bluuebunny/crossref_metadata_2025 huggingface dataset:
Die Unterscheidung zwischen Leitungs‐ und Rumpfelektronen bei der feldtheoretischen Behandlung des Vielelektronen‐Problems
Authors: Brand P.
Published: July 2007

Für die Greensche Funktion der Elektronen eines Festkörpers wird eine reelle Spektralfunktion aufgestellt, welche die Bedeutung einer verallgemeinerten Zustandsdichte besitzt. Die Beiträge der Leitungs‐ und Rumpfelektronen eines Metalls zu dieser Spektralfunktion lassen sich voneinander trennen, ohne daß dabei die Austauschkräfte zwischen Leitungs‐und Rumpfelektronen vernachlässigt werden. Der Zusammenhang mit der Pseudopotential‐Methode wird aufgezeigt; die Pseudopotential‐Methode wird kritisiert.
The Transverse Magnetic Resistance in Semiconductors with Non‐Standard Energy Band
Authors: Askerov B. M. , Gashimzade F. M.
Published: July 2007

The transverse electrical conductivity σxx in a strong magnetic field is calculated for semiconductors with spherical but nonparabolic energy band. The calculation is carried out for the case of electron scattering by acoustical phonons. In the quantum limit non‐degenerate and degenerate semiconductors are considered. It is shown that in the formula for the transverse electrical conductivity in the non‐degenerate case the effective mass at the bottom of the parabola shifted by the magnetic field and in the degenerate case the effective mass at the Fermi surface are included. The temperature dependence is the same as for a standard energy band. Therefore an assumed non‐parabolicity does not change the dependence of σxx on the electrical field. The effect of the non‐parabolicity is reduced to the above renormalization of the effective mass.
On the Spin Broadening of Mössbauer Lines of Impurities in Ferromagnetics and of Atoms in Antiferromagnetics
Authors: Krivoglaz M. A. , Kvashnina L. B.
Published: July 2007

The broadening and shift of Mössbauer lines for the nuclei of impurity atoms in ferromagnetics due to the interaction between the nucleus and atomic spins are discussed. Detailed examination is made of the effects associated with quasi‐local and local spin excitations. It is shown that low‐frequency quasi‐local excitations can lead to a value of broadening some orders greater as compared with the case of ideal ferromagnetics. The broadening of Mössbauer lines is also determined for the ideal antiferromagnetic.
Electronic Energy Bands for Rubidium Chloride and the Face‐Centered Cubic Alkali Bromides
Authors: Kunz A. B.
Published: July 2007

The Schrödinger equation was solved for the valence and conduction bands of rubidium chloride and the face‐centered cubic alkali bromides by the orthogonalized‐plane‐wave method. Results are presented for several points of high symmetry in the first Brillouin zone, and the results are compared with experiment.
Nuclear Magnetic Resonance and Susceptibility of Equiatomic Rare‐Earth‐Aluminum Compounds
Authors: van Diepen A. M. , de Wijn H. W. , Buschow K. H. J.
Published: July 2007

The Knight shift of the NMR of 27Al and the susceptibilities of the compounds LaAl, GdAl, TbAl, DyAl, HoAl, and ErAl have been measured in dependence on temperature. The results are discussed in terms of the Ruderman‐Kittel‐Kasuya‐Yosida theory. The exchange integral γ between conduction electrons and 4f electrons is found to be −0.39 eV.
Small Angle Scattering of Subthermal Neutrons from Deformed Polycrystalline Copper
Authors: Taglauer E.
Published: July 2007

The small angle scattering of subthermal neutrons provides a method of investigating dislocations in cold worked crystals. The scattering from polycrystals has several components, and these were investigated systematically in the case of copper. 1. One component can be ascribed to density fluctuations caused by distortion fields of statistically arranged edge dislocations. The dislocation density is approximately proportional to the flow stress and decreases with increasing grain size. 2. The double Bragg scattering observed at appropriate wavelengths agrees with theoretical predictions of Ogier et al. and can be explained by the fact that on deformation the grains are divided into subgains. 3. At very small angles there is strong scattering that depends on the grain size. A few possible causes are discussed.
One‐Phonon Relaxation of Hydroxyl Ions in Alkali Halide Crystals
Authors: Dick B. G.
Published: July 2007

An expression is derived for transition rates of OH− dipole orientation in alkali halides due to one‐phonon assisted tunneling. This rate is expressed in terms of host crystal constants, a stress energy splitting parameter, and a tunneling matrix element. Comparison of calculated and observed relaxation rates for KCl implies that the tunneling matrix element deduced from the one‐phonon relaxation time is about an order of magnitude smaller than that deduced from recent paraelectric resonance experiments.
Herstellung dünner Bor‐Folien und elektronenmikroskopische Beobachtung ihrer Baufehler
Authors: Kleinhenz K. , Runow P.
Published: July 2007

Aus polykristallinem Bor der β‐rhomboedrischen Modifikation wurden durch chemisches Ätzen, Kathodenzerstäubung und eine Kombination beider Verfahren dünne Folien hergestellt und im Elektronenmikroskop untersucht. In geätzten Proben wurden Zwillinge, Stapelfehler und Korngrenzen beobachtet und analysiert. In zerstäubten Proben traten Kontraststrukturen auf, die nicht mit Sicherheit gedeutet werden konnten, deren Entstehung aber offensichtlich auf die Zerstäubung zurückzuführen ist. In getempertem Material wurden gelegentlich kristalline Ausscheidungen gefunden, die vereinzelt auch in dichten Ketten in bestimmten kristallographischen Vorzugsrichtungen auftraten und als Borkarbid (B4C) identifiziert werden konnten.
Vibrational Spectra of U1‐Centres in KI
Authors: Bäuerle D. , Fritz B.
Published: July 2007

