bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetically Influencable Defect Annealing and Other Recovery Effects in Nickel, Observed with Electrical Resistance and Magnetoresistance Data
Authors: Hellenthal W. , Lotter U.
Published: July 2007

Electrical resistivity and magnetization processes (using a new magnetoresistance compensation method in alternating fields) were simultaneously observed at 77 °K in connection with recovery between 20 and 300 °C on nickel wires after low tensile deformation. Thn latter method, being very sensitive to recovery processes, reveals numerous details. Anneale ing the samples in different magnetic fields permitted a quantitative evaluation of field‐influencable effects and their separation from other contributions occurring simultaneously‐By careful analysis of some results it was also possible to distinguish transient from simple stage type contributions to the field‐insensitive recovery.
Die Spannungsabhängigkeit der Versetzungsdichte reiner und Mg‐dotierter LiF‐Einkristalle
Authors: Reppich B.
Published: July 2007

Hochreine und Mg‐dotierte 〈100〉‐orientierte LiF‐Einkristalle wurden verschieden thermisch vorbehandelt und im Druck unter konstanter Last bei Raumtemperatur verformt. Der Zusammenhang zwischen Schubspannung τ und Versetzungsdichte N wurde mittels der Ätzgrübchenmethode untersucht. Die Auswertung berücksichtigt Inhomogenitäten in der Versetzungsanordnung. Ätzversuche unter Spannung zeigen, daß sich Ätzgrübchen‐dichte und ‐anordnung verfestigter Kristalle nach Entlasten nicht sichtbar verändern. τ wird als Funktion von N beschrieben durch τ = αGb \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt N $\end{document}(G: : Schubmodul, b: Betrag des Burgersvektors) über den gesamten Spannungsbreich bis zum Bruch. Die Konstante der Versetzungswechselwirkung ergibt sich zu α = 0,25 unabhängig vom Mg‐Gehalt und der thermischen Vorbehandlung.
On Crossings of Polariton Branches in Uniaxial Crystals
Authors: Lamprecht O. , Merten L.
Published: July 2007

It is shown that there are no common crossing points for the ordinary polariton branches within the whole k‐space. For the extraordinary polariton branches crossing points are only possible for directions parallel or perpendicular to the optical axis.
The Dislocation Structure of Glide Bands in LiF Crystals Stressed at T = 300 to 1.4°K
Authors: Klyavin O. V. , Nikiforov A. V. , Smirnov B. I. , Chernov Yu. M.
Published: July 2007

The etch pit density and the shear strain in screw and edge glide bands were measured on LiF crystals, stressed at temperatures of 1.4 to 300°K, and the temperature dependence of the average slip distance of screw dislocations and the probabilities of cross slipping are estimated. The slip distance decreases with the temperature down to 78°K, remaining constant, however, at lower temperatures. The cross slip probabilities increase continuously with decreasing temperature.
Phénomènes accompagnant l'ordre directionnel dans un ferrite de fer renfermant un peu de cobalt au‐dessus de la température ambiante
Authors: Marais A. , Merceron Th. , Porte M.
Published: July 2007

On a étudiè l'influence de faibles additions de cobalt sur les propriétés de la magnetite polycristalline. La présence des ions Co2+ contribue à la formation d'une forte anisotropie uniaxiale Ku induite sous champ magnétique aux environs de 100°C. La mesure de Ku à la balance de torsion permet d'obtenir la valeur de l'énergie de couplage élémentaire w de l'ion Co2+ au réseau. Dans le même domaine de température on observe une forte augmentation de la rectangularité par traitement sous champ, ainsi qu'un phénomène nouveau “d'accommodation” de la perméabilité que l'on explique. On étudie aussi l'apparition de cycles d'hystérésis multistables, et les conditions de formation de ces cycles.
A Quasichemical Theory for a Short Range Ordered Alloy with Vacancies.
Authors: Sohoijet M.
Published: July 2007

A quasichemical theory for a short range ordered binary alloy containing vacancies is developed using a kinetic approach. The vacancy–atom a posteriori probabilities are obtained. It is shown that if the vacancies are in their equilibrium environment then the atom–atom pair probabilities should also have the values corresponding to the state of thermodynamic equilibrium.
Reformulation of the Theory of Impurity States in Non‐Metallic Crystals
Authors: Glodeanu A.
Published: July 2007

The theory of impurity states is reformulated by using a pseudopotential method. The effective mass and two‐band approximations are obtained. A simple criterion in order to estimate the errors introduced by some hypotheses is found. Finally an equation in a single‐band approximation valid for both deep and shallow levels is derived but with one effective mass and dielectric function in terms of the impurity pseudopotential.
Spin Fluctuations in a Magnetically Ordered Cr2O3–Fe2O3 System
Authors: Srivastava J. K. , Sharma R. P.
Published: July 2007

The study of Mössbauer spectra of the solid solution 0.905 Cr2O3—0.035 Fe2O3 at different temperatures in the range 10 to 293 °K has revealed spin relaxation effects in this antiferromagnetically ordered system in a wide temperature range (100 to 289 °K) below the Néel temperature (289 °K). The variation of the hyperfine field with temperature is found to be almost linear from 10 °K onward. Above 100 °K the hyperfine field calculated from the total splitting is more than that obtained from ground state splitting. The observed results are compared with the existing spin‐flip theory based on a stochastic model.
The Deformable Shell Model Calculation of Infrared Absorption Frequencies of Ionic Crystals
Authors: Roy D. , Basu A. N. , Sengupta S.
Published: July 2007

