bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and Electrical Properties of Solid Polymeric Carbon Disulphide
Authors: Chan W. S. , Jonscher A. K.
Published: July 2007

It is known that liquid CS2 when subjected to high pressure forms a stable solid polymer. Our studies revealed the existence of two distinct forms designated here A and B. Chemical evidence suggests that type A has the composition CS2 and contains no free sulphur, while type B does contain free sulphur and may be a sub‐sulphide. Infrared structural studies suggest that type A has a highly conjugated polymeric chain structure. X‐ray evidence suggests absence of long range order in both the A and B materials. The dc resistivity of type A is about 1013 Ωcm at 300 °K with an activation energy of 0.7 eV and that of type B is about 103 Ωcm with about 0.02 eV activation energy. The resistivity of both is strongly pressure dependent. Both types show strong frequency dependence of conductivity and permittivity with a region of σ ∼ f2 at high frequencies and saturating at 109 and 1010 Hz, respectively. Although it is impossible to prove that the observed ac data are not related to some form of Maxwell‐Wagner mechanism, it is pointed out that, at least in the case of the A material, the pressure, frequency, and temperature dependences of resistivity are more likely to be associated with two processes in which partially localized electrons hop within chains at high frequencies and between chains at lower frequencies.
Decoration of Strain Bands with F‐Centres in Potassium Chloride Crystals Deformed by Indentation
Authors: Damm J. Z. , Suszyńska M.
Published: July 2007

It is shown that the strain bands introduced into potassium chloride crystals by an indentor can be decorated with F‐centres in a simple procedure involving coloration by ionizing radiation and optical bleaching. The method reveals the existence of strain bands distributed along 〈110〉, 〈111〉, and 〈120〉 directions. On assuming that the macroscopic accumulations of vacancies responsible for the above effect are due to dislocations intersecting each other the formation of 〈120〉 bands necessitates the operation of {112} 〈110〉 or {122} 〈110〉 glide systems in which the screw dislocations are moving.
Investigations of Photoelectric Phenomena on p‐type Germanium with Dislocations
Authors: Jastrzębska M. , Figielski T.
Published: July 2007

Steady state and transient photoconductivity are investigated in plastically bent p‐type Ge. At low temperatures a trapping effect is observed. All characteristics of photoconductivity are qualitatively the same as for plastically deformed n‐type Ge in which recombination occurs through dislocations. The experimental results are explained on the basis of a barrier model of recombination at dislocations assuming that in p‐type Ge a dislocation which gives up the unpaired electrons to the valence band becomes positively charged. It is found (from experiment) that the dislocation donor level lies (0.28 ± 0.02) eV above the top of the valence band at 0 °K. The comparison with previous results obtained for n‐type Ge shows that the location of the donor as well as of the acceptor dislocation level is approximately the same in the energy gap. This result is consistent with the assumption that the states connected with the broken bonds at dislocation form an one‐dimensional energy band.
Strain Aging of Niobium in the Temperature Range 100 to 200 °C
Authors: Soo P.
Published: July 2007

Strain aging experiments have been conducted on polycrystalline niobium, containing approximately 100 ppm by weight of interstitial impurities. For aging temperatures in the so‐called stage III recovery region, which lies between 100 to 200 °C, recovery occurs in two separate and independent substages. The first substage is thought to be caused by the detrapping of self‐interstitials which are then able to migrate through the lattice and form new defect configurations. The second substage is probably connected with the migration of oxygen interstitials. The study indicates that the pinning of dislocations may also occur during the recovery and, under suitable conditions, dislocations may be successively pinned by self‐interstitials, oxygen interstitials, and carbon (or nitrogen) interstitials.
Electron and Neutron Damage in MgF2 Crystals
Authors: Facey O. E. , Lewis D. L. , Sibley W. A.
Published: July 2007

A comparison of electron‐ and neutron‐radiation damage in MgF2 single crystals has been made by studying changes in the optical absorption. It is found that reactor irradiation introduces many more cluster centers than does electron irradiation. Annealing studies show that above 700 °K F‐centers are apparently mobile and aggregate to form M‐centers. Zero phonon and phonon‐assisted lines are observed at 382.6, 384.5, 385.7, and 387.3 nm and have been shown to be associated with the broad absorption band at 370 nm which is due to M‐centers.
X‐Ray Diffraction Topography of Zinc Single Crystals
Authors: Nanev Chr. , Wilkens M.
Published: July 2007

Crystal imperfections in zinc single crystals were studied by X‐ray topography. The zinc single crystals were obtained in a glass ampule from a molten droplet which, after solidification, acted as a nucleus for further growth from the vapour phase. The crystals adhered strongly to the glass support. The X‐ray topographs give informations on the modes of plastic deformation, which occurred in the crystals during cooling. The existence of dislocations with Burgers vectors of type 1/3 〈1123〉 is demonstrated. This agrees well with the observed whisker growth in these directions. Some other phenomena connected with the crystal growth are also discussed.
Non‐Equilibrium Surface Space Charge in Semiconductors for Arbitrary Ionization Degree of Impurities
Authors: Dmitruk N. L.
Published: July 2007

The theory of the surface space charge region has been generalized to the case of non‐equilibrium conditions and arbitrary occupation of local centres within the band gap. The contribution of different local levels to the non‐equilibrium surface charge has been analysed in detail. Non‐equilibrium surface effects (capacitance, field‐effect, barrier photovoltage) are calculated for the model considered which is often realized at low temperatures and in broad band gap semiconductors (GaAs, CdS etc.).
High Temperature Expansions of Spin Correlation Functions for Ising and Heisenberg Ferromagnets
Authors: Binder K.
Published: July 2007