U1‐centres in KI have local mode absorption bands in the region of 700 cm−1 and an in‐gap absorption band at 86.7 cm−1. The absence of any splitting in the main line (718cm−1) indicates centres of cubic symmetry (Td). The main line is accompanied by phonon sidebands. One of the strongest sidebands, 89 cm−1 above the main line, may be correlated with the directly excited phonon in the far infrared at 86.7 cm−1.
The Study of Deformation of Thin Foils of Mo under the Electron Microscope
Authors: Veselý D.
Published: July 2007

The slip geometry in molybdenum has been studied at room temperature by tensile deformation of thin foils under an electron microscope. The orientation of the tensile axis was in the middle of the stereographic triangle, consequently the system with maximum resolved shear stress was (101) [111]. Observations have shown that the choice of slip systems depends not only on the orientation factor of the slip systems but very strongly on the orientation of the foil plane. In the present work this phenomenon is explained by assuming that the difference in the mobilities of screw and edge dislocations is sufficiently large to influence the choice of slip systems. The most active systems are those where the dislocation loops can easily lose their screw component to the surface leaving the edge component to propagate through the foil.
Exoemission of Electrons without Photostimulation
Authors: Simoi C. , Hrianca I. , Crăciun P.
Published: July 2007

Reproducible parameters of exoemission of electrons without photostimulation in an aluminium sample are investigated. These parameters were found to be energetic levels of electrons in the emissive sample, inferred by analysis of the decay curve of the emission.
Mainly on the Fresnel Mode in Lorentz Microscopy
Authors: Guigay J. P. , Wade R. H.
Published: July 2007

We consider the problem of the determination of magnetic structures by transmission electron microscopy. A stationary phase approximation to the Kirchoff diffraction integral yields a criterion for the validity of geometrical optics in calculating image intensity distributions at any diffraction plane. Our criterion is particularly useful for the Fresnel diffraction case since the usual criterion Δφ ≫ h c/e [1] is strictly valid only for the Fraunhofer diffraction condition.
Conduction Bands of GaSb‐InSb Mixed Crystals with a Low Concentration of InSb
Authors: Averous M. , Bougnot G. , Calas J.
Published: July 2007

An investigation is made of resistivity, Hall effect, and piezoresistance of n‐type GaSb–InSb mixed single crystals with 0 to 6 at% InSb. We show that a) two conduction bands contribute to conduction; b) the deformation potential Ξu and the rate of change of ΔE referred to the volume, dΔE/d In V, decrease when the InSb concentration increases.
Optical Absorption of Mn2+‐Doped Alkali Halides
Authors: Mehra A.
Published: July 2007

The absorption spectra of Mn2+‐doped KCl and NaCl are discussed over 0.1 to 15 mol% cange of dopant concentration. The spectra observed for concentrations > 5 mol% are characteristic of divalent manganese and the bands are assigned to various excited quartet levels of the ion in a cubic crystalline field. The band positions are fitted by adjusting B, C, Dq, and α parameters. Fine structure of the bands observed at 77 °K is interpreted in terms of the vibrational–electronic and spin–orbit splitting of the cubic field levels. The different types of Mn2+ centres in the alkali halides at different concentrations are discussed in the light of the observed spectra. The formation of K4MnCl6 and NaMnCl3 complexes is thought to be probable at high concentrations.
Polymorphism of Rubidium Nitrate
Authors: Salhotra P. P. , Subbarao E. C. , Venkateswarlu P.
Published: July 2007

Rubidium nitrate exists in four polymorphic forms in the solid state, three of which (IV, III, and I) have been well characterized. Data are presented, from dilatometric and X‐ray studies, to confirm a rhombohedral symmetry for phase II rather than the tetragonal, suggested by Brown and McLaren (1962). The mechanism of structural changes, at the III → II → I phase transitions, is described.
Calculation of the Generalized Grüneisen Parameters for Acoustic Waves in Uniaxial Crystals from the Third Order Elastic Constants
Authors: Rao R. Ramji , Srinivasan R.
Published: July 2007

The generalized Grüneisen parameters involved in the theory of thermal expansion of uniaxial crystals are defined. These GP's for the acoustic waves determine the behaviour of the anisotropic expansion at low temperatures. The calculation of these GP's from third order elastic constant data in uniaxial crystals is described. As an example, the third order elastic constants of a h.c.p. lattice with nearest neighbour central interaction are worked out and the GP's of acoustic waves propagating in different directions in the crystal are calculated for the case where this interaction is represented by a (6,12) Lennard‐Jones potential.
The Magnetic Properties of Uranium Oxyselenide
Authors: Murasik A. , Suski W. , Troć R. , Leciejewicz J.
Published: July 2007

