bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical properties and energy band structure correlation of sphalerite (A3B5) and chalcopyrite (A2B4C52) Crystals
Authors: Donetskich V. I. , Poplavnoi A. S. , Sobolev V. V.
Published: July 2007

The reflectivity spectra of Galls, ZnGeAs2, InAs, and CdSnA2 have been investigated in the range 1.5 to 5 cV at 77 and 293 °K by improved methods and in the range 5 to 12.5 cV at 293 °K by means of a spectrometer VMR‐2. A more complex structure of the spectra than earlier known have been established. Group‐theoretical analysis of the zero slopes and selection rules for chalcopyrite interband transitions have been performed and a correlation model of the interband transitions of GaAs and ZnGeAs2 type crystals have been proposed. Good agreement of experimental and theoretical energy transitions have been obtained.
Uniaxial stress effects of the UV‐absorption bands of In+ and T1+ doped alkali halide crystals in a molecular treatment
Authors: Dultz W.
Published: July 2007

The stress‐induced dichroism of the UV‐absorption bands of KCl:In+ and KI:Tl+ is investigated. The splitting ratio of the A‐and C‐band under stress is not consistent with predictions of a crystal field model of the defect. This discrepancy is explained by introducing a stress‐dependent axial term of the spin‐orbit coupling which depends on the covalent character of the bond between the defect and its neighbour ions. The strong temperature dependence of the stress effects is a consequence of the anharmonicity of the local elastic constants near the defect.
Single phonon x‐ray scattering from alkali halides I. The influence of eigenvectors
Authors: Reid J. S.
Published: July 2007

Variations in the eigenvectors given by a number of force models for the alkali halides are examined for wave vectors lying along the: [1,0,0], [1,1,0], and [1,1,1] directions. Among the models considered are least‐squares‐fitted shell models for NaF, NaCl, NaBr, NaI, KCl, and KBr. Substantial differences in the eigenvectors given by different models for one material are found, even when the models fit phonon frequencies well. In addition it is found that the fractional variation of the eigenvectors with temperature is similar to the fractional variation of the square of the phonon frequencies. The method of determining the ratio of the eigenvectors of the two ions from the one‐phonon X‐ray scattering is discussed, and the sensitivity of this method is numerically examined. Although this sensitivity varies widely in reciprocal space it is possible to choose values of the scattering vector where this ratio can be determined to about ± 0.03 for a 20% accuracy in the one‐phonon scattering. The effect of the eigenvectors on the Debye‐Waller factors is also considered and shown to produce an uncertainty in the Bkvalues of the order of 1% at 300 ° K. It is concluded that measurements of the X‐ray intensity scattered by a transverse mode could distinguish between the eigenvector ratios given by fitted shell models and models determined by macroscopic data. Measurements to an accuracy of 1% could further distinguish different good shell models.
Migration and incorporation of tellurium in CdS
Authors: Nebauer E. , Lautenbach J.
Published: July 2007

The diffusion (D) and solubility (S) properties of tellurium in CdS are investigated by means of the vapour pressure method. The concentration profiles measured by special microtome and by tracer techniques consist of two parts in most cases: the first is attributed to bulk diffusion and the second is assumed to be caused by dislocations. The first region of profiles shows usual erfc‐behaviour only under sulfur pressure annealings, and only for this case the pressure dependences of D and S have been determined simultaneously and quantitatively. The van Gool exponents found experimentally are compared with values estimated on the basis of a simple dissociative diffusion model and good agreement is obtained.
A model of the temperature dependent part of stage I work‐hardening due to jog‐dragging (II)
Authors: Messerschmidt U.
Published: July 2007

The system of differential equations, established in Part I, of the density of nonconservatively moving mono‐jogs and of the concentration of excess point defects during plastic deformation has been solved asymptotically as well as numerically. The jog density is a linear function of strain, resulting in a temperature dependent contribution to work‐hardening. The excess point defect concentration reaches a steady state value in a constant strain rate experiment and should be caused by interstitials. The results are discussed in terms of the plastic properties in stage I deformation of alkali halides.
Nuclear relaxation and NMR saturation in a crystal with a magnetic impurity
Authors: Buishvili L. L. , Khutsishvili G. R. , Zviadadze M. D.
Published: July 2007

A theoretical treatment of nuclear relaxation in non‐metallic diamagnetic crystals with a magnetic impurity is carried out for the case when the dipole—dipole reservoir of magnetic ions plays an important role. The theoretical results are compared with the data of the Leiden group on relaxation of protons in lanthanum magnesium nitrate with neodymium impurities. An elementary theory of NMR saturation is given taking into account saturation transfer from the nuclear Zeeman reservoir to the dipole‐dipole reservoir of magnetic ions. A special analysis is made of the possible role in nuclear relaxation of an inhomogeneous broadening of the EPR line, of a phonon bottleneck in the spin‐lattice relaxation of magnetic ions, and of exchange pairs.
Optical properties of transition metal impurities in CdSe II. Photoionization spectra
Authors: Raranowski J. M. , Langer J. M.
Published: July 2007

