bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monovalent‐Copper (I; 3d10,S= 0) Induced Oxygen‐2p Valence Band Holes with Concomitant Attractive Interaction inside Low‐Dimensional Oxygen Networks
Authors: van Bruggen C. F. 
Published: July 2007

AbstractResults of electrical transport and magnetic measurements on coldpressed compacts of La2CuO4and La1.70Ba0.30CuO4provide strong evidence for their p‐type metallic and Pauli paramagnetic character at room temperature connected with the existence of low density‐of‐states oxygen‐2p valence band holes induced by ground state monovalent copper (3d10,S= 0). The host La2CuO4exhibits an electronic phase transition at ≈85 K from a p‐type broad‐band metal (p= 2.5 × 10−2holes/La2CuO4, μh= 10−4m2/Vs,m= 0.5m0,EF= 0.26 eV,N(EF) = 0.15 states/eV‐La2CuO4) to a p‐type polaron‐mediated ICDW state (p≈ 2.5 × 10−2holes/La2CuO4, μh≈ 10−4m2/Vs,m≈ 10m0,EF= 11 meV,N(EF) = 3.4 states/eV‐La2CuO4). The attractive interaction attending the O‐2p VB holes inside low‐dimensional oxygen networks is discussed in the framework of recent papers on structural distortions, electronic structures, and phase transitions in copper containing oxidic hosts and doped superconducting derivatives.
The Coexistence of Unstable, Metastable, and Separated Frenkel Pair Defects in Solids. II. Theory of the Impact Mechanisms for Defects Formation in Metals
Authors: Khabibullaev P. K. , Dzhumanov S. 
Published: July 2007

AbstractThe coexistence of unstable, metastable, and separated Frenkel pair defects in metals under nonequilibrium conditions generated via impact displacement of lattice atoms by incident particles is studied theoretically. The extent of a spontaneous annihilation (SA) zone of defects along their attraction directions is determined in the framework of elasticity theory. The value of defect formation threshold energy (DFTE) along the basic crystallographic directions is calculated and the degree of DFTE anisotropy is found. The displacement probability function and the damage function depending on the kinetic energy E of knock‐on atoms, the scattering law of colliding atoms, and the degree of DFTE anisotropy are obtained. The damage function found differs essentially from the well‐known Kichin‐Pease formula. It is shown that the cascade multiplication of defects is possible at E ≧ Ed, max ≈ 3 × Ēd (where Ed, max and Ēd are the maximum and average values of DFTE, respectively). The damage function found takes also into account the SA effect of metastable and separated pair components at overlapping of their existence zone with the SA zone of another partner. This effect is noticeable especially at low knock‐on energy. The results obtained are in good agreement with the experimental data.
Theoretical Calculations of EPR Parameters and Absorption Spectra in Chromium‐Doped α‐LiIO3 Crystals and Determination of Local Compressibilities
Authors: Zheng Wen‐Chen 
Published: July 2007

AbstractThe EPR parameters (g∥, Δg, D) and the absorption spectra of Cr3+ in α‐LiIO3 are calculated by crystal‐field theory. In the calculation the influence of Li+ vacancies in the vicinity of Cr3+ ions is taken into consideration and four parameters (N, μ, q2, α) are used. The results calculated agree well with experimental data. On this basis it is found that the host crystal compressibility can not be assumed to be the local compressibility in the vicinity of Cr3+ ions to explain the effect of pressure on EPR spectra. The possible local compressibilities are obtained from the EPR spectra under pressure. These values are supported by macroscopic thermodynamic analysis and microscopic crystal‐field theory.
Transport Coefficients and Einstein Relation in a High Density Plasma of Solids
Authors: Mnatsakanov T. T. 
Published: July 2007

AbstractGeneral expressions for charge carriers transport in the high density isothermal plasma of semiconductors and semimetals are derived. In addition to the usual drift and diffusion ones extra terms arise which describe a mutual drag of charge carriers due to electron‐hole scattering. A generalised matrix form of the Einstein relation is established. It is shown that nondiagonal elements in transport coefficients matrices arise due to electron‐hole scattering.
Optical Properties of the Alloy System SnTeGeTe from Reflectance Measurements
Authors: Lewis J. E. 
Published: July 2007