The deformable shell model which includes many‐body effects and accounts for the breakdown of Cauchy relation is extended to the case of the CsCl structure. The TO mode frequencies for q = 0 are calculated for eight ionic crystals of both NaCl and CsCl structures. For comparison, the shell model values are also calculated. The results are compared with the infrared absorption frequencies. It is found that the deformable shell model gives better agreement than the shell model. The result is particularly striking for crystals showing a large Cauchy relation breakdown.
On the Behavior of Interstitials Produced by Ionizing Radiation in Alkali Halides
Authors: Sonder E.
Published: July 2007

The reactions occurring among radiation‐produced defects after the primary production step are the subject of this paper. For KCl, at liquid nitrogen temperature, the interstitial members of the radiation‐produced Frenkel defects are known to be mobile. A model that has been mentioned repeatedly in the literature is compared with experimental data. In the model, rate equations are used to describe radiation‐produced mobile interstitials which can either recombine with vacancies or can be trapped at other defect sites, causing the corresponding vacancies (F‐centers) to be stabilized. Asymptotic forms and analog computer solutions of simple forms of the equations are obtained. The experimental results include F‐center growth curves which are approximately linear with irradiation dose and which demonstrate that for a wide range of radiation intensities the F‐center production rate is proportional to the dose rate. The predictions of the model are in accord with experimental results only for a rather extreme asymptotic case, for which a different description, which does not require the solution of rate equations, may be equally valid.
Charge Compensation of Impurities and Electrical Properties of MoO3
Authors: Ioffe V. A. , Patrina I. B. , Zelenetskaya E. V. , Mikheeva V. P.
Published: July 2007

An investigation was made of the EPR spectra of MoO3 single crystals grown in air and in argon. In the crystals grown in air and not specially doped no EPR signal was found. For crystals grown in argon a spectrum is observed due to electrons localized on two different sites of the lattice. This spectrum shows a hfs from a nuclear spin I = 1/2. The spin‐Hamiltonian constants are: S = 1/2, I = 5/2 gx = 1.942, gx = 1.953, gx = 1.878, Ax = 32 G, Ay = 69 G. The operator of the hyperfine interaction is of the form

equation image

The splitting of the transitions with ma ≠ mb is equal to 1/3 A. The splitting by the nuclear spin I = 1/2 is nearly isotropic 3 to 4 G. The same spectrum is observed in air‐grown crystals after irradiation with a quartz‐mercury lamp. In copper doped crystals grown in argon the copper is found to be in the state 3d10. After heating the crystal in air the Cu2+ (3d9) spectrum is observed. The constants of the spin Hamiltonian are: S = 1/2, I = 3/2 gx = 2.087, gy = 2.054, gz = 2.416, Ax = 6 G, Ay = 22.5 G, Az = 93.5 G, Qx = 2.9 G, Qy = 3.0 G, Qz = 5.9 G. Suppositions are made about a reason for the unstability of the electrical conductivity of MoO3 according to the data obtained.
On the Higher‐Order Response of a Superconductor
Authors: Weller W.
Published: July 2007

The response of a superconductor to external fields is considered in arbitrary order. The response is calculated for an imaginary time interval and then analytically continued to real times. In this way it is possible to make use of the theorem proved by Kadanoff and Baym on the identity of the correlation functions connected with the physical and the unphysical problem. The result justifies the method of Gorkov and Eliashberg in which the analytic continuation has been performed in the frequency representation.
The Complex Susceptibility of a Uniaxial Ferromagnet
Authors: Potapkov N. A.
Published: July 2007

A method is developed for an approximate solution of a chain of equations for two‐time Green's functions. The method is applied to the calculation of the complex susceptibility of a Heisenberg ferromagnet with uniaxial anisotropy. The damping of the uniform precession and the width of the resonance line in the vicinity of the Curie point are found.
Green's Function Formalism for an Anharmonic Metal
Authors: Högberg T.
Published: July 2007

The Green's function formalism for an anharmonic metal has been worked out. From an Hamiltonian which includes the mutual interaction between the electrons, between the ions and between the electrons and ions, the equation of motion of the Green's function for the phonon has been derived, including anharmonic terms to fourth order. The conditions for assuming an effective ion‐ion potential for an anharmonic metal are investigated.
Elektronenspektrum in der Lavesphase MgZn2
Authors: Rennert P. , Lehmann G. , Paasch G. , Taut M.
Published: July 2007

Die Energiebandstruktur für MgZn2 wird mit der Pseudopotentialmethode auf den Symmetrielinien der Brillouinzone berechnet. In der Nähe der Fermifläche ergeben sich infolge vieler, eng benachbart liegender Bänder auch bei kleinen Fourierkomponenten des Pseudopotentials wesentliche Abweichungen von der Bandstruktur freier Elektronen.
ESR in Oxygen‐Doped AgBr Crystals
Authors: Höhne M. , Segsa K. H. , Stasiw M.
Published: July 2007

At 14 °K and below oxygen‐doped AgBr crystals irradiated in the temperature range of 100 up to 220 °K show an ESR spectrum, which was not observed in AgBr crystals doped with Ag2Te, Ag2Sc, or Ag2S. The spectrum has axial symmetry with a [100] direction as axis. In order to explain the g‐values and the hyperfine structure a complex consisting of an oxygen atom and six neighbouring silver ions with an electron bound to this complex is proposed.
LCAO–HCO Calculation of Condensed Aromatic Hydrocarbons
Authors: Jäger J.
Published: July 2007

The energy band structure of the π‐electron system of crystalline anthracene was calculated in the LCAO–HCO approximation. The results show a mean band width of the filled bands (in the ground state) of about 0.1 β‐units and an energy gap between the highest filled and lowest unfilled band of about 0.7 β‐units.
Electroreflection of Amorphous Selenium
Authors: Weiser G. , Stuke J.
Published: July 2007

