bluuebunny/crossref_metadata_2025 huggingface dataset:
Cation Distribution in Aluminum‐Substituted Yttrium Iron Garnets by Mössbauer Effect Spectroscopy
Authors: Czerlinsky E. R. , Macmillan R. A.
Published: July 2007

As a part of continuing search for magnetic materials with improved properties and broader applicability in microwave devices, recoil‐free nuclear resonance absorption was measured on eleven different compositions of Y3AltFe5−tO12 powder specimens with t ranging from 0.39 to 4. To avoid magnetic line splitting, measurements were made above the Curie temperature. The quadrupole splittings of the Fe57 nuclei in the garnet structure caused two absorption doublets for each composition. From the intensities of the lines, the distribution of Fe3+ and Al3+ on the tetrahedral and octahedral sites with regard to the composition was obtained. Some of the powders had been subjected to an identical and controlled heat treatment to establish their cation equilibrium at the same temperature. With both the cation distribution and the equilibrium temperature defined, the stabilization energy was determined for each compound. This quantity is a measure for the “site preference”, in our particular case of Al3+ in AlYIG materials. The results on the distribution are compared with earlier work on AlYIG, GaYIG, and AlYGaG. The electric field gradients resulting from the position of the doublet lines are compared with other investigations on the same compounds.
Nuclear Magnetic Resonance Study of Hyperfine Fields in Dilute Fe Alloys
Authors: Mendis E. F. , Anderson L. W.
Published: July 2007

The hyperfine field spectra of ten Fe alloy systems have been studied. Nuclear magnetic resonance fast‐passage techniques have been used to obtain direct plots of the distributions of hyperfine fields. The systems studied were FeAl, FeSi, FeV, FeCr, FeMn, FeCo, FeNi, FeGe, FePd, and FeSn. In general, four alloys of each system were studied, with the impurity concentration varying from 10−3 to 1.5 × 10−2. All the experimental hyperfine field distributions include satellite resonances. These satellites are interpreted as arising from different sets of Fe near‐neighbours of an impurity. The intensities and line shapes of the satellites are studied. The results of the study are compared with the results of spin‐echo NMR and Mössbauer effect studies to obtain (for most of the alloys) the hyperfine field shifts at the first five near‐neighbor sites.
Nucleation in Solid Solution Stimulated by Non‐Equilibrium Electrons. I. General Theory
Authors: Stoyanov S. , Kashchiev D. , Geoegiev M.
Published: July 2007

A nucleation process proceeding at trapped electron sites in a solid solution of metal atoms within an insulating solid is considered. As a result of the more difficult migration of the condensing atoms, nucleation in a solid may follow a way which differs essentially from the condensation in a Wilson cloud chamber. By means of a properly defined effective supersaturation, expressions for the quasi‐steady state nucleation rate as well as for the total number of nuclei formed within a given time are derived. The analysis indicates that the presence of even a small number of trapped non‐equilibrium electrons may lead to a substantial increase of the nucleation rate. Inasmuch as the occurrence of non‐equilibrium electrons in a solid may be due to various reasons an application of the present theory might be attempted in various cases.
On the Role of Collective Oscillations in the Electron Mechanism of Superconductivity
Authors: Geilikman B. T.
Published: July 2007

The spectrum of collective oscillations for a metal with overlapping — broad and narrow — bands is found. The essential influence of acoustical plasmons on the pairing in the high temperature electronic mechanism of superconductivity for such metals is shown. The conditions for high temperature superconductivity in the case of metal—nonmetal compounds, specifically with organic substances are discussed.
Theory of Cyclotron Resonance of Fröhlich Polarons in High Magnetic Fields
Authors: Evrard R. , Kartheuser E. , Devreese J.
Published: July 2007

Cyclotron resonance of polarons in ionic crystals is studied by means of a Born‐Oppenheimer type method. The Lee, Low, Pines approximation is made for the electron—phonon interaction and so the translational invariance along the magnetic field direction is exploited. Our approach is therefore valid at weak and intermediate couplings and cyclotron frequencies ωc larger than the L.O. phonon frequency ω, which requires rather intense magnetic fields. For relatively large electron—phonon coupling (α ≧ 4) the results also apply qualitatively for weak magnetic fields. The ground state energy and the energy of two excited levels are obtained. The excited states which are treated here are internal excited states of the polaron system and they are different from the normal Landau levels. The stability of some of these states is enhanced under the action of the magnetic field. This leads us to predict absorption at new cyclotron frequencies in ionic crystals especially relevant for intermediate coupling strengths α ≈ 4.
Zur statistischen Begründung der Kontinuumsphysik
Authors: Kröner E.
Published: July 2007

Eine strenge Begründung der Kontinuumsphysik bedarf der Grundlagen der Statistik. Dies wird am Beispiel der Elektrostatik gezeigt. Die Betrachtung ergibt, daß zur vollständigen phänomenologischen Beschreibung des Zustands der Materie die Angabe der mittleren Felder nicht genügt, daß vielmehr das Wahrscheinlichkeitsdichte‐Funktional oder — gleichwertig — der unendliche Satz von Korrelationsfunktionen der betreffenden Felder angegeben werden muß, weil man andernfalls nur bei hinreichender Kleinheit der Fluktuationen im Material zu befriedigender Näherung kommt. Dies wird durch eine Rechnung über die Elastizität von regellos aufgebauten Kupfervielkristallen quantitativ belegt. Der Ansatz Spannung = Elastizitätsmodul × Dehnung für das Materialgesetz enthält hier eine grundsätzliche Unsicherheit von 0,6%.
Characteristic Energy Loss Studies of V2O5 and Vanadium
Authors: Fiermans L. , Vennik J.
Published: July 2007