Linked cluster expansions are given for the static spin pair correlation functions in the case of Ising and Heisenberg interactions. Formulae valid for general values S of the spin are derived including terms of fifth order in 1/(kT). These expansions are discussed numerically in the temperature region Tc/T ≦ 1/2 for the simple cubic, the body‐centered cubic and the face‐centered cubic lattice assuming interactions between nearest neighbours only. A comparison with the usual Ornstein‐Zernike treatments shows considerable deviations due to the anisotropy of the correlations. This anisotropy can be neglected only in the immediate neighbourhood of the critical temperature Tc.
Rare Gas Diffusion in Alkaline‐Earth Fluorides (Kr, Xe in SrF2, BaF2)
Authors: Felix F. W. , Lagerwall S. Y. T.
Published: July 2007

The diffusion of Kr and Xe in SrF2 and BaF2 has been studied after reactor neutron irradiation using both pure single crystals and single crystals doped with uranium. The activation energies for migration of Kr and Xe in SrF2 are 1.2 and 3.7 eV, in BaF2 1.5 and 3.5 eV, respectively. The results are discussed and compared with results on CaF2.
Anisotropic Spin–Orbit Coupling for Cr3+ in ZnWO4
Authors: Hagston W. E.
Published: July 2007

The anisotropic orbital effects produced by admixture of ligand wave‐functions into 3d‐orbitals is shown to account for the apparent incompatibility of the results of optical and e.p.r. results for Cr3+ in ZnWO4.
The Effective Field and the Differential Susceptibility in Ferromagnetic Films
Authors: Hoffmann H.
Published: July 2007

A theory of the differential susceptibility is given for two‐dimensional ferromagnetic samples. The susceptibility depends on the intrinsic demagnetizing field which is caused by the magnetization inhomogeneities. The susceptibility is related to the mean “effective field” as well as to the magnetization fluctuation. Its measurement can be used to determine quantitatively these properties which are related to the structure constant, S. The latter results from the inhomogeneity of the anisotropy.
On Space Group Selection Rules
Authors: Streitwolf H. W.
Published: July 2007

Proceeding from full group considerations a general derivation of space group selection rules is given which leads to simple subgroup formulae. The matrix elements considered may be subject to additional symmetry conditions or not. The results are applied to symmetry properties of the energy band structure.
On the Mathematical Description of Electrical Processes in Semiconductors. II. Phase Space Analysis in Subspaces of Dimension Three
Authors: Oberländer S.
Published: July 2007

In Part I of this paper classes of systems of solutions without approximation, so‐called N‐dimensional systems of solutions, have been given for N < 3 for the system of differential equations consisting of the continuity equations with a recombination law based upon the law of mass action, the common current equations, and Poisson's equation. In the present Part II systems of solutions for N = 3 are given. Applications to stationary problems of transport of non‐equilibrium carriers in semiconductors are discussed. Especially an interesting example with a non‐monotonous hole concentration in a semi‐infinite homogeneous semiconductor is treated. An approximation method for three‐dimensional systems of solutions is shown for the example of the so‐called anti‐neutrality approximation.
Ionic Conductivity of Crystalline CsBr
Authors: Chadwick A. V. , McNicol B. D. , Allnatt A. R.
Published: July 2007

The electrical conductivity of pure CsBr was measured between 295 and 895°K and the results analysed by least squares. Schottky disorder provides an adequate description of the results for the intrinsic conductivity except at the highest temperatures. The predicted diffusion coefficients are compared with the experimental values of Lynch [1].
Point de Curie de KDP avec et sans effet tunnel
Authors: Villain J. , Aubry S.
Published: July 2007

Nous étudions la thermodynamique de KDP en ne considérant que les interactions entre les spins fictifs associés aux protons premiers voisins dans des modèls plans et spatiaux. On montre d'abord qu'on découple complètement le mouvement des spins fictifs du mouvement des ions en définissant une nouvelle énergie d'interaction entre les premiers et en renormalisant les seconds. On étudie ensuite l'effet tunnel entre protons formant un cycle fermé, en regardant successivement son influence sur les états à une et deux excitations élémentaires. Ceci permet de penser qu'une transition du 2ème ordre n'est pas exclue. Nous notons enfin que ce modèle conduit à un mode mou correspondant à une diffusion de spins fictifs et non à un phonon optique.
X‐Ray Diffraction by a Crystal Containing a Translation Fault
Authors: Bonse U. , Hart M.
Published: July 2007

We consider the diffraction of X‐rays by a bicrystal consisting of a thick part and a thin part separated by a rigid body translation. Both parts have identical lattice parameters. This simple model and the plane‐wave diffraction theory developed herein describe very well the contrast and geometry of the fringes obtained in X‐ray diffraction topographs of some silicon crystals bombarded by monoenergetic ions.
Anisotropic Penetration of Positrons in Monocrystalline RbBr
Authors: Behnisch R. , Bell F. , Sizmann R.
Published: July 2007

An investigation was made of the dependence of K‐line‐X‐ray yield by positrons with an energy spectrum from 120 to 480 keV (average energy 220 keV) on the angle between the positron beam (divergence ± 0.6°) and 〈100〉 of a RbBr single crystal. There is a nearly 90% reduction of the yield with a HWHM of nearly 2° in the case of bombarding parallel to 〈100〉. In particular, a comparison is given between this positron effect and the behaviour of X‐ray excitation by channelled protons.
On the Dynamical Behaviour of Excitons in CdS Single Crystals. II. Correlation between Intrinsic Excitonic Absorption and Photoconductivity
Authors: Voigt J. , Ost E.
Published: July 2007

