bluuebunny/crossref_metadata_2025 huggingface dataset:
Dipolar Broadening of the NMR Spectrum of 19F in UF4
Authors: Gabuda S. P. , Falaleeva L. G. , Gagarinskii Yu. V.
Published: July 2007

The influence of internuclear dipole–dipole and electron–nuclear dipolar interactions on the NMR spectrum shape was examined for UF4. It is shown that only the dipolar interaction of the 19F nuclei with the magnetic moments of the U4+ ions leads to such a broad NMR spectrum in polycrystalline UF4 that there is no ground for separating it into several components corresponding to the seven nonequivalent fluorine nuclei in the UF4 structure. A certain additional broadening of the experimental spectrum may be accounted for by anisotropic hyperfine interaction, due to the transfer of the spin density from U4+ to fluorine.
Production of Vacancies and Other Defects in KBr at Low Temperatures
Authors: Comins J. D.
Published: July 2007

The production rate of vacancies and interstitial defects formed by ionizing radiation in KBr has been studied at low temperatures. It has been found that the large difference between the production rate of vacancies at liquid helium temperature (LHeT) and liquid nitrogen temperature (LNT) may be accounted for by a combination of thermal annealing processes, interstitial stabilizing processes, and certain additional processes requiring the action of the radiation at LNT. The increase in the production efficiency of vacancies between LHeT and LNT, as predicted by the excitonic mechanism of defect production, is not observed. Studies of the bands produced on warming a crystal irradiated at LHeT to LNT indicate that the V4‐band is the major band produced and that it is produced from the H‐band. The V4‐envelope formed during irradiations at LNT is shown to consist of the V4‐band produced as above, with the addition of bands at 266 and 306 nm.
Glide Band Broadening in Crystals
Authors: Vladimirov V. I. , Orlov A. N. , Petrov V. A. , Smirnov B. I.
Published: July 2007

A theory of glide band broadening at the yield point in crystals of alkali halide and b.c.c. metals is presented. The glide band is assumed to broaden by double cross slip of segments of screw dislocations entering into regions near the edge of the glide band that are free from dislocations. Dislocation loops emitted by the sources created in this way expand until they are stopped by other loops in neighbouring slip planes. The shape of the glide band edge is calculated as well as its rate of broadening and the densities of mobile and stopped dislocations. These results contain no arbitrary constants and are confirmed by special experiments carried out on LiF crystals.
On the Problem of Electron Capture Coefficients of the Group III Acceptors in Silicon
Authors: Pokrovskii Ya. E. , Svistunova K. J.
Published: July 2007

The data on the electron capture coefficients of the neutral group III acceptors in silicon published by various authors differ by many orders of magnitude. Principal features of the methods of determining these coefficients are discussed and possible sources of such a disagreement are pointed out.
Plasma Reflection Edge in Crystalline MB6 Compounds
Authors: Kierzek‐Pecold E.
Published: July 2007

The room temperature ultraviolet reflectivity and plasma reflection edge in crystalline samples of MB6 such as LaB6, PrB6, NdB6, and SmB6 have been investigated. The theoretical analysis of the experimental curves in the region of plasma edge allows to determine the dielectric constant ϵ, the relaxation time τ, and the N/m* ratio. The optical constants such as refractive index n, extinction coefficient k, and absorption coefficient α are evaluated in the region 1.2 to 6.0 eV using the Kramers‐Kronig relation.
On the Theory of Pseudopotential
Authors: Poplavnoi A. S.
Published: July 2007

The pseudopotential theory of Austin, Heine, and Sham [6] is generalized. An optimized pseudopotential is obtained. In the case of small cores it may be replaced by the selfconjugate operator.
The Investigation of Trapping Levels in CdWO4, ZnWO4, and CaWO4
Authors: Furtak S. P. , Pashkovskii M. V.
Published: July 2007

Local trapping levels in unactivated monocrystals of CdWO4, ZnWO4, and CaWO4, were investigated by the method of thermoluminescence (TL), thermally stimulated conductivity (TSC), and photoelectret state (PES). Thermal activation energies for various trapping levels were found, and the order of recombination kinetics in these materials was determined. From the obtained data on temperature dependence of the stationary X‐ray luminescence the thermal activation energies for non‐radiative transitions were found. On the basis of the obtained experimental data a model is suggested, which explains the relation between thermoluminescent and luminescent properties of the investigated tungstates.
Infrared Spectra of Cubic and Tetragonal Manganese Ferrites
Authors: Brabers V. A. M.
Published: July 2007

The infrared absorption spectra in the range from 200 to 700 cm−1 of cubic and tetragonal manganese ferrites, MnxFe3–xO4, are reported. An analysis of the spectra is made with a model by which the lattice vibrations are classified into species of the point group D2 d on the analogy of the results for gas molecules of equivalent symmetry. For cubic spinels with manganese concentrations x ≦ 1.0 the classification can be made according to the model of Waldron into the species of the point group Td. However, at 335 cm−1 an absorption has been observed which is out of the scope of the Td or D2 d classification, and which is caused by the substitution of a part of the octahedral Fe3+ ions by Mn2+ ions. The IR spectra of manganese ferrites with compositions 1 < x ≦ 3 can be analysed with the D2 d classification. The spectra of these materials do not change suddenly with the manganese concentration or with the crystal structure. From the splitting of the absorption bands in cubic ferrites with x > 1 it is concluded that there are local tetragonal distortions originating from the Jahn‐Teller effect of the octahedral Mn3+ ions.
Temperature Dependence of Mean Free Path in Secondary Electron Emission
Authors: Taub H. , Stern R. M. , Dvoryankin V. F.
Published: July 2007

