bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamics of Aluminium‐ and Magnesium‐Base Interstitial Solutions I. Analysis of Interaction Parameters
Authors: Bogdanov V. I. , Mikhailov A. V. , Fuks D. L.
Published: July 2007

The pseudopotential method is used to calculate first‐ and second‐order interaction parameters in f.c.c. and h.c.p. interstitial solutions of aluminium and magnesium alloys. Values calculated of interaction parameters are used for an estimation of the series convergence for the logarithm of the boron and carbon activity coefficient. The results show that the series convergence depends, to a great extent, on the selection of the alloying element and its concentration.
On the Theory of Isostructural Phase Transitions in Crystals
Authors: Schneider V. E. , Tornau E. E.
Published: July 2007

The thermodynamics of two types of isostructural phase transitions (IPT) is investigated in the framework of the Mitsui model using the molecular field approximation. The first type of IPT is obtained including four‐particle interaction members into the Hamiltonian. The consideration dealing with the temperature dependence of the asymmetry parameter explains IPT of the second type. It is shown that the maximum of dielectric constant may appear either in the point of IPT or above it. The investigation carried out gives a qualitative explanation of the experimental facts in numerous crystals undergoing IPT.
Isomerization and Disorder of Polyacetylene Induced by Doping
Authors: Schügerl B. , Kuzmany H.
Published: July 2007

Raman scattering experiments are reported for cis‐(CH)x and cis‐(CD)x doped with AsF5 in a concentration range between 3 and 13%. The typical cis‐lines in the spectrum decreased with increasing doping concentration until they disappear completely at around 8%. Simultaneously the non‐resonant trans‐line at 1291 cm−1 is observed to increase and a special high‐frequency mode develops around 1590 cm−1. From the experimental results it is shown that the generation of disorder and isomerization by doping is a general phenomenon. A strong increase of the scattering cross‐section observed for red laser light for the heavily doped material is correlated to a band gap closure.
Light Scattering by the Surface Wake
Authors: Kamohara I. , Ohtsuki Y. H.
Published: July 2007

Light scattering by the surface wake induced by ions moving near the solid surface is studied theoretically. It is shown that soft X‐rays scattered by surface wake present very characteristic angular and energy distribution. The detectability of this effect is estimated in the case of synchrotron radiation.
Dynamical Properties of Excitons in Layer Crystals of PbI2
Authors: Brodin M. S. , Blonskii I. V. , Nitsovich B. M. , Krochuk A. S. , Franiv A. V.
Published: July 2007

Experimental studies of the temperature shift and halfwidth of the exciton absorption band in pure and intercalated PbI2 single crystals are performed. The exciton–phonon interaction feature are revealed, namely the highly effective scattering of excitons on the bending vibrations of the layer.
Elastic Field and Self‐Force of Dislocations Emerging at the Free Surfaces of an Anisotropic Halfspace
Authors: Lothe J. , Indenbom V. L. , Chamrov V. A.
Published: July 2007

The problem of dislocations emerging at free surfaces is considered. This complicated threedimensional elastic problem can be reduced to a superposition of two‐dimensional fields of infinite straight dislocations which are well defined. A plane fan‐shaped distribution of infinite straight dislocations is introduced which replaces the condition of a free surface. This allows one to construct the whole elastic field of inclined dislocations in the anisotropic halfspace. As an example of the suggested method the formula for the self‐force acting on dislocations emerging at a free surface is obtained. The connection of self‐moments acting on dislocations with the orientational dependence of the dislocation energy is discussed.
Phonon Scattering in Plastically Deformed Ge
Authors: Singh S. R. , Singh S.
Published: July 2007

The measurements of Sato and Sumino on the low temperature phonon conductivity of plastically deformed germanium single crystals are analysed quantitatively using a cooperative model for the scattering of phonons by static and vibrating dislocations. The discrepancies observed between the experimental and theoretical results around 20 and below 2.2 K are resolved by considering the scattering of phonons by dislocation induced point defects and by modifying the value of phonon scattering by crystal boundaries, respectively.
Chemical Shifts of Auger Lines in Solids on the Example of the KL23L23 Transition in Silicon and Its Compounds
Authors: Fellenberg R. , Streubel P. , Meisel A.
Published: July 2007

The line position of the Si KL23L23 Auger transition is measured in silicon, silicon carbide, silicon nitride, silicon dioxide, and sodium hexafluorosilicate. The chemical shifts with reference to silicon are estimated and compared with the corresponding shifts of photoelectron peaks of Si 1s and Si 2p. The change of the extra‐atomic static relaxation energy ΔRsea determined in this way is proportional in first approximation to Pauling's electronegativity. The described method makes possible to estimate parameters of bonding in atomic ranges in solids containing silicon.
Relaxation of Interband Disturbances. A Phenomenological Theory
Authors: Allen P. B.
Published: July 2007

A recent phenomenological theory of Garik and Ashcroft (GA) is generalized to permit interband electron–hole pairs to couple to intraband pairs. The enlarged theory differs in important respects from GA theory and corresponds closely to the microscopic theory of Chakraborty and Allen. The theory is explicitly solved for σ(ω), and the corrections to Boltzmann dc transport are discussed. The new theory has an additional parameter, the phase of the interband–intraband coupling constant η, which cannot be eliminated a priori.
Carrier Statistics in Zero‐Gap Semiconductors in the Presence of a Quantizing Magnetic Field
Authors: Chakravarti A. N. , Ghatak K. P. , Rao G. B. , Ghosh K. K.
Published: July 2007