An investigation is made of the excitation spectra of photoconductivity of CdS single crystals in the region of the fundamental absorption edge from 77°K to room temperature. The results are compared with those of excitonic absorption measurements. On the basis of conclusions about the dynamical behaviour of excitons, equally drawn from absorption, emission, and photoconductivity measurements, a model is proposed of the photoconductivity in the region of exciton transitions, which explains the correlation between the exciton absorption and photoconductivity. This model involves that the diffusion length of the excitons don't exceed that of the ambipolar electron–hole pair diffusion.
Unstable Directions of Shockley Partial Dislocations
Authors: Clarebrough L. M. , Head A. K.
Published: July 2007

Sharp bends are observed in Shockley partial dislocations in a Cu + 15.6 at% Al alloy. Computations using the method of Head [1] suggest that these bends arise from unstable directions for Shockley partial dislocations in elastically anisotropic f.c.c. crystals.
Interband Faraday Rotation in Germanium
Authors: Byszewski P. , Kołodziejczak J.
Published: July 2007

A theoretical analysis is made of the interband Faraday rotation in Germanium. Using an electronic computer the calculations of this effects are performed including the real structure of the energy bands in germanium. The results are compared to our experiments and quite good agreement is obtained.
Self‐Diffusion Measurements in Gold Single Crystals between 286 and 412°C
Authors: Rupp W. , Ermert U. , Sizmann R.
Published: July 2007

By means of an electrochemical peeling technique the self‐diffusion coefficients in 99.99% gold single crystals were determined at 285.9, 299.6, 321.0, 349.7, and 411.7°C. Assuming a linear dependence of log D on 1/T the result is in this temperature range . There is no evidence for short circuiting interferences in the range of the evaluated diffusion profile depths of < 3000 Å.
Electron–Phonon Interaction of Crystal Electrons in High Electric Fields
Authors: Hacker K.
Published: July 2007

The electron–phonon interaction in high electric fields is investigated. The calculation of the electron lifetime shows that Wannier–Stark levels may exist. It is furthermore shown that there is a field dependent phonon production. It can possibly be measured by Raman scattering and serve to demonstrate the existence of the Wannier–Stark levels.
Calcul des courbes de dispersion de phonons des oxydes de magnesium, de calcium, et de strontium
Authors: Mon J. P.
Published: July 2007

Nous avons calculé les courbes de dispersion de phonons de MgO, CaO et SrO en utantilis le “breathing‐shell‐Model”. La comparasion des courbes obtenues montre qu'il se produit un plus grand nombre de croisements de branches dans MgO que dans CaO ou SrO, ce qui doit se traduire par la présence d'un plus grand nombre de points critiques singuliers dans le spectre de MgO.
Spontaneous Magnetization of Iron‐Rich Iron–Germanium and Iron–Silicon Alloys at 298°K
Authors: Arajs S.
Published: July 2007

The mass magnetization of 19 iron‐rich binary iron alloys containing different amounts of silicon and germanium has been studied as a function of magnetic field at 298°K using a vibrating sample magnetometer. The mass spontaneous magnetizations have been determined from these data by means of the Belov‐Arrott‐Kouvel method. The curve of the spontaneous magnetization versus composition for iron–silicon alloys lies below the simple dilution curve while that for the iron–germanium system lies above it. The results of this investigation are compared with those of the previous studies on the saturation magnetization of the above‐mentioned solid solutions.
Long Wavelength Optical Lattice Vibration of Selenium–Tellurium Mixed Crystals
Authors: Geick R. , Hassler J.
Published: July 2007

The reflectivity of selenium–tellurium mixed crystals is studied in the far infrared spectral region. The eigenfrequencies, oscillator strengths etc. of the strongly infrared active lattice vibrations are deduced from the reflection spectra by means of a classical oscillator model. The two modes which give rise to a pronounced reststrahlen band show “one mode behaviour”. Moreover, an impurity mode is observed existing in the mixed crystals only. By means of a random‐element‐isodisplacement model (REI) adapted to the trigonal structure of these crystals, the eigenfrequencies and oscillator strengths are calculated as a function of composition and, at least, qualitative agreement with the experimental data and also some insight into the nature of the impurity mode is achieved.
Residual Resistivities of Binary Iron Alloys
Authors: Arajs S. , Schwerer F. C. , Fisher R. M.
Published: July 2007

Electrical resistivities of iron‐rich binary alloys containing seventeen different solutes have been measured at 4.2°K and the resistivity increment per atom percent solute tabulated. Apparent departures from Matthiessen's rule at room temperature have also been determined. The non‐transition elements cause considerably larger increases in the resistivity at 4.2°K and smaller deviations from Matthiessen's rule than do the transition elements. Cobalt, nickel, and tin are exceptions to this classification. This behavior is discussed in terms of electron screening and resonating s‐ and p‐orbitals in the electron bands of the iron matrix. A correlation of the observations with solute size and valence effects is also presented.
Mössbauer Study of Oxidized Iron Silicate Minerals
Authors: Häggström L. , Wäppling R. , Annersten H.
Published: July 2007

Biotites and Ca‐amphiboles have been studied. Certain changes in composition of the Ca‐amphiboles could be correlated to changes in the Mössbauer parameters. The ordering of iron in biotites is discussed. The ferrous‐ferric iron ratio could be determined in all the silicates.
The Contribution of Three‐Body Overlap Forces to the Dynamical Matrix of Alkali Halides
Authors: Verma M. P. , Singh R. K.
Published: July 2007