AbstractThe reflectance spectra of bulk samples of the alloy series Sn1−xGexTe are measured at room temperature in the wavelength range 0.2 to 50 μm. The principal optical constants are obtained using Kramers‐Kronig analysis. The variations of the optical dielectric constant, the carrier effective mass, the optical mobility, and the optical energy gap are given as functions of the alloy fraction x. For the Sn‐rich alloys (x < 0.3) the energy gap and the dielectric constant do not follow the trends established for the series at the Ge‐rich side, and are possibly related to the cubic‐rhombohedral phase transition that occurs in this system. The mobility and effective mass, though, behave reasonably for all alloy fractions.
X‐Ray Brillouin Scattering of Mössbauer Radiation by an Oscillating Quartz Crystal
Authors: Jex H. , Müller U. 
Published: July 2007

AbstractThe elastic and inelastic scattering from x‐cut quartz single crystal is investigated by means of Mössbauer diffractometry from the (1120) Bragg plane using 57Co‐source and a Mössbauer absorber for the energy analysis. When the crystal is excited to piezo‐electric vibrations in the MHz‐range, inelastically scattered quanta are resolved. The phonon energies are in the range 40 neV < < ħΩq < 150 neV.
Electron‐Phonon Interaction in Semiconductor Superlattices
Authors: Wendler L. , Haupt R. 
Published: July 2007

AbstractThe single‐particle Hamiltonian of the electron–(long‐wave optical) phonon interaction is discussed for semiconductor superlattices. In detail the dispersion relations are analyzed of long‐wave optical phonons, i.e. of the interface‐like bulk phonons (IBP's) and of longitudinal optical (LO) phonons, of the polar semiconductor superlattice. The IBP's are composed from ordinary interface phonons on adjacent interfaces coupling through their macroscopic electric fields to form a collective excitation of the whole superlattice. The coupling function of the electron–phonon interaction is calculated using a continuum theory. The coupling functions describing the modified Fröhlich interaction of a single electron with the continuous field of polarization of the IBP's and LO phonons are discussed and presented in graphical form.
Phenomenological Treatment of the Departure from the Picture of Ideal One‐Dimensional Conductor
Authors: Bâldea I. 
Published: July 2007

AbstractA statistical distribution w(kF) of the Fermi wavevectoi values is postulated for the one‐dimensional (1D) electron–phonon system in order to account for some effects inherently present in real (quasi‐) 1D conductors. The relevant properties are obtained by taking the ensemble average with the distribution w(kF). It is found that the charge‐density‐wave (CDW) instability is suppressed if the spread ∧ in kF is large enough. For lower values of ∧, the Peierls‐CDW distortion still exists, but the electronic gap is reduced. In this case, the broadening of the optical conductivity peak as well as the increase in the value of the phason pinning frequency measured in neutron experiment with respect to that deduced from optical data are obtained. A gapless CDW state may also occur. Fair agreement with the data reported for KCP is found.
Thermal E.M.F. Anomalies Due to Axial Compression and the Band Structure of Bi1‐xSbx (x = 0.27) Alloys
Authors: Brandt N. B. , Lavrenyuk M. Yu. , Minina N. Ya. , Savin A. M. , Kraak W. , Herrmann R. 
Published: July 2007

AbstractThe electron Fermi surface (FS) in single‐crystal Bi0.73Sb0.27 alloys and its change under axial compression are investigated with the help of magnetoresistance quantum oscillations. An additional frequency in the oscillation picture due to the minimum FS cross sections is observed. This is consistent with the assumption that the FS in the unstrained alloy investigated consists of three dumbbell‐shaped pockets. When the specimen is compressed the maximum FS cross‐section abruptly decreases by a factor of two at some critical deformation ϵcr. This phenomenon indicates that the “neck” of the dumbbell‐shaped FS disrupts at the moment when under compression the Fermi level crosses the saddle point of the energy spectrum. In the vicinity of the singular point the strain dependences of thermal e.m.f. and resistance reveal an anomalous behaviour what is a manifestation of the electronic topological transition.
Some Exact Results on the Ising Antiferromagnet with General Spin S on the Triangular Lattice
Authors: Hajdukovć D. , Vujičić B. U. 
Published: July 2007

AbstractA triangular lattice is considered which consists of five chains, i.e. a lattice with N = 5 × L sites. In the thermodynamic limit (L → ∞) and in the critical magnetic field, the exact ground‐state entropy for such a lattice is obtained as an explicit function of spin S. It is shown that this exact result for the lattice finite in one and infinite in the other dimension is an excellent approximation for the triangular lattice infinite in both dimensions.
Fine Structure in the Free Exciton Region of the Emission Spectrum of γ‐InSe
Authors: Paraskevopoulos K. M. , Julien C. , Balkanski M. 
Published: July 2007

