bluuebunny/crossref_metadata_2025_split huggingface dataset:
Higher Energy Levels of Cr3+ Ion Pairs in Ruby and Lanthanum Aluminate
Authors: Heber J. , Platz W. , Leutloff S. 
Published: July 2007

AbstractThe excitation and absorption spectra were investigated of the doubly excited states |2E × 2E〉, |2E × 2T1〉, |2T1 × 2T1〉 × 2T1, and |2E×2T2 of the first nearest neighbour Cr3+ ion pairs in LaAlO3, and of the first, second, third, and fourth nearest neighbour Cr3+ pairs in ruby. The spectra were analyzed for electronic and vibronic transitions.
Fluorine Superhyperfine Structure in the EPR of CdF2:Gd3+
Authors: Naehring F. K. 
Published: July 2007

AbstractThe fluorine superhyperfine structure (SHFS) in the EPR spectrum of Gd3+ in cubic environment has been investigated in CdF2 crystals. The measured 9 GHz EPR spectra of the SHFS are explained using the formalism of Ranon and Hyde and the principal values of the SHFS tensor from the ENDOR results of Borcherts, Cole, and Horn. A formula for the intensities of the SHFS lines is presented.
Self‐Consistent Normal Mode Analysis of the One‐Mode Polaron
Authors: Trubatch S. L. 
Published: July 2007

AbstractThe self‐energy of the one‐mode polaron model is calculated in both the weak and strong coupling regimes by using a variational principle which removes all linear Bose coupling terms and diagonalizes all quadratic Bose terms in the Hamiltonian. It is clearly demonstrated that this approximation scheme is not powerful enough to yield the correct strong coupling behavior.
Mössbauer Lineshape in the Presence of Radio‐Frequency Fields
Authors: Krishnamurtht B. , Sinha K. P. 
Published: July 2007

AbstractA general expression for the Mössbauer lineshape in the presence of a radio frequency field is derived. As an example the effect of the rf field on Fe57 nuclei is discussed for a situation where the 3/2 sublevel of 14.4 keV state of Fe57 is selectively populated. At resonance, both the diagonal and non‐diagonal matrix elements contribute to the correlation function. As a result, in addition to a slight rf induced distortion of the main Mössbauer line. additional transition lines are obtained. Thus the present calculation supports the experimental observations of Heiman et al. [5].
EPR of Mn2+ Ions in Mixed Crystals Znw, Hg1−wSe and ZnmHg1−mTe
Authors: Leibler K. , Giriat W. , Cęllciński K. , Wilamowski Z. , Iwanowski R. 
Published: July 2007

AbstractThe results of EPR measurements are presented of mixed crystals ZnmHg1−mTe and ZnwHg1−wSe doped with Mn2+. The spectroscopic splitting factor g and the hyperfine structure constant A were determined as a function of the composition of the crystals investigated and measurements are made of electrical conductivity and electron concentration.
Phonon Assisted Interband Optical Transitions in Disordered Semiconductors
Authors: Esser B. 
Published: July 2007

AbstractThe absorption coefficient of a disordered semiconductor, α(ω), is calculated in the case of indirect transitions. The absorption coefficient is influenced by a random force field present in disordered semiconductors. The case of a smooth random field is considered. The same exponential optical tail is obtained as in the case of direct transitions: In α(ω) ∼S (ℏω – ℰg,i), where S is the inverse of some characteristic energy and ℰg, 1 is the indirect band gap. Par enough in the allowed band the absorption coefficient takes on the usual quadratic frequency dependence.
Order States and Magnetic States of CrPt3
Authors: Besnus M. J. , Meyer A. J. P. 
Published: July 2007

AbstractOrdered CrPt3 which has the AuCu3 type structure is known to be ferrimagnetic. The f.c.c. disordered CrPt, phase has been obtained by severe cold work and is found to behave as a paramagnet. Through thermomagnetic analysis and consideration of neighbours. this paramagnetism is tentatively ascribed to a kind of antiferrornagnetism. The forced disordered atomic arrangement results in a incoherent distribution of localized moments without apparent external moment. The magnetic properties of partially ordered samples have also been studied.
Intervalence Band Transitions in Tellurium. I. Polarization E ‖ c
Authors: Fischer D. , Bangert E. , Grosse P. 
Published: July 2007