An attempt is made to formulate the carrier statistics in zero‐gap semiconductors in the presence of a quantizing magnetic field. Numerical computations are done taking n‐HgTe as an example. It is concluded that the electron–electron interactions significantly affect the carrier statistics in such semiconductors, particularly at relatively low values of the electron concentration, i.e. under pure and lightly doped conditions at relatively low values of the temperature.
An Interatomic Pair Potential for Aluminium Calculation of Stacking Fault Energy
Authors: Rautioaho R. H.
Published: July 2007

A potential function for aluminium is derived from phonon dispersion curves. The contribution from short‐range multi‐ion interactions is substracted from the phonon data, and this affects markedly the short‐range characteristics of the potential. The potential function is used for the calculation of the energies of intrinsic and extrinsic stacking faults. Certain multi‐ion contributions to these energies are also evaluated. The calculation cannot explain the experimentally observed difference between γintr and γextr, which is attributed here to the interpretation of loop annealing observations in such faults. A re‐interpretation gives approximately 120 mJ/m2 for γintr and γextr.
ESR and Optical Absorption Studies of ClO3 in Ba(ClO4)2 · 3H2O Single Crystals
Authors: Sastry D. L. , Rama Rao K. V. S.
Published: July 2007

The ClO3 radical observed in γ‐irradiated Ba(ClO4)2 · 3 H2O is studied by ESR and optical absorption techniques. The radical orientation and stability with increased irradiation and thermal and UV light bleaching are discussed. A temperature variation study by ESR reveals that there is an increase of 13.8% and a decrease of 4% in the chlorine p‐orbital and s‐orbital spin densities, respectively, when the temperature is lowered from 300 to 77 K. A comparison of the results obtained for ClO3 with the other iso‐electronic trioxide radicals shows that the maximum fractional change in the spin densities occurs in the case of ClO3 and that these changes depend on the electronegativity of the central atom.
Electron Transport in a Magnetic Field
Authors: Gerlach E. , Harbecke B.
Published: July 2007

Lindhard's dielectric function is discussed and displayed for an electron gas in an external magnetic field. Using these results the energy loss method is applied to calculate the dynamical resistivity in the quantum limit assuming scattering by ionized impurities. For a degenerate electron system at T = 0 a finite transverse resistivity is found whereas for a nondegenerate one a divergency is obtained.
The Coherence Description of the Dynamical X‐Ray Diffraction from Randomly Disordered Crystals II. Some Numerical Results
Authors: Holý V.
Published: July 2007

The mutual coherence approach to the problem of the dynamical X‐ray diffraction from crystals with randomly distributed microdefects is applied to crystals with small amorphous regions. The rocking curves of such crystals are computed for various diameters of these regions. It is shown that the differences in the results of this theory and the usual kinematical theory of diffusion scattering are not negligible even in the vicinity of the Bragg maximum of the rocking curve. It is shown that the coherence approach to the X‐ray diffraction can give useful results also in the case of diffraction from randomly disordered crystals.
Conduction Processes in High Acceptor Concentration HgTe
Authors: Lombos B. A. , Averous M. , Fau C. , Calas J.
Published: July 2007

The effects of vacancy induced acceptors in zero gap semiconductors, like in HgTe, are treated by the resonant state theory. First, one scattering center is considered, then multiple scattering is developed in the case of acceptor concentrations up to 1 × 1022 m−3. In this investigation the effects of even higher acceptor concentrations (N ≥ 1 × 1023 m−3) are elucidated. It is shown that in this case the resonant state model is no longer applicable since the randomly distributed impurities result in a fluctuating potential field. Thus the impurity disorder introduces an Anderson type conduction process. This is characterized by a large change in the mobility when the Fermi level goes through the acceptor band. These mobilities, related to the Anderson type conduction mechanisms, are in good agreement with the experimentally determined ones in the case of HgTe. While using the resonant state theory, the predicted mobilities are not in satisfactory agreement with the measured ones in the high acceptor concentration range analyzed in this investigation.
Spectral Point Schemes for Evaluating the Expansion Coefficients of State Densities into Orthogonal Functions
Authors: Pisani C. , Ugliengo P.
Published: July 2007

An expansion technique for calculating densities of states (DOS) of crystalline systems previously presented is here tested by evaluating numerically the expansion coefficients. To this purpose, existing special point schemes for Brillouin zone integrations are critically compared. It is shown that schemes where the sampling points are arranged according to a commensurate net are of unpaired efficiency for cubic systems. Very efficient sets of sampling points are also easily generated owing a closed diophantine technique, which can become competitive when lower‐symmetry crystals are considered. The DOS of one of the d‐bands of tight‐binding cubic systems is chosen to test the quality of the results obtained using Legendre polynomials and trigonometric functions as orthogonal sets. 220 sampling points are used to evaluate 16 expansion coefficients; the reconstructed curves are affected by an average relative error of about 4% over the whole band interval. As few as six expansion terms provide an estimate of the position of the Fermi level with an error within 1% of the band interval.
On the Theory of Nonlinear Cyclotron Resonance
Authors: Kopasov A. P. , Molkov I. N.
Published: July 2007