The photoionization absorption spectra of Cr and Fe impurities in CdSe are presented. They are very well described in terms of photo‐transitions from the localized 3d shell to the conduction band. The ionization energies and the matrix elements of electric dipole transitions are determined. It is found that deep donor levels of Cr2+ and Fe2+ arc 0.62 and 0.63 eV above the top of the valence band, respectively and are temperature‐indepenent. Observed spectra of CdSe:Fe2+ are succesfully correlated with previously published results of photosensitive EPR of CdSe:Fe3+. The photoionization processes for other transition metal impurities are discussed. The ionization energies for some of them are estimated.
Raman scattering intensity of polaritons for general wave vectors. II. Experimental investigations in BeSO4·H2O
Authors: Unger B.
Published: July 2007

The theory presented in Part I [1] for the Raman scattering efficiency of polaritons in uniaxial piezoelectric crystals is used to interpret experiments on the dependence of the scattered intensities on the direction of the polariton wave vector kp. The measurements have been performed with BeSO4 · 4 H2O in the v3‐region of the SO ions at 1100 cm−1 for the limit (kp ≫ ωp/c). kp is rotated in the (x, y) and (x, z) planes, and a good agreement between theory and experiment is obtained. The contributions of the defromation potential and the macroscopic electric field to the scattering efficiency are determined in relative units as a function of the direction of k.
Raman‐ and infrared measurements and the study of phase transitions in DyVO4
Authors: D'Ambrogio F. , Brüesch P. , Kalbfleisch H.
Published: July 2007

The observed Raman and infrared active lattice vibrations of DyVO4 are calculated using a valence force field for the internal vibrations of the VO4 complexes and a central force field for the external vibrations. On this basis the degree of coupling between internal and external lattice modes is calculated and found to be small for most of the modes. In addition, the frequencies for the low temperature orthorhombic structure below 13.8 K are calculated by adopting a slightly modified force field with the appropriate symmetry. The effect of such an orthorhombic deformation is very small for the non‐degenerate frequencies but yields splittings of the degenerate frequencies of the order of 10 cm−1. These predictions are in agreement with the observations.
Chaleur spécifique et propriétés magnétiques de I'oxysulfure d'ytterbium
Authors: Rossat‐Mignod J. , Quezel G. , Berton A. , Chaussy J.
Published: July 2007

L'étude de la susceptibilité magnétique de monocristaux d'Yb2O2S et les mesures de chaleur spécifique à basse température ont montré que le niveau fondamental de l'ion Yb3+ est un doublet isolé et peu anisotrope. Les processus d'aimantation ont été étudiés par des expériences de diffraction neutronique sous champ et par des mesures d'aimantation jusqu'à 80 kOe. De l'ensemble de ces résultats nous avons déterminé le champ cristallin agissant sur l'ion Yb3+ et estimé l'ordre de grandeur des interactions magnétiques.
Resolution of apparent APW–OPW energy band differences in NaCl
Authors: Melvin J. S. , Smith T.
Published: July 2007

The electron energy bands in NaCl have been calculated by the augmented plane wave (APW) method. Substantial agreement is obtained with earlier orthogonalized plane wave and empirical pseudopotential calculations. There are large differences from two earlier APW calculations in which, it is suggested, numerical problems may have been present.
Impurity spin states in the paramagnetic phase of ferromagnets
Authors: Timmesfeld K. H.
Published: July 2007

A theory has been developed for impurity spins in a Heisenberg ferromagnet in the temperature range above Tc for which numerical calculations have been performed using as a simple model a simple cubic crystal with nearest‐neighbour exchange constant and a defect spin with different spin and nearest‐neighbour exchange values. The calculations show that there exist in certain cases resonances and localized spin states for the impurity spin the intensity of which goes to zero with increasing temperature. Since no coupling between the normal modes of the spin system has been included, the width of those states is nearly unchanged with temperature.
Far infrared reflectivity of Cdas2
Authors: Gregora I. , Petzelt J.
Published: July 2007

Far infrared reflectivity of Cdas2 bulk crystals in polarized light has been measured at room and liquid‐nitrogen temperature in the 30 to 400 cm−1 frequency range. It is shown that the model of classical non‐interacting oscillators represents the experimental curves adequately. The results are in agreement with the group‐theoretical analysis of the zonecentre lattice modes. Parameters of the best‐fit oscillators, longitudinal‐mode frequencies, and real and imaginary parts of the corresponding dielectric‐function tensor are given. The influence of the free‐carrier effects on the optical properties investigated is shown to be negligible.
On the properties of the KDP type ferroelectrics with impurities
Authors: Stamenković S. , Zeković S.
Published: July 2007

The properties of KDP type ferroelectrics with impurities (D in KH2PO4 and H in KD2PO4) are considered using the method of zero‐temperature Green function. The linewidth of the polarization waves caused by their scattering on such impurities as well as the local frequency of impurity itself are calculated. The obtained results can be tested by measuring an intensity of the coherent (for H in KD2PO4) or incoherent (for D in KH2PO4) inelastic scattering respectively of slow neutrons scattered by such impure ferroelectrics.
Spin relaxation of conduction electrons in highly doped semiconductors (InSb, Si, Ge)
Authors: Gershenzon E. M. , Pevin N. M. , Fogelson M. S.
Published: July 2007

Experimental data of the temperature and concentration dependence of the ESR line‐width in highly doped n‐InSb, Ge: As, and Si: P are compared with theoretical calculations. For the spin–phonon interaction the temperature dependence and the values of the constants obtained agree within one or two orders of magnitude with theoretical results. Only qualitative agreement has been obtained for the contribution of relaxation by ionized impurity scattering. Possible sources of the line‐broadening are discussed in the limit of low temperatures, where the linewidth does not depend on temperature.
The magnetic scattering of neutral particles in polar media and the study of the permittivity dispersion in space and time
Authors: Dogonadze R. R. , Kornyshev A. A.
Published: July 2007