The temperature dependence of the anisotropic secondary emission of electrons from a single crystal is determined by the relative effect of thermal scattering on the inelastic mean free path for the incident electrons, and the escape depth for the secondaries. A diffraction model for the anisotropic secondary emission based on the two‐beam dynamical theory of Bethe is discussed. This model predicts a temperature dependence for the anisotropy that is qualitatively observed for a (110) surface of a tungsten single crystal.
Optische und photoelektrische Eigenschaften von β‐rhomboedrischem Bor. I. Optische Konstanten, Bandkante und Absorption freier Landungsträger
Authors: Jaumann J. , Werheit H.
Published: July 2007

Der Temperaturgang des Absorptionsspektrums zwischen Kante und Gitterschwingungen kann durch indirekte Bandübergänge und Anregungen aus einem thermisch besetzten Haftniveau großer Zustandsdichte beschrieben werden, welches bei tiefen Temperaturen durch Untersuchung der starken Beeinflussung optischer Absorption und Photoleitung durch Lichteinwirkung im Teil II dieser Arbeit nachgewiesen wird. – Die Absorption freier Träger ist bei hohen Temperaturen dem Gitterspektrum überlagert; ihr Anstieg ∼λ3 deutet auf Streuung an geladenen Zentren hin, deren Konzentration von etwa 5 × 1020 cm−3 der Zahl der Elementarzellen des Gitters entspricht und die Zahl der Fremadtome um zwei Größenordnungen übersteigt. Eine Abschätzung der effektiven Masse freier Löcher liefert 8 m0; dies entspricht einem hopping‐Modell der elektrischen Leitfähigkeit. Das komplizierte Gitterschwingungsspektrum ist zwischen 4 und 13 μm fast temperaturunabhängig; es liegen dort also keine Kombinationsbanden vor.
Crossed and Parallel‐Field Magneto‐Electro‐Reflectance of Germanium in Nonuniform Electric Fields
Authors: Evangelisti F. , Frova A.
Published: July 2007

Room‐temperature magneto‐electro‐reflectance experiments near the fundamental edge of germanium have been performed in both the crossed and parallel‐field configuration, using a “day” field‐effect system to achieve zero‐to‐peak modulation of the electric field. The results show that the E ‖ H spectra can be described in terms of photon‐assisted tunneling at each of the Landau levels, although the interpretation of the data is not straightforward due to the strong nonuniformity of the electric field. For E ⊥ H the period of the Landau levels is smaller than in the E ‖ H case and there is evidence that quantization effects are absent in the region of high electric field immediately below the surface. The results suggest that the technique described here may be a convenient tool to investigate magneto‐electro‐effects.
Radiation‐Induced Interstitial Centres in Alkali Halides
Authors: Itoh N. , Saidoh M.
Published: July 2007

Formation of H‐, H′‐, and V1‐centres in pure KBr and KCl in Na+‐doped KBr is studied. It is shown that the growth of the H‐band is suppressed and the growth of the V1‐band is enhanced by Na+ impurity, and that the height of the V1‐band is proportional to the height of the H‐band. It is shown also that the height of the H′‐band is proportional to the square of the height of the H‐band below a certain H‐centre concentration, suggesting that the centres associated with the H′‐band are di‐H‐centres. The kinetics of the formation of these three centres is discussed in terms of the interaction volume of ejected halogen interstitials with H‐centres and impurities.
Transmission Electron Microscope Study of the Dislocations in Plastically Deformed Synthetic Quartz
Authors: McLaren A. C. , Retchford J. A.
Published: July 2007

Transmission electron microscopy has been used to study the dislocations associated with the plastic deformation and recovery of single crystals of synthetic quartz. The crystals were deformed in compression at a constant strain rate under confining pressure over the temperature range 300 to 900°C. At 300°C rapid work‐hardening occurs due to the development of a high uniform density of tangled dislocations. The dislocation substructures which are produced during deformation at higher temperatures correspond closely to the substructures which develop on annealing a work‐hardened crystal. There is evidence that the rate of this recovery is strongly dependent upon the concentration of hydrogen present due to the influence of this impurity on dislocation climb. It is suggested, therefore, that the well‐established hydrolytic weakening of quartz occurs when the rate of recovery exceeds the rate of work‐hardening. This hypothesis predicts the observed variation of the hydrolytic weakening temperature with hydrogen concentration, strain rate, and crystal orientation.
Thermosensitive Discontinuities and Hystereses of the Photoemission of Alkali–Antimonide Cathodes at High Light Intensities
Authors: Hora H. , Kantlehner R.
Published: July 2007

Anomalies of the dependence of the photoemission from multialkali and Cs3Sb cathodes on temperature between 12 and 300°K were analysed. The sublinearities, discontinuities, and hystereses of the emission current at varying intensities were measured in dependence on the spectral properties of the incident light, temperature of the cathode, time, geometry of illumination, preillumination and, partial pressure of helium. We find the optical absorption independent of the effects and conclude that the mechanism does not depend on the decreased dark conductivity of the non‐illuminated cooled cathode. An explanation is possible on the base of an increase of the surface potential due to trapped photoelectrons, creating consequently an electric field in the border zones of illumination where charge transport processes excite and emit additional electrons.
Systematic Reflections in Transmission Electron Diffraction
Authors: Serneels R. , Gevers R.
Published: July 2007

