bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Uniaxial Stress and Doping on the One‐Phonon Raman Spectrum of GaP
Authors: Balslev I. 
Published: July 2007

AbstractThe Raman spectrum of long‐wave optical phonons in n‐type GaP is investigated under the presence of uniaxial stress. The splitting ofthe LO‐phonon is found to be doping‐dependent for (001)‐stress and is explained by phonon—plasmon coupling in connection with repopulation of the electrons. At zero stress the 2 LO‐phonon cut‐off in the second order spectrum does not follow the doping‐induced shift of the LO (k  O) phonon. This indicate avery flat LO‐dispersion curve.
Calculation of the X‐Ray K and L Emission Bands in AlSb and GaP
Authors: Topol T. , Leonhardt G. , Unger K. , Hess E. 
Published: July 2007

AbstractUsing an EPM‐k · p method the K and L emission bands in AlSb and GaP have been calculated based on the corresponding band structures. The results are in good agreement with experimental data in particular for the K bands. For the L bands there is a larger sensitivity with regard to the quality of the valence‐band wave‐functions used. Due to the influence of the transition probability marked differences between the spectra of the A and B components both for K and L emission are obtained. The antisymmetric form factors of the pseudopotential influence the value of the antisymmetric gap such that they may be tested or corrected with the help of X‐ray spectra.
Peculiarities of Raman Scattering by Polaritons and Polar Optical Phonons in Anisotropic Crystals
Authors: Strizhevskii V. L. , Yashkir Yu. N. 
Published: July 2007

AbstractThe theory of the gain factor of the stimulated Raman scattering by polaritons in biaxial crystals is carried out in the fixed stationary pump field approximation. By sufficient length of the polariton wave vector the polariton scattering turns into the scattering by polar optical phonons which may be regarded as quasilongitudinal electromagnetic field quanta. Typical features of scattering by anisotropic polar phonons whose energy depends on the wave vector direction are investigated. Mixing of different symmetry mechanicalvibrations is analysed in anisotropic crystals. The Fermi resonance of polar mechanical phonons is studied in detail. Numerical calculations made for some particular cases agree with available experimental data.
Cluster Theory of a Dilute Antiferromagnet. Application to the Mn1–cZncF2 System
Authors: Dzyub I. P. 
Published: July 2007

AbstractA cluster theory of a dilute antiferromagnet which simultaneously takes into account the fluctuations in the longitudinal and transverse part of the exchange interaction is proposed. The present theory allows to describe the dependence of the line shapes of the spin excitation spectrum on the nonmagnetic atom concentration and the wave vector. A comparison with experimental results indicates that the predictions of the theory are valid in a wide range of concentrations when the long‐range order persists. It is pointed out that the coherent wave approximation accounts for the gross behaviour of the spin excitation spectrum. It is demonstrated that the results of the cluster theory are close to those of the coherent potential approximation, but more transparent and more suitable for comparison with experiment.
ENDOR Investigation of Cu++ Centres in NH4Cl I. Experimental Results
Authors: Boettcher F. , Spaeth J. M. 
Published: July 2007

AbstractTwo Cu++ centres in NH4Cl single crystals grown from acid (I) and neutral (II) aqueous solution were investigated by ESR and ENDOR at 4.2 °K. From the superhyperfine and quadrupole data obtained for several shells of neighbour nuclei the following centre models are proposed: in both centres Cu++ is at an interstitial site with 2 NH4+ vacancies along [001] at both sides of the Cu++. In centre I the vacancies are filled by H2O, in centre II by NH3. The precise configuration of the H2O and NH3 molecules could be determined.
On the Influence of the Transition Probability on the Shape of X‐Ray Emission Spectra of AIIIBV Semiconductors
Authors: Topol I. , Unger K. , Leonhardt G. , Hess E. 
Published: July 2007

AbstractExactly computed transition probabilities governing the X‐ray emission spectra of cubic AIIIBV semiconductors are analyzed. They show remarkable dependences of the energies as well as of the k vector involved. It is demonstrated that the K influence yields different spectra for the two components of the same compound due to the nocks and nodes of the valence wave functions at X1, X3 in the planes where the atoms of the different components are located. Different inner wave functions of the components furnish mainly a shift of the spectra, however, they have only little influence on their shape.
Effect of Irradiation on Impurity–Vacancy Dipoles in KBr Crystals Doped with Strontium
Authors: Muccillo R. , Rolfe J. 
Published: July 2007