AbstractThe fine structure of the emission spectrum of γ‐InSe in the free exciton region has been investigated. The complete behaviour is given and the quantitative analysis is described in detail. Also, the doublet structure is examined and the possible stacking faults contribution is considered. It is found that the origin of the second peak is bound excitonic. The phonon modes involved in the temperature variation of the exciton energy are obtained from fitting the experimental data to previous theoretical calculations. An explanation is given for the temperature variation of the half width anomaly.
Noncentrosymmetry Observed in CaC4H4O6 · 4H2O Crystals by Nonlinear Optical Measurements
Authors: P. C. Medrano , Günter P. , Arend H. 
Published: July 2007

AbstractCalcium tartrate tetrahydrate (L‐CTT) is reported to have point group symmetry mmm at room temperature. Second harmonic generation experiments indicate that calcium tartrate tetrahydrate prepared from pure L‐tartaric acid has the noncentrosymmetric point group mm2. All the nonlinear optical d‐coefficients are determined. Linear optical properties of this material such as: refractive indices and absorption constant are measured in the range 200 nm < λ < 2000 nm and the phase matching conditions for optical frequency doubling are derived. Non critical type I phase matching can be achieved in L‐CTT at room temperature for a fundamental wavelength of λ = 816 nm.
Overtone Spectroscopy of the OH and OD Stretch Modes in LiNbO3
Authors: Förster A. , Kapphan S. , Wöhlecke M. 
Published: July 2007

AbstractInfrared absorption bands due to the fundamental and the overtone of OH and OD stretch modes are investigated in undoped, Mg‐doped, and benzoic acid treated LiNbO3. The different bands are interpreted using an anharmonic oscillator model. Spectroscopic parameters determined from the isotope shift and the overtone frequencies are in good agreement. The anharmonicity found is comparable to that of OH in other ABO3 compounds and in alkali halides.
A New Luminescent Band Induced in NaF by Ion Implantation
Authors: Afonso C. N. , Gomez I. M. , Ortiz C. 
Published: July 2007

AbstractHigh concentrations of defects are induced in a thin surface layer of pure and doped NaF crystals by ion implantation with 280 keV H+, H+2, B+, and Ne+ ions. Laser induced luminescence in these crystals shows a new band peaking at 750 nm. It presents a high stability under thermal annealing and optical treatments. The experimental results point out that those centers responsible for this emission band are F2 disturbed centers which are only created under ion implantation.
VUV Optical Constants of Liquid and Solid Xenon at the Triple Point
Authors: Subtil J. L. , Laporte P. , Reininger R. , Saile V. 
Published: July 2007

AbstractAccurate optical constants for solid and liquid Xe are reported. The samples are prepared under ideal conditions in a closed cell. Reflectivity spectra between 7 ≦ hv ≦ 11 eV are recorded for normal and grazing incidence of the radiation and at temperatures T = 161.2 and 163.2 K. By a special evaluation technique optical constants are deduced. They are compared to previous data for solid Xe and the differences are found to be very large. The reasons for these discrepancies and the consequences are discussed.
Alternative Quasi‐Classical Transport Equations. III. Charge Transport in MIS Systems with Inclusion of Diffuse Surface Scattering and Quantum Size Effects
Authors: Scherf S. , Schnittler Ch. , Paasch G. 
Published: July 2007

AbstractOn the basis of the results of two preceding parts in this paper new expressions for the current density, the conductivity, and the local and effective mobility in the channel of a MIS field effect transistor are presented. For the first time in these expressions the following two different effects of the interface are taken into account simultaneously: (i) the vanishing of the wave functions at the interface as a quantum mechanical effect and (ii) incomplete specular reflection at the interface. Numerical results are given for the SiSiO2 system both, in the constant field approximation and for self‐consistent potentials in the range of surface fields between 2 × 104 and 3 × 105 V cm−1. The main new result is that the decrease of the mobility due to surface scattering is reduced by wave function effects giving so a much better agreement with experimental data of other authors. Problems of the influence of temperature and the consideration of an energy dependent relaxation time are discussed.
Displacement Cascades. Dynamics and Atomic Structure
Authors: Seidman D. N. , Averback R. S. , Benedek K. 
Published: July 2007

AbstractThe seminal ideas of Seeger, in 1958 and 1962, on the nature of a displacement cascade (DC) in irradiated crystalline materials have played an important role in the field of radiation damage. This paper first reviews the early history of displacement spikes, replacement collision sequences (RCSs), “diluted” or depleted zones and thermal spikes. Then the use is discussed of molecular dynamics (MD) simulations and field‐ion microscopy as techniques by which one can study the dynamics of the formation of DCs and the spatial array of point defects — on an atomic scale — associated with quiescent DCs, respectively. These techniques demonstrate quantitatