bluuebunny/crossref_metadata_2025 huggingface dataset:
Migration of Ni2+ Ions and Ferrimagnetic Resonance in NiFe2O4 Crystals
Authors: Krishnan R.
Published: July 2007

In the X‐band ferrimagnetic resonance has been observed on NiFe2O4 crystals of varying degrees of cation disorder in the lattice between 4.2 to 500 °K. This disorder was created by heating the crystals to temperatures in the range 650 to 1140 °C and then subsequently quenching them in water. This heat treatment results in an increase of the A‐site Ni2+ ions concentration. The resonance properties are shown to be very sensitive to this cation disorder. The per‐ion contribution of the A‐site Ni2+ ions to the anisotropy K1 is measured to be + 1.4 × 10−15 and + 6.6 × 10−15 erg cm−3 at 293 and 77 °K. This contribution is seen to be of the same order of magnitude as that from Co2+ ions in Fe3O4. These ions also contribute to K2. The linewidth contribution at 293 °K is of the order of 200 Oe per % of A‐site Ni2+ ions. ΔH and the g‐factor of the quenched samples show an increase at lower temperatures, a behaviour which is totally absent for the slowly cooled ones. The change in the anisotropy (ΔK1/M) brought about by quenching has been used to study the Ni2+ ion migration to the A‐sites. This process is found to consist of two different ones, one with an activation energy of 0.6 eV in the range 800 to 1000 °C and the other with 0.24 eV in the range 1000 to 1100 °C. Finally quenching from 1140 °C is shown to introduce defects in the crystal.
Light Absorption by Impurity Centres and Urbach's Rule
Authors: Lubchenko A. F. , Zushman I. M.
Published: July 2007

An investigation is made of the shape of the absorption spectra due to impurity centres in a solid, taking into account the variation of its quasi‐elastic constants during phototransitions in impurity centres. An analytical expression for the long‐wavelength edge of the absorption curve, similar to the well‐known Urbach rule, is obtained.
Distortion of an FeSi Single Crystal and X‐Ray Topographic Contrast Due to a 90° Ferromagnetic Domain Wall
Authors: Polcarová M. , Gemperlová J.
Published: July 2007

A crystal lattice distortion due to a plane‐shaped 90° wall between ferromagnetic domains has been found. This distortion is characterized by a matrix ΔP from which the parameter δ(Δθ), corresponding to the variation of the departure from the Bragg condition of the incident X‐ray wave, can easily be calculated for any diffracting plane. The matrix ΔP has been calculated for the (110) and (111) walls, but the calculation can be performed for any magnetically allowed 90° wall. Some qualitative conclusions about the contrast on a 90° wall have been made. The results can be used for further contrast calculations on X‐ray topographs using the dynamical theory of diffraction.
Transmission Electron Microscope Study of Anti‐Phase Boundaries in Alexandrite (Al2−xCrxBeO4)
Authors: Phakey P. P.
Published: July 2007

A study has been made of the diffraction contrast fringe patterns observed by transmission electron microscopy in alexandrite (Al2—xCrxBeO4), the chromium bearing variety of chrysoberyl. Evidence is presented that the fringe patterns are due to anti‐phase boundaries resulting from faults in the cation stacking within the same oxygen lattice. Models for the probable ionic configuration of such boundaries are proposed and discussed. It is shown that the diffraction contrast fringe patterns observed with different operating reflections are consistent with those expected from the proposed models.
The Thermoelectric Power and the Conduction Mechanism in Nearly Stoichiometric Uranium Dioxide Single Crystals
Authors: de Coninck R. , Devreese J.
Published: July 2007

The thermoelectric power and the electrical conductivity have been measured on nearly stoichiometric UO2 single crystals in the temperature range of 170 to 1250 °K. The activation energies deduced from the thermoelectric power and the electrical conductivity curves remain unchanged between 170 and 1000 °K. However their values are different from each other. The results have been explained in terms of the small polaron theory which is in agreement with our previous analysis.
Anharmonic Effects on Phonons in Aluminium
Authors: Högberg T. , Sandström R.
Published: July 2007

Using a pseudopotential model the wave number dependence of the anharmonic phonon widths and shifts as well as the dispersion curves have been calculated for aluminium. The results are compared with experiments by Stedman and Nilsson. The size and general shape of the widths and shifts agree with the experimental values.
Resistance Measurements of the Kinetics of the Elastic After‐Effect in AuCu (75, 25) and AgZn (69, 31)
Authors: Chardon J. Th. , Radelaar S.
Published: July 2007

The kinetics of the elastic after‐effect (Zener relaxation‐effect) in AuCu (75,25) and AgZn (69,31) is studied by measuring the resistance changes accompanying the elastic after‐effect. The results of this method are compared with data obtained by more conventional techniques.
Résonance paramagnétique électronique de Fe3+ dans ZrO2 et HfO2 monoclinique
Authors: Gervais F. , Cabannes F.
Published: July 2007

Le champ cristallin de symétrie la plus basse, en liaison avec la structure de ZrO2 et HfO2 monoclinique, influence profondément le spectre RPÉ d'un ion dans un état S, ici Fe3+; ce qui se traduit en particulier par l'apparition de la raie intense g ≈ 4. Pour interpréter le spectre, les approximations habituelles sont inapplicables et l'on est conduit à effectuer un calcul formel à partir de l'Hamiltonien du second ordre.
Temperature Dependence of the Paramagnetic Resonance Spectra of Cu° and Ag° Stabilized in Alkali Halide Crystals
Authors: Baranov P. G. , Zhitnikov R. A. , Melnikov N. I.
Published: July 2007

