bluuebunny/crossref_metadata_2025 huggingface dataset:
Dislocation Structures in Fatigued CuZn Single Crystals
Authors: Lukáš P. , Klesnil M.
Published: July 2007

Dislocation structures in CuZn alloy single crystals were examined by means of transmission electron microscopy. The overall dislocation structure, typical for the whole volume of fatigued crystals, strongly depends on the degree of difficulty of cross slip. In crystals with sufficiently easy cross slip the surface extrusions and intrusions were found to be related to the persistent slip band structure, differing from that in the remaining volume, while in crystals with very difficult cross slip no persistent slip bands lying under the surface relief were found. Further, the role of the persistent slip bands in fatigue process is discussed.
Antiferromagnetism of Zn0.87Mn0.13Fe2O4
Authors: Fayek M. K. , Leciejewicz J. , Murasik A. , Yamzin I. I.
Published: July 2007

The magnetic structure of Zn0.87Mn0.13Fe2O4 polycrystalline samples has been studied by neutron diffraction at 4.2 °K. The indices of the magnetic peaks observed are hkl/2 with l and h + k odd only, where hkl are the indices for the spinel‐type unit cell. The absence of magnetic contributions in the reflections with even l indicates the antiferromagnetic type of ordering. The appearance of a liquid‐type diffuse peak under the strong magnetic reflections (10 1/2) suggests that the long‐range magnetic order both in the A and B sites is still not complete at 4.2 °K. In the proposed model the long‐range magnetic ordering in the A sublattice has been neglected. The magnetic ordering inthe B sites can be described in terms of four sublattices, 1, 2, 3, 4, each containing the positions: x, y, z; XY, z; Y, x, 1/2 — z; y, X, 1/2 — z; +(0, 0, 0); (1/2, 1/2, 1/2) where x, y, z are: 1/8, 1/8, 5/16; 1/8, 1/8, 13/16; 1/8, 5/8, 9/16; 1/8, 5/8, 1/16. The sublattice 1, 2 (and 3, 4) have opposite spin alignment. The angle between 1, 3 (and 2, 4) lattices could not be determined from the powder neutron data. The value of the magnetic moment for Fe3+ was determined to be (3.0 ± 0.1) μB. The magnetic transition temperature was found to occur at (11.0 ± 0.5) °K.
On the Monomolecular Recombination Luminescence and Its “Blowing‐up” by the Electric Field
Authors: Antonov‐Romanovskii V. V.
Published: July 2007

On the basis of the diffusional theory of luminescence the fraction of the monomolecular luminescence and the effect of not very strong electric fields on recombination processes in uniformly excited phosphors are estimated taking into account the smallness of the free carrier mean path. The fraction of the luminescence of short duration caused by a recombination before the localization and that one of long duration caused by the recombination after localization are also estimated. A formula which determines the probability of the recombination of electron‐hole pair components is derived. Some calculations for alkali halide phosphors are carried out.
Electron Emission Spectra of Alkaline Earth Fluorides
Authors: Petrescu P. , Giurgea M.
Published: July 2007

The photostimulated electron emission spectra of CaF2, SrF2, and BaF2 crystals, coloured by electron bombardment, are analysed. The comparison with optical absorption spectra leads to some conclusions with respect to the kind of colour centres corresponding to the various bands observed. The results verify a relation of the Mollwo‐Ivey type. Some complex bands are resolved.
Jahn‐Teller Effect and Partially Covalent Bond as Causes of Low Symmetry of Ga+, In+, and Tl+ Centres in CsCl‐Type Alkali Halides
Authors: Zazubovich S. G.
Published: July 2007

Partially polarized luminescence is observed for Ga+, In+, and Tl+ centres in alkali halides of CsCl‐type structure at liquid nitrogen temperature. The symmetry of excited Ga+, In+, and Tl+ centres is established to be tetragonal in the most crystals investigated. The symmetry of Tl+ centres in CsI:Tl crystals is trigonal. The possible causes of the low symmetry are discussed. The interaction of the optical electrons of the activator with tetragonal vibrations of the lattice may be the main cause for the low symmetry of the excited Ga+, In+, and Tl+ centres in most of the alkali halides. The partial covalent bond between thallium and some of the surrounding iodine ions seems to be essential for CsI:Tl crystals.
Calculation of Structure Constants Needed in the Kohn‐Korringa‐Rostoker Method for Lattices with N Atoms per Unit Cell
Authors: Lehmann G.
Published: July 2007

A new technique is suggested for the calculation of structure constants used in the KKR method for lattices with N atoms (N > 1) per unit cell. This new method has the advantage that the coefficients B, must not be calculated separately for every pair i j of atoms and for every special position of these atoms in the unit cell. It has the disadvantage that the structure constants DL necessary for the calculation of B, must be known for higher values of angular momentum L than in the usual approach. But an estimate shows the superiority of the proposed method for greater numbers N of atoms.
Étude de la perméabilité de l'eutectique supraconducteur CdSn à structure lamellaire
Authors: Dobrosavljevic L. , Petipas‐Dupuis C. , Racek R.
Published: July 2007

Nous avons étudié la perméabilité superficielle R.F. de l'eutectique Cd–Sn à structure lamellaire SNSN … pour des températures inférieures à la température critique du système (TCNS ≈ 3,6 °K). Le champ magnétique H est toujours dans le plan des lames et l'épaisseur des lames normales N(Cd) est grande par rapport à la longueur de cohérence. On interpréte les résultats en terme d'une pénétration (dans chaque lame de cadmium) d'un réseau unidimensionnel de vortex, pour des champs supérieurs à une certaine valeur Hc 1 (faible).
The Anisotropy of the Thermoelectric Power in the (100) Plane of As‐ and P‐TCNQ Single Crystals
Authors: Zosel D. , Ritschel H. , Hänsel H.
Published: July 2007

