bluuebunny/crossref_metadata_2025 huggingface dataset:
Intrinsic Stacking Faults on {112} Planes in the B.C.C. Lattice
Authors: Eichler H. , Pegel B.
Published: July 2007

The possibility of intrinsic stacking faults in the b.c.c. lattice is discussed for a central force model. The existence of stable stacking faults depends on the cut‐off radius of the interatomic potential. For rather small cut‐off radii the model predicts stacking faults. However, we obtain stacking fault vectors different from those predicted by the hard‐sphere model. Further, the asymmetry of the stacking fault energy surface with respect to displacements in ± 〈111〉 directions depends on the cut‐off radius.
Diffusion of Zinc in Lithium
Authors: Mundy J. N. , Ott A. , Löwenberg L. , Lodding A.
Published: July 2007

Experimental details are given of a thin film sectioning technique for the measurement of tracer diffusion in lithium metal. Results are given for 65Zn in Li between 57 and 173 °C. They are expressed by D = D0exp ( − Q/RT), where \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {0.57\begin{array}{*{20}c} { + 0.31} \\ { - 0.20} \\ \end{array}} \right){\rm cm}^{\rm 2} {\rm /s} $\end{document} and Q = = (12.98 ± 0.24)kcal/mol. The activation energy equals, within margins of error, that of self‐diffusion in Li. The agreement between vacancy based theories and the present results appears rather doubtful.
Optical Effects of Free Carriers in Thin α‐Ag2S Films
Authors: Geserich H. P. , Suppanz W.
Published: July 2007

The intrinsic and the free carrier absorption has been investigated in thin α‐Ag2S films as a function of carrier concentration. By producing an excess of silver the electron concentration in α‐Ag2S increases from the intrinsic concentration value ne = np = 1.2 × 1018 cm−3 up to ne = 3.6 × 1019 cm−3 (at 200 °C). Since the silver to sulfur ratio cannot be frozen in, either the chemical potential of silver or that of sulfur must be fixed by external conditions during the measurements. From the spectral dependence of the dielectric constant direct transitions (ΔEdirect = 0.87 eV), the conduction band mass (m*e = 0.24 m0) and the scattering mechanism of the electrons (scattering by charged centres) were determined. It was not possible to deduce the band gap (≈ 0.1 eV from electrical data) from optical measurements.
The Change of Sound Velocity at the Bose‐Einstein Condensation of Excitons in Crystals
Authors: Miglei M. F. , Moskalenko S. A. , Lelyakov A. V.
Published: July 2007

Belyaev's equations are generalized for the case of a non‐ideal gas of excitons interacting with the phonons in the crystal at T = 0. In the first approximation of the perturbation theory the energetic spectrum of the elementary excitations is received. The change of sound velocity in some crystals is calculated for different assumptions with reference to the constants of exciton‐exciton and exciton‐phonon interactions.
All Effective Mass Approximation for Several Bands
Authors: Lukes T. , Roberts M.
Published: July 2007

The effective mass formalism is generalized to include the effect of several bands by constructing an approximate Green's function for the periodic lattice. Energy levels are obtained for a hydrogenic impurity in a periodic lattice described by two and three parabolic bands. In addition to the energy levels predicted by effective mass theory a deep level is found. An explicit expression for the deep level is given in terms of the band parameters and a comparison with the experimentally observed deep levels in gallium arsenide is made.
Propriétés galvanomagnétiques des alliages bismuth‐étain à 4°K et à faible champ magnétique
Authors: Malgrange J. L.
Published: July 2007

Les propriétés galvanomagnétiques des alliages bismuth‐étain ont été mesurées à 4,2°K pour des dopages allant de 8×1017 à 5×1019 cm−3. On déduit des expériences le nombre de porteurs dans chaque bande, et leurs mobilités. Les résultats obtenus sont interprétés dans divers modèles de bande. On met ainsi en évidence la forme non parabolique de la principale bande de valence. On observe une augmentation des mobilités des porteurs légers près des limites des bandes. Ce résultat s'interprète comme résultant de la diffusion sur des impuretés ionisées écrantées par plusieurs types de porteurs de densités d'états très differentes. La comparaison des mobilités dans les bandes centrées aux points L de la zone de Brillouin met en évidence la similitude de ces bandes.
Diffraction by H.C.P. Crystals with Extrinsic Faults — The Solution by Difference Equations
Authors: Holloway H.
Published: July 2007

Diffraction by h.c.p. crystals with randomly arranged extrinsic faults is analysed using the difference equation method. The results confirm the random‐walk calculation by Lele et al. An earlier difference‐equation calculation is shown to be in error.
Phase Relations, Crystal Structures, and Magnetic Properties of Erbium—Iron Compounds
Authors: Buschow K. H. J. , van der Goot A. S.
Published: July 2007

The phase relations, crystal structures, and magnetic properties of intermetallic compounds occurring in the Er–Fe system have been investigated. A phase diagram is given. The lattice constants of the compounds ErFe2, ErFe3, Er6Fe23, and Er2Fe17 have been determined. These compounds are ferrimagnetic with the Fe moments coupled antiparallel to the Er moments. Their Curie temperatures decrease with increasing Fe concentration. The compounds ErFe2, ErFe3, and Er6Fe23 have been observed to show a compensation point.
Time‐Dependent Ginzburg‐Landau Equation for Superconducting Alloys in High Magnetic Fields
Authors: Weller W.
Published: July 2007

