bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Fine Structure of Weak Kinematical Diffraction Beams. Observations on Coherent Domain Boundaries
Authors: de Ridder R. , van Landuyt J. , Gevers R. , Amelinckx S. 
Published: July 2007

AbstractThe fine structure of a weak kinematical diffraction beam, arising from the presence of a coherent domain boundary in the selected area for transmission electron diffraction, is analysed by comparing the positions and intensities of the observed satellites with the theoretical predictions deduced in a previous paper. Because of the large variations in relative intensity only a limited number of the seven predicted satellites could be revealed. In order to observe and identify a larger number of satellites, diffraction patterns are made of an area containing a number of parallel boundaries. The observed satellite configuration is analysed in detail; the positions and intensities are in good agreement with the theoretical predictions.
Localized and Self‐Trapped Excitons in CsI
Authors: Lamatsch H. , Bossel J. , Saurer E. 
Published: July 2007

AbstractAdditionally to the well‐known 3380 Å band in the excitonic transitions of CsI at LHeT a new emission band at 2900 Å is reported and its behaviour is studied as a function of temperature. Experimental evidence is given which establishes the connection of the 2275 Å absorption band with localized exciton transitions. Measurements using ionizing β‐irradiation especially the temperature dependence of the β‐excited emission give further support to this model.
A Formal Theory of Electron Diffraction by a Crystal Slab
Authors: Kerre E. , Phariseau P. 
Published: July 2007

AbstractA formal theory of electron diffraction by a crystal slab is developed using a Green's function formalism. The inner potential due to the occurrence of potential barriers at the crystal surfaces is also taken into account. Explicit expressions for the reflection and transmission amplitudes are obtained and a detailed comparison with Kambe's treatment of the problem is given.
Total Coherent Cross Sections for the Scattering of Neutrons from Crystals
Authors: Binder K. 
Published: July 2007

AbstractA calculation of the cross sections for polycristalline bismuth and aluminium is presented. Various methods are applied to calculate the incoherent part and the interference part of the cross section. A description of the scattering is obtained which is valid for the whole range of neutron energies. Previous treatments are critically discussed.
On the Dynamical Theory of X‐Ray Images of Real Crystals
Authors: Chukhovskii F. N. , Shtolberg A. A. 
Published: July 2007

AbstractA dynamical theory of the X‐ray image of a crystal with a given distortion field is developed. A method for constructing the asymptotic solution of the wave field equations in the crystal is proposed. As an example of applying an analytic expression is obtained for both the transmitted and Bragg reflected waves in a slightly distorted crystal with a characteristic length of the deformation field change of the order of the crystal thickness. The numerical calculation of the X‐ray contrast of the edge dislocation normal to the sample surface has been carried out, taking into account the radiation absorption in the crystal. It is shown that in this case the analytic and numerical results for the X‐ray image problem solution are in accordance with the experimentally observed intensity distribution of the diffracted wave. The possibility of determining the sign of the Burgers vector of an edge dislocation normal to the sample surface from the X‐ray dynamical scattering data is discussed.
On the Influence of Relativistic Contributions to Spin‐Wave Spectrum on the Thermodynamics of Ferromagnets
Authors: Mitsek A. I. , Noskov A. S. , Kolmakova N. P. 
Published: July 2007

AbstractThe influence of magnetostatic contribution and magnetic anisotropy on the thermodynamics of ferromagnets at low T is discussed. Two example are considered: Eu3O4 — a one‐dimensional ferromagnet with large anisotropy constant K1, and EuO with a large spontaneous magnetization. It is shown that these relativistic contributions to spin‐wave spectrum are essential in the range T < TA(TM), where TA(TM) is proportional to K1(2 π M). The question of applicability of restricted statistics to spin waves with an arbitrary k is discussed on the basis of the symmetry of wave functions of the spin‐wave states.
The influence of correlations on the energy of defect crystals
Authors: Siems R. 
Published: July 2007

AbstractIn a crystal containing a distribution of point defects the locations of the defects are correlated. A simple and important correlation is one which prevents two defects from occupying the same position. Such correlations influence the average interaction energy of one defect with all others. The respective contributions to the energy are calculated for isotropic and cubic materials, and the results are applied to the problem of ferroelasticity.
Excitonic effect in the piezoreflectance of GaSb
Authors: Camassel J. , Auvergne D. , Mathieu H. , Pistoulet B. 
Published: July 2007