AbstractHigh resolution measurements of the intervalence band transitions of electrons in tellurium (hole concentration p = 1014 to 1018 cm−3) were performed for polarization E ∥ c in the spectral range 60 to 200 meV a t low temperatures. The absorption spectra were calculated on the basis of a k · p perturbation method. The transition probabilities show a considerable variation ∼(ℏω)−2. A procedure is described for the determination of the valence band parameters from the optically measured data. With these parameters it is possible to determine the hole concentration of the samples from their absorption spectra.
On Different Perturbation Theoretical Approaches to the Heisenberg Ferromagnet with Spin 1/2
Authors: Kühnel A. 
Published: July 2007

AbstractThe results of the drone‐fermion representation (DFR) in application to the Heisenberg ferromagnet with spin 1/2 are compared with the corresponding results obtained by means of Pauli operators. The expressions calculated in DFR by Spencer for the perturbational expansion of the one‐particle Green function are shown to coincide with the corresponding expressions arising in the calculations using Pauli operators. In spite of that, different ways of summation of diagrams lead to different results for physically interesting quantities; these differences can be explained explicitely as resulting from certain neglections made in the use of DFR.
Defect‐Induced Optical Absorption near the Electronic Band Edge of Tellurium
Authors: von Alpen U. , Doukhan J. C. , Escaig B. , Grosse P. 
Published: July 2007

AbstractBecause of the plasticity of tellurium at room temperature many physical properties are strongly influenced by the preparation technique. Systematical inquiries about the influence of dislocations on the optical constants near the electronic band edge of tellurium are reported. Comparison of the absorption spectra of samples in which defined dislocations had been introduced by plastic deformation clearly shows that these defects cause sharp absorption lines near the electronic band edge. Models for the interpretation of the absorption mechanism are discussed.
Motional Averaging of Electric Field Gradients. Temperature Dependence of Nqr in Sodium Chlorate and Copper Chlorate
Authors: Vijaya M. S. , Ramakrishna J. 
Published: July 2007

AbstractThe temperature dependence of CI35 nuclear quadrupole resonance in sodium chlorate and copper chlorate is studied in the temperature range 77 to 300 °K. It is shown that the assumptions made in Bayer's theory, are valid for the case of chlorates and hence the frequency of the torsional oscillations of the ClO3 group is calculated using Bayer's theory. The calculated value of the torsional frequency compares well with available Raman spectroscopy data.
Impurity‐Induced First‐Order Raman Spectrum in Cesium Halides
Authors: Ram P. N. , Agrawal Bal K. 
Published: July 2007

AbstractA theoretical study of impurity‐induced first‐order Raman scattering has been made in cesium halides. The defect model parameters obtained earlier by the analysis of infrared absorption experiments have been used in the calculation. The frequency dependence of the Raman intensity is found to be quite insensitive to variations in the force constants describing the defects. The Raman technique may therefore be employed for detailed study of the perfect phonon without having a detailed knowledge of the defect perturbation.
Pinning of Single Crystals of Niobium Irradiated at Helium Temperature
Authors: Andronikashvili E. L. , Ashimov S. M. , Tsakadze J. S. 
Published: July 2007

AbstractThe influence of neutron irradiation at 4.2 °K on the pinning of Abrikosov flux lines in single crystals of niobium was studied. It is shown that the irradiation with fast neutrons of 3.5 × 1012 cm−2 increases the mean value of the pinning force. Exposition of the specimen during 80 h at T = 100 °K and the recooling do not eliminate the irradiation effect. It is assumed that the observed increase in the pinning force is caused by additional pinning of dislocations available in the specimen (pinning‐centres) by point defects, formed during irradiation.
Variation de x⟂ avec une tension uniaxiale dans FeCl2 et FeBr2 à 4,2 ° K
Authors: Hammann J. , Nasser J. A. 
Published: July 2007

AbstractDans la structure hexagonale de FeCI2 et FeBr2 les plans réticulaires perpendiculaires à l'axe ternaire ne contiennent qu'un seul type d'atomes. Les propriétés de ces deux métamagnétiques ont été analysées en introduisant l'anisotropie cristalline, un échange ferromagnétique entre ions Fe2+ d'un měme plan, et un échange antiferromagnétique entre ions Fe2+ de deux plans successifs. Nous rapportons ici les mesures de la variation de x⟂ à 4,2 °K (phase antiferromagnétique) lorsqu'on rapproche les plans contenant les ions Fe2+ par une contrainte uniaxiale. Nous en déduisons les variations au cours de cette deformation des paramètres microscopiques précédents.
Mössbauer Study of a Stressed Single Crystal of KFeF3
Authors: Varret F. , Imbert P. 
Published: July 2007