A superconductor containing nonmagnetic impurities is considered in the limit of small mean free path (l ≪ ξ0) and high magnetic field (H ≈ Hc 2). With the help of the method developed by Gorkov and Eliashberg the time‐dependent Ginzburg‐Landau equation and the differential equation for the vertex part are derived from the microscopic theory. The resulting Ginzburg‐Landau equation is appreciably simplified in the cases, in which the vertex part reduces to the scalar electromagnetic potential. It is shown that this simplification is possible for the case of slow motion of the lattice of the vortex lines (flux‐flow) caused by a static electric field.
Collision Integrals for Displaced Maxwellian Distribution
Authors: Bløtekjær K. , Lunde E. B.
Published: July 2007

The rate by which particles, momentum, and kinetic energy are transferred in collisions is considered for charge carriers with displaced Maxwellian velocity distributions. The collision integrals are expanded in power series of the average momentum and exact expressions are obtained for the general term of the series. The following scattering processes are considered: deformation potential and piezoelectric coupling to acoustical phonons, polar and nonpolar coupling to optical phonons, intervalley scattering, equivalent valley scattering, ionized impurity scattering, and electron‐hole scattering. Exact analytic summation of the series is possible for some processes. It is shown that, to second order in the average momentum, the loss of particles and energy (but not momentum) depends only on the average kinetic energy of the carriers, and not on how the energy is distributed among thermal and drift energy.
Radiative Recombination in Highly Doped Germanium
Authors: Benoit à la Guillaume C. , Cernogora J.
Published: July 2007

Using optical injection the recombination radiation in germanium doped up to 3.2 × 1019 cm−3 with arsenic has been studied at low temperatures (4, 14, and 77 °K). Several spectra have been reported previously. The purpose of this paper is to explain: a) the extent to which the momentum conservation is ensured by the impurities; b) the shape and position of the spectra at least qualitatively for the highly doped samples by taking into account the density of states tail of the holes.
ESR Spectra of Gd3+‐Doped SrMoO4 and CaWO4 in External Electric Field
Authors: Nepsha V. I. , Sherstkov Yu. A. , Legkikh N. V. , Meilman M. L.
Published: July 2007

Linear splitting of ESR signals of Gd3+ ions introduced into SrMoO4 and CaWO4 lattices were observed under applied electric field. Measured signal shifts can be described quite accurately in terms of a correction which is added to the spin Hamiltonian and at most includes only quadratic terms of spin projection operators. It has been found that the constant Re (R), characteristic of the signal shifts of Gd3+ impurity ions, is somewhat greater for SrMoO4 than for CaWO4. The experimental results can be explained consistently only by assuming that the local symmetry of the neighbourhood of Gd3+ ions in SrMoO4 and CaWO4 is represented by the S4‐group. By way of a specific example it is shown that the study of ESR spectra in an externally applied electric field gives a wide opportunity for establishment and more exact definition of a symmetry group of the local neighbourhoods for impurity ions in crystals.
Conduction in Strongly Compensated p‐Type GaSb
Authors: D'olne Campos M. , Gouskov L. , van Mau A. Nguyen
Published: July 2007

Hall coefficient and resistivity of strongly compensated p‐type GaSb are measured between 10 and 300 °K. The results are interpreted in the high temperature range by free hole transport in the valence band. In the low temperature range hopping charge transfer between impurity centres is supposed to account for conduction.
The Preparation of Graded‐Band‐Gap Single Crystals of II–VI Compounds
Authors: Reimers P.
Published: July 2007

Graded‐band‐gap single crystals of ZnxCd1−xSe, CdS1−xSex, CdSe1−xSx, Zn1−xCdxS, and ZnxCd1−xSySe1−y with x and y increasing along the direction of growth have been prepared by two different vapor phase methods. Typical crystal dimensions in the systems CdS1−xSex and CdSe1−xSx are 6 × 7 × 20 mm3, in the other systems 2 × 3 × 8 mm3. The gradient of the band gap in the system CdS1−xSex could be varied between 0.1 and 2.0 eV/cm. The change in band gap vs. crystal position was determined by absorption measurements. All crystals show edge emission at liquid air temperature under excitation by uv light.
The Coercivity of Hard Ferrite Single Crystals
Authors: Jahn L. , Müller H. G.
Published: July 2007

Magnetic properties of Sr‐, Ba‐ and Sr‐Ba‐ferrite single crystals are reported. From torque measurements results: Sr‐ferrite: Ms = (380 ± 20) G, K1 = (3.5 ± 0.1) × 106 erg cm−3; Ba‐ferrite: Ms = (380 ± 20) G, K1 = (3.2 ± 0.1) × 106 erg cm−3. A large difference was found by a comparison of Hci, theor (coherent rotation) with Hci, meas (oriented Sr‐ferrite magnet). The very small (generally even positive) nucleation fields, measured on single crystal plates of different chemical composition and different crystal sizes can qualitatively explain the low values and the grain size dependence of Hci.
Transverse Elementary Excitations of the System of Interacting Crystal Electrons
Authors: Stolz H.
Published: July 2007

From many‐body theory the dielectric tensor is calculated for a system of crystal electrons under the assumption of a statically screened interaction. For an insulator with cubic symmetry the result is inserted into the dispersion equation defining the transverse elementary excitations. The discrete roots of this equation are shown to correspond to excitons and, under certain conditions, to collective excitations which may be characterized as “transverse plasmons”. Since the transverse elementary excitations determine the surface impedance and thus the optical properties of the system, one should expect the transverse plasmons to be observable in optical investigations. In the framework of the systematic many‐particle approach the notions of bare excitons, true transverse and longitudinal excitons, and polaritons are discussed.
Electrical Properties of Monocrystalline Uranium Diphosphide
Authors: Henkie Z. , Trzebiatowski W.
Published: July 2007