Single crystals of triphenylmethylarsonium 7, 7, 8, 8‐tetracyanoquinodimethane (As‐TCNQ) and triphenylmethylphosphonium 7, 7, 8, 8‐tetracyanoquinodimethane (P‐TCNQ) show an important anisotropy of the thermoelectric power. The anisotropy of the thermoelectric power in the (100) plane has been measured in the temperature range of about 200 to 400 °K using a special 13‐probe thermoelectric power measuring cell. The direction dependence of the thermo‐e.m.f. in the (100) plane is described by ΔU = (φ1 cos2 ψ + + φ2 sin2 ψ) ΔT, although not all of the underlying assumptions for this relation are satisfied in the whole temperature range. The measured shapes of the curves are considerably influenced by crystal defects.
Numerical Analysis of Properties of Dislocations in Anisotropic Media within the Range of Linear Elasticity
Authors: Malén K.
Published: July 2007

The analysis of a curved dislocation in an anisotropic medium must be done numerically. The fields can be expressed in various line integral forms. In the analysis used in this paper the basic data are derived from data for straight dislocations. For comparison some other line integral expressions are given. The explicit expressions for the roots to the sextic equation in terms of hypergeometric functions do not seem to have advantages over a direct iterative solution of the equation. The angular derivatives of field quantities for straight dislocations can be found using the transformation properties of the elastic constants. A simple example is given of the use of an integration over angle using data for straight dislocations to estimate the force on a dislocation.
Relaxation von Fehlstellendipolen in AgCl‐Kristallen II. Ergebnisse an AgCl:Ti3+, AgCl:V3+ und AgCl:Cr3+
Authors: Kunze I. , Müller P.
Published: July 2007

Die in AgCl‐Kristallen aus dreiwertigen Fremdkationen und zwei Leerstellen gebildeten Komplexe wurden mit Hilfe von ITC (ionic thermo‐current)‐Messungen untersucht. AgCl:Cr3+ lieferte dabei ein Signal mit zwei getrennten Maxima. In AgCl:V3+ wurde ein komplizierteres Signal gemessen, das aus drei sich überlagernden Maxima besteht, während in AgCl:Ti3+ nur ein einfaches ITC‐Maximum auftrat. Diese Signale unterschieden sich vollständig von den früher in AgCl:Cr2+ und AgCl:V2+ gefundenen. Zur Diskussion der Ergebnisse wurde die Zahl der elektrisch aktiven Relaxationsmodi für verschiedene Fälle der Verteilung der beiden Leerstellen auf die nächsten und übernächsten Nachbarplätze des Fremdkations berechnet.
Das Spinwellenspektrum von Eisen–Aluminium‐Legierungen in der Nähe des stöchiometrischen Verhältnisses 3:1
Authors: Elk K.
Published: July 2007

In der Nähe des stöchiometrischen Verhältnisses 3:1 existieren drei Phasen, die sich durch ihre Atomanordnung unterscheiden. Die zugehörigen Spinwellenspektren werden berechnet, wobei für die beiden ungeordneten Phasen ein Variationsverfahren benutzt wird. Die Spektren ergeben sich als deutlich voneinander verschieden, insbesondere entstehen drei stark verschiedene Steifigkeits‐Konstanten.
The Effect of a Short‐Range Three‐Body Potential on the Properties of Inert Gas Solids
Authors: Roy D. , Basu A. N.
Published: July 2007

A short‐range three‐body interaction which arises from the deformability of the charge cloud of an atom is included in the interaction between atoms of an inert gas solid and its effect on the dispersion curves and elastic constants is discussed. The result is applied to krypton. Experimental dispersion curves, the bulk modulus at absolute zero, and the Debye temperature are compared with calculated values. It is found that on the whole the inclusion of the three‐body potential improves the agreement.
Optical Properties of Na and Li Halide Crystals at 55 °K
Authors: Baldini G. , Bosacchi B.
Published: July 2007

New results on the low temperature reflectivity of Li and Na halides between 5 and 10 eV are reported and discussed on the basis of recent band structure calculations. Furthermore, fine structure accompanying the lowest exciton has been detected in some crystals. This structure is examined in detail and attributed to the exciton‐phonon interaction.
On Bonding and Structure of Epitaxial Bicrystals I. Semi‐Infinite Crystals
Authors: Ball C. A. B. , van der Merwe J. H.
Published: July 2007

The bonding in epitaxial bicrystals and its influence on their structural properties, assumed to be governed by lowest energy configurations, are considered. The Peierls‐Nabarro model for the interfacial interaction between two semi‐infinite crystals, used previously, is extended in Part I to include the second term in a Fourier series. This is believed to represent the true interaction more closely. Three approximate expressions for the energy are obtained, one of which is in the form of a useful analytical expression. In Part II the considerations are extended to thin films.
Conductivity of Hot Holes in Silicon at 77 °K
Authors: Asche M. , von Borzeszkowski J. , Sarbei O. G.
Published: July 2007

The conductivity of holes in p‐Si is measured as a function of electric field strength in the 〈100〉, 〈110〉, and 〈111〉 directions of crystals with different resistivities (6000 Ω cm ≧ ≧ Q300 °K ≧ 0.45 Ω cm) at 77 °K. The values obtained for samples from highly purified crystals are compared with the heavy hole mobility calculated theoretically within the framework of the same model which allowed to explain the dependence of mobility on lattice temperature. The different influence of the interaction with optical phonons on both the effects is caused by the non‐parabolic band structure, reflected more strongly by the field dependence of the mobility.
Measurement of Forbidden Energy Gap of Semiconductors by Diffuse Reflectance Technique
Authors: Tandon S. P. , Gupta J. P.
Published: July 2007