The characteristic energy losses of V2O5 are interpreted using collective oscillations of groups of electrons, forming the O2p valence band. These observations provide valuable information concerning the energy band model of this material. The losses observed on vanadium are interpreted as due to free electron bulk and surface plasmons and combinations of both. Characteristic ionization losses confirm the ODS peaks observed in the vanadium valence band and indicate high transition probabilities for the top and bottom of this band.
Intrinsic Optical Properties of CrCl3
Authors: Pollini I. , Spinolo G.
Published: July 2007

The intrinsic optical absorption spectrum of CrCl3 has been investigated in the 0.6 to 6 eV region at temperatures from 80 to 300 °K. A careful analysis of the crystal field bands in the 0.6 to 3 eV region has revealed some structures and details, such as an Urbach's rule edge, not previously reported. The optical anisotropy of CrCl3 was also studied over the same spectral range. In the region between 3 and 8 eV reflectivity spectra were also obtained. The refractive index of CrCl3 has been determined on evaporated films from 1000 to 380 nm [n(500nm) = 1.85 ± 0.1]. The spectral distribution of photocurrent at ≈ 80 °K was measured and showed weak peaks associated with the main crystal field bands and a sharp increase at shorter wavelengths; maximum photoconductivity yield was reached at (3.2 ± 0.2) eV. The data on the crystal field bands are discussed and some new structures are assigned to specific electronic transitions. Account is taken of the spin—orbit interaction among the various multiplets and the trigonal distortion of the octahedral symmetry of the Cr3+ environment. A discussion of the optical and photoconductivity data in the 3 to 8 eV region is given and alternative explanations of the absorption edge at 3.2 eV are proposed.
Thermal Expansion of Tellurium
Authors: Ibach H. , Ruin E.
Published: July 2007

Coefficients of thermal expansion α‖c and α⟂c have been measured from 1.6 to 300 °K in a capacitor cell and from 300 to 500 °K in a Perot‐Fabry interferometer. In the whole temperature range α‖c is negative and α⟂c positive. The negative sign of α‖c must be considered mainly as a result of the elastic anisotropy of tellurium, since the Grüneisen parameters γ‖c(T) and γ⟂c(T) are almost equal and positive. The decrease of γ‖c(T) and the increase of γ⟂c(T) at low temperatures is attributed to an anisotropy in the strain dependence of low lying phonon frequencies and can be qualitatively understood by inspection of the lattice and its similarity to the hexagonal primitive lattice.
Electric‐Field‐Induced Anisotropy in the High Frequency Conductivity of CdS
Authors: Sodha M. S. , Chakravarti A. K. , Sharma S. K.
Published: July 2007

The dependence of ac conductivity on the orientation of a steady electric field (< 40 V/cm) in CdS has been studied at low temperatures considering isotropic piezoelectric and deformation potential scatterings simultaneously. It is shown that the perpendicular high frequency conductivity is always greater than the parallel one for the same dc field. Further, it is seen that the induced anisotropy in the high frequency conductivity of CdS due to different orientation of the heating field, increases faster at lower fields and seems to attain a saturated value at relatively higher heating fields (< 40 V/cm) and diminishes with the rise in temperature.
Lattice Dynamics of Potassium Fluoride
Authors: Bührer W.
Published: July 2007

By slow neutron inelastic scattering the phonon dispersion relation was measured in potassium fluoride at room temperature for waves propagating along symmetry directions [00ζ], [ζζ0], and [ζζζ]. The experiments were performed on the reactor Diorit at Würenlingen, using a triple axis spectrometer. The results were analyzed in terms of various interionic‐force models. A satisfactory fit is provided by an eleven‐parameter dipole approximation model, which allows for the polarizability of both ions. This model was then used to calculate a frequency distribution from which the specific heat and Debye temperature were evaluated for comparison with thermodynamic data.
The Effects of Interstitial Impurities on the Yielding Behaviour of Niobium Single Crystals
Authors: Kim H. C. , Pratt P. L.
Published: July 2007

The effect of the overall impurity content on the yielding behaviour of niobium single crystals has been investigated in tension between 77 and 473 °K. In the 〈110〉 orientation the amount of yield drop depends on the impurity level of the crystal, and the temperature dependence of the yield stress was decreased significantly for both 〈110〉 and 〈100〉 orientations for purer crystals. Current theories of solution and lattice hardening were applied to try to account for the observed temperature dependence of the yield stress. Gilman's reaction rate theory is found to be the best explanation for the observed yielding behaviour. The twinning stress of 〈110〉 oriented single crystals in compression showed no systematic variation with impurity content when tested at 20.4 °K.
Light‐trapping as a lattice resonance phenomenon
Authors: Piekara A. H.
Published: July 2007

Existing molecular models of the light‐trapping effect are not suitable to explain particularities of this phenomenon. A resonant interaction is proposed between a self‐modulated light pulse and thermally excited lattice standing waves. Such a mechanism leads to a double space periodicity of the “filament” number as well as of the intensity of stimulated Brillouin and Raman scattering. Only thermal periodicity of this phenomena has been observed [5, 18, 19] which may be understood in terms of thermal expansion [15]. To proof the validity of the resonant mechanism some new experiments are suggested.
On the nature of excess current oscillations in CdS, CdSe crystals
Authors: Vinetskii V. L. , Shakhovtsova S. I. , Konozenko I. D.
Published: July 2007

