bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractFluorescence 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

AbstractPhosphorescence, 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractProperties 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

AbstractThe 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

AbstractResidual 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

AbstractThe 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

AbstractThe 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

AbstractTime‐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

AbstractA 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

AbstractTwo 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

AbstractLinearly 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractAn 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

AbstractIt 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.
The one‐ and two‐photon absorption due to surface state excitons
Authors: Bobrysheva A. I. , Beryl S. I. , Zyukov V. T. , Moskalenko S. A. , Pokatylov E. P. 
Published: July 2007

AbstractThe oscillator strengths are calculated for one‐ and two‐photon absorption by surface state Wannier excitons. The model of two surface bands is used, and excitons and electron‐hole pairs act as intermediate states. The cases of direct allowed and forbidden dipole transitions are investigated. Numerical calculations of the ratios of two‐ and one‐photon oscillator strengths are performed for (100) GaAs.
Induced polarization charge density around an electron in a polar semiconductor
Authors: Peeters F. M. , Devreese J. T. 
Published: July 2007

AbstractA calculation is presented of the polarization charge density induced by an electron in a polar semiconductor subjected to a magnetic field. The result, which is derived for the anisotropic Feynman polaron model studied earlier, is expected to be applicable for arbitrary values of the electron—phonon coupling strength (α), temperature (T), and magnetic field strength (ℋ︁).
Approximate wave functions for the F+‐centers in LiNbO3 and LiTaO3
Authors: Ho Fat Duen 
Published: July 2007

AbstractThe improved hydrogen‐like wave function is used as a trial wave function of the 1s‐state to calculate the energy levels of F+‐centers in lithium niobate and lithium tantalate. The point‐ion model is employed. The Schrödinger equation is solved variationally. The transition energies agree within 6.4% and 13.4% with the observed peaks in the absorption spectra for LiNbO3 and LiTaO3, respectively. In comparison with previous work along this line the results obtained here are much better in the case of LiTaO3, and are rather compatible in the case of LiNbO3. Furthermore, in order to save computer time various groups of ions out of the “lattice” of 810 ions are examinated to find the minimum numbers of ions needed to guarantee an essential physics of the systems. The advantages of using this more accurate one‐parameter wave function are discussed.