AbstractThe concentration of impurity–vacancy dipoles in potassium bromide crystals doped with strontium bromide was measured using the ionic thermocurrent (ITC) technique. The parameters of the dipole relaxation are: fundamental relaxation time 4 × 10−14s, activation enthalpy 0.66 eV. The effect of 60Co γ‐irradiation at room temperature was to reduce the number of dipoles and to increase the number of trapped holes and electrons, but the number of trapped holes and electrons, measured by optical absorption, was about 30 times smaller than the number of dipoles destroyed. It is proposed that the effect of irradiation is to increase the rate of aggregation of dipoles, primarily into trimer aggregates, through temporary electron trapping by strontium ions.
Influence of the Electron‐Phonon Coupling on Energy States of Wannier Excitons
Authors: Mahler G. , Schröder U. 
Published: July 2007

AbstractTheen ergies of Wannier excitons are investigated taking into account the electron‐phonon coupling described by the Fröhlich‐type interaction. The energies of the ground and the first excited states are calculated by a variational treatment. The exciton is treated as an interacting polaron pair, the electron‐phonon coupling of which is mutually disturbed. The expansion in terms of the particle momenta reproduces in the first order the effective potential derived by Haken. The following terms can be interpreted as additional mass renormalizations depending on the exciton radius. These terms are found to improve the agreement with experiment.
Schottky Defects in Sodium and Potassium Chloride
Authors: Roy D. , Sen S. K. , Manna A. 
Published: July 2007

AbstractThe energy of formation of Schottky defects, the binding energy of the Schottky pair in the ground state and the entropies of formation of isolated vacancies and vacancy pairs for NaCl and KCl have been computed assuming an elastic displacement in the form proposed by Boswarva and Lidiard. In the calculation of the displacement of the ten immediate neighbours of the vacancy pair, the relaxation of the distant neighbour was also considered. The calculations show a reasonable agreement with the recent experimental values.
NGR, EPR, and Optical Characteristics of Sn Centres in CaS
Authors: Jaek I. , Realo E. , Seman V. , Mürk L. 
Published: July 2007

AbstractNGR, EPR, and optical spectra of Sn centres in CaS have been measured. An established correlation between the NGR and optical data enabled to identify the luminescence centres in CaS host containing Sn2+ and Sn4+. A preliminary interpretation of the optical spectra for the Sn2+ centres is proposed using the MO method. Paramagnetic Sn3+ centres have been found by EPR spectroscopy and their identification has been made on the basis of the differences in the nuclear characteristics of Sn isotopes. Some aspects of covalent bonding between different Sn centres and their ligands are discussed.
Trigonal Centre of Gd3+ in CdS Investigated by Variable‐Frequency EPR
Authors: Urban W. , Siegel E. , Hillmer W. 
Published: July 2007

AbstractFor the new axial centre of Gd3+ in hexagonal CdS, reported recently, a more detailed analysis of results obtained by variable‐frequency EPR is carried out, establishing trigonal symmetry and giving spin‐Hamilton parameters b = + 1853 × 10−4cm−1,b = (±)2.6 × 10−4 cm−1. The model of Newman and Urban has been applied to estimate b for various local arrangements and these are compared with the experimental values of all three axial centres reported so far for Gd3+ in CdS.
Proton Spin–Lattice Relaxation in the Hydrogen‐Bonded Ferroelectrics Colemanite, KFCT, and TGS
Authors: Brosowski G. , Buchheit W. , Müller D. , Petersson J. 
Published: July 2007

AbstractThe nuclear spin–lattice relaxation time T1 of protons in single crystals of the hydrogen‐bonded ferroelectrics colemanite, KFCT, and TGS is measured between 8 and 60 MHz and between +80 °C and −100 °C by applying 90°‐t −90° pulse sequences. In all crystals there are several contributions to the relaxation rate T. Near the ferroelectric transition a ferroelectric contribution appears which is superimposed on a general behaviour according to one or two BPP type curves from which the corresponding activation energies are estimated. In colemanite and KFCT the ferroelectric relaxation rate shows a. frequency independent logarithmic singularity whereas in TGS a more complicated behaviour is observed. With respect to colemanite and KFCT these results are interpreted by applying established theories whereas for describing the behaviour of TGS several models are discussed.
On Variable Range Hopping near the Fermi Energy. Two‐Dimensional Systems
Authors: Maschke K. , Overhof H. , Thomas P. 
Published: July 2007