The scattering of a compound particle by a bound system in the case of weak interaction is considered. The Born cross‐sections for positronium and muonium scattering by a polar nonmagnetic medium were expressed by the complex permittivity function εαß(q, ω). The possibility of an experimental study of the frequency and wave vector dependence of the permittivity of homogeneous isotropic media using data on the scattering of leptonic atoms with spin transitions is investigated. The determination of Im {1/ε∥(q, ω)} by small‐angle thermal scattering data is also discussed.
Electron–phonon interaction in tellurium
Authors: Braune W. , Herrmann Karin , Herrmann R.
Published: July 2007

In the present work two temperature dependent microwave absorption lines (I and II) in tellurium are investigated for the case (1 ≧ h ω/kBT ≧ 0.4). The semiclassical formalism for piezoelectric electron‐phonon cyclotronresonance [1] describes the temperature behaviour of the absorption line II. The ttemperature dependence of the amplitude of line I permits the interpretation as an absorption of an impurity level of about 0.3 meV above the valence band.
Resonance Raman scattering in III–V semiconductors and their alloys
Authors: Renucci M. A. , Renucci J. B. , Cardona M.
Published: July 2007

The resonances in the Raman cross section of InAs and several pseudobinary alloys of III–V compounds in the neighbourhood of the E0 and E1 gaps were investigated. The alloying technique was used to bring the gaps to the region where the lines of the Ar‐ion laser occur. The E0‐Raman resonance shifts with temperature the same as the corresponding absorption gap, while a much smaller shift is exhibited by the E1 resonance. These resonant gaps shift with alloy concentration less than the corresponding absorption gaps, a fact which seems to be a reflection of the more localized nature of the Raman scattering phenomenon. The LO phonon exhibits in the forbidden scattering configurations a strong resonance near E1 at 77 °K. This resonance disappears rapidly as the temperature is increased.
Interionic potentials in liquid alkali metals
Authors: Waseda Y. , Suzuki K.
Published: July 2007

The Born‐Green equation has been analyzed numerically to derive the effective interionic potentials from the observed structural data for liquid alkali metals (Li, Na, K, Rb, Cs) using a linearized simultaneous equation method. The temperature insensitive long‐range oscillatory potentials are found and the wavelength of the oscillations observed is in good agreement with that expected from the electron theory of metals in all cases. The viscosity coefficient and surface tension were calculated and compared with experimental data.
High field transport in semiconductors. The drifted maxwellian approach. II. Application to n‐Insb
Authors: Stokoe T. Y. , Cornwell J. F.
Published: July 2007

The drifted Maxwellian approach to the transport properties of semiconductors is applied to Insb at high and low fields assuming Kane's model. Polar optical, acoustic, and ionised impurity scattering mechanisms are considered with band structure non‐parabolicity and the mixing of Bloch states with spin‐reversal effects being taken into account. The inclusion of the mixing of Bloch states leads to an increase of 17% in the low‐field mobility of Insb at 77 °K. Consistency between theory and experiment is obtained by taking Sanderson's static dielectric constant of 17.50, and Ehrenreich's acoustic deformation potential of −7.2 eV. A deformation potential of −30 eV seems inappropriate.
On the decay of the excited triplet state of the M centre in KCl
Authors: Bertolaccini M. , Bosi L. , Spinolo G.
Published: July 2007

The results of lifetime measurements of the relaxed excited triplet state of the M centre, 3M*, in KCl are given. The emission has the same decay time constant when exciting in the 1M and in the 3M bands: τ = τ(1M*). The conclusion may be drawn that a conversion 3M* → 1M* occurs with high probability.
Relativistic theory of low energy electron diffraction: Formalism and application to KKRZ‐pseudopotentials
Authors: Feder R.
Published: July 2007

A relativistic theory for calculating low energy electron diffraction intensities and spin polarizations is developed. The presentation of the general framework is followed by the construction of a relativistic KKRZ‐type electron–ion‐core pseudopotential and subsequent application of the framework to a crystal model that consists of this potential plus a complex self‐energy part to incorporate inelastic effects.
X‐ray photoemission studies of the electronic structure of rare earth metals
Authors: Hedén P. O. , Löfgren H. , Hagström S. B. M.
Published: July 2007

X‐ray photoemission (XPS) measurements are reported on evaporated films of the rare earth metals Eu, Gd, and Yb. For comparison additional measurements are reported on Ba. The results provide an unambiguous determination of the 4f energy levels. In Yb the spin–orbit splitting is also clearly resolved. The locations of the 4f levels below the Fermi level are determined to be 2.1 eV for Eu, 7.7 eV for Gd, and 1.4 eV and 2.7 eV for Yb all with an error of ± 0.4 eV.
The radiationless transfer of electronic excitation energy between impurity atoms in crystals characterized by broad absorption and luminescence bands
Authors: Kudžmauskas Š. P. , Batarňas J. V.
Published: July 2007

The theory of the energy transfer of electronic excitation between impurity atoms is developed for the case when broad absorption and luminescence bands exist. Perturbation theory is not employed. The probability of transfer is defined by a change of the quantum yield of the secondary donor radiation. The results are compared with the Förster‐Dexter theory.
Lattice dynamics and elastic constants of holmium and yttrium
Authors: Menon C. S. , Rao R. Ramji
Published: July 2007