AbstractIn the case of gap modulated semiconductor, a theoretical treatment is given for the differential reflection coefficient relative to transitions with an excitonic character. The influence of the various parameters is shown by means of a serie of calculated theoretical curves. Satisfactory agreement between theory and experiment is obtained with samples of undoped p‐type GaSb and degenerate n‐type GaSb. In the first case a pronounced excitonic effect is observed and the excitonic relaxation time is determined for temperatures between 300 and 80 ° K. In the second case, the high density of free carriers screens the interaction potential between electrons and holes and piezoreflectance curves without excitons are obtained.
Neutron measurements on the hydrogen bond potential in paraelectric KDP
Authors: Grimm H. , Stiller H. , Plesser Th. 
Published: July 2007

AbstractDiffraction effects observed in elastic incoherent scattering of thermal neutrons from a single crystal of KDP are compared to two models for the proton ground states in the paraelectric phase. The comparison, taken together with the results of recent infrared absorption measurements, indicates that the protons fluctuate between two equilibrium sites at the hydrogen bonds. The distance of these two sites, the mean square proton amplitude, the overlap integral, and an approximate value for the energy difference of the symmetric and the antimetric ground states are determined.
Crystal structure and magnetic properties of cerium‐iron compounds
Authors: Buschow K. H. J. , van Wieringen J. S. 
Published: July 2007

AbstractThe crystal structure, the magnetic properties, and the phase relations of cerium‐iron compounds have been investigated. A phase diagram is presented. Lattice constants are given for CeFe2, α‐Ce2Fe17, and β‐Ce2Fe17. The compound CeFe2 is ferromagnetic with Tc = 230° K. Investigations by means of the Mössbauer effect and bulk magnetization indicate an antiferromagnetic–ferromagnetic transition near 70° K and an antiferromagnetic‐paramagnetic transition close to 270° K for the compound β‐Ce2Fe17. The ordering temperatures and saturation moments for the CeFe compounds are compared with magnetic data presented for the isostructural YFe compounds.
Déformation plastique du tellure monocristallin. I. Faits expérimentaux
Authors: di Persio J. , Doukhan J. C. , Saada G. 
Published: July 2007

AbstractNous avons fait une étude expérimentale systématique de la déformation de monocristaux de tellure entre 78 et 293° K. Nous indiquons comment surmonter les problèmes expérimentaux (taille, polissage, orientation des échantillons, obtention de lames minces pour l'observation en microscopie électronique) et nous montrons que: 1. Le tellure obéit à la loi de Schmid et Boas et possède quatre systèmes de glissement indépendants. 2. Sa limite élastique varie très rapidement avec la température et de manière différente selon les systèmes de glissement utilisés. 3. Ce fait est en accord avec la propriété qu'ont les dislocations de s'aligner parallèlement à l'axe c.
La réflectivité du chrome antiferromagnétique
Authors: Caillé A. , Wallace P. R. 
Published: July 2007

AbstractLes deux minima locaux de la courbe de réflectivité du chrome dans sa phase antiferromagnétique apparaissent à cause: 1. d'une diminution du coefficient de réflectivité, dans le domaine de fréquence oú on a une contribution importante à la conductivité provenant des électrons et trous liés; 2. d'un changement de signe de la partie réelle de la constante diélectrique du systéme provenant de l'action conjuguée des porteurs libres et des paires électron–trou.
Excitonic thermoreflectance of CdS
Authors: Iliev M. , Assenov I. 
Published: July 2007

AbstractThermoreflectance spectra of high‐resistive CdS single crystals were measured in the region 108 to 320° K. The main features of the spectra can be explained on the basis of simple models derived from existing theories. The genesis of the spectra shows that the excitonic transitions determine the thermoreflectance structure even at room temperature.
Isotope effects in defect‐induced infrared absorption
Authors: Benedek Giorgio 
Published: July 2007

AbstractAn investigation is made of the splitting of the defect‐induced infrared absorption peaks produced by the isotope mixture of defect ions (defect isotope effect) or nearest‐neighbour ions (nn isotope effect). The defect isotope effects in the systems KI:Cl−, KI:Br−, KBr:Li+, and KCl:Li+ are calculated within the harmonic approximation by means of a defect model in which the elastic relaxation is taken into account. Concerning the nn isotope effect, the F‐centre is found to be a suitable system for the detection of relatively large nn isotope effects.
The diffusion coefficients of hydrogen and deuterium in vanadium, niobium, and tantalum by gorsky‐effect measurements
Authors: Schaumann G. , Völki J. , Alefeld G. 
Published: July 2007