Electric resistivity (2 to 600 °K), thermoelectric power (100 to 700 °K), and Hall effect (290 to 450 °K) were determined for single crystals and polycrystalline samples of UP2. This compound possesses tetragonal structure and exhibits a strong anisotropy of the transport properties. At room temperature the resistivity along the c‐axis is about three times larger than in the perpendicular direction (≈ 700 and 205 μΩ cm, respectively), while the thermoelectric power is two times lower along the c‐axis (≈ +20and +37.8μV/°K). The ordinary Hall coefficient with negative sign is equal to ‐3 × 10−12 V cm/A Oe, the carrier concentration is 2 × 1022 cm−3 and the estimated Fermi energy is about 3.2 eV. The phenomenological interpretation of the obtained data is based on a model with a conduction band resulting from the overlap of 7 s and 6d bands while the 5f electrons yield a narrow band of lower energy lying apart from the conduction band.
Observation of Dislocations in Tellurium by Transmission Electron Microscopy
Authors: Doukhan J. C. , Doukhan N. , Saada G. , Thomas B.
Published: July 2007

A method of thinning tellurium single crystals by chemical polishing has been developed for the study of dislocations by transmission electron microscopy. The preliminary results concerning the identification of the glide planes and the Burgers vectors of dislocations in this material are described together with some comments on the contrast phenomena resulting from the high elastic anisotropy of tellurium.
Physico‐Chemical Properties of 1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazacyclooctane (HMX)
Authors: Maycock J. N. , Verneker V. R. Pai , Lochte W.
Published: July 2007

The electronic absorption spectrum of β‐HMX has been measured and discussed in terms of two processes, 1. an intramolecular excitation of the group and 2. possible exciton structure. The photochemical decomposition of α‐, β‐, and γ‐polymorphic forms of HMX has been investigated and shown to be a one photon process with an associated thermal process whose energy depends on the energy of photon excitation. Irradiation with 2537 Å light produces a coloring of the crystals. A tentative model for the photo‐decomposition of HMX into formaldehyde and nitrous oxide is discussed. ‐ Radiation (2537 Å) effects on the α‐, β‐, and γ‐polymorphs of HMX have been investigated by a simultaneous DTA‐TGA technique. Shifts in both exotherms and endotherms have been found with the effects being proportional to the polymorph densities, i.e. β > α > γ for the phase change endotherms and β < α < γ for the main decomposition exotherm. A possible explanation based on the different conformational structures has been proposed for the sequential radiation damage.
The Shape Parameter of Donor Band Tails in Gallium Arsenide
Authors: Wittmann H. R.
Published: July 2007

The shape parameter of the donor band tail in heavily n‐doped GaAs and in GaAs p‐n junctions has been obtained from absorption and electroluminescence measurements. The experimentally determined dependence of the shape parameter on donor concentration follows a power law as predicted by Kane.
Galvano‐Thermo Magnetic Transport Coefficients in n‐InSb at Low Temperatures
Authors: Sodha M. S. , Dubey P. K. , Sharma S. K.
Published: July 2007

GTMTC have been calculated in n‐InSb using Kane's model and the ionized impurity scattering at low temperatures (20 to 90 °K). The theoretical results have been compared with the corresponding experimental data; it is seen that the theoretical results agree satisfactorily with the experimental values at low magnetic fields.
The Green's Function Method and the Many‐Band Model in the Study of a Short‐Range Perturbation
Authors: Goossens P. , Phariseau P.
Published: July 2007

The convergence of the Green's function method is tested on a simple linear model, for which the exact position of the extra energy states is known. It is found that this computation technique gives very accurate results, under the condition that in the sums over the energy bands a sufficient number of terms is considered. On the other hand, the numerical data agree with the recently published critical studies on the energy band problem. The approximative results in the one‐band model appear to be very unsatisfactory. Furthermore, the position of the extra energy levels is essentially determined by the bands lying nearest to the examined state.
Pressure Dependence of the Elastic Constants for Silver from 77 to 300 °K
Authors: Ho P. S. , Poirier J. P. , Ruoff A. L.
Published: July 2007

The pressure derivatives of the isothermal elastic constants for Ag have been measured from 77 to 300 °K, which were found, within the accuracy of the experiment, to be almost independent of temperature. Cook's self‐consistent method, as described by Ho and Ruoff, was applied in analysing the ultrasonic data. The high‐ and low‐temperature limits of the Grüneisen constants, γH and γL, calculated from our results are compared with γt calculated from thermal properties. In the temperature range studied, γt is found to be close to γt. However, at 0 °K, γt is in good agreement with γL. The compression data of several static and shock‐wave experiments have been re‐analyzed according to the Murnaghan equation of state. The bulk modulus and its pressure derivative so obtained agree well with the values measured by ultrasonic methods.
Radiation Defects Created by Co60 γ‐Rays in p‐ and n‐Type Si of High Purity
Authors: Konozenko I. D. , Semenyuk A. K. , Khivrich V. I.
Published: July 2007

