bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inelastic neutron scattering by cerium hydrides. IV. Crystal field
Authors: Vorderwisch P. , Hautecler S. , Suck J. B. 
Published: July 2007

AbstractThe crystal field splitting of the 2F5/2 ground state of the Ce3+ ion in CeDx is investigated by means of the inelastic neutron scattering technique. Polycrystalline samples with 1.94 ≦ x ≦ 2.74 are studied. A consistent description of the results can only be obtained assuming that, over the investigated concentration range, the samples have tetrahedral vacancies. For CeD1.94 an effective charge of −0.30 |e| is derived, both for octahedral and tetrahedral deuteriums. For CeD2.42 an effective charge of −1.44 |e| has to be attributed to the octahedral deuteriums. For CeD2.74 scattered intensity due to crystal field transitions is also observed but as a structureless component of the spectra.
Density of states of expanded liquid mercury an effective medium approach
Authors: John W. , Keller W. 
Published: July 2007

AbstractNumerical results for the density of electron states for expanded liquid mercury are presented in the density range from 13.55 to 5.0 g cm−3. The calculations are based on a single‐site effective medium approximation for the muffin‐tin model of a liquid metal. The energy‐dependent effective medium is determined from a generalized Wigner‐Seitz condition. The gap between the 6s and 6p states occurs at ∂ = 5.6 g cm−3, in good agreement with nonrelativistic band‐structure calculations for hypothetical forms of crystalline mercury.
Renormalization of polaritons due to virtual formation of biexcitons at high densities of excitation
Authors: May V. , Henneberger K. , Henneberger F. 
Published: July 2007

AbstractThe change of polariton dispersion is investigated theoretically if a large number of polaritons is present at frequencies near half the biexciton energy. A renormalization process takes place for polaritons via virtual formation of biexcitons and stimulated by the intense polariton distribution. Assuming an energetically sharp distribution as is realised e.g. by dye laser excitation the original polariton dispersion is shown to split into two new branches. These effects should manifest if e.g. an additional but weak probe light is used to testify the optical properties of the laser excited crystal. Furthermore the scattering lines of the two‐photon resonance Raman process via biexcitons are characteristically modified due to both selfrenormalization of the incoming polaritons and renormalization of the scattered polaritons. Explicit results are presented for CuCl where agreement with experimental data recently published is found.
Third‐order elastic constants, thermal expansion, and bulk modulus of body‐centered cubic crystals
Authors: Rao R. Ramji , Rajput A. 
Published: July 2007

AbstractThe method of homogeneous deformation is used to derive the expressions for the second‐order elastic and third‐order elastic (TOE) constants of a body‐centered cubic crystal. Two‐ and threebody interactions are taken into account. The TOE constants of the four alkali metals Li, Na, K, and Rb and of the two transition metals Ta and Nb, are then evaluated, and these, in turn, are employed to calculate the low‐temperature limit of thermal expansion for these metals following Thurston and Brugger's equation for the elastic waves propagating in a homogeneously strained crystal. The Anderson‐Grüneisen parameter δ is calculated for each of the metals from its TOE constants, and used to investigate the temperature dependence of the bulk modulus via Anderson's theory.
Impurity‐induced infrared absorption in AgBr
Authors: Ram P. N. , Tiwari M. D. 
Published: July 2007

AbstractThe impurity‐induced infrared lattice absorption is calculated for AgBr crystal in the low‐concentration limit of substitutional impurities. Employing a nearest‐neighbour perturbation model, where along with the change in mass at the impurity site the changes in the central and non‐central impurity‐host crystal interactions are considered, the localized mode frequency and band‐mode additional absorption due to lithium and sodium impurities are discussed. The main features of the experimentally observed absorption are reasonably explained.
Point defects in NaCl crystals doped with divalent ions the NaCl‐NaF:Pb++ crystal
Authors: Pinatti D. M. G. , Zílio S. C. , de Souza M. 
Published: July 2007