The transmission and diffraction of electrons by a perfect plate‐shaped foil is considered. It is assumed that the crystal orientation with respect to the incident beam is such that there is only a single family of lattice planes, defined by the reciprocal lattice vector g, at the exact Bragg orientation, i.e. sg = 0. The active reflection g is the reflection of lowest order on the reflecting planes. Reflections on other families of lattice planes are ignored. Furthermore one considers only the case of a crystal with a center of symmetry, or that of reflecting plane in a non centro‐symmetrical crystal, which is a mirror plane or belongs to the zone of a symmetry axis of even order. The systematic reflections 2 g, – g, 3 g, – 2 g, 4 g, – 3 g, etc. on the reflecting plane are taken into account. First it is shown that the four‐beam case (0, g, 2 g, – g) can be solved analytically, giving rise to very simple formulae, which can be easily discussed. In particular one obtains a simple expression for the corrected extinction distance. Next the influence of the further beams is discussed. It is shown that the four‐beam case is a good approximation, and a quick method is described for obtaining the further corrections on the extinction distance.
Optical Absorption at the Surface of a Semiconductor
Authors: Bartoš I.
Published: July 2007

The existence of bands of surface states in the energy gap of an infinite crystal gives rise to additional absorption of light. The characteristic features of behaviour of the absorption coefficient are discussed.
The Influence of Internal Stress Fields on the Velocity of Dislocations
Authors: Guiu F.
Published: July 2007

The influence of periodic internal stress fields of various types on the average dislocation velocity is investigated. An Arrhenius type equation is used to describe the dislocation velocity, and the calculations are carried out assuming that the activation volume is a) constant, and b) a function of the stress. It is shown that for almost any type of periodic field the average dislocation velocity can be expressed as a simple function of the ratio α = τ0/τa, where τ0 is the amplitude of the stress field and τa is the applied stress. The average value of the internal stress, or the hardening produced by the internal stress field, is not strictly athermal, although its temperature dependence is small. Both the temperature and stress dependence of the average dislocation velocity is influenced by the presence of internal stresses. However, this effect is small and can be neglected for most practical cases, especially at low temperatures.
The Influence of Local Potential Fluctuations on the Low‐Temperature Radiative Recombination of Compensated Germanium
Authors: Dobrego V. P. , Shlimak I. S.
Published: July 2007

The luminescence of p‐Ge doped both with Ga and As impurities in the region of “intermediate” concentrations (1016 to 1018 cm−3) has been investigated. Potential fluctuations due to random distribution of impurities in a crystal were shown to be the main factor in compensated semiconductors affecting the spectrum of radiative recombination in this region of concentrations. Under conditions of low temperatures and low excitation nonequilibrium carriers localize in close‐to‐generation‐site potential wells. The character of their recombination therewith is similar to inter‐impurity recombination with the difference that the carriers are captured not by separate impurity atoms but by their aggregates. The distances between recombination carriers in this case are shown to depend on optimal dimensions of fluctuations rather than on impurity concentration. It has also been shown that at low temperature the energy distribution of non‐equilibrium electrons does not correspond to the density‐of‐states function in the impurity band of donors.
Magnetic Field Influence on the Gunn Effect
Authors: Levinshtein M. E. , Nasledov D. N. , Shur M. S.
Published: July 2007

The magnetic field influence on the Gunn vibrations and the low‐frequency oscillations of the Gunn diode are investigated up to magnetic fields of 20 000 G. A considerable increase of the threshold field and a decrease of the threshold current are observed. The obtained results are explained in the limits of the two‐valley model.
Photostimulated Luminescence due to Hole Release in KCl and NaCl
Authors: Jaek I. , Kink M.
Published: July 2007

In the stimulation spectra of KCl–Ag and NaCl–Ag crystals, X‐rayed at 80°K, additional bands have been found for the visible emission, due to the tunneling between Vk‐ and Ag°‐ centres. The temperature dependence of these bands and the kinetics of the initial growth curves of the photostimulated luminescence allows one to connect these bands with the optical release of holes from Vk‐centres.
Fieldless Heating of Charge Carriers and Excitons in Semiconductors
Authors: Bonch‐Bruevich V. L.
Published: July 2007

The stationary distribution function of the charge carriers or excitons is calculated for a spatially inhomogeneous system. The fluctuational stability of such a non‐equilibrium stationary state is studied.
On Some Properties of TlInS2 (Se2, Te2) Single Crystals
Authors: Guseinov G. D. , Mooser E. , Kerimova E. M. , Gamidov R. S. , Alekseev I. V. , Ismailov M. Z.
Published: July 2007

The results of studies on the structure and physical properties of grown TlInS2 (Se2, Te2) single crystals are presented. Based on an X‐ray investigation the parameters of the tetragonal cells of these crystals have been determined. The electric conductivity and the Hall effect for the TlInS2(Se2, Te2) crystals have been measured over a wide temperature range. It has been revealed that in the purest crystals of the above compounds the mobility obeys the usual T−3/2 law. Some data on the photoelectric and optical properties of these materials are also reported. These crystals are shown to be photoconductors in the infrared and visible regions of the spectrum. The photoconductivity maxima for the TlInS2, TlInSe2, and TlInTe2 crystals correspond to the wavelengths of 0.525, 0.87, and 1.36 μm, respectively. In photoconductivity the respective values for the forbidden gap width are 2.3, 1.07, and 0.68 eV. From the experimental data obtained the main characteristic parameters of the crystals have been calculated.
Microscopic Theory of Band and Local States in Ionic Crystals
Authors: Evseev Z. Ya. , Tolpygo K. B.
Published: July 2007

