bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of anharmonicity on the K ≈ 0 modes of MgO and ZnS
Authors: Srivastava S. P. , Singh R. D. 
Published: July 2007

AbstractExperimental investigations are made of the infrared transmission spectra of MgO and ZnS in the region of the fundamental lattice absorption at room temperature. The magnitude of the effect of anharmonicity has been calculated and discussed in the light of symmetry of spectra at the resonance frequencies. The effective ionic charge and compressibility of Szigeti's relations are calculated and the significance of these results is discussed from the point of view of various models of dielectric behaviour.
The origin of the structural phase transition in Gd2(MoO4)3
Authors: Dvořák V. 
Published: July 2007

AbstractThe phase transition in Gd2(MoO4)3 at 159 °C is investigated on the base of symmetry changes using standard group‐theoretical methods. It is shown that a two‐dimensional representation exists with k = 1/2 (b1 + b2) which induces a symmetry change from Dd to Cv and could be responsible for the phase transition. The appropriate form of the free energy is developed and compared with that proposed by Levanyuk and Sannikov [1].
Ionicité des liaisons interatomiques et distribution de la densité électronique dans les composés semiconducteurs III–V
Authors: Bailly F. 
Published: July 2007

AbstractL'étude de la distribution électronique observée expérimentalement entre les atomes dans les composés semiconducteurs binaires III–V permet de définir et calculer théoriquement la ionicité de liaisons λ en fonction de la position x0 du centre de gravité de la distribution électronique. L'évaluation de x0 en fonction de λ, à partir de considérations théoriques, permet d'obtenir une relation qui est en accord avec les resultats expérimentaux.
On the calculation of surface states of silicon
Authors: Alstrup I. 
Published: July 2007

AbstractSurface bands of two LCAO models of silicon (110) slabs are calculated. Comparison with previously calculated surface bands of similar models of (111) slabs and with the surface bands calculated by Jones [3] using a pseeudopotential‐matching method suggests that only small differences exist between the surface state density distribution of the (111) and that of the (110) surface, in harmony with experiments, and that the position and form of the surface bands depend sensitively on the model used for the surface region. Estimates of the position of the neutral Fermi level at the surface of the LCAO slab models indicate that they are far from being self‐consistent in the surface region. More refined models are thus necessary for obtaining reliable surface state results.
Low‐field magnetoconductivity of metals in the half‐space
Authors: Fischbeck H. J. 
Published: July 2007

AbstractA surface scattering model that makes allowance for nearly specular reflexion of shallow magnetic surface states and diffuse scattering of deep‐lying surface states is used to calculate the low‐field magnetoconductivity of metals in the random‐phase approximation. The conductivity is separated into the resonant part due to shallow surface states and the nonresonant contribution of the other electrons. For the former a new summed expression is derived whereas the latter is shown to be equal to the conductivity of the anomalous skin effect in case of diffuse surface scattering. The Fourier cosine transform is calculated using asymptotic methods.
Hot‐electron second‐harmonic generation in non‐degenerate CdS at low temperatures
Authors: Sodha M. S. , Sharma S. K. , Rattan I. 
Published: July 2007

AbstractIn order to study analytically hot‐electron second‐harmonic generation due to high‐frequency electromagnetic waves in non‐degenerate CdS the Boltzmann transfer equation has been solved in the relaxation time approximation. Scattering of electrons by acoustic phonons (both isotropic deformation and anisotropic piezoelectric interactions) has been taken into account. To get an idea of the order of magnitude of the second‐harmonic generated, some calculations have been performed and the results are presented in form of graphs. The plot of the second‐harmonic intensity versus applied dc electric field shows a maximum. This means that there is an optimum value of the dc field for which the second‐harmonic yield is maximum. At very low temperatures and for weak dc fields, the second‐harmonic component exhibits anisotropy with respect to the direction of the applied dc electric field. Anisotropy of 0.80% can be observed for the optimum value of the dc field (Ed = 0.6 V/cm) at liquid helium temperature. The anisotropy effect vanishes as the lattice temperature (or the dc field) increases. For the optimum value of the dc electric field it has been found that the percentage of harmonic generation is ≈ 30%, for incident wave fields of 0.06, 0.57, and 1.62 V/cm at 4.2, 20, and 40 °K, respectively.
Influence of mechanical deformations on the irreversible Bloch‐wall jumps in electrolytic nickel
Authors: Aczel O. F. G. 
Published: July 2007

AbstractExperimental results are presented of the influence of small static torsional deformations on the magnetomechanical damping in electrolytic nickel as a function of surface shear strain amplitude. The peak which appears in the undeformed state decreases and shifted towards higher amplitudes as a result of the deformation. Simultaneously, the peak becomes flatter, i.e., the magnetomechanical damping tends towards a constant value, which is interpreted as a limitation of the number of the irreversible Bloch‐wall jumps. These results are interpreted theoretically and the expression of the magnetomechanical damping as a function of the shear strain amplitude is established, including the effect of the deformation. A good correspondence between the theoretical and experimental results is found.
Thermotransport of substitutional impurities in copper
Authors: Schroerschwarz R. , Heitkamp D. 
Published: July 2007

AbstractThermotransport of antimony, tin, indium, silver, cobalt, and nickel in copper is investigated in the temperature range between 950 and 1050 °C. The heats of transport were measured by the method of stationary redistribution of these elements in tracer amounts in a linear temperature gradient. The experimental results confirm both the intrinsic and electron interaction contribution to the heat of transport, theoretically anticipated for substitutional impurities in f.c.c. metals on the basis of a pair interaction model and Gerl's theory.
Anisotropie in kubischen Supraleitern.II. Die Flußverteilung in Blei‐Thallium‐und Blei‐Indium‐Einkristallen mit x > 2−1/2
Authors: Obst B. 
Published: July 2007

AbstractBlei‐Thallium‐Legierungen mit Ginzburg‐Landau‐Parametern x > 2−1/2 (mit mehr als 1,5 Gew% Tl) zeigen eine Anisotropie der Flußlinienanordnung. Die Orientierungen des Flußliniengitters und des Kristallgitters sind korreliert. Es wird zwischen den Flußlinien eine Wechselwirkungsenergie vom Londonschen Typ angenommen. Setzt man hier die mikroskopischen Größen ein und beschreibt die Anisotropie allein durch den Parameter der Energielücke Δ, so ergibt sich die gleiche Winkelabhängigkeit der Energielücke, wie sie aus der Analyse des Grenzflächenverlaufs zwischen flußführender Phase und Meissner‐Phase in reinen Metallproben folgt. Im Zwischenzustand von PbTl‐ und PbIn‐Legierungen mit x > 2−1/2 bilden in der Schubnikow‐Phase isoliert eingebettete diamagnetische Gebiete eine Art “Übergitter”. Dieses hat die Symmetrie des Kristallgitters in Feldrichtung und ist gegenüber dem Flußliniengitter in charakteristischer Weise gedreht.
Role of Dislocation Annihilation during Steady‐State Deformation
Authors: Blum W. 
Published: July 2007

AbstractThe relations between generation, glide, and annihilation of dislocations during plastic deformation are represented in terms of control theory. It is inferred that the rate of steady‐state deformation is proportional to the rate of dislocation annihilation and that annihilation is even rate‐controlling at least in certain ranges of temperature and strain rate. A model of annihilation‐controlled steady‐state deformation is proposed, which assumes that cell boundaries form barriers for dislocation glide and allows for local variation of the mean effective stress for glide according to the cellular dislocation structure. The model explains steady‐state deformation behaviour at low stresses. Modifications of the model necessary in the high stress range are discussed.
The Application of Green's Functions to a System of Two Almost Magnetic Impurities
Authors: Middleton R. B. , Doman B. G. S. 
Published: July 2007

AbstractThe method of double time Green's functions is used to show that two almost magnetic impurities in a non‐magnetic conductor could under certain circumstances stimulate one another to become magnetic. Although the theory allows the formation of both parallel and antiparallel moments on the impurities, it predicts that no moments are induced when the separation of the impurities is most favourable for antiparallel alignment, and that either parallel or antiparallel moments may be induced when the separation is most favourable for parallel alignment.
Band Structures of GaAs1−xPx and In1−xGaxP
Authors: Hunter J. F. , Ball G. , Morgan D. J. 
Published: July 2007

AbstractThe band structures of GaAs1−x and In1−xGaxP are calculated in the virtual crystal approximation using the empirical pseudopotential method. The effects of disorder and of spin‐orbit coupling are neglected. The lattice parameter is assumed to vary linearly with the mole fraction of one compound x and the six non‐zero pseudopotential form factors Vj(x) (j = 1 to 6) are assumed to vary as Vj(x) = Vj(0) + (Vj(1) – Vj(0)) × ((1 ‐ α) x + α x2), where α is a constant independent of j. It is found that the calculated bowing parameter of the lowest direct band gap E0(γv15 ‐ γc1) varies linearly with α, and this enables a value for α to be found. Results are presented for the bowing parameters of the indirect gaps, and for the values of x at which two of the gaps become equal. Graphs of the variation of effective masses with x are also given. The results indicate that, contrary to what has been reported in the literature, the empirical pseudopotential method is applicable to alloy systems.
Electroreflectance on Trigonal Selenium
Authors: Weiser G. , Stuke J. 
Published: July 2007

AbstractMeasurements of transverse electroreflectance and of its temperature dependence were performed on trigonal selenium crystals in the energy region between 1.8 and 4.2 eV. The observed structures which show a strong dependence on polarization of light and on orientation of electric field are mainly correlated to exciton transitions. The discussion of the results gives a good accordance with band structure calculations. The direct gap is located at point H of the Brillouin zone and shows a positive temperature coefficient between 5 and 160°K. The first valence band is split into three subbands which lie close together with distances of 42 and 13 meV. Besides the electroreflectance spectrum which is independent of the direction of electric field a signal is observed which depends on its sign. Probably this spectrum is due to lattice deformation created by piezoelectric effect.
The Kinetics of Donor–Acceptor Transitions in ZnS Type Phosphors
Authors: Döhler G. H. 
Published: July 2007

AbstractThe kinetics of luminescence of ZnS type phosphors is treated in the view of the donor‐acceptor model. The probabilities for different kinds of inter‐impurity transitions at zero temperature are compared. The kinetics for the decay of luminescence after flash excitation [1] is extended to the case of luminescence during and after excitation by a constant light source. The decay law in this case is completely different from the former one and agrees well with experimental results. The degree of excitation is given as function of acceptor and donor concentration and depth, and the dependence of light storage on these parameters is discussed. The kinetics developed here is shown to apply also to the thermally activated luminescence at finite temperature. In this way it is easily understood that decay curves at T = 0 and at finite temperatures may be very similar in spite of different mechanisms for the luminescent transitions.
The Energy Band Structure of Binary Alloys of Vanadium with Elements at the end of Transition Series (Co, Ni, Rh, Pd, Ir, Pt)
Authors: Nemnonov S. A. , Kurmaev E. Z. , Ishmukhametov B. Kh. , Belash V. P. 
Published: July 2007

AbstractThe fluorescent V Kβ5 emission bands from the pure metal and binary alloys of transition elements Co, Ni, Rh, Pd, Ir, and Pt have been investigated. In the alloys V3Rh, V3Pd, V3Ir, and V3Pt the V Kβ5 bands are split in two principal subbands. These spectrum changes are related to the energy separation of d‐band components.
Exciton–Magnon Optical Absorption in Antiferrodielectrics at Strong Magnetic Fields
Authors: Petrov E. G. , Gaididei Yu. B. 
Published: July 2007

AbstractThe role of the sublattice spin non‐collinearity in antiferrodielectrics (AFD) in exciton‐magnon pair absorption is investigated using exciton theory. An expression for the effective dipole moment of the pair transition of AFD is obtained depending on the value of the external magnetic field breaking the spin collinearity. The role of the magnon density of states of AFD in the absorption intensity under strong magnetic fields is investigated. A formula is obtained for the dependence of the relative integral absorption intensity on the magnetic field.
A New Method for Solving the Boltzmann Equation for Electrons in Crystals
Authors: Seeger A. , Clausecker K. 
Published: July 2007

AbstractA new method for solving the linearized Boltzmann equation, based on the combination of Fourier and degenerate kernel techniques, is developed. It permits to reduce the transport problem for electrons in crystals with arbitrary energy surfaces to a system of linear equations for scattering both by phonons in metals and by localized defects. The transport coefficients, in the absence or presence of magnetic fields of all strengths of practical interest, may be expressed in terms of the solutions of the system of linear equations and quantities characterizing the energy bands of the crystal.
Micromagnetic Treatment of Néel Walls
Authors: Riedel H. , Seeger A. 
Published: July 2007

