bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Magnetic Behaviour of FeAl Alloys of B2‐Structure Investigated by Mössbauer Spectroscopy
Authors: Hergt R. , Wieser E. , Gengnagel H. , Gladun A. 
Published: July 2007

AbstractFeAl alloys in the concentration range 25 to 50 at% Al were investigated between 1.3 °K and room temperature by Mössbauer spectroscopy and magnetic measurements. These alloys are characterized by the simultaneous appearance of Fe atoms in two kinds of very different neighbourhood: 8 nn Fe and 4 or less nn Fe. This fact causes the appearance of strong fluctuation effects observed above 30 at% Al. At 33 at% Al two kinds of domains coexist, such which order magnetically above room temperature (“Fe3Al”) and other with a magnetic transition temperature of about 100 °K (“FeAl”). The concentration dependence of the observed hyperfine fields and the magnetic transition temperature is explained by the decrease of the iron magnetic moment with increasing Al‐content, which in this concentration range is not correlated to the number of next nearest neighbour Fe atoms but seems to be determined by the absolute Al‐content.
Contribution to the Quantum Theory of the Seond‐Harmonic Generation in a Molecular Crystal
Authors: Lebon F. 
Published: July 2007

AbstractThe quantum theory of the second‐harmonic generation is developed for diamagnetic molecules through a variational perturbation method. The advantage of this method is that it requires only to know the wave function Ψ of the ground state of the non‐perturbed molecule; thus, the coefficient characterizing the second‐harmonic generation can be expressed as a function of the wave function Ψ and of vectors determined by a variation calculus; so this coefficient can be computed numerically. This calculation is achieved for the hexamethylene‐tetramine crystal.
The Effect of Concentration Gradients of Impurities on the Temperature Dependence of the Spin—Lattice Relaxation Time in Lithium and Beryllium
Authors: Orchard‐Webb J. H. , Watts A. J. , Smithard M. A. , Cousins J. E. 
Published: July 2007

AbstractMeasurements are presented of the conduction electron spin resonance linewidths for various samples of lithium and beryllium at frequencies of 9.27 GHz and 33 and 80 MHz, the samples having dimensions which are large compared with the appropriate skin depth. An increase in the linewidths and certain line shape anomalies as measured at 9.27 GHz at low temperatures, are discussed in terms of relaxation in an impure surface layer. A value of χs = 1.6 × 10−7 c.g.s. units has been deduced for the spin susceptibility of beryllium.
Acousto‐Electric Phonon Distributions Measured by X‐Ray Brillouin Scattering
Authors: Lemke H. , Müller G. O. , Schnürer E. 
Published: July 2007

AbstractEvaluation of phonon distributions from satellites of X‐ray Bragg reflections is complicated by convolutions with spectral and angular distributions of the primary beam. Assuming only first‐order processes an integral equation fitting the experimental situation is derived and numerically solved. First results indicate higher phonon frequencies than previously obtained by optical Brillouin scattering on different samples and expected from Hutson and White [3] gain and McFee and Bateman [9] losses.
Interpretation of Positron Annihilation Curves for Lithium by Mijnarends' Method. Has the Fermi Surface of Lithium a Neck?
Authors: Stachowiak H. 
Published: July 2007

AbstractThe positron annihilation curves of Donaghy and Stewart for lithium have been reinterpreted using Mijnarends' method. In this way it has been possible to split the total number of counts into two parts, one corresponding to electron momenta inside the main Fermi surface, the other arising from higher momentum components of the conduction electron wave functions and core annihilation. Evidence is found for the possible existence of a neck in the Fermi surface in the (110) direction with a radius of the order of 13% of the free electron sphere radius. The need for more detailed experimental investigations of positron annihilation in lithium is emphasized.
Invariant Piezoelectric Coefficients for Crystals
Authors: Srinivasan T. P. 
Published: July 2007

AbstractIn writing out tensors which represent physical properties of crystals, it is customary to choose a Cartesian frame of reference which has a specific orientation with respect to the crystallographic axes. A new formulation is proposed in which the physical properties (in particular the piezoelectric property) of crystals can be specified without reference to any coordinate system.
Calculation of ϵ2‐Spectra for Amorphous Selenium, Germanium, and Silicon Using the Non‐Direct Transition Model with Energy Dependent Matrix Elements
Authors: Maschke K. , Thomas P. 
Published: July 2007