Diffuse reflectance technique for the measurement of forbidden energy gap, Eg, is discussed. The energy coordinate of the point at which the linear increase in the Kubelka‐Munk function starts gives the Eg‐value. The Eg‐values of fifteen semiconductors are reported. These Eg‐values are found to be in good agreement with those measured by other methods.
Cottrell‐Stokes Ratios and Dislocation Distributions in Copper
Authors: Bullen F. P. , McK. Cousland S.
Published: July 2007

The Cottrell‐Stokes ratio in polycrystals remains sensibly constant at low and intermediate flow stresses [1]; in single crystals deformed in simple tension it increases with flow stress, beyond stage I [2]. The present paper describes the C‐S ratio/flow‐stress relationship in single crystals in which “alien” dislocation distributions were produced by twisting, by constrained tensile strain, or by change of glide plane after prestrain. The C‐S ratios of such crystals were independent of their initial flow stress (beyond the range of normal stage I values) and remained constant during further tensile strain; at intermediate flow stresses, the C‐S ratios were always greater than those for single crystals deformed in simple tension and approximately equal to those for deformed polycrystals. It is proposed that the common value for our alien distributions and polycrystals corresponds to an isotropic dislocation distribution, and that “forest‐rich” anisotropic distributions approach isotropy more rapidly with increasing strain than those with excess primary dislocations. The difference in rate of approach is compatible with the different roles of primary and secondary dislocations in “single‐slip” deformation and with the single‐valued nature of the C‐S ratio/flow‐stress relationship for unconstrained tensile deformation of single crystals [2].
Description of Elastic and Dielastic Interactions in Superconductors by Quasidislocations
Authors: Kronmüller H. , Riedel H.
Published: July 2007

The interaction between dislocations and the superconducting state is usually attributed to the ΔV‐effect, the ΔE‐effect, and to non‐linear elasticity effects. It is shown that all three types of interactions may be described in a unified manner in terms of quasidislocations. For the interaction forces between crystal dislocations and quasidislocations which are generated by the superconducting state a generalized Peach‐Koehler‐type formula is derived.
Contribution à la théorie de la résistivité électrique des joints de grains métalliques
Authors: Guyot P.
Published: July 2007

On présente une méthode de calcul de la résistivité électrique des joints de grains de forte désorientation, pour les métaux à surface de Fermi anisotrope. Elle consiste à évaluer la fraction d'électrons de conduction complètement réfléchis sur les joints, dont on déduit une valeur limite inférieure de la résistivité. Une moyenne, effectuée sur des joints d'orientation simple dans le cuivre, donne un ordre de grandeur raisonnable comparé aux résultats expérimentaux trouvés dans la littérature.
Transition Temperature of Superconducting Amorphous Bismuth, Gallium, and Alloys of Bismuth
Authors: Benda R.
Published: July 2007

A formula for the superconducting transition temperature is derived in the framework of the strong coupling theory and applied to amorphous materials. The actual structure of the phonon spectrum is taken into account. Good quantitative agreement between theory and experiment is obtained.
Theory of F‐Centres in Alkaline Earth Fluorides
Authors: den Hartog H. W.
Published: July 2007

F‐centres in alkaline earth fluorides have been investigated by means of optical and ESR experiments. From these results we can obtain information about the charge distribution, which appears to deviate from that observed in the alkali halides. We have found some evidence that LCAO‐type wave functions give a better description of the physical properties of F‐centres in alkaline earth fluorides than the conventional central wave functions, which were quite successful in describing the F‐electron in the alkali halides. Some new relations between the optical transition energy and the hfs constants and the radius of the monovalent cations surrounding the vacancy are given.
Effect of Impurity Precipitations on the Anomalous X‐Ray Transmission in Heavily Arsenic‐Doped Germanium
Authors: Efimov O. N. , Sheikhet E. G. , Datsenko L. I.
Published: July 2007

Experimental data of quantitative studies of the integral characteristics of anomalous X‐ray transmission are given for germanium with different dislocation densities, doped with arsenic up to a concentration of ≈4 × 1019 at/cm−3 at various stages of existence and decomposition of the solid solution. The state of solid solution was controlled by electrophysical measurements and X‐ray topographs (Borrmann's method). On the basis of the results obtained some conclusions are drawn about the character of the disturbances generated by the above mentioned decomposition of the solid solution. Particularities of the solution behaviour are considered when the concentration of arsenic is near the limit.
Émission thermo‐électronique, conduction électrique et thermogravimétrie dans l'étude des défauts ponctuels de la zircone
Authors: Loup J. P. , Anthony A. M.
Published: July 2007

L'émission thermo‐électronique de la zircone non activée est étudiée en présence d'oxygène de 10−6 à 10−11 atm dans le domaine de température 1650 à 1900 °K. Le réseau d'isothermes fait apparaitre deux domaines de pression; sous basse pression le courant émis varie en Po−1/62 et sous pression plus élevée en Po−1/32. L'énergie „d'activation apparente”︁ de l'émission à pression fixe, est trés proche dans les deux domaines. On montre que l'émission de l'oxyde ne dépend pas de son état de surface mais est liée à la nature et à la concentration des défauts atomiques ponctuels présents dans le volume du solide. Le désordre anti‐Frenkel, avec des ions oxygène simplement chargés, est proposé; il permet d'effectuer la synthèse des résultats expérimentaux d'émission, de conductivité, de nombre de transport et de thermogravimétrie.
Effect of Tensile Stress on the Magnetic Domain Structure of Iron Foils
Authors: Finbow D. C. , Havard D. A.
Published: July 2007

