculated from the knowledge of a one particle Green's function. The plasma waves are identified to be the soft modes driving the metal‐insulator transition.
Neutral Manganese Centers at the Anion Site in NaCl
Authors: Ikeya M. 
Published: July 2007

AbstractOptical and EPR studies are made of atomic manganese centers formed above room temperature in NaCl following previously published work on Mn0‐A, ‐B, and ‐C centers formed below room temperature. Optical absorption spectra corresponding to the EPR spectrum of Mn0‐D and to that of Mn0‐E were found. These bands are located at higher energy than the transition energies of free Mn0 from the ground state 6S to the excited states 6P. The blue shift of the transition energies is explained by the change in the Madelung potentials between the ground and diffuse excited states at the negative ion site assuming that the centers are located at anion sites.
Effect of Pressure on the Resistivity of AgAu Alloys
Authors: Edwards L. R. 
Published: July 2007

AbstractThe effect of pressure on the resistivity of Ag1−cAuc solid solutions has been measured up to 4 kbar in the temperature range 4 to 273 °K. Solid and fluid helium were used as the pressure transmitting media. The pressure derivatives of the total resistivity, ϱ−1 dϱ/dP, for the alloys in the concentration range c = 0.1 to 0.9 were observed to be negative and to increase in magnitude with increasing temperature. It is shown that the magnitude and sign of ϱ−1 dϱ/dP is primarily determined by the pressure derivative of the residual resistivity. The volume derivative of the residual resistivity, d In ϱ0/d ln V, was found to be positive and concentration dependent. It is suggested that the influence of the filled d‐bands on the scattering potential is responsible for the behavior of d ln ϱ0/d ln V.
On the Energy of the Hexagonal Frank Loop in Face Centred Cubic Metals
Authors: Gaboriaud R. J. , Grilhé J. 
Published: July 2007

AbstractThe energy of the hexagonal Frank loop is calculated taking into account the dissociation of the partial Frank dislocation surrounding the defect. This energy is compared to those obtained for such classical defects as circular or triangular Frank loops and a tetrahedron of stacking fault. The discussion is made in terms of stacking fault energy, shear modulus, and critical number of precipitated vacancies per defect.
Effect of an Electric Field on the F‐Band in Cesium Bromide
Authors: Grassano U. M. , Margaritondo G. 
Published: July 2007

AbstractThe unrelaxed excited states of the F‐centre in CsBr have been studied by measuring the changes in the F‐band caused by an external ac electric field. The following energy distances from the ground state 1S(Γ1) have been evaluated: (1.911 ± 0.005) eV and (1.945 ± ± 0.005) eV, respectively for the two 2P(Γ8) levels splitted by non‐cubic lattice vibrations; (1.992±0.005) eV for the 2P½(Γ6) level and (2.01 ±0.01) eV for the 2S(Γ1) level. A small substructure of the F‐band, probably due to the cubic lattice vibrations, has also been revealed.
Frequency‐Dependent Relaxation Time in Electron–Impurity Systems
Authors: Šimánek E. , Smith J. Scott 
Published: July 2007

AbstractA general expression for the frequency‐dependent conductivity of an electron‐impurity system is derived by the method of generalized Langevin equation. The conductivity has the form of the classical Drude formula with complex frequency‐dependent relaxation time derived from the correlation function of the random force. The correlation function of the total force is calculated in the Born approximation. The asymptotic long time behavior of this function indicates that its time integral has a plateau for times larger than the duration of a collision. This result and the absence of the exponential decay enables to define an approximate relaxation time from the total force correlation function calculated in the Born approximation.
Ordinary Magnetoresistance of Heavily Doped Semiconductors at Low Temperatures in a Weak Magnetic Field
Authors: van Cong H. , Mesnard G. 
Published: July 2007