The lattice dynamics and the elastic constants of the hexagonal metals holmium and yttrium have been investigated using the approach of Keating. In holmium, the dispersion curves are fitted using eleven force constant parameters and the six elastic constants are evaluated. The dispersion relations and the elastic constants of yttrium are fitted using twelve parameters.
Excitons in ZnS crystals with stacking faults
Authors: Ryskin A. I. , Suslina L. G. , Khilko G. I. , Shadrin E. B.
Published: July 2007

The exciton reflection spectra of ZnS crystals with stacking faults have been investigated at 4.2 °K. It has been found that in the range of available concentration of stacking faults (0 <α<0.35) (and especially at α = 0.1 to 0.2) the shift and splitting of the ground state (n = 1) exciton lines are considerably smaller than it should be expected in the case of linear dependence of these values on α. Spectra of ZnS crystals with a high concentration of stacking faults (α = 0.3) have a doublet structure of the B exciton line. It has been shown that this effect is due to the exchange interaction of the ground exciton state in ZnS crystals. An analogy between the spectra of crystals with stacking faults and the spectra of sphalerite crystals under tension along 〈III〉 is pointed out. The study of the spectra of ZnS crystals with stacking faults has shown that the exchange interaction of the excited exciton state does not need to be considered.
Angular‐correlation data analysis in terms of positron trapping by vacancies in metals
Authors: Kusmiss J. H. , Goland A. N. , Snead C. L.
Published: July 2007

Cross sections and rates for the trapping of positrons by vacancies in Aj, Cd, In, Zn, and Cu are derived from measurements of the angular correlation of positron‐annihilation radiation. The assumptions which usually accompany the application of the trapping model to angular‐correlation data are discussed in some detail.
Weak magnetic field enhancement of the luminescence from F centre pairs in alkali halides
Authors: Jaccard C. , Ruedin Y. , Aegerter M. , Schnegg P.‐A.
Published: July 2007

Whenever a member of a F centre pair is excited optically at low temperature, it can return to the ground state either radiatively or by formation of a F′ centre, the excited electron being transferred by a fast tunnel effect to the neighbouring centre. This process is dependent on the spin symmetry of the pair, which is in turn determined by the competitive influence of the different local hyperfine fields and of an applied magnetic field. The latter causes a decrease of the tunnelling probability, i.e. an increase of the luminescent yield in two steps; the first critical value is given by the hyperfine field and the second one by the temperature according to the Boltzmann factor. The quantum yield is found to have an exponential dependence of the concentration, of the volume in which tunnelling is possible, and of the average tunnelling frequency. Spin‐lattice relaxation and EPR, by mixing between the spin state populations, reduce the effect. Application of the theory to experimental values obtained for the luminescence intensity as a function of the applied field in KI, KCI, and KBr yields the average tunnelling frequency (about ten times the radiative probability), the effective range (85 Å), and the absolute value of the luminescent quantum yield.
Diffusion theory of luminescent emission from a doped organic solid
Authors: Selsby R. G. , Swenberg C. E.
Published: July 2007

Using a rate equation for exciton diffusion, with a new theory for the probability per second of exciton capture by impurity traps, the time dependence of the luminescent emission from a doped organic solid for both impurity and host is calculated. The satisfactory agreement of this theory with recent measurements indicates that exclusion of diffusion as the major means of excitation energy transfer is premature.
The optical properties of GaAs:Co
Authors: Baranowski J. M. , Grynberg M. , Magerramov E. M.
Published: July 2007

The absorption due to optical transitions from the valence band to empty cobalt‐acceptor states in GaAs has been investigated. The results are well explained in terms of Lucovsky's model, and the hole ionization energy of 0.14 eV was determined. The crystal‐field spectrum of the 3d7 configuration is observed when the acceptor states are filled by electrons from shallow donors. The experimental results indicate that the acceptor state is due to hole in 3d‐shell of the cobalt impurity on substitutional gallium sites.
Phase transitions in a uniaxial antiferromagnet at low temperatures
Authors: Morozov V. G.
Published: July 2007

Field‐induced phase transitions in a uniaxial antiferromagnet are studied with help of the Green's function method. The critical fields are found for low temperatures and the behaviour of magnetization and susceptibility near the flop para‐transition is investigated.
Frequency distribution function of solid ammonia
Authors: Goyal P. S. , Dasannacharya B. A. , Thaper C. L. , Iyengar P. K.
Published: July 2007

The frequency distribution function, g(ω), for solid ammonia has been derived from neutron inelastic scattering experiments at 106° K. It is used to calculate the specific heat and to analyse it in terms of Debye temperatures for translational and rotational parts. A comparison of the Debye temperatures with those obtained from the measured specific heat shows an excellent agreement up to 100°K, suggesting that the anharmonicity is not large below this temperature. Translational and rotational moments of the frequency distribution function calculated from the obtained g(ω) and the specific heat data are found to agree within about 10%.
Anslysis of piezospectroscopy of defects in wurtzite‐type crystals
Authors: Goede O.
Published: July 2007

A general analysis is made of the effect of uniaxial stress on optical transitions between localized electronic states in wurtzite‐type crystals. The energy shift, the splitting pattern, and the polarization of no‐phonon lines are derived for the different defect symmetries and stress directions. It is shown that the piezospectroscopy of defects in wurtzite‐type crystals enables an unambiguous determination of the symmetry group of the defect and may yield valuable informations on the symmetry of the electronic states involved.
Retardation Effects in the Theory of Sensitized Luminescence in Molecular Crystals
Authors: Golubov S. I. , Konobeev Yu. V.
Published: July 2007

A theory is given of the effective dipole‐dipole interaction between two identical interstitial guest molecules at large intermolecular distances the effects of retardation of the interaction taking into account. The corresponding generalization of the well‐known Förster‐Dexter formula of the electronic excitation energy resonance transfer in solids is found.
The Equilibrium States of the Impurities in the Dynamic Lattice
Authors: Tovstyuk K. D. , Baran S. R. , Rakin G. V.
Published: July 2007

The equilibrium states of two kinds of impurities in semiconductors are studied. At some conditions a jump‐like redistribution of the impurity states has been observed.
Some Thermomagnetic and Adiabatic Effects in Heavily Doped Semiconductors at Low Temperatures for Weak Magnetic Field
Authors: van Cong H. , Mesnard G.
Published: July 2007

Thermomagnetic and adiabatic effects at low temperatures for weak magnetic fields are investigated by a simplified model of heavily doped semiconductors. The treatment is based on the Green's function methods, using the Feynman‐path integral formulation, applied to disordered systems and developed already in six previous papers. Two typical cases concerning the relation between the carrier and donor concentrations are discussed.
The Change of Model Potentials in Alloying
Authors: Taut M. , Paasch G.
Published: July 2007

The different influences giving rise to a change of the screened form factors of model potentials in alloying are discussed. A special problem is the evaluation of the Fermi energy and the energy shift. The method for the calculation of these quantities proposed by Animalu and Heine for pure metals is not applicable to alloys. A new systematic perturbation treatment is developed to evaluate these quantities for pure metals, dilute and ordered alloys. The Shaw model potential is used. Numerical results are given for pure metals and dilute alloys. For the latter a change of the parameters of the bare model potential smaller than 3% is found giving only a small influence on the residual resistivity. This indicates that the assumption that the bare model potential of an ion is nearly independent of its surroundings is quite good. Approximations for the calculation of the change of the depletion hole are investigated also.
Relation of Long‐Range Interatomic Interactions to the Sign and Type of Short‐Range Ordering in Alloys
Authors: Katsnelson A. A.
Published: July 2007

The relation of long‐range interatomic interactions to the sign and type of short‐range order is investigated in alloys. It is found, that sign and type of short‐range order are determined by the spectrum of the ordering energy, which may be obtained from the dependence of the interatomic interaction potential on the distance. It is shown in the approximation of spherical Fermi surfaces, that an electron concentration of n = 1 causes a short‐range ordering of Cu3Au‐type. Both, increasing and decreasing of n give rise to a change of the type and then of the sign of the short‐range order.
Quantum Theory of Free Carrier Absorption
Authors: von Baltz R. , Escher W.
Published: July 2007

The theory of photon absorption by free carriers in degenerate semiconductors is given taking into account the influence of nonparabolic energy bands and the effects of scattering by impurities, phonons, and plasmons. Analytical formulas for the imaginary part of the dielectric function, ϵ2(ω), are derived. The quality of the asymptotic expansions of ϵ2(ω) for low and high photon energies to approximate ϵ2(ω) over a wide range of frequencies is investigated numerically. It is found that within a few percent the classical Drude theory gives an excellent approximation for photon energies up to twice the Fermi energy of the electrons. In the opposite case, the approximation for high photon energies gives a rather poor approximation of ϵ2(ω) near the Fermi energy, except for ionized impurity scattering.
Résonance paramagnétique acoustique de TiO2: Cr irradié
Authors: Boiteux M. , Doussineau P. , Ferry B.
Published: July 2007

Des monocristaux de rutile contenant du chrome et irradiés aux rayons γ ont été étudiés au moyen de la résonance paramagnétique acoustique. La présence de raies dues à l'ion Cr3+ a été établie et deux constantes de couplage spin‐phonon de Cr3+ ont été mesurées: |G44| ≈ 3 cm−1 et |G66| ≈ 7 cm−1. L'attribution de raies supplementaires aux ions Cr2+ et Cr4+ est discutée.
Energy of Screw Dislocations in Metals
Authors: Simon G.
Published: July 2007

The contribution of the band structure energy to the energy of a screw dislocation in a metal is calculated within the framework of pseudopotential theory. The total energy of the dislocation is the sum of the change in electrostatic energy of the point‐ion lattice and the band structure energy. Numerical results are given for the alkali metals using Ashcroft's atom form factors.
Estimation of the Influence of Lattice Resonant Modes on the Nuclear Quadrupole Spin–Lattice Relaxation
Authors: Mühle E.
Published: July 2007

The influence of nonparamagnetic point and line defects in the crystal lattice on the nuclear quadrupole spin‐lattice relaxation is studied. Under the assumption of simple models for defects in a cubic lattice it is shown that lattice resonant modes cause at low temperature an increase of the local relaxation rate around the defects. The efficiency of spin diffusion is estimated. Measurable effects are expected only with relatively high concentrations of defects.
Dissociation of Frenkel Excitons at the Interface between a Molecular Crystal and a Metal
Authors: Killesreiter H. , Baessler H.
Published: July 2007