Thin electropolished foils of iron have been strained in an electron microscope. Their magnetic domain structures have been observed with the technique of Lorentz electron microscopy. The observed changes are consistent with theoretical predictions and macroscopic experimental studies. A simple geometrical construction is shown to explain some of the qualitative features of stress magnetization curves in small constant magnetic fields.
Low Temperature Motion of Néel and Bloch Walls
Authors: Bostanjoglo O. , Kreisel P. , Oelmann A.
Published: July 2007

The motion of Néel and Bloch walls in a quasistatic magnetic field was investigated by Lorentz microscopy in the range 4 to 300°K. Below a critical temperature (28 °K for polycrystalline Permalloy and 40°K for poly‐ and monocrystalline iron and cobalt films) the usual Barkhausen jumps of the wall motion with jump size 1 to 50 μm were abruptly quenched. The wall then moved by tiny jumps (size ≈ 0.1 or < 0.03 μm) and in a constant field. These effects – associated with the motion of Néel, Bloch, cross‐tie walls and circle Bloch lines along the walls of locked domains – were ascribed to the suppression of the diffusion and orientation after‐effect of crystal defects.
Energy Transfer from Donor–Acceptor Pairs to Deep‐Lying Impurity States in Semiconductors
Authors: Shaffer J. , Williams F.
Published: July 2007

After briefly reviewing the formulation of resonance energy transfer, we consider resonance transfer from effective mass electronic states of donor‐acceptor pairs to tightly‐bound electronic states of impurities in semiconductors. Two general cases requiring different theoretical analyses are considered: 1. transfer from the donor‐acceptor pair to a distant point fluorescer and 2. transfer from the pair to intra‐core fluorescer states of the donor or acceptor. The energy transfer matrices for both cases are shown to depend on the radiative transition matrix for the fluorescer. For case 1, the transfer matrix depends on the overlap of the effective mass function of donor and acceptor; for case 2 the main contribution arises from effective mass functions in the unit cell within which is the fluorescer core. The analyses are applied qualitatively to ZnS:Cu, Ga, Mn and to ZnS:Cu, Tb, and comparisons made with other transfer mechanisms. Finally, transfer involving intra‐donor transitions is predicted.
Lattice‐Scattering Ohmic Mobility of Electrons in Silicon
Authors: Costato M. , Reggiani L.
Published: July 2007

The ohmic mobility of electrons affected only by lattice scattering has been investigated theoretically in Si. Using a displaced Maxwell‐Boltzmann distribution function and considering the permitted electron‐phonon interactions experimental data have been fitted to the results obtained. The results support the importance of intervalley scattering by low‐energy LA phonons in agreement with Dumke, with Onton, and with previous results of the authors on non‐ohmic mobility, and in disagreement with Long.
About the Crystal Field Theory of Tetrahedral Sites in Spinel Lattices
Authors: Jäger E. , Perthel R.
Published: July 2007

In a foregoing paper [1] the crystal field potential of an octahedral site in a spinel lattice was calculated using the point charge model and considering the ten nearest environments. Analogous to these calculations the crystal field potential of a tetrahedral site in the lattice of a normal spinel is calculated. As an example for application the spectrum of Co2+ions in a diamagnetic spinel is considered, taking into account also the influence of a magnetic field, and compared with experimental data.
Ionic Displacement in Currents in Irradiated Alkali Halides
Authors: Fuchs W. , Taylor A.
Published: July 2007

A brief theoretical discussion is given of possible ionic and electronic displacement currents associated with the random walk annealing of Br− interstitials in KBr. Experimentally we have observed displacement current peaks during isochronal annealing at 22.0, 24, and 27°K subsequent to cobalt gamma irradiation at 10°K. Only the lowest temperature peak appears to be ascribable to an ionic current due to interstitial‐vacancy recombination. It is concluded that less than 1% of the Br− interstitials in the irradiated crystals were free to participate in a random walk annihilation process.
The Validity of the Tenth‐Power Law of the Magnetic Crystal Energy
Authors: Hausmann K.
Published: July 2007

A general derivation of the M10‐law for the anisotropy constant K1 of cubic ferro‐ and ferrimagnets is presented in the frame of spin wave theory. No assumptions on the degree of localization of the magnetic electrons are needed. The M10‐law is valid if the vacuum state of magnons is temperature independent. The anomalous temperature dependence of K1 in the case of nickel is explained by the hypothesis of indirect anisotropic exchange.
Temperature Effects on Zircon Structure Lattice Parameters and Zero‐Field Resonance for Substituted Gd3+
Authors: Kahle H. G. , Schopper H. C. , Urban W. , Wüchner W.
Published: July 2007

The linear expansion coefficients of the unit cell of several zircon structure crystals were determined from high‐temperature X‐ray data and compared with the temperature dependence of the rotational parameters in the corresponding spin Hamiltonian for Gd3−, taken from zero‐field resonance work.
Faraday Rotation due to Excitons in Evaporated CuCl Films
Authors: Koda T. , Segawa Y. , Mitani T.
Published: July 2007