The temperature dependence of the hyperfine (A) and superhyperfine (As) structure constants of copper and silver atoms stabilized in LiCl, NaCl, and KCl were discovered and studied by the PR (paramagnetic resonance) method. As a rule, with increasing temperature of the crystals studied, a decrease in both constants was observed. An interpretation of the data obtained is discussed.
A Study of Non‐Equilibrium Contact Potential Difference on the Surface of Photoconducting CdS Crystals
Authors: Tyagai V. A. , Shirshov Yu. M. , Snitko O. V. , Yarinovskii V. D.
Published: July 2007

The contact potential difference (CPD) and field effect have been measured at room temperature on photoconductive CdS crystals with real surfaces. It is shown that the CPD is determined by the surface position of the electron quasi‐Fermi level. The surface band bending was found to be accumulative on the surface of photoconductive crystals under illumination and to be depletive on the surface of semiconductive crystals in darkness. The non‐equilibrium analogue of the well‐known thermal stabilization of the Fermi level by surface states was observed on photoconductive crystals. It was denoted as “an optical stabilization” and results from the high density of surface recombination centres.
Die Versetzungsdichte in stark verformtem NaCl
Authors: Matucha K. H. , Franzbecker W. , Wilkens M.
Published: July 2007

〈110〉‐orientierte NaCl‐Einkristalle wurden bei Raumtemperatur im Stauchversuch bis zu verschiedenen Schubspannungen τ im Bereich II und III der Verfestigungskurve verformt. Die Versetzungsdichte N der verformten Einkristalle wurde mit zwei Methoden untersucht: (i) Ätzgrübchenzählungen it Hilfe elektronenmikroskopischer Abdrücke; (ii) Bestimmung von N aus der Verbreiterung von Röntgenbeugungsreflexen. Beide Methoden ergeben τ = α G b √N (G Schubmodul, b Betrag des Burgersvektors) mit α = 0,37 (Methode i) bzw. α = 0,39 (Methode ii). Dieses Ergebnis stimmt gut mit der Extrapolation der von Hesse mit lichtoptischen Ätzgrübchenzählungen im Bereich I gefundenen linearen τ–√N‐Beziehung überein. Hesses Befund, wonach im Gegensatz dazu im Bereich II eine lineare τ–N‐Beziehung gelten soll, wird der mangelnden Auflösung der lichtoptischen Ätzgrübchenzählung zugeschrieben.
Measurement of Thermal Release and Transit Time in Case of Multiple Trapping
Authors: Juška G. , Matulionis A. , Viščakas J.
Published: July 2007

The time‐dependent current due to the drift of a small charge is investigated in an insulator with a single trap level. A theoretical study of multiple trapping gives the criteria to determine the transit time from the moment when the current is equal to 0.5 of its equilibrium value. A method to measure the thermal release time from the current relaxation which is due to charge ejection into the collecting electrode is proposed. The theoretical data are verified experimentally in high‐polymeric vitreous selenium. The hole Hall mobility is measured to μpH = (0.37 ± 0.03) cm2/Vs, and the hole trap parameters are determined to ΔEM = 0.30 eV, M/Pv = 1.0 × 10−5, Sp = 3.2 × 10−16 cm2. The results confirm the idea of the structural nature of the mobility‐controlling traps.
Determination of the Temperature Dependence of the Piezo‐Optical and Elasto‐optical Coefficients of Crystals
Authors: Reznikov B. A. , Sirotin Yu. I. , Voropaeva N. E.
Published: July 2007

The residual strains e, e, e, parallel to the surface of the plate, are shown to be independent of temperature, provided the plate can expand without hindrance and no relaxation of stresses occurs in it. This makes it possible to derive relations connecting the piezo‐optical coefficients πkl (elasto‐optical coefficients Pkl) of crystals at different temperatures with the refraction indices n0, yield stress coefficients skl, and the birefringences δ at the same temperatures. A method for determining the temperature dependence of piezo‐ and elasto‐optical coefficients is proposed, which consists in measuring the birefringences within a given temperature range in a plate with residual stresses, and then in calculating (using the relations derived) the values of these coefficients in the same temperature range. The results of a determination of the piezo‐ and elasto‐optical coefficients of the crystals of LiF, NaCl, and KCl in the temperature range 20 to 500°C are given.
Eigenstates of the (sp) 3P Multiplet for Two‐Electron Atoms and Phonon‐Induced Optical Transitions
Authors: Fowler W. Beall
Published: July 2007

Eigenfunctions of L2, S2, J2, and Jz have been obtained for the (sp) 3P multiplet. Matrix elements of the linear electron‐lattice interaction show how only Γ12 and Γ′25phonons relax selection rules to permit electric dipole transitions to 3P0 and 3P2 states. It is suggested that the 3P0 state may play a significant role in both absorption and emission processes for mercury‐like impurities in alkali halides.
Oscillatory Magneto‐Photoconductivity in Ge
Authors: Byszewski P.
Published: July 2007

An oscillatory character of the photoconductivity in Ge in the presence of an external magnetic field was observed. The measurements were carried out at liquid nitrogen temperature using magnetic fields up to 26.5 kG. A number of oscillations are observed in the photoconductivity measured as a function of the photon energy. It is shown theoretically that these oscillations are associated with optical transitions between corresponding Landaulevels in the valence and conduction bands. The theoretical curves are in good agreement with experimental results.
Internal Friction Peaks in Pure Aluminum Observed between 45 and 72°K after α‐Particle Irradiation
Authors: Riggauer M. , Schilling W. , Völkl J. , Wenzl H.
Published: July 2007

