bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties of DyAsO4 at low temperatures
Authors: Kahle H. G. , Klein L. , Müller‐Vogt G. , Schopper H. C.
Published: July 2007

The magnetic properties of DyAsO4 were investigated by specific heat and magnetic moment measurements. The specific heat shows two λ‐type anomalies, one at TN = 2.44 K caused by a magnetic phase transition, and the other at Tc = 11.2 K. Magnetic measurements show an antiferromagnetic ordering perpendicular to the optical axis with magnetically nonequivalent a‐ and a′‐axes. Exchange integral and critical parameters were determined in different ways and compared with theory. The splitting of the two lowest components (Kramers' doublets) which is constant above Tc becomes temperature dependent below Tc; it increases with decreasing temperature and originates from a cooperative phenomenon.
Microscopic theory of lattice dynamics for ionic crystals. I. Theoretical framework
Authors: Gliss B. , Zeyher R. , Bilz H.
Published: July 2007

A microscopic theory of lattice dynamics of the ionic crystals is developed in the self‐consistent Hartree‐Fock approximation. The work is based on a splitting of the dynamical matrix into two parts, a rigid ion and a polarization part. For ionic crystals such a splitting is especially convenient, because here the rigid ion contribution represents the dominant contribution to the total dynamical matrix. In the theory presented, this part results from the classical Coulomb interaction of the cores and electrons among themselves and with each other within the Heitler‐London approximation. It is obtained without using perturbation theory, therefore no excited states are involved. For a special choice of the localized wave functions the energy expression of Löwdin [23] and Lundqvist [24] is obtained which describes the perturbation of the electron density during a lattice mode by a rigid displacement of localized electron densities including exchange effects. The polarization part takes into account virtual electronic transitions caused by a weak driving electron‐ion potential additively to the rigid ion part. This part is determined by a variational method.
The green function method in the theory of magnetic thin films. I. Calculation of a general expression for the magnetization of magnetic thin films
Authors: Brodkorb W.
Published: July 2007

An anisotropic magnetic thin film is considered with atomic spins, S, arranged in a lattice with inversion symmetry and arbitrary surface orientation. The Hamiltonian of the system contains the Zeeman term, the Heisenberg exchange term, and a term for the uniaxial volume anisotropy in the film plane. An implicit system of equations calculated on the basis of the Green function method is given in order to estimate all layer magnetizations in the film.
Interaction of singlet excitons in organic materials with an absorbing surface
Authors: Kallmann H. , Vaubel G. , Baessler H.
Published: July 2007

It is shown both experimentally and theoretically that the fluorescence of an anthracene crystal is strongly quenched if the crystal is excited close to a metal layer. The fluorescence is reduced by a factor of two if the penetration depth of the exciting radiation is equal to the diffusion length of singlet excitons. This is caused by energy transfer taking place across distances of 10 to 30 Å. The experimental values for the energy‐transfer parameters are in agreement with a theoretical estimate assuming a metal absorption index of about one. This energy‐transfer process also influences the fluorescence decay time. Its significance for the probability of exciton induced electron ejection from the crystal into a metallic or non‐metallic electrode is discussed.
Anomalous skin‐effect in inclined magnetic field
Authors: Naberezhnykh V. P. , Tsymbal L. T. , Purchinskii M. S.
Published: July 2007

The dependence of the effective depth of penetration of an electromagnetic field in a metal on the inclination angle of the magnetic field to the sample surface and the temperature is studied by the radio‐frequency size effect on Cd under conditions of anomalous skineffect and l ≫ D.
The magneto‐optic Kerr effect and Faraday rotation of CdCr2S4 for radiation between 0.1 and 4 eV
Authors: Wittekoek S. , Rinzema G.
Published: July 2007

The complex polar Kerr effect (rotation and ellipticity) of CdCr2S4 has been measured between 1.6 and 4 eV at temperatures between Tc = 84 and 6 °K. Four well separated magneto‐optical transitions have been identified. Two sharp peaks at 2.12 and 2.29 eV are attributed to the Cr3+ crystal field transitions 4A2 → 2T2 and 4A2 → 4T1, respectively. Crystal field parameters satisfying the optical data have been derived. Only one transition at 1.9 eV shows a magnetic red‐shift. It depends on sample‐stoichiometry and doping. The strongest resonance is found at 3.4 eV and is assigned to a charge transfer transition of an electron from a p‐orbital of sulphur to a chromium orbital. The Faraday rotation in the infrared region is also reported and shown to be caused by the charge transfer transition at 3.4 eV.
On the theory of magnetic anisotropic exchange interactions
Authors: Nikiforov A. E. , Mitrofanov V. Ya. , Men A. N.
Published: July 2007