Faraday rotation spectra which may be ascribed to excitons were measured on evaporated films of CuCl. The observed rotation anomaly due to the Z3 exciton was successfully analyzed in terms of a classical dispersion theory, thereby yielding data of the temperature‐dependent damping constant, the oscillator strength, and the effective g‐value for the Z3 exciton. On the basis of the effective mass approximation, estimates were made for the effective mass and g‐values of the relevant conduction and valence bands.
Effect of Three‐Body Interactions on the Shell Model of Alkali Halides: Application to KF and KCl
Authors: Singh R. K. , Verma M. P.
Published: July 2007

A modified shell model of ionic solids described in two earlier communications [1, 2] has been applied to study the lattice dynamics of KF and KCl. The theoretical results obtained are found to agree excellently well with available experimental data.
Ultrasonic Attenuation in Nickel in the Vicinity of Curie Temperature
Authors: Basu B. K.
Published: July 2007

An investigation is made of the critical attenuation of longitudinal ultrasonic waves in nickel single crystals of different purity and the influence of small magnetic fields is examined. The attenuation is less in crystals of lower purity. In a magnetic field the attenuation shows considerable anisotropy. The data show that the critical temperature Tc lies above the temperature corresponding to the peak attenuation. Tc has been evaluated using the observations in transverse magnetic fields. The results support the dynamical scaling hypothesis.
Some Features of ESR and Spin–Lattice Relaxation of Electrons in Ge and InSb with Different Donor Concentrations
Authors: Gershenzon E. M. , Pevin N. M. , Fogelson M. S.
Published: July 2007

The concentration and temperature dependence of the ESR linewidth in n‐Ge and n‐InSb and spin–lattice relaxation times in Ge: As have been investigated in the X‐band. ESR line narrowing and the increase of the spin‐lattice relaxation rate with concentration in the low concentration range are explained by overlap of the donor electron wave functions. In the high concentration range the ESR data are compared with the theories of the spin relaxation of conduction electrons.
Optical and Photoelectrical Properties of β‐Rhombohedral Boron II. Photoeffects
Authors: Werheit H.
Published: July 2007

β‐rhombohedral boron is characterized as infrared phosphor. Below 100 °C the optical absorption in the region between absorption edge and lattice vibrations as well as the electrical conductivity show a considerable rise during illumination with white light caused by two trapping levels of great density of states. At low temperatures both levels cannot be occupied simultaneously. Optical ionization spectra of charged traps (“photoabsorption”) give high activation energies confirmed by glow curves derived from the temperature dependence of photoabsorption. The recombination of trapped electrons and free holes does not take place directly but via the conduction band. Therefore it is considerably delayed especially at low temperatures because of the high ionization energies of the traps.
ESR Study of Cadmium Boracites Doped with Nickel
Authors: Baberschke K. , Reich S. , Dormann E.
Published: July 2007

The ESR spectra of nickel in Cd boracites can be described by S = 1/2 and an axially symmetric g‐tensor. The spectra of nickel in Cd‐Cl boracites show a resolved superhyperfine structure. To describe it, we suggest Ni+ with a halogen vacancy. The results are compared with spectra of Mn‐doped Cd boracites.
Theory of Anharmonic Crystals. III. Three‐Dimensional Lattice
Authors: Plakida N. M. , Siklós T.
Published: July 2007

The properties of the f.c.c. lattice with central nearest neighbour interaction are investigated on the basis of the dynamical theory of the anharmonic crystal developed in [1]. It is shown that in the case of constant external pressure the lattice becomes unstable at sufficiently high zero point energy or temperature. The behaviour of the physical quantities in the vicinity of the unstability point is investigated.
Generation of a Longitudinal Electric Field in CdS by Intense Laser Irradiation
Authors: Vladimirov V. I. , Pyshkin S. L. , Ferdman N. A.
Published: July 2007

The paper is concerned with the investigation of longitudinal electric fields (≈ 1 V/cm) arising in a homogeneous piezoelectric crystal at high level of optical excitation. The sign of the effect corresponds to the drag of free carriers (electrons in the case of CdS) in the direction of light propagation. The magnitude of the effect and its kinetics have been related to light intensity, temperature, crystal orientation, and the distance between the probe points. The effect is assumed to be a result of the generation of a phonon packet, referred to by the authors as acousto‐optical domain, and carrier drag by this domain. Calculations based on the Boltzmann equation for the electron distribution function give a reasonable phonon density inside the domain which is necessary for generating the electric field observed. The estimations based on the calculated phonon density show that considerable mechanical stresses exist in the domain area which can result in the destruction of the crystal when increasing the light intensity; so far the effect examined can be directly related to the problem of optical strength.
Wave‐Number Integration for F.C.C. Lattices — An Extension of Houston's Method
Authors: Ra Ø.
Published: July 2007

A simple wave‐number integration scheme applicable to functions of fully cubic symmetry is presented. The procedure, which is an extension of the Houston method, accounts for the non‐spherical shape of the Brillouin zone in a systematic fashion and remains useful in cases of non‐negligible contributions from the zone boundary regions. The method is applied, by way of illustration, to an investigation of local modes due to mass substitutions in BaF2. Local mode frequencies within gaps in the frequency spectrum as well as above the optical branches are computed for impurity ions of both signs, and of masses both greater and less than those of the host ions. When applied to the calculation of diagonal Green's function matrix elements, the integration procedure offers a substantial reduction of the numerical effort otherwise required in a direct summation over a discrete grid of points in k‐space.
Optical Emission from Surface Plasmons
Authors: Ritchie R. H.
Published: July 2007