The so‐called S2‐approximation in the Heitler‐London theory of ionic crystals as developed by Löwdin gives rise to a three‐body contribution in the cohesive energy. The present paper describes a method of deriving the coupling coefficients for the three‐body potential from expressions given by Lundqvist. These coupling coefficients involve certain lattice sums which can be evaluated in terms of incomplete gamma functions by a method due to Born and Bradburn. A new lattice dynamical model of ionic solids has been suggested which is obtained by injecting the three‐body coupling coefficients into the shell model of Woods et al. in a way that preserves symmetry in the wave vector space. Preliminary calculations show that this model can prove superior to other current models.
Magnetisierung in der Umgebung unmagnetischer Einschlüsse in Ferromagnetika. III. Wechselwirkung eines kugelförmigen unmagnetischen Einschlusses mit einer Blochwand
Authors: Schröder K.
Published: July 2007

Die Wechselwirkungsenergie eines kugelförmigen Hohlraums mit einer Blochwand besteht aus einem Fremdkörper‐ und einem Streufeldanteil. Der Streufeldanteil wird ohne Berücksichtigung der Auslenkung der Magnetisierung durch innere Felder berechnet. Gegenüber früheren Abschätzungen ergeben sich erhebliche Abweichungen. Das Ergebnis wird auf die Theorie der Koerzitivfeldstärke angewandt.
Electron Absorption in UO2
Authors: Blank H.
Published: July 2007

Specimens of UO2 and U4O9 have been observed by transmission electron microscopy at electron energies of 100, 500, and 1000 kV. Approximate values of the absorption parameters μ0 and tg/τg for UO2 have been deduced from bright field pictures of crystal wedges in two beam cases with s > 0. The results are compared with data of other substances given in the literature. The stability of the oxygen sublattice in UO2 and U4O9 with respect to 1 MeV electrons is discussed.
Current Instability in Germanium due to Excitation of the Recombination Waves
Authors: Karpova I. V. , Kalashnikov S. G. , Konstantinov O. V. , Perel V. I. , Tsarenkov G. V.
Published: July 2007

Spontaneous current oscillations were observed in n‐type germanium containing manganese. The latter was compensated with antimony so that the upper level Ec −0.37 eV was only partly filled with electrons. The spontaneous current oscillations were observed at room temperature or near it, and for an electric field strength of several tenths of V/cm. The oscillation frequency was in the range of 0.1 to 1 MHz. The relative amplitude of the current oscillations reached 50 to 90%. As was shown by the probe measurements, the instability was a bulk phenomenon and contact effects were not essential. It was proved that this phenomenon might be interpreted in terms of excitation of the recombination waves predicted in [1].
Anisotropy of the Hall Effect of n‐Ge in Strong Non‐Quantizing Magnetic Fields
Authors: Babich V. M. , Baranskii P. I. , Dakhovskii I. V. , Samoilovich A. G.
Published: July 2007

The magnetic field dependence of the Hall coefficient, RH = ‖(H), has been investigated theoretically and experimentally in n‐Ge at 77°K on samples with different orientations (H ‖ [100] and H ‖ [110], I ‖ [110] in both cases) within wide interval of concentration. Calculations of the RH = f(H) dependence were carried out on the basis of the anisotropic scattering theory up to H = 106 Oe and measurements were made in the whole interval of magnetic fields (H ≦ 105 Oe) up to quantizing. Attention is attracted to a necessity of refusal from formal application of H → ∞ for the analysis of the field dependence RH = f(H), since the Boltzmann equation validity has an upper limit of H‐values, corresponding to quantizing effects set up. Taking into account this circumstance in the concrete case of n‐Ge both the results of calculations and the experimental data lead to conclusions that a) throughout the interval of classically strong H (up to 105 Oe at 77°K) the Hall coefficient remains anisotropic; b) when the impurity scattering contribution increases, then beginning with some values of this contribution, the saturation of RH = f(H) throughout the whole classically strong field range cannot be achieved.
Fundamental Reflectivity Spectrum of CdxHg1−xTe Crystals from 1.5 to 4 eV
Authors: Gałązka R. R. , Kisiel A.
Published: July 2007

Reflectivity measurements of solid solutions of CdxHg1−xTe for x from 0.02 to 0.74 and for x = 0 and x = 1 have been performed in the range from 1.5 to 4 eV at the temperature of 315°K. Two maxima in the reflection spectrum were observed. They are interpreted as connected to the transitions E1 and E1 + Δ1 at the Λ‐point of the Brillouin zone. The values of E1, E1 + Δ1, and Δ1 are nonlinear functions of the composition x. The change of the peak position E1 with the composition between x = 0.00 and 0.10 is nonmonotonous. The reflection spectra for HgTe and CdTe are in a good agreement with previously reported ones.
Wechselwirkungskräfte zwischen einer Flußlinie und einer parallelen Versetzung
Authors: Kammerer U.
Published: July 2007