An interpretation is given of the earlier described phenomenon of low‐frequency current oscillations induced by light, X‐ and γ‐rays in CdS, CdSe crystals, basing on the instability of a stationary state of the crystal with unequilibrium electron occupation of traps; the instability being caused by Joule's heating. It is shown that in the space of variables E, L, T0 (electric field, intensity of radiation, temperature of the crystal surface) an instability region exists. The boundaries experimentally found are in good agreement with calculations. The dependences of the oscillation period on E, L, and T0 are also explained.
Effect of atomic force constant changes on the localized vibrational modes — a perturbation approach
Authors: Croitoru M. , Grecu D.
Published: July 2007

A general formalism is developed to treat the influence of small perturbations on localized vibration modes. The method is applied to cubic crystals, the perturbation being attributed to the atomic force constant changes between a substitutional impurity and its nearest neighbours. In the first order, the frequencies of the localized modes are obtained from simple equations involving only a few perfect‐lattice Green's functions. For frequencies very high above the perfect‐lattice spectrum these equations are solved leading to asymptotic results in agreement with those of other authors. A comparison with the exact result for a simple cubic lattice is drawn too.
Energy release and electrical resistivity recovery in nickel and nickel with silicon impurity contents following electron irradiation at 20° K
Authors: Cotignola J. M. , Minier C. , Paillery A. , Bonjour E.
Published: July 2007

The stored energy release in Ni and Ni– (0.014, 0.073, and 0.29) at% Si has been measured in the temperature range 40 to 400° K after irradiation with 2 MeV electrons. The resistivity of the samples was measured simultaneously between 40 and 70° K. The ratios of stored energy and resistivity obtained in stage I are magnified image
A Kinetic Approach to Fracture of Solids I. General Theorie
Authors: Petrov V. A. , Vladimirov V. I. , Orlov A. N.
Published: July 2007

It is shown that the fracture of a solid is a kinetical process which starts immediately after applying the load and proceeds during the whole time till the rupture of the specimen. This process begins with the opening of microcracks and proceeds by their growth and coalescence until a macroscopic crack arises. A general kinetic equation is derived governing the distribution function ϱ(q,t) of cracks depending on their dimensions and on other parameters q and on the time t. Together with the equation for the probability of crack coalescence and some auxiliary conditions it forms a system of equations from which ϱ(q,t) can be determined. A method for solving this system is proposed based on a division of all cracks into three groups and on an iteration technique. The method is illustrated in a simple special case. More complicated problems will be considered in future papers.
Lattice dynamics of zirconium
Authors: Bezdek H. F. , Schmunk R. E. , Finegold L.
Published: July 2007

Using coherent inelastic neutron scattering, phonon dispersion curves for zirconium, at room temperature, were measured for two high symmetry directions, [0001] and [0110]. The data were analyzed on the basis of a six‐neighbor modified axially symmetric model. A frequency distribution calculated from the parameters obtained from the model is also presented.
Superconductivity for ternary F.C.C. BiPbTl Alloys
Authors: Claeson T. , Munkby L. , Wingbro T.
Published: July 2007

The superconducting transition temperature has been measured for several f.c.c. ternary BiPbTl alloys. The transition temperature is essentially determined by the number of valence electrons per atom. A phase transition to a h.c.p. phase extends from BiTl3 into the ternary system giving rise to broad transitions to the superconducting state. The Tc of a hypothetical f.c.c. Tl phase was extrapolated to 1.75° K. The electron–phonon coupling strength could be estimated from Tc and the Debye temperature using a theory by McMillan. The variation of the coupling strength with concentration of Tl in Pb shows a greater similarity with expectations regarding the density of electron states at the Fermi level than with an empirical curve by McMillan based upon the phonon distribution.
The correlation between dislocation structure and work‐hardening behaviour of molybdenum single crystals deformed at 293° K
Authors: Luft A.
Published: July 2007

The dislocation structure of high‐purity molybdenum single crystals after tensile deformation at 293° K is studied by transmission electron microscopy. Dislocation and debris densities were determined as function of strain. The stress–strain curve is characterized by a high initial work‐hardening rate and a subsequent stress plateau. At low strains long jogged screw dislocations and dislocation debris predominate while at higher strains additionally large dislocation tangles are formed. The resolved flow stress τ and screw dislocation density ϱ1 obey τ = τ0 + α1 G b √ϱ1 with α1 = 1.1. It is suggested that the interaction between primary and secondary screws involving the formation of jogs, debris, and attractive dislocation junctions is the relevant dislocation strengthening mechanism.
Absorption spectrum and crystal field parameters of Er3+ in YAsO4
Authors: Kahle H. G. , Klein L.
Published: July 2007

The optical absorption spectrum of trivalent erbium in single crystals of yttrium arsenate is measured in the range from 15000 to 29000 cm−1 and analysed with a crystal field of 42m symmetry. The values of the five crystal field parameters of the arsenate are compared with those of the isostructural phosphate and vanadate. Differences and similarities are discussed.
Lattice dynamics of crystals of the calcite structure. I. Normal frequencies and normal modes at zero wave vector
Authors: Plihal M. , Schaack G.
Published: July 2007

Normal frequencies and normal modes of the lattice vibrations for the wave vector |y| = 0 have been calculated for the isomorphic series of NaNO3, CaCO3, and MgCO3. The calculated frequencies of the infrared‐ and Raman‐active modes have been fitted to the experimentally known values for T = 300 °K by variation of the coupling constants. Three different models have been used: a) In model 1 only the short‐range interactions by central forces have been taken into account. b) In model 2 the Coulomb‐interaction has been included (rigid‐ion model). c) In model 3 the anisotropic polarizability of the anion has been considered in addition (shell model). The best fit has been obtained with the shell‐model. The calculated frequencies and eigen‐vectors are given and discussed in comparison with experimental results.
Optical second‐harmonic generation in SbSI
Authors: Häfele H. G. , Wachernig H. , Irslinger C. , Grisar R. , Nitsche R.
Published: July 2007

The optical second‐harmonic generation in antimonysulfoiodide (SbSI) was studied with a Q‐switched CO2‐laser. The temperature dependence for various crystals was observed in the range −140 to +40 °C which includes the ferroelectric phase transition at about 20 °C. The nonlinear susceptibility χ33 is about one order of magnitude smaller than χ11 in tellurium. The coherence length lc is estimated to be 165 μm. The SH signal in plane‐parallel samples shows strong temperature dependent modulation produced by interference of fundamental waves. Two further modulations with smaller periods are observed but not explained. Applied electric fields influence the SH power by the electro‐optic effect and by an unidentified mechanism, which causes striking enhancement.
Unusual dissociation of dislocations in Ni3Ta
Authors: Hayashi Y. , Delavignette P. , Amelinckx S.
Published: July 2007

Dislocations in ordered Ni3Ta are examined by transmission electron microscopy. [100] super‐dislocations dissociate visibly into two dislocations both of which presumably consist of closely spaced partial dislocations. [001] super‐dislocations dissociate into two dislocations one of which is a partial dislocation and the other consists presumably of three very closely spaced partial dislocations. These dissociations seem to occur when the antiphase boundary energy is much larger than the stacking fault energy. The dissociation of the [100] superdislocations allows an estimation of the order fault energy which is found to be of the order of 130 erg/cm2.
NMR of proton conductor borax
Authors: Valic M. I. , Pintar M. M.
Published: July 2007

A comprehensive NMR study of powdered proton conductor borax provides information on one rotary mode of crystal water. This mode is fast enough to maintain the conductive chain depolarized. The proton conductivity “bottleneck” mode is a flipping mode of another water molecule in the conductive chain.
Exciton electro‐reflectance of cuprous oxide crystals
Authors: Shestatskii S. N. , Sobolev V. V. , Likhobabin N. P.
Published: July 2007

The electro‐reflectance spectrum of Cu2O single crystals was measured in the region of blue and violet exciton series (5000 to 4000 Å) at T = 77.3 °K. Both the modulating voltage Uac and the dc bias voltage Udc were varied. The electro‐reflectance structure obtained is due to the electric field effect on the n = 1 and n = 2 exciton lines of the blue and violet exciton series of cuprous oxide. The inversion of the electro‐reflectance structure occurs for some values of the ac voltage being different for various dc biases. This phenomenon is due to the presence of surface band bending of Cu2O samples investigated. Agreement was obtained with the basic conclusions of Aspnes and Frova's theory taking into account the influence of the surface field non‐uniformity on the line‐shapes of the electro‐reflectance spectra.
Compressibility and polymorphism of the elements
Authors: Plendl J. N. , Gielisse P. J.
Published: July 2007

Volumetric compressibility of elements is expressed by a general atomistic formulation without apparent need for restrictive terms. The elements are assigned to one of three fundamental types of structures: “reduced”, “basic” or “elevated”.
Pseudopotential band structures of Mg2Si, Mg2Ge, Mg2Sn, and of the solid solution Mg2(Ge, Sn)
Authors: Aymerich F. , Mula G.
Published: July 2007

The band structures of Mg2Si, Mg2Ge, Mg2Sn, and of the solid solution Mg2(Ge, Sn) are calculated with an “a priori” version of the pseudopotential method. In the computation of the Mg form factors the Heine‐Abarenkov model potential and a Penn‐type dielectric function have been used. Our results settle the disagreement between previous calculations and recent experimental information.
Effective field distribution in gallium‐substituted ferrites
Authors: Kostikas A. , Simopoulos A. , Gangas N. H. J.
Published: July 2007

Mössbauer spectra of GatFe3−tO4 (t = 0.44) were taken at temperatures from 88 to 740 °K. The A‐ and B‐site Zeeman patterns are resolved. The B‐site pattern displays a variation of hyperfine field arising from a distribution of the non‐magnetic gallium ions in the A‐site. The spectra were analyzed by a least‐square fit computer program. A detailed statistical treatment tested the hypothesis of a binomial distribution of the Ga3+ ions in the A‐site. The temperature dependence of the hyperfine fields at the inequivalent B‐sites was fitted with an effective field model which gave considerably enhanced B—B interaction relative to Fe3O4.
Angular dependence of critical magnetic fields in superconducting films
Authors: Krätzig E. , Keller J.
Published: July 2007

The angular dependence of the critical magnetic field Hc in superconducting films is studied by measuring the attenuation of ultrasonic surface waves. In the case of thin films (phase transitions of second order) good agreement with an interpolation formula derived by Tinkham [1] is found. Thick films (film thickness large compared to coherence length and penetration depth) are studied too showing first order phase transitions or surface superconductivity in a magnetic field parallel to the film. In the case of surface superconductivity the measurements are compared with a new interpolation formula for Hc which can be derived from the Ginzburg‐Landau equation.
Inelastic exciton‐exciton scattering in CdS at He temperatures
Authors: Büttner H.
Published: July 2007

The cross‐section for inelastic exciton–exciton scattering leading to an excited exciton and a polariton is calculated in the Born approximation. It turns out that the transitions to the excited p‐states are most important. Furthermore, it is found that the transitions are mainly due to exchange effects. The results are compared with recent experiments.
Aspects of the theory of F‐centres
Authors: Hagston W. E.
Published: July 2007

The formal errors associated with a recent pseudopotential calculation of F‐band energies [4] are investigated, and the arbitrary reduction made by these authors in one of the coefficients appearing in this pseudopotential is shown to be equivalent to an overestimate of the amount of core admixture into the final F‐centre wave function. Implications of this over‐admixture for the theory of hyperfine coupling, spin–orbit splitting of the excited state, and g‐shifts are discussed.
Neutron diffraction on lattice planes deformed by flexural vibrations of quartz single crystals
Authors: Petržílka V. , Vrzal J. , Michalec R. , Chalupa B. , Mikula P. , Zelenka J.
Published: July 2007

A description is given of neutron diffraction effects due to the deformation of lattice planes by flexural vibrations of a quartz single crystal cut in the shape of a bar. The relative increase of the diffracted neutron intensity in dependence on the exciting voltage, i.e. on the amplitude of vibrations was measured for different lattice planes of the quartz single crystal. The modulation degree of the neutron intensity as function of the exciting voltage was determined. A qualitative explanation of the results observed is given.
Phonon Polarization Operator in the Random Phase Approximation
Authors: Kashcheev V. N.
Published: July 2007

In the random phase approximation the imaginary part of the phonon polarization operator is calculated in the left vicinity of the Curie point as well as the renormalization of the sound velocity due to the spin‐phonon interaction of exchange origin in a cubic ferrodielectric.
Temperature Dependence of Defect Production in KBr and KCl (I)
Authors: Comins J. D.
Published: July 2007

The rate of production of defects by ionizing radiation in Harshaw KBr and KCl has been studied as a function of temperature. It is found that the production rate increases in a fairly progressive manner between 81 and about 200 °K. A correlation is found between the increases in defect production and a progressive broadening of the V‐centre absorption envelopes formed at the various temperatures of irradiation. Studies of the growth of the major V‐centres responsible for these absorption envelopes show that they are interstitial defects. It is considered that the enhanced defect production results from an increased probability of interstitial trapping as the temperature of irradiation is raised, and that the interstitial defects are trapped in clusters, either intrinsic or nucleated by impurities.
Many‐Band Impurity States in Semiconductors
Authors: Hawton M. H. , Paranjape V. V.
Published: July 2007

Impurity states have been calculated in semiconductors using the prescription proposed by Lukes and Roberts. It is shown that deep levels predicted are not necessarily possible for weak impurity potentials.
Effect of High Pressure on the Electronic Density of States of Aluminium
Authors: Schlüter M.
Published: July 2007

A generalized Wigner‐Seitz method is applied to the band structure of aluminium. The calculation is based on a muffin‐tin potential derived from the electronic density of the free atomic states normalized with respect to the volume of the Wigner‐Seitz cell. Because of the spherical symmetry of the potential the wave function can be expanded in terms of spherical harmonics. Their number has to be limited to 12 according to the number of central points of the 12 rhombohedrons constituting the Wigner‐Seitz surface. The method provides E(k) in any direction of the Brillouin zone (BZ). For reasons of saving computer time E(k) is computed for each band at 300 points of the irreducible wedge of the BZ and properly fitted to a Fourier expansion of 10 terms. By means of this expansion E(k) is easily obtained at 5 × 105 k‐points. The density of states and its variation under pressure can be computed then by simply ordering those 5 × 105 E‐values of each band into a sequence of energy intervals of 0.01 Ryd width, by counting their number in each of those and finally summing up the contributions of all bands.
High‐Temperature Susceptibility of Uranium Compounds with Th3P4‐Type Crystal Structure
Authors: Troć R. , Mulak J. , Suski W.
Published: July 2007

Magnetic susceptibility measurements for six uranium compounds with P, As, Sb, Bi, Se, and Te having Th3P4‐type crystal structure, have been performed in the temperature range 77 to 1200 °K. In the higher temperature region, the dependence of χ−1 on T is found to be curvilinear or all these compounds. The experimental results, corrected for the presence of magnetic exchange interactions, are compared with theoretical ones, obtained by taking into account the influence of the crystal field on the central U+4 ion in the tetragonal D2d‐symmetry. The increase of the paramagnetic moment of U+4 in U3X4 compounds from 2.75 to 3.14 BM is explained by the assumption that the pseudo‐doublet is the ground state. The anisotropy of the magnetic properties of an individual U+4 ion and the relation between the paramagnetic and the ferromagnetic moment are theoretically established and found to be in accordance with the experiment.
The Ferromagnetic Domain Structure of the 〈110〉 SiFe Crystals
Authors: Dedié G. , Niemeyer J. , Schwink Ch.
Published: July 2007