A theory of light emission by surface plasmons created on a semi‐infinite plane‐bounded electron gas by grazing incidence fast electrons is presented. Photon‐surface plasmon coupling is assumed to occur through surface roughness and is taken to be weak enough so that it may be treated in low‐order perturbation theory. Formulae are given for the distribution in angle and energy of emitted photons of both polarizations, assuming that the surface roughness may be described by a stochastic model.
On the Semi‐Classical Theory of Piezoreflection and Magneto‐Piezoreflection
Authors: Pistoulet B. , Mathieu H. , Camassel J. , Auvergne D.
Published: July 2007

The influence of the relaxation time on the position of the minimum of ΔR/R in the absence of an applied field, or on the position of its successive extrema in the presence of a magnetic field is shown. In this first article we neglect the role of excitons. and consider that in the neighbourhood of a critical point the variation of the matrix element due to the stress is negligible in comparison with the energy band displacements, so that
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The curves were calculated for germanium and compared with some of the results found experimentally.
Field‐Enhanced Ionization
Authors: Dussel G. A. , Böer K. W.
Published: July 2007

At field strengths which can lie markedly below the critical values for impact ionization and Zener extraction, field induced changes in the capture cross section, barrier height, and frequency factor of Coulomb‐attractive centers due to a deformation of the potential around the center and induced by the external field can cause a marked redistribution of carriers over these centers (field‐enhanced ionization). These changes in the kinetic parameters of the centers are estimated, using a classical model, and are given as a function of the external field. For a typical semiconductor at T = 200 °K, a possible decrease of trap‐occupation up to a factor of two, already, at fields of the order of 102 V/cm is calculated.
Field Quenching as Mechanism of Negative Differential Conductivity in Photoconducting CdS
Authors: Dussel G. A. , Böer K. W.
Published: July 2007

It is shown that the observed steep decrease of the electron density in photoconducting CdS(Al, Ag) with field in the range between 20 and 70 kV/cm is caused by a redistribution of holes from slow to fast recombination centres (field quenching). This redistribution is produced by field‐enhanced ionization of holes from Coulomb‐attractive slow recombination centers. The abrupt onset of the field quenching occurs because of the slow recombination traffic masking the fast center traffic until it becomes predominant. Competing infrared quenching reduces the masking effect and uncovers the earlier phases of field quenching already near 1 kV/cm (at 200 °K). Impact ionization and Zener extraction of holes from slow centers cannot explain the observed behavior. However, quantitative agreement between experiment and field quenching via field‐enhanced ionization can be reached.
Landau's Theory of Second‐Order Phase Transitions and the Magnetic Phase Transitions in Some Antiferromagnetic Oxides
Authors: Cracknell A. P. , Cracknell M. F. , Davies B. L.
Published: July 2007

It is argued that many magnetic phase transitions are not, according to Landau's theory, strictly second‐order phase transitions. A detailed discussion of the application of Landau's theory of second‐order phase transitions to antiferromagnetic UO2, MnO, FeO, CoO, and NiO is given in terms of Jahn‐Teller distortions and of soft phonon modes.
Influence of Pressure on the Shape of γ‐Lines Emitted by Sm‐Nuclei Recoiling with 3 eV in Eu‐Metal
Authors: Kalus J.
Published: July 2007

The deceleration of the Sm152 nuclei recoiling with an energy of 3 eV after the electron capture decay of Eu152, and thus the shapes of γ‐lines emitted after the neutrino emission, depends on the condition of the source material. The change of the γ‐line shape of a Eu‐metal source as a function of pressure was ascertained by measuring the yield of resonantly scattered 963 keV γ‐rays for pressures of 3.54 and 16.6 kbar. Features of the forces acting between the Sm‐atom and the Eu‐atoms are presented. In view of the low recoil‐energies involved and of the short lifetime of the nuclear state, the line shapes could be calculated to a good approximation by assuming that the recoiling nuclei were moving in a spherical potential [1, 2].
Die theoretische Deutung der magnetischen Anisotropie plastisch verformter Nickel‐Einkristalle
Authors: Gessinger H.
Published: July 2007

Die Anisotropie der Einmündungssuszeptibilität wurde für einige bei der plastischen Verformung kubisch‐flächenzentrierter Metalle wichtige Versetzungstypen berechnet. Durch lineare Überlagerung der theoretisch bestimmten Effekte von Einzelversetzungen verschiedenen Typs konnten pauschale Versetzungsverteilungen angegeben werden, welche die in einer vorhergehenden Arbeit dargestellten Ergebnisse der Anisotropiemessungen befriedigend erklären. Danach ist die Versetzungsstruktur bei niederen Verformungsgraden über‐wiegend durch primäre Versetzungen bestimmt, die mit zunehmender Verformung mehr und mehr 60°‐Orientierung aufweisen. Bei stärkerer Verformung machen sich zunehmend isotrop angeordnete Sekundärversetzungen bemerkbar. Jedoch bleibt die Hauptgleitebene bis zu den höchsten Verformungsgraden ausgezeichnet.
Polarization Reversal for Electromagnetic Waves in Semiconductors
Authors: Holter Ø. , Leer E.
Published: July 2007

Extrinsic semiconductors have three charged species, and hence satisfy the requirement for polarization reversal of the two electromagnetic wave modes. This effect is investigated by using cold plasma wave theory in the limit of small collision frequencies. It is shown that polarization reversal is possible for frequencies less than the hole cyclotron frequency in n‐type materials, and for frequencies above the electron cyclotron frequency in p‐type materials, when the angle between the magnetic field and the wave vector exceeds a certain critical value. For this angle the modes are critically coupled. As a particular example for application an n‐InSb sample is considered.
Plastic Deformation and Creep of Sodium Chloride Crystals at Liquid Helium Temperatures
Authors: Tesh J. R. , Whitworth R. W.
Published: July 2007