Radiation defects created by γ‐irradiation of Co60 at 300 °K in high purity p‐Si (ϱ = 5 × 103 to 4 × 104 Ω cm) and n‐Si (ϱ = 440 to 5 × 103 Ω cm) are investigated by measurements of Hall effect and minority carrier lifetime. The oxygen concentrations in Si are in the range of 5 × 1014 to 5 × 1015 cm−3; compensation of electrically active impurities is low. It is shown that defects in high purity Si created at 300 °K are divacancies and complexes of vacancies with donor or acceptor impurities. Divacancies introduced by γ‐irradiation are not the primary defects. They become predominant after “exhaustion” of the dopant. When divacancies become the predominant defects the Fermi level occupies its limit position Ev + 0.390 eV in the gap. At low doses (Φ < 1016 photons/cm2 vacancy‐impurity complexes and at heavy doses (Φ > 1017 photons/cm2 divacancies play the main role in the recombination process.
Diffusion of Impurities in Semiconducting Substitutional Solid Solutions InAs1−ηPη and GaAs1−nPη
Authors: Arseni K. A. , Boltaks B. I. , Dzhafarov T. D.
Published: July 2007

A break was found in the dependence of the diffusion coefficient of zinc on the composition of GaAs1−ηPη at a phosphorus content in the solid solution η ≈ 0.4. The same break is observed in the dependence of the Fermi level on the composition of GaAs1−ηPη. The experimental data obtained agree with the theory. The diffusion of zinc in inhomogeneous solid solutions of GaAs1−ηPη (gradual heretojunctions) was found to increase which can be attributed to the effect of an internal electric field produced by a gradient in the hetero‐junction energy gap width as well as to a coordinate dependence of the zinc diffusion coefficient.
The Edge Emission and Phonon Effects in the Photoluminescence of CdTe
Authors: Panossian J. R. , Gippius A. A. , Vavilov V. S.
Published: July 2007

In the photoluminescence spectra of CdTe four series of lines can be resolved in the temperature range 4.2 to 78 °K; each of them is due to the electron transitions involving LO phonons (I. II. III, IV). The relative intensities of these series (the zero‐phonon lines at 1.528; 1.539; 1.548; and 1.556 eV at 20°K) depend on the sample temperature and the present impurities. The series I and II are similar in their intensity dependence on temperature to the so‐called LT (low temperature, long wavelength) and HT (high temperature, short wavelength) series of the green edge emission of CdS. Series I is dominant in crystals doped with shallow donors; this fact in connection with the temperature dependence and the dependence of the line shape on the excitation intensity leads to the conclusion that it is due to radiative transitions between shallow donors (ED = 0.015eV) and acceptors (EA = 0.0067 eV). The temperature dependence of the intensity of series II and the lines' shape suggest that this series is due to radiative transitions of electrons from the conductivity band to acceptor levels (EA = 0.0067 eV). The variation of the relative intensities of series I and II with the type and content of impurities in the samples correlates with the variation of the relative intensities of the lines in the 1.59 eV region ascribed to the exciton annihilation at donors and acceptors. The distribution of phonon replica intensities in series I and II corresponds to the expression In = I0Nn/n!(n = 0,1,2,…). The changes of the parameter N observed in some cases are due to the overlapping of series I and II with the series III or IV. the nature of which is not quite clear. The variation of the parameter N (which depends on the intensity of the electron‐phonon interaction) with the level depth is found to agree qualitatively with the theory of Hopfield. The band at 0.50 eV corresponding to the transitions involving deeper levels shows a structure which may be due to the interaction of electron transitions with local phonons having an energy of 0.045 eV.
The Interaction of Intersecting Flexible Dislocations in the Presence of Friction Forces in the Lattice. (The Case for Repelling Dislocations)
Authors: Predvoditelev A. A. , Bushueva G. V. , Bulygina T. I. , Vodzinskaya N.
Published: July 2007

The interaction of flexible repelling dislocations and their passage through one another is considered. It is shown that the process of dislocation interaction may be broken into two parts: a) gradual bending accompanied by the increase of the energy of the dislocation configuration; b) loss of stability; here the dislocation system undergoes a transition from the quasi‐static to the dynamic state. Dislocation intersection takes place under dynamic conditions. The analysis was performed for two cases: infinite crystal and thin plate. There is a certain difference in the dislocation shapes in both cases. The theoretical calculations are found to be in agreement with experimental data.
On the Mechanical Properties of Crystals with Covalent Bond
Authors: Gridneva I. V. , Milman Yu. V. , Trefilov V. I.
Published: July 2007

The parameter α = H/kTm characterizes the resistance of a crystal lattice to dislocation motion. For crystals with a covalent component of the interatomic bond the parameter α increases with the degree of the interatomic bond orientation. At high temperatures α determines the value of the critical shear stress and the temperature t* at which a sharp change of the temperature dependence of the critical shear stress begins. It is shown that t* = \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt {\alpha /} \sqrt {3\,c} $\end{document}, where c characterizes the slope of the curve τcr = f(T) at the temperature t*. Passage of the temperature t* is accompanied by a change in the mechanism of plastic deformation. The correlation of strength and plastic properties with the degree of the interatomic bond orientation is discussed.
Non‐Adiabatic Transitions in Crystals
Authors: Osherov V. I. , Medvedev E. S.
Published: July 2007

The problem of non‐adiabatic transition within an impurity centre is considered in the presence of dynamic diffusion of the vibrational wave‐packet. Using the term‐interaction constant as expansion parameter limits are found for the applicability of perturbation theory depending on the dispersion of the vibrations.
Dislocation Structure and Macroscopic Characteristics of Plastic Deformation at Creep of Silicon Crystals
Authors: Myshlyaev M. M. , Nikitenko V. I. , Nesterenko V. I.
Published: July 2007