AbstractFluorine anions in the NaCl lattice act as capture centers for Pb2+ diffusion. ITC measurements show four dielectric relaxation peaks, one due to unperturbed Pb2+ vacancy dipole and the other three at lower temperatures. The perturbed Pb2+ ions also show new optical absorption bands that grow during annealing at RT. The defects produced by quenching crystals from high temperature are found to be strongly dependent on the lattice parameter. The temperature of the maximum of the three new ITC peaks are nearly independent of the divalent ions Eu2+, Sn2+, Zn2+, Pb2+, or Mn2+ that are also used to dope the NaCl‐NaF crystals.
Resonant scattering of light by slowly fluctuating localized electrons
Authors: Hizhnyakov V. , Tehver I. 
Published: July 2007

AbstractThe effect of slow fluctuations on resonant scattering of light by localized electrons is considered in the systems with a central peak. The cases of excitation in the regions of broad phonon wing of the absorption spectrum and of zero‐phonon line are discussed. It is shown that the spectrum of resonant scattering essentially depends on the fluctuation amplitude ≪0 and rate γ as well as on the radiative damping rate γ. In particular, in case γ ≪ γ ≪ ε0 (limit of nearly static fluctuations), at an excitation in the region of zero‐phonon line, the resonant emission line becomes fluctuationally broadened by ε0 (γ/2γ)1/2. In glasses at T → O this broadening mechanism should be dominant as its contribution decreases slowly with temperature (∼ T2).
Resonant Raman scattering in crystals with self‐trapping excitons
Authors: O'Connel‐Bronin A. A. , Plekhanov V. G. 
Published: July 2007

AbstractThe multiphonon resonant Raman scattering spectra in NaI and LiH (LiD) cubic crystals characterized by self‐trapping of excitons are investigated experimentally. The first‐order scattering cross section is established to depend on the wave vector. The frequency dispersion of the secondorder scattering cross section is in agreement with the theory. The 1S and 2S excitons as intermediate states as well as the damping of excitons are taken into account. The temperature dependence of the second‐order intensity in both luminescence and resonant Raman scattering is studied in the region of 2 to 300 K. This dependence is shown to weaken with the shifting of the exciting light frequency from the exciton band bottom towards the red. The temperature behaviour of the frequency dispersion of the second‐order Raman cross section at the temperature change in the crystals with self‐trapping excitons is discussed.
Evidence for a landé‐factor g =2 in n‐type inverted silicon MOSFET surfaces
Authors: Köhler H. , Roos M. 
Published: July 2007

AbstractThe determination of the spin splitting in quantities of the cyclotron energy in quantizing electric and magnetic fields from the application of the “tilted field method” on n‐type inverted silicon MOSFET surfaces is re‐examined under the additional consideration of a finite valley splitting. The procedure shows up to be very complicated since various important parameters and their angular variation are not known exactly. The summary of a series of different experiments yields an almost equal number of differing results for the g‐factor evaluated from the particular cases for M* ==g · mc/(2m0 cos ξ) =1/2 and 1, even after an exact correction of the data. The assumption of an interaction of the two “inner” of the four broadened levels belonging to a Landau quantum number n and a modification of the line shapes in their interspace allows a complete discussion of all data on the basis of a g‐factor equal to 2.
A simple linear method in band theory application to B.C.C. tantalum
Authors: Lopez‐Aguilar F. 
Published: July 2007

AbstractUsing a variational expression generalization for the APW method and radial part wave functions at fixed energies a diagonalizable secular matrix is obtained. A parameter relationship of the variational expression with potential depending variables is established. This method is applied to tantalum for which various band calculations by means of typical methods exist. It is noticed that, if there is some divergency, this is only a small one, and, in any case, can be solved by exchange and correlation potential parametrization.
Electronic polarization (relaxation) effects in the core level spectra of semiconductors II. Application to Ga3d and Si2p levels
Authors: Bechstedt F. , Enderlein R. 
Published: July 2007

AbstractCore electron binding energies of semiconductors are strongly influenced by core hole polarization (relaxation) effects. Polarization energies are calculated for the Ga3d hole in Ga–V semiconductors and the Si2p hole in Si. The values range between 4 and 7 eV. From the polarization energies, atomic core level energies, and solid state core level shifts theoretical values for the core electron binding energies are derived. Good agreement with experimental results is obtained.
On the hopping mechanism of dispersive transport
Authors: Zvyagin I. P. 
Published: July 2007