The generation of the second harmonic (SH) of an electromagnetic wave in a conductor in a constant magnetic field parallel to its surface, is studied under the anomalous skin effect. Absolutely diffuse as well as almost diffuse reflection of electrons by the surface is considered. The last case takes account of the growth in the specularity degree of reflection when the angle of electron incidence is ψ → π/2. It is shown that at almost diffuse reflection, the amplitude of the reflected SH can more highly increase in even resonance ω = l'extr (ω is the wave frequency, Ωextr is the extreme value of cyclotron frequency Ω, l is an integer) than in odd one ω = (l + 1/2) Ωextr, just as observed for bismuth.
EPR of Copper‐Doped (NH4)2C2O4 · H2O Single Crystals
Authors: Korkmaz M. , Korkmaz Ö. , Kospançali S.
Published: July 2007

EPR studies are made on Cu2+‐doped ammonium oxalate monohydrate. Two Cu2+ lattice sites, Cu2+ (I) and Cu2+ (II), are identified. These sites exhibit two sets of four hyperfine lines in all directions except some special directions. The g‐factors and the hyperfine splittings are calculated for both Cu2+ ions which enter into the substitutional NH4+ sites in the lattice. The spectra for Cu2+ (I) and Cu2+ (II) lattice sites are found to have intensities in the ratio 1:1 suggesting non preferential occupation of the positions by the Cu2+ ions.
The Dielectric Response of a Charge Density Wave (CDW) Distorted Electron–Phonon System in the Precritical Region I. The Self‐Consistent Method
Authors: Heiner E.
Published: July 2007

A self‐consistent method is presented, in order to calculate the precritical behaviour of a quasionedimensional electron–phonon system above the Peierls transition temperatureTp.
Energy of the Exciton–Ionized Donor Complex in Anisotropic Semiconductors
Authors: Stauffer L. , Munschy G.
Published: July 2007

For the problem of the anisotropic exciton–ionized donor complex, the wave function is written as a linear combination of products of distance and angle functions. The unknown distance functions are expanded in terms of given radial basis functions and are determined by means of variational calculations. The presented results concern the energy eigenvalue of the complex as a function of the anisotropy parameters and of the electron to hole effective mass ratio.
Thermoluminescence of NaF:Ca2+ Single Crystals
Authors: Bhan S.
Published: July 2007

Thermoluminescence (TL) of NaF:Ca2+ single crystals after room‐temperature γ‐ray irradiation exhibits six glow peaks at 75, 114, 128, 160, 240, and 290 °C. The 75 and 240 °C peaks are assigned to hole centres; the 114 and 290 °C peaks are attributed to F and F centres, respectively. Involvement of Ca2+ aggregates is suggested in the origin of the 160 °C peak. The origin of the 128 °C peak is explained by assuming the presence of di‐interstitials. It is inferred that F centres are created, even prior to optical bleaching of F centres, to some extent during γ‐ray irradiation. It is also found that on re‐irradiation of the samples containing F centres, these F centres are destroyed. TL spectra show two bands at 420 to 450 and 580 nm. Photoluminescence spectra also show two bands at 450 and 580 nm.
Fourth‐Order Elastic Constant, C1111, of Cubic Crystals
Authors: Prasad O. H. , Suryanarayana M.
Published: July 2007

A method for the evaluation of C1111, the fourth‐order elastic constant of the octahedral class of cubic crystals is being suggested which does not involve measurements on crystals using uniaxial stress. Values of C1111 of twenty six cubic crystals are evaluated at room temperature and also at some lower temperatures in seven cubic crystals, namely NaCl, KCl, RbCl, RbBr, RbI, Ge, and Si.
Radiative Decay of Surface Collective Excitations in Polarizable Cylinders
Authors: Burmistrova O. P. , Kosobukin V. A.
Published: July 2007

The dispersion relation and the quantized electrostatic potential are considered for surface collective excitations (SCE, i.e. plasmons and optical phonons) in circular cylinders with frequency dispersion. The operator of potential is used to calculate the matrix elements for the interaction Hamiltonians describing light emission by SCE decaying and also the processes of inelastic scattering of photons and electrons by SCE. The cross sections are derived for the processes of the first and second order relative to the above interaction Hamiltonians, resulting in the emission of a photon at the SCE frequency.
Ionic Thermal Currents under Uniaxial Stress A New Method to Determine Electric and Elastic Dipole Properties
Authors: Siu Li M. , De Souza M. , Kapphan S. E.
Published: July 2007

The method of thermally stimulated depolarization (ITC) is expanded to allow the determination of elastic dipole properties. During sample polarization by the electric field a uniaxial stress is applied simultaneously (mostly parallel to it for practical reasons). Depending on the shape of the elastic dipole associated with the reorienting electric dipole, the total polarization will be either enhanced or reduced by the elastic dipoles being turned either parallel or perpendicular to the stress direction. The change of polarization (i.e. integrated ITC signal) for stress applied in several crystalline directions, yields additional information about the equilibrium orientation and stress splitting coefficients of the dipoles. This novel procedure is tested with a dipolar system known to exhibit a well defined ITC peak at about 25 K, off‐center Ag+ in RbI. The results for the first time reveal clearly the elongated ellipsoidal (cigar‐shaped) form of the elastic distortion around this dipolar center. The question of equilibrium orientation, however, must remain open since both, a <111> and a restricted <110> (90° transitions only) off‐center model, suggested in recent elasto‐optic work by Lüty et al., allow a good fit of the available experimental data.
Transition Temperature for Effective Field Ising Systems
Authors: Silva P. R. , Sábarreto F. C.
Published: July 2007

