bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristic Energy Loss Studies of V2O5 and Vanadium
Authors: Fiermans L. , Vennik J. 
Published: July 2007

AbstractThe 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

AbstractThe 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

AbstractCoefficients 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

AbstractThe 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

AbstractBy 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

AbstractThe 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

AbstractExisting 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

AbstractAn 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

AbstractA 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

AbstractThe 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

AbstractIt 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

AbstractUsing 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractNormal 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

AbstractThe 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

AbstractDislocations 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

AbstractA 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

AbstractThe 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.
Pseudopotential band structures of Mg2Si, Mg2Ge, Mg2Sn, and of the solid solution Mg2(Ge, Sn)
Authors: Aymerich F. , Mula G. 
Published: July 2007

AbstractThe 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

AbstractMössbauer 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractA 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.
Temperature Dependence of Defect Production in KBr and KCl (I)
Authors: Comins J. D. 
Published: July 2007

AbstractThe 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.
Effect of High Pressure on the Electronic Density of States of Aluminium
Authors: Schlüter M. 
Published: July 2007

AbstractA 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

AbstractMagnetic 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

AbstractThe 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.