The plastic deformation of single crystals of NaCl in uniaxial compression was studied between 1.5 and 4.2 °K and also at 77 °K. The flow stress increased rapidly with decreasing temperature, being about 2.3 kp mm−2 at 2 °K. Flow occurred by the widening of dislocation bands, and considerable amounts of transient creep were observed. Analysis of the creep constant, stress dependence of strain rate, and temperature dependence of flow stress lead to the conclusion that the deformation can be explained in terms of the thermally activated motion of dislocations.
Plastic Deformation of Corundum Single Crystals
Authors: Klassen‐Neklyudova M. V. , Govorkov V. G. , Urusovskaya A. A. , Voinova N. N. , Kozlovskaya E. P.
Published: July 2007

The stress‐strain curves and the defect structure of corundum single crystals (sapphire and ruby) were studied. The influence of impurity (Cr) presence, crystallographic orientation, temperature, and deformation rate was investigated. Chromium makes corundum harder and causes a yield point phenomenon. The yield point was also increased by the transition from 60° to 90° orientation of the specimens, by lowering the temperature, and by an increase in the deformation rate. In 60°‐specimens the deformation occurs by means of gliding on basal planes in 〈1120〉 and 〈1010〉 directions. In 90°‐samples beside this one gliding in (1010), (1011), (2021) and (2243) is found.
The Electronic Structure of 3d Transition Metals
Authors: Galperin F. M. , Gavrilov N. A.
Published: July 2007

In the present paper each point of the lattice is assumed to be surrounded by a neutral sphere of the radius R < rs for pure ferromagnetic metals and R > rs for non‐ferromagnetic 3d‐metals while in the Stern method the neutral sphere is the Wigner‐Seitz sphere of radius rs. The atom in the sphere is taken as characterized by the starting electronic configuration depending on the type of the crystal structure: 3dC−24s2 for f.c.c. (Ni and Sc), 3dC−14s1 for h.c.p. (Co and Ti), 3dC for b.c.c. (Fe, Cr, V. α‐Mn), C being the number of electrons out of the argon shell of the neutral atom in the ground state. Only one of all the lattice points is surrounded by the so‐called central sphere; the atom in it interacts with its nearest neighbours when R < rs as also with next‐nearest neighbours, when R > rs. Owing to this interaction the starting electronic configuration mentioned is transformed into an electronic configuration actually realized in metals. The electronic structure calculated on this basis is in agreement with that calculated by some other methods.
Spatial Distribution of Magnetic Moments
Authors: Galperin F. M. , Alpaev Yu. A. , Kizhaev F. G.
Published: July 2007

An attempt is made to calculate the various contributions to the atomic magnetic moment and to express them in terms of the electronic structure parameters. In a previous paper the authors consider the metal as consisting of neutral atoms of one and the same kind while in the present one two kinds of neutral atoms in a crystal are considered and a calculation is made of the configurational interaction between them, the spin polarization of hybridized unpaired conduction electrons, and the effect of this polarization on the electronic structure.
Parametric Instability and Resonance Effects in Semiconductors
Authors: Karageorgy‐Alkalaev P. M. , Leiderman A. Yu.
Published: July 2007

The possibility of distortion of stable distributions of non‐equilibrium carriers in semiconductors (dielectrics) due to the dependence of dielectric permittivity and mobility on the electric field strength or filling rate of impurity centres is considered. It is shown that a semiconductor possesses resonance properties in the self‐oscillation regime.
Optical Absorption in the Visible Range of Cu0.8−xZn0.2Pdx Alloys with 0 ≦ x ≦ 0.2 at Room Temperature1)
Authors: Mamola K. , Schröder K.
Published: July 2007

The optical absorptivity A of Cu0.8−xZn0.2Pdx alloys (0 ± x ± 0.2) was measured as a function of the wavelength between 250 nm < λ < 800 nm at room temperature in a vacuum system with < 10−6 Torr. A has a peak (or shoulder) close to 380 nm for x = 0.1. The alloy with x = 0.2 has a minimum at this wavelength. It is proposed that palladium impurities are responsible for virtual energy states which lead to an increase in A below 300 nm and above 500 nm. Additionally palladium in higher concentrations absorbs part of the extra electrons of zinc in the copper‐zinc matrix. This leads to the minimum of A in the alloy with 20 at% palladium.
The Effect of Pressure on Superconducting State Parameters and Transition Temperature of Simple Metal Superconductors
Authors: Rajput J. S. , Gupta A. K.
Published: July 2007

A method is presented for the theoretical calculation of the logarithmic volume derivatives of the three superconducting state parameters, the phonon interaction parameter, the coulomb pseudopotential, and the energy renormalization parameter. The two representative cases of lead and aluminium have been studied. The initial linear drop of Tc when plotted against change in volume, which is experimentally observed fact, is theoretically confirmed.
On the Diffusion of H and D in Pd between 50 and 300 °K
Authors: Arons R. R. , Tamminga Y. , de Vries G.
Published: July 2007

From 50 to 300 °K the jump rates of H and D in the β‐phase of Pd are described by the sum of two thermally activated processes. At higher temperatures the activation energy is found to be 2500 °K, whereas at low temperatures values of 1750 and 1450 °K for H and D, respectively, are obtained. The results are explained by tunneling from activated states.
General Threshold Theory of Electronic Emission from the Surface of a Metal
Authors: Brodskii A. M. , Gurevich Yu. Ya. , Levich V. G.
Published: July 2007