AbstractThe non‐direct transition model for calculation of amorphous ϵ2‐spectra is considered with respect to energy dependent matrix elements. It is shown how these amorphous matrix elements may be obtained from the crystalline matrix elements. The model is discussed for amorphous Selenium, Germanium, and Silicon.
Optical Study of the Crystal Field Splitting of Excited 5d States of Ce3+:YPO4
Authors: Briffaut J. P. , Denis J. P. 
Published: July 2007

AbstractFluorescence and absorption ultraviolet spectra of Ce3+: YPO4 are reported. They appear as bands which are assigned to 4f ↔ 5d transitions. From fluorescence quantum efficiency measurements the values of the parameters A (9014 cm−1), A (45320 cm−1), and A (5406 cm−1) characterizing the crystal field acting on the 5d states of Ce3+:YPO4 are obtained.
Two‐Photon Absorption of CaF2:Eu2+
Authors: Bayer E. , Schaack G. 
Published: July 2007

AbstractThe technique of two‐photon‐absorption spectroscopy with polarized laser‐light is applied to localized excitations of 4f‐electrons in crystals. The relevant selection rules are discussed. A method is outlined for the unique determination of the relative magnitude of partial transition‐probabilities with different types of symmetry using linear and circular polarization of the incident light. The anisotropy of the two‐photon absorption has been measured in single crystals of cubic CaF2:Eu2+ at five different wavenumbers. The relative intensities of transitions belonging to the three different types of symmetry active in two‐photon absorption are constant in the range of the e‐band (26,000 to 29,000 cm−1) but differ from these values at 37,700 cm−1 in the range between the e‐ and the t‐band. This result is discussed in the frame of existing interpretations of the 4f65d‐configuration of Eu2+ in CaF2.
Calculation of the Coulomb Integral for Ni, Co, Fe
Authors: Galperin F.M , Amelin I.I , Yorkin V.M 
Published: July 2007

AbstractFor the calculation of the Coulomb interaction between 3d‐electrons of a metal atom the authors have used the Slater radial wave function. The Coulomb integral calculated by the Hartree method is KAB = 2.62Z* (eV), where Z* is the effective charge. Substituting Z* = 9/R, into this integral, where R, previously calculated by one of the authors, is the effective radius of the 3d‐electrons of the metal atom, we find KAB = 9.1; 9.85; 10.3 eV for Fe, Co, Ni, respectively. Exactly the same values are afforded by the empirical formula suggested here KAB = [C + m/(2 MB)] eV, where C is the number of electrons outside the argon shell of the free atom in the ground state, m is the atomic magnetic moment of a pure ferromagnetic metal in Bohr magnetons MB.
Light scattering and ionic conductivity in NaCl:Ba and NaCl:Cd single crystals
Authors: Baltog I. , Ghit̃ă C. , Giurgea M. 
Published: July 2007

AbstractSimultaneous measurements are made of light scattering and ionic conductivity as a function of temperature in the range 20 to 650°C on Ba‐ and Cd‐doped NaCl single crystals submitted to different heat treatments. In case of Ba‐doped crystals, the results are interpreted by changes in the decoration of the precipitates with cation vacancies; in case of Cd‐doped crystals by dissolution and reformation of the precipitates as a consequence of appropriate heat treatments.
Splitting of superdislocations in ordered CuAu‐type structure
Authors: Greenberg B. A. 
Published: July 2007

AbstractThe various splittings of superdislocations in an ordered CuAu‐Type structure have been investigated. A new possible type of superdislocations has been considered. Such a type of superdislocations are sessile configurations arising from glissile configurations as already known due to certain transformations. It has been shown that under definite conditions the sessile configurations are energetically more favourable as compared with glissile configurations. The features of the transformations of the glissile configurations into the sessile ones and the reverse transformations have been investigated. A new model of twin nucleation has been proposed which is associated with the possibility of the transformations considered.
Zur nichtlinearen Antworttheorie quantenmechanischer Systeme
Authors: Fick E. , Sauermann G. 
Published: July 2007

AbstractIn diesem Beitrag zur nichtlinearen Antworttheorie werden für die Erwartungswerte von Observablen exakte Integralgleichungen hergeleitet. Man erhält aus ihnen, selbst in der niedrigsten Näherung für die Kerne, eine Antwort, die nichtlineare Effekte enthält. Als Beispiel für die Theorie werden zwei Probleme der magnetischen Relaxation behandelt: Das Einschalten eines Magnetfeldes h0 θ(t) und ein periodisches Störfeld h0 cos ω t mit nicht kleinen Amplituden h0.
Vibronic spectra of crystals at arbitrary shifts of the atomic equilibrium positions in the molecules
Authors: Davydov A. S. , Serikov A. A. 
Published: July 2007