On amorphous selenium layers electroreflectance has been measured in the energy range from 1.7 to 4.2 eV. Only one relatively broad structure was found near 2.1 eV, i.e. below the electrical band gap and the photoconduction edge. It has a temperature coefficient of about −2.7 × 10−4 eV/°K. The explanation of this structure by a Frenkel type exciton seems to be the most plausible.
On the Resistivity of Inhomogeneous Metals
Authors: Geszti T.
Published: July 2007

The current flowing in a metal with an inhomogeneous distribution of impurities is investigated by means of a Boltzmann equation accounting for the conservation of matter in the collision term. The treatment extends that of Herring for the case where the extension of inhomogeneities is comparable to the electron mean free path. The results offer a method to measure the average extension of randomly distributed inhomogeneities.
Transport Phenomena in Degenerate Simple Model Semiconductor at High Electric Fields
Authors: Kamal J.
Published: July 2007

Expressions are derived for some transport coefficients in a simple model degenerate semiconductor in the presence of a strong d.c. electric field and a weak magnetic field using a distribution function of carrier velocities corresponding to an elevated carrier temperature. Te has been calculated following Shockley's treatment. The variation of these transport coefficients with electric field strength, the impurity parameter \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {b/a} $\end{document}, and the chemical potential η has been studied. The results are presented in the form of graphs.
Physico‐Chemical Properties of 1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazacyclooctane (HMX)
Authors: Maycock J. N. , Verneker V. R. Pai , Rouch L. L.
Published: July 2007

The dc electrical conductance of single crystal and pelleted β‐HMX and also polycrystalline δ‐HMX has been measured. These data clearly show a discontinuity at the β‐ to δ‐crystal transformation temperature. The conductance of δ‐HMX has been interpreted as being intrinsic and associated with the electronic excitation of the groups. The data for the δ‐polymorph can be interpreted in terms of impurity conduction processes associated with trapped decomposition products. The crystal and conformational changes as observed by conductance techniques agree very well with thermal data related to these changes. Similarly the energetics of the β‐conductance agree well with the optical energetics of the β‐form.
Shell Model Calculation of Microscopic Grüneisen Parameters for Rocksalt‐Type Materials
Authors: Barsch G. R. , Achar B. N. N.
Published: July 2007

The microscopic Grüneisen parameters have been calculated for the two optical modes in the Brillouin zone center and for the four modes at the Brillouin zone edge in [100] for nine alkali halides and MgO. A six parameter shell model which takes into account anion polarizability, non‐central first nearest neighbor interaction and central forces between second neighbors has been used, and the pressure dependence of the frequencies is obtained from the assumption of a pressure independent core‐shell force constant. The parameters of the model are determined from experimental data of the elastic constants, from the high and low frequency dielectric constants, from the pressure derivatives of these quantities, and from the zero pressure value of the transverse optical frequency in the zone center. Good to fair agreement with the available experimental data is found. It is suggested that the discrepancies are mainly due to the limited experimental accuracy. The results confirm that the B1 → B2 phase transformation in alkali halides is not due to an instability of the TA mode at the [100] zone boundary.
Influence of Additional Illumination on the Photoemission from n‐ and p‐Type Gallium Arsenide Single Crystals
Authors: Wojas J.
Published: July 2007

A study was made of the photoemission of electrons from oriented monocrystals of GaAs with special reference to the effect of additional infrared illumination. The retarding potential method was used in a spherical capacitor arrangement. The current‐voltage characteristics of n‐type material shift to the right upon additional illumination, while those of the p‐type material shift to the left. The shift is weaker for the p‐type samples, for which also the saturation current diminishes with illumination. These effects are explained by the change of the curvature of the energy bands near the surface with illumination.
A Study of Dislocation Arrays at Spherical Indentations in LiF as a Function of Indentation Stress and Strain
Authors: Swain M. V. , Lawn B. R.
Published: July 2007

A systematic study has been made of the dislocation arrays produced by indenting (001) surfaces of LiF with steel and nylon spheres. The arrays are discussed in terms of position along a curve relating “indentation stress” to “indentation strain”, these parameters being determined by the geometry of the contact between indenter and specimen. Three stages of behaviour are distinguished: (i) elastic stage, to which the classical Hertzian contact theory is applicable; (ii) initial yield stage, to which standard yield criteria may be applied to predict the spatial location and critical resolved shear stress for initiation of dislocation motion; (iii) subsequent growth of plastic zone, in which the relative activity of the various slip systems determine the indentation behaviour. A mechanism for the initiation of dislocation flow below an indenting sphere has been proposed on theoretical grounds, and subsequently supported by experimental evidence; this mechanism differs from alternative proposals in that the dislocation sources operate within the interior of the crystal rather than at the crystal surface. An evaluation of the dislocation activation stress for LiF is thereby made, the value obtained being in reasonable agreement with results taken from conventional compression tests. The indentation stress‐strain behaviour is then discussed in the light of current thought on indentation theory, and some shortcomings in present ideas are pointed out.
An Accurate Method of Determination of the Magnetostriction Coefficients. Application to YIG
Authors: De Lacheisserie E. , Dormann J. L.
Published: July 2007

The use of computerized Fourier analysis of magnetostriction data to obtain a high accuracy for the magnetostriction coefficients is described. This technique has been applied to measurements on a single crystal of YIG. Room temperature data were obtained using a dilatometer method. Corrections due to anisotropy and form effects were applied. Accurate values for the second degree coefficients of magnetostriction are given as well as an upper limit for the modulus of the fourth degree coefficients.
Ground‐State Properties of Finite Antiferromagnetic Chains
Authors: van de Braak H. P. , Caspers W. J.
Published: July 2007

Exact calculations are presented for the ground state of linear antiferromagnetic Heisenberg chains with open ends. The wave function and the energy are given for chains with N = 4, 6, and 8, and quantum number S = 1/2. It is shown that in the limit for N → ∞ the ground state is probably nondegenerate and the long‐range order tends to zero. The short‐range order shows a strongly oscillating character due to end effects persisting over relatively long distances. A comparison with closed rings is made and the connection with the observation of a reduction of the zero‐point deviation in the neighbourhood of non‐magnetic impurities in more‐dimensional systems is pointed out.
Infrared Absorption of AIN in the One‐Phonon Region and Finite Size Effects
Authors: Pastrňák J. , Hejda B.
Published: July 2007

The absorption of single crystals and microcrystalline samples of AlN, pressed in pellets of halides, has been measured in the region of 1000 to 400 cm−1. Three intensive absorption maxima have been found in the region between ωT and ωL. They are connected with the finite size and shape effects and their location depends on the material of the surrounding medium. Further, intensive maxima at 610 and 590 cm−1 occur in microcrystalline samples. The absorption by surface modes may be interpreted with the help of Englman and Ruppin's theory assuming that the frequencies ωT(A1) = 622 cm−1 and ωT(E1) = 660 cm−1. It is shown that it is necessary to distinguish between surface and bulk modes for the absorption measurement of microcrystalline samples and that the absorption in the region of surface modes is decisive in materials with sufficiently fine grains, i.e. in measurements with pressed pellets.
Infrared Absorption of AlN Single Crystals in the Two‐Phonon Region
Authors: Pastrňák J. , Hejda B.
Published: July 2007

Two‐phonon infrared absorption was measured on AlN single crystals in polarized light. Contrary to previous results obtained from other materials with wurtzite structure, the full polarization of some absorption bands was found. The results are interpreted with the help of the fundamental frequencies of the BZE 738, 668, 658, 627, 507, 444, and 413 cm−1.
Dichroïsme circulaire magnétique de films minces de EuTe
Authors: Briat B. , Billardon M. , Suryanarayanan K. , Paparoditis C.
Published: July 2007

Des mesures de dichroïsme circulaire magnétique, à 300 et 27 °K, ont permis de résoudre le spectre d'absorption de EuTe en ses différentes composantes dans le domaine spectral 250 à 600 nm. Tous les effets dichroïques observés sont du type paramagnétique dépendant de la température et doivent problablement être attribués aux excitations 4f7 → 4f6 5d.
Surface‐Induced Cross Glide of Screw Dislocations
Authors: Appel F. , Messerschmidt U.
Published: July 2007

Surface‐induced cross glide of screw dislocations can be well investigated electron‐microscopically with help of the gold decoration technique. The cross slip distances observed agree well with values obtained by the line tension concept. Surface‐induced cross glide rarely occurs during the dislocation motion. Therefore, the dislocation multiplication is surely not initiated by the surface‐induced cross slip.
The High‐Temperature Recovery of Neutron‐Irradiated Rhenium
Authors: Vandenborre H. , Stals L. , Nihoul J.
Published: July 2007

The recovery of rhenium after neutron irradiation at ≈ 390 °K has been studied up to 1130 °K by means of electrical resistivity measurements at 4.2 °K. Two irradiations were performed in the BR2 reactor at Mol: one up to a fluence of 7.6 × 10−18 n cm−2 (thermal) and 4.3 × 1017 n cm−2 (fast, E > 1 MeV) and the other one up to a fluence of 3.2 × 1019 n cm−2 (thermal) and 1.8 × 1018 n cm−2 (fast, E > 1 MeV). The irradiation induced resistivity is only partially recovered at 1130 °K, where the annealing of defects is supposed to be complete. This effect is attributed to the transmutation of rhenium into osmium and tungsten. The annealing spectrum between 400 and 1130 °K consists of several peaks, the main peak occurring at about 650 °K (0.19 Tm) preceded by a subpeak at about 620 °K. The latter one is more clearly resolved for the lower irradiation dose. This is also the case for the minor peaks occurring at about 490 and 540 °K. Towards higher temperature continuous recovery occurs in the temperature interval 800 to 1000 °K, whereas a small annealing stage has been observed at about 0.32 Tm. The 0.19 Tm stage shows a peak shift towards lower temperatures for higher defect concentration. It is believed that this stage corresponds to stage III of the pure f.c.c. metals.
Die Behandlung von Fehlern im Flußliniengitter der Supraleiter 2. Art in der London‐Näherung
Authors: Brandt E. H.
Published: July 2007

Es werden Methoden angegeben, die in der Nähe von Hc1 die Berechnung der Energie und des Verschiebungsfeldes von Gitterfehlern des Flußliniengitters in Supraleitern 2. Art mit ≫ 1 gestatten. Die elastischen Konstanten des Flußliniengitters und die Bindungs‐energie einer Flußlinien werden berechnet. Es zeigt sich, daß man bei allen Rechnungen die Wechselwirkung der Flußlinien mit vielen Nachbarn berücksichtigen muß; andernfalls wäre das Gitter instabil.
Photoluminescence (λm = 1.1 μm) in InSe Single Crystals and Its Relation to Photoconductivity
Authors: Akhundov G. A. , Ermolovich I. B. , Kaziev F. N. , Sheinkman M. K.
Published: July 2007