AbstractGorsky‐effect measurements on vanadium‐, niobium‐, and tantalum‐samples loaded with different concentrations (0.2 to 4.3 at%) of hydrogen or deuterium are reported. From the relaxation strength the trace of the dipole‐moment tensor of hydrogen and deuterium was determined and found to be consistent with the lattice parameter changes. From the relaxation time of the Gorsky effect the diffusion coefficients of hydrogen and deuterium in vanadium, niobium, and tantalum were determined in the temperature range from 600 to about 270° K (in the case of hydrogen in niobium down to 120° K). The diffusion coefficients are very large and show only a weak exponential temperature dependence, which moreover decreases for hydrogen in niobium below 300° K. In contrast to classical rate theory the activation energies are isotope dependent whereas the pre‐exponential factors are isotope independent within the experimental errors.
Untersuchung der Kreuzrelaxation von Cr3+‐Ionen in Al2O3
Authors: Cremer R. 
Published: July 2007

AbstractDie Kreuzrelaxationen von Cr3+‐Ionen in Al2O3 wurde mit der Dispersions–Absorptionsmethode in Magnetfeldern bis zu H = 3 kOe untersucht. Die Messungen erfolgten im Frequenzbereich zwischen 10 Hz und 5 kHz bei einer Temperatur von 1,24 °K, bei der in diesem Frequenzbereich keine Spin‐Gitter‐Relaxationsprozesse mehr beobachtet werden. Für Konzentrationen zwischen 0,025 und 0,2% Cr3+ in Al2O3 wurden die Relaxationsraten einer Reihe von Kreuzrelaxationsprozessen als Funktion des Magnetfeldes und des Winkels zwischen Magnetfeld und Kristallachse bestimmt. Die Ergebnisse werden anhand einer von Sauermann und Schwegler entwickelten Theorie diskutiert.
ESR study of covalent bonds in some copper (II) complexes
Authors: Buluggiu E. , Dascola G. , Giori D. C. , Varacca V. , Vera A. 
Published: July 2007

AbstractBy means of ESR and spectrophotometric measurements the bond parameters of the magnetic orbitals in the copper (II) compounds:magnified image are evaluated. The covalency character of the copper–ligand bonds results remarkable and almost the same in all the compounds examined. This confirms the poor influence of the out‐of‐plane ligands on the magnetic parameters of the complex ion.
The separation of coherent and incoherent cross‐sections in inelastic neutron scattering using polarized nuclear targets
Authors: Jauho P. , Pirilä P. 
Published: July 2007

AbstractThe coherent and incoherent neutron scattering cross‐sections have different dependences on the polarization of neutrons and target. This fact can be used to separate the coherent and incoherent part of the inelastic cross‐section and to enhance the otherwise very weak coherent scattering in the cases of H1 and V51. Some details of this method are studied and the results are applied to the case of ZrH2. It seems evident that the dispersion curves of phonons in ZrH2 can be measured by this method.
Binding energy and related properties of silicon
Authors: Weaire D. 
Published: July 2007

AbstractPseudopotential theory has in the past been applied with considerable success to the calculation of the binding energy and related properties such as equilibrium atomic volume for non‐transition metals, particularly Na, Mg, Al. Its application to Si is considered here. Results for the f.c.c. structure, as well as the observed semiconducting phase with diamond structure and the metallic (white Sn) phase found under pressure, are presented and discussed. In the case of the semiconducting phase, the theory must be modified to include “covalent” contributions to the binding energy, and this is done in a crude way using Van Vechten's result for the total energy of occupied states in the isotropic semiconductor (“Penn”) model.
Hyperfine interaction of F‐centres in alkali‐halide crystals
Authors: Wood R. F. 
Published: July 2007

AbstractThe Fermi contact term of the hyperfine interaction is calculated for the first eight shells of ions surrounding the F‐centre in KCl. The smooth part of the F‐centre wave function is taken from earlier work of Wood and Öpik and contains a g‐like component which, though small, appears to be necessary for understanding the details of the interaction. A symmetrical orthogonalization procedure is used to construct orthogonal “core” orbitals from free‐ion Hartree‐Fock functions. The importance of this step is demonstrated. The overall agreement with the experimental results is good, and therefore it is concluded that these results can be explained by detailed calculations with appropriate vacancy‐centred wave functions.
N14 nuclear quadrupole resonance in ferroelectric NaNO2
Authors: Kadaba P. K. , O'Reilly D. E. , Blinc R. 
Published: July 2007