AbstractA single crystal 〈111〉 platelet of the cubic perovskite KFeF3 has been submitted to a stress parallel to its plane. By this means, a single magnetic domain may be obtained in the magnetic region having a trigonal symmetry. By measuring the relative intensities of the Mossbauer lines, the orientation of the hyperfine field and of the electric field gradient tensor with respect to the plane of the platelet have been determined throughout the temperature range 4.2 ≦ T ≦ 110°K.
Variational Estimate of the Energy Spectrum of a Bound Polaron
Authors: Clark T. D. , Bajaj K. K. 
Published: July 2007

AbstractVariational estimates of the energies of the ground state and of a few low lying excited states of a system consisting of a single electron coupled simultaneously to a point defect via the Coulomb potential and to a longitudinal optical phonon field are obtained. The trial functions used are linear combinations of intermediate coupling free polaron functions and thus the results are felt to be valid into the intermediate coupling region. The numerical results obtained from the above are compared wit.11 a closed form, analytic approximation and a good agreement is found between the two.
Hydrostatic Pressure Dependence of First‐Order Raman Frequencies in Se and Te
Authors: Richter W. , Renucci J. B. , Cardona M. 
Published: July 2007

AbstractMeasurements of the effect of hydrostatic pressure on the first order Raman frequencies of Se and Te are reported. All the frequencies of the Raman active modes decrease with pressure. The valence force field model proposed by Nakayama and Odajima is used to explain this behaviour.
Transport of Heat between Electrons and Phonons in Copper below 0.2 K
Authors: Peterson R. E. , Anderson A. C. 
Published: July 2007

AbstractThe thermal resistance between phonons and electrons has been measured in thin copper samples at temperatures from 0.03 to 0.2 K. The measurements are in qualitative agreement with a calculation based on the free‐electron model, except the temperature dependence changes to T‐3 from the expected T‐4 as the electron mean free path becomes limited by sample boundaries.
Zero‐Field NMR and Electronic Structure of MnSb and Related Compounds
Authors: Bouwma J. , Haas C. 
Published: July 2007

AbstractMeasurements of zero‐field NMR of MnSb and related compounds are reported. The spin‐echo signals of Mn1.00Sb show quadrupole splittings. Broad unresolved signals have been observed in Mn2Sb. Non‐stoichiometric B8‐type compounds Mn1 +xSb1 ‐ySny (Mn, V)1+xSb and (Mn, Cr)1+xSb show broad unresolved signals or no signals at all. In all compounds the observed frequencies of the Mn55 and Sb123 resonances at 4.2 °K arc about 200 and 210 to 220 MHz, respectively. A comparison of the properties of MnSb with the properties of related compounds leads to a metallic band model for MnSb with about six d‐electrons per Mn atom.
One‐Phonon Far‐Infrared Absorption of NaI Crystalline Powder
Authors: Novák L. 
Published: July 2007

AbstractFar‐infrared transmission measurements of crystalline NaI powder samples at 300 and 100 K have been performed. Except for the strongest absorption band at the frequency of the pseudo‐surface polariton mode, all the lattice bands were correlated with energies at some critical points of the Brillouin zone of the perfect crystal. The measured spectra are assumed to be a manifestation of the grain‐boundary activated band‐mode absorption. The interpretations of other authors are discussed.
Evidence for Strain Broadening in the ESR Absorption Spectrum of Tetragonally Distorted Cr3+ Ions in MgO
Authors: Serway R. A. , Marshall S. A. , Robinson R. B. 
Published: July 2007

AbstractAn anisotropic line broadening has been observed in the ESR absorption spectrum of Cr3+ ions located at tetragonally distorted sites of single‐crystal MgO. For an impurity ion whose tetragonal distortion is along a crystal [100] direction. a sin2φ dependence is observed in the linewidth when the Zeeman field is rotated in the plane perpendicular to this direction. The broadening is interpreted by introducing strain induced terms in the conventional spin‐Hamiltonian, where it is assumed that the strain‐coupled coefficients are the same as those measured for Cr3+ at the cubic sites of MgO. This formalism is consistent with both the angular dependence that is observed in the linewidth and the order of magnitude of the line broadening after correcting for contributions from other mechanisms such as variations in the crystalline electric field parameter D. Analysis of the linewidth data gives C44 α/g β = (2.13 ± 0.2) Oe and ΔD/g β = (1.3 ± 0.3) Oe, where a is the parameter that characterizes the distribution of strains within the crystal.
Tl0, Ga0, and In0 Centres in KCl Crystals
Authors: Jaek I. , Kink M. 
Published: July 2007