AbstractThe hopping mechanism of dispersive transport is discussed starting directly from the hopping transport equation, in contrast to the conventional approach using the continuous‐time random‐walk model. The power‐law decay of the transient current due to the spread of the packet of photo‐injected carriers, is obtained for impurity‐band hopping both in the presence of trapping and without it. The analysis shows that variable‐range hopping generally cannot be ruled out as a probable mechanism of dispersive transport in disordered semiconductors.
Logarithmic derivative reflectance spectra of BaO and SrO
Authors: Rao A. S. , Kearney R. J. 
Published: July 2007

AbstractExperimental studies of both reflection and wavelength derivation reflection spectra from freshly cleaved SrO and BaO crystals at 55 K are presented. The data are interpreted in a manner consistent with optical data on MgO and CaO crystal surfaces, in terms of Γ‐, X‐, and L‐excitons.
NMR studies of the effect of alloying Cu, Ag, Tl, I, and Ge into amorphous As2Se3
Authors: Ueda S. , Shimizu T. 
Published: July 2007

Abstract77Se and 205Tl NMR measurements are carried out for a‐As2Se3 with different additives. It is found that the NMR chemical shift and the increase in electrical conductivity with the addition of different elements have a close relationship. The results can be explained by assuming that some fraction of additive elements are positively ionized, resulting in an increase in the density of negatively charged Se dangling bonds and a shift of the Fermi level.
EPR investigation of Gd3+ and Eu2+ in the α‐ and β‐phases of lead phosphate
Authors: Razeghi M. , Buisson J. P. , Houlier B. 
Published: July 2007

AbstractThe X‐band EPR spectra of Gd3+ and Eu2+ diluted in Pb3(PO4)2 crystals are studied. Lead phosphate exhibits a ferroelastic phase transition at 180°C and the EPR spectra obtained in each phase differ from each other. The spectra are very complex because the zero field splitting has the same order of magnitude as the Zeeman term. The spin Hamiltonian parameters and the energy levels are computed. “Forbidden” or “missing” transitions and line intensities can be explained. Very likely Gd3+ substitute a PbI ion. For Gd3+ in β‐phase g ≈︁ 2 and b = 990 × × 10−4 cm−1 (200°C); for Gd3+ in α‐phase at 25°C g ≈︁ 2, b = 930 × 10−4 cm−1 and b = −77 × × 10−4 cm−1.
The effect of oxygen on the properties of evaporated amorphous silicon
Authors: Kubler L. , Jaéglé A. , Koulmann J. J. 
Published: July 2007

AbstractThe influence on the ESR centres of oxygen incorporation into evaporated amorphous Si is studied. The main effect is not the reduction of the spin density NS, which can be only reduced of a factor 10 after an intitial contamination, but a strong enhancement of the spin–lattice relaxation time T1, which makes the signal very saturable and apparently weak for usual microwave powers. This T1‐ rising is correlated with a slight g‐factor decrease, and lineshape changes from Lorentzian to Gaussian. This was also observed by others with alternative treatments for reducing the spin density, such the rise of the substrate and annealing temperature or hydrogen incorporation. This initial spin density reduction seems always to imply the passivation of the same kind of defects, accessible to the gases and located at the internal surfaces of porous samples. But many other defects with T1‐times in the range 10−5 s at 300 K are not suppressed by this way.
On the indirect exciton energy levels in crystals of diamond and sphalerite type with spin–orbit interaction
Authors: Tolpygo K. B. , Zubkova S. M. 
Published: July 2007

AbstractThe theory of direct excitons in crystals of diamond and sphalerite type is generalized to the indirect exciton case. The problem is solved by the variational method taking into account the anisotropy and the nonparabolicity of the electron band. The comparison with the theoretical and experimental data known from literature is carried out.
Effect of temperature on the off‐diagonal alloy properties
Authors: Wysokiński K. I. , Piłat M. 
Published: July 2007

AbstractA version of the coherent potential approximation is applied to study the density of states and the conductivity of binary and/or ternary alloys. A tight‐binding one‐band Hamiltonian including diagonal thermal and diagonal and off‐diagonal substitutional disorders is used. The superposition of thermal and off‐diagonal disorders produces some effects not observed in the previous one‐band theories. The concentration dependence of the AuxAg1−x alloys density of states is calculated.
Temperature dependence of electron concentration in intrinsic‐like HgTe
Authors: Szlenk K. 
Published: July 2007