AbstractThe N14 NQR frequency and linewidth have been measured in ferroelectric NaNO2 as a function of temperature. It is shown that the results can be explained by an order‐disorder model where the NO2 ions are flipping between two equilibrium sites.
Transport Phenomena in Nonparabolic Semiconductors at High Electric Fields
Authors: Dubey P. K. , Chakravarti A. K. 
Published: July 2007

AbstractGalvano‐ and thermo‐magnetic transport coefficients have been calculated for an n‐type nondegenerate sample of indium antimonide at high electric fields at temperatures 300 °K and above. The isotropic and anisotropic parts of the distribution function have been obtained from the Boltzmann transport equation in a relaxation time model, using the appropriate high‐field collision term for a nondegenerate sample given by Matz [1]. Electron scattering by polar optical phonons and ionized impurities have been chosen as the responsible mechanisms for the energy and momentum losses. The nonparabolicity of the conduction band has been accounted for by Kane's model. It is seen from a numerical evaluation of the results that the electrical conductivity exhibits a typical behaviour of reversal with the magnetic field below 300 °K and above fields ≈ 200 V/cm. The results have been compared with earlier theoretical and available experimental results at 77 °K, and important features of the comparison have been discussed in the last section.
On the Theory of Photoconductivity and Photoelectromagnetic Effect at High Concentrations of Non‐Equilibrium Charge Carriers
Authors: Aronov D. A. , Zaitova V. , Kotov E. P. 
Published: July 2007

AbstractIn this paper, the theory of photoconductivity (PC) and photoelectromagnetic (PEM) effect is developed for arbitrary injection levels taking into account the trapping of non‐equilibrium carriers. On the basis of the calculations performed, the conclusion is drawn that it is possible to determine the lifetimes and capture cross‐sections of electrons and holes as well as the concentration of traps from measurements of PC and PEM effects at low and high illumination levels.
Iron Whiskers under the Effect of Time‐Dependent Fields
Authors: Trueba A. 
Published: July 2007

AbstractMagnetization reversal has been studied in iron whiskers under the influence of time‐dependent magnetic fields. Switching sometimes occurs by propagation of a single Bloch wall. If the applied field is H = λ t, where λ, is a constant, it is possible to investigate various magnetic magnitudes as a function of λ. If λ < 1011 A m−1 s−1, and because of the low value of the wall mass, the results are very simple and all the magnetic magnitudes are strongly dependent on λ. Specifically, the switching time is ts = Kp λ−1/2, where Kp is a constant which depends upon the viscous damping parameter, whisker's size, and other magnitudes; the coercive “dynamic” field is given by Hc = Hp + (Kp/), λ1/2, where Hp is the propagation field. These relations have been tested on several {100} oriented whiskers and values of Kp have been computed by measuring Hc and ts vs. λ. The results are consistent for λ < 107 A m−1 s−1 and agree very well with theory. It is possible to deduce the wall mobility (C) from Kp taking into account that K = 2 l/C (l is the length of the whisker). All this enables us to understand the deformations of hysteresis loops when the frequency or other parameters of the applied field are changed.
EPR Investigation of the Internal Electric Field in Copper‐Doped Rochelle Salt
Authors: Völkel G. , Windsch W. 
Published: July 2007

AbstractThe EPR spectra of copper doped ferroelectric Rochelle salt and their change due to the ferroelectric polarization are studied. The spectra are described by a model using ligand field theory. The influence of the ferroelectric polarization on the EPR spectra can be explained by the formalism of the linear electric field effect. The measured g‐factor shifts at a polarization P = ±9 × 10−8 C cm−2 give a tilting of the copper complex around the y‐ and z‐complex axes by λ = ± 0.15° and ψ = ±0.23° respectively. One can conclude that the local electric field acting on the copper complex results from a superposition of effects of more than one unit cell.
New Temporary Infrared Absorption Bands in the Alkali Halides
Authors: Borms F. , Jacobs G. 
Published: July 2007