UOSe is antiferromagnetic at 4.2°K with a magnetic unit‐cell twice the size of the chemical one in the c‐direction. The magnetic moments are aligned along the c‐axis, μ = (2.21 ± 0.05) Bohr magnetons. The magnetic structure is of the UOS type. The temperature dependence of 1/X shows a change in the slope at 300°K. The effective moment and the Weiss constant below this point are 2.87 and −10 °K respectively. Above 300 °K the effective moment is 3.30 Bohr magnetons and the Weiss constant −120 °K. At 90 °K a maximum occurs on the log ϱ against temperature curve.
Absorption and Infra‐Red Emission of Nickel and Cobalt Doped Alkali Halides
Authors: Reynolds M. L. , Hagston W. E. , Garlick G. F. J.
Published: July 2007

Investigations of the optical spectra of nickel and cobalt doped alkali halides show that observations are consistent with distorted octahedral and tetrahedral coordination of these transition metal ions.
Calculation of Quadrupole Broadening from (111) 〈110〉 Dislocations in Cubic Cystals
Authors: Kanert O.
Published: July 2007

The electric field gradient resulting from the stress field around a screw dislocation and an edge dislocation with a (111) 〈110〉 slip system is calculated. For the case of randomly located dislocations the distribution function of the corresponding quadrupole frequencies is presented and explicitly calculated in a normalize form for certain examples. From the absolute first moment of this function a converging expression of quadrupolar width is obtained that depends on position and density of the dislocations.
Green Functions for “One‐Body” Equations Describing the Disordered State
Authors: Morgan G. J.
Published: July 2007

A method for calculating average Green functions for disordered systems is described. The approach consists of a combination of the “equation of motion” method and perturbation theory and is illustrated by considering a simple situation, namely an electron moving in a system of weak potential wells, where there are a number of previous calculations for comparison purposes. The basic idea is, however, applicable to more complex situations where there is no adequate theory, such as the vibrational properties of an amorphous solid.
Paramagnetic Relaxation in Neodymium‐Ethylsulfate: Phonon Re‐Absorption and Spectral Spin Diffusion
Authors: Schedewie F. J.
Published: July 2007

The transient magnetic behaviour of a Nd‐ES single crystal at low temperatures have been investigated by the microwave pulse method (X‐band), utilizing for detection the magneto‐optical Faraday effect. At temperatures below 2 °K and magnetic fields below 2 kG the magnetic relaxation is non‐exponential in time. This is explained by the simultaneous occurence of spin‐lattice and cross relaxation. The T−3‐law observed for the temperature dependence of the relaxation time at 2kG indicates a phonon bottleneck caused by multiple reabsorption of the “hot” phonons by the spin system. On the basis of this conception the intrinsic spin‐lattice relaxation time T1 is quantitatively calculated.
Electron and Hole Conductivity of Donor‐Acceptor Complexes of Oligoanilinic Substances and Their Thermoelectric Properties
Authors: Hádek V.
Published: July 2007

A relation has been found between the occurence of electron and hole conductivity in complexes of oligonanilinic substances and the different acceptors and the influence of their relative amount in the complexes is discussed. It has been found that for electron conductivity the acceptor component is decisive, while the donor component is responsible for the hole conductivity. It is shown that there is a possibility of governing of the type of conductivity even in organic semiconductors.
Transition between Stationary and Moving High‐Field Domains in CdS in a Range of N‐Shaped Negative Differential Conductivity due to Field‐Quenching
Authors: Böer K. W. , Voss P.
Published: July 2007

In CdS, unstable moving domains are observed, which exist in a current‐voltage range between the range for stationary electrode‐adjacent domains and the range for transitions to undeformed moving domains. These current–voltage ranges have been investigated in the same crystal by changing the electron concentration at the boundary of a pseudocathode. Several CdS crystals, differently doped with Ag, Al, and Cu, have been investigated. An electro‐optical method using the Franz‐Keldysh effect was employed for domain observation. The influence of the distance between the electrodes on domain formation is discussed.
Nonequilibrium Thermodynamics of Superconducting Alloys in High Magnetic Fields
Authors: Weller W.
Published: July 2007

A superconductor with nonmagnetic impurities is considered in the limiting case of small mean free path (l ≪ ξ0) and high magnetic field (H ≈ Hc2). The principles of the phenomenological nonequilibrium thermodynamics are applied to the superconductor and the dissipation function is calculated. For the free energy of the superconductor a functional is used which leads in the equilibrium case to Maki's generalized Ginzburg‐Landau equation. However, the current density resulting from this functional differs in the order of the operators from Maki's expression. The results of the phenomenological considerations are in agreement with the time‐dependent Ginzburg‐Landau equation recently obtained by Caroli and Maki from the microscopic theory.
Bound Exciton Complexes in CdSe Crystals
Authors: Gross E. F. , Razbirin B. S. , Fedorov V. P. , Naumov Yu. P.
Published: July 2007

The emission and absorption spectra of bound exciton complexes (bound excitons) in CdSe single crystals have been investigated at liquid helium temperature. Emission and absorption lines corresponding to creation and annihilation of (Γ9 − Γ7) bound excitons in both the ground and the excited states have been observed. From an analysis of the observed spectra some conclusions are drawn on the nature of the defects forming the bound exciton complexes. Some new informations about the (Γ9 − Γ7) free exciton spectrum are presented. An analogy between the bound excitons in CdSe and CdS is pointed out.
Crystallography of Antiphase Boundaries in FeSi Alloys
Authors: Gemperle A.
Published: July 2007