AbstractThe vibronic spectra of molecular crystals are investigated for the case of a combination of the electronic excitation with the totally symmetrical intramolecular vibration at arbitrary shifts ξ of the atomic equilibrium positions in molecules. It is shown that three types of excitations can correspond to the vibronic excitations of molecules in the crystal: a) the vibronic excitons, i.e. the one‐particle excitations with definite value of the wave vector; b) the two‐particle excitations corresponding to a simultaneous formation of free excitons and intramolecular vibrations in the crystal; c) the unstable one‐particle excitations decaying into free excitons and intramolecular vibrations. The relative disposition of the corresponding absorption bands and their intensities depend on the three parameters ξ2, ΔΩ and L.
Optical absorption in crystals containing impurities
Authors: Hacker K. 
Published: July 2007

AbstractA model calculation is made of the optical absorption coefficient for semiconductors containing impurities with short‐range potentials. An averaged Green's function method, developed by Yonezawa [1, 2] and Soven [3, 4] is used. Results are given for impurities with the same and with different valencies as the host crystal and for different temperatures.
Zero‐field splitting of the R‐centre ground state in KCl
Authors: Lehmberg H. , von der Osten W. , Weber J. 
Published: July 2007

AbstractFrom optical investigations of the R2 zero‐phonon absorption line in γ‐ and X‐irradiated KCl under uniaxial stress at low temperatures the 2E ground state of the R‐centre is suggested to be split without external field. Measuring the changes of integral absorption and of energetic position of the line for stress along 〈100〉, a zero‐field splitting of 2 Z = 0.9 cm−1 is found. This result is confirmed from studying the spectral shift of the line when the crystal is cooled from 4.2 to 1.5 °K. The results are analysed using the zeroth and first moments of the line. The origin of the zero‐field splitting is discussed.
ESR and ENDOR investigation of interstitial hydrogen atoms in alkali halides
Authors: Spaeth J. M. , Sturm M. 
Published: July 2007

AbstractWe report on the results of ESR and ENDOR investigations of H centres in KF, NaCl, KCl, RbCl, NaBr, KBr, and RbBr. New ESR results were obtained for KF, NaBr, and RbCl. The g‐factor and the proton hyperfine constant for all mentioned alkali halides have been measured precisely. In addition to the previously published ENDOR results in KCl and RbCl we obtained well resolved ENDOR spectra in NaCl and KBr. All superhyperfine and quadrupole constants known at present for H centres in alkali halides are given and compared.
On the strain‐enhanced diffusion of α‐iron
Authors: Watanabe T. , Karashima S. 
Published: July 2007

AbstractIn order to explain the origin of strain‐enhanced diffusion in α‐iron, the concentration of excess vacancies generated by non‐conservative motion of jogs on screw dislocations during creep deformation was estimated under various creep conditions. In the estimation the values of activation volume for high temperature creep obtained by the stress‐relaxation test during creep were used. It was concluded that the reported strain‐enhanced diffusion is well explained by the excess vacancies due to the non‐conservative motion of jogs on screw dislocations.
Luminescence decay and delayed spectra of CaWO4 single crystals
Authors: Scharmann A. , Schwarz G. 
Published: July 2007

AbstractLuminescence decay and delayed spectra of single crystals have been measured under 15 keV electron pulse excitation. Significant differences in the spectral decay for temperatures below and above Debye temperature are observed. For low temperatures (T < θD) the delayed spectra show a pronounced red shift during decay. The results are discussed in the model of the “small polaron”.
Kramers‐Kronig analysis of exciton spectra in case of spatial resonance dispersion
Authors: Skettrup T. 
Published: July 2007

AbstractThe reflection spectrum of excitons exhibiting spatial resonance dispersion yields in a Kramers‐Kronig analysis values for the optical constants that deviate from the ones determined directly by transmission measurements. This is due to the extra polariton mode present in case of spatial resonance dispersion. In spite of this discrepancy, these values permit to derive sufficiently accurate the resonance frequencies, oscillator strengths, and background dielectric constants. The damping constant obtained in this way contains a mass‐dependent term in addition to the true damping of the excitons. We derive a necessary condition for the observation of spatial dispersion effects. An estimate for the exciton masses of some II–VI compounds is obtained from their low temperature reflection spectra.
Experimental phonon frequencies and widths of lead at 5, 80, and 290 °K
Authors: Furrer A. , Hälg W. 
Published: July 2007