The theory of band and local states of electrons in ionic crystals with due regard for interelectronic interaction and with some approximation to the interelectron correlation was proposed [1]. It is developed for NaCl crystals having one excess electron. The law of dispersion and the wave functions of a band electron are defined here. The minimum E(k) is at k = 0 and the effective mass is equal to 0.624 m, where m is the mass of the free electron. The energy and the radius of the polaron in strong‐bond approximation practically coincide with the results of the macrotheory [2]. This gives an opportunity to apply its methods and the approximation of intermediate and weak bonds, for at \documentclass{article}\pagestyle{empty}\begin{document}$ \mu /m = 0.624,\,\alpha = 3.95\sqrt{2\,.} \left[3 \right] $\end{document}
. The calculated potential of deformation and the acoustic mobility are in good agreement with the results of experiments [4] in a temperature range of 30 to 200°K.
Triboluminescence of Some Alkali Halide Crystals
Authors: Belyaev L. M. , Martyshev Yu. N.
Published: July 2007

A photoelectric method for the registration of the triboluminescence spectra is described. Using this method the triboluminescence spectra of LiF crystals at destruction in air, vacuum, and in an argon atmosphere are obtained. The experimental study of triboluminescence of some alkali halide crystals have been carried out under the simultaneous control of the deformation and fracture processes, surface electrization, and electromagnetic radiation in the radio range. The correlation between the nature of these processes and the light emission is established.
X‐ray Topographic Study of Defects in Quartz I. Brazil Twin Boundaries
Authors: Phakey P. P.
Published: July 2007

A systematic investigation has been made of the diffraction contrast effects observed by X‐ray traverse topography at Brazil twin boundaries in natural quartz. Evidence is presented to show that the crystal axes are not coincident across the Brazil twin boundaries but are displaced by a vector R which depends upon the composition plane of the boundaries. Consequently the displacement vectors for intersecting Brazil twin boundaries are not identical. These displacement vectors have been determined from the observed vanishing conditions for the diffraction contrast fringes at the boundaries. The expected stair‐rod type dislocations at the intersections of the twin boundaries have been found. Probable atomic models for the Brazil twin boundaries are proposed and discussed.
Field Effect and Surface Photoconductivity Studies on InSb Single Crystals
Authors: Pagnia H.
Published: July 2007

Surface photoconductivity (SPC) under light, electron, and X‐ray irradiation, and the field effect were measured below 100°K on single crystalline samples of InSb (weakly p‐doped mainly). CP‐4A etched samples have bands bent upwards on the surface (about 0.1 eV). The main excitation processes are interband transitions in InSb. Electrons then surmount the 2 eV oxide barrier of the real surfaces (internal emission) and are captured and frozen‐in in surface states, or escape into the vacuum (external emission). Information is further obtained on surface state positions, state densities, SPC kinetics, and a slowly relaxing component of SPC at the low temperature.
Binding Energy and Compressibility of Body‐Centered Cubic and Close‐Packed Hexagonal Sodium
Authors: Saxena V. K. , Kapoor Q. S. , Bhattacharya D. L.
Published: July 2007

The binding energies of the b.c.c. and c.p.h. phases of sodium have been computed using Hellmann‐type and modified Coulomb pseudopotentials. The binding energy of the c.p.h. structure is found to be about 2% more at 5°K than that of the b.c.c. structure as calculated from these pseudopotentials. The compressibility of the b.c.c. phase has also been calculated. The computed values give a fair agreement with the experimental results wherever available.
On Tunnelling and Avalanche Processes at Electroluminescence of SiC p–n Junctions
Authors: Vereshchagin I. K. , Kirichuk A. S. , Kosyachenko L. A.
Published: July 2007

The processes of the influence of a strong electric field on p–n junctions biased in reverse direction have been investigated. At voltages sufficient for electroluminescence almost in all samples a multiplication of the charge carriers created by light in the region of the SiC fundamental absorption was observed. The dark current of the initial charge carriers entering the junction increases with the rise in voltage both at low voltages when there are no luminescence and multiplication and at high voltage when such phenomena are observed. In this case the dependence of the initial current on voltage and temperature agree with tunnel effect theory. In some samples the luminescence was not accompanied by a marked carrier multiplication; both impact and tunnel mechanisms of electroluminescence exitation occur in SiC.
Influence of Lattice Vibrations on the Hyperfine Structure Constants of VK‐ and VF‐Centres in Earth Alkaline Fluorides
Authors: Assmus W. , Dreybrodt W.
Published: July 2007

The ESR spectra of diatomic F molecules of the type VK and VF in CaF2, SrF2, and BaF2 show temperature‐dependent hyperfine structure constants. This temperature dependence results from a vibration with sharp frequency ω, coupling to the hfs. It can be described by A(T) = A0 + α coth (ħ ω/2 kT). The frequencies ω for the VK‐ and VF‐ centres are determined from the experimental data. Molecular vibrations of the centre or lattice vibrations may produce change of the hfs‐constants. The frequencies of such vibrations are calculated. From the comparison with the measured ones it is concluded that the change of the hfs‐constants results from a lattice vibration of the cation sublattice in [110] direction with k at the vicinity of the edge of the Brillouin zone.
Brillouin Scattering Studies of Acoustoelectric Domain Formation in Semiconducting CdS
Authors: Wettling W. , Bruun M.
Published: July 2007

The growth of the flux intensity in acoustoelectric domains in semiconducting CdS has been followed over five orders of magnitude for frequencies between 0.2 and 5 GHz using the Brillouin scattering technique. The form of the flux domains is exponential on both sides with a halfwidth of about 300 μm. By studying their formation in the very early stage before the current decay, it was found that the frequencies and amplification factors of the flux appearing first are close to those predicted by the linear theory. After the current has started to decay, higher and lower frequencies are observed, the lower with much higher amplification and intensities. It seems that the electric field inside the domain does not have an essential influence on the flux growth. The experimental results are compared with some acoustoelectric amplification models.
Injection and Field‐Induced Excitation of charge Carriers in CdS single Crystals
Authors: Rohde H. J.
Published: July 2007