AbstractThe ordinary longitudinal and transverse magnetoresistance of electrons at low temperatures in a weak magnetic field is calculated from a simplified model of heavily doped semiconductors. The treatment which is based on the Green's function methods using Feynman‐path integral formulation, is applied to disordered systems and developed already in five previous papers. Two important cases are discussed within the present model. In the first one, an ordinary n‐type semiconductor is considered, assuming that the carrier concentration is equal to the donor concentration; in the second case, the carrier concentration rises as the third root of the total concentration of impurities.
Inelastic Scattering of Neutrons in Crystals Containing Linear Defects
Authors: Ivanov M. A. , Fishman A. Ya. 
Published: July 2007

AbstractAn investigation is made of the cross section of inelastic neutron scattering in crystals, containing a system of parallel linear defects. The model of the crystal with simple cubic la ttice and equal central and noncentral force constants for interactions only between the ne arest neighbours is used. The linear defects in the crystal are described by a change in the force constants for both the interactions between themselves and between the defect an d host atoms. It is shown that the cross section of the coherent scattering has a maxim um in the spectral distribution at the frequencies of the localized vibrations and of the volume vibrations renormalized by the scattering on the defects. For the cross section of t he incoherent scattering peculiarities appear typical for one‐dimensional crystal lattices.
On the Lattice and Dislocation Mechanism of Colloid Formation in Alkali Halide Crystals
Authors: Tsal N. A. , Didyk R. I. 
Published: July 2007

AbstractA thorough investigation of F → X conversion in NaCl crystals heat‐treated at different temperatures as well as the results of the high‐temperature X‐irradiation made it possible to conclude that there exist two types of X‐centres which differ in the formation sites. X‐centres localized in the crystal lattice (XL‐centres) are responsible for the absorption band with the peak position at 620 nm, while X‐centres responsible for the 550 nm band are localized along dislocation lines (XD‐centres).
Electron States in Crystals with “nipi‐Superstructure”
Authors: Döhler G. H. 
Published: July 2007

AbstractA semiconductor with a zigzag‐shaped superstructure potential, caused by the introduction of narrow n‐and p‐doped layers into an intrinsic crystal (“nipi‐crystal”), is considered. For high amplitude and long period of this potential the low lying conduction‐ and the upper valence‐subband states are concentrated around the n‐and p‐layers, respectively. The subbands, as obtained for an idealised mode, neglecting fluctuations of the superstructure potential, are extremely narrow with respect to the direction perpendicular to the layers. Approximative calculations show, that the discrete subband structure should be clearly distinct also if electron‐impurity and electron‐phonon interaction is taken into account. The density of states in crystals with “nipi‐superstructure” is completely different from that in the corresoponding n‐ and p‐doped normal crystals. A non‐equilibrium situation can be quasi‐stable due to the low electron‐hole recombination probality.
Comparison of Cyclotron Resonance Width and Collision Frequency when the Scattering Force is of Short Range
Authors: Raju C. S. , Ching‐Lung Ko M. Wu, , Fujita S. 
Published: July 2007

AbstractThe cyclotron resonance width Γ and the collision frequency ωf owe their existence to the same origin: the electronic transition among energy levels caused by the interaction between electrons and scatterers. By starting with the current correlation formulas and using the connected diagram expansion, both Γ and ωf can be calculated from one and the same collision operator in the case of an electron‐impurity system. By assuming a weak Gaussian potential of a short range, it is explicitly shown that a) Γ is of the same order of magnitude as hωf and b) except in the 'extreme quantum limit' ħω0 ≫ kBT, Γ is a fraction of ħωf and levels off to about 1/4 ħωf.
On Spin‐Lattice Interactions in the Heisenberg Ferromagnet
Authors: Gluck P. , Wohlman‐entin O. 
Published: July 2007