AbstractResults of a computer study on variable range hopping in two‐dimensional systems are presented. A 2D system was chosen to allow for a treatment of models of considerable size with modest computational effort. The convergence properties of the results with respect to the model size have been carefully examined. It is found that an extrapolation to quasi‐infinite samples is possible. The results are discussed in connection with percolation results. Conditions for a strict T−1/3(T−1/4) law of the conductivity in 2D (3D) systems are derived. The influence of a non‐constant density of states is discussed.
Optical Phonon Analysis in the AVBVICVII Compounds
Authors: Teng M. K. , Balkanski M. , Massot M. , Ziolkiewicz M. K. 
Published: July 2007

AbstractThe Raman spectra of SbSBr, BiSI, SbSeI, and BiSeI are investigated and compared with those of SbSI. Following the analysis of each observed mode from one substituted compound to another, a set of normal mode functions is proposed to account for the overall spectral feature of these compounds. The results are then tentatively interpreted in terms of the mass change based on a semi‐ionic model. It is shown that the agreement with experimental data is excellent for the system SbSBrSbSIBiSI. In the contrary, a serious discrepancy exists in the SbSeIBiSeI system suggesting that the binding of sulfur and neighbouring atoms is substantially affected by the SSe substitution in these compounds.
Local Magnetic Field near Mn Atoms in CuMn Dilute Alloys
Authors: Tompa K. 
Published: July 2007

AbstractA satellite line shifted in the direction to lower internal fields as compared with the main line has been observed in the NMR spectrum of 63Cu in CuMn alloys diluted to 0.5 or 2.5 at% Mn. The shift of the satellite is independent of the Mn concentration but varies with the applied field and the temperature as H/T. This indicates that the satellite is due to the spin density perturbation around the localized magnetic moment. The experimental data suggest that the satellite originates most probably from the 63Cu nuclei on the first coordination shell of the Mn atoms. The NMR spectrum of the same nuclei shows no second order quadrupole effect within the experimental error.
Secondary Electron Emission from Some Aromatic Hydrocarbons
Authors: Ya. Bubnov L. , Frankevich E. L. 
Published: July 2007

AbstractResults of the investigation of secondary electron emission from polycrystalline films of tetracene and pyrene and from both amorphous films and single crystals of anthracene are reported. The determination of the relative number of true secondary electrons which lose their initial energy by exciting intramolecular vibrations (≈︁60%) and excitons (≈︁40%) has permitted an estimation of ranges of energy loss in these two processes: more than 70 Å in the former and from 50 to 150 Å in the latter process. The former group of electrons is named subexciting electrons. The mean distance covered by the subexciting electron while it still has sufficient energy to excite intramolecular vibrations is estimated to 200 to 500 Å. All these estimates are essentially new as compared to those used at present. Comparison of secondary electron emission coefficients in anthracene single crystals and amorphous films leads to the conclusion that motion of subexciting electrons in the anthracene crystal is not diffuse. Experimentally obtained range of subexciting electrons, as related to angular scattering (greater than 70 Å), is large in comparison with lattice constant and indicates that in contrast to assumptions of the “compressed gas” model in molecular crystals angular scattering is a relatively rare phenomenon.
A Point Charge Model for the Ferroelectric Transition in Ammonium Sulphate
Authors: Jain Y. S. , Bist H. D. 
Published: July 2007

AbstractIn ammonium sulphate the distortion of the SO42− ion, which has almost tetrahedral symmetry in its paraelectric phase, occurs in a narrow region near the ferroelectric transition temperature Tc = 223 °K. A point charge model has been used to compute the spontaneous polarization (P) due to NH and SO ions in the crystal. The computed value of P (0.42 μC/cm2) agrees well with the experimentally reported ones. The nature of phase transition has also been discussed.
Bound Small Polaron Optical Absorption in V−‐Type Centres in MgO
Authors: Schirmer O. F. , Koidl P. , Reik H. G. 
Published: July 2007

AbstractA theory, based on the method of moments, is described which predicts exact lineshapes for the optical absorption of bound small polarons. This theory explains the position, large width, and high oscillator strength of the optical absorption of the V centre in MgO and the polarisation of V− in MgO, which has been observed under uniaxial stress.
Calculation of Phonon Dispersion Curves and Mode Grüneisen Parameters in RbI
Authors: Kress W. 
Published: July 2007