Relaxation peaks in aluminum found after α‐irradiation at 21.4°K are discussed. In the temperature region of 40 to 75°K, four peaks are observed which anneal out in stage II with first order kinetics. Two of them show the natural line‐width. From the annealing behaviour, the peaks are ascribed to the reorientation of interstitial clusters containing more than two interstitials. The activation energy for reorientation is significantly different from that for annealing.
Change of the Concentration of Wannier Excitons in Molecular Crystals Caused by a Magnetic Field
Authors: Rusin B. A. , Frankevich E. L.
Published: July 2007

A calculation is made of wave functions of para‐ and ortho‐states of excitons of the Wannier type in a magnetic field. These functions are used for the calculation of the changes in the population rates and lifetimes of para‐ and ortho‐states and also of the rate constant for a para‐ortho‐transition in a magnetic field. The results obtained are used for the calculation of the changes in the total concentration of Wannier excitons, which are generated by excitation of molecular crystals in a magnetic field. It is found that in a magnetic field the total concentration of Wannier excitons can either be increased by excitation of only Wannier para‐excitons, or decreased when both para‐ and ortho‐excitons are generated. Expressions are obtained for the relative change in the total concentration of excitons (Δn/n) depending upon the strength of the magnetic field (H), the lifetimes of para‐ (τ1) and ortho‐ (τ3), excitons, and the rate constant of the para‐ortho‐transition (λ). These results can be used for the interpretation of the effect of a magnetic field on photocurrent and luminescence of organic molecular crystals, which was discovered earlier. A relative change of the photocurrent in tetracene thin films (Δi/i) in a magnetic field is investigated. The relationships Δi/i (H) are measured for different thicknesses of tetracene polycrystalline films. The increase of the sample thickness is shown to be equivalent to that of the lifetime ratio of ortho‐ and para‐states (τ3/τ1) of the Wannier excitons. The magnetic field strength (H1/2), consistent with Δi/i(H1/2) = 1/2 (Δi/i) (H → ∞), is found to decrease with the sample thickness. The obtained results agree with the predictions of the developed theory.
Electric Field Effect on the ground State Splitting of Mn++ Ions in NaCl Measured by EPR
Authors: Dreybrodt W. , Pfister G.
Published: July 2007

The influence of electric fields on the splitting of the 6S5/2 Mn++ ground state is investigated in NaCl on two centres with charge compensating cation vancancy. The change of the ground state splitting is described by Σ Ri j k Si Sj Fk. The tensor components Ri j k are determined. Electric‐field‐induced orientation effects of the dipole moment of the centre with n.n. cation vacancy enable us to determine the signs of the tensor components Ri j k.
The Effect of Grinding on the Dislocation Structure of As‐Grown Molybdenum Single Crystals
Authors: Luft A. , Kaun L.
Published: July 2007

The effect of centreless grinding and abrasion of zone‐melted molybdenum single crystals on their dislocation structure is investigated by thin‐foil transmission electron microscopy. The observations reveal that typical dislocation arrangements result from the mechanical pretreatment of the crystals. It is possible to distinguish between grown‐in dislocations and those configurations introduced by grinding. In addition some etch‐pit studies are carried out to test the reliability of this method. The results are discussed in relation to adequate preparing tensile specimens and correct analysing electron micrographs.
On the Theory of Excitons in High Magnetic Fields
Authors: Fritsche L.
Published: July 2007

A theory of excitonic optical absorption at high magnetic fields previously published by Elliott and Loudon is studied in detail in view of recent experiments on GaSe. According to an estimate of Elliott and Loudon their theory should become applicable at fields far above 500 kG for an excition binding energy of 20 me V in GaSe. In contrast, it is shown in the present paper that the theory does very well fit the observed field dependence of the excitonic states already in range of 40 to 100 kG, except for the first two states. Moreover, it provides a simple explanation of weaker satellite lines in the absorption spectrum observed above ca. 40 kG.
Energy Bands of CsI (Green's Function Method)
Authors: Rössler U.
Published: July 2007

Energy bands of CsI in the s.c. and f.c.c. modification have been calculated using the full relativistic Green's function method. Results for ionic and atomic potentials are presented. The splitting of d‐like conduction bands, which is characteristically different in both crystal modifications, is explained by tight‐binding considerations. The binding energy of the Γ8− – Γ6+ excition turns out to be about 30% larger in f.c.c. than in s.c. CsI. The calculated band separations and deformation potentials for hydrostatic pressure are in good agreement with experimental results.
Helicon Wave Propagation in a Two‐Component Solid State Plasma
Authors: Schilz W.
Published: July 2007

The existence of two helicon resonances with opposite polarization has been observed in HgTe samples. In order to explain these experimental results the theory of the helicon propagation in a two‐component plasma has been extended to the case of low mobilities. Numerical results of this theory are in qualitative agreement with the experiments.
A Simple Model of a Magnetic Impurity
Authors: Hunt J. T.
Published: July 2007

The effect of a single spin impurity on the energy spectrum of the one‐dimensional X‐Y model of magnetism is investigated. Two localized spin deviation states are found when the exchange constant between the impurity and its two nearest neighbors exceeds a critical value.
Phonons in Mixed CdxZn1−xS Semiconductors
Authors: Lisitsa M. P. , Valakh M. Ya. , Konovets N. K.
Published: July 2007

The vibrational spectrum of CdxZn1−x crystals has been studied experimentally by optical methods. The results for limiting cases of pure CdS and ZnS are compared with theoretical calculations of wurtzite lattice dynamics. A detailed picture of the phonon spectrum reconstruction of mixed crystals is established as a function of the components composition. The character of the change of optical vibration frequencies at the centre of the Brillouin zone is qualitatively similar to that at its boundary, differing from the type known for the other AIIBVI mixed crystals. Further an analysis of the simple linear chain model is made in order to explain the dependence of the qualitative picture of the phonon spectrum reconstruction on the masses of the substituted components.
Kontinuumstheoretische Untersuchung einer bewegten Schraubenversetzung
Authors: Stenzel G.
Published: July 2007