AbstractBy means of the micromagnetic equations the wall shape of one‐dimensional Néel walls is calculated. Starting point is the decomposition of the micromagnetic equation into two contributions, one of them describing the core of the wall, and the other the tail of the wall. The results agree very well with the published results of numerical computations. In particular the existence of a tail with logarithmic variation of the direction cosine of the magnetization as a function of the distance from the wall centre has been verified analytically.
Structures, Compressibilities, and Phase Transitions of Ionic Crystals in a Quantum‐Statistical ab Initio Theory
Authors: Dubejko M. , Olszewski S. 
Published: July 2007

AbstractThe structures of about 50 ionic crystals of cubic symmetry have been calculated in terms of a quantum‐statistical ab initio theory. In most cases agreement with experiment has been attained; in particular, the changes of the phases of alkali halides when the cation is replaced by a Cs ion have been obtained. In a refined crystal model the changes of size of the same ion in different lattices and the crystal compressibilities have been calculated. The examination of the phase transitions under pressure gives rather satisfactory results for the transition pressures in the cases of Na compounds. The validity of the virial theorem for the refined crystal model has been checked for the cases of CsBr and KCI.
Crystal Structures of III–V Semiconductors in a Quantum‐Statistical ab Initio Theory
Authors: Olszewski S. , Dubejko M. 
Published: July 2007

AbstractUsing a quantum‐statistical ab initio theory it is shown that the radii of weakly interacting or zero‐valent crystal ions can be responsible for the structure of a III–V semiconducting crystal, whereas the non‐ionic character of the semiconductor is due to the charge polarization in the crystal. The polarization shifts the minima of the electron dnsity from the ionic boundaries towards inside of the negative ions giving practically neutral atomic systems. The differences between the structures of the Al and Ga compounds on the one hand, and those of the La compounds on the other, are explained by the theory.
Resistivity of Solid Be, Mg, and Zn
Authors: Borchi E. , de Gennaro S. , Tasselli P. L. 
Published: July 2007

AbstractA theoretical study is made of the resistivities of the solid h.c.p. metals Be, Mg, and Zn. Information about the lattice dynamics is derived from inelastic neutron scattering using a slight modification of the Gilat‐Raubenheimer computer program for calculating the frequency distribution functions. Empirical and Heine‐Animalu pseudopotentials are used to calculate the electron‐phonon coupling. Umklapp processes are explicitly evaluated. Good agreement is obtained with experimental data except in the low‐temperature region.
Thermodynamics of Finite Spin Systems
Authors: Binder K. 
Published: July 2007

AbstractNumerical calculations are presented for very small spin systems with free surfaces. Both Ising and classical Heisenberg spin systems are considered. The effect of the smallness on the phase transition of the system is investigated. The results can be discussed in terms of the analysis given by Ferdinand and Fisher [1] for the two‐dimensional Ising model.
Asymptotic Solution of the Boltzmann Equation for Hot Carriers
Authors: Mocker M. 
Published: July 2007

AbstractThe steady‐state Boltzmann equation for hot carriers is solved asymptotically for the case of predominate inelastic scattering by nonpolar optical phonons in the limit of high carrier energies. This solution has a simple analytic shape and permits one to define a temperature T and an anisotropy parameter η for the hot carriers. The analytic relation between T, η, the lattice temperature TL, and the applied field strength E is demonstrated. In the high‐energy limit the applicability of conventional approaches, which are based on a Legendre polynomial expansion, is discussed by comparison with the asymptotic solution.
Second‐Order Doppler Shift of Fe57 Mössbauer Resonance in Al‐0.01% Fe57 Alloy Solid Solution
Authors: Nasu S. , Murakami Y. 
Published: July 2007

AbstractThe Mössbauer effect of Fe57 in aluminum was measured over a temperature range from 4.2 °K to 453 °K, using a specimen of supersaturated solid solution of Al‐0.01% Fe57 alloy. From the temperature dependence of the Mössbauer peak position, the second‐order Doppler shift and the isomeric shift of Fe57 in aluminum were estimated separately from the observed total shifts assuming the isomeric shift to be temperature independent. The estimated temperature independent isomeric shift was (0.52 ± 0.02) mm/s relative to metallic iron, somewhat different from the usual room temperature value of (0.43 ± 0.02) mm/s. The temperature dependent second‐order Doppler shift was analysed by the recent Mannheim's expression and the Debye formula. The best fitted force‐constant ratio, λ′/λ, for the iron atom in aluminum host lattice was estimated to be 0.5 < λ′/λ < 1. The zero point kinetic energy of Fe57 in Al was also evaluated by differences between the shifts at 4.2 °K and those at high temperatures.
Free Exciton Optical Transitions Induced by Impurities in Germanium
Authors: À la Guillaume C. Benoit , Voos M. , Salvan F. 
Published: July 2007