AbstractThe phonon frequencies and lifetimes of lead have been measured in a (110) plane at 5, 80, and 290 °K using the neutron inelastic scattering technique. The importance of special conditions required to minimize the experimental error is pointed out. The phonon lifetimes do not show anomalies which could be presumed in consequence of the strong phonon‐electron interaction in lead. The phonon widths and frequency shifts have been analysed on the basis of anharmonic effects taking account of phonon‐phonon and phonon‐electron scattering processes.
Détermination microcalorimétrique de l'énergie et de l'entropie de formation des lacunes dans l'or
Authors: Moya G. , Lagarde L. 
Published: July 2007

AbstractL'énergie dégagée, au cours de revenus, par des défauts bloqués après trempe a été mesurée au moyen d'un microcalorimètre différentiel de grande précision. L'évaluation précise de la chaleur restituée, pour différentes températures de trempe, fournit des résultats sur l'énergie de formation (Ef= (0,92 ± 0,04)eV), l'entropie de formation (Sf ≈︁ 0,4 k) et sur les concentrations des monolacunes. Ces valeurs sont discutées.
On the Calculation of the Complex Susceptibility of a Heisenberg Ferromagnet in the Vicinity of the Curie Point
Authors: Potapkov N. A. , Shelkov N. V. 
Published: July 2007

AbstractThe behaviour of the Fourier component of a longitudinal spin pair correlation function near the Curie point is considered on the base of results of [1, 2]. It is shown, that in the small wave vectors limit when T → Tc the results of [1] and [2] are equal. The formula obtained is substituted in the general expressions for the r.f. susceptibility and the width of the resonance line.
Measurement of Stabilization Fields for 180° and 90° Bloch Walls in Iron Single Crystals Containing Solute Nitrogen Atoms
Authors: Tahara Y. , Sugeno T. 
Published: July 2007

AbstractIn order to ascertain Néel's prediction stabilization fields were measured for 180° and 90° Bloch walls using iron single crystals containing solute nitrogen atoms. Initial magnetization curves were measured when solute nitrogen atoms were distributed in a uniform or equilibrium state. The observed stabilization field for 180° walls showed a sharp maximum in low induction region and tended to zero for large induction. That for 90° walls, however, didn't show such a maximum but approached asymptotically to a finite value. These results support qualitatively Néel's theory. The coefficient w of the interaction energy between nitrogen atoms and the spontaneous magnetization is found to be 9.0 × 10−16 erg per atom for solute nitrogen atoms in α‐iron.
Temperature Dependence of Defect Production in KBr and KCl (II)
Authors: Comins J. D. 
Published: July 2007

AbstractStudies of the growth of F‐centres in Harshaw KBr and KCl during X‐irradiation as a function of temperature show that the “late‐stage” production rate progressively decreases as the temperature of irradiation T is increased above ≈ 195 °K for KBr and above ≈ 213 °K for KCl. Various mechanisms are examined to explain this effect. The results are found to be in semi‐quantitative agreement with the predictions of the excitonic mechanism of defect production, but arguments are presented to show that the mechanism of suppression involving mobile vacancies makes some contribution. The V‐bands formed in the range investigated (195 °K < T < 298 °K) show a continuing progressive change in shape and peak position with increasing temperature of irradiation. Their growth behaviour becomes increasingly non‐proportional to F‐centre growth as T increases, but nevertheless the overall “late‐stage” rate decreases in a manner comparable with that found for F‐centres, and provides evidence that they are of an interstitial nature. The growth of the 213 nm band shows a two‐stage behaviour, the first resulting from decomposition of OH− centres to form the U‐band, while the later stage is considered to be due to the formation of V3‐centres.
Dielectric and Anelastic Relaxation in Ca‐Doped Cerium Dioxide
Authors: Lay K. W. , Whitmore D. H. 
Published: July 2007