A unified theory of field‐, thermo‐, and photoemission from metal surface is considered, and the general quantum‐mechanical methods for the investigation of the threshold phenomena are applied. As result the corresponding final expressions are obtained in such a form that it is possible to apply immediately the well known methods of scattering theory for their investigation. Thus, a rigorous foundation for existing formula of emission phenomena is given leading to a more exact form and to restrictions of the frames of their applicability without using any concrete model. Some explanations of the emission phenomena which by traditional theory could not be explained, are suggested. Beside this the new approach to emission phenomena permits further generalization.
The Effect of Charged Impurities on the Yield Point of Silicon
Authors: Siethoff H.
Published: July 2007

Dislocation‐free silicon single crystals heavily doped with phosphorus and boron are dynamically deformed in compression at high temperatures. Doping in the extrinsic region affects the yield point of silicon in two different ways: At high strain rates the activation energy of dislocation velocity as measured by the lower yield stress is decreased by phosphorus but is not changed by boron. At low strain rates marked deviations from this behaviour are observed. The lower yield stress becomes independent of strain rate, but still depends exponentially on deformation temperature and linearly on doping concentration. These results are interpreted on the basis of a strong short‐range electrostatic interaction between charged dislocations and oppositely charged solute atoms leading to impurity clouds around the dislocations.
Nonlocal Model Potential Calculation of Phonon Spectra of the Hexagonal Close‐Packed Metals
Authors: Eschrig H. , Wonn H.
Published: July 2007

The influence of nonlocality of the Heine‐Abarenkov model potential on phonon spectra is investigated. A simple approximation for the nonlocality is used to evaluate this influence. Calculations are carried out for the h.c.p.‐metals. It is shown that the usual local approximation of the potential is not valid for calculations of the phonon spectra.
ENDOR, the F‐Center Ground State, and Conduction Bands in Alkali Halide Crystals
Authors: Fowler W. B. , Kunz A. B.
Published: July 2007

Although both experiment and theory indicate that the lowest conduction‐band minimum in most alkali halides is at k = 0, recent theoretical analysis by Grachev, Deigen, and Pekar of ENDOR data on the F‐center ground state suggests that in KCl and NaF the lowest minima may be away from k = 0, along the (100) direction. In this paper we discuss the problem of precise calculation of the F‐center ground state and interpretation of ENDOR data. We present the result of a calculation, based on a new local‐orbital approximation to the Hartree‐Fock equations, of the F‐center ground state in KCl. This calculation does not agree in all respects with experimental results. We present a critical analysis of the technique of Grachev et al., and show that if one uses different ENDOR data and a slightly different approach, the case for (100) minima in KCl is considerably weakened.
Surface States on Clean and on Cesium‐Covered Cleaved Silicon Surfaces
Authors: Mönch W.
Published: July 2007

The surface conductivity of p‐type Si crystals cleaved in UHV and covered with Cs up to a monolayer was measured. With increasing Cs coverage θ the surface conductivity, Δσ, initially decreases from the value of the clean surface and reaches the minimum at θ = 0.005. After a subsequent increase Δσ remains constant from θ = 0.015 to 0.25 and exhibits a steep increase for further coverage up to θ = 1. From these surface conductivities the positions of the Fermi level EF at the surface are calculated. At the clean surface the intrinsic level Ei lies 0.27 eV above EF and shifts with increasing θ to 0.27 eV below EF at θ = 1. From the dependence of (EF – Ei)s on Cs coverage the distribution of surface states can be calculated since the adsorbed Cs atoms are ionized, giving one electron to a Si surface state. At the clean surface there are two surface state bands, one with donor states 0.31 eV below Ei and a density of 8.5 × 1013 cm−2eV−1, and another one with acceptor states 0.13 eV below Ei, 0.05 eV wide and with a density of 5.7 × 1013 cm−2 eV−1. For each adsorbed Cs atom a new surface acceptor state is created in a band 0.1 eV above Ei and 0.03 eV wide.
On the Phonon Avalanche Generated by Spin‐Lattice Relaxation in a Bottlenecked Crystal
Authors: Böttger H.
Published: July 2007

The phonon avalanche phenomenon is investigated using Zubarev's density‐matrix formalism. A system of differential equations is derived which determines the time dependence of the spin and phonon temperatures. This system essentially differs from that gained from simple rate equations. The relevance of the phase‐memory time T2 for the decay of the inverted spin system is revealed.
On the Nature of X‐Centres in NaCl Crystals with Anionic Impurities
Authors: Tsal N. A. , Didyk R. I.
Published: July 2007

The effects of heat treatment and light on the conversion of F‐ into X‐centres have been investigated in specially treated NaCl crystals with hydroxyl impurities. The mechanism of the stimulating action of the impurity in the F → X conversion is analysed. The results of the work are treated from a viewpoint of a new model of X‐centres, according to which these centres are “quasicolloidal” formations, occurring at the initial stage of F‐centre coagulation. Suggestions are presented about the mechanism of a direct formation of quasicolloidal centres (X‐centres) in crystals under high‐dose γ‐irradiation.
Intraband Magnetic Breakdown in Tellurium
Authors: Anzin V. B. , Bresler M. S. , Farbshtein I. I. , Kosichkin Yu. V. , Veselago V. G.
Published: July 2007

The investigation of the Shubnikov‐de Haas effect in tellurium revealed some unusual phenomena which can be explained by an intraband magnetic breakdown of hole trajectories in k‐space close to the saddle‐point of the hole energy spectrum. These features of the magnetoresistance behaviour including, for example, the occurrence of the zeroth oscillation maximum in a magnetic field perpendicular to the trigonal axis in the case of an energy band with completely lifted spin degeneracy, are in satisfactory quantitative agreement with the existing theory of intraband magnetic breakdown.