Antiphase domain boundaries in alloys with 11.2 to 15.4 at% Si are studied by electron microscopy. It is found that the boundaries of the types 1/4 α 〈111〉 and 1/2 α 〈100〉 in the DO3 structure have a pronounced crystallographic character and lie approximately on {100} planes. The FeSi alloys are essentially different in this respect from other alloys of the same structure. It can be further assumed on the basis of experiments that in the B2 structure region the boundaries of the type 1/4 α 〈111〉 have noncrystallographic character. The behavior of the boundaries in both structures is compared with existing theories, and it is found that for the DO3 structure a satisfactory explanation based on these theories is not possible. The reasons for the disagreement between theory and experiment are discussed and the previously observed deformation of the crystal lattice in the boundary is proposed as a possible explanation.
Critical Conditions for Transitions between Stationary and Non‐Stationary High‐Field Domains in Semi‐Insulators
Authors: Döhler G.
Published: July 2007

An analysis of a fluctuation in the neighborhood of singular points of the Poisson and transport equations for a semi‐insulator with negative differential conductivity due to field enhanced recombination yields a criterion for the transitions between stationary and non‐stationary high‐field domains. Critical voltages (domain lengths) and current oscillation frequencies are given for different saturation currents and agree well with experimental results reported for field‐quenched CdS. It has been shown that, with increasing applied voltage, alternating regimes of stationary and non‐stationary solutions exist for the model discussed, in agreement with recently reported experimental indications.
The Optical Absorption Spectra of Co and Ni in ZnWO4
Authors: Reynolds M. L. , Hagston W. E. , Garlick G. F. J.
Published: July 2007

The optical absorption spectra of zinc tungstate crystals doped with divalent cobalt or nickel ions have been measured and the energy states shown to be consistent with the assumption of a trigonal field acting on the impurity centres. No observable associated luminescence transitions from first excited states to ground states could be detected from any of the crystals investigated.
General Theory of the Bloch Electron in a Magnetic Field
Authors: Fischbeck H. J.
Published: July 2007

From the translational symmetry of the Bloch electron in a magnetic field the main features of the magnetic energy band model are derived. Matrix elements and expectation values of the Bloch electron in a magnetic field as well as its dynamic properties in an additional electric field are calculated in far‐reaching analogy to the ordinary Bloch case. Some of the related problems are discussed.
The Dependence of Extinction Distance on Deviation from the Bragg Condition in Silicon
Authors: Cann C. D. , Sheinin S. S.
Published: July 2007

The dependence of the (111) and (220) extinction distances in silicon on deviation from the exact Bragg condition has been investigated. The results obtained for the (220) reflection show good agreement with both the two‐beam and multi‐beam dynamical theories. For the (111) reflection, however, the results are in poor agreement with the two‐beam theory and in only partial agreement with the multi‐beam theory. The agreement with the multi‐beam theory is improved when electron scattering factors obtained from recent X‐ray measurements are employed in the multi‐beam calculations.
The Fine Structure of Spots in Electron Diffraction Resulting from the Presence of Planar Interfaces and Dislocations. IV. Wedge Crystals
Authors: de Ridder R. , van Landuyt J. , Gevers R. , Amelinckx S.
Published: July 2007

The fine structure of electron diffraction spots caused by the presence of wedge shaped crystal parts in a selected area, is derived theoretically and compared with observations. The same method has been applied in parts I and III i.e. a Fourier transformation of the transmitted and scattered intensities. Two general types of wedges are considered; wedges formed by grain‐boundary and twin boundary arrangements where only one crystal part is in a reflecting position and general wedges as e.g. the genuine wedges of geometrically shaped crystals. Normal and anomalous absorption are taken into account, as well as refraction effects in the case of a genuine wedge. MgO crystals and twin boundaries in stainless steel were used to compare the theoretical results with experiment. The observations are in very good agreement with the predicted fine structure.
The Effect of Electric Field in a Space Charge Layer on the Photoresponse Edge of Si p‐n Junctions
Authors: Gutkin A. A. , Janicki T.
Published: July 2007

The influence of the reverse bias on the photoresponse of Si p‐n junctions is investigated in the vicinity of the fundamental absorption edge at room temperature. Besides the increase of photosensitivity caused by the broadening of the space charge layer at electric fields of 104 to 105 Vcm−1 in the energy region near 1.05 eV an additional increase in the photoresponse is found. Its field dependence is in accordance with the theory given for the change of the absorption coefficient in electric fields (Franz‐Keldysh effect). It is also found that avalanche multiplication of electrons changes the spectra of the relative photoresponse increase at fields higher than 1.1 × 105 Vcm−1.
Effects of the Non‐Equilibrium Depletion in Germanium at the Electrolyte Interface
Authors: Konorov P. P. , Shvetsov V. N. , Shegolikhina S. V.
Published: July 2007

Non‐equilibrium depletion effects in thin high resistivity n‐type germanium specimens during anodic polarization in an electrolyte are investigated by conductivity and Hall effect measurements. It is shown that first diffusion depletion by minority carriers takes place which spreads practically over the whole specimen when the thickness of the specimen is much less the diffusion length of minority carriers. A further increase of the polarization leads probably to a breaking of the inversion layer formed on the n‐type germanium surface during anodic polarization. In this case the field penetrates deep into the specimen and causes the appearance of a region near the germanium–electrolyte interface depleted by both electrons and holes. An estimate shows that the thickness of this region is not less than 40 μm. In the state of non‐equilibrium depletion, the sample sensitivity for generating minority carriers increases considerably; this is especially important for the Hall effect.
Paramagnetic Resonance of Silver Atoms Stabilized in Alkali Halide Crystals
Authors: Baranov P. G. , Zhitnikov R. A. , Melnikov N. I.
Published: July 2007