Starting from Callen's exact relation for the Ising Model the transition temperature of different lattices is calculated within an effective‐field‐type treatment. The method treats the spins of the same cluster on different footing. The results for the transition temperature are shown to be better than other effective‐field calculations.
On the Theory of Acoustic Properties of Many‐Domain Ferromagnets
Authors: Mitsek A. I. , Sirota D. I. , Kolmakova N. P.
Published: July 2007

The interaction of a sound wave and a movable domain structure which appears near orientational phase transitions of the first‐order type is considered. The viscous friction is taken into account. The wavelength is considered as being comparable with the domain structure period. The spectrum of magnetoelastic oscillations is calculated, it has a zone character. The evolution of the spectrum branches is investigated when the natural frequency of the domain wall oscillations changes. The attenuation and reflection of sound waves caused by the redistribution of energy between the direct and reverse waves are studied.
Calculation Model for Valence Electrons and Hydrogen Concentration in a‐Si:H
Authors: Ance C. , Ferraton J. P. , Berger J. M. , de Chelle F.
Published: July 2007

A simple model is developped to relate the valence electron number to the dispersion energy Ed and the static dielectric constant ϵ(0). This model is applied to hydrogenated amorphous silicon films prepared by glow discharge decomposition of silane. It is shown that the variation of valence electron number and anion valency explain the variation of the dispersion energy. This model allows to determine the hydrogen concentration in a‐Si:H films from two spectroscopic parameters Ed and ϵ(0).
Investigations of the Photovoltaic Tensor in Doped LiNbO3
Authors: Festl H. G. , Hertel P. , Krätzig E. , von Baltz R.
Published: July 2007

The photovoltaic current density in crystals without a center of symmetry depends bilinearly on the components of the light polarization vector via a third‐rank tensor. For LiNbO3:Fe and LiNbO3: Cu the tensor properties are confirmed and three of the four non‐vanishing components determined. The dependence on impurity concentration and on photon energy is also investigated.
Specific Heat Anomaly Connected with a High‐Spin–Low‐Spin Transition in Metallic MnAs1−xPx Crystals
Authors: Krokoszinski H.‐J. , Santandrea C. , Gmelin E. , Bärner K.
Published: July 2007

Peaks in the specific heat of ≦ 4 R are observed in metallic conducting MnAs1–xPx crystals with 0.03 ≦ x ≦ 0.13 above the magnetic ordering temperatures and are attributed to high‐spin–low‐spin transitions. This suggests a strong local character for the spin moments and would contradict spin‐polarized extended d‐electron states.
A Proof of Aspherical Valence Charge Parts in the Rock‐Salt Structure Compounds by Means of an X‐ray Bond Charge Model
Authors: Pietsch U.
Published: July 2007

The aspherical valence charge parts are deduced for the rock‐salt structure compounds NaF and MgO by means of a bond charge (BC) model. The valence charge density is described by spherical atoms and an additional particle near the anions in the 〈100〉 directions. The BC amount is smaller according to the dielectric theory, but the other parmeters as position and extension follow its tendency. The anharmonic core vibrations of atoms, the asphericity of the bond charge and its dynamical properties are essential for the zincblende to rock‐salt phase transition.
Influence of Resonance Tunneling on Resistivity in Semiconductors With Ionized Impurities and on Tunneling Current Between Superconductors
Authors: Takács S. , Janetka I.
Published: July 2007

The general results for tunneling of electrons through the system barrier—well—barrier (double barrier, DB) are used to show the importance of resonance tunneling in semiconductors and superconductors. The transmission time for electrons through the double barrier, as well as the transition time between “free” states of the incoming particle and the “bound” states of the well are calculated for determining the trapping probability of electrons by ionized impurities in semiconductors. It is shown that the temperature and electric field dependence of this trapping probability has maxima, which lead to negative resistance effects due to changing the conduction electron concentration. The tunneling current between two superconductors separated by double Schottky barrier (DSB) is derived in the WKB approximation and its dependence on the applied voltage is numerically calculated for a Pb—CdS—Pb system at various temperatures. It is shown that sharp changes of the tunneling current can be detected not only at V = 2Δ (Δ energy gap of the superconductor) but also at higher voltages due to the resonance tunneling effect. These “steps” can be used for very precise measuring the temperature or magnetic field dependence of the energy gap, as well as of some parameters of the Schottky barrier.
Lattice Vibrations of Alkaline‐Earth Hydride‐Fluoride Mixed Crystals Determined from Infrared Spectroscopy
Authors: Vergnat‐Grandjean D. , Vergnat P. , Brice J.‐F.
Published: July 2007

Solid solutions of composition MF2–xHx (M = Ca, Sr, Ba) crystallize in CaF2‐type cubic symmetry. The infrared spectra (100 to 4000 cm−1) give informations about the distribution of the H− ions in tetrahedral sites and confirm the character of mixed crystals with a two‐optical‐mode behaviour: the H− ion localized vibration and the fundamental TO mode. Studies of the absorption spectra as a function of x show MF2 clusters with a low H− concentration — the mean value of which is evaluated — and therefore the existence of cubic MH2 clusters — the transverse optical mode of which is determined.
Electron—Phonon Interaction in Disordered Transition Metal Alloys
Authors: Wysokiński K. I. , Kuzemsky A. L.
Published: July 2007

