bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sulphur Impurity Level Dependence on Band Structure Variation with Pressure in GaxIn1−xSb
Authors: Campos M. D'olne , Gouskov A. , Gouskov L. 
Published: July 2007

AbstractResults of Hall effect and resistivity measurements under hydrostatic pressure (up to 15 kbar) between 300 and 77°K are given for three samples of GaxIn1−xSb. The values of x are 1; 0.96; and 0.865. These results are interpreted on the basis of a simple model of charge exchange between one donor level ES and one occupied band minimum. It is shown that for x = 1 andx = 0.96 the sulphur level ES localized in the forbidden band gap has the same pressure coefficient as the X1 minimum: E d (E − E)/dP = d (ES − E)/dP = 16 meV/kbar. For x = 0.865, ES is merged in the conduction band and is no more rigidly associated to the X1minimum. ES shows various pressure coefficients depending on its position in the band structure.
Dynamical Susceptibility for Interacting Electrons in a Narrow Energy Band
Authors: Nolting W. 
Published: July 2007

AbstractAn approximate expression for the dynamical susceptibility χ (q, ω) of the paramagnetic phase of an interacting electron system in a narrow energy band is derived. The treatment is based on the “method of spectral moments”, χ (q, ω) is used to look for instabilities of the paramagnetic state toward ferromagnetic ordering. If the number of electrons is less than the number of sites, χ (q, ω) signals the possibility of two different types of ferromagnetism for both the s.c. and b.c.c. structure, while the paramagnetic system is stable for the f.c.c. structure. For the f.c.c.‐lattice a single ferromagnetic solution exists, if the band is more than half‐filled.
Extension of the Unsaturable Trap Model to One‐Dimensional Interstitial Migration
Authors: Gösele U. , Frank W. 
Published: July 2007

AbstractFor most f.c.c. metals the increase of the electrical resistivity due to stage‐II temperature irradiation may be interpreted in terms of trapping of mobile interstitials at unsaturable traps. This model originally elaborated for interstitials migrating in three dimensions predicts that the inverse of the production rate of defects retained in an irradiation‐exposed sample increases linearly with the defect concentration. Using three different methods (rate equation approach, diffusion theory, and a computer simulation technique) it will be shown that this relationship remains valid if the mobile interstitials are off‐line crowdions and thus constrained to a long‐range migration in one dimension. It is therefore not admissible to draw any conclusions about the nature of self‐interstitials in f.c.c. metals from radiation damage curves measured at stage‐II temperatures, contrary to what has repeatedly been done in the literature.
Influence of Acoustic Lattice Vibrations on Dynamical X‐Ray Diffraction
Authors: Köhler R. , Möhling W. , Peibst H. 
Published: July 2007

AbstractA dynamical X‐ray diffraction theory for crystals with acoustic lattice vibrations is presented. The fundamental equations derived for the general case are specified to monochromatic vibrations of wavelengths shorter than the pendellösung distance taking into account higher harmonics. It is shown that each satellite reflection, caused by these vibrations, can be treated as a usual dynamical two‐beam case using a modified dielectric susceptibility χ which depends on the amplitudes and phases of the vibrations.
Temperature Dependence of the 1S Line of the Yellow Series of Cu2O
Authors: Merle J. C. , Nikitine S. , Haken H. 
Published: July 2007

AbstractThe behaviour of the shape of the quadrupolar n = 1 line of the yellow serie of Cu2O is described as a function of temperature. The total anisotropy ofthis line enables one to use a highly sensitive polarization modulation technique, with ahigh dispersion set‐up. The behaviour of the line being inexplainable in the scopeof previous theories, is discussed with a new theoretical model in which both the defectsof the crystal and the phonons are taken into account, and which leads to an absorption having a Voigt shape. The analysis of the experimental results enables one to evaluate theparticipation of the defects and shows that both acoustic and optical phonons scatter theconsidered exciton, in good agreement with the theory.
Shubnikov‐de Haas Oscillations in CdvHg1−vSe
Authors: Stankiewicz J. , Giriat W. , Dobrowolski W. 
Published: July 2007

AbstractOscillations of the magnetoresistivity in CdvHg1−vSe for v = 0.05; 0.075; 0.10 and 0.19 are reported. From the temperaturedependence of the amplitudes of the oscillations, the effective mass of electrons was determined. The effective mass is dependent on concentration. In order to find the energy band gap, E0, and the matrix element, P, the k · p method, including interaction with higher bands and finite Δ, was used. It was foundthat the dependence of E0 on composition at 4.2 K is linear for v < 0.2.
Calculated Infrared Absorption Due to Impurities in Cesium Halides
Authors: Ram P. N. , Agrawal Bal K. 
Published: July 2007