The current‐voltage characteristics of CdS single crystals were investigated in the temperature range of liquid nitrogen up to fields of the order 105 V/cm. At low electrode separations double injection predominates. At larger distances, however, impact ionization of a shallow trapping state, positioned in the range of 0.1 to 0.2 eV below the conduction band is found. An investigation of the characteristics at different electrode separations and temperatures as well as different directions of the electric field intensity with respect to the c‐axis supports the statements.
Contribution to the Theory of the Electric Impedance of Crystals in the Presence of an Acoustic Instability
Authors: Ioffe I. V. , Shapiro B. I.
Published: July 2007

It is shown that the real part of the electric impedance of a semiconductor can oscillate with a definite frequency in the presence of an acoustic instability. Conditions of the change of the sign of the real part of the impedance are found.
The ESR of Cu2+ ions in Lithium Chloride
Authors: Pilbrow J. R. , Stevenson R. W. H.
Published: July 2007

Electron spin resonance measurements on lithium chloride containing copper at 20°K show that Cu2+ ions with an |x2 – y2〉 ground state are produced in cation sites by X‐irradiation at low temperatures. The Cu2+ centres, which are thermally unstable at room temperature, possess [100] tetragonal symmetry which is believed to arise solely from the Jahn‐Teller effect. Analysis of the g‐values and the Cu2+ hyperfine structure indicates that the admixture of the |3 z2 – r2〉 level into the |x2 – y2〉 ground state is unimportant.
Raman Scattering by Manganese Impurities in Zinc Sulphide
Authors: Beserman R. , Nusimovici M. A. , Balkanski M.
Published: July 2007

The experimental study of Raman scattering of light in a cubic crystal of zinc sulphide by a substitutional manganese impurity has been achieved. A theoretical approach based on symmetry properties of the lattice gives a satisfactory interpretation of the resonant modes of vibration of the manganese impurity for various concentrations.
GaAsGaP Heterojunctions
Authors: Davis M. E. , Zeidenbergs G. , Anderson R. L.
Published: July 2007

GaAsGaP n–n, n–p, and p–n heterojunctions were fabricated by growing GaAs onto GaP substrates using HCl as the transport agent in an open‐tube system. It is found that the conduction band is continuous at the interface. This is in contrast to reported discontinuities of 0.65 and 0.22 eV. A high concentration of interface states is present in such junctions as evidenced by the frequency dependence of capacitance, and the I–U characteristics. Photocurrent response is as expected in n(GaAs)–p(GaP) heterojunctions, but a modulation effect was observed in p(GaAs)–n(GaP) junctions. This effect is not well understood.
The kohler rule of magnetoresistance in neutron‐irradiated aluminium at 4.6°K
Authors: Böning K. , Fenzl H. J. , Olympios E. , Welter J. M. , Wenzl H.
Published: July 2007

An investigation is made of the range of validity of the Kohler rule for the transverse magnetoresistance of aluminium at 4.6°K by introducing structural defects with different concentration and configuration by low temperature reactor irradiation and subsequent annealing. – During irradiation the Kohler rule is extremely well satisfied, because in this case only the concentration of identical defects is enlarged. After step‐annealing, however, there are large deviations, because the structural defects not only recombine but also rearrange to other configurations, which corresponds to a change in the mean scattering anisotropy. The influence of small angle scattering is to be seen well in the measurement curves.
The Investigation of Electroconductivity and Viscosity of the Melt CdGeP2
Authors: Serednii A. P. , Goryunova N. A. , Tychina I. I. , Nikolskaya G. F. , Evfimovskii I. V. , Novikova A. N. , Kovaleva I. S.
Published: July 2007

An investigation of the conductivity and viscosity of semiconducting compound CdGeP2 in the liquid state has been made. It has been found that the transition of this compound from the solid to the liquid state coincides with the pattern “semiconductor → semiconductor”. The value for the activation energy of the conductivity of the melt completely coincides with the energy gap of vitreous CdGeP2. It might be explained with the similar structure of the short‐range order.
Creep Kinematics of Cross‐tie Domain Walls
Authors: Telesnin R. V. , Ilyicheva E. N. , Kanavina N. G. , Osukhovskii V. E. , Shishkov A. G.
Published: July 2007

Domain‐wall creep was studied by the powder pattern method. To increase the resolution of the boundary pictures, microphotometry of the photographs was made. The centre of the boundary on the film was determined to an accuracy of ± 0.05 μm. The direct observation of elementary acts of creep enables to substantiate and refine the kinematic creep model – the model of varying boundary curvature. The curvature variation is due to the variation in the boundary rigidity as a result of the induction of magnetostatic “charges”.
Cation Distribution in Gallium‐Substituted Yttrium Iron Garnets by Mössbauer Effect Spectroscopy
Authors: Czerlinsky E. R.
Published: July 2007

