bluuebunny/crossref_metadata_2025_split huggingface dataset:
Displacive Vibronic Phase Transitions in Narrow‐Gap Semiconductors
Authors: Kristoffel N. , Konsin P. 
Published: July 2007

AbstractDisplacive phase transitions are considered in small‐gap semiconductors due to the electron‐phonon interaction of two bands. The Helmholtz free energy of the system is obtained on the basis of the electron spectrum renormalized by the interaction. The temperature dependent low‐symmetry lattice distortion, renormalized frequencies of the active “soft”; optical branch in both phases, the Curie temperature, etc., are obtained. By means of the Green's function method combinative vibronic frequencies of the system are found. The dielectric susceptibility which is essentially determined by active vibrations is calculated and the general picture of similar (ferroelectric) phase transitions is discussed.
Die Unterscheidung zwischen Leitungs‐ und Rumpfelektronen bei der feldtheoretischen Behandlung des Vielelektronen‐Problems
Authors: Brand P. 
Published: July 2007

AbstractFür 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractAn 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

AbstractAus 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

AbstractU1‐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

AbstractThe 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.
Mainly on the Fresnel Mode in Lorentz Microscopy
Authors: Guigay J. P. , Wade R. H. 
Published: July 2007

AbstractWe 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

AbstractAn 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

AbstractThe 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

AbstractRubidium 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

AbstractThe 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

AbstractUOSe 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

AbstractInvestigations 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractIn 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

AbstractA 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

AbstractThe 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

AbstractAntiphase 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

AbstractAn 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

AbstractThe 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

AbstractFrom 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

AbstractThe 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

AbstractThe 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

AbstractThe 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.