An investigation has been made of both the luminescence (λm = 1.1 μm) and photo‐conductivity in not intentionally doped photosensitive InSe single crystals. It is shown that the luminescence is due to the emissive capture of free electrons by sensitizing recombination centres. The parameters of the luminescence centres, namely concentration, energetic position, and both electron and hole capture cross‐sections have been determined.
Frenkel's Mechanism of Thermoelectronic Ionization in Single Crystals of Gallium Selenide
Authors: Tagiev B. G. , Guseinova E. S. , Gadzhiev V. A.
Published: July 2007

Measurements are made of the current‐voltage characteristics of monocrystalline GaSe specimens within the strong field region of up to 4 × 104 V/cm in the temperature range from 300 to 125 °K. The data obtained are discussed in terms of Frenkel's mechanism of thermoelectronic ionization \documentclass{article}\pagestyle{empty}\begin{document}$(\sigma = \sigma _0 {\rm e}^{\beta \sqrt E })$\end{document}. The low field value for the activation energy of carriers, is found to be ΔE0 = 0.18 eV, and decreases with increasing electric field according to the formula ΔE = ΔE0 −2 \documentclass{article}\pagestyle{empty}\begin{document}$ e\sqrt {e\,E/\varepsilon} $\end{document} ab (e electronic charge, E electric field intensity, ϵ high‐frequency dielectric constant). Correlating the experimental data with Frenkel's theory, values of ϵ = 8 are obtained for gallium selenide.
A Calculation of the Strain Dependence of the Harmonic Frequency Distribution
Authors: Mock W.
Published: July 2007

The strain dependence of the harmonic frequency distribution f(ω) has been investigated through third order using the Lagrangian strain parameters. The theory is applied to a crystal which interacts through a pair potential. In particular values for the strain coefficients are obtained for Mie‐Lennard‐Jones and Buckingham potentials. This work indicates that the shape of f(ω) changes significantly with strain and that the change is greater for shear strain than for simple expansion in agreement with earlier work.
Propagation of Electromagnetic Waves in a Longitudinally Magnetized Germanium Plasma Waveguide. II. Experimental
Authors: Pedersen N. F.
Published: July 2007

Experiments on the transmission of circularly polarized electromagnetic waves through non‐degenerate n‐type germanium in a magnetic field has been made in order to compare to a theoretical dispersion relation given in part I of this paper. The experimental frequency was 45 GHz and liquid helium temperatures has been used. The dispersion relation is found to explain the experimental results very well, and by comparison between theoretical and experimental data information about the transverse and longitudinal effective mass, the lattice dielectric constant, the electron density and the relaxation time has been obtained.
Influence of Point Defects and Dislocations on the Line Shape of Nuclear Magnetic Resonance Signals
Authors: Kanert O. , Kotzur D. , Mehring M.
Published: July 2007

The quadrupolar part of the line shape of a NMR signal is determined by lattice imperfections in the case of cubic crystals. This quadrupolar shape function is presented under the assumption of randomly distributed point defects, dislocation dipoles, and dislocations. Experimental quadrupole shapes were obtained by a line shape analysis of the NMR wide‐line signal and the spin echo signal in the case of different alkali halide crystals. The resulting quadrupolar lines can be compared with the calculated functions. The comparison shows an agreement of the measured shape with the point defect model in the case of undeformed crystals, whereas in the case of deformed crystals the dislocation model is valid.
Localized Orbitals in Polyatomic Systems
Authors: Kunz A. B.
Published: July 2007

Adams und Gilbert have derived a rigorous extension to the Hartree‐Fock equation which allows one to obtain localized orbitals in some polyatomic systems. This extension is valid for all closed shell systems and all systems which may be represented by a single Slater determinant and is approximately valid for any system which one may approximate by a single Slater determinant. In this paper these results are put in a more convenient form and are analysed in powers of the interatomic overlap, where only first order terms in overlap are retained. A perturbative form of the equation is also developed. Wave functions are obtained for the LiH crystal.
On the Stress Dependence of Steady State Creep Rate in Alpha Iron
Authors: Čadek J. , Pahutová M. , Ryš P.
Published: July 2007

Stress dependence of steady state creep rate in alpha iron is analysed assuming that the non‐conservative motion of jogs on screw dislocations is the rate controlling process. It is shown that the moving screw dislocation density ϱs is a more complicated and more sensitive function of stress than the total dislocation density ϱ. The density ϱs increases, reaches a maximum and then decreases again with the increasing stress. The model of creep based on non‐conservative motion of jogs on screw dislocations is in a good qualitative agreement with experimental results.
Leerlinie und Stapelfehler im Flußliniengitter der Supraleiter 2. Art in der London‐Näherung
Authors: Brandt E. H.
Published: July 2007

Mit den in einer vorangehenden Arbeit [1] entwickelten Methoden werden die Energie und das Verschiebungsfeld der Leerlinien höchster Symmetrie und des unendlichen Stapelfehlers im Flußliniengitter von Supraleitern mit χ ≫ 1 in der Nähe von Hc1 berechnet. Die mit verschiedenen Methoden gewonnenen Ergebnisse werden verglichen. Dabei wird der Gültigkeitsbereich und der Rechenaufwand für diese Methoden diskutiert.
Thermal Conductivity Study of GeTe and SnTe Alloys in the Homogeneous Region
Authors: Okhotin A. S. , Krestovnikov A. N. , Gorbachev V. V. , Aivazov A. A. , Pushkarskii A. S.
Published: July 2007