Ausgehend von den in einer früheren Arbeit entwickelten Berechnungsmethoden für das auf dem Volumeffekt beruhende Eigenspannungsfeld einer isolierten geraden Flußlinie und für das auf dem ΔC‐Effekt beruhende Eigenspannungsfeld einer Flußlinie in der Nachbarschaft einer parallelen Versetzung, wird die Wechselwirkungskraft zwischen einer Flußlinie und einer parallelen Versetzung in Störungstheorie 1. Ordnung (entsprechend 1. Potenzen in der Änderung des spezifischen Volumens und der elastischen Konstanten innerhalb der supraleitenden Phase) berechnet. Für beliebigen Versetzungscharakter und beliebige Wahl der zwölf die Kopplung im elastisch isotropen Fall beschreibenden Materialkonstanten läßt sich aus dem mitgeteilten numerischen Ergebnissen für \documentclass{article}\pagestyle{empty}\begin{document}$\chi = 1/\sqrt 2 $\end{document}, 1, 2 und 5 der Kraftverlauf zwischen Flußlinie und paralleler Versetzung ermitteln.
Uniaxial Stress Effects on Parity‐forbidden Transitions in NaCl:Cu+ and KCl:Ag+
Authors: Dultz W.
Published: July 2007

The temperature dependence of the stress‐induced dichroism in the UV absorption bands of NaCl:Cu+ and KCl:Ag+ is investigated. The experiments are explained by a frequency splitting of the IR active resonance mode and an off‐centre displacement of the defect in the excited state. The value of the quadratic electron—lattice interaction is determined.
On the UV Absorption of Heavy Metal Ions in Alkali Halide Crystals I. Experimental Results
Authors: Fussgaenger K.
Published: July 2007

UV absorption spectra of Ag+, Cu+, and Tl+ centres in alkali halide crystals are measured between 5 and 300°K in order to determine the electronic fine structure of the bands as well as the magnitude and temperature dependence of the UV dipole strength. The structure and temperature dependence of the spectra are interpreted in terms of electron—phonon interaction and off‐centre effects.
Investigation of the Structure of Ferromagnetic Films by Means of the Differential Susceptibility
Authors: Kempter K. , Hoffmann H.
Published: July 2007

The differential susceptibility of thin polycrystalline iron–nickel‐films has been measured. From the results the structure constant, S, could be determined. The experiments gave the same field dependence for the susceptibility as was expected by former calculations. The values for S, evaluated from the experiment, can be explained quantitatively by the mean crystallite diameter, the magnetocrystalline anisotropy, the magnetostriction constants, and the intrinsic stresses, if one uses the Doyle‐Finnegan formula for the calculation. The measurements show quantitatively the existence of the intrinsic demagnetizing field, which has been predicted by micromagnetic calculations and which contributes to the whole effective field.
Charged 90° Walls in Iron platelets
Authors: Gemperle R. , Kaczér J.
Published: July 2007

Thin platelets of iron single‐crystals containing 90° Bloch walls charged by an application of an external field or mechanical stress have been investigated using the magnetic colloid technique. It is found that these walls are rotated in such a manner that their area increases thereby decreasing the charge density. In very thin platelets the area of the walls increases by more than one order of magnitude.
O− Centers as Strong Phonon Scatterers in KCl and KBr Crystals
Authors: Kurz G.
Published: July 2007

The thermal conductivity of pure and hydroxide doped KCl and KBr crystals and its change upon OH− dissociation was measured. The temperature range covered is 1.8 to 22°K. The dissociation of OH− ions into O− and U2 centers causes a marked reduction of the thermal conductivity curve below 10°K. The scattering cross section of the U2 centers is shown to be small, thus the strong phonon scattering can be attributed to the O− centers alone. The O− ion is suggested to occupy an off‐center equilibrium position in the anion vacancy, the accompanying tunnel splitting thus giving rise to a low lying resonance.
ESR of Ni2+ in AgCl and Isotope Effect in Crystal Field
Authors: Höhne M. , Stasiw M. , Watterich A.
Published: July 2007

ESR measurements are made on Ni‐doped AgCl at low temperatures. As in the case of AgBr:Ni, already investigated, a line with isotropic g‐value is found, due to isolated Ni2+. Moreover an angular dependent spectrum with nearly [100]‐axial symmetry is observed, which is attributed to complexes of Ni2+ with a silver vacancy. Contrary to the results on AgBr:Ni a structure of the anisotropic spectrum is observed in a small angular range, which may be explained only by the presence of very small orthorhombic perturbations. It is shown, that these orthorhombic perturbations of different quantities result from the variant distributions of both the isotopes 35Cl and 37Cl in the plane perpendicular to the axis of the centre.
Lineare Kontinuumstheorie bewegter Versetzungen
Authors: Stenzel G.
Published: July 2007

Mit einer mechanischen Lagrange‐Funktion wird eine Integralgleichung hergeleitet, die die Bewegung einer Versetzung in einem elastischen Kontinuum beschreibt. In der Näherung tiefer Frequenzen kann diese Gleichung in ein äquivalentes Variationsproblem umgewandelt werden, das nur die Koordinaten der Versetzung enthält. Dieser Ausdruck läßt sich als Lagrange‐Funktion eines verbesserten Saitenmodells deuten, in welchem auch die nichtlokale Wechselwirkung berücksichtigt ist.
ESR of Neutron‐Irradiated BaF2 Crystals
Authors: Kazumata Y.
Published: July 2007

Neutron‐irradiated BaF2 was studied by ESR. The thermal stability of the F‐centre formed by neutron‐irradiation was investigated. Three types of V‐centres (VK, VF, and V111) were also observed. The spin Hamiltonian parameters of the three V‐centres were calculated from experimental data and the thermal stability of the centres were studied by a pulse annealing method. A model of the new type of V‐centre (F2− molecule‐ion in [111] direction) is proposed.
A Calculation of the Wavefunction and Isotropic Hyperfine Structure Constants of the U2‐centre in NaCl and KCl
Authors: Sammel B.
Published: July 2007