AbstractA next‐nearest neighbour perturbation model has been employed to remove the discrepancies observed earlier in the infrared absorption data of cesium halides containingsome impurity ions such as Tl+ and Rb+. Improvement in the locations of absorption peaks in CsCl:Rb+ and some structure in the high frequency region in thalium doped CsBr and CsI have been seen but discrepancies still exist in the intensity of absorption. The experimental data in CsI:Na+ and CsI:Li+ have been discussed on the basis of nearest neighbour defect model. Very good agreement between theory and experiment has been found. Further, the earlier calculated absorption in CsI due to impurities using the phonons of Mahler show much improvement when phonons of a better calculation recently performed by Jex are used. The results showthe necessity of a revised calculation for phonons in pure cesium halide crystals.
Linear Magnetic Birefringence in Transition Metal Oxides: CoO
Authors: Germann K. H. , Maier K. , Strauss E. 
Published: July 2007

AbstractThe optical linear magnetic birefringence (LMB) of cobalt oxide single crystals was determined as a function of temperature near the antiferromagnetic Néel point. The measurements were taken from single‐domain crystals with the tetragonal c‐axis oriented parallel or perpendicular to the direction of the light beam. Below TN the change of LMB with temperature in perpendicular arrangement is found to be proportional to the c‐axis contraction and to the square of the long‐range order parameter. Magnetic short‐range order effects have been observed even far above TN. The results are discussed by means of a magnetostriction model.
Crystal Field Splitting of S‐State Ions in Crystalline TeO2 and Amorphous TeO2‐V2O5
Authors: Sperlich G. , Urban P. 
Published: July 2007

AbstractThe parameters of the spin‐Hamiltonian of Gd3+ in TeO2 single crystals are determined and the ESR spectra of polycrystalline TeO2:Gd3+ samples are compared with those of Gd3+ ions on Te sites in amorphous TeO2‐V2O5 compounds. It turns out that the microenvironment of the tellurium ion in the amorphous samples is similar to that in crystalline TeO2. Further ESR signals of Fe3+ ions in amorphous TeO2‐V2O5 are discussed.
Ionic Raman Scattering and Ionic Frequency Mixing
Authors: Martin T. P. , Genzel L. 
Published: July 2007

AbstractTwo closely related effects based on the nonlinearity of ionic polarizability are considered, ionic Raman scattering and ionic frequency mixing. A simple model is used to make explicit calculations for quartz. Both effects have two resonances associated with each reststrahl band. In addition, antiresonances may occur due to the interference between the ionic process and the corresponding normal process. Although two resonance conditions may be satisfied simultaneously in quartz, the Raman efficiency seems to be below the present limits of observation. On the other hand, the calculation shows that resonant ionic frequency mixing should be observable in quartz.
Thermally Activated Plastic Deformation of High‐Purity Copper Single Crystals
Authors: Zeyfang R. , Buck O. , Seeger A. 
Published: July 2007

AbstractChanges in strain rate during dynamical tensile deformation of high‐purity copper single crystals are used to determine the activation volume associated with plastic deformation as a function of flow stress, temperature, and strain rate. In work‐hardening stage I the activation volume is almost constant, whereas in stage II the reciprocal activation volume increases linearly with flow stress. It is shown that the flow‐stress ratios are not constant in any of the stages I to III, in violation of the so‐called Cottrell‐Stokes law. The experimental results are discussed in terms of the work‐hardening model of Seeger and co‐workers and indicate that the strain‐rate dependent (thermally activated) but not the temperature independent contribution to the flow stress is determined by the intersection of dislocations.
Lattice Dynamics of Graphite
Authors: Mani K. K. , Ramani R. 
Published: July 2007

AbstractThe lattice dynamics of graphite have been studied using a tensor force model. Force constant values for interactions between atoms in‐plane have been transferred from the naphthalene molecule. It is shown that the agreement between theory and neutron scattering data is very good, indicating that the molecular constants form a very good approximation to the crystal force constants. Significant differences are, however, found between the present calculations and those of Nicklow et al. using an axially symmetric model, regarding some out‐of‐plane modes. It is assumed that these arise from the restrictions of the axially symmetric model. It is also shown that restoring forces corresponding to twisting motions about CC bonds in the plane are very small.
Study at 108 and 2 × 108 Hz of the Electrical Conductivity and Dielectric Constant of the Highly Anisotropic Organic Semiconductor TEA (TCNQ)2
Authors: Farges J. P. , Brau A. 
Published: July 2007