The Hamiltonian of the electron‐phonon interaction is derived and applied to the description of disordered transition metal alloys. The coupled set of equations for the electron and phonon Green functions is derived with the help of the equation‐of‐motion technique. Neglecting the vertex corrections in the self‐energy operators the closed self‐consistent system of equations is obtained. The relevant configurational averaging is performed in the framework of the CPA. The electronic specific heat in the low‐temperature limit is calculated.
Faraday Effect in III— VI Layer Compounds
Authors: Gavaleshko N. P. , Lyakhovich A. N. , Vatamanyuk P. P. , Savchuk A. I.
Published: July 2007

The Faraday effect is investigated in fields up to 20 T and at temperatures from 77 to 300 K applied to the layer semiconductors GaS, GaSe, and InSe. As an example applicable to the InSe crystals, it is shown possible to separate the direct and indirect forbidden transitions both contributing to the Faraday rotation (FR). The oscillatory nature of the FR spectrum at lower temperatures is proved to be due to the exciton contribution. This is the original report about the FR observed in the depth of the fundamental absorption of InSe crystals. The linearity of the FR in the magnetic field is shown to hold for all the compounds under consideration up to 20 T. The observed data are analyzed in order to estimate some band and exciton parameters of the III—VI semiconductors.
On the Theory of Conductivity of Disordered Semiconductors
Authors: Bonch‐Bruevich V. L. , Nguyet To Thi Bich
Published: July 2007

The temperature dependences of the conductivity and mobility of delocalized carriers is calculated in terms of the critical indices describing the behaviour of the energy‐dependent conductivity. Results suggest a possibility to obtain both the indices and the minimum metallic conductivity (if any) from mobility measurements.
Spectrum of the F‐Center
Authors: Katriel J. , Bar‐Adon R.
Published: July 2007

A simple one‐electron model, sufficient to account for the main deviations of the spectrum of the F‐center in alkali halides from that of H, is studied. Qualitative features of the spectrum, such as the non‐existence of a 2sσg and 3dσg crossing, are stressed.
Investigation of Transport Coefficients in Semimetals by the Variational Method III. Commutational Effect of Magnetothermo‐E.M.F. in Bismuth
Authors: Gitsu D. V. , Golban I. M. , Kantser V. G.
Published: July 2007

The possibility of the commutational effect (CE) of thermo‐e.m.f. at different orientations of the magnetic field and temperature gradient is investigated in the frames of the variational method of calculation of transport coefficients. It is found that for some of the components of the magnetothermo‐e.m.f. tensor CE appears only in strong and intermediate fields. The importance of strict orientation of sample relative to external affects for the measurement of CE of magnetothermo‐e.m.f. is pointed out.
ESR Investigation of a [Cr(V)O4Pb8] Center in PbMoO4. Origin of the Yellow Coloration of Lead Molybdate
Authors: Gourier D. , Parant J. P. , Vivien D.
Published: July 2007

The ESR spectra of Cr doped PbMoO4 originate from CrO ions at normal MoVI sites with a d ground state interacting with 207Pb nuclei of two sets of four first‐neighbour lead sites. The principal values and the directions of the principal axes of the two Cr5+−Pb2+ hf tensors are determined and discussed according to the nature of the cation—cation interactions. The temperature dependence of the spectrum intensity, which falls to zero outside the 10 to 45 K region is explained as a combination of a very short Cr5+ spin lattice relaxation time and a long spin diffusion time. The yellow coloration of oxidized samples of PbMoO4 (Cr) results from the existence of an intense line (f = 0.14) in its absorption spectrum peaking at 430 nm. This band is attributed to a charge transfer transition of CrO ions which is red shifted from its normal position in most chromates because of a mixing with a Pb2+ → Cr6+ intervalence transition.
Effective Medium Theory for the DC Conductivity and Hall Effect of Inhomogeneous Semiconductors in High Electrical Fields
Authors: Fishchuk I. I.
Published: July 2007

The effective medium theory is extended to the calculation of the dc conductivity and Hall effect of macroscopic inhomogeneous semiconductors in high (just after ohmic region) electrical fields. A cubic network of the macroscopic barriers with random heights is used as a model of the considered semiconductors. The electrical field dependences of the direct and Hall current densities are calculated. As it follows from calculations on the direct and Hall current differential conductivities and also the Hall angle decrease with increasing electrical field in the non‐ohmic region.
General Consideration of the Loss of Information on the Orientation Distribution Function of Texturized Samples in Pole Figure Measurements
Authors: Matthies S. , Helming K.
Published: July 2007

The properties of symmetry of the crystal lattice of the constituents of a texturized sample as well as the properties of symmetry of the diffraction mechanism or of the sample itself lead as a rule to symmetries of the pole figures higher than the symmetries of the orientation distribution function (ODF). This is connected with a loss of information on the ODF in pole figures. Reproducing the ODF from pole figures “ghost phenomena” may appear which can be correctable or not. The loss of information and the character of the ghosts are analysed for all possible crystal structures.
Localized Excitons in CdS1−xSex Solid Solutions
Authors: Permogorov S. , Reznitskii A. , Verbin S. , Müller G. O. , Flögel P. , Nikiforova M.
Published: July 2007