Stabilized silver atoms are obtained at 77 °K by irradiating alkali halide crystals (LiCl, NaCl, and KCl) containing silver ions with X‐ray. The properties of these stabilized atoms are studied by PR (paramagnetic resonance). It is found that the silver atoms occupy the cationic sites of the crystals studied. The dependences of the hyperfine and superhyperfine interaction constants on the lattice constant, i.e. on the distance from the surrounding chlorine ions, are studied. The temperature dependences of the hyperfine and superhyperfine structure constants of silver atoms in the case of LiCl: Ag are also studied.
Theoretical Study of Properties of Copper and Silver Atoms Stabilized in Alkali Halide Crystals
Authors: Baranov P. G. , Zhitnikov R. A. , Melnikov N. I.
Published: July 2007

A theoretical analysis of the hyperfine and superhyperfine interaction of copper and silver atoms stabilized in alkali‐halide crystals [1 to 4] is carried out. The hyperfine interaction is investigated on the basis of Adrian's theory [5] whose application to atoms stabilized in ionic crystals requires its further development. Particularly, the influence of the crystal field is taken into account. The results of theoretical calculations of hyperfine and superhyperfine interaction constants of copper and silver atoms in the lattices of alkali halide crystals are given. The overlap integrals for the wave functions of the unpaired electrons of copper and silver atoms and the wave functions of the nearest chlorine ions are calculated. The results of these theoretical calculations show a reasonable good agreement with the experimental data previously obtained [1 to 4].
Ferromagnetic Resonance in Ga0.85Fe1.15O3
Authors: Petrov M. P. , Kizhaev S. A. , Smolenskii G. A.
Published: July 2007

The angular dependences of the position and width of the ferromagnetic resonance line in Ga0.85Fe1.15O3 are investigated. An anomalous angular dependence of the line width is found. The anisotropy fields for intermediate and easy magnetic directions are calculated. The effect of an electric field on the position of the ferromagnetic resonance line is discussed.
Influence of the Electron Scattering Anisotropy upon the Phonon Drag Effect in n‐Ge and n‐Si
Authors: Iskra V. D. , Gostyuk G. T.
Published: July 2007

The Boltzmann equation is used to study the influence of the scattering anisotropy upon the phonon drag effect in n‐Ge and n‐Si. Assuming the electrons to be scattered mainly by acoustical phonons and the only mechanism of the phonon relaxation to be phonon‐phonon scattering, explicit formulae are obtained for the components of the thermoelectric force tensor due to a single valley as well as for the total thermoelectric force. Composition with the experimental data allows to evaluate both contribution of the transverse phonons to the drag effect and the interaction parameters for the longitudinal and transverse phonons.
Dielectric Function of Semiconductors
Authors: Kübler J. K.
Published: July 2007

The real part of the dielectric function ϵ(q, ω) is obtained in the random phase approximation for semiconductors. If the first interband transition is forbidden, the following limits are obtained from the general formula for ϵ(q, ω) involving a finite energy gap EG: EG → 0, ω = 0, then ϵ(q, 0) ∝ q−1; EG → 0, q = 0, then ϵ(0, ω) ∝ ω−1/2; EG small, q = ω = 0, then ϵ(0, 0) α EG−1/2.
Atomistische Behandlung von Kinke und Sprung einer Stufenversetzung in NaCl. I. Die Kinke
Authors: Eisenblätter J.
Published: July 2007

Es wurde zunächst die Energie der abrupten Kinke im Bornschen Modell des Ionenkristalls berechnet. Da diese näherungsweise quadratisch von der Kinkhöhe abhängt, war es möglich, die Betrachtung des allmählichen Übergangs bei der Kinke auf ein etwas abgewandeltes Frenkel‐Kontorova‐Modell zurückzuführen. Die Ergebnisse sind in guter Übereinstimmung mit denen von Seeger u.a.
Theory of Ultrasonic Attenuation by Magnetic Surface States in Metals
Authors: Fischbeck H. J. , Mertsching J.
Published: July 2007

A theoretical expression for the resonant absorption of longitudinal ultrasound by magnetic surface states is given, and the basic physical ideas are explained. The interaction matrix element showing quasi‐geometric oscillations is calculated and discussed, and the order of magnitude of the absorption is estimated. The experimental realization of the effect appears to be very difficult. From the theoretical point of view it is pointed out that on favourable conditions such ultrasonic investigations should be more convenient for determining the relevant physical parameters than microwave experiments.
Leerstellenausheilung in Platin nach Abschrecken unter Argonatmosphäre und in Wasser
Authors: Rattke R. , Hauser O. , Wieting J.
Published: July 2007