A generalization of expressions for the anisotropic exchange interaction is developed for the case of nonequal spins of separate ions for the ground and excited states.
Dynamical theory of AIII BV‐type crystals with fractional and variable charges of ions
Authors: Korol E. N. , Tolpygo K. B.
Published: July 2007

An adiabatic theory of lattice vibrations is developed for sphalerite type crystals, based on the concept that each pair of nearest atoms is bound by two electrons which state is a superposition of three parts, both electrons “belong” to one or the other atom or form a σ‐bond between them. The distortion of the electron wave function by atomic vibrations is described by a system of dipole moments of the electron shells 𝒫n, the coefficients of mentioned linear combination change by changing the mean charges of ions en. The adiabatic potential, containing all 𝒫n, en, and the equations of motion are introduced. For long wavelength oscillations the electrodynamical forces due to currents which flow along n‐n′‐bonds and which appear by the change of the charges en, become of great importance. Concrete calculations and comparisons with an experiment are given for GaAs.
Effect of anharmonicity on the K ≈ 0 modes of MgO and ZnS
Authors: Srivastava S. P. , Singh R. D.
Published: July 2007

Experimental 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

The 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

L'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

Surface 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

A 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

In 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

Experimental 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

Thermotransport 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

Blei‐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

The 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

The 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

The 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

Measurements 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

The 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.
Theory of Dilute Magnetic Alloys
Authors: Fischer K.
Published: July 2007

[Russian Text Ignored].
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

The 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

The 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

A 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

By 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

The 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

Using 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

A 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

Numerical 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

The 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

The 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

A 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

For 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

The 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

A 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

The 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

A 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

Hall 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.
Electroabsorption near the n = 1 lines of the yellow and green series of Cu2O
Authors: Deiss J. L. , Daunois A. , Nikitine S.
Published: July 2007

The effect of an ac electric field on the n = 1 lines of the yellow and green series of Cu2O has been studied at 4.2°K using single crystals, polarized light, and a modulation technique. In the field, an “ignition” of the two lines λ = 6098 Å and λ = 5830 Å is observed. This ignition effect depends on the geometry of the experiment, and gives information on the nature of both transitions as well as on the bands involved in the formation of these IS excitons. The line λ corresponds to an orthoexcitonic electric quadrupole transition Γ, while the line λ is a mixed electric quadrupole Γ and magnetic dipole Γ transition, with a stronger magnetic dipole character.
Semiconductor–metal phase transformation of tetrahedrally coordinated semiconductors
Authors: van Vechten J. A.
Published: July 2007

The standard Drickamer high‐pressure resistance cell has recently been recalibrated. With this recalibration, it is shown that, within experimental uncertainty, the difference in internal energy between the diamond and the β‐tin forms of group IV elements is equal to the difference in energy between the corresponding Penn‐model semiconductor, corrected for d‐core dehybridization for Ge and Sn, and a free electron gas.
Electronic polaron formulation of the optical properties of U2 centres in various alkali halides
Authors: Hagston W. E.
Published: July 2007

A semi‐empirical formulation of the optical properties of U2 centres is presented which incorporates a many‐body treatment of electronic properties in terms of the concept of the electronic polaron. The results of the analysis provide further confirmation for the model which attributes the optical absorption process of the U2 centre to the transfer of an electron from the surrounding halide ions onto the interstitial hydrogen atom.
A kinetic approach to fracture of solids. II. The time to the fracture of a specimen under constant load in the presence of propagating cracks
Authors: Orlov A. N. , Petrov V. A. , Vladimirov V. I.
Published: July 2007

The fracture of solids under creep conditions is considered as a process consisting of nucleation due to thermal fluctuations and subsequent coalescence of numerous interacting microcracks. The main crack causing the rupture of the specimen is produced by coalescence of several microcracks and propagates by joining other microcracks which nucleate in its neighbourhood due to local stress concentration. The time to the fracture τ of a homogeneous specimen under constant stress is calculated and is shown to be the sum of the time of generation τg and the time of propagation τp of the main crack. τg is governed by stochastic processes and displays a size effect (dependence on the volume of the specimen), whereas τp is determined by the stress concentration near the crack during the initial stages of its propagation. Both times are proportional to the time of nucleation τm of a microcrack.
On the use of zero‐range potentials in some energy band problems
Authors: Bhagwat K. V. , Subramanian R.
Published: July 2007