The wavefunction of the U2‐centre is determined by a variational procedure taking into account the charge distribution of the nearest neighbour ions. All wavefunctions concerned are mutually orthogonalized using a combined Schmidt‐Löwdin procedure. The influence of the 2‐centre exchange integral and of a possible distortion of the crystal near the centre is discussed. The isotropic hyperfine and superhyperfine structure constants are calculated.
Effect of the Polariton–Phonon Coupling on the Spatial Dispersion
Authors: Hizhnyakov V. V.
Published: July 2007

A formula is obtained for the transverse dielectric constant ϵt(ω, k) in the region of exciton transition which appears to be correct for an arbitrary intensity of the polariton—phonon coupling. The renormalization of polaritons caused by this coupling and the influence of the renormalization on the damping constant of ϵt(ω, k) are examined.
Electrical Pinch in Intrinsic Elastically Bent Germanium
Authors: Boiko I. I. , Zhadko I. P. , Romanov V. A.
Published: July 2007

Theoretical and experimental investigations of the conductivity of elastically bent intrinsic Ge are performed. An high asymmetry of the current—voltage characteristic is predicted and observed in plates with a high velocity of surface recombination. It is connected with the deviation of the spatial distribution of carriers for two opposite directions of current, flowing through the crystal. It is shown that a negative differential resistance in thin crystals may arise at great electrical fields. Current oscillations connected with the Joule heating of the specimen are observed.
Zum Peierls‐Modell bewegter Versetzungen
Authors: Stenzel G.
Published: July 2007

Zur Beschreibung der Versetzungsbewegung unter dem Einfluß äußerer Kräfte wird ein leicht modifiziertes Peierls‐Modell vorgeschlagen. Die Bewegungsgleichungen lassen sich in ein Variationsproblem umformen. Es enthält nur die Relativverschiebungen der beiden atomistisch behandelten Gitterebenen.
Magnetic Domain Wall Motion at Low Temperatures
Authors: Bostanjoglo O. , Fichtner H.
Published: July 2007

The magnetic reversal in polycrystalline iron foils was investigated by means of Lorentz microscopy at 4 to 300 °K no usual Barkhausen jumps exist. The wall motion of cross‐tie walls consists of small‐size (55 to 3000 å) Bloch line jumps, formation of bordering domains of the order 1 × 1 μm2, and their reversal by rotation. Above a minimum field these processes proceed at constant field. This aftereffect in constant field is influenced by crystal defects.
On the Shift of the Reflectivity of Polarized Light with Applied Uniaxial stress in Silicon
Authors: Leonhardt H.
Published: July 2007

The shift of the reflectivity maximum of polarized light found in silicon at 3.4 eV with applied uniaxial strain in the [1, 0, 0] direction is described by a simple model within the framework of the pseudopotential method. The shift results mainly from contributions close to the centre of the Brillouin zone and is a consequence of the rapid decrease of the pseudopotential for large K‐values.
Interpretation of the Electric Field Effect on the Ground State Splitting of Mn++ Ions in NaCl
Authors: Dreybrodt W. , Silber D.
Published: July 2007

The cS5/2 ground state splitting of Mn++ centres with an associated nearest neighbour cation vacancy in NaCl is calculated from a point ion model of the centre by using various theoretically proposed mechanisms. It is shown that the main contribution to the ground state splitting parameters results from a relativistic effect. The electric field induced changes of the ground state splitting are calculated from this mechanism. There are two contributions: 1. The combined effect of the external field and internal odd fields. 2. The change of the internal even fields from field induced relaxations of the centre. The results agree in sign and order of magnitude with the experimental data.
Investigations on Evaporated Films of Bismuth Oxide II. Determination of Type of Conductivity and Photoconductivity Measurements on Doped and Undoped Layers
Authors: Gobrecht H. , Seeck S. , Bergt H. ‐E. , Märtens A. , Kossmann K.
Published: July 2007

The type of conductivity of pure Bi2O3 layers is determined by the change of conductivity under the influence of chemisorbed oxygen. The spectral photoconductive sensitivity is measured on undoped and doped Bi2O3 layers within the range of 0.8 to 3.5 eV. The time constant of the photoelectric effect of pure Bi2O3 layers can be reduced by photoadsorption of oxygen. A sulfur or selenium doping of the layers causes a shift of the wavelength limit towards the near infra‐red. The time constant is greatly reduced. The doped layers are suitable for vidicon use.
Positive and Negative Infrared Photoconductivity of CdS Single Crystals near the Double Injection Threshold
Authors: Vateva E.
Published: July 2007

An increase or a decrease of the dark conductivity of CdS is observed by irradiation with infrared light at threshold voltages of the appearance of negative resistance due to double carrier injection. The experimental results show that the positive as well as the negative infrared photoconductivity is due to release of holes of the slow recombination centres. For an explanation of the appearance and the sign of the observed photoconductivity a model is proposed which is fit to the peculiarities of CdS and the presence of injected electrons and holes.
A Modified Formulation of Lattice Dynamics
Authors: Achar B. N. , Barsch G. R.
Published: July 2007

A modified formulation of lattice dynamics based on two‐dimensional Fourier‐transforms of the coupling parameters is presented. This approach will be useful for the study of twodimensional defects, surfaces, and layer structures. Subsequent Fourier‐transform in the third dimension recovers the conventional formulation of lattice dynamics. The method is applied to the eigenfrequencies of rocksalt in the approximation of the point ion model and is shown to reproduce Kellermann's results.
Étude des propriétés électriques des structures AlAl2O3–métal
Authors: Barriac C. , Pinard P. , Davoine F.
Published: July 2007