The first part of the paper deals with the non‐radiative decay modes of n π* triplet excitons at the interface between a p‐chloranil crystal and an aluminum contact studied by means of extrinsic photocurrents. Utilizing the technique of inserting fatty acid mono‐layers between crystal and metal, which allows variation of the interaction distance, it is shown (i) that the dominant exciton decay process is a fast charge transfer reaction and (ii) that its rate constant decreases exponentially with increasing reaction distance. In the second part of the paper a model is presented to treat exciton dissociation processes at a metal surface in general. It is based on the concept of configuration interaction between the bound molecular exciton state and a continuum of ionized states.
Spatial Charge Displaced by Impurity Scattering: T‐Matrix Approach
Authors: Brereton M. G.
Published: July 2007

The spatial charge displaced by an impurity is calculated using the T‐matrix formalism together with the aid of Green's function theory. For a certain class of T‐matrices an exact result, which explicitly obeys the Friedel sum rule is obtained. In other cases it represents an improved preasymptotic form.
Calculation of the Structural Energy of the Intermetallie Compound MgIn
Authors: Mrosan E. , John W. , Eschrig H.
Published: July 2007

The crystalline structure of the intermetallic compound MgIn is studied using pseudopotentials and perturbation theory. The potential is obtained from Shaw's non‐local model potential of the pure metals Mg and In recalculated for the changed model potential parameters and for the changed electron density of the compound. The c/a ratio for the L10 phase of MgIn is calculated. Conditions for the appearance of a long‐periodic superlattice like in the system CuAu are studied.
Formalism of the Rhombic Spin Hamiltonian with S = 2 and Its Application to EPR Spectra of Copper Aggregates in TGFB: Cu2+
Authors: Maćkowiak M. , Kurzyński M.
Published: July 2007

The properties of the spin Hamiltonian for S = 2 in a crystal field of rhombic symmetry are analysed up to terms with a, b, c proportional to the fourth power of spin operators, and a method for the determination of constants of this Hamiltonian is proposed. By perturbation calculation, the parameters a, b, c are shown to affect very strongly the anisotropy of the EPR spectrum; in certain directions, they can lead to new extrema in the graphs of EPR spectrum anisotropy. The results are applied to the description of the EPR spectrum of copper aggregates in TGFB. The spin Hamiltonian parameters are determined, and the spin level energies are given as function of the magnetic field strength. Full agreement with the experimental data is achieved showing, in conjunction with other data in reference [8], that in Cu2+‐ion‐admixtured TGFB there are present four‐ion copper complexes with spin S = 2 coupled by exchange interaction.
Experimental Study of Surface Optical Modes in Ionic Crystal Slabs
Authors: Bryksin V. V. , Gerbstein Yu. M. , Mirlin D. N.
Published: July 2007

Surface optical vibrations have been revealed and investigated in slabs of a number of alkali halide crystals and crystals of CaF2 and CdF2. The measurements were carried out by the attenuated total reflection technique. The frequency dependence of reflection coefficient has been calculated in accordance with the experimental set‐up. For NaCl and CaF2 crystals dispersion curves of the surface modes have been measured at room and liquid nitrogen temperatures. The comparison of experimental and calculated data shows that the anharmonic term of the dielectric constant should be taken into account in the calculation of the surface modes.
Isotropic Limiting Behaviour of the Six‐Dimensional Formalism of Anisotropic Dislocation Theory and Anisotropic Green's Function Theory.ii. Perturbation Theory on the Isotropic N‐Matrix
Authors: Nishioka K. , Lothe J.
Published: July 2007

Perturbation expansions in terms of the deviation from isotropy are developed for the eigenvalues and eigenvectors of the N‐matrix, which appears in the six‐dimensional formalism for anisotropic dislocation theory and anisotropic Green's function. The strongly degenerate behaviour in the limit of isotropy is elucidated. It is shown that divergent terms in fact cancel among themselves in certain sums to leave well‐behaved isotropic limits. It was necessary to develop a perturbation method applicable to a non‐semisimple matrix.
Optical Generation of Charge Carriers in Solid and Liquid Benzene (C6H6)
Authors: Hirth H.
Published: July 2007

Free electrons and holes have been generated optically near one electrode via exciton states. At high excitation strengths the charge is proportional to the square of the illumination. At low excitation levels it is proportional to the illumination. In solid benzene the quadratic process dominates. Approaching the melting point this process decreases. At the melting point and in the liquid only the linear process remains. The dependence of these two processes has been investigated as a function of the electric field and the temperature. The quadratic process can be explained by a mutual annihilation of two excitons in the bulk of the material and the linear process by an Auger type recombination of an exeiton at the surface.
Crystal Field Theory of Magnetic Anisotropy of RbNiF3
Authors: Jäger E.
Published: July 2007

Basing on crystal field theory the constants K1 and K2 of the magnetocrystalline anisotropy and the anisotropy of magnetization of RbNiF3 are calculated. The coupling of the spins to the crystal field via spin‐orbit coupling is responsible for the magnetic anisotropy, the interaction of the spins is treated in the molecular field approximation. Using experimental values of the splitting in cubic crystal fields, 10 Dq, of the spin‐orbit coupling constant λ, and of the molecular field Hex the calculated values of K1 and K2 at T = 0 K agree with the experimental ones up to a factor two. The influence of the parameters 10 Dq, λ, Hex, and the splitting in the trigonal crystal field, 3 r, on K1 and K2 is discussed.
On the Dispersion Relation of Holes in Bismuth
Authors: Dittmann H. , Herrmann R.
Published: July 2007