Es wird über Untersuchungen zum Ausheilverhalten abgeschreckter Platinproben in Abhängigkeit von der Abschrecktemperatur, der Abschreckgeschwindigkeit und vom physikalischen Zustand der Proben berichtet. Dabei zeigt es sich, daß niedrige Wanderungsenergien für Leerstellen von 1,0 bis 1,1 eV unabhängig von der eingefrorenen Leerstellenkonzentration immer dann erhalten werden, wenn bereits vor dem Abschrecken eine hohe Versetzungsdichte vorliegt oder wenn bei hohen Abschreckgeschwindigkeiten durch Verformungen während des Abschreckens die Senkendichte verändert wird. Höhere Wanderungsenergien von 1,3 bis 1,4 eV treten bei gut vorgeglühtem Material und hinreichend langsamen Abschreckgeschwindigkeiten ebenfalls unabhängig von der Leerstellenkonzentration auf. Sie sollten der freien Wanderung von Einzelleerstellen zugeschrieben werden, während die kleineren Energien zusätzliche Wechelwirkungen mit den Senken enthalten. Unter diesen Umständen stellt die chemische Reaktionsgleichung keine gute Näherung für die Beschreibung des Ausheilvorganges dar. Ein Einfluß von Doppelleerstellen auf die Ausheilung kann erst erfaßt werden, wenn bei hinreichend senkenarmem Material eine Verformung während des Abschreckens ausgeschlossen werden kann.
Trägerbeweglichkeit in verformtem Germanium
Authors: Schröter W.
Published: July 2007

Die Hallbeweglichkeit schwach dotierter Germaniumeinkristalle wurde vor und nach plastischer Verformung zwischen 50 und 250 °K gemessen. Die streuenden Verformungszentren wurden als Versetzungen identifiziert, die durch ihre Ladung und ihr Verschiebungsfeld die Beweglichkeit freier Löcher beeinflussen. Zur Bestimmung der Ladung der Versetzung wurde das Modell des Versetzungsbandes herangezogen. Die Ergebnisse der Beweglichkeitsmessung wurden unter der Annahme analysiert, daß freie Löcher bzw. ionisierte Fremdatome die Versetzungsladung abschirmen.
Measurements of the Zener Effect and Kinetics of Short‐Range Order in Two AuCu Alloys (Containing 14 and 25 at% Cu)
Authors: Radelaar S. , Ritzen J. M. J.
Published: July 2007

Measurements of the Zener relaxation effect and resistivity measurements of the establishment of short‐range order in two AuCu alloys (containing 14 and 25 at% Cu, respectively) are described. The relaxation times of both effects agree quite closely for the 14 at% Cu alloy. However, for the 25 at% Cu alloy the relaxation time determined from the resistivity measurements shows an anomalous increase as the critical temperature for long‐range order is approached from the high temperature side. This effect is discussed in terms of a current model for short‐range order above the critical temperature. The activation energies obtained from the Zener effect data are compared with the results of quenching experiments in these alloys.
Quenched‐in Electrical Resistivity of Dilute Binary Alloys
Authors: Liu G. C. T. , Girifalco L. A. , Maddin R.
Published: July 2007

The quenched‐in electrical resistivity of dilute binary alloys has been calculated, assuming that the alloy system contains single vacancies, di‐vacancies, single solutes (impurities), di‐solutes, and solute—vacancy pairs in an otherwise perfect matrix. Some numerical computations have been made for dilute binary alloys of Au. By assuming that the electrical resistance of a point defect in the paired or associated state is less than that of the unpaired or single state, it is shown that the solutes do have a significant effect on the quenched‐in electrical resistivity if the perturbation introduced into the alloy by the solutes is large. For instance, the change of the binding energy or the concentration of solute‐vacancy pairs will change the slope of the curves in the logarithmic resistivity vs. reciprocal temperature plot and the contribution due to di‐solutes will give rise to a non‐linearity of the curves at lower quenching temperatures. The results are discussed in the light of experimental observations.
Infrared Absorption in Heavily Doped n‐Type Si
Authors: Balkanski M. , Aziza A. , Amzallag E.
Published: July 2007

Transmission measurements are reported on highly phosphorous‐doped n‐type Si, at three different temperatures 300, 85, and 35°K, and for carrier densities ranging from 6 × 1018 to 4.9 × 1020 cm−3. Below the fundamental energy gap, the data are analysed in terms of three different processes: free carrier absorption, indirect transitions including the phonon contribution as well as the impurity or electron—electron scattering, and interconduction‐band transitions. The absorption band due to inter‐conduction‐band transitions is observed to shift to higher wavelengths, when the doping increases. An explanation is given, taking into account the rise of the Fermi level in the conduction band.
Current Oscillations in GaAs under Acoustic Amplification Conditions. II. Calculation of the Threshold Field
Authors: Hugon P. Leroux
Published: July 2007

In the preceding paper

See this issue, page 331.

, experimental investigations of current oscillations in GaAs are reported. In this paper the conditions of occurrence of a current instability is discussed in the limits of the small‐signal theory. Calculated values of the threshold field and of his variations with the involved parameters are found in agreement with the experiments.
Field‐Ion Microscopic Contrast from Partial Dislocations and Stacking Faults in B.C.C. Metals
Authors: Smith D. A.
Published: July 2007

The geometrical contrast theory of dislocated surfaces is extended to include faults in b.c.c. metals. A general approach to the problem of dislocation and fault contrast is indicated; the characteristic spiral and step configurations from any dislocation and any fault can be deduced from simple crystallographic parameters. In some cases a fault can be characterised completely by noting its line of intersection with an imaged pole and the multiplicity of associated spirals. The limitations of the theory are pointed out.
Grain Growth in Polycrystalline Ice
Authors: Jellinek H. H. G. , Gouda V. K.
Published: July 2007