Die erzwungene Schwingung einer an Fixpunkten verankerten Schraubenversetzung wird kontinuumstheoretisch berechnet. Bei tiefen Frequenzen erweist sich das Saitenmodell mit geeignet gewählter Saitenspannung und ‐masse als gute Näherung. Außerdem werden die Resonanzschwingungen, die Strahlungsdämpfung und der Einfluß der Oberfläche untersucht.
The Chemical and Iso‐Concentration Diffusion of Cd in AlSb
Authors: Shaw D. , Showan S. R.
Published: July 2007

The chemical and iso‐concentration diffusion of Cd in AlSb has been investigated at 900°C as a function of Cd surface concentration. The diffusion coefficients are found to be strongly concentration dependent showing a very similar behaviour to that of Zn in the III–V compounds. It is concluded that Cd occupies both interstitial and substitutional (Al) sites but only diffuses via interstitial sites. The difference between chemical and iso‐concentration diffusion is attributed to the existence of defect equilibrium in the latter case but not in the former.
Surface Carrier Waves in Intrinsic Semiconductors
Authors: Hervouet C.
Published: July 2007

A theory is given of the amplification of surface carrier waves in nearly intrinsic semiconductors in crossed electric and magnetic fields. It takes into account the magnetoresistance effect, the diffusion, and the surface recombination of carriers and shows that because of diffusion a threshold drift velocity of electrons exists for obtaining gain. This threshold increases as ω1/2 and T1/2. It decreases when B0 increases and has a minimum as a function of ne/nh. The gain has a maximum for a drift velocity which is the lower the higher is the magnetic field. The wavelength is a linear function of voe/ω even near the threshold drift velocity (for a given magnetic field).
Luminescence Properties of Rare Earth Activated Cadmium Sulphide in the Range 4000 to 15000 cm−1
Authors: Apperson J. , Garlick G. F. J. , Lamb W. E. , Lunn B.
Published: July 2007

Microcrystalline powders of rare earth activated cadmium sulphide, with copper as a co‐dopant, are investigated for line emission spectra, where (excluding Pm) the rare earth is anyone of the series from Pr to Yb. Seven of the eleven rare earths investigated have line emissions in the range 4000 to 15 000 cm−1. All lines are attributable to trivalent rare earth ions and most are characterized by similar broad band excitation spectra. An explanation for the appearance or non‐appearance of line spectra is sought on the basis of models proposed by previous workers in which resonance transfer of energy occurs, after absorption at the copper site, to the associated rare earth ion.
Interaction des défauts ponctuels avec les atomes étrangers dans des alliages dilués aluminium‐magnésium irradiés aux neutrons à 78 °K
Authors: Dimitrov C. , Dimitrov O.
Published: July 2007

La restauration de la résitivité électrique d'une série d'alliages alliages aluminium‐magnésium (≦ 0,3 × 10−6 à 3200 × 10−6 atomiques) est étudiée après irradiation aux neutrons à 78 °K, à des doses de quelques 1017 n/cm2. La présence de magnésium produit un accroissement important du stade II de restauration qui devient constant aux concentrations supérieures à 1000 × 10−6. Le stade III augmente lentement sans atteindre une valeur constante, même aux plus fortes concentrations. Un petit stade III' aparaît au‐dessus du stade III. Les additions de magnésium ne modifient pas l'énergie d'activation mesurée au stade III: (0,59 ± 0,02) eV. Les résultats sont interprétés en admettant que des interstitiels mobiles à 78 °K sont piégés par les atomes de magnésium et que le dépiégeage se produit au stade II. A partir de ce modèle, nous avons déduit de nos essais les valeurs suivantes: énergie d'interaction intersititiel‐magnésium E1−mg = (0,29 ± 0,03) eV; énergie d'interaction lacune‐magnésium Elac‐mg = (0,15 ± 0,09) eV.
Experimental Evidence for the Validity of Lampert's Theory in the Negative Resistance Region of the GaSe(Sn)
Authors: Romeo N.
Published: July 2007

GaSe(Sn) crystals having negative resistance also show a negative photoconductivity effect at voltages near the threshold value in a wavelength region between 1 and 2.3 μm. This effect is ascribed to a level located in the forbidden gap 0.5 to 0.55 eV above the valence band. This level is identified as that assumed by Lampert for explaining negative resistance in insulators in which double injection occurs.
Propagation of Electromagnetic Waves in a Plate‐Like Semiconductor at Nonstandard Dispersion Law of Carrier Energy
Authors: Dykman I. M. , Tomchuk P. M. , Almasov L. A.
Published: July 2007

An investigation is made of the propagation of electromagnetic waves through a semiconductor plate to which a constant electric field F is applied. In the case when the dispersion law of carrier energy differs from the isotropic parabolic one, a specific mechanism, depending on the energy band structure, arises which affects the complex part of the refractive index. For a dispersion law of Kane type [3] this mechanism causes additional attenuation of the wave. For a weakly anisotropic law, similar to that in p‐type germanium, it amplifies or attenuates the wave depending on the polarization. In both cases the effect increases proportional to F2. Therefore, by means of the electric field, the reflection and transmission can be influenced, and also the reflected and passed radiation can partly be polarized with varying degree of polarization. The derived formulas make it also possible to obtain additional information on the semiconductor properties, in particular the carrier temperature, from the measured reflection and transmission coefficients.
Investigation of the Heisenberg Model on the Basis of the Real Spin‐Wave Theory
Authors: Praveczki E.
Published: July 2007