It has been proved that the creep curve of silicon crystals under uniaxial compression at 2 to 15 kp/mm2 and 900 to 1300 °C consists of five characteristic portions, each of them exhibiting a typical dislocation structure. The stationary stage is characterized by misoriented subgrains. The stationary creep rate at stresses up to 10 kp/mm2 is governed by the kinetic equation

and controlled by barriers associated with dislocations in the subboundaries.
Magnetic Susceptibility and Energy Band Structure of Zirconium Monocarbide
Authors: Borukhovich A. S. , Dubrovskaya L. B. , Matveenko I. I. , Geld P. V.
Published: July 2007

The magnetic susceptibility of zirconium monocarbide has been studied as a function of temperature and concentration in the homogeneity region 0.58 ≦ x ≦ 1.0 and at temperatures from 20 to 1300 °K. It is shown that the temperature dependence χ(T) of all the samples may be described by the equations

The obtained results are discussed in terms of concepts available on the electronic structure of the cubic carbides of the group IVa and Va transition metals. A “flat” minimum was found in the curve N(E) lying near stoichiometric composition of the monocarbides.
Magnetic Moment Measurements on Caesium and Rubidium Manganese Chloride
Authors: Hoel L. A.
Published: July 2007

Cs2MnCl4 · 2 H2O and Rb2MnCl4 · 2 H2O are two antiferromagnetic substances with a similar triclinic structure, but with different Néel temperatures of 1.84 and 2.24°K respectively. The magnetic moments have been measured at 0.5 °K in external fields up to 70 kOe. In order to calculate the exchange and anisotropy fields the measurements were made on single crystals which were oriented with the ordering direction first parallel and then perpendicular to the field. The alignment axis is the O‐Mn‐O direction.
X‐Ray Determination of the Debye Temperature of Uranium Monocarbide
Authors: Colella R. , Dragone D. , Merlini A.
Published: July 2007

Bragg reflections by single crystals of UC, cleaved along (100) planes, were found to have negligible extinction for values of sin ϑ/λ in the range from 0.4 to 1.2 Å−1. The integrated intensities of these reflections were measured by using MoKα radiation at various temperatures from 77 to 773 °K. Plots of the logarithm of the integrated intensities vs. temperature, or vs. (sin ϑ/λ)2 at a fixed temperature, were straight lines. The slopes of the plotted lines yielded an average value θM = (265 ± 5). °K for the Debye temperature defined in terms of the uranium atoms only, and θM = (366 ± 7) °K, using the average of the U and C masses in the Debye‐Waller factor. These values are compared with those determined by different experimental techniques.
Propagation of Electromagnetic Waves in a Longitudinally Magnetized Germanium Plasma Waveguide. I. Theory
Authors: Pedersen N. F.
Published: July 2007

The propagation of electromagnetic waves in a longitudinally magnetized plasma waveguide with perfectly conducting boundary has been investigated. Numerical calculations of the wave vector have been performed for the case where the direction of both the magnetic field and the wave vector coincide either with the [111] or the [100] crystallographic direction in n‐type germanium. The frequency used is 45 GHz, and the calculation applies to non‐degenerate germanium where the applied frequency and the plasma frequency ωp are of the same order of magnitude. For small plasma radius r0 strong guiding effects are found both in the real and imaginary part of the wave vector.
Condensation and Evaporation of Vacancies at the Surface of Aluminium as a Result of Cooling and Heating
Authors: Lohne O. , Nøst B.
Published: July 2007

Black dots at the surface of one aluminium crystal were observed by X‐ray topography to develop subsequent to small positive and negative temperature changes, ±5 °C, at temperatures from 350 to 430 °C. In another crystal a one to one correspondance between black dots and thermal etch pits was observed. It was concluded that the phenomenon studied by X‐ray topography was thermal etching. Further, it was concluded that the surface did not absorb or emit vacancies as easily as the surface of the pits, and that the nucleation of the pits did not take place at termination points of dislocations at the surface.
Peak Effect in Type II Superconductors: Yield Point of the Fluxon Lattice
Authors: Chang C. C. , McKinnon J. B. , Rose‐Innes A. C.
Published: July 2007

The complicated current‐voltage (flux flow) curves obtained from type II superconductors which show the peak effect are compared to the stress‐strain curves of crystalline materials in which plastic flow at low stresses is prevented by pinning of dislocations. It is suggested that the unstable step in the current‐voltage characteristic is the result of “yield” and subsequent shearing of the fluxon lattice by dislocation motion.
Stress Relaxation and the Activation Energy for Plastic Flow in Solids: Commercially‐Pure Aluminum
Authors: Clough R. B. , Demer L. J.
Published: July 2007

A new technique of studying plastic flow using stress relaxation is presented, related in derivation to the conventionally used creep and tensile methods. No specific deformation model, such as those used in related derivations, is assumed in this derivation, in which machine deformation and the change in elastic constants with temperature are taken into account. To illustrate the technique, it is applied to plastic flow in commercially‐pure aluminum, and the results obtained are compared with those obtained by creep and tensile methods.
Equilibrium State of Slip Bands in Plastically Bent NaCl Crystals
Authors: Kästner G.
Published: July 2007

The slip bands known from ionic crystals and being typical for the initial stage of plastic deformation are found to have a limited, narrow width and a defined long‐range stress field in the present case of NaCl crystals tested in bending. This deformation structure has been investigated by combining special methods of photoelasticity, interferometry, and electron microscopy. The stress field of the slip band is described by a pile‐up of edge dislocations which are necessarily in excess within a bent crystal. The superposition of the slip‐band stress field to the applied stress leads to a stress equilibrium which can be reached “statically” or “dynamically” and which explains the limitation of the width and of the integral step height of the slip band. As a consequence of this limitation, the number of slip bands increases considerably during further bending. Thereby the atomic slip steps will cover the surface more and more homogeneously so that after a surface strain of about 1% individual slip bands can no longer be distinguished.
Magnetic Circular Dichroism of the K‐Band in Alkali Halides
Authors: Krätzig E. , Staude W.
Published: July 2007