Recoil‐free nuclear‐resonance absorption was measured on Y3GatFe5‐tO12 powders with 1.75 ≦ t ≦ 4.0. A constant acceleration spectrometer was used, and the investigations were performed at room temperature, that is, above the Curie temperature of these compounds. For each material, we observed three resonant absorption maxima with different heights. The position of the maxima on the velocity scale is independent of composition. For each spectrum, two doublets which arise from the quadrupole splitting of the 57Fe nuclei are assigned; one doublet arises from the 57Fe nuclei in the tetrahedral(d) sites, whereas the other arises from the 57Fe nuclei in the octahedral (a). From the relative values for the intensities D and A for the d‐and a‐sites together with the known amount of t, the fraction x/t of the Ga3+ ions in the d‐sites was determined for each compound. The results were compared with work on cation distribution in substituted garnets obtained from 1. magnetization measurements, 2. X‐ray and neutron diffraction, and 3. thermodynamics of solid solutions. At Ga concentrations t ⪆ 2.0, our results deviate from the ones obtained from magnetization data. The distribution function proposed under 3. from the equilibrium conditions for ions in multisublattice structures is consistent with the experimental data presented in this paper.
Effect of Doping on the Shift of the Optical Absorption Edge for Circularly Polarized Waves in a Magnetic Field and on the Interband Faraday Rotation in n‐Type GaAs
Authors: Theilemann W.
Published: July 2007

The difference of the shift of the optical absorption edge for σ‐ and σ+ polarized waves in a magnetic field is measured on a series of n‐type GaAs samples with various doping levels. The measurements are performed at 77 and 300°K. Following the theory of Luttinger and Kohn[1] the shift of the absorption edge was calculated under the assumption of a broadening of the Landau levels in such a manner as to yield exponential tails with decreasing energy. The assumption of such a broadening is justified since it is known that there are state density tails which extend exponentially decreasing into the gap [2,3]. The effect of doping is considered by applying the Fermi distribution function to the electrons in the Landau levels of the conduction band. The position of the Fermi level and the shape of the absorption edge are determined by absorption measurements. The calculation is in good agreement with the experiment and permits also the explanation of the effect of doping on the interband Faraday rotation near the absorption edge.
Mößbaueruntersuchungen an Sn119‐dotiertem AgCl
Authors: Meisel W. , Schnorr H. , Hennig K.
Published: July 2007

Es wurden die Mößbauerspektren des Sn119 in AgCl‐Polykristallen, die mit 0,05 mol% Sn119 dotiert waren, gemessen. Die Spektren zeigen jeweils eine einzelne Linie mit einer sehr geringen Temperaturabhängigkeit ihrer Intensität. Aus der Isomerieverschiebung folgt, daß das Zinn als Sn4+ vorliegt. Als mikroskopisches Modell wird der Einbau von Sn119 auf Zwischengitterplatz, umgeben von vier Kationenlücken, erörtert.
Internal Friction due to Long‐Range Diffusion of Hydrogen in Niobium (Gorsky Effect)
Authors: Cantelli R. , Mazzolai F. M. , Nuovo M.
Published: July 2007

The Gorsky effect is investigated by internal friction measurements in the niobium‐hydrogen system at a vibration frequency of 16 Hz. The diffusion coefficient D of hydrogen in niobium is measured as a function of temperature. It is found that D, in the temperature range from ≈︁ 235 to ≈︁ 830 °K, obeys the Arrhenius relation D = D0 exp [– W/kT] with D0 = 5.4 × 10−4 cm2/s and W = (0.109 ± 0.005) eV. A deviation from the exponential law is observed at lower temperatures.
Study of Symmetrical Walls in Permalloy and Lorentz Microscopy
Authors: Vigier P. , Haymann P.
Published: July 2007

It is shown that the deformations in thin ferromagnetic films submitted at a magnetic perpendicular field involve the existence of “symmetrical walls”, energies which widths are calculated. The experimental study is achieved by the Lorentz microscopy where a peculiar contrast is associated with those walls.
Scattering of Carries by Charge Centres Under Conditions of Quantum Size Effect
Authors: Shik A. Ya.
Published: July 2007

The relaxation time of electrons in very thin films is calculated assuming the electrons are scattered by a screened Coulomb potential. The specific peculiarities of the screening in thin films is taken into account. It is shown that the conductivity may decrease with the film thickness. Comparison with experimental results is made.
Paramagnetic Relaxation in Dysprosium and Terbium Ethyl Sulfate with Regard to Various He Baths
Authors: Kump U.
Published: July 2007

The relaxation behaviour of dysprosium and terbium ethyl sulfate immersed in liquid 3He and 4He was studied. In the case of dysprosium ethyl sulfate measured in the temperature range 0.8 ⪅ T ⪅ 1.4 °K there was found a direct process for an external magnetic field parallel to the crystallographic symmetry axis of the crystal. The contribution of heat conduction in the 3He and normal fluid 4He to the measured relaxation times has been estimated from the results on terbium ethyl sulfate.
Linear Stark and Pseudo‐stark Effect of the F Centre in LiF and NaF
Authors: Johannson G. , Von Der Osten W. , Piehl R. , Waidelich W.
Published: July 2007

A linear Stark and pseudo‐Stark effect is observed at the zero‐phonon absorption lines 5456 Å in NaF and 4874 Å in LiF at 4.2 °K. From the combination of uniaxial stress and electric field results the corresponding colour centre is found to belong to the C3v point symmetry group. In accordance with the model for the ionized R centre (F centre) the lines are due to transitions between a single ground state and a degenerate excited state. For the analysis of the experimental results the method of moments is used and a comparison with the Stark and pseudo‐Stark effect of the R centre is presented.
The Conduction Mechanism of Self‐Compensated Highly Disordered Semiconductors (A Possible Model for Semiconducting Glasses)
Authors: Böer K. W.
Published: July 2007