The operator formalism of real spin‐waves is introduced. Applying this formalism to the Heisenberg model and making use of a new method of calculation, the energies of the real spin‐waves are renormalized taking into account their interactions. The formula derived for the magnetization in this way leads to better results than those derived by Tyablikov [5], Tahir‐Kheli and ter Haar [6], and in an another approximation by Callen [8].
An Analysis of the Thermodynamics of Dislocation Glide
Authors: Hirth J. P. , Nix W. D.
Published: July 2007

A general treatment of thermally activated dislocation motion is presented following the approach first suggested by Basinski and making use of Leibniz's formula to analyze the properties of arbitrarily shaped obstacles. The small region surrounding a dislocation obstacle is shown to be an acceptable thermodynamic system with the effective stress, defined as the difference between the applied stress and the long range internal stress evaluated at the obstacle, as an appropriate thermodynamic variable. All of the thermodynamic properties of such a local system are self consistent. The question of the choice of a thermodynamic system is discussed in connection with the results of prior treatments of the problem. Whether one considers a local system using the effective stress as the operative thermodynamic variable, or the entire crystal as a system using the applied stress, the value of the effective stress and the conditions for which it is zero must be known, in general, in order to relate measured thermodynamic quantities to the properties of an obstacle. The thermodynamic methods are illustrated with the use of a simple sinusoidal model for the backstress produced by an obstacle. The difficult problem of relating the stress and temperature dependence of plastic flow to the results of thermodynamic analysis is treated. The discussion indicates that serious errors can be made either when the effective stress is not precisely known, as is commonly the case for high temperature creep, or when the stress and temperature dependence of the preexponential constant are not taken into account.
Space‐Charge‐Limited Current and Band Structure in Amorphous Organic Films
Authors: Caserta G. , Rispoli B. , Serra A.
Published: July 2007

Electrical conduction phenomena in thin films of some organic polymers have been investigated. The current‐voltage characteristics of polymethylmetacrilate, polyvinylformal, and polyethylene‐terephthalate films display a space‐charge‐limited current (SCLC). The steady‐state SCLC and the back current are interpreted in terms of an energy band model with localized states uniformly distributed in energy within a region of the forbidden band. This region is (0.353 + 0.025) eV wide and seems to be independent of the chemical nature of the amorphous material, the sample preparation procedure, and the sample thickness. The density per unit energy of localized states ranges from 1014 to 1018 cm−3 eV−1.
The Energy Dependence of Lattice Disorder in Ion‐Implanted Silicon
Authors: Marsden D. A. , Bellavance G. R. , Davies J. A. , Martini M. , Sigmund P.
Published: July 2007

The energy dependence of lattice disorder has been studied by implanting bismuth ions of energy 20 to 225 keV into silicon crystals at room temperature. Implant doses have been kept below 6 × 1013 ions cm−2 to avoid approaching “saturation” disorder. Lattice disorder has been measured by means of the orientation dependence of the backscattered yield of a 1.0 MeV helium ion beam (i.e. by the “channeling” technique). Within the experimental precision, the observed disorder increases linearly with implantation energy over the whole range studied. This linear dependence is consistent with the Kinchin‐Pease equation, but its slope is at least a factor of two greater than the predicted value. Possible explanations for this discrepancy are discussed. The most reasonable one is that the disorder measured by the channeling technique includes not only the atoms that have been ejected into interstitial positions by the implantation, but also some of the lattice distortion resulting from this primary damage.
Isotope Effect and Divacancies for Self‐Diffusion in Copper
Authors: Rothman S. J. , Peterson N. L.
Published: July 2007

The simultaneous diffusion of 64Cu and 67Cu has been measured in copper single crystals from 890 to 1061 °C. The strength of the isotope effect f ΔK is 0.684 ± 0.014 and is independent of temperature within the experimental error. This indicates that the contribution of divacancies to self‐diffusion in copper is small. The diffusion coefficient of 67Cu in copper single crystals was measured from 700 to 1060 °C and is given by

.
Spin‐Wave Relaxation in Single Crystals of Cobalt‐Substituted Nickel‐ and Nickel–Zinc Ferrite
Authors: Voigt F. , Manzel M. , Schmitz A.
Published: July 2007

The effect of small concentrations of substitutional cobalt ions on the spin‐wave relaxation was measured using parallel‐pumping. The cobalt contribution to the anisotropy of spin‐wave relaxation is found to be very small. The fraction of cobalt ions which contribute to the relaxation is larger than the fraction expected from the theory. The departure from the theory and the temperature behaviour suggest that the cobalt ions contribute to a direct relaxation process to the lattice.
Characteristics of Anomalous Transmission of X‐Rays in the General Case of Laue Diffraction
Authors: Kovev E. K. , Efimov O. N. , Korovin L. I.
Published: July 2007

The characteristics of the anomalous transmission of X‐rays for crystals without a centre of symmetry and for the unsymmetrical Laue diffraction are obtained on the basis of the dynamical theory of scattering by a perfect absorbing crystal. The characteristics are connected with the real and the imaginary parts of the structure factor and with the geometry of the experiment. The characteristics suggest a possibility to use them for the investigation of the crystals with different types of defects.
On the Types of Electrical Domain Instability in Hot Electron Semiconductors
Authors: Bonch‐Bruevich V. L. , Serebrennikov P. S.
Published: July 2007

Various types of an electrical instability of a homogeneous sample are considered. The nature of the instability is studied in detail and the role of the boundary conditions stressed.
Electrical Conductivity of Single Crystalline Nickel Oxide
Authors: Eror N. G. , Wagner J. B.
Published: July 2007