The magnetic circular dichroism of the K‐band in the alkali halides RbCl, RbBr, RbI, KCl, KBr, and KI has been measured at temperatures between 4.2 and 77 °K. The magnetic field up to 50 kG was produced by a superconducting solenoid. We interpret the experimental results using the method of moments. The spin‐orbit splitting and the orbital g‐factors of the excited states due to the K‐band are determined. Furthermore we obtain matrix elements describing the mixture of the excited states giving rise to F‐and K‐bands. In accordance with calculations of Smith [15] the measurements confirm the Mott‐Gurney model, which attributes the K‐band mainly to 1s‐3p transitions.
Temperature‐Dependent Ground State Splitting of Mn++ Ions in Alkali Halides Induced by Resonant Vibrations
Authors: Pfister G. , Dreybrodt W. , Assmus W.
Published: July 2007

The temperature dependence of the rhombic ground state splitting tensor D of Mn++ centres with nearest cation vacancy was measured at NaCl and LiCl. The experimental data reveal a behaviour of the tensor D, which can be described by D(T) = D0 + D coth ℏ ω/2 kT. This result is interpreted by assuming a resonant vibration of frequency w coupling to the centre. This vibration changes the rhombic crystalline fields which produce the ground state splitting of the Mn++ ion according to the theory of van Heuvelen [4]. It is possible to find resonant modes in both systems NaCl and LiCl which lead to good agreement between the calculated and the experimental data.
Many Body Interaction in Alkali Halides
Authors: Sarkar A. K. , Sengupta S.
Published: July 2007

The effect of the many body interaction proposed by Sarkar and Sengupta is considered in detail. The method of homogeneous deformation is extended to include many body interactions in which the potential depends on several scaler distances. The general expressions for the elastic constants obtained by this method are compared with those obtained from the long wave theory. Including the various central interactions the model is applied to calculate the elastic constants, the cohesive energy, and the phase transition pressure for the six halides of potassium and rubidium. It is found that the inclusion of the three body interaction considerably improves the agreement.
Non‐Ohmic Behaviour in CdS Acousto‐Electric Oscillators
Authors: Janus H. M.
Published: July 2007

In thin plane parallel photoconducting CdS platelets the current is observed to deviate from the ohmic value also outside the electric field range for net round trip gain in the longitudinal wave configuration. A N‐type negative differential conductivity is observed for pulsed as well as for CW operation. Domain formation may take place and give rise to low‐frequency current oscillations superposed on the well known high‐frequency modes of the acousto‐electric oscillator. The negative differential conductivity is most likely ascribed to field‐dependent free carrier trapping though acousto‐electric effects may also be important.
Die Leerlinie im Flußliniengitter der Supraleiter 2. Art in der Nähe von Hc2
Authors: Brandt E. H.
Published: July 2007

Es werden die Energie, das Verschiebungsfeld, die Ginsburg‐Landau‐Funktion (bzw. der Ordnungsparameter) und das mikroskopische Magnetfeld einer Leerlinie mit höchster Symmetrie im Flußliniengitter der Supraleiter 2. Art in der Nähe von Hc2 mit einer in einer vorangehenden Arbeit entwickelten Methode berechnet. Das Verschiebungsfeld des Gitters in großer Entfernung von einem beliebigen lokalisierten Gitterfehler wird angegeben.
On the Problem of Construction of the Crystal Potential
Authors: Dyakin V. V. , Egorov R. F. , Shirokovskii V. P.
Published: July 2007

A model of the crystal potential for energy band calculations of solids is suggested in the muffin‐tin approximation for the electron density.
Effect of Colour Centres on the Cr3+ Spectrum in Ruby
Authors: Arkhangelskii G. E. , Morgenshtern Z. L. , Neustruev V. B.
Published: July 2007

It is found that the colour centres in ruby cause an increase of the oscillator strength in the transitions corresponding to the R‐ and B‐lines of the Cr3+ absorption and a decrease of the relaxation time τ of the luminescence in the R‐lines. These effects can be explained by a partial forbiddenness violation for the transitions 4A2 → 2E and 4A2 → 2T2 induced by the change in the intercrystalline field due to the charged colour centres (by Cr2+ and Cr4+ ions). From the broadening of the ESR lines the effective field due to the colour centres is estimated.
Electrical Instability in Half‐Insulating GaAs
Authors: Vorob'ev Yu. V. , Karkhanin Yu. I. , Tretyak O. V.
Published: July 2007

Energy spectrum and capture cross sections of local electronic states have been investigated in half‐insulating (oxygen‐doped) GaAs. The resulting spectrum of energy levels gave us a possibility to offer a general scheme of arising of negative differential conductance (DNC) for recombination non‐linearity; this scheme includes in particular two mechanisms discussed earlier [1, 2]. It was shown that in the case investigated the DNC appears as a result of recharging of impurity levels under the action of electric field. To study the effect of a uniformly distributed electric field upon semiconductor, high frequency field was employed; with the help of it we have obtained a falling region on volt‐ampere characteristic. If constant electric field is applied to the sample, a domain instability can be observed under conditions when mean field corresponds to the ohmic part of I‐U characteristic of a uniform sample; the smallest field corresponding to instability could vary within wide limits, depending on the situation at the cathode. Conceptions are developed about creation of a high‐field space charge region next to the cathode, where field reaches the value sufficient for displaying of DNC mechanism. Some information is obtained on the initial phase of creation of such a region under different conditions.
Localized Exciton States of Doped Naphthalene Crystals
Authors: Ostapenko N. I. , Shpak M. T.
Published: July 2007