AbstractNew temporary infrared absorption bands are observed in several alkali halides. In NaCl a short‐lived centre with a transition at 4 μm is formed by excitation of the electron excess centres at low temperatures. Decay times have been measured simultaneously in the M, F, and 4 μm band. They indicate a bimolecular decay with the same time constant for the three bands. The 4 μm band is attributed to a transition of an electron in a shallow trap. Simultaneous absorption measurements were made in the F, M, and 4 μm band after ruby laser excitation in the F band, and in the F, F', and 4 μm bands after laser excitation in the F' band. From these measurements it was concluded that the shallow trap is the F centre. This implies the existence of a metastable form of the F' centre. A triplet state is postulated. Absorption bands analogous to the 4 μm band in NaCl have been observed in KCl at 6 μm, in NaF at 2.4 μm, in KBr, and KI.
Best Localized Symmetry‐Adapted Wannier Functions of the Diamond Structure
Authors: Teichler H. 
Published: July 2007

AbstractBy application of proper unitary matrices the four Bloch functions of each bandgroup with equal wave vector k are transformed into modified Bloch functions in such a way that the resulting four sets of Wannier functions are adapted to the tetrahedral symmetry of the lattice. The Wannier functions behave like the “equivalent MO's” of the tight‐binding approximation (but with vanishing non‐orthogonality integrals). Furthermore, we give explicitely those phases of the Bloch functions that lead to best localized Wannier functions. Values of energy matrix elements between these functions are determined for Ge and Si.
Electron Spin Polarization due to the s‐d Exchange Interaction
Authors: Kishore R. , Joshi S. K. 
Published: July 2007

AbstractAn expression for the electronic spin polarization p(r) due to s‐d exchange interaction between the conduction electrons and the localized impurity of spin 1/2 in a dilute magnetic alloy is obtained by using the one particle Green function approach. For large distances p(r) is found to exhibit exponentially damped behavior. This feature of p(r) was also predicted earlier by Bose, Tanaka, and Halow by using the method of cluster variation of the co‐operative phenomena.
The Relationship between the Work‐Hardening of B.C.C. and F.C.C. Metals
Authors: Šesták B. , Seeger A. 
Published: July 2007

AbstractThe paper develops and supports in some detail the hypothesis that the well‐known “three‐stages work‐hardening” curve of b.c.c. metals is closely analogous, beyond its inflexion point, to stage‐III work‐hardening of f.c.c. metal single crystals. The basic reason for this correspondence is that in both cases screw dislocations may cross‐slip easily. A qualitative picture for stage‐III hardening in f.c.c. metals and for the work‐hardening of b.c.c. metals based on the internal stresses originating from dislocation sheets parallel to the primary glide plane (or the glide plane of maximum shear stress) is proposed.
Approximate Theoretical Treatment of Weak‐Beam Dislocation Images
Authors: De Ridder R. , Amelinckx S. 
Published: July 2007

AbstractA simple approach is reported allowing to deduce the well‐known approximate criterion which relates the strain field of a dislocation to its image position in a weak beam. The proposed approximations also permit to make predictions about the width of the image peaks and the image contrast. The obtained results are compared with the intensity profiles calculated by performing the kinematical integral. It is shown that the mentioned position criterion, deduced within the one‐beam kinematical theory, can easily be adapted for a more realistic many‐beam theory, e.g. the two‐beam kinematical theory.
Elastic Constants of Argon at 4.2 °K from Phonon Measurements
Authors: Dorner B. , Egger H. 
Published: July 2007

AbstractPhonon measurements with inelastic neutron scattering have been analysed carefully, by use of the resolution ellipsoids of the three‐axis spectrometer. The slopes of the dispersion curves at the low frequency phonons are taken to be the sound velocities. From these sound velocities the elastic constants are calculated: C11 = (3.67 ± 0.14).1010 dyn cm−2, C12 = (1.74 ± 0.17).1010 dyn cm−2, C44 = (2.34 ± 0.11).1010 dyn cm−2. Theoretical calculations with an accurate pair potential in the self‐consistent phonon approximation give the best agreement for a model without anharmonicity and without three‐body forces.
Local Mode Broadening by Impurity‐Impurity Interactions
Authors: Harrington J. A. , Walker Ch. T. 
Published: July 2007

AbstractConcentration and temperature dependences of the bandwidth of the Raman and infrared active local mode for H− in BaF2 have been determined. The bandwidth is observed experimentally to vary as the square root of the impurity concentration, and as T1.5 at high temperatures. This concentration dependence is in qualitative accord with the theoretical predictions of Dawber and Elliott.