The emission spectra of CdS1–xSex solid solutions (x ≦ 0.3) at helium temperatures are studied under monochromatic excitation in different regions of the absorption spectrum. In all samples very intense luminescence due to excitons localized by composition fluctuations is observed. High intensity of luminescence and complete absence of free exciton emission indicate a high probability of exciton localization. A model for exciton localization is proposed. It is assumed that only the hole component of the exciton is localized by the potential fluctuations. The electron is bound to this hole by Coulomb attraction. The energy migration between the localized states is discussed. Three different regions can be distinguished in the excitation spectrum of localized excitons. The first region corresponds to the excitation of free excitons which are trapped to localization sites in the process of energy migration. There is no energy migration in the third spectral region and all the emission is caused by directly photo‐excited states. In the intermediate region II a limited energy transfer between the localized states takes place via phonon assisted tunneling.
Electronic Structure of Molybdenum Dioxide Calculated by the Xα Method
Authors: Sasaki T. A. , Soga T. , Adachi H.
Published: July 2007

The discrete variational‐Xα method employing a [Mo2O10]12− cluster is applied to electronic‐structure and density of states calculations of rutile family MoO2. Level profiles obtained are generally in good agreement with the optical conductivity data and observations by photoelectron spectroscopy. The splitting of the Mo 4d predominant levels just below the EF level is attributed to the formation of a partially filled Mo‐O(π*) type band which is lower in the binding energy by ≈︁ 0.7 eV than the completely filled Mo‐Mo(σ) type level or the nonbonding Mo 4d orbital, consistent with a recent UPS measurement. Intensity analyses of the XPS spectra indicate that the O 2p and Mo 4d predominant regions are substantially underestimated if the atomic‐subshell photoionization cross‐section is used.
Measurements of the Ionic Conductivity of NaI and Calculation of the Bulk Modulus and Specific Heat of Vacancies
Authors: Grammatikakis J.
Published: July 2007

The conductivity is measured of NaI at high temperatures up to the melting point. A strong up‐ward curvature is observed of the plot In σT = f(1/T) in which the exact conductivity values depend on the surrounding atmosphere. The isothermal bulk modulus B is calculated at high temperatures from the measurementes of the self‐diffusion coefficient D. A deviation from the straight line results. The specific heat Cp of vacancies at high temperatures and the coefficient connecting the expansivity and the compressibility of the vacancies are also given.
Photoluminescence Spectrum of NH4Br:TI after First‐Order Crystallographic Phase Transformation
Authors: Mukherjee R. N. , Srivastwa D. N. S. , Sen S. C.
Published: July 2007

Fluorescence spectra and excitation spectra of ammonium bromide activated by thallium (0.14 mol%) are investigated at various temperatures in order to determine the spectral change due to the phase transformation. It is observed that the visible emission bands disappear and the ultraviolet emission band shifts from 390 to 365 nm whereas its corresponding A absorption band shifts from 258 to 262 nm, when the NH4Br:TI undergoes first‐order crystallographic phase transformation. The ultraviolet fluorescence band is composite and can be resolved into two components peaking at 314 and 365 nm. These two emission bands are attributed to AT and AX emission, similar to these reported for KBr:TI and RbBr:TI.
Delayed luminescence of organic mixed crystal. Delayed excimer fluorescence of pyrene in p‐terphenyl
Authors: Talapatra G. B. , Misra T. N.
Published: July 2007

Phosphorescence, fluorescence, delayed fluorescence, excimer fluorescence, and delayed excimer fluorescence of pyrene are studied in the host p‐terphenyl system. The delayed fluorescence and delayed excimer fluorescence are biexcitonic and exhibit a similar dependency of the emission intensity on temperature; they both originate in identical kinetic events. The excitation spectra for all the emissions are presented. The trapping of the host triplet excitons occurs more efficiently at monomer pyrene sites than at nascent excimeric pyrene sites. The conclusion is that the delayed excimer and delayed fluorescence are produced by the homofusion of defect triplets and the heterofusion of defect and guest triplets. The defect level situated below the host exciton band controls the thermal excitation processes and the luminescence characteristics by the thermal event
\documentclass{article}\pagestyle{empty}\begin{document}$ T_{{\rm 1D}} \to T_{1{\rm D}}^* \to T_{1{\rm H}} |_{\to T_{{\rm 1G}}}^{\to T_{{\rm 1D}}}. $\end{document}.
Internal energy and short‐range order in ising models
Authors: Silva P. R. , Barreto F. C. SÁ
Published: July 2007

The short‐range order contribution to the internal energy in Ising models is calculated in an effective type treatment. However, the method incorporates correlation effects through a phenomenological approach and the results obtained are an improvement over other effective field calculations when compared with exact (z = 4) or series results (z = 6).
Rydberg potential in diatomic ionic crystals
Authors: Gupta V. P. , Agrawal C. P.
Published: July 2007

The short‐range Rydberg potential function is used to calculate the transverse optical mode frequency (ωto), transverse optical mode Grüneisen parameter (γto), and Grüneisen parameter (γ) for rock salt and caesium chloride structure ionic solids. The pressure derivative of bulk modulus (dB/dP) and Debye characteristic temperature (θD) are also evaluated using this short‐range interaction. The results obtained using Rydberg potential are found in good agreement with recent experimental data.
The electronic structure of a hydrogen impurity in aluminium II. The bandstructure model
Authors: Craig B. I.
Published: July 2007