AbstractThe properties of the compressible Heisenberg model are discussed. The spin‐phonon interactions are taken into account by an expansion of the exchange coupling in powers of the atomic displacements. The coupled system of spins and phonons is treated by a series of unitary and Bogolyubov transformations. Expressions are derived for the lowering of the magnetic critical temperature due to first and second derivatives of the exchange integral and for the phonon spectrum as renormalized by the magnetic coupling. The change in the excitation spectrum of the spins at high temperatures induced by the presence of phonons is also found by using Callen's decoupling for the spin propagator in the random phase approximations. Where appropriate, the results are in qualitative agreement with previous work and experiment.
Thermodynamics of Ferroelectric Solid Solutions (I)
Authors: Yurkevich V. E. , Rolov B. N. 
Published: July 2007

AbstractA generalized Ginzburg‐Devonshire thermodynamic theory is considered in the case of ferroelectric solid solutions in which the dependence of the corresponding thermodynamic potential on the impurity concentration is used. The analytical expressions of a number of physical characteristics are obtained as a function of impurity concentration: the phase transition temperature, the polarization, the dielectric constant, and the heat capacity. The effect of an external electric field on the behaviour of different physical characteristics near the phase transition of the second order is considered as well.
Transport Properties of a Polar Semiconductor in a Quantizing Magnetic Field
Authors: Magnusson B. 
Published: July 2007

AbstractMomentum distribution functions for electrons are calculated for a polar semiconductor with parallel applied electric and magnetic fields. The derivative of the distribution function has singularities at certain electron energies due to the singularity in the density of states at zero energy. The interaction between the levels leads in some cases to a double hump in the distribution function.
Evidence of Phonon Drag in the Electrical Resistivity of Silver
Authors: Kos J. F. 
Published: July 2007

AbstractThe temperature dependence of the electrical resistivity of four samples of pure silver was measured between 1.4 and 4.2 °K. The variation of resistance could not be satisfactorily represented by the Bloch T5 law. The resistances of the three purest samples were best described by an equation R = A T3 + B T5. According to calculations by Dworin a T3 term may be attributed to the effects of phonon drag. On the other hand the resistivity of the fourth samples which contained 3 ppm of magnetic impurities (about ten times that of the other samples) behaved differently, indicating the influence of Kondo scattering.
The Semiempirical LCAO‐MO Treatment of [NiF6]4− Cluster
Authors: Málek J. , Polák K. 
Published: July 2007

AbstractA parameter‐free SCCC‐MO calculation including interatomic effects was performed for the ground and the first excited state of [NiF6]4− cluster of crystalline KNiF3. The influence of alternative choices of metal basis functions and particular models of population analysis on the values of crystal field parameter 10 Dq, spin‐orbit coupling constant λcrys, and covalency parameter ϵ was investigated. In contrast to the Wolfsberg‐Helmholz model the above parameters depend significantly on the choice of metal basis functions while the effective charges in the system are nearly the same for a chosen type of population analysis. Based on the performed calculations it is stated that the present method is more efficient than previous semiempirical procedures.
Wall Displacement and Bulging in Magnetization Mechanisms of the Hysteresis Loop
Authors: Globus A. , Guyot M. 
Published: July 2007

AbstractMagnetization mechanisms related to wall displacement and wall bulging are analyzed using a model previously proposed. In the case of the hysteresis loop, where both these combined mechanisms act, it is shown that the coercive force, the remanence and the shape of the loop, can be determined from the values of the internal field and the grain size. This analysis is experimentally confirmed by the fact that the loops corresponding to several YIG samples can be reduced to a single one. In addition, it is shown that, contrary to a general belief, the coercive force is practically independent of the porosity of the samples.
F‐Centres of Two Types in BaFCl Crystals
Authors: Nicklaus E. , Fischer F. 
Published: July 2007

AbstractF‐centres in X‐irradiated and additively coloured tetragonal BaFCl single crystals have been studied. An F‐centre at a fluorine site absorbs light polarized parallel to the crystallographic c‐axis in a band at 438 nm and light polarized perpendicular to c in a band at 550 nm. A chlorine F‐centre has a band at 532 nm (E ‖ c) and a double band at 440 nm (E ‖ c). This dichroism arises from the tetragonal surroundings of the F‐centres. The splitting of the double bands is probably due to a dynamic Jahn‐Teller effect. In an X‐irradiated crystal there is a partial transformation of fluorine into chlorine F‐centres. In additively coloured BaFCl predominantly fluorine type F‐centres are formed above 300 °C in thermal equilibrium.
Dependence of Silver Halide Energy Bands on Lattice Constant and Halogen
Authors: Fowler W. B. 
Published: July 2007