The main and closure domain structures of cylindrical and prismatic 2.5% silicon‐iron single crystals with 〈110〉 axes are investigated using powder pattern technique and Kerr magnetooptic effect. The main domains are leaf‐shaped only in small effective fields. As closure domains we find on (110) faces the chess‐board structure at zero effective field and Q‐domains combined with the complicated zigzag pattern in the field range of magnetization rotation. The zigzag pattern is found to be independent of side face orientation in a wide range of orientation. Models of these closure domain structures are presented. Aspects of the calculation of the domain period and its field dependence are discussed.
Interpretation of the Ultraviolet Spectrum of Trigonal Selenium
Authors: Sandrock R.
Published: July 2007

Based on an earlier pseudopotential calculation [1] the imaginary part of the dielectric function for Se is recalculated between 6 and 11 eV including lifetime broadening. Our results agree well with UV reflectivity measurements by Leiga [3], a detailed interpretation of which is given. In particular, the strong polarization dependence of several peaks is explained, and also the crossover of the ∥ and ⟂ spectra at 10 eV. The spectrum is shown to be largely determined by additional gaps between the subbands of both the valence band and the conduction band.
Magnetic Susceptibility for a Dilute Magnetic Alloy
Authors: Kjöllerström B.
Published: July 2007

For a dilute magnetic alloy the two‐body Coulomb interaction U is replaced by the interaction with two external fields, and the partition function is then transformed into a Gaussian average over these fields. In the case of static external fields the magnetic susceptibility is calculated. When A(0) U > 1 there are localized magnetic moments which have a Curie‐law susceptibility with the correct limiting value of the Curie constant for large U. When A(0) U < 1 there are no moments and the susceptibility is temperature independent approaching the correct Pauli‐enhanced susceptibility.
Optical Spectra of M, F‐Singlet, and F‐Triplet Centres in NaF
Authors: Elsässer K. , Seidel H.
Published: July 2007

X irradiated NaF crystals contain after bleaching the F band mainly M and F centres. Complete orientation of the M centres and partial orientation of the F centres can be achieved. The F centres, identified by their 545.6 nm zero‐phonon line, have broad absorption bands at 512 and 303 nm. Upon strong excitation in the region of the 303 nm band a temporary bleaching of both the bands and the zero‐phonon line is found and ascribed to population of a metastable F‐centre triplet state with a lifetime of τ = 1.9 s at 77 °K.
Infrared Modulation and Energy Band Parameters in Multivalley Semiconductors through Uniaxial Stress Dependence of Free Carrier Contribution to Optical Constants
Authors: Walton A. K.
Published: July 2007

The influence of uniaxial stress in 〈111〉 direction on the free carrier contribution to the optical constants of multivalley semiconductors is considered according to the electron transfer model. Calculations are made of the resulting change in absorption and shift of the wavelength for minimum reflection. It is shown that these effects may be large and experimental observation of them provides a method of determining the effective mass and relaxation time parameters and their anisotropies. The possibility of constructing infrared modulators based on these phenomena is also examined.
Mössbauer Effect Study of Calcium Magnetites
Authors: Hrynkiewicz A. Z. , Kulgawczuk D. S. , Mazanek E. S. , Pustówka A. J. , Sawicki J. A. , Wyderko M. E.
Published: July 2007

Mössbauer effect measurements for a series of iron compounds of the type CaxFe3−xO4 (0 ≦ x ≦ 0.55), known as calcium‐magnetites, are performed at room temperature and liquid nitrogen temperature. A single calcium‐magnetite phase giving Mössbauer spectra with magnetite‐like Zeeman splitting was observed up to x ≈ 0.28. For higher Ca concentrations a second phase, represented by the additional quadrupole doublet, was detected. This new phase may be identified as CaFe2O4 ferrite.
Pinch Effect in Semiconductors in the Case of an Injected Plasma — The Field‐Controlled Current Regime
Authors: Boiko I. I.
Published: July 2007

The pinch effect in semiconductors is considered for the case when excess current carriers are injected from contacts into a semiconductor. A crystal with dimensions long compared to the bipolar diffusion length, permits to use the field‐driven current approximation [1, 2]; in most of the volume of the solid the longitudinal field flows of carriers dominate over the longitudinal diffusion flows and the volume of the solid absorbs most of the applied voltage and hence determines the current‐voltage characteristic. The treatment is limited to the high injection level situation, when a local density of non‐equilibrium carriers significantly exceeds that of equilibrium electrons and holes. The carriers are supposed to be non‐degenerate. For crystals of plate and cylinder geometry the current‐voltage characteristics, the electric field, and the carrier density distribution are calculated. The calculations are performed for two aspects of space recombination kinetics — the monomolecular and the bimolecular recombination. It is shown that the bimolecular recombination reduces the current at pinch conditions.
Role of Jahn‐Teller Effect in the Ligand Field Theory of Octahedrally Coordinated Trisacetylacetonato Manganese
Authors: Bhattacharyya B. D.
Published: July 2007