An investigation is made of the temperature dependence of the thermal conductivity of GeTe and SnTe alloys in the homogeneous region. The phonon component of the thermal conductivity has been determined and the dependence on the tellurium content has been analysed in terms of a theory describing the influence of spot defects upon the thermal resistance of the lattice. Good agreement between experimental and theoretical isotherms of phonon heat transfer has been obtained.
On Heat Transfer in Ag2Se and Ag2Te
Authors: Okhotin A. S. , Krestovnikov A. N. , Aivazov A. A. , Pushkarskii A. S.
Published: July 2007

A study is made of the temperature dependence of the thermal conductivity in Ag2Se and Ag2Te in the temperature range from room temperature to the melting point. On the basis of measurements of electric and physical properties an analysis is made of the heat transfer mechanism of these compounds. It has been found that the thermal conductivity in Ag2Se is determined by a phononic and an electronic component and that of Ag2Te by a phononic, an electronic, and a photonic component.
On the Effective Field Retarding the Process of Incoherent Rotation
Authors: Kolotov O. S. , Pogozhev V. A. , Telesnin R. V.
Published: July 2007

The internal effective field He retarding the process of incoherent rotation during the switching of thin magnetic films was investigated. The principal results of the work are as follows. If the switching field Hs exceeds the incoherent threshold field, He increases rapidly with time t (from the value ≈︁ Hk), reaches (t ≦ 10 ns) the maximum value H close to (0.9 to 0.95)Hs, then falls off monotonically, tending in the limit to a value close to ‐Hk. The main contribution to the value of He is made by the effective anisotropy field and the stray fields formed as a result of the initial rotation of the local magnetization vectors.
The Overshoot Phenomena in Single Crystals of Cu‐15 at% Al Tested in Tension. I. Electron Transmission Studies
Authors: Tisone T. C. , Brittain J. O. , Meshii M.
Published: July 2007

Electron transmission observations were made at different positions of the shear stress‐strain curve for Cu‐15 at% Al single crystals tested in tension into the state of overshoot. Dislocation interactions between the primary slip system and other slip systems were systematically examined. It was determined that the conjugate slip system was the most important secondary system and that the interactions between primary and conjugate dislocations forming short lengths of Lomer‐Cottrell dislocations were responsible for the latent hardening of the conjugate system, and therefore the overshoot phenomenon. The densities of conjugate dislocations and subsequent Lomer‐Cottrell interactions increased with increasing strain during stage II work hardening.
Chemical Bonding and Energy Bands in ANB8−N Crystals with Sphalerite‐Type Lattice
Authors: Levin A. A.
Published: July 2007

With the semiempirical equivalent orbital method the relation between band structure, interband transitions, and the character of bonding in ANB8−N crystals is considered.
Effect of Plastic Deformation on the Recovery of Stage I after Neutron Irradiation
Authors: Okuda S. , Takamura S. , Maeta H.
Published: July 2007

The recovery of point defects in copper after fast neutron irradiation at 15 °K was studied by measurements of residual resistivity. Especially, the effect of deformation before and after low‐temperature irradiation on the recovery spectrum was studied. The amount of stage I recovery was reduced by 20% by deformation after irradiation where the deformation was such that only 2% of atomic planes were swept by dislocations. This result suggests the transformation of some of stage I defects into more stable ones due to deformation and the fairly large distance between the interstitial and vacancy in a close pair of stage I. Also, the recovery spectra observed in the present experiments seem to show the annealing of interstitial clusters in stage II (≈︁ 130 °K recovery peak) in cold‐worked copper.
Abdampfstrukturen und Versetzungen in NaCl
Authors: Keller K. W.
Published: July 2007

Es wird der Zusammenhang der durch Abdampfen im Hochvakuum erhaltenen Strukturen (Abdampfgruben) auf der Oberfläche eines NaCl‐Kristalls mit den in diesem Kristall enthaltenen Versetzungen diskutiert. Die Existenz der bereits früher für das Zustandekommen von Abdampfspiralen angenommenen Versetzungen mit einem Burgersvektor d0/2 〈110〉, der eine Komponente senkrecht zur Oberfläche hat, bzw. einem zur Oberfläche senkrechten Burgersvektor d0 〈100〉 und der Versetzungsreaktion d0 〈100〉 ⇌ d0/2 〈110〉 + + d02 〈110〉 wird bestätigt (d0/2 Netzebenenabstand). Durch wiederholte Lochkeimbildung an Versetzungen, deren Burgersvektor in der Kristalloberfläche liegt, entstehen aus konzentrischen, geschlossenen Kreisstufen mit der Höhe d0/2 oder aus Viereckstufen mit der Höhe d0 aufgebaute Gruben. Die unterschiedliche Lochkeimbildung wird mit dem Vorhandensein von Inhomogenitäten molekularer Größe an den Versetzungslinien erklärt. Der Unterschied zu den durch Umwandlung von Spiralstrukturen entstandenen konzentrischen Kreisstufen wird deutlich gemacht.
On the Influence of Conduction Electrons on the Ferroelectric Curie Temperature
Authors: Hallers J. J. , Caspers W. J.
Published: July 2007

The frequency dependence of the transverse optical mode in the long‐wavelength limit on the density of conduction electrons is calculated. This dependence is a consequence of the dielectric properties of the free electron gas which gives a change of the effective ion‐ion interaction. By putting the limiting frequency equal to zero one finds an equation for the ferroelectric Curie temperature.
On the Plasma Minimum in Semiconductors with Anisotropic Energy Bands
Authors: Zukotynski S. , Saleh N.
Published: July 2007