L'interprétation théorique du phénomène de résistance négative présenté par des structures AlAl2O3–M, basée sur l'existence d'une charge d'espace ionique positive au voisinage de la cathode et l'émission, à partir de celle‐ci, d'un courant électronique par effet tunnel, permet de déterminer l'influence des divers facteurs et les variations du courant émis. Les résultats expérimentaux obtenus sont en parfait accord avec les prévisions théoriques, et prouvent qu'il est possible de caractériser la résistance négative par deux coefficients dépendant de la nature de l'oxyde et de celle de la contre‐électrode.
Experimental Evidence of Plane Wave Rocking Curve Oscillations
Authors: Lefeld‐Sosnowska M. , Malgrange C.
Published: July 2007

A double crystal spectrometer is used to obtain a nearly planar incident wave on a thin silicon crystal. A theoretical study of the experimental arrangement has been made and it is shown that the same oscillations should occur in the rocking curves as predicted by the dynamical theory for an incident plane wave. The oscillations have been observed using crystals of several thicknesses and several wavelengths. The position of the fringes are in very good agreement with theory and their contrast is quite good.
Slip line Studies of the Deformation of Copper–12 at% Aluminium Crystals in Stage I
Authors: Charsley P. , Desvaux M. P. E.
Published: July 2007

The deformation in tension during stage I, of Cu–12 at% Al crystals, has been studied by observing the development of slip lines with the use of a new replica technique. The deformation is macroscopically inhomogeneous and in the less deformed regions consists of clusters of lines which widen asymmetrically as deformation proceeds. It is suggested that cross‐slip does not play a significant part in the widening of the slip clusters. The variation with local strain of slip line growth and initiation has been investigated quantitatively.
The Influence of Heat Conductivities of He Baths on the Decay Functions In paramagnetic Relaxation
Authors: Kalbfleisch H.
Published: July 2007

The structure of the decay functions in paramagnetic relaxation is found to differ depending on whether they are measured in normalfluid or superfluid 4He. Therefore the concept of a phonon bottleneck is extended to the case of different heat conductivities of the cooling baths. The various measured decay functions can be explained in this way.
Paramagnetic Resonance of γ‐Irradiated N2H6SO4 and N2D6SO4 Single Crystals
Authors: Barbur I.
Published: July 2007

An ESR study was made of defects produced by γ‐irradiation in hydrazonium sulphate (N2H6SO4 and N2D6SO4). The analysis of the experimental data shows that N2H and N2D defects are formed. The mechanism of the appearance of these defects is a breakage of N–H and N–D bonds, respectively. Some remarks about the character of the singly occupied orbital are made.
On the Dependence of Photocurrents on the Excitation Strength
Authors: Stöckmann F.
Published: July 2007

Frequently the relation between the electron concentration n and the excitation density G in a photoconductor can be exactly or approximately described by a power law n ∼ Gv. General and clear conditions for the exponent v can be derived provided the recombination of free carriers runs mainly through one channel and in the neutrality condition one group of positive and one of negative charge carriers dominate. The method is described in detail for a general model and the results are discussed.
Solution of the Micromagnetic Equations of Superconductors
Authors: Kronmüller H. , Seeger A.
Published: July 2007

For the solution of the micromagnetic equations of superconductors a method is developed which allows the determination of the elastic stresses from a stress function tensor. It is shown that the elastic strains present in a superconductor have the following sources: 1. Spontaneous volume dilatations. 2. Dielastic effects. 3. Effects of the non‐linear elasticity theory. The interaction energy of the elastic strains of a superconductor with stress active lattice defects is determined. The general theory is applied to the discussion of the discussion of the elastic strains due to a planar S‐N‐wall.
Étude des lacunes dans le cadmium
Authors: Hillairet J. , Martinet B. , Schumacher D.
Published: July 2007

On étudie les lacunes thermiques à l'équilibre dans le cadmium au moyen de mesures de résistance électrique sur un échantillon polycristallin. L'augmentation de résistivité déterminée par rapport à l'extrapolation de la loi de variation de la résistivité à basse température conduit à une énergie de formation comprise entre 0,36 et 0,39 eV, et à une concentration d'équilibre au point de fusion de l'ordre de 3 × 10−3. Ces valeurs sont discutées et comparées, en l'absence de résultats de trempe, aux valeurs correspondantes obtenues par d'autres méthodes d'équilibre.
Electron Paramagnetic Resonance of Mn2+ at the Three Sites of Yttrium Aluminium Garnet
Authors: Hodges J. A. , Dormann J. L. , Makram H.
Published: July 2007

Electron paramagnetic resonance measurements have been made at 17.4 GHz at room and liquid helium temperatures of divalent manganese substituted into the three sites of yttrium aluminium garnet (YAlG). The relative intensities of the tetrahedral, octahedral, and dodecahedral spectra were respectively 3:2:30. Data at liquid helium temperatures in units of 10−4 cm−1 are for tetrahedral site: gz = 2.001, B = −170.6, B = 0.062, Az = −69.1; for octahedral site: gz = 2.001, B = −139.3, B = −0.088, Az = −82.3; for dodecahedral site: gz = gy = 2.001, B = −102.2, B22 = −167.8, B = −0.006, (B + B) = 0.11, Az = −85.1, Ay = −85.9. The second order zero field splittings were compared to the various existing crystal field models using the local crystalline fields at the three sites obtained by summing up the contributions of the point monopoles to convergence. Poor agreement was obtained.
Crystal‐Field Splitting of Levels and X‐Ray Spectra of Transition Metal Monoxides
Authors: Menshikov A. Z. , Brytov I. A. , Kurmaev E. Z.
Published: July 2007