From the known change of energy band structure of bismuth and bismuth‐antimony alloys Bi1−xSbx under hydrostatic pressure the dependence of carrier concentration on the Fermi energy of holes is calculated. This dependece points to a non‐parabolic dispersion relation of holes.
LCAO Energies and Wave Functions in a Covalent Semiconductor with Topological Disorder
Authors: Hulin M.
Published: July 2007

The free electron model is used as a guide for an algebraic transformation of the LCAO Hamiltonian for a semiconducting material which exhibits topological disorder. The energies and wave functions are obtained in terms of the eigenvalues and eigenvectors of the “connectivity matrix” previously introduced.
Compression‐Induced Magnetic Anisotropy and Superlattice Dislocation in Long‐Range‐Ordered Iron‐Aluminium Alloys
Authors: Takahashi S.
Published: July 2007

Magnetic anisotropy induced by plastic deformation in Fe3Al is calculated for various types of dislocations in the DO3 and B2 superlattices on the basis of the slip‐induced directional order. It is found that the induced magnetic anisotropy depends largely upon the dislocation density, its configuration, and state of order; also, it is found that the direction of easy magnetization in the DO3 long ‐ range ‐ordered superlattice is that of hard magnetization in the B2 long‐range‐ordered superlattice for the same slip systems. Further, it is shown that the magnitude of the induced magnetic anisotropy is about 105 to 105 erg/cm3 for usual deformation when the individual dislocation distributes independently.
Hyperfine Field at Rh Nuclei in Fe‐Rh Alloys
Authors: Keszthelyi L. , Demeter I. , Szőkefalvi‐nagy Z. , Varga L. , Mezei G.
Published: July 2007

The concentration dependence of the hyperfine field at Rhnuclei in Fe‐Rh alloys measured after Coulomb excitation deviates from the concentration dependence measured by NMR method. In the case of Fe51.5Rh48.5 alloy the field was observed to decrease exponentially with the irradiation dose. Both effects may be understood in terms of radiation damage theory.
Hartree‐Fock Band Structure of Alkali Fluorides and Chlorides
Authors: Perrot F.
Published: July 2007

The APWHF method, previously described and used in solid neon and argon is applied to the calculation of the Hartree‐Fock band structure of alkali fluorides (LiF, NaF, and KF) and chlorides (LiCI, NaCl, and KCl). The important polarization effects are then taken into account and the calculations are repeated for the conduction band, including an additional potential which is an extension to solid of Mittleman's polarization potential. The correlation effects lead to a constant shift of the valence band. The optical gaps obtained from these energy band calculations are in good agreement with experiment. Some other band‐to‐band transitions are compared with previous theoretical results and experimental data.
The Strak Effect of M and N Color Centers in Alkali Halides
Authors: Dewerd L. A.
Published: July 2007

The Stark effect of the M center in LiF, KCl, and NaCl and of the N centers in KCl and NaCl was measured with an alternating electric field along the 〈100〉 direction. The data for the Stark effect of the M band were analyzed to find the difference in energy of two mixing nondegenerate energy levels of opposite parity and to find the matrix element between these two energy levels when the electric field was applied. Measurements of the Stark effect for the N centers in KCl and NaCl were resolved into two components representing contributions from the N1 and N2 centers.
Symmetrische verallgemeinerte Wannierfunktione. I. Definition und Grundlagen
Authors: Krüger E.
Published: July 2007

Einer beliebigen abgeschlossenen Bandgruppe, die aus v miteinander entarteten Bändern bestehe, werden v verallgemeinerte Wannierfunktionen zugeordnet, die nach einer Darstellung der Punktgruppe des Kristalls transformiert werden und optimal lokalisiert sind. Es wird untersucht, wie weit die Struktur der verallgemeinerten Wannierfunktionen durch die Symmetrie des Kristalls und das Symmetrieverhalten der Blochfuktionen, die zu der betrachteten Bandgruppe gehören, bestimmt wird. Insbesondere wird gezeigt, daß durch den Symmetrietyp der Bandgruppe das Symmetrieverhalten der verallgemeinerten Wannierfunktionen und ihr Symmetriemittelpunkt festgelegt wird.
Thermal Conductivity and Poiseuille Flow of Phonons in Dielectric Films and Plates
Authors: Bausch W.
Published: July 2007

By an extension of the Callaway ansatz for the solution of the Boltzmann equation it is possible to calculate the phonon thermal conductivity of thin layers and plates for all values of combined relaxation time to thickness, in particular also for the region of Poiseuille flow of phonons. The integral equation for λ, the parameter that describes the drifting phonon distribution that results from the normal processes, is solved approximately. The model is applied to NaF and 7LiF of various thicknesses, impurity concentrations, and dislocation densities and it can be shown that the phonon interaction in NaF is probably too weak to make the observation of Poiseuille flow possible. In plates of LiF there is a distinct maximum for thicknesses greater 0.5 cm which is suppressed by 6Li concentrations > 0.1% or dislocation densities > 5 × 105cm−2. Measurements on thin plates allow the investigation of scattering processes at such temperatures where boundary scattering prevails for quadratic samples.
Effect of Electron Exchange Interactions on Nuclear Relaxation
Authors: Buishvili L. L. , Kh. Khalvashi E.
Published: July 2007

Nuclear relaxation is considered taking into account electron exchange interaction. An expression for the nuclear relaxation rate is obtained and it is shown that at exact resonance EPR saturation can produce NMR saturation under specified conditions.
Exact Treatment of the Coupled Coherent and Incoherent Motion of Triplet Excitons and Its Influence on the Lineshape of ESR
Authors: Reineker P.
Published: July 2007