Semiconductors with ellipsoidal and non‐parabolic energy bands are considered. A relaxation time of tensor character is assumed. The solution of the transport equation obtained by Zukotynski and Grynberg [1], is generalized to include a time‐dependent electric field. The results are then used in the Maxwell equations and the condition of minimum reflection is obtained. Both the Faraday and Voigt configurations in a small magnetic field are considered. The position of the plasma minimum is found to depend on the state of polarization of the incident radiation with respect to the energy surfaces.
Anomalous X‐Ray Absorption and Photocurrent in CdS Single Crystals (Symmetrical Laue Case)
Authors: Brümmer O. , Stephanik H.
Published: July 2007

It is shown that the photocurrent in CdS single crystals can be used for detecting the existence of wavefields in crystals as well as a method for proving the X‐ray‐intensity distribution in the regions of the individual atoms. The investigation was carried out by means of a double‐crystal spectrometer in (2, −2) position under the application of MoKα and CuKα radiation. Agreement between theoretical calculation and experimental results has been found.
Dielectric Properties of KCl, KBr, and KI Single Crystals in the Extreme Ultraviolet up to 35 eV
Authors: Blechschmidt D. , Klucker R. , Skibowski M.
Published: July 2007

The reflectance of freshly cleaved single crystals of KCl, KBr, and KI has been measured for 15° angle of incidence at room temperature for photon energies between 5 and 35 eV, using the continuous spectrum of synchrotron radiation. For photon energies from 12 to 30 eV the optical constants, the dielectric constant, and the energy loss function were determined by reflectance measurements with parallel polarized light at several angles of incidence between 15° and 75°. A prominent doublet near 20 eV is found for all potassium halides. It is assigned to excitonic transitions from the K+3p core level to the conduction band at Γ and X. Energy differences between some critical points at Γ and X are estimated by comparing the position of the fundamental doublet and the K+3p doublet.
Piezotransport and Piezoabsorption of Tellurium‐Intrinsic Effects
Authors: Herrmann K. H. , Ochel M. , Puhlmann J.
Published: July 2007

Dynamic piezo‐Hall effect and piezoabsorption of tellurium single crystals have been measured. The results are compared with dynamic piezoresistance reported previously. General features are outlined for intrinsic piezotransport and intrinsic piezoabsorption of a material showing an exponential absorption edge. The measurements are evaluated with respect to band structure parameters and pressure derivatives of the gap.
Absorption Spectrum and Zeeman Effect of Ho3+ in YPO4
Authors: Becker P.‐J. , Kahle H. G. , Kuse D.
Published: July 2007

The optical absorption spectra of trivalent holmium in single crystals of HoPO4 and (Y, Ho)PO4 have been measured in the range from 15000 to 29000 cm−1 including the Zeeman effect of the ground level 5I′8 and the two excited levels 3K′8 and 5G′5 at 85 and 4.2 °K. The splitting factors of the degenerate components of the ground level and the level 3K′8 indicate a small mixing of the states ΨγJ M with different M. With this fact some special features of the transitions between these two levels can be explained qualitatively.
F‐, FA‐ and Z1‐Center Calculations Using Approximate Pseudopotentials
Authors: Weber W. , Dick B. G.
Published: July 2007

The authors carried out variational calculations on F‐, FA‐, and Z1‐centers, using a technique which was proposed by Bartram, Stoneham, and Gash. To illustrate how the method works, ionization potentials of alkali atoms are calculated for different trial wave functions. Plausible criteria are used to limit the choice of wave functions in a manner which avoids the necessity of using experimentally determined parameters. The agreement with F‐, FA‐, and Z1‐data is good. For the Z1‐center, the experimentally favored so‐called model I is given further theoretical support. Moreover, there is found evidence for a possible displacement of the divalent cation impurity of the Z1‐complex.
The Spin‐Wave Dispersion Relations and the Spin‐Wave Contribution to the Specific Heat of Antiferromagnetic UO2
Authors: Cracknell A. P. , Joshua S. J.
Published: July 2007

We have used the recently measured spin‐wave dispersion relations of antiferromagnetic UO2 to calculate the spin‐wave contribution to the specific heat of this material as a function of temperature below 20 °K. The symmetries of the spin‐wave dispersion relations are also discussed.
Nonlinear Optical Effects in a System with Degenerate or Closely Spaced Levels in Solids
Authors: Kovarskii V. A. , Perlin E. Yu.
Published: July 2007

The influence of two external high‐frequency electric fields (one of them being the field of strong laser beam) on a three‐level system with doubly degenerated excited states is considered. The change of the refractive index and of the ground‐frequency light‐absorption coefficient in the presence of laser radiation are predicted.
The Elastic Behaviour of NiCo Alloys
Authors: Leamy H. J. , Warlimont H.
Published: July 2007

The adiabatic, elastic stiffnesses of five f.c.c. Ni—Co alloys in the range from 10 to 62% Co were determined by the ultrasonic pulse‐echo technique at temperatures between 77 and 300 °K. As Co is added to Ni the bulk modulus increases linearly while (C11 − C12)/2 and C44 decrease and increase, respectively. The alloy stiffnesses were extrapolated to 100% Co to yield the following estimates for the stiffnesses of f.c.c. Co at room temperature: B = 1.89, (C11 − C12)/2 = 0.38, C44 = 1.33 (dynes/cm2 × 1012). Debye temperatures calculated from the extrapolated 0 °K stiffnesses indicate that the high temperature instability of h.c.p. Co is due to the more favorable vibrational entropy of f.c.c. structure.
Commutation Effect in Bismuth Type Semimetals
Authors: Bivol V. G. , Bodiul P. P. , Fedorko A. S. , Gitsu D. V.
Published: July 2007