The electronic properties are discussed of hydrogen impurities in aluminium resulting from a realistic bandstructure description of the pure metal. A Green's function matrix technique is used to solve the anisotropic impurity interaction to self‐consistency. The results show that the accurate treatment of this non‐spherical nature yields a significant concentration of electronic charge between a proton occupying a tetrahedral site and the neighbouring aluminium ions. In contrast, a proton occupying the more open octahedral position yields an electronic structure which is similar to that obtained from the simple, spherically symmetric, jellium—proton model.
Core energy and peierls stress of edge dislocations on {110} and {001} slip planes in NaCl
Authors: Bucher M.
Published: July 2007

Properties of straight edge dislocations on {110} and {001} slip planes are calculated by means of atomistic procedures. The energies of dislocation cores of radius 3b are 6.86 × 10—5and 7.43 ×10—5 erg/cm, respectively. Detailed investigations on convergence yield similar Coulomb interactions for both slip systems which leads to a correction of earlier assumptions. The calculated Peierls stresses of 75 and 90 MPa, respectively, fall between the experimental data of critical shear stresses. This finding might indicate that, in plastic deformation, dislocations do not move as ua whole bt by migrating in atomic steps.
Electronic states of ordered overlayers on a tight‐binding metal surface two‐level adsorbate
Authors: Masuda K.
Published: July 2007

The electronic states of ordered overlayers, with c(2 × 2), p(2 × 1), and c(4 × 2) structures, are investigated using the Green's function formalism and the phase‐shift technique. A two‐level (at E1 and E2) adsorbate on a tight‐binding (TB) metal surface is used which is applicable to the adsorption of di‐atomic molecules on transition metal surfaces It is shown that the indirect interactions between two‐level adsorbates play an important role in determining the electronic states of the chemisorbed layers. Also the change in the electronic density of states (DOS) is investigated during the dissociation of di‐atomic molecules and it is pointed out that there are marked differences in the electronic structures between the dissociated and undissociated adsorbate states.
Cluster model residual resistivities in 35 Copper Alloys
Authors: Lodder A. , Boerrigter P. M. , Braspenning P. J.
Published: July 2007

Residual resistivities are calculated for dilute copper alloys with 4d and 3d transition metal impurities and sp impurities from the third, fourth, and fifth row of the periodic system. Finite cluster model (FCM) results are compared with values obtained from the simple Friedel formula, from the Gupta‐Benedek (GB) formula which accounts for backscattering, and from the formula by Coleridge, Holzwarth, and Lee (CHL), accounting in addition for Fermi surface effects. In the FCM the effect of lattice distortion is studied by placing the first shell of host atoms around the impurity at relaxed positions. Self‐consistent potentials are used for host and impurities. In general the FCM accounts for backscattering in a more sensitive way than the GB formula.
Conductivity and transverse fields in n‐Si for currents in the {110} and {100} planes
Authors: Asche M. , Gribnikov Z. S. , Ivastchenko V. M. , Kostial H. , Mitin V. V.
Published: July 2007

The mechanism of N‐type ndc in heating electric fields which is connected with the rapid rise of transverse fields is described in detail. The contribution to the total current caused by the transverse fields is directed opposite to the current contribution explicitly caused by the applied field and increases rapidly with growing transverse fields. By numerical calculations it is shown that in n‐Si at low temperatures N‐type ndc can be realized on account of this mechanism for all current directions in {100} and {110} planes with exception of a narrow surrounding of the 〈111〉 axis, for which the behaviour of the transverse fields and their influence on the currentüvoltage characteristics is more complicated. Experimental investigations are performed for the {110} plane for current orientation between 〈110〉 and 〈111〉 where a multivalued Sasaki effect can be realized — as well as between 〈111〉 and 〈100〉 — where the common single valued Sasaki effect is present.
Investigation of mixed‐mode polariton dispersion in AgGas2
Authors: Fröhlich D. , Reimann K. , Koidl P.
Published: July 2007

The observation of mixed‐mode exciton polaritons is reported in high quality AgGaS2 crystals grown by a Bridgman technique. By changing the magnitude of the total K‐vector and its direction with respect to the crystalline axis in the two‐photon experiments it is possible to excite resonances on the upper polariton and on the pure longitudinal exciton. The results are quantitatively explained by the polariton theory for uniaxial crystals.
Temperature dependence of the hopping mobility in amorphous tetracene
Authors: Lange J. , Bässler H.
Published: July 2007

Time‐dependent photocurrent transients are measured with vapour deposited amorphous tetracene layers as a function of temperature employing the technique of sensitized hole injection from a selenium layer. The time dependence is exponential and reflects trapping. The trap‐free mobility, derived from the t = 0 current amplitude, obeys a μ (T) = μ ∞ exp [— (T0/T)2] law with μ ∞ ≈ 0.4 to 0.8 cm2/Vs as predicted by previous Monte Carlo computer simulations for hopping across a Gaussian distribution of hopping sites in the long‐time limit. The Gaussian width, σ, given by T0, is of the order 0.1 eV, its dependence on sample formation temperature TF is in quantitative agreement with spectroscopic as well as TSC work, indicating that lattice relaxation around a localized charge carrier is irrelevant for carrier transport and σ is of purely electronic origin. A comparison is made with photoelectrons‐pectroscopic works.
Mössbauer study of the PbxSn1—x125Te system
Authors: Antonini A. , Fano V. , Ortalli I. , Vera A.
Published: July 2007