The motion of excitons is considered by a stochastic model comprising both its coherent and incoherent motion. The coherent motion is determined by the exchange interaction integral J whereas the incoherent motion is described by the strengths of local (γ0) and non‐local (γ1) fluctuations. The spin motion is described by the usual spin Hamiltonian of two differently oriented molecules. The equation of motion of the density matrix of the system is solved and the lineshapes of ESR are calculated for several sets of the above parameters by computer calculation. Especially, it is shown that the coherent motion too may lead to a single absorption line as previously obtained for incoherent exciton motion. Furtheron, it is inferred that the transition from coherent to incoherent exciton motion is determined mainly by the ratio of γ0 and J and that γ1 is a decisive quantity in the transition from the broadening of one or several ESR lines to the narrowing of a single line.
Hole Transport in Polar Semiconductors
Authors: Costato M. , Jacoboni C. , Reggiani L.
Published: July 2007

The transport properties of holes in cubic semiconductors have been studied with a Monte Carlo technique taking into account polar scattering within and between the two valence bands degenerate at K = 0. The predominant p‐like symmetry of the valence band wave functions has been found to enhunce the polar ohmic mobility of about a factor two with respect to the case in which it is neglected. The comparison between theoretical results and experimental data evidences the dominant importance of polar scattering mechanism for a typical II‐VI compound (CdTe)in the region of temperatures between 100 and 400 °K. On the contrary, this scattering mechanism alone cannot explain the low field transport of a typical III‐V compound (GaAs) in the same temperature range, according to its lower ionicity.
Pair Interaction and Magnetic Relaxation of Yb3+ ion YasO4
Authors: Kalbfleisch H. , Kumberg H. , Müller‐vogt G. , Stengel M.
Published: July 2007

Using an EFP absorption spectrometer the pair interaction of Yb3+ ions was stukdied in YAsO4 crystals. Also an investigation of the relaxation behaviour was performed concerning with the temperature and angular dependence of hte relaxation times of the isolated ions. The relaxation is partially affected by cross relaxation between the single ions and the Yb3+ ion pairs. The direct process at the lowest temperatures is bottlenecked.
Symmetrische verallgemeinerte Wannierfunktionen. II. Eigenschaften und Beispiele ‐ Bandstruktur des Germaniums
Authors: Krüger E.
Published: July 2007

Ausgehend von der Symmetrie des Kristalls und dem Symmetrieverhalten der Blochfunktionen einer beliebigen abgeschlossenen Bandgruppe werden die Eigenschaften der zugehörigen verallgemeinerten Wannierfunktionen untersucht. An einigen Beispielen in einem Kristall mit kubisch‐flächenzentriertem Gitter ‐ insbesondere an der Bandstruktur des Germaniums ‐ wird gezeigt, wie man ihr Symmetrieverhalten und ihren Symmetrie‐mittelpunkt bestimmen kann.
Thermal Expansion of a Linear Lattice
Authors: Ninio F. , Oitmaa J.
Published: July 2007

If the thermal expansion of a lattice with periodic boundary conditions is calculated exactly, the result is zero. An expression is derived for the thermal expansion is of a monatomic linear chain with free ends using the exact normal modes and it is shown that this result may be reproduced to thermodynamic accuracy by using at some stage of the calculation, normal modes appropriste to a periodic chain.
Ginzburg‐Landau‐Parameter x1(T) und x2 (T) in der Nähe von 1/√2
Authors: Kumpf U.
Published: July 2007

Anhand von Magnetisierungsmessungen an Pb‐TI‐Einkristallen mit 0,572 ≦ x ≦ 0,948 wurde die Temperaturabhängigkeit der verallgemeinerten Ginzburg‐Landau‐Parameter x1 (T) und x2 (T) untersucht. Dabei ergibt sich beim Übergang vom Supraleiter I. Art zum Supraleiter 2. Art für T < Tc eine Diskrepanz zwischen x1 (T). Die Temperatur abhängigkeit von x1 (T) und x2 (T) in der Nähe der Übergangstemperatur Tc wird mit den Beziehungen aus der Neumann‐Tewordt‐Theorie verglichen.
Jahn‐Teller Theory of the Ti3+ Ion in Corundum
Authors: Rai R.
Published: July 2007

The apparent reductions in the trigonal field and spin‐orbit interactions in Ti3+ ion doped in Al2O3 is explained to be due to the presence of a moderate Jahn‐Teller effect. The spin‐orbit, trigonal field, and a part of the Jahn‐Teller interaction which causes three equivalent oscillations along the three pseudo‐fourfold axes of the complex, are treated on equal footing. The effect of the tunnelling through the potential barriers between these equivalent oscillations is considered as a perturbation. The resulting ground wave functions are used to calculate the EPR g‐values. The theoretical values are compared with the experimental magnetic and spectroscopic results.
Non‐Even Dependence of Conductivity of Hot Electrons on Magnetic Field Strength in Many‐Valley Semiconductors
Authors: Asche M. , Sarbei O. G. , Savyalov Yu. G.
Published: July 2007

The transverse magnetoresistivity of n‐Si with different impurity densities was investigated theoretically and experimentally for a nonsymmetrical orientation of the current in strong electric fields. The experimental results for the linear change of conductivity with respect to the magnetic field are compared with numerical data and qualitative agreement is shown.