Ambipolar conduction in a self‐compensated highly disordered semiconductor with the Fermi‐level pinned close to the middle of the band gap is discussed and it is shown that predominant p‐type conduction occurs because of a higher effective level density in the narrower valence band, which usually is not compensated by a lower hole mobility due to a higher effective mass of holes. Because of a non‐negligible contribution of minority carriers, the Hall‐mobility is considerably lower than the actual carrier mobilities and can vanish and even invert its sign, if the major carrier transport takes place higher inside the bands where the effective masses increase markedly and/or if the Fermi‐level lies slightly above the middle of the band gap. The shift of the carrier transport into the bands is assumed to be caused by small potential barriers extending from the band edges into the band and being due to a sufficient density of charged centers. The results of this model are compared with experimental findings on a chalcogenide Ge0.33As0.2Te0.2S0.27‐glass yielding mn = 0.2 m0, mp = 1.6 m0, μn = 210 cm2/Vs, μp = 75 cm2/Vs, n = 5 × 107 cm−3, and p = 4 × 108 cm−3 for an observed semiconductivity of 5 × 10−9 Ω−1 cm−1 and Hall‐mobility of −0.5 cm2/Vs at room temperature. The activation energy for semiconductivity is 0.72 eV, the optical band gap ≈︁ 0.9 eV, yielding a barrier height within the bands of ≈︁ 0.25 eV.
The Conduction Mechanism of Highly Disordered Semiconductors (A Possible Model for Semiconducting Glasses) II. Influence of Charged Defects
Authors: Böer K. W.
Published: July 2007

The band perturbation due to a high density of charged defects is discussed, and it is shown that the saddle point between Coulomb‐repulsive centers can act as a potential barrier, above which conductivity takes place, if the average distance between these saddle points is small compared to the mean free path of the carriers. For a defect density of 1020 cm−3 the saddle points lie ≈︁ 0.25 eV from the respective band edges and are an average of 20 Å apart from each other, while the mean free path, as calculated from ion‐scattering for carriers of an energy 1 kT above these saddle points is about three times as large. These potential barriers are suggested to be responsible for the fact, that for glasses the thermal activation energy for semiconductivity is usually 0.1 to 0.3 eV larger than half the optical band gap.
Superlinear Photoconductivity
Authors: Stöckmann F.
Published: July 2007

Using the method described in the preceding paper [1] general conditions are derived for the case that a photocurrent increases stronger than linear with the excitation strength G. If this so‐called superlinear photoconductivity is caused by a superlinear dependence of the majority carrier concentration on G, the necessary and sufficient conditions for an n‐type conductor are as follows: 1. With increasing G a group of imperfections whose concentration is sufficiently large and which were essentially unoccupied before, has to be fully occupied by electrons. 2. There must not simultaneously be a group of hole traps fully occupied by holes. 3. The rate determining slowest process in the recombination mechanism must be the capture of holes by the recombination centres.
Experimental Study of the Conduction Band of GaSb
Authors: Bordure G. , Guastavino F. , Llinares C.
Published: July 2007

Simultaneous Faraday rotation, reflectivity, and Hall effect measurements made on two Te doped, n‐type GaSb single crystals of various doping, have been used to determine the characteristics of the L1 conduction band minimum as a function of the ratio K = m1*(L1)/mt*(L1).

Using the theoretical value K = 13, we have obtained for the transverse effective mass of the (111) minimum electrons and for the energy separation of the L1 and Γ1 minima: mt*(L1) = 0.12 me and ΔE = 83 meV at 300°K with d(ΔE)/dt = 5.5 × 10−5eV/°K. Complementary conductivity measurements were made to obtain the mobilities of the two conduction band carriers.
F Band Absorption in Alkali Halides as a Function of Temperature
Authors: Dawson R. K. , Pooley D.
Published: July 2007

Measurements have been made of the F centre optical absorption function for all twenty alkali halides at seven temperatures between ≈ 5 and 300 °K. The measurements have been fitted with a shape function consisting either of an unsymmetrical Gaussian band or, for the halides of cesium, of three symmetrical Gaussian bands of equal intensity, and the appropriate band parameters derived. The results are given of fitting the temperature variations of these parameters with the predictions of theory using one and two interacting vibrational modes. The variation of basic parameters from halide to halide is discussed.
The Influence of Hindered Rotation of Molecules in Molecular Crystals on the Spectral Parameters of Nuclear Quadrupole Resonance
Authors: Lotfullin R. Sh. , Semin O. K.
Published: July 2007

The influence of anisotropic reorientation movements of molecules in molecular crystals on NQR spectral parameters (frequency v; quadrupole coupling constant e2qQ, asymmetry parameter of the electric field gradient η, spin–lattice (T1) and spin‐spin (T2) relaxation times) has been considered theoretically by the spectral density method. The calculations were performed considering the different nuclear spins. It is necessary to differentiate between models with “rapid” and “slow” (compared to the experimental frequency) reorientations.
Dislocation Helices in Molybdenum
Authors: Pegel B. , Becker C.
Published: July 2007

A description and theoretical discussion of an experiment is given where the plastic deformation of a molybdenum specimen is entirely due to dislocation helices moving along their glide cylinders and leaving, as the final dislocation state, arrays of parallel screw dislocations.
Reactions between Perfect Dislocations in Semiconductor Devices
Authors: Sauvage M. , Simon D.
Published: July 2007

Semiconductor devices of “thyristor structure” are studied by the X‐ray topographic method. Typical perfect dislocations are generated in n‐p junction and glide in neighbouring {111} slip planes close to the crystal surface, thus contributing to the relaxation of stresses located at the boundary between the two regions of different lattice parameters. — Dislocation reactions are observed and interpreted on the basis of a cross‐slip mechanism. The reaction product is an edge segment of sessile type increasing the brittleness of the silicon sample.
Preparation and Some Physical Properties of ZnGeP2
Authors: Ray B. , Payne A. J. , Burrell G. J.
Published: July 2007