AbstractMeasurement of the Hall effect and the conductivity are performed on HgTe sample characterized by an electron mobility of 106 cm2/Vs at 1.6 K. The range of temperatures investigated is 1.6 to 32 K and the external magnetic field covers the region 50 to 800 G. The interpretation of the data based on the conductivity tensor components analysis shows that the sample contains 5 × 1016 cm−3 acceptors. The acceptor ionization energy is estimated to be 2 meV. It is shown that a simple one‐carrier expression for the Hall constant may give wrong results for the electron concentration, differing by a factor of two from the correct value. From the behaviour of conduction electron concentration below 6 K it is found that the conduction–valence band overlap is smaller than 0.3 meV.
Evidence for excitonic absorption in metallic MnAs0.88P0.12
Authors: Bärner K. , Stearns R. , Braunstein R. 
Published: July 2007

AbstractThe derivative spectra of the reflectivity are measured for the double exchange ferromagnet MnAs0.88P0.12 at 300, 100 K and for quantum energies between 1.6 and 5.0 eV. Excitonic absorption is found beyond interband transitions and is tentatively assigned to a triangular resonant state.
Statistical continuum theory of heterogeneous solid media  information theory approach. I. Static field theory
Authors: Pompe W. , Vojta G. , Kreher W. 
Published: July 2007

AbstractA new approach to the statistical continuum theory of random heterogeneous solids is developed This approach is based on the consistent use of the principles of information theory in an effort to connect observable quantities of real solids with fundamental quantities of solid state theory. The physical entities to be treated are space and time‐dependent generalized stochastic fields leading necessarily to a functional formalism. As an example the static elastic properties of a heterogeneous solid are calculated. Starting from a variational principle for the entropy functional a probability functional for the deformation field and the Hooke tensor field is given from which the expectation values of all relevant quantities can be evaluated. The physical implications of the formulae derived are discussed. The conception of structure temperature is introduced.
Dielectric spectrum of BaTiO3 single crystals
Authors: Turik A. V. , Shevchenko N. B. 
Published: July 2007

AbstractThe dielectric spectra of BaTiO3 single‐domain and polydomain tetragonal crystals with 180° domain structure are investigated over the wide range of frequencies 103 to 1010 Hz. It is shown that the dielectric permittivity ε33 of the single‐domain crystals has three regions of dispersion including two regions of the high‐frequency relaxation. There is no relaxation contribution to the permittivity ε11 of the single‐domain crystals. In polydomain crystals the decrease of the low‐frequency dielectric permittivity and the increase of the high‐frequency one, due to the domain piezoelectric interaction, are observed. The results obtained are discussed from the point of view of the structural disorder in a real crystal. Conclusions are made concerning the ion potential relief character and the phase transition nature in BaTiO3.
X‐ray absorption edge shifts of cobalt and rare earth ions in rare earth–cobalt intermetallic compounds
Authors: Hatwar T. K. , Malik S. K. , Ghatikar M. N. , Padalia B. D. 
Published: July 2007

AbstractChemical shifts ΔE of K‐absorption edge of Co and L3‐absorption edge of Gd, Tb, and Dy in GdCo3, TbCo3, and DyCo3 intermetallic compounds are measured and effective charges on the absorbing ions are estimated. It is found that the magnitudes of ΔE and q for Co in RCo3 (R refers to rare earth ions) lie in between those reported for RCo5 and RCo2 compounds. Further, ΔE and q of Co increase with increasing number of rare earth atoms per cobalt atom (RCo5 < RCo3 < RCo2) while the magnetic moment of cobalt in these intermetallic compounds indicates the opposite trend (RCo5 > RCo3 > RCo2).
Quantum‐chemical calculations of electronic and hole centres and surface of NaCl crystals (I)
Authors: Shluger A. , Kotomin E. , Dzelme Yu. 
Published: July 2007

AbstractA new parametrization scheme for electronic structure calculations of defects in alkali halides by the CNDO semiempirical method is presented and developed. The model of a molecular cluster is used taking into account, for the first time, the non‐point nature of ions outside the cluster, which considerably reduces the surface effect. The derived parameters reflect the ionic nature of the NaCl crystal. An attempt to calculate the F centre properties (first of all the position of its ground state level within the gap and the spin density on the neighbouring ions) indicates the necessity to extend the valence basis set by introducing an additional wave function centered at the vacancy. The parameters of the latter are derived.
Polariton effects in crystalline xenon
Authors: Kink R. , Selg M. 
Published: July 2007