A theoretical expression for the magnetic susceptibility and anisotropy of an Mn (111) ion having trigonal symmetry in octahedral trisacetylacetonato manganese have been derived on the basis of the more general molecular orbital method of Van Vleck, Stevens, and Bose et al., considering quantum mechanical tunnelling which links equivalent vibronic states of the Jahn‐Teller ion. Attempts have been made to fit the experimental data of optical absorption and magnetic susceptibility with a unique set of parameters in the theoretical expressions at all temperatures. From this an estimate of the parameters which describe the Jahn‐Teller potential is made.
Comments on the Theory of Anharmonic and Tunnel‐Phonon Interactions in KCl:Li+
Authors: Benedek Giorgio
Published: July 2007

The local third‐order anharmonicity, the tunnel splitting of phonon levels, and the interaction between phonons and tunnel excitations, occurring for an off‐centre defect ion in crystals, are considered in connection with the resonant mode isotope shift. The phonon self‐energy related to the above interactions is evaluated to the lowest order of perturbation theory. The first two mechanisms are found to be responsible for the anomalous isotope shift recently discovered by Kirby and Sievers in KCl:Li+.
Screening of a Fixed Charge in Metals
Authors: Pathak A. P.
Published: July 2007

Using a modified Hubbard formula for the dielectric function which has been previously shown to give results for the pair distribution function which are better than those given by the original Hubbard dielectric function, numerical calculations of the screening charge density around a fixed foreign charge in an electron liquid are presented for values of rs corresponding to the metallic density range. The results are compared with those calculated by Langer and Vosko based on the original Hubbard approximation and appreciable differences are found at distances corresponding to the first three shells of ions around the impurity.
Theory of Plasma Electroreflectance of Light from Semiconductors
Authors: Dmitruk N. L. , Tyagai V. A.
Published: July 2007

A calculation of the influence of the surface field on the plasma reflection coefficient (plasma electroreflectance) is presented. It is shown that the field and spectral dependences of plasma electroreflectance are significant for the determination of a considerable number of semiconductor parameters (that of free carriers, surface parameters, etc.). An oscillatory behaviour of the plasma electroreflectance is predicted when the Debye screening length is small enough with respect to the spatial inhomogeneity length of the light wave.
Electronic Transitions in Some Alkali and Chromium (III) Chloride Double Salts
Authors: Musa M. , Lébl M. , Botez M. , Lulea C.
Published: July 2007

Investigations are made of the absorption spectra — d‐d transitions — of a series of A3CrCl6 double salts, where A = Li, Na, K, Rb, and Cs. Using Tanabe and Sugano's energy matrices for d3 configuration in Oh point group an assignment of the bands is made. An influence of the next alkali cation on the Racah parameter B is observed and qualitatively explained by introducing a new parameter μ depending on both the charge and the radius of cations.
Study of the Temperature Dependence of the Resistivity in the Kondo Side‐Band Model
Authors: Maranzana F. E. , Bianchessi P.
Published: July 2007

The influence of the crystal field on the Kondo effect in a magnetically non‐dilute inter metallic compound is analysed. An expression for the resistivity versus temperature is obtained. Some resistivity versus temperature curves are reported and discussed.
Dislocations at and near Planar Interfaces
Authors: Brækhus J. , Lothe J.
Published: July 2007

Dislocations at and near the planar interface between two anisotropic media are considered. It is shown that the energy factor for a dislocation at the interface can be expressed simply in terms of the K‐matrices for the two media. The K‐matrix is defined so that E=(1/2)biKijbj where E is energy factor and the bj are the components of Burgers vector. It is also shown that the force on a dislocation in one of the media and parallel with the interface is simply given in terms of the energy factor for the dislocation in that medium and the energy factor for the interface dislocation.
Properties of Sodium Halide Molecules from Shell Model Parameters
Authors: Pirie J. D. , Smith T.
Published: July 2007

Model parameters which give a good description of measured phonon dispersion curves have been used in a shell model description of the corresponding molecules. The internuclear distance, the binding energy, the electric dipole moment, and the vibrational frequencies were then calculated. A comparison of these results with experiment provides a test for the model parameters over much larger displacements than are encountered in lattice vibrations at normal temperatures, and suggests which models may provide a useful description of the forces associated with the displacements near defects in crystals.
Origin Dependence of the Symmetry Labelling of Electron and Phonon States in Crystals
Authors: Cornwell J. F.
Published: July 2007

The general theory is given of the origin dependence of the labelling of electron and phonon states in crystals. All types of space group are considered. The space groups T, O, and C are studied as examples.
Electronic band structure of the layer‐type crystal MoS2 (atomic model)
Authors: Harper P. G. , Edmodson D. R.
Published: July 2007

The theory is presented for the electronic band structure of the dichalcogenide layer‐type crystal MoS2 in its 2H form. Group theory is used to treat an LCAO model based on s, p, d Mo atomic states, and s, p S atomic states. Hybridised spin‐orbit bands are examined along the Δ‐axis, and at the M‐ and K‐points in the Brillouin zone. A simple choice is proposed for the valence and conduction band Δ‐axis symmetry types.
Étude cristallographique et magnétique de MnGeO3
Authors: Herpin P. , Whuler A. , Boucher B. , Sougi M.
Published: July 2007

Le composé MnGeO3 possède une structure orthopyroxène. Ses Paramètres réticulaires sont a = 5,44 Å b = 19,24 Å, c = 9,23 Å et son groupe d'espace Pbca. On affine les positions atomiques des divers atomes. Les mesures de diffraction de neutraons permenttent de déterminer la structure magnétique, la température de Néel (TN = 16 °K) et la valeur des moments magnétiques de chacun deux sites cristallographiques occupés par les ions Mn2+ pour 1,1 °K < T < TN. On étdie, à 1,1 °K la variation de la direction des moments magnétiques en fonction d'un champ magnétique (H ≦ 15 kOe) appliqué suivant le vecteur de diffusion. Le signe et l'ordre de grandeur des intégrales d'échange des trois premiers voisins sont discutés.
Determination of optical constants: Disordered germanium
Authors: Jungk G.
Published: July 2007