AbstractA calculation of the transition probabilitiy is given for the radiative decay and creation of free excitons interacting with a neutral donor in the case of germanium. The theoretical results are then compared with the available emission and absorption data obtained in doped germanium at low temperature.
The State of Molybdenum Impurity in Yttrium‐Aluminium Garnet
Authors: Bagdasarov Kh. S. , Bershov L. V. , Martirosyan V. O. , Meilman M. L. 
Published: July 2007

AbstractFor the first time, an EPR spectrum of Mo3+ ions in yttrium‐aluminium garnet has been obtained. The ions isomorphously replace Al3+ ions in the trigonally distorted oxygen octahedra of the garnet. The spectrum may be described by an axial spin‐Hamiltonian with the parameters S = 3/2, I = 5/2, g∥︁ = g⟂ = 1.967, b = 26.0 GHz, A = (131 ± 2) MHz, and B = (139 ± 2) MHz. The results have been correlated with the data reported earlier for other compounds, and the parameters of the fine structure of Cr3+ and Mo3+ ions have been compared. This allows to discuss certain regularities which govern the variation in the spectroscopical parameters of the ground state of similar ions in going from the 3d3 to the 4d3 configuration.
Microwave Faraday Effect in Anisotropic n‐Type Silicon
Authors: Srivastava G. P. , Mathur P. C. , Kumar A. 
Published: July 2007

AbstractThe theory of free carrier Faraday effect in anisotropic semiconductors, previously developed by Donovan and Webster [1,2], is extended to the case of n‐type silicon. The high‐frequency magnetoconductivity tensors are derived taking into account the detailed structure of conduction band. The Faraday rotation measurements in some [111] oriented samples of n‐silicon are performed at room temperature and microwave frequencies. These results and the results of previous workers with different orientation of silicon samples, show reasonable agreement with the theory.
A Thermodynamic Theory of Gadolinium Molybdate
Authors: Dvořák V. 
Published: July 2007

AbstractA thermodynamic theory of the elastic and dielectric properties of gadolinium molybdate is developed on the basis of a free energy expansion, which properly describes the space group symmetry change of gadolinium molybdate at 159 °C. The temperature dependence of the material constants is qualitatively explained and it is shown to be connected with the sixth order terms in the phase transition parameters. The magnitude of coupling of the polarization with the phase transition parameters and the origin of the spontaneous polarization are discussed.
The Structure of the 0.9 eV Quenching band of Photoconductivity in CdS
Authors: Opanowicz A. 
Published: July 2007

AbstractThe temperature dependence of the structure of the 0.9 eV quenching band of the photoconductivity in CdS crystals has been investigated. The results indicate that the 0.9 eV band has Pekarian shape. The estimated Franck‐Condon shift value (0.168 eV) suggests that the 0.66 eV emission band is connected with the inverse hole transitions corresponding to the 0.9 eV quenching band of photoconductivity.
Nonequilibrium configurations and peierls potential of screw dislocations in the b.c.c. lattice
Authors: Heinrich R. , Schellenberger W. 
Published: July 2007

AbstractA model for the calculation of the Peierls potential of straight screw dislocations in the b.c.c. lattice is developed. The method takes into account the detailed atomic nonequilibrium structure of the dislocation. Those nonequilibrium configurations which play a leading part during the dislocation motion have been classified by two core‐structure parameters, which can be regarded as “generalized dislocation position”. The Peierls potential, i.e. the dislocation energy as a function of these parameters, has been calculated. The equipotential contours of the Peierls potential and the saddle‐point configurations of screw dislocations are presented, and several types of the dislocation motion are discussed. Further, the influence of external stress has been analyzed. It turns out that the macroscopic slip of screw dislocations is composed of elementary {110} slip processes.
Sulphur impurity state in Ga1–xInxSb
Authors: Campos M. D'Olne , Gouskov A. , Gouskov L. , Pons J.‐C. 
Published: July 2007

AbstractHall effect and conductivity measurements show that in Ga1–xInxSb the position of the sulphur donor level depends on the alloy composition. This level is associated with subsidiary conduction bands in the alloy as well as in GaSb. The results are discussed and compared with those obtained by other workers from pressure experiments.