AbstractMeasurements of dielectric losses and internal friction in Ca‐doped CeO2 have been made over the temperature range 253 to 573 °K on specimens with up to 2.5% of the Ce4+ ions replaced by Ca2+ ions. The observed internal friction and dielectric loss peaks have relaxation times which are in close accord with the predictions of an eight‐position, nearest‐neighbor model, namely, that the relaxation time for electrically‐active modes is equal to twice that for mechanically‐active modes. These relaxations occur because of the redistribution of oxygen vacancies (bound to substitutional Ca2+ ions) among eight sites which are initially equivalent, but which become inequivalent in the presence of the external electric or mechanical stress field. From the temperature dependence of the relaxation times and the peak shape, the activation energy required for such oxygen vacancy jumps is calculated to be 0.86 eV, with the pre‐exponential factor estimated to be 2.4 × 1014 s−1.
Effect of Hydrostatic Pressure on the Diffusion of Silver in Indium
Authors: Ott A. 
Published: July 2007

AbstractThe pressure effect on the silver impurity diffusion has been measured parallel and perpendicular to the tetragonal axis in single crystals of indium metal. A thin film radioactive tracer deposition and sectioning method was used. The experiments were performed at 96.1 and 112.3 °C, and at hydrostatic pressures varying from 0.9 to 7.7 kbar. The diffusion rate was observed to decrease with increasing pressure and the activation volume for the diffusion process was determined to (6.4 ± 0.6) cm3/mol, with no detectable dependence on either temperature or crystallographic orientation. Comparison with systematics and theoretical arguments suggests interstitial diffusion.
X‐Ray Spectra and Energy Band Structure of Some Noble and Transition Metal Aluminides
Authors: Nemnonov S. A. , Zyryanov V. G. , Minin V. I. , Sorokina M. F. 
Published: July 2007

AbstractThe Al L2,3 and Kβ emission bands of noble and several transition metal aluminides have been investigated. In the spectra of the alloys long‐wavelength intensity peaks are observed which are not present in the spectrum of pure aluminium. The appearance of these peaks is associated with the energy bands originating from the d‐states of the noble and transition metal atoms. For the Al bands in CuAl2, Cu2Al, and PdAl3 the position of the long‐wave‐length peaks relative to short‐wavelength edges is found to correspond approximately to the position of the copper and palladium L2,3‐band peaks with respect to the absorption edges. It is assumed that the energy region of the d‐like bands in the vicinity of aluminium atoms contains an appreciable amount of states arising from the s and p aluminium atom states. This is suggested to be the reason for the long‐wavelength intensity peaks to appear in the Al L2,3‐and Kβ‐bands of the alloys.
Mössbauer Study of Isomorphous Substitution in Ilvaite
Authors: Borshagovskii B. V. , Marfunin A. S. , Mkrtchyan A. R. , Nagyaryan G. N. , Stukan R. A. 
Published: July 2007

AbstractThe isomorphous substitution of manganese for Fe in ilvaite has been studied. It has been found that in the absence of manganese or at low manganese content (up to 4.5%) the spectrum consists of two doublets, corresponding to bivalent and trivalent iron. When the degree of substitution increases the spectrum becomes complex. For a manganese content above 12%, hyperfine structure is observed. Values of Heff have been determined. Heff of Fe2+ is equal to (210 ± 7) kOe, Heff of Fe3+ –(340 ± 7) kOe. The low value of Heff of Fe3+ is accounted for by the fact that the temperature at which the experiment was carried out is close to the Curie point. The value ΔEQ derived from magnetic spectra is less than half the value derived from paramagnetic samples. This can be attributed to the existence of an angle between the direction of the magnetic field and the main axis of the electric field gradient tensor of the iron ions.
A Method for Computation of Equilibrium Dislocation Configurations
Authors: Shtolberg A. A. 
Published: July 2007

AbstractA numerical method for the solution of non‐linear integro‐differential equations typical for problems on equilibrium dislocation configurations is developed which makes it possible to pass to the ordinary differential equations at every step of the iterative procedure. The presented method contrary to the existing ones provides automatic computation of the equilibrium dislocation shapes and guarantees the equilibrium (with given precision) of all the points of the dislocation line. As an example a problem has been solved which is of importance for the dislocation theory of dispersion strengthening, concerning a dislocation breaking through an array of obstacles. The dependence of the critical applied stress (at which the dislocation becomes unstable) both on the concentration of obstacles and their size is obtained, which is in accordance with the experimental data. In conclusion possible applications and modifications of the method are discussed, which can be used in different (not only dislocation) problems.