The transition from the amorphous to the crystalline state has been studied by ellipsometric determination of the room‐temperature optical constants on evaporated germanium films and single crystals in the spectral range from 2.0 to 4.0 eV. For evaporated samples the substrate temperature varied over the range 20 °C ≦ Ts ≦ 400 °C. For Ts ≦ 200 °C no any fine structure but an increase of ϵ2(ω) with decreasing disorder has been found. For Ts > 200 °C characteristic structures occurred at energies comparable with critical points of the crystalline state. The absolute value and the line shape of ϵ(ω) however are different for single crystals and films.
Formation of twist boundaries in germanium deformed in torsion
Authors: Wagner R. , Wöhler F. D. , Haasen P.
Published: July 2007

Germanium single crystals of [111] orientation were deformed in torsion at several temperatures to various specific angles φ0 [deg/cm]. Slip lines showed the deformation to occur only on (111) planes. The plastic torsion was stable with annealing up to 900 °C. Electron transmission showed that (111) twist boundaries with hexagonal dislocation networks are formed already during deformation at 685 °C. The percentage of network dislocations increased with φ0 and with the temperature of annealing. The fraction of screw dislocations increased by 15% during an anneal up to a total of about 80%. The dislocation arrangement after annealing closely corresponds to theoretical expectations.
The atomic configuration of screw dislocations in the b.c.c. lattice
Authors: Diener G. , Heinrich R. , Schellenberger W.
Published: July 2007

A new simplified model for the calculation of the atomic structure of screw dislocations in b.c.c. metals is suggested. The results for the two different equilibrium configurations are discussed. They are in good agreement with those obtained by lattice relaxation techniques. In contrast to the high energy metastable configuration, the low energy configuration was found to be asymmetric with respect to the {112} planes; therefore, two energetically degenerated equilibrium configurations are possible.
The asymptotic behaviour of wannier functions
Authors: Lix B.
Published: July 2007

The treatment of many problems in electron theory is considerably simplified if the Wannier representation is used, provided the Wannier functions are well localized and decrease exponentially for large distances from their centres. It is shown that in the case of band groups with point and line degeneracies it is possible to define pseudo‐Wannier functions with exponential tails, which everywhere in the crystal deviate as little from conventionally defined Wannier functions as one wants. The question how far the Wannier functions extend with appreciable magnitude from their centres into the crystal is not considered.
Anisotropie current decay in tellurium due to the acousto‐electric effect
Authors: Arnold J.‐U. , Nimtz G. , Roth E.‐P.
Published: July 2007

The time dependence of the current decay due to the acousto‐electric effect was measured in p‐type tellurium at 77 K. The dependence of the current decay on the crystallographie orientation, the carrier density, and the carrier mobility was investigated. The experimental results for drift fields parallel to the x‐ or y‐axis agree with the theory of acousto‐electric amplification. A current decay was also found for a drift field along the z‐axis. This coupling is about a third of that in the x‐direction, but according to the theory of piezoelectric effect in tellurium no coupling is expected.
Electromultipole interaction and paramagnetic relaxation in ruby. III. Distant wing shape of EPR lines
Authors: Peskovatskii S. A.
Published: July 2007

It is found that the wings of the EPR lines in ruby are an order of magnitude longer than they should be according to the theory of the magnetic dipole‐dipole broadening. The observed wings and calculated shape of the lines broadened by the electric quadrupole‐quadrupole interaction [I] are in good agreement.
X‐ray emission spectra of manganese borides
Authors: Shashkina T. B.
Published: July 2007

X‐ray Kβ5‐emission spectra from manganese and five borides have been obtained under primary and secondary excitation. The investigation of the borides included also measurements of the B K‐emission band of each compound and of pure boron. The resolution for the Mn K‐band was 0.2 eV and for the B K‐band 0.1 eV. The structures of the spectra of both components are compared and discussed in view of their concentration dependence.
On the theory of optical interband transitions in the presence of resonance scattering
Authors: Keiper R.
Published: July 2007

The effect of resonance states on the behaviour of the density of states ϱ(E) and the absorption coefficient α(ω) is studied for a doped semiconductor having a special band structure. It is shown that if the photon energy is higher than the absorption edge (ħ ω > Eg) characteristic thresholds and peaks appear in the absorption spectrum, the magnitude and position of which depend on the impurity concentration n, the energy Er, and the width Γr of the resonance levels, the effective masses mv and mc of the valence and conduction bands.
Optical properties and electronic structure of white tin
Authors: Schwarz H.
Published: July 2007

The optical properties of a tin single crystal and of a tin film deposited by vacuum evaporation were measured in the energy range from 0.5 to 5.5 eV in dependence on temperature and crystal orientation. The absorption curves differ appreciably for the two polarizations and show many structures which become more pronounced at low temperatures. These structures in the optical absorption are related to regions of the band structure where the bands are nearly parallel. The results show that existing band structure calculations of tin are accurate near the Fermi energy, for energies above and below EF, however, the shape of some of the bands should be corrected.