bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamical Theory of the Optical and Energy Loss Properties of the Crystal Electron System
Authors: Stolz H. 
Published: July 2007

AbstractApplying many‐particle methods, a theory is presented of the optical and energy loss properties as revealed by ϵ(ω) and ϵ−1(ω) for the system of interacting crystal electrons. The results are discussed for an ideal insulator and the different relations of the quantities ϵ(ω) and ϵ−1(ω) to the two‐particle and collective excitations of the system are studied. Special attention is paid to the question of the relative positions of exciton peaks in the optical and the energy loss spectra and it is demonstrated that first‐order exchange processes only influence the positions of the latter and are of no appeal for the positions of the optical peaks.
Migration of Ni2+ Ions and Ferrimagnetic Resonance in NiFe2O4 Crystals
Authors: Krishnan R. 
Published: July 2007

AbstractIn 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

AbstractAn 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractUsing 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

AbstractThe 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

AbstractLe 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

AbstractThe 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

AbstractThe 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

Abstract〈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

AbstractThe 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

AbstractThe 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

AbstractEigenfunctions 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

AbstractAn 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

AbstractRelaxation 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractEnergy 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

AbstractThe 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.
Phonons in Mixed CdxZn1−xS Semiconductors
Authors: Lisitsa M. P. , Valakh M. Ya. , Konovets N. K. 
Published: July 2007

AbstractThe 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

AbstractDie 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

AbstractThe 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

AbstractA 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

AbstractMicrocrystalline 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

AbstractLa 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

AbstractGaSe(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.