A study is made of the 125Te Mössbauer parameters dependence on the composition in PbxSn1—xTe. It is concluded that, in concomitance with the decrease of the gap value up to zero, there is both, a significant variation of tellurium electronic configuration and a change of the phonon spectrum.
Coulomb correlation effects in the spin polarized band structure of Eu2O2
Authors: Lóez‐aguilar F. , Costa‐Quintana J.
Published: July 2007

Two spin polarized‐band structures of Eu2O2 with and without considering Coulomb correlation effects are calculated. The exchange potential depending on the fractional spin direction Vex(r), locates the 4f bands below the 2p ones, avoiding the 2p‐4f mixing. This fact reduces sensibly the width of the occupied 4f band.
On the field‐dependent broadening of NMR lines in paramagnets
Authors: Bakonyi I. , Kovács I. , Pócsik I.
Published: July 2007

Linearly field‐dependent broadening of NMR lines in paramagnetic materials is dealt with. Sources leading to this kind of broadening are considered and the effect is taken into account in a uniform manner by introducing a relative line shift distribution function. If this is super imposed on a fieldindependent broadening it results in the additivity of the second moments of both kinds of broad ening in agreement with what is expected for independent broadening mechanisms. The possible influence of the presence of interdependent or not linearly field‐dependent broadening effects are briefly discussed.
Conductivity of semiconductors influenced by strong electromagnetic radiation
Authors: Fomin V. M. , Pokatilov E. P.
Published: July 2007

A method of solving the equation of motion for the density matrix of a non‐degenerate electronic ensemble in semiconductors in a strong electromagnetic radiation field is developed on the basis of a self‐consistent determination of the coefficients in an approximated Fokker‐Planck equation. The influence of a strong electromagnetic radiation field on the conductivity of semiconductors in a constant electric field is considered. At high temperatures the non‐linear conductivity is shown to be isotropic and caused mainly by heating while at low temperatures the nonlinear conductivity is essentially anisotropic and contains contributions due to both the influence of a strong electromagnetic radiation field on the scattering probability and to the heating of electrons. The relative value of the contributions due to the mentioned non‐linearity sources is analysed at intermediate temperatures.
Spin centres on clean germanium and silicon surfaces and their interaction with adsorbed molecules
Authors: Demidovich G. B. , Karyagin S. N. , Kiselev V. F.
Published: July 2007

The nature of surface states on clean Ge and Si surfaces is discussed. New experimental data about the interaction of different acceptor molecules with clean Ge and Si surfaces are presented. New paramagnetic adsorption centres are detected by the EPR method. The characteristic feature of the EPR signal detected is a superfine splitting on the 29Si nuclei. This result shows that the unpaired electron in paramagnetic complexes formed by adsorption are largely drawn into the Si atoms. The initial heats of O2 adsorption on clean Ge and Si surfaces, measured by calorimetric method, confirm the dissociative character of the first stages of oxidation and double bond formation.
Electronic energy loss of channeled negative pions
Authors: Taratin A. M. , Vorobev S. A.
Published: July 2007

The orientational dependence of energy loss for 70.5 MeV negative pions at planar channeling in Si crystals and the evolution of particle flux with crystal depth is investigated by computer simulation of particle trajectories and by using averaged potentials of atomic planes. It is shown that for sub‐barrier channeled particles the mean energy loss is significantly higher and for near‐barrier particles it is lower than under random scattering whereas for the above‐barrier particles the mean energy loss practically coincides with the random energy loss. The rate of meson dechanneling from the bound states with atomic planes is also determined.
The electronic structure of a hydrogen impurity in aluminium III. The energy and the metal‐impurity interaction
Authors: Craig B. I.
Published: July 2007

A theoretical approach to the study of both, the energy of a hydrogen impurity in a metal and the metal‐hydrogen impurity interaction is described. The analysis involves the virial and Hellmann Feynman theorems and the Kohn‐Sham formalism. Detailed calculations are performed for the case of hydrogen in aluminium. It is found that the non‐spherical component of the hydrogen induced electronic structure greatly modifies the hydrogen‐aluminium interaction, and the aluminium lattice expands about both, octahedrally and tetrahedrally sited impurities. These results, and the determination of the electric field gradient, compare favourably with those obtained from muon spin rotation experiments on such systems.
Dielectric and anharmonic behaviour of silver halides, thallous halides, alkaline earth fluorides, and lead fluoride crystals
Authors: Shanker J. , Sundaraj R.
Published: July 2007

An analysis is made of the dielectric behaviour and the anharmonic contribution to the dielectric constants of AgCl, AgBr, TlCl, TlBr, CaF2, SrF2, BaF2, and PbF2 crystals. The volume and temperature derivatives of static and electronic dielectric constants, and of the energy gap between bonding and antibonding states are derived from the experimental data using Phillips‐Van Vechten dielectric theory. The temperature derivatives of dielectric constants at constant volumes are used to estimate the magnitudes of anharmonic contributions. The effect of anharmonicity is discussed in terms of different theories. The volume derivatives of static dielectric constant are calculated using the Born‐Meyer theory of interionic potentials. The calculated quantities are compared with available experimental data. The applicability of the Mott‐Littleton theory of dielectric polarization is also discussed for the crystals under study.
Fermi surface of noble metals using the eight‐cone model
Authors: Nautiyal T. , Auluck S.
Published: July 2007

It is shown that the eight‐cone model together with a non‐local pseudopotential can give a good representation of the Fermi surface geometry of the noble metals. However, it is unable to give the correct anisotropy of the electron velocity at the Fermi surface.