AbstractThe ac electrical conductivity and anisotropy, including an evaluation of the dielectric constant, at 108 and 2 × 108 Hz in the range 77 to 350°K is investigated. A hopping mechanism is evidenced from the dispersion of conductivity observed below 200°K, and is associated with the existence of tails of localized states at the edges of a band gap. The vanishing dispersion in the upper temperature range is likely to indicate that an interband transition process may then become important for conduction.
Phonon Dispersion Relations and Two‐Phonon Raman Spectra of Cesium Fluoride
Authors: Gupta H. N. , Singh R. K. 
Published: July 2007

AbstractThe phonon dispersion relations and two‐phonon Raman spectra of cesium fluoride have been calculated with a three‐body force shell model employing core and shell charge modifications which account for the Cauchy‐discrepancy and electronic polarizability. The results show an excellent agreement with the observed data. A brief description of the modification introduced by three‐body interactions in the electronic polarizability is also presented.
Antimony Centres in Potassium Halides
Authors: Radhakrishna S. , Karguppikar A. M. 
Published: July 2007

AbstractAntimony doped potassium halide crystals give one optical absorption band at 205 nm in KCl, 215 nm in KBr, and 243 nm in KI at RT. These bands are ascribed to the divalent state of antimony. Correlated EPR studies show that the paramagnetic antimony (Sb2+) state is associated with a vacancy in the second neighbour position. Experiments have also been performed on the conductivity and dielectric loss. The impurity–vacancy binding energy is found to be ≈ 0.30 eV in these crystals.
Die Bedeutung der Elektron–Elektron‐Wechselwirkung in Halbleitern
Authors: Jäger I. 
Published: July 2007

AbstractDer Einfluß der Streuung von Ladungsträgern aneinander auf die Gestalt ihrer Verteilungsfunktion wird mit Hilfe einer erweiterten „Path‐Variable‐Methode”︁ diskutiert. Es wird als Beispiel die Verteilungsfunktion warmer Elektronen in n‐Germanium berechnet und gezeigt, daß unter der getroffenen Wahl eines abgeschirmten Coulombpotentials für die Wechselwirkung der Elektronen untereinander die Rechnungen mit und ohne Berücksichtigung dieser Wechselwirkung kaum differieren, sowie, daß die so berechnete Verteilungsfunktion den Koeffizienten der warmen Elektronen (β), eine von der Gestalt der Verteilungsfunktion stark abhängige Größe, gut wiedergibt, obwohl die Berechnung absichtlich in einem für die Rechnung ungünstigen Bereich der Ladungsträgerkonzentration durchgeführt wird.
Acceptor States in Selenium–Tellurium Mixed Crystals with Low Selenium Concentrations
Authors: Yoshikawa A. , Takagi T. , Mizushima Y. 
Published: July 2007

AbstractTransport properties of undoped Se–Te mixed crystals containing up to 5 at% Se are investigated in the temperature range from 1.7 to 300 K. The behaviour of the Hall coefficient at low temperatures shows sudden changes at 1 to 2 at% of Se concentration. In mixed crystals with more than about 2 at% Se, the magnetic freeze‐out effect and impact ionization effect of impurities are found. These experimental results indicate that, contrary to undoped Te, shallow acceptor states exist above the top of the valence band in these mixed crystals.
Covariant Forms of the Third‐ and Fourth‐Rank Tensors such as Piezoelectric Moduli and Piezo‐Optical Coefficients
Authors: Iosilevskii Ya. A. 
Published: July 2007

AbstractCovariant forms of the third‐rank tensor Likl invariant under the permutation k ⇄ I and the fourth‐rank tensor Lpiklm invariant under the permutations i ⇄ k and I ⇄ m are suggested for all the crystal classes. A covariant procedure of reducing the given tensor to principal axes is presented when these axes are not completely determined by the symmetry elements of the crystal. A covariant method of constructing the fourth‐rank reciprocal tensor is given.
Conductivity Tensor Components of n‐Bi2Se3
Authors: Köhler H. 
Published: July 2007