Literature is not available on the grain growth in polycrystalline ice. The present paper deals with such grain growth in pure ice and ice doped with sodium chloride. The technique consists in measuring grain size distributions as a function of time and deriving the numberaverage equivalent “diameter”, considering the grains as spheres. The functional relationship between the average diameter and time of growth is, for pure and doped ice, of the same form as that found for metals. Arrhenius plots show that the energy of activation is higher for doped ice than for pure ice. The results are discussed in terms of interfacial free energy as being ultimately responsible for grain growth. On a molecular scale, processes take place, which lead to diffusion of units consisting of a number of water molecules across the boundaries.
Polarization Investigations of Localized Exciton States of Doped Benzene Crystals
Authors: Ostapenko I. N. , Shpak M. T.
Published: July 2007

The absorption spectra of localized exciton states of benzene crystals doped with heterocyclic compounds are studied at T = 4.2 °K using polarized light. When the localized level approaches the exciton A‐band edge, the intensity of the localized absorption is shown to increase anomalously in the a‐component and to decrease in the c‐component of the absorption spectrum. Simultaneously the A‐band is partly depolarized and shifts towards the violet side. The experimental results obtained favour certain conclusions about the exciton band structure and the exciton effective mass and are qualitatively interpreted on the basis of current theories of localized states.
An APW Calculation for Silver
Authors: Christensen N. E.
Published: July 2007

Various “muffin tin” potentials have been examined, and a potential leading to a band structure and a Fermi surface in agreement with experiments has been found. This potential is based on relativistic Dirac‐Slater atomic wave functions. In the atomic calculations as well as in the crystal calculations inclusion of full Slater exchange led to the best results. Cyclotron masses, thermal effective mass, optical mass, drift velocities, and group velocities have been calculated.
Tensile Properties of Cu3Au Single Crystals
Authors: Audero M. A. , Victoria M. P. , Vidoz A. E.
Published: July 2007

The tensile properties of ordered and disordered Cu3Au single crystals have been investigated. Measurements have been made to determine the influence of initial orientation of the tensile axis and of the domain size on the work hardening characteristics of Cu3Au. It is shown that the work hardening rate of the ordered crystals increases with the domain size and the occurrence of secondary slip. The nature of the effects is discussed in terms of previous results on Ni3Fe. It is concluded that they can be explained by the antiphase boundary tube mechanism.
Pyroelectric Properties of Rubidium, Cesium, and Thallium Nitrates
Authors: Bury P. C. , McLaren A. C.
Published: July 2007

The pyroelectric properties of single crystals of rubidium, cesium and thallium nitrates have been investigated by direct observation of the dipole moment in an electric field and by measurements of the pyroelectric coefficient (dP/dT) using the Chynoweth technique. These observations have shown that the trigonal forms of these crystals are primary (or secondary) pyroelectrics in which the c‐axis is the polar axis. The Chynoweth technique also indicated the presence of 180° pyroelectric domains which were subsequently revealed by decoration with charged particles from a xerographic developer. Measurements of (dP/dT) versus T have been used to determine the form of the spontaneous polarization as a function of temperature. These results, together with new optical and X‐ray observations, indicate the space group P31 (or P32) for the trigonal form of these crystals, rather than P31 (or P3212) as previously reported on the basis of X‐ray evidence alone.
Zur Theorie der Biexzitonen in monomolekularen Kristallen
Authors: Patzer K.
Published: July 2007

Es wird ein Hamiltonoperator hergeleitet, der die Schwierigkeiten beim Übergang von Paulionen zu Bosonen vermeidet und es erlaubt, exakte Gleichungen für die Greenschen Funktionen zu erhalten. Als Spektrum der Biexzitonen wird eine Serie von Energiebändern erhalten. Es wird gezeigt, daß die Bildung von Biexzitonen aus longitudinalen und transversalen Exzitonen unwahrscheinlich ist.
Neutron investigation of the Spin System Dynamics in α‐Cr2O3
Authors: Alikhanov R. A. , Dimitrijević Ž. , Kowalska A. , Kraśnicki S. , Rżany H. , Todorović J. , Wanic A.
Published: July 2007

Inelastic magnon scattering of neutrons (λ = 1.124 Å) on a single crystal of Cr2O3 at a temperature of 85 °K is investigated by the neutron diffraction technique. The magnon dispersion relation is measured along several tracks in the reciprocal space. A calculated dispersion relation, including four different exchange integrals Ji, is fitted to the experimental results. A good fit is obtained for: J1 = −0.2 meV, J2 = −0.5 meV, J3 = −3.3 meV, and J4 = −7.4 meV.
Creation of U2—F Centre Pairs in U‐Centre Doped KBr Crystals
Authors: Kurz G.
Published: July 2007

Detailed measurements have been made on the conversion of U1‐α centre pairs into U2‐F centre pairs in KBr: KH crystals extending the results and suggestions made earlier by Delbecq et al. It is shown that part of the thermally most stable vacancy—interstitial pairs undergo further conversion upon U1 bleaching. Furthermore at 4.5 °K a complete reverse reaction can be induced by bleaching with F light. From these quantitative results the oscillator strength of the U2 band can be determined. A refinement of Delbecq's conversion model is proposed.
The Diffusion of Zn in the III‐V Semiconducting Compounds
Authors: Shaw D. , Showan S. R.
Published: July 2007