The method of zero‐range potentials is described and its applicability to the study of some qualitative features of electron energy bands in three‐dimensional crystals is discussed. It is shown that the Saxon‐Hutner conjecture on band gaps is true for the special case of a linear periodic chain of three‐dimensional zero‐range potentials.
Optical properties of the ion‐radical salts of tetracyanquinodimethane in the solid state
Authors: Vlasova R. M. , Gutman A. I. , Rozenshtein L. D. , Kartenko N. F.
Published: July 2007

Absorption spectra of TCNQ salts with different donors — metals, organic conjugated compounds, dyes in solid state‐are investigated. The study was carried out on thin films obtained by grinding of salt on quartz substrate. For the Cs(TCNQ) salt reflection and absorption spectra were investigated on single crystals. Salt spectra in the solid state differ greatly from the isolated anion‐radical spectrum. For simple salts there is a close resemblance between thin film spectra and the spectrum of the () dimer, which proves that in the solid state pair interaction of ion‐radicals predominates. Complex salt spectra are characterized by strongly smeared absorption bands, especially in the Qn+ (TCNQ) salt. The correlation between absorption spectra and electrical and magnetic properties of the salts is noted. For Cs(TCNQ) single crystals a stronganisotropy of reflection and absorption is found. Both intensity and character of the absorption spectra depend on the polarization direction. The obtained data are correlated with the strong intermolecular interaction along TCNQ molecule stacking directions and the translational symmetry of the crystal. Absorption spectrum changes during destruction of the crystalline structure are found. The absorption spectra of TCNQ derivatives of dyes in solution are the result of superposition of ion‐radical bands and the initial dye band. The character of the solid film spectrum is connected with the influence of the steric factor on the intermolecular interaction.
On the electrical resistivity by scattering on metallic grain boundaries
Authors: van der Voort E. , Guyot P.
Published: July 2007

The contribution to the residual electrical resistivity of high angle grain boundaries due to the scattering of conduction electrons by voids into the boundaries is calculated for Au, Cu, and Al. Two types of geometries are considered: array of cylindrical voids for symmetrical tilt boundaries and point voids for boundaries with lower symmetry. In both cases a self‐consistent potential, solution of a linearized Thomas‐Fermi equation, is used. This contribution, of about a few 10−13 Ωcm2, accounts for at maximum 25% of the experimental specific grain boundary resistivity, which seems to indicate that bulk effects predominate.
On glow curves obtained by ionizing and non‐ionizing radiation
Authors: Kristianpoller N. , Israeli M.
Published: July 2007

Two distinct groups of glow peaks have recently been observed in nominally pure, uv excited alkali halides. These glow peaks are investigated in comparison with those obtained by X‐irradiation. Different processes are assumed to be responsible for the excitation of the thermoluminescence (TL) emitted at the various peaks. One process, which is connected with the creation of Frenkel pairs, causes the excitation of TL by uv light in the region of the first exciton band. This process appears also to be dominant in the excitation of “virgin”, pure samples by X‐rays. Another process is involved in the excitation of TL by ionizing uv light. This excitation, which is restricted in this case to a thin surface layer, is attributed to the presence of oxygen impurities and the generation of VK centres.
Electronic structure and optical properties of amorphous germanium and silicon
Authors: Kramer B.
Published: July 2007

The complex band structures, the imaginary parts of the dielectric constant, and the densities of states of electrons in amorphous Ge and Si are calculated using a generalized pseudopotential formalism based on the Green's function techniques. The short range order is assumed to be the same as in the cubic crystalline systems. The long‐range order is relaxed by using a two particle correlation function, consisting of Gaussian functions centered at the lattice points. The half widths of the Gaussian functions increases with increasing lengths of the lattice vectors. It turns out, that the band edges near axis Γ‐L are less influenced by disorder than for other k‐points in the Brillouin zone. This is confirmed by comparing the calculated imaginary part of the dielectric constant with the experimental one.
Polaron scattering of free carriers in tellurium
Authors: Selders M. , Gspan P. , Grosse P.
Published: July 2007