AbstractFrom Shubnikov‐de Haas experiments a single‐valley model for the lowest conduction band of Bi2Se3 was derived. The determination of non‐parabolic contributions to the ϵ(k) relation enabled the calculation of conductivity tensor components, which should be zero in an ellipsoidal approximation. The results are compared with own measurements and earlier data, which had been interpreted in an ellipsoidal six‐valley model.
Theory of the Residual Resistivity of Bloch Walls. II. Inclusion of Diamagnetic Effects
Authors: Cabrera G. G. , Falicov L. M. 
Published: July 2007

AbstractDiamagnetic effects are included in the calculation of the electrical resistivity of a Bloch wall in a ferromagnetic metal. The resulting electron orbits, which are convoluted zig‐zag‐ging trajectories near the wall, produce an increase in the resistivity which is roughly proportional to (ωcτ)2, where ωc is the cyclotron frequency of the electron due to the internal magnetization. Such an effect explains satisfactorily the experimental data reported in the literature.
Crystal Field Determination in Rare‐Earth Oxysulfides. I. Optical Experiments for Tb3+ Ion
Authors: Rossat‐Mignod J. , Souillat J. C. , Quezel G. 
Published: July 2007

AbstractThe crystalline electric field (CEF) acting on a Tb3+ ion in rare‐earth oxysulfides has been determined. By analysing fluorescence spectra of Y2O2S: 1% Tb3+, it is possible to obtain the energy levels of the 7FJ (J = 1 to 6) manifolds of Tb3+ in this host and therefore the CEF Hamiltonian of C3v symmetry. In order to explain the particular magnetization processes in Tb2O2S, particular attention has been paid to the ground state. It has been found that the ground state consists of four levels lying very close one another (0, 6, 15, 26 cm−1). Both the direction and the value of the magnetic moment calculated according to this level scheme agree well with neutron diffraction data.
Analytic Expression for the Electronic Charge Density Distribution in Diamond‐Structure Crystals
Authors: Chadi D. J. , Cohen M. L. 
Published: July 2007

AbstractThe explicit dependence of the valence band electronic charge density distribution on the pseudo‐potential form factors for the diamond structure crystals has been obtained using a weighted sum of the charge densities at the symmetry points Γ, X, and L of the Brillouin zone. The charge densities and energies for the bands at Γ X, and L, and their dependence on the lattice constant and pseudopotentials are also discussed.
Optimal CC, CH, and HH Potential Curves for the Naphthalene Crystal
Authors: Mirskaya K. V. , Kozlova I. E. , Bereznitskaya V. F. 
Published: July 2007

AbstractOn the basis of experimental data on the structure and elasticity tensor of naphthalene crystals at low temperatures a more accurate fitting of the parameters of the C‐C, C‐H, and H‐H potential curves was made. The potential curves involved have the form φ − (A/r6)+ Be−αr and the following numerical parameters: Acc= 421 (kcal/mol)Å6, Bcc = 7.16 × 104 kcal/mol, αcc = 3.68 Å−1; ACH = 118 (kcal/mol) Å6, BCH = 1.86 Å 104 kcal/mol, ÅCH = 3.94 Å−1;AHH = 29(kcal/mol) Å6, BHH × 0.49 × 104kcal/mol,αHH = 4.29 Å−1.
Effect of Anharmonicity on Urbach's Exponential Tail in Amorphous Semiconductors
Authors: Bhatia K. L. , Bhat P. K. 
Published: July 2007

AbstractAt the crystal‐glass transition the overall short range order is retained but a distortion exists in the interatomic bonds which introduces a nonlinearity in the interatomic forces. The characteristics of amorphous materials have been studied taking into account the nonlinearity of the interatomic forces. This anharmonicity in amorphous semiconductors is related with the decreased slope of the exponential part of the fundamental optical absorption edge of a semiconductor.
On the Definition of the Current Operator Application to the Hubbard Model
Authors: Monecke J. 
Published: July 2007

AbstractA disagreement existing in the literature between various calculations of the electrical conductivity y in the single‐band Hubbard model is resolved. It is replied to an article by Cabib and Kaplan who tried to disprove that there are no absorption and emission lines near ω = U due to the translational invariance. The physical reason for this result and some of its consequences are discussed.
Ionized‐Beam Energy Loss to Electron Gas
Authors: Shah S. , Srivastava M. P. , Kothari L. S. 
Published: July 2007