The electrical conductivity of single crystalline NiO was found to be proportional to the 1/4 power of the oxygen pressure for oxygen partial pressures between 100and 10−4atm over the temperature range of 900 to 1200 °C. These results are in agreement with singly ionized cation vacancies as the predominant nonstoichiometric defect. The sum of the enthalpies of formation of nonstoichiometric disorder and activated enthalpy of movement of an electron hole was found to remain constant when thermodynamic equilibrium was maintained. The activated enthalpy of movement of an electron hole, however, was found to obey the “Meyer‐Neldel” relationship, that is, it increased as the concentration of electron holes decreased. An argument has been offered for the explanation of the “Meyer‐Neldel” rule. This explanation involves consideration of another equilibrium between free electron holes and those trapped at imperfections (such as dislocations) which are not usually considered in the usual theory of point defects in nonstoichiometric compounds.
Gestörte Diffusion von Tritium in einer Silber‐Lithium‐Legierung nach Neutronenbestrahlung. Edelgase (und Wasserstoffisotope) in Festkörpern 44
Authors: Migge H.
Published: July 2007

Es wurde die Abgabe von Tritium aus einer Ag–20 At% Li‐Legierung im Bereich zwischen 280 und 600 °C nach Neutronenbestrahlung gemessen. Die Diffusionskoeffizienten weisen unterhalb von 390 °C eine größere Temperaturabhängigkeit auf als oberhalb (Aktivierungsenergien 1,3 bzw. 0,49 eV). Bei Erhöhung der Neutronendosis von 3,6 × 1016/cm2 auf 1,3 × 1017/cm2 wird die Temperaturabhängigkeit in beiden Temperaturbereichen größer (2,34 bzw. 1,14 eV), und die Diffusionskoeffizienten werden deutlich kleiner. Es tritt im gesamten Temperaturbereich zu Beginn ein Anlaufvorgang auf. Aus dem Anlauf wird eine Zeitkonstante b [s−1] für den Austritt der Tritiumatome aus Fallen bestimmt. Die Aktivierungsenergie und der Vorfaktor von b sind praktisch unabhängig von der Neutronendosis.
Band Structure and Nature of Lattice Defects in GeTe from Analysis of Electrical Properties
Authors: Lewis J. E.
Published: July 2007

The measured transport properties of non‐stoichiometric GeTe have been satisfactorily analysed on the basis of a two‐carrier model and the various band parameters have been evaluated. In particular the variation of the carrier density of the system with composition has been obtained and then compared to the total number of excess atoms in the non‐stoichiometric lattice. It is found that the defects occurring in GeTe due to these excess atoms are of a complex nature, except for compositions close to stoichiometry where singly ionized vacancies are the dominant defect.
Diffusion Length and Lifetime of Triplet Excitons and Crystal Absorption Coefficient in Tetracene Determined from Photocurrent Measurements
Authors: Vaubel G. , Kallmann H.
Published: July 2007

By comparing the decrease of the i+ and i− currents as function of the exciting wavelength and from the maximum of the i− current the crystal absorption coefficient of tetracene can be determined. With the penetration depth of the radiation thus known the diffusion length and lifetime of triplet excitons are determined from the dependence of the currents on the wavelengths. The diffusion length is found to be (0.4 ± 0.2) μm, the lifetime about 100 μs.
Mössbauer Studies of Tin 119m Recoil Atoms in Some Mixed Oxides of Tin. I. The Nature of the Recoil Effects in Mg2SnO4
Authors: Hannaford P. , Wignall J. W. G.
Published: July 2007

The Mössbauer spectrum emitted following thermal neutron irradiation of the spinel Mg2Sn118O4 displays a subsidiary line which can be associated with Sn119m recoil atoms at abnormal sites in the crystal. The isomer shift and (unresolved) quadrupole splitting of this line suggest that it originates from divalent tin ions in which there is an admixture of 5p‐electrons having predominantly pz‐character. The temperature dependence of the Mössbauer fraction indicates a weak average binding which, according to the computed intensities of the quadrupole doublet, may result from a large 〈z2〉 along the principal axis of the electric field gradient. Isochronal and isothermal annealing data indicate that the defect line disappears irreversibly above 600 °C and that the annealing processes are distributed over a fairly narrow band of activation energies in the range 3 to 4 eV. These results are interpreted in terms of a defect complex comprising a divalent tin ion and an associated charge‐compensating oxygen vacancy.
EPR of Cr3+ Ions in Alexandrite
Authors: Barry W. R. , Troup G. J.
Published: July 2007

Results on the EPR of Cr3+ ions occupying mirror symmetry sites in alexandrite are described. The Spin Hamiltonian parameters are: D = ( −7.31 ± 0.02) GHz, E = = (‐1.71 ± 0.02) GHz with gx = 1.978 ± 0.003, gy = 1.980 ± 0.004, gz = 1.969 ± ± 0.004 with a corresponding zero‐field splitting between the Kramer's doublets of (15.7 ± 0.05) GHz. The relationships between the crystallographic axes and the axes of the magnetic complexes show slight departures from the crystallographic symmetry of pure chrysoberyl.
Sulphur Diffusion in Copper: Departure from the Arrhenius Plot
Authors: Moya F. , Moya‐Gontier G. E. , Cabane‐Brouty F.
Published: July 2007

A study is made of sulphur diffusion in copper single crystals using 35S between 550 and 1000 °C. The plot log D = f(1/T) was not a straight line. Different models were examined to explain the departure from linearity in the Arrhenius plot. A simple model is proposed, basing on classical mechanisms: monovacancy diffusion and diffusion along randomly distributed dislocations. For T > 800 °C, Q = 2.14 eV, and D0 = 23 cm2 s−1, the unusually high diffusion coefficients do not agree well with the value of Q, similar to that of self diffusion. For T < 800 °C, the dislocation model gives a binding energy of some tenths of an electron‐volt.
On One of the Possible Mechanisms of Formation of Induced Anisotropy in Ferromagnetic Films
Authors: Lesnik A. G.
Published: July 2007