Because the polaron coupling constant in tellurium is relatively large, polar optical scattering should be important in the charge transport by free carriers. Reflection and transmission measurements on heavily doped samples in the far infrared yield the amount and the frequency dependence of the free carrier scattering in the spectral region of the reststrahlen bands. From the amount of the increase in scattering at the eigenfrequency of the LO phonons the contribution of polaron scattering can be determined.
The effect of intersite correlation on the metal–insulator transition
Authors: Schneider J. , Heiner E. , Haubenreisser W.
Published: July 2007

The effect of intersite correlation on the metal–insulator transition is investigated considering an extended Hubbard model. It is shown that it is impossible to describe consistently the transition by a variation of the lattice parameter a within the one‐electron picture, using an one‐particle Green function.
Exciton–exciton annihilation in pyrene crystals
Authors: Vol E. D. , Goloyadov V. A. , Kukushkin L. S. , Naboykin Yu. V. , Silaeva N. B.
Published: July 2007

Specific features of the exciton–exciton annihilation process for slow diffusion systems are considered in terms of excimer luminescence in pyrene crystals. In this case luminescence decay curves allow a direct determination of the diffusion coefficient and the mean free path of the excitation during its lifetime. Analogy between excimer excitations and the well‐known slow excitons is discussed. The importance of the experimental separation of excimer and monomer excitons whose kinetic parameters are greatly different is emphasized.
Quantum theory of localized defect migration in solids
Authors: Yakhot V. S.
Published: July 2007

A theory of solid state diffusion of localized defects, i.e. defects whose formation is accompanied by large deformation of the crystal lattice, based on the theory of multi‐phonon processes, is presented. An expression for the jumping probability is given. The independence of the diffusion coefficient on temperature at low temperatures and an Arrhenius law with temperature dependent pre‐exponent at high temperatures were established.
Self‐diffusion of Zn and Se in ZnSe
Authors: Hexkicberg M. M. , Stevexsok A.
Published: July 2007

The high‐temperature defect equilibria of ZnSe have been studied by self‐diffusion measurements on single crystals as a function of temperature, component partial pressure, and added impurity content. The self‐diffusion of Zn was found to be independent of component partial pressure and is expressed as Dzn = 9.8 exp (3.0 eV/kT) cm2 s−1, for the temperature range 760 to 1150 °C. Doping with Cu or A1 enhanced the self‐diffusion of Zn under Zn saturation at lower temperatures. The self‐diffusion of Se was found to be Dse = 0.13 × exp (2.6 eV/kT) cm2 s−1, for Se‐saturated crystals in the temperature range of 860 to 1020 °C, and decreased with decreasing pressure of Se2. Doubly‐ionized Frenkel defects are proposed as the dominant mobile defect on the Zn sublattice and a combination of neutral Se interstitials and doubly‐ionized Se vacancies on the Se sublattice. A tentative defect equilibrium isotherm for ZnSe is given.
Raman scattering intensity of polaritons for general wave vectors I. Theory
Authors: Unger B. , Schaack G.
Published: July 2007

Relations for the Raman scattering efficiency of polaritons in uniaxial piezoelectric crystals have been formulated for general directions of the wave vector. These relations are well suited for evaluating experimental data on the various mechanisms of the electron‐lattice interaction. For this purpose a phenomenological description of the dispersion of polaritons has also been given, starting from Huang's equations of motion of long wavelength polar lattice vibrations. The case of large wave vectors (k ≫ ωph./c, angular dispersion of phonons) is included in the theory.
On the theory of piezothermopower anisotropy in n‐type si in the region of phonon drag
Authors: Lutsyak V. S. , Wrrsowcir V. M.
Published: July 2007

The effect of phonon drag on the thermoelectric properties of n‐type Si is studied. Basing on the theory of anisotropic scattering, the influence of elastic deformations on the ther‐niopower at low temperatures is considered. The role of different scattering mechanisms for elcctrons and phonons is discussed. The theoretical results are compared with the experimental data of papers [3] and 191.
Temperature dependence of the creep strain jump in lead and indium at the transition to superconductivity
Authors: Soldatov V. P. , Startsev V. I. , Vainblat T. I.
Published: July 2007