AbstractThe stopping power and other transport coefficients have been calculated for ionized beams channeling through a crystal using a statistical method developed by Chandrasekhar. Only the interaction of beam particles with conduction electrons, treated as a free gas, is considered. Unlike earlier investigations, also the effect on the test particles of encounters with faster field particles is considered. Two types of potentials have been used, a Debye and a Coulomb one. Both potentials give nearly the same results. It is found that the values of energy loss and transport coefficients increase with increasing energy of the incident beam. The stopping power is nearly the same as that obtained by earlier workers.
Crystal Field Determination in Rare‐Earth Oxysulfides. II. Optical Experiments for Ho3+ and Dy3+ Ions
Authors: Rossat‐Mignod J. , Souillat J. C. , Quezel G. 
Published: July 2007

AbstractThe crystal field levels of the 5I8 ground state manifold of Ho3+have been obtained from the luminescence spectrum of Y2O2S:5%Ho3+. The ground state of the Ho3+ ion is found to be a set of five levels (0, 8, 14, 18, 23 cm−1). An attempt has been made to deduce the parameters of the CEF Hamiltonian from the experimental level energies. For Dy3+, the breaking up of the fundamental 6H15/2 multiplet has been obtained by analysing the fluorescence spectrum of Y2O2S:1% Dy3+ and the absorption spectrum of Dy2O2S. The ground state is found to be a doublet relatively well separated (21 cm−1) from the first excited level. In these two compounds, CEF calculations give satisfactory agreement with both the value and direction of the magnetic moment obtained from neutron diffraction experiments.
Static Structure of Liquid Noble and Transition Metals by X‐Ray Diffraction
Authors: Waseda Y. , Ohtani M. 
Published: July 2007

AbstractX‐ray diffraction patterns were obtained from liquid noble and transition metals (Cu, Ag, Au, Fe, Co, Ni) at temperatures between melting point mid 1650 °C. After calculating the structure factor (Fourier analysis), the atomic radial distribution function was evaluated from which interatomic distance and coordination number were obtained. Comparing the results with those observed previously by other researchers, adequate agreement was found.
Low‐Symmetry Crystal Fields in CrCl3
Authors: Majer M. , Szymczak H. 
Published: July 2007

AbstractA crystal field study has been performed for CrCl3 crystals. The energy matrix has been diagonalized within the 120 states of the complete d3 configuration. In the calculation the trigonal field, spin–orbit interaction as well as Tree's correction have been taken into account. The results of the calculations have been compared with the experimental data on the specific magnetic rotation, optical absorption, and EPR spectra.
Lattice Vibrations and Free Carrier Dispersion in PbSe
Authors: Burkhard H. , Geick R. , Kästner P. , Unkelbach K.‐H. 
Published: July 2007

AbstractThe reflectivity of n‐type PbSe has been measured in the infrared region from 10 to 400 cm−1 at 5, 77, and 300 K. A Kramers‐Kronig analysis has been performed as well as a fit with a dispersion formula including a Drude term for free carriers. The transverse phonon frequency was observed at 39 cm−l and found to be independent of temperature. The contribution of the lattice oscillator to the static dielectric constant of 180 is relatively high. The longitudinal excitations are determined considering the coupling between phonons and free carriers. Finally the plasma frequency has also been found to be independent of temperature and in reasonable agreement with Hall effect and effective mass data.
Temperature Dependence of Paraelectric Resonance of OH− Centres in KI Single Crystals
Authors: Hundhausen R. , Osswald R. , Wolf H. C. 
Published: July 2007

AbstractPER spectra of OH− in KI have been measured in the X‐band (11 GHz) and the Q‐band (35 GHz) with several orientations of the electrostatic field at liquid helium temperatures. The temperature dependence of the Q‐band spectrum (E0 ‖ E1 ‖ 〈100〉) indicates a zerofield splitting in the range of about 120 GHz.
Stark Effect of Wannier‐Mott Excitons Due to Disorder
Authors: Majerníková E. 
Published: July 2007

AbstractThe averaged canonical density matrix of a large orbit exciton with a diameter ϱ in a Gaussian random potential field with the correlation length L and the mean square root of the random potential η, has been calculated using the Feynman path integral approach. It has been shown that in the case when the condition ϱ < L – De is fulfilled the influence of the random field on the internal state of the exciton is equivalent to the Stark splitting of the excitonic levels due to an effective Gaussian random electrical field. The theory permits to interpret the experiments of Nikitine et al. on the excitonic absorption spectra of structurally perturbed Cu2O and to make conclusions about the parameters of the structure of disordered solids (correlation functions, correlation lengths). The respective density of states has been calculated with a strongly marked asymptotic tail behaviour.