AbstractAbsorption bands of In0 and Ga0 centres are observed in KCl : In and KCI : Ga which are related, by analogy with the corresponding bands of Tl0 centres in KCI: Tl, to the electronic transitions 62P1/2 → 72S1/2 (the 1.80 eV band in KC1:In and 1.95 eV band in KC1:Ga) and 62P1/2 → 6 2P3/2 (the 0.75 eV band in KCl: In) in free In and Ga atoms. The luminescence of Tl0 and In0 centres at about 0.82 and 0.70 eV, respectively which may be excited in the absorption bands of Tl0 and In0 centres, as well as in the F band, is found and investigated. Luminescence of {In0 + Vk} pairs is detected in KCl: In and is analogous to that observed earlier in KCl: Tl.
Theory of Paraelectric Resonance (PER) Lineshape
Authors: Vikhnin V. S. , Glinchuk M. D. , Gordon A. Ya. , Deigen M. F. 
Published: July 2007

AbstractA study is made of the shape of paraelectric resonance (PER) lines broadened by internal electric fields and stresses. The calculation was made using the first‐ and second‐order statistical theory. The low‐field PER lines of the allowed transitions (E ‖ Eshf ‖ [001]) are shown to be asymmetric. An essential dependence of the lineshape of some transitions on the direction of the electric illumination is obtained. The contribution of the cross‐relaxation in the ion‐ion interaction reservoir into the broadening of PER lines is estimated. The agreement between the theory and the experiment for KCI:Li+ is obtained.
Positron Annihilation in Potassium Chloride and Potassium Iodide
Authors: Hautojärvi P. , Nieminen R. 
Published: July 2007

AbstractPositron lifetime spectra have been measured in several single crystals of KCI and KI. Angular correlation measurements of 2 γ annihilation radiation have been made in polycrystalline materials. The positron wave function calculated by the spherical symmetric Wigner‐Seitz approximation in the neighbourhood of the anion is similar to that in metals and indicates that positrons are free in alkali halides. The experimental angular correlation curves are much narrower than those calculated with positrons in crystalline states, when Wigner‐Seitz wave functions of the positron were used and only annihilations with anion shells were taken into account. The assumption that positrons are trapped by crystal defects explains the observed differences in lifetime measurements. The angular correlation curve caused by trapped positrons has been constructed by subtracting the calculated momentum distribution of the ground state positrons in the crystal bulk from the total experimental curve.
An Extended Breathing Shell Model for Alkali Halides and Its Test at Experimental Results
Authors: Bluthardt W. , Schneider W. , Wanger M. 
Published: July 2007

AbstractGroup‐theoretical as well as quantum‐mechanical arguments require an extension of Schröder's breathing shell model (BSM) to include axial deformations. An extended model (EBSM) is presented and numerical results are given for KBr and KI. The dispersion curves do not differ appreciably from those of the BSM and the agreement with the experimental curves is equally good. In contrast, however, the eigenvectors, as tested indirectly via a calculation of the U‐center sideband, evidently are improved by the EBSM.
Diffuse X‐Ray Scattering from the Displacement Field of Point Defects in KBr Single Crystals
Authors: Spalt H. , Lohstöter H. , Peisl H. 
Published: July 2007

AbstractDiffuse X‐ray scattering from the displacement field of point defects in low temperature X‐irradiated KBr single crystals was measured. The distribution of diffuse scattered intensity in reciprocal space confirms the theoretical predictions of scattering from isolated point, defects. From absolute scattered intensities the double force tensors describing the long range displacement field of an interstitial anion and anion vacancy are derived. The volume changes per interstitial anion and anion vacancy are determined to be (2.5 0.2) atomic volumes and (0.7 ± 0.2) atomic volumes, respectively. The displacement field of the interstitial ion has tetragonal symmetry. Models for the interstitial ion configuration which are in accordance with this symmetry are proposed.
Excitonic Effects on the Valence Absorption Edge of Solid Rare Gases
Authors: Rössler U. , Schütz O. 
Published: July 2007

AbstractBound exciton states and excitonic resonances have been computed at the valence absorption edge of the solid rare gases Xe, Kr, and Ar. A two‐band model was used to calculate the Green's function of the uncoupled electron–hole pairs and the Coulomb interaction was treated in the resolvent formalism. The matrix elements of the electron–hole interaction were calculated in the pseudopotential approximation. The computed binding energies, oscillator strengths, relative hydrogenic defects, and spectral functions are compared with experimental data.
Electron Magnetic Susceptibility and the Band Structure of Silicon‐Rich n‐Type Silicon–Germanium Alloys
Authors: Geist D. , Balck F. 
Published: July 2007