The experimental results for chemical and isoconcentration diffusion of Zn in AlSb, GaAs, and GaP have been interpreted using Longini's interstitial/substitutional model. Satisfactory agreement is found with the isoconcentration data if the substitutional Zn is a fully ionized monovalent acceptor and the interstitial is a monovalent donor. The characteristic features of chemical diffusion are explained in terms of a non‐equilibrium situation dominated by the rate of supply of vacancies on the group III sub‐lattice and the flux of interstitial Zn donors. Diffusion‐induced dislocations are assumed to play a major role in the supply of vacancies. Satisfactory qualitative agreement with the chemical diffusion data is found.
On the Orientation Changes during Plastic Deformation of Individual Crystallites in Polycrystalline Aggregates
Authors: Bunge H. J. , Fuchs R.
Published: July 2007

The orientation changes of individual crystallites in aluminium wires were studied during 1% plastic deformation. The crystals near the [111]‐ideal orientation rotated towards this orientation according to the Taylor theory. The crystals of the weak [100]‐texture component showed no resulting rotation component towards [100] in contradiction to the Taylor theory.
Experiments on the Motion of Bubbles in Solids by Sublimation in a Temperature Gradient
Authors: Diez W. , Biersack J.
Published: July 2007

The sublimation mechanism of bubble migration in solids in a temperature gradient has been investigated by microscopic observation of artificial bubbles in ammonium chloride single crystals. The dependence of the bubble velocity on temperature, temperature gradient, and bubble size corresponds with the theory, which takes into account the influence of the evaporation coefficient. Changes in the shape can be understood qualitatively by means of the calculated temperature fields. The shrinking velocity of bubbles, not being in equilibrium of forces, is evaluated and compared with experiments. The polyhedral form of the bubbles and the lenticular shape of pores in UO2 is explained by the low value of the evaporation coefficient for certain crystallographic planes.
Low‐Temperature Lorentz Microscopy on “Weak” Ferromagnetics
Authors: Bostanjoglo O. , Vieweger W.
Published: July 2007

Magnetic domains in CrBr3 and CrI3 were investigated down to 3 °K in an electron microscope in the Fresnel and Foucault mode of Lorentz microscopy, and by Fraunhofer diffraction. The experimental domain width was found in agreement with the theoretical value calculated by crystal and magnetic energy considerations. In all modes of Lorentz microscopy the electron optical contrast of the ferromagnetic domains in films with low magnetization and small wall width as occur in CrBr3 and CrI3 is found to deviate markedly from the predictions of the geometric optical theory but is satisfactorily understood by wave optics.
On the Polarization Vectors of Lattice Vibrations
Authors: Grimvall G.
Published: July 2007

The polarization vectors of lattice vibrations in anisotropic crystals of cubic structure are considered from a quantitative point of view. A new anisotropy index A = c11/(c12 + 2c44) is shown to be more adequate as a measure of anisotropy than the conventional s = (c11 — c12)/2c44. The reason for anisotropy is discussed briefly, with special emphasis on simple metals. The approximation of assuming the lattice vibrations to be strictly longitudinal or transverse is discussed for several properties of metals, with sodium taken as an example.
Stray‐Field‐Free Magnetization Configurations
Authors: Hubert A.
Published: July 2007

The concept of stray‐field‐free micromagnetic configurations in applied to Bloch‐ and Néel‐walls, to stripe domains, and to the ripple structure in thin magnetic films. We propose a new structure of Bloch‐walls with a lower energy than the most general classical Bloch‐walls as calculated by LaBonte. In general a stray‐field‐free configuration has a lower symmetry than the simpler structures considered previously. It is concluded that the real structure, if not completely stray‐field‐free, should have at least the same symmetry as a possible stray‐field‐free solution. The significance of Brown's equations, which in general cannot be satisfied without admitting stray‐fields, is analysed with regard to the micromagnetic boundary condition.
Paramagnetic Impurities in Superconductors with Overlapping Energy Bands
Authors: Kon L. Z. , Moskalenko V. A.
Published: July 2007

The influence of paramagnetic impurities on the thermodynamic properties of two‐band superconductors at zero and near zero temperatures is investigated. It is shown that due to interband scattering of electrons there is one gap in two‐band superconductors with impurities. The extreme cases of low and large impurity concentrations are investigated. In the first limiting case an increase in the concentration is accompanied by a linear decrease of order parameters. The expression for the energy gap, densities of states near the energy gap, and the specific heat as functions of impurity concentration are given.
Electric Properties of Dislocations in n‐Type Germanium
Authors: Kryłow J. , Auleytner J.
Published: July 2007

On the basis of the Read theory the position of dislocation acceptor level in n‐type germanium was determined. It amounts to 0.13 to 0.18 eV below the bottom of the conduction band and is independent of the type of introduced dislocations. The influence of the inhomogeneity of deformations and non‐dislocation defects generated in the course of heating and deformation on the precision of determination of the position of dislocation level was taken into account. — Diffusion of impurities was reduced to minimum by covering the samples with tin. A strong effect on non‐dislocation defects generated in the processes of heating and deformation on mobility and magnetoresistance was detected as well as some changes in mobility for the current flow parallel to the direction of dislocation lines.
Dynamical Theory of the Optical and Energy Loss Properties of the Crystal Electron System
Authors: Stolz H.
Published: July 2007

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