AbstractThe polariton theory is applied to the calculation of reflectivity, absorption, and resonant luminescence spectra in the region of Γ(3/2) exciton band in crystalline xenon. Agreement with experimental curves is achieved when the value of deformation potential C = (1.3 ± 0.2) eV is used. Approximately the same value is independently determined for C by the exciton self‐trapping barrier theory.
On the adhesion theory for two metallic surfaces
Authors: Kobelev A. V. , Kobeleva R. M. , Ukhov V. F. 
Published: July 2007

AbstractUnlike the foregoing investigations of surface features of two contiguous metals in terms of the density functional formalism the value of the variational parameter characterizing the inverse size of the electron tail is treated as a function of the distance between the metals. Electron distribution, surface energy, adhesion energy, and interaction force at various distances are found both in the jellium model and with consideration of the discreteness of the ion charge.
Angular behaviour of the polar optical phonons in AIIIBVI layered semiconductors
Authors: Allakhverdiev K. R. , Babaev S. S. , Salaev E. Yu. , Tagyev M. M. 
Published: July 2007

AbstractThe behaviour of the infrared‐active lattice vibrations of GaS, GaSe, InSe are studied by measuring the room‐temperature reflectivity in the 100 to 500 cm−1 frequency range when the incident wave vector is inclined at an angle θ to the crystallographic Z‐axis. The experiments are performed in polarized light. The transverse and longitudinal mode frequencies are obtained by Kramers‐Kronig analysis of the reststrahlen bands observed in these crystals with θ between θ and 90°. The experimentally observed changes of the lattice frequencies with an angle θ are interpreted on the basis of the theory of long‐wavelength lattice vibrations in anisotropic crystals. Good agreement between the experimentally observed dependence and the calculated one according to the theory gives the possibility to elucidate the nature of a fine structure observed in the reststrahlen region of the layered GaS, GaSe, InSe crystals.
Density functional approach to point defect properties of copper–germanium alloys
Authors: Gollisch H. 
Published: July 2007

AbstractPoint defect properties of copper–germanium alloys are studied by using a recently developed method which is based on the density functional formalism. The charge density is approximated by superimposing the charge densities of the respective free atoms. The kinetic energy is obtained from a modified Thomas‐Fermi‐v. Weizsäcker expression. To test the reliability of this method, some properties of the perfect copper lattice and of Cu2 and Ge2 molecules are studied. Results on the formation energy of vacancies and divacancies in copper are presented. Further calculations are concerned with the interaction energy of two Ge atoms embedded in Cu and with the influence of two neighbouring Ge impurities on the formation energy of a vacancy in copper.
Thermally activated domain wall motion and coercive field in materials with extremely narrow domain walls
Authors: Fähnle M. , Kronmüller H. , Barbara B. 
Published: July 2007

AbstractBy computer simulation the shapes and energies of displacement nuclei are calculated for thermally activated domain wall motion in materials with so‐called ferroelectric, i.e. monoatomic domain walls. The energies of the critical nuclei decrease with increasing magnetic field, H, however, a simple 1/H‐law is only obtained for very small values of H. Thermally activated domain wall motion only occurs at high values of H. It is shown that the intrinsic coercive field Hc corresponding to the critical field for the movement of domain walls in multi‐domain particles is appreciably lowered by thermal instabilities.
Interatomic potentials from experimental phonon spectra I. Prototypes
Authors: Esterling D. M. , Swaroop A. 
Published: July 2007

AbstractThe systematic procedure developed by Brosens et al. to derive the interatomic pair potential from the experimental phonon spectra is modified and generalized to cover a variety of metals. A set of metals (Na, K, Al, Cu, Fe) is investigated as prototypes for the general class of simple, noble, and transition metals. Comparisons are made between this potential and other potentials including those obtained from liquid metal structure factor data and pseudopotential theory. Reliability of the potentials is argued on the basis of comparison with experimental data, reliable theoretical potentials (where available), and internal consistency. The potentials are not recommended in modeling defects (vacancies, cracks) which introduce large inhomogeneities in the electron density.