With the assumption that the concentration of nonmagnetic inclusions (lattice defects, impurity atoms, oxides) is higher at the grain boundary than inside the grain, a steady state distribution of inclusions is determined along the grain boundary in a ferromagnetic film. It appears to be nonuniform since inclusions leave those boundary sections where the jump of the normal component of magnetization at the boundary is maximum and go into sections where the jump is minimum. Nonuniformity of the inclusion distribution at the boundary results in a magnetic anisotropy. Expressions are derived for the anisotropy energy. The numerical evaluation shows that the experimental value of anisotropy energy is obtained by such a mechanism in the case when inclusions decrease strongly the magnetization of the boundaries.
Calculations of the Contrasts of Moiré Patterns from Twisted Lattices by the Dynamical Theory of Electron Diffraction
Authors: Izui K. , Nishida T.
Published: July 2007

Calculations are made of electron microscope image contrasts of moiré patterns from twisted lattices by using the dynamical theory of electron diffraction. The distinctions between the image profiles for a twisted crystal and those for two superposed crystals are presented. The influences of various factors such as the way of twisting, the deviation from the Bragg diffraction condition, the absorption parameters and crystal thickness on the image profiles of the twisted lattices are clarified for some specified cases.
Étude en microscopie électronique d'un alliage possédant une surstructure à longue période: Ag3Mg
Authors: Vanderschaeve G.
Published: July 2007

Les différents défauts résultant des processus d'ordre dans l'alliage Ag3Mg sont étudiés en microscopie électronique. La nature cristallographique de ces interfaces, ainsi que les différents types de contraste auxquels elles donnent lieu sont discutés et les preuves expérimentales sont présentées.
ESR Studies of Covalency Effects between Cu2+ and Chalcogen Ions in AgCl Crystals
Authors: Schwarz D.
Published: July 2007

After irradiation in AgCl crystals doped with Cu and Se or S, respectively, an ESR spectrum of a Cu2+ ion is observed the octahedral chlorine environment of which is distorted by a Se2− or S2− ion. The centre has [100] tetragonal symmetry and a essentially |3 z2‐r2 > ground state. The superhyperfine structure in AgCl: 77Se, Cu indicates a strong interaction with one selenium nucleus. If σ‐bonding is assumed the magnitude of the covalency between the Cu2+ and the Se2− ion can be estimated: the hole spends about 20% of its time in a pz state of the Se2−. From the existence of this covalent bonding in the paramagnetic complex follows that the spin‐orbit coupling is more reduced in [Cu2+ Se2−] than in [Cu2+ S2−].
Negative Resistance in GaS Single Crystals
Authors: Romeo N.
Published: July 2007

The I‐U characteristic of GaS single crystals has four distinct zones: a low‐voltage zone which is ohmic, a zone in which the current depends on the voltage by a relationship of the I ∝ U2 type, a third zone in which the slope of the characteristic is very sharp and current pulses are present and a fourth in which the characteristic is negative. Experimental findings have led us to suppose that this behaviour of GaS can be explained by Lampert's theory of negative resistance in insulators.
Shallow States in Semiconductors by Impurity Model Potential Method
Authors: Jaroš M.
Published: July 2007

A impurity model potential is constructed using the method of Heine et al. The treatment of the short‐range forces in this method is refined making the theory applicable to the impurity problem. It is shown how a simple spherical screened model potential can be used for the ground state calculation of shallow donors in semiconductors; the ionization energies of P, As, and Sb in silicon are given.
Ein Diffusionsmodell zur Behandlung der Doppelkinkrelaxation in kubisch‐flächenzentrierten Metallen
Authors: Engelke H.
Published: July 2007

Das Seegersche Modell der Doppelkinkrelaxation wird erweitert mit dem Ziel, die sogenannten sekundären Eigenschaften der Bordoni‐Maxima in k.f.z. Metallen zu deuten. Eine Untersuchung der Eigenschaften von Versetzungsbögen im Peierls‐Potential ergibt, daß auf jedem Bogen nur ein Kinkpaar explizit zu berücksichtigen ist. Kinkbildung und Kinkdiffusion werden einheitlich mit Hilfe der von Kramers und Brinkman für chemische Reaktionen abgeleiteten Diffusionstheorie beschrieben. In zwei Näherungsschritten wird ein Mehrmuldenmodell für die Bogenbewegung im Peierls‐Potential abgeleitet. Die auftretenden Relaxationszeiten weisen eine Abhängigkeit von der Bogenlänge auf, welche in qualitativer Übereinstimmung mit den Dämpfungsmessungen ist.
Fine Structure of the “One‐Dimensional” Exciton in Germanium in Parallel Magnetic and Electric Fields
Authors: Seysyan R. P. , Zakharchenya B. P.
Published: July 2007

The excited states of a one‐dimensional exciton in finite magnetic fields represent doublets consisting of even and odd components. The differential electroabsorption technique was used to observe transitions to odd states of the one‐dimensional exciton in germanium in parallel magnetic and electric fields. An analysis of the differential electroabsorption spectrum in parallel magnetic and electric fields is given.
Dichroïsme circulaire magnétique et absorption de I'ion Nd3+ dans CaWO4
Authors: Boccara A. C. , Ferré J. , Badoz J.
Published: July 2007