The temperature dependence of the creep strain jump was invcstigated on Pb and In single and polycrystals of 99.999% purity in the region of the N → S transition. To achieve the strain jump the creeping sample was switched from the normal to superconducting state by taking off the magnetic field, H > He, of the solenoid that contained the sample. A tcmperaturc run was followed in the range 1.65 to 4.2 °K for lead and 1.65 to 3.4 °K for indium. The magnitudes Δε(T) of the step in creep strain at various temperatures were reduced to the value at T= 0 7deg;K and the curve Δε(T)/Δ ε(0)= f(T/Tc) as fit to Δε(T)/Δε(0) = α(T/Tc)2 in the interval 0.2≦ T/Tc ≦ 1. Possible mechanisms are discussed that might be responsible for the jump of the creep strain at N → S.
Magnetic phase transitions in the UAs‐use system
Authors: Leciejewicz J. , Troć R. , Murasik A. , Palewski T.
Published: July 2007

The transition between antiferromagnetic UAs and ferromagnetic USe has been studied by neutron‐diffraction. The addition of Se to UAs produces a rapid disappearance of the high‐temperature magnetic phase of UAs (type I) and a stabilization of the low‐temperature magnetic modification (type I A). When the amount of Se further increases four transient magnetic structures appear gradually. All are cosinusoidally modulated along the c‐axis with periodicity c/2. Their magnetic unit‐cells are N‐multiples of the f.c.c. chemical unit cells along one direction: N = 5, 7, 9, and 11. The stability ranges of all magnetic phases present in the solid‐solution UAs‐Use and their corresponding Néel points have been determined.
Mobility of electrons in CdxHg1xTe under high hydrostatic pressure
Authors: Stankiewicz J. , Giriat W.
Published: July 2007

An investigation is made of the influence of high pressures on the electron mobility in CdxHg1−xTe. It is shown, that the established energy band structure for this material is in full agreement with the experimental results obtained. Scattering on ionized impurities and on optical phonons was considered in the calculation of μ = f(x) at 77 K. The calculation of μ = f(x) is qualitatively consistent with the measured data.
Determination of exciton diffusion length from photoconductivity low‐temperature spectra
Authors: Novikov B. V. , Ilinskii A. V. , Lieder K. F. , Sokolov N. S.
Published: July 2007

The spectral distribution of the photoconductivity of CdS and CdSe single crystals has been investigated at 77 °K in a wide spectral range. The values of the exciton diffusion lengths in these compounds have been obtained from the photocurrent spectra using the absorption coefficient data. The exciton diffusion lengths were found to be within the range of 2000 to 10000 Å for CdS and 2000 to 4000 Å for CdSe. The proposed model involves the diffusion of the excitons to the surface, where they dissociate into free carriers interacting with the near‐to‐surface centres. The role of the space charge layer in these phenomena is discussed.
Influence of pressure on the mobility in heavily doped n‐type indium antimonide
Authors: Litwin‐Staszewska E. , Porowski S. , Filipchenko A. A.
Published: July 2007

The resistivity ϱ of n‐type InSb doped with Te, Se, and S was measured as a function of the hydrostatic pressure up to 12 kbar, at 77 and 300 °K. We observed that samples doped with different impurities have different ϱ(P) dependences. The experimental results were compared with theoretical calculations based on the papers of Korenblit and Shestobitov [2] and Zawadzki and Szymańska [3]. The agreement between theory and experiment is good for Te‐doped samples and is highly unsatisfactory for S‐ and Se‐doped samples. It is suggested that the discrepancies of the latter are caused by the existence of short‐range potential centres in S‐ and Se‐doped samples.
Scattering on short‐range potentials in InSb
Authors: Litwin‐Staszewska E. , Porowski S. , Filipohenko A. A.
Published: July 2007

Formulae are given for the relaxation time of scattering on short‐range potential centres associated with ionized and neutral defects in n‐type InSb. The effect of pressure on the partial resistivity associated with this mechanism of scattering and, also for this mechanism, the scattering parameter r' which is used in describing thermomagnetic effects are calculated. The results obtained confirm the suggestions of a previous paper [1] concerning the contribution of short‐range potentials to the scattering in heavily doped n‐type TnSb.
Transformation of tellurium valence band induced by hydrostatic pressure
Authors: Anzin V. B. , Bresler M. S. , Farbstein I. I. , Itskevich E. S. , Kosichkin Yu. V. , Sukhoparov V. A. , Teleynev A. S. , Veselago V. G.
Published: July 2007

The investigation of the Shubnikov‐de Haas effect in tellurium under hydrostatic pressure up to 12 kbar revealed a significant distortion in the shape of the Fermi surface of the holes indicating a disappearance of a saddle point in the valence band energy spectrum. A simple linear model of the energy spectrum transformation is proposed which describes quantitatively the whole set of the experimental data.