Single crystal ZnGeP2 has been prepared by slow cooling from the melt and by vapour transport of the constituent elements in a phosphorus atmosphere. X‐ray powder studies lead to a c/a ratio for the chalcopyrite‐structured ZnGeP2 of 1.961. Thermal analysis measurements give a phase change at (952 ± 2) °C, probably disordering of chalcopyrite to zinc blende, and congruent melting at 1025 °C. Resistance‐temperature investigations suggest that acceptor levels at 0.10 and 0.62 eV control the free carrier concentration above and below room temperature, respectively. Undoped ZnGeP2 is always p‐type. Minority carrier studies point to an electron mobility between 103 and 104 cm2/Vs. Photoconductivity and optical absorption measurements lead to the conclusion that the direct energy gap in ZnGeP2 is 2.25 eV.
Conducting and Insulating Incorporation of Antimony into the BaTiO3 Lattice
Authors: Schmelz H.
Published: July 2007

Sb‐doped BaTiO3 is semiconducting only within a relative narrow concentration range. An explanation of this fact requires the knowledge of the lattice site occupied by the Sb. By means of X‐ray diffraction, neutron diffraction, and microprobe analysis it could be shown that Sb concentrations up to 10 at% are completely incorporated on Ti sites if an equivalent amount of Ti vacancies is offered, whereas the Sb substitutes Ba sites only partly even in the presence of an excess of TiO2. The Sb can cause conductivity in BaTiO3 only if it is incorporated on Ba sites. For this purpose a high excess of TiO2 is required. The transition from conducting to insulating incorporation is explained by a trapping mechanism caused by coupling of Sb with Ba vacancies taking into account the influence of the barrier layers.
Cyclotron Resonance in Tellurium
Authors: Radoff P. L. , Dexter R. N.
Published: July 2007

Cyclotron resonance of electrons and holes has been observed in tellurium single crystals at 24 and 70 GHz and at liquid helium temperatures. In pure specimens and at low temperatures the surfaces of constant energy for the holes are well described by 4 prolate ellipsoids of revolution about the c‐axis located near the Brillouin Zone corners. At higher hole energies produced by thermal or optical excitation or by heavily doping the crystals, pairs of these ellipsoidal surfaces degenerate into dumbbell‐shaped surfaces of revolution. The observed isotropic resonance of high mass electrons (m* = 0.75 m0) suggests an indirect gap at low temperatures.
Epitaktisches Wachstum von Oxiden auf Eisen im Hochtemperatur‐Elektronenmikroskop
Authors: Golob P. , Horn H. , Warbichler P.
Published: July 2007

Es wird die Erscheinung der Epitaxie von Eisenoxiden auf Eisen untersucht, wobei zwei Oxidmodifikationen beobachtet wurden. Während die hexagonalen plättchenförmigen Kristalle zwanglos dem α‐Fe2O3zugeordnet werden können, gelingt eine Identifizierung nur auf Grund ihrer Erscheinungsform bei den würfelförmigen Kristallen nicht. Es wurde deshalb dieses Oxid mittels streifender Elektronenbeugung untersucht und als γ‐Fe2O3identifiziert. Die Epitaxie beider Modifikationen konnte gittergeometrisch erklärt werden.
Stopping Cross Sections of Li+ Ions with Energies from 30 to 100 keV in Various Target Materials
Authors: Bernhard F. , Müller‐Jahreis U. , Rockstroh G. , Schwabe S.
Published: July 2007

The electronic stopping cross sections for lithium ions in carbon, aluminium, titan, nickel, and copper are reported. The dependence on energy in the interval from 30 to 100 keV and on the atomic number of the target atoms are investigated. By using some data from other authors a characteristic dependence of the electronic stopping cross section on the atomic number of the target atoms is found.
Phonon Widths in Nacl, KCl, and RbCl from Neutron Measurements
Authors: Raunio G.
Published: July 2007

In a systematic study of phonon dispersion relations in NaCl, KCl, and RbCl results were also obtained on phonon widths in some branches, primarily at 80 °K, but to some extent also at 300 °K. The widths for all three chlorides are found to be mostly between 0.04 and 0.10 (in units of 1013 rad s−1). In all cases the increase of the width between 80 and 300 °K is less than the estimated error of the width at 80 °K. The results are discussed and some of the difficulties of such measurements are pointed out.
Interpretation of Self‐Diffusion and Vacancy Properties in Copper
Authors: Mehrer H. , Seeger A.
Published: July 2007

Recent tracer measurements of the self‐diffusion coefficient by Rothman and Peterson are analysed in conjunction with the determination of equilibrium concentrations of vacant lattice sites by Simmons and Balluffi and the isotope effect on self‐diffusion. The following values for monovacancy and divacancy properties are obtained (in the usual notation): E = 1.03 eV, E = 1.06 eV, S ≈ 0.3 k, E − E 0.54 eV, divacancy association entropy ΔS2 V ≈ 2 k, temperature coefficient of monovacancy self‐diffusion energy 2 α = d (E + E)/d(kT) ≈ 0.5, frequency factors for mono‐ and divacancy migration v exp (S) = 1.4 × 1014 s−1, v exp (S/k) = 1.6 × 1014s−1. The monovacancy jump frequencies near room temperature are in excellent agreement with the values obtained from dislocation pinning experiments of Thompson and Paré.