Bands due to localized exciton states in a crystal arising near guest molecules have been obtained and studied in the absorption and luminescence spectra of a naphthalene crystal (T = 4.2 °K) doped with heterocyclic compounds (thionaphthene, i = T, indole, i = I, and benzofurane, i = B). The luminescence spectrum of these states is similar to the exciton luminescence spectrum of naphthalene: the polarization ratio Pi(b/a) for 0‐0 bands in the luminescence and absorption spectra decreases with 0‐0 bands approaching to the a‐component of the Davydov doublet. Simultaneously depolarization of the A1‐band occurs. From comparison between the polarization ratios for 0‐0 bands of the localized and impurity states (the case of isotopic mixtures) their common features as well as differences are found the latter being apparently due to the localized centre structure. The results are qualitatively explained on the basis of the theory of localized exciton states.
On the Magnetic Properties of Dy3+ Ion in Dysprosium Ethylsulfate Single Crystal
Authors: Taneja S. P.
Published: July 2007

Principal magnetic susceptibilities of single crystal of dysprosium ethylsulfate have been computed in the temperature range of liquid‐nitrogen to room temperature, assuming that the crystal field has C3h symmetry around the Dy3+ ion. It is observed that magnetic anisotropy increases with the decrease of temperature. The calculated magnetic moment of Dy3+ ion at room temperature is 10.48 μB, which is in good agreement with the experimental value 10.60 μB and the free ion moment 10.62 μB. Computed g‐values of the lowest level of ground state are: g∥ = 10.748, g⊥ = 0.0, which agree well with the experimental values g∥ = 10.76 ± 0.1, g⊥ = 0.0.
Radiation Damage in Selenium Single Crystals
Authors: Tiainen O. J. A. , Tunkelo E.
Published: July 2007

New radiation damage studies have been performed on a single crystal of trigonal selenium. The conductance and the thermoelectric power of the crystal were measured along the hexagonal c‐axis before, during, and after irradiation in a reactor. The temperature range covered in the measurements was 15 to 300 °K. The conductivity decreased with increasing fast neutron dose. The thermoelectric power did not change markedly during one irradiation period although a decrease of the thermoelectric power was observed when the crystal was irradiated several times at low temperatures. It seems that a decrease of the hole concentration is not sufficient to explain the conductance at low temperatures.
On the UV Absorption of Heavy Metal Ions in Alkali Halide Crystals II. Interpretation of the Temperature Dependences of the UV Dipole Strength
Authors: Fussgaenger K.
Published: July 2007

The different temperature dependences of the UV dipole strength of forbidden electronic Ag+, Cu+, and Tl+ transitions in alkali halide crystals are interpreted by electron‐phonon interaction, anharmonicity of phonons, off‐centre effects, and thermal relaxations of the centres.
Donor Levels in n‐InSb and Their Ionization in Electric Field
Authors: Ismailov I. M. , Nasledov D. N. , Smetannikova Uy. S. , Felitsiant V. R.
Published: July 2007

The temperature dependences of the Hall coefficient RH, the conductivity σ, and the electron mobility μ in n‐type InSb samples with different degree of compensation have been investigated. Deep donor levels have been found at Ec −1.8 × 10−2eV and Ec −6.7 × 10−2eV. The parameters of these levels were estimated in terms of the many‐level model. The voltage‐current characteristics and the dependences RH = f(E) and RH σ = f(E) have been studied in detail at T=4.2 °K. It is shown that at E ≈︁ (2 to 8) × 10−2 V/cm a partial ionization of the shallow donor level Ec −6 × 10−4 eV can occur (tunnel transition), whereas at E > 10−1 V/cm an impact ionization of the donor level Ec − 1.8 × 10−2 eV is produced by electrons heated by the electric field.
Investigation of Germanium conductivity Relaxation in High Microwave Fields
Authors: Banys T. , Dargys A. , Pozhela J.
Published: July 2007

A method of determining short conductivity relaxation times in semiconductors at high electric fields is presented using the microwave field harmonics due to the nonlinearity of the I‐U characteristic of the bulk of the semiconductor. It is found that the amplitude of these harmonics depends on an additional dc electric field and the semiconductor conductivity relaxation time. The method is applied to the study of conductivity relaxation of n‐type germanium at high microwave fields.
Faraday Rotation and Faraday Ellipticity in the Exciton Absorption Region of GaAs
Authors: Zvára M.
Published: July 2007

Faraday rotation and Faraday ellipticity in the exciton absorption region were measured in GaAs single crystals at room and liquid nitrogen temperatures. The experimental curves are interpreted as a sum of the contributions both of excitons and of free Landau level transitions. The value of the effective g‐factor was determined to be g* = −2.1.
Photoeffect in Metal‐Free Phthalocyanine Crystals
Authors: Usov N. N. , Benderskii V. A.
Published: July 2007