The crystal‐field splitting of the ground state of a transition metal ion in transition metal monoxides is calculated for the case of cubic symmetry. An investigation is made of the X‐ray emission bands of metal and oxygen ions in the monoxides. The observed and calculated splittings of the levels are in good agreement.
Rotational Structure of Vibronic Absorption and Luminescence Spectra of NO Impurity Molecules in Potassium Halide Crystals
Authors: Avarmaa R. , Rebane L.
Published: July 2007

The rotational structure of the pure‐electronic (near 4000 Å) and other zero‐phonon lines associated with v1 and v2 modes is observed in the vibronic spectra of NO ions in KCl and KBr crystals at liquid helium temperature. Three components in the (0, 0) group of the absorption spectrum of KCl‐NO have the intervals 7 and 10 cm−1, the resonant (0, 0) group in emission consists of two components. In the KBr host some components show additional splitting. The rotation of NO in KCl about the top axis a is found to be somewhat hindered in the ground state and nearly free in the excited electronic state. Some emission occurs from thermal nonequilibrium rotational states which gives evidence for rather slow rotation‐phonon relaxation. Several groups of the absorption spectra exhibit rotational perturbations which are suggested to be caused by Coriolis interaction between the vibrations v′1(A1) and v′3(B1).
Crystal Field The ory and Optical Absorption of Cobalt and Nickel Boracites
Authors: Pisarev R. V. , Druzhinin V. V. , Prochorova S. D. , Nesterova N. X. , Andreeva G. T.
Published: July 2007

In the boracite structure the local symmetry of paramagnetic ions is characterized by a strong tetragonal distortion of the cubic component of the crystal field caused by spatial and charge non‐equivalency of nearest neighbours of 3d‐ions and also by the lack of an inversion centre. The crystal field operator for ferroelectric and paraelectric phases has been calculated using the point charge model. The expressions connecting crystal field parameters and ion displacements have been derived. The optical absorption of boracites Me3B7O13X where Me = Co, Ni and X = Cl, Br, I has been studied in the spectral range 0.25 to 25 μm from 77 to 700 °K. The absorption spectra are much more complicated than the known spectra of Co2+ and Ni2+ in octahedral cubic crystal field. It was found that the intensity of many transitions in boracites drops when the temperature is raised. The most rapid decrease was observed in the vicinity of the ferroelectric Curie temperature Tc. Such unusual behaviour was assigned to the change of the crystal field odd component connected with unequivalent displacements of halogen ions relatively to the 3d‐paramagnetic ion. The temperature dependence of the tetragonal crystal field parameters Ds and Dt was studied in cobalt boracites. An increase of Ds and decrease of the Dt was observed at Tc in accordance with the theoretical predictions.
The Exciton Binding Energy of III–V Semiconductor Compounds
Authors: Kübler J. K.
Published: July 2007

The experimental data on band structure parameters, external dielectric constants, and exciton binding energies of the III–V semiconductors have been correlated and the deviations of the experimental exciton binding energies from the values predicted by a hydrogenic formula involving the external dielectric constant have been explained. It is shown that the external dielectric constant must be multiplied by an enhancement factor to obtain the dielectric screening constant for the electron‐hole interaction if the energy gaps are small. This enhancement factor is explained theoretically and is obtained explicitely as a function of the gap from the experimental data for the III–V semiconductors.
On the Magnetic Relaxation of Iron‐Rich Ferrites in the Temperature Range 300 to 450 °C
Authors: Maxim Gh.
Published: July 2007

Using the induced anisotropy, the magnetic relaxation effect of MexFe3−xO4+γ ferrites is investigated in the temperature region 300 to 450 °C. It is shown that this effect appears only in the Mn‐Fe and Zn‐Fe ferrites. At small concentrations (x < 0.1) the induced anisotropy is proportional to the concentration of Mn and Zn ions, respectively. It is presumed that this relaxation effect is caused by the directional ordering of some configurations of Mn and Zn ions, respectively, on the tetrahedral sites of the spinel lattice. The ordering is produced by cation diffusion via vacancies.
Evidence for the Coulomb Interaction of Be Valence Electrons by Compton Scattering Cross‐Section Measurements
Authors: Schülke W. , Berg U. , Brümmer O.
Published: July 2007

The effect of Coulomb interaction on the Compton scattering cross‐section (CSCS) of a free electron gas has been calculated theoretically by Ohmura and Matsudaira within the framework of the random phase approximation (RPA). These calculations have shown that plasmon emission during the scattering process diminishes the CSCS against its value within the Hartree‐Fock approximation, which neglects the Coulomb interaction. A method is presented to measure relative values of the CSCS of metal valence electrons by separating the core electron part from the valence electron part of the Compton line profile. The relative values of the CSCS have been brought onto an absolute scale by means of a sum rule for the imaginary part of the dielectric constant given by Noziére and Pines. The measured values of the CSCS of Be valence electrons are in good agreement with the RPA calculations of Ohmura and Matsudaira.
Déformations de cohérence d'un précipité quadratique
Authors: Faivre G.
Published: July 2007

On établit les expressions exactes du champ élastique provenant d'un précipité parfaitement cohérent avec la matrice, en forme de parallélépipède rectangle, en supposant le corps élastiquement homogéne et isotrope. On discute la validité de quelques approximations usuelles. Les déformations calculées sont comparées aux résultats de mesures par rayons X sur des précipités d'un alliage Fe–Ni–Nb. On examine de plus l'influence de la forme du précipité sur l'énergie élastique de cohérence.