On étudie les spectres de dichroïsme circulaire magnétique et d'absorption en lumière polarisée d'un cristal CaWO4:Nd3+ dans le visible et le proche infra‐rouge, à plusieurs températures. Cette étude permet de déterminer expérimentalement un grand nombre de facteurs de Landé des états excités. Ces résultats sont comparés à ceux obtenus à partir de la théorie du champ cristallin.
Temperature Change Experiments during Secondary Creep of the Intermetallic Compound MgZn2
Authors: Hinz D. , Paufler P. , Schulze G. E. R.
Published: July 2007

From temperature change experiments (between 260 and 435°C) during secondary creep of the intermetallic compound MgZn2 an activation enthalpy ΔH = (2.25 ± 0.20) eV for basal slip has been derived. The shear strain rate γ can best be described by the empirical relation γ = 7 × 1011 s−1 × τ5.5 ± 1.0 exp (‐ ΔH/kT) where τ is the applied shear stress. X‐ray topographies show the formation of low angle boundaries during steady‐state creep.
Kinetics of Clustering under Vacancy Annealing
Authors: Srinivasan N. K. , Ramachandran V.
Published: July 2007

An equation is derived for the total vacancy concentration in quenched alloys containing impurities under the condition of free vacancies annealing by migration to fixed sinks. The time to reach maximum in resistivity in isothermal aging experiments need correction if the total vacancy concentration which decays exponentially after the transients has a small time constant. A procedure for this correction is outlined.
Influence of Resonance Transfer and Exciton Diffusion on Luminescence Decay
Authors: Swenberg C. E. , Stacy W. T.
Published: July 2007

Theoretical equations are formulated to describe the luminescence decay of donors and acceptors including both the effects of exciton diffusion and resonance energy transfer. Closed form expressions for the population and decay of excited donors and acceptors are developed using the Padé approximant method with the diffusion coefficient as an expansion parameter. Possible experiments are suggested.
Effect of Channeling on Damage Rates Associated with Heavy‐Ion Irradiation of Gold
Authors: Noggle T. S. , Barrett J. H.
Published: July 2007

Electron microscope studies of radiation damage produced by 60‐MeV iodine ions in thin gold crystals have been made to determine the dependence of damage rate on orientation of the ion beam relative to [011] and (111). Experimental values of the minimum damage rates and half‐widths were compared with calculations made with a Monte Carlo computer program using either the Thomas‐Fermi or the Bohr potential and incorporating thermal vibrations. The thermal vibrations were found to be necessary for agreement with experiment, and agreement was better with the Thomas‐Fermi potential than with the Bohr. Experimental observations by a stereo technique gave a tentative confirmation of a calculated depth dependence and showed in addition a deficiency of damage clusters near the surface.
Ultra‐Violet Excited Paramagnetic Centres in Calcium Tungstate
Authors: Sayer M. , Lynch G. F.
Published: July 2007

Two sets of paramagnetic species having a spectroscopic splitting factor slightly higher than the free electron value are produced in CaWO4 doped with copper after irradiating the crystal with ultra‐violet light. One set of lines is identified as being due to a hole trapped at a single tungsten site and is found to bleach out on warming the crystal through the thermoluminescence glow peak at 160 °K. The other set of lines increases in intensity first with the emission of light in the 160 °K peak and then again with the 260 °K peak and bleaches out on heating the crystal through the thermoluminescence glow peak at 400°K. The copper does not take part in the excitation process directly. It is suggested that the low temperature paramagnetic species arises from the loss of an electron from the tungstate complex.
Electronic Structure of PbS, PbSe, and PbTe
Authors: Overhof H. , Rössler U.
Published: July 2007

The electronic band structures of PbS, PbSe, and PbTe have been calculated using the relativistic Green's function method. The choice of a relativistic atomic potential for Pb and of nonrelativistic atomic potentials for S, Se, and Te inthe muffin‐tin spheres results in similar band models for the lead salts. Thus a nearly uniform interpretation of experimental data for these materials can be presented. A good agreement of calculated band separations with results from reflectivity, electroreflectance, and photoemission measurements is achieved.
Magnetic Transformations in the Mn2GeySb1−y System in Strong Magnetic Fields under High Pressure
Authors: Galkin A. A. , Zavadskii E. A. , Morozov E. M.
Published: July 2007

At temperature changes some magnetic phase transformations are observed in the Mn2Gey Sb1−y system, which are accompanied by magnetic structure changes. The main characteristics of such transformations, magnetization change, change of the entropy of the spin system, and transition heat, were determined on the basis of magnetic measurements over a wide range of magnetic fields. The effect of pressure on the magnetic transformation temperature was also studied. An analysis of the experimental results is made on the basis of Kittel's exchange inversion theory.
Self‐Diffusion in Selenium
Authors: Brätter P. , Gobrecht H.
Published: July 2007

Self‐diffusion measurements have been carried out in single crystals of the semiconductor element selenium using a residual activity method and Se‐75 as the tracer in the temperature range 152 to 215 °C. In the direction of the trigonal axis (| c‐axis) the data of the lattice diffusion can be represented by D⟂ = 0.2 exp (—1.2 eV/kT) cm2 s−1. The diffusion along the short circuit paths can be approximately described by the values Q≈︁ 0.5 eV and Q≈︁ 0.7 eV for the activation energy and by diffusion coefficients between 5 × 10−10 and 10−8 cm2 s−1 in the temperature range considered. The vacancy formation enthalpy in selenium is estimated to be about 0.75 eV. From the diffusion data determined the vacancy migration enthalpy is estimated to be about 0.5 eV along the c‐axis and 0.7 eV perpendicular to the c‐axis. It is possible to explain the self‐diffusion in selenium on the basis of a vacancy mechanism. The anomalous self‐diffusion behaviour of the elemental semiconductors and correlation considerations are discussed. Several typical features were found and the presented results for selenium are shown to be in agreement.