The drift mobilities of electrons (0.43 to 0.70 cm2 V−1s−1) and holes (0.24 to 0.56 cm2 V−1s−1) in thoroughly purified metal‐free phthalocyanine crystals have been measured by illumination with short light pulses. The mobilities of carriers of both sign diminish with increasing temperature: μ ∽ T−n, n = 1.3 to 1.5 for holes, n = 1.5 to 1.9 for electrons. The quantum yields of holes and electrons are equal in magnitude (7 ± 6 × 10−5 at 295 °K) and increase exponentially with temperature. Probably, the generation of photocarriers is caused by thermal dissociation of singlet excitons. The difference between the energy gap and the singlet exciton energy is equal to the activation energy of quantum yield (0.19 cV). Under the giant ruby laser pulse the photocurrent in pure crystals is a linear function of light intensity, whereas in crystals containing impurities the square dependence is observed. The mechanism of charge carrier production under high light intensity is probably the singlet exciton annihilation, the rate constant being 4 × 10−15 to 8 × 10−14 cm3s−1.
Intrinsic Photoconductivity in Single Crystals of Cadmium Iodide
Authors: Wright D. K. , Tubbs M. R.
Published: July 2007

Photoconductivity measurements have been made on single crystals of cadmium iodide for illumination over a wide range of photon energies from the fundamental absorption edge to more than 3 eV inside the region of intrinsic absorption. These photoconductivity spectra show all the structure that is normally seen in a reflectivity spectrum. Additional information has been obtained by studying the spectral distribution of photocurrent corrected to a constant number of absorbed photons. The corrected photocurrent is considerably larger than expected near the high energy excitons with absorption peaks at 5.7 and 6.2 eV. This may be accounted for by assuming that these excitons are able to diffuse over significant distances in the crystal before dissociating into free charge carriers. The structure observed in the photoconductivity and optical absorption spectra of CdI2 is discussed in terms of an empirical model for the energy band structure near k = 0.
Ionic Conductivity of Sodium fluoride
Authors: Bauer C. F. , Whitmore D. H.
Published: July 2007

The electrical conductivity of single crystals of pure NaF and NaF doped with CaF2 has been measured as a function of temperature from 450 to 970°C. Analyses of these data by a leastsquare method to yield the usual defect parameters have been based on two models: 1. a perfect crystal perturbed by isolated cation vacancies, isolated anion vacancies, divalent cation impurity, and divalent cation impurity‐cation vacancy complexes, and 2. one which includes the long‐range Coulomb interactions between isolated defects in addition to the four defects of the first model. More satisfactory agreement with the experimental results is apparent when the latter model is employed, but non‐random deviations between experiment and theory were evident for both models over the entire temperature range of observation.
Mechanical Relaxation and Nonlinearity in Strontium Titanate Single Crystals
Authors: Sorge G. , Hegenbarth E. , Schmidt G.
Published: July 2007

The temperature dependence of the resonance frequency of longitudinally vibrating [;100] bars of SrTiO3 single crystals exhibits two maxima atTa = 103 °K and Tb = 30 °K. Between these temperatures exact measurements are only possible if the exciting voltage is sufficiently low. At higher amplitudes nonlinear response can be observed. The maximum at Ta is shifted to higher temperatures by applying a uniaxial stress P (dTa/dP = 18 × 10−3 deg/at) and hydrostatic pressure p (dTa/dp = 1.5 × 10−3 deg/at). After changing the mechanical and electric bias, mechanical relaxation occurs in the temperature range between 30 and 80 °K.
Instabilités des ondes guidées de type hélicon dans un plasma soumis à un champ électrique
Authors: Vassallo Ch.
Published: July 2007

On présente une théorie des ondes du type hélicon dansun plasma soumis à la fois à un champ électrique et à un champ magnétique. On utilise des courbes de dispersion dans le plan complexe des k qui tiennent compte des pertes; ces courbes sont formellement indépendantes du champ électrique. Dans un milieu infini on peut avoir une instabilité absolue avec un champ électrique aussi petit que l'on veut. Ce n'est plus vrai dans un plasma limité transversalement. On étudie la modification des courbes de dispersion due au guidage et on présente un calcul des seuils d'instabilité que l'on compare à une théorie antérieure. Dans les milieux finis réels, ce genre d'instabilité demande des mobilités comparables et des porteurs nombreux; elle semble peu probable dans InSb.
Effect of Neutron Irradiation on the Temperature Dependence of the Flow Stress for Niobium Single Crystals
Authors: Reed R. E. , Guberman H. D. , Armstrong R. W.
Published: July 2007

Yield stress and strain‐rate data were obtained in compression at various temperatures. Niobium single crystals were tested both in the irradiation and unirradiated condition. The neutron irradiation largely affected the athermal component of the flow stress, however, it also induced a smaller but measurable increase in the thermal component of stress. The data indicate that increasing solute content effects an athermal strengthening similar to that of neutron irradiation.
Magnetic Anisotropy in F.C.C. Single Crystal Cobalt—Nickel Electrodeposited Films. II. Thickness Dependence of the Magnetocrystalline and Uniaxial Anisotropy Constants from (110) Deposits
Authors: Lord D. G. , Goddard J.
Published: July 2007

Torque magnetometry has shown a pronounced variation with film thickness of the magnetocrystalline anisotropy constants K1, K2, K3 of Co—Ni f.c.c. films, of between 100 and 1000 Å, electroplated on to (110) copper single crystal substrates. A thickness dependent uniaxial anisotropy Ku of the order of K1 was found to be present for all alloy compositions, its axis being a <001> direction in the plane of the film. An empirical relationship which describes the thickness variation of Ku has been constructed containing three terms representing pseudomorphic, ‘unnatural‐phase’, and occluded hydrogen strain energies.