AbstractEarlier measurements have been extended to a larger number of samples of high crystalline perfection, high purity, and well‐defined homogeneous doping. Furtheron the measuring equipment has been improved. The before made statement could be confirmed, that the transverse electron mass as derived from the magnetic susceptibility in silicon–germanium alloys with a silicon content between 65 and 100 at% Si is constant with a value m⟂ = 0.27 m (m free electron mass).
On the Influence of Electronic Exchange and Correlation on Pseudopotential Calculations I. Form Factors, Energy‐Wave Number Characteristics, and Effective Interionie Pair Potentials
Authors: Hafner J. 
Published: July 2007

AbstractThe influence of electronic exchange and correlation on pseudopotential calculations is discussed within the framework of Harrison's first principles pseudopotential formalism. The Xα local exchange and correlation approximation is used for the calculation of the core states and for the conduction band–core exchange interaction. Exchange and correlation between the conduction electrons are taken into account using different modified forms of the dielectric function. The influence of these approximations on the form factors, normalized energy‐wave number characteristics, and effective interionie pair potentials of 14 simple metals is discussed.
Exchange‐Quadrupole Forces and Phonon Dispersion for the Simplest Cubic Crystals
Authors: Tolpygo K. B. 
Published: July 2007

AbstractSystematic discrepancies between the experimentally observed phonon dispersion law and that predicted by the theory of the lattice with polarizable ions in the short wavelength region are discussed. The discrepancies appear to be due to the quadrupole deformation of ions, primarily of anions. The adiabatic lattice potential which depends on the displacements, uls, on the dipole moments, P1s, and on the quadrupole moments, Qlsαβ, of all the atoms is determined and equations for the lattice vibrations are derived. Besides the Coulomb forccs the adiabatic potential includes the short‐range forces which are due to the alteration of the exchangc interaction of neighboaring atoms with the quadrupole deformation of one of them. Equations for the Fourier components of dynamic variables using the Ewald transformation for sums of the Coulomb potential of dipole and quadrupole interactions are given.
Investigation of the Electronic Structure of Molybdenum Single Crystal Surfaces by Means of the Positron Annihilation Method
Authors: Adonkin V. T. , Dekhtyail I. Ya. , Silantev V. I. 
Published: July 2007

AbstractA model is proposed explaining the “fine structure” of angular distribution curves of annihilation photons (ACAP) obtained by the interaction of positrons with the electron density on the crystal surface. Data were presented which prove the influence of a deformation on the (110) plane of Mo and of weak magnetic fields (1.2 Oe) on the shape of ACAP curves obtained from the surface of this crystal face. The deformation effect is discussed in conjunction with the interaction between positrons and crystal structure defects on the crystal surface. The influence of a weak magnetic field is discussed with the excitement of the surface magnetic levels.
Perturbation Theory in Transmission Electron Diffraction II. The Perturbing Matrix is Constant but not Hermitian
Authors: Serneels R. , Gevers R. 
Published: July 2007

AbstractInstead of using the usual Schrödinger equation, perturbation theory is directly applied to the system of Howie and Whelan. According to the nature of the perturbing dynamical matrix generally three different types of perturbation are distinguished. The perturbing matrix may be a) constant and Hermitian b) constant but not Hermitian c) not constant but depth dependent. The first case has been discussed previously, now case b) is considered. In full matrix notation both generate and degenerate perturbation theory is presented. Special attention is given to the usual treatment of absorption effects. General recurrence relations are presented for the calculation of the corrections on eigenvalues and eigenvectors. The influence of these corrections on the amplitudes and the intensities of the constituent beams is discussed.
Colour Centres near Ionic Crystal Surfaces I. The Surface VK Centres
Authors: Bartczak W. , Sugier H. 
Published: July 2007

AbstractA simple theoretical model of the Vk‐centre situated on the (001) external surface of the f.c.c. alkali halide crystal has been derived. The energy of the VK‐centre calculated for the case of KCI using this model appeared to be about 0.49 eV less then that inside the crystal.
One‐dimensional anion vacancy diffusion in the calcium apatites
Authors: Welch D. O. , Royce B. S. H. 
Published: July 2007

AbstractCorrelated random walk statistics are used to derive an expression for the diffusion coefficient for vacancies in a linear chain containing impurities. The results are applied to the problem of anion mobility in the calcium apatites. For fluorapatite the analysis indicates energies of motion for fluorine and oxygen ions to be 0.77 and 2.0 eV, respectively.