The dependence of the Nernst‐Ettingshausen longitudinal effect on the direction of the magnetic field for the case of semimetals is studied theoretically and experimentally. A quite unique correspondence is found between the anisotropy of the effect and the band structure near the Fermi level. It is shown that the commutation effect which determines the dependence of the magneto‐thermo‐e.m.f. magnitude on the direction of the induction vector, permits to judge about the number and localization of band extrema in the k‐space. This is an effective way for studying band structures of bismuth and its alloys at high temperatures.
On Sensitizing Recombination Centres in GaSe Single Crystals
Authors: Abdullaev G. B. , Kh. Alieva M. , Belenkii G. L. , Mamedova A. Z.
Published: July 2007

An investigation is made of the stationary photoconductivity and its kinetic, the thermally stimulated conductivity, and the mobility of current carriers of tin‐doped p‐GaSe single crystals. It is shown experimentally that the recombination in such crystals is controlled by two types of recombination centres: one of them being “slow” (r), another “fast” (s). The principal parameters of “slow” recombination centres (r), thermal (E = 0.58 eV) and optical (E = 0.78 eV) energetic depth from C‐band, electron (Sn r = 5 × 10−14 cm2) and hole (Sp r = 3 × 10−20 cm2) capture cross‐sections, are measured. The concentration is found to be equal to Nr = 3 × 1014 cm−3. It is shown that the r‐centre is a single charged donor which may be due to substituting Ga atoms by Sn atoms in the GaSe lattice.
Galvanomagnetic Effects in Tellurium in Magnetic Fields up to 160 kG at Temperatures between 150 and 350 °K
Authors: Zimmermann W.
Published: July 2007

All components of the Hall effect and the magnetoresistance were measured in magnetic fields up to 160 kG at temperatures between 150 and 350 °K. The experimental results are interpreted by a six‐ellipsoid model for the valence band maxima. The ellipsoids are centered on the mirror planes of the reciprocal lattice. It is assumed that the collision time depends on energy only and that scattering takes place mainly on acoustical phonons. Only four of the twelve measured values are used to determine free parameters, the others to test the model. The hole mobilities perpendicular to the direction of the c‐axis and parallel to it are at 200 °K μ⟂ = 926 cm2 V−1s−1 and μ⟂ = 1755 cm2 V−1s−1. Results in the intrinsic range are reported.
Analysis of Defect Annealing in Monocrystalline Gold Foils after Gold Ion Irradiation
Authors: Wittmaack K.
Published: July 2007

Monocrystalline gold foils were irradiated at −196 °C with gold ions parallel to [101] or at random incidence. Defect production and subsequent isochronal recovery between −180 and 40 °C were examined by means of the electrical resistance for energies from 5 to 30 keV and doses from 5 × 1012 to 5 × 1015 ions/cm2. The annealing spectra are characterized by an intense dose‐dependent peak between −40 and −25 °C which is interpreted as being due to the recombination of freely migrating interstitials (E = (0.77 ± 0.07) eV) with vacancies. After high‐dose preirradiation and subsequent annealing the recovery in the dominant peak is reduced in favour of a new peak appearing between 0 and 40 °C. This is explained in terms of a migration of vacancies to defect clusters.
Sur le modèle de l'électron collectif de Stoner
Authors: Munschy G.
Published: July 2007

Dans l'approximation de Hartree‐Fock, il s'ajoute à la somme des énergies à une particule une énergie d'interaction électrostatique qui leur reste irréductible. En attribuant à celle‐ci la signification d'une moyenne statistique dans le cadre du modèle de ferromagnétisme de l'électron collectif, l'auteur aboutit à une condition d'équilibre statistique différente de celle de Stoner. Elle permet d'expliquer pourquoi les courbes d'aimantation calculées décroissaient trop vite et laisse prévoir aussi un comportement plus correct de la chaleur spécifique au voisinage du point de Curie.
Acoustoelectric Phenomena in Piezoelectric Semiconductors
Authors: Quentin G. , Thuillier J. M.
Published: July 2007

Current saturation and growth of stationary domains of high electric field are observed for many piezoelectric semiconductors. It is shown that such phenomena may be explained when a constant‐current pulse is applied to the sample. To study the steady state we include in the dc current the acoustoelectric term. With some simplifying assumptions, a simple theoretical calculation of the current—voltage characteristic and of the electric field repartition is given. A comparison is made with experimental results.
Ferroelectric and Antiferroelectric Symmetry Groups
Authors: Schelkens R.
Published: July 2007

The theory of the color or Shubnikov groups can be used to work out a difference between those groups associated with antiferroelectric and those associated with ferroelectric structures. A comparison with the magnetic symmetry groups shows that a symmetry group for a ferroelectric structure is, in general, different from a symmetry group for a ferromagnetic structure, having the same point group. These general results are applied to the study of a ferroelectric crystal, and, in particular the substance barium titanate.
Electronic Properties of Tetracyanoquinodimethane (TCNQ) Salts: Hall Effect in Crystals of the Triethylammonium (TCNQ)2 Complex
Authors: Farges J.‐p. , Brau A. , Vasilescu D. , Dupuis P. , Néel J.
Published: July 2007

A report is given of a successful measurement of the Hall effect in single crystals of the organic salt triethylammonium (TCNQ)2 at room temperature. A Hall mobility of the order of 0.6 cm2/Vs was found, the sign of the Hall constant being that appropriate for hole carriers. A study of the thermoelectric power sign was in agreement with the existence of holes. Study of the temperature dependence of the conductance indicated that some electrically active, gaseous impurities, which were believed to act as acceptors, were present in the samples. An interpretation of the experimental results is presented, including a discussion of the effect of the impurities on the electronic properties of the material. Some indications about the conduction process are suggested on the basis of a two‐band model.