AbstractThe mixed basis method has been used to compute the energies of selected electronic states of AgF, AgCl, and AgBr at their normal lattice constants, and in addition AgCl at lattice constants appropriate to AgF and AgBr. From these a fairly clear physical picture emerges regarding chemical shifts, hybridization effects, Madelung shifts, and other effects which determine the locations of various states. Results for AgCl and AgBr at their normal lattice constants compare favorably with earlier calculations and with earlier experiments. More recent optical experiments on these solids by Carrera and Brown appear to be in accord with some of these results. The absorption data of Marchetti and Bottger on AgF are discussed, and it is suggested that the low‐energy peak which is observed arises from a direct forbidden excition at T. Band gap deformation Potentials for AgCl are obtained which are in qualitative agreement with results deduced from stress experiments by Aust and by Brothers and Lynch. Finally, the temperature dependent photoemission reported by Bauer and Spicer in AgCl is discussed with respect to the dependence of various energies on lattice constant.
The Ferromagnetic After‐Effect at 55 K in Electron‐Irradiated Nickel
Authors: Schaefer H. E. , Lampert G. 
Published: July 2007

AbstractThe ferromagnetic after‐effect (MAE) was measured on high‐purity nickel samples (resistivity ratio RRT/R4K > 2000) that had been irradiated with electrons (2.5 MeV) at 27 K with different doses and subjected to several annealing treatments. It was possible to separate the MAE from annealing effects taking place simultaneously. Taking into consideration annealing measurements of the MAE amplitude and the electrical resistivity published elsewhere, it is concluded that the 55 K‐MAE and the corresponding recovery stages ID, IE have to be attributed to the free diffusion of crowdions.
Dislocation and Disclination Contents of Line Defects
Authors: Dundurs J. 
Published: July 2007

AbstractThe dislocation and disclination contents are defined as integrals of the discontinuities in displacement and rotation taken along the line defect. These quantities allow one to uniquely decompose a discrete line defect into a dislocation and a disclination. Moreover, the results for the discrete line defects suggest a new definition of dislocation density.
The Temperature Dependence of the Absorption Edge in Some Amorphous Semiconductors
Authors: Connell N. 
Published: July 2007

AbstractThe implicit and explicit contributions to the temperature dependence of the absorption edge in some amorphous forms of Si, Ge, GaP, and GaAs are reported. The results are used to test a model in which the valence (conduction) band states in amorphous material are a superposition of crystalline valence (conduction) band states of about the same energy. In the case of the III–V compounds, it is concluded that such a model may be invalid owing to the probable existence of “wrong” bonds.
Influence of Neutron Irradiation at Low Temperature on Internal Friction and Bulk Modulus of Silver
Authors: Chountas K. , Dönitz W. , Papathanassopoulos K. , Vogl G. 
Published: July 2007

AbstractThe internal friction and the bulk modulus of silver were studied after irradiation at 25 K with fast neutrons. The Frenkel defects produced by irradiation cause dislocation pinning and a consequent decrease in the Bordoni internal friction peak. With increasing irradiation dose the bulk modulus first increases, reaches a maximum and then decreases below its original value. The behaviour of the modulus with annealing up to room temperature essentially corresponds to that of the residual electrical resistivity after low‐temperature neutron irradiation. A Frenkel defect concentration cFD gives rise to a relative dielastic modulus decrease ΔG/G which was determined to be ΔG/(GcFD) = −33 ± 9.
Electron Mobility in Ge, Si, and GaP
Authors: Rode D. L. 
Published: July 2007