AbstractThe phonon dispersion curves of RbI are calculated using the breathing shell model, allowing for the force constants of the isotropic deformation to be unequal to the shell‐core force constants. The model is extended to include the proper third order anharmonic contributions. The mode Grüneisen parameters are calculated within this model using first order perturbation theory. The parameters entering the calculation of the mode Grüneisen parameters are the isothermal pressure derivatives of the harmonic breathing shell model parameters and are obtained from the pressure derivatives of the long wavelength measurements in a similar way as are the harmonic parameters. Using this model the specific heat and the linear thermal expansion coefficient as functions of temperature are calculated.
A General Cluster Expansion and the Definition of Self‐Consistent n‐Site Approximations in the Theory of Disordered Systems
Authors: Fischbeck H. J. 
Published: July 2007

AbstractA general cluster expansion of the averaged transition operator of a disordered system in terms of the distribution functions of its constituents is given. Self‐consistent n‐site approximations are defined by requiring that a truncated version of this series should be zero in an effective medium. In the alloy case these are shown to be equivalent to previously derived approximations. For amorphous systems a new type of n‐site approximations is obtained.
Jahn‐Teller Effect on Excited Orbital Triplet States of 3dn Ions in Eightfold Cubic Coordination. Co2+ and Fe2+ in CdF2
Authors: Ulrici W. 
Published: July 2007

AbstractThe ions Co2+ and Fe2+ can be substitutionally incorporated on Cd2+ sites in CdF2. The optical absorption bands of the transitions 4A2g → 4T1g(F), → 4T1g(P) and 5Eg → 5T2g are no single bands but exhibit a pronounced triplet structure measured up to 500 K. The splittings increase linearly with \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt T $\end{document} at high temperatures. These results are explained as due to a strong dynamical Jahn‐Teller effect (interaction with τ2g modes) on the excited orbital triplet states based on the theory by Toyozawa and Inone [3]. The frequencies of the τ2g modes and the coupling constants (Jahn‐Teller energies) are determined. The doublet structure of the 4A2g → 4T2g absorption band and additional fine structures of the → 4T1g(F) band at low temperatures are discussed as probably being caused by the simultaneous action of first order spin‐orbit coupling and strong T ⊗ τ2g coupling.
Diffuse Scattering and Surface‐Plasmon Generation by Photons at a Rough Dielectric Surface
Authors: Elson J. M. , Ritchie K. H. 
Published: July 2007

AbstractFirst‐order perturbation theory has been employed to compute the scattering and conversion to surface plasma oscillations of photons incident normally on a nearly planar vacuum‐dielectric surface. The calculation proceeds through a classical solution of Maxwell's equations. Transformation to a non‐orthogonal system of coordinates is effected. The Green function tensor for the Hertz vector potential appropriate to the plane surface geometry is found and applied to a determination of the scattered fields. The results are valid for arbitrarily large damping of fields due to electronic transitions in the dielectric.
Kondo Effect in the Transport Properties of the CsCl‐Type Compounds Fe1−xTi1+x. I. Their Anomalous Behaviors in the Titanium‐Rich Compositions
Authors: Ikeda K. 
Published: July 2007

AbstractA resistance minimum at 30 to 60 °K and a negative and giant valley of the thermoelectric power near 47 °K were observed in the CsCl‐type compounds, Fe1−xTi1+x, with titanium‐rich compositions. This anomalous behavior of the transport phenomena, which are distinct from those of the stoichiometric compound showing an ordinary temperature dependence of the resistivity and a positive and monotonically increasing thermoelectric power, have features similar to the Kondo effect in dilute magnetic alloys. It is suggested that such anomalous phenomena may be caused by the existence of the iron atoms occupying the wrong atomic sites in a slightly disordered CsCl‐type lattice.
The Masses of Free Holes and Electrons in Tellurium
Authors: Lutz M. , Stolze H. , Grosse P. 
Published: July 2007

AbstractThe transverse effective hole masses of tellurium samples with p = 1016 to 1018 cm−3 have been determined from Faraday rotation measurements at 10, 90, and 300 K. The comparison of the experimental values with the calculated Faraday masses enables to prove the validity of various band models for large k. The model presented by Bangert gives the best fit. Thus the strong temperature dependence of the hole mass determined from transport measurements by many authors is shown to be due to the nonparabolicity of the valence band. At higher temperatures (300 to 400 K) also the free electrons contribute to the Faraday effect. This rotation could be explained by Bangert's model, too.
On the Theory of an Impurity Molecule. II. The Born‐Oppenheimer Method
Authors: Liapzev A. V. , Kiselev A. A. 
Published: July 2007

AbstractA nonlinear impurity molecule is considered. The molecule is assumed to show almost free rotations about one axis which can librate. The Born‐Oppenheimer method is applied to solve the Schrödinger equation transformed from cartesian coordinates to coordinates defined by the Eckart conditions and describing the vibrations and rotations. The Hamiltonian, the eigenvalue, and eigenfunction are expanded in power series in the Born‐Oppenheimer parameter and these expansions are inserted in the Schrödinger equation. The eigenfunction and eigenvalue expansions are calculated up to the first and the fifth terms, respectively. Some kinetic corrections caused by the libration are shown to appear in the first order term of the eigenfunction expansion and in the fourth order term of the eigenvalue expansion.
Investigation of Magnetoplasma Wave Dispersion in Pure and Doped Bi92Sb8 at Liquid Nitrogen Temperature
Authors: Brazis R. , Požela J. , Tairov B. , Shakhtakhtinskii M. 
Published: July 2007

AbstractThe bulk magnetoplasma wave dispersion and its relation to peculiarities of the energy band structure in Bi92Sb8 are investigated. The electron mobility tensor components and the carrier cyclotron mobilities are estimated in pure single crystals and those doped with tin and tellurium.
Magnetische Bereichsstrukturen in Typ‐I‐Dünnschichtsupraleitern. II. Der zweidimensionale Mischzustand
Authors: Lischke B. , Rodewald W. 
Published: July 2007

AbstractDie Flußquantenstrukturen in dünnen supraleitenden Schichten (Pb) in senkrechten Magnetfeldern wurden durch die Dekoration mit Eisenteilchen sichtbar gemacht. Die Dekorations‐ Technik wird mit der Elektronenmikroskopie dünner Schichten kombiniert. Diese „Dekorations‐Mikroskopie”︁ erlaubt es, die Wechselwirkung von Flußlinien mit Korngrenzen direkt zu beobachten. Der Übergang von den Strukturen des Zwischenzustands in die des zweidimensionalen Mischzustands erfolgt unterhalb einer kritischen Schichtdicke, die mit theoretischen Ergebnissen verglichen wurde.
Asymptotic and Pre‐Asymptotic Region of Charge Density Oscillation around Impurities in Dilute Copper‐Based Alloys
Authors: Serfőző G. 
Published: July 2007

AbstractComparison of the wipe‐out numbers for the first and second order quadrupole effects in the magnetic resonance of matrix nuclei shows that Friedel's asymptotic charge density perturbation formula is not valid for the near‐region around the impurity. On the basis of Alfred's and Van Ostenburg's pre‐asymptotic theory, wipe‐out numbers characteristic of the second order quadrupole effect are calculated for Cu‐Zn, Cu‐Ga, and Cu‐Ge dilute alloys and good agreement with the experimental results is found. I n spite of this success this theory is unable to describe adequately, the field gradients measured a t the first and second coordination shells near the impurity.
LCAO Calculations for the Boron and Nitrogen Interstitial in the Diamond Lattice
Authors: Weigel C. , Peak D. , Cobbett J. W. , Watkins G. D. , Messmer R. Y. 
Published: July 2007

AbstractLCAO‐MO cluster calculations based on the extended Hückel theory are carried out for boron and nitrogen atoms in various interstitial configurations in the diamond lattice. The results favor the (100) split interstitial configuration for both the boron and nitrogen interstitial and suggest a change of the energy minimum configuration with charge state.
The Interaction between s‐n‐Domain Walls and Lattice Defects in Type‐I Superconductors
Authors: Riedel H. , Kronmüller H. 
Published: July 2007

AbstractThe interaction between crystal dislocations and sn‐walls in type‐I superconductors is treated on the basis of the micromagnetic equations of superconductors. The elastic properties of the sn‐walls are described by quasi‐dislocations and the interaction force with the dislocations is derived from a generalized Peach‐Koehler formula. A statistical analysis of the total force exerted by randomly distributed dislocations on sn‐walls yields characteristic differences between the δV‐effect and the nonlinear elastic effects (δE‐, P‐effect) concerning the mean wavelength of the field of force and the dependence on the dislocation density. The relative changes of the magnetization curve caused by wall pinning due to dislocations are shown to amount to 5 to 15% for large plastic deformations.