AbstractTheoretical calculations of electron mobility in the indirect crystals Ge, Si, and GaP are presented. The model assumes parabolic and spherical conduction band minima and includes piezoelectric, acoustic, polar, Coulomb, and intervalley scattering with appropriate electron‐phonon selection rules in all cases. Fermi statistics are accounted for and no further approximations (e.g. relaxation, trial function) are made, since drift mobility is calculated from an exact iterated solution. Recent selection rules for Si and GaP lead to agreement with experiment and suggest that low‐energy LA phonons are unimportant for intervalley scattering.
Exchange Interactions and Local Field Effects in Exciton Theory
Authors: Stolz H. , Zimmermann R. 
Published: July 2007

AbstractThe role of local field corrections in the linear response of the crystal electron system is investigated using Green's function technique. The macroscopic conductivity can be calculated directly from the solution of a Bethe‐Salpeter equation containing in addition to the screened direct an unscreened exchange interaction, the latter being of pure local field type. The formalism is applied to the Frenkel exciton theory.
Functional Integral Approach for an Extended Hubbard Model: Two‐Centre Coupling
Authors: Albani B. , Goedsche F. , Heber G. , Röpke G. 
Published: July 2007

AbstractThe behaviour of two neighbouring magnetic centres imbedded in an effective energy band is studied with the aid of the functional integral formalism. The model includes the parts of intra‐atomic and inter‐atomic Coulomb interaction which can be written in terms of occupation number operators. Orbital degeneration is not considered. The magnetic susceptibility calculated within the static approximation gives a continuous interpolation between the Pauli‐band susceptibility and the case of two ferromagnetically or antiferromagnetically coupled Ising spins in the atomic limit.
Formation d'images électroniques de monocristaux d'or à basse température
Authors: Renard D. 
Published: July 2007

AbstractNous étudions par microscopie électronique (électrons de 100 kV) des monocristaux d'or courbes dont l'épaisseur est uniforme et bien connue. Des mesures directes d'intensité transmise dans l'image en fond clair sont effectuées suivant plusieurs orientations et pour plusieurs épaisseurs. Associées à un calcul de théorie dynamique à n ondes et à un calcul de perturbation, elles permettent de déterminer certaines composantes V'(g) de la partie imaginaire du potentiel cristallin. De ces valeurs à basse température, on peut dissocier la partie due aux phonons de la partie due aux excitations d'électrons individuels. On compare l'effet du processus dǔ aux phonons, à température ambiante et à basse température. Les micrographies et les mesures d'intensité à basse température donnent également des informations sur les potentiels réels et sur l'orientation des monocristaux.
Anisotropic Magnetization and Magnetic Anisotropy Energy of Co—Fe (8 at%Fe)
Authors: Nowicki L. , Aubert G. , Frazao L. 
Published: July 2007

AbstractMagnetic anisotropy energy and anisotropic magnetization of the non‐magnetostrictive Co—Fe alloy have been investigated between —60 and +40 °C. The anisotropic magnetization exhibits a broad maximum near —30 °C. The influence of surface effects is discussed. A good agreement between the results and literature data concerning magnetic anisotropy energy has been found.
Ligand Hyperfine Interaction of Ti2+ in CdS and CdSe on Sites with Trigonal Symmetry C3v
Authors: Böttcher R. , Dziesiaty J. 
Published: July 2007

AbstractAn EPR investigation is made of the hyperfine interactions with ligand nuclei (SHFS) of the Ti2+ centre in single crystals of hexagonal CdS and CdSe on sites with trigonal point symmetry C3v. From the spectra experimental evidence is given for the magnetic nonequivalence of the twelve next‐nearest ligands (cadmium) in wurtzite‐type crystals. The SHFS‐constants for the first three cadmium lattice shells for wurtzite are calculated using MO‐theory. From the SHFS‐constants the probability is estimated of finding the delocalized 3d‐electrons of the Ti2+ ion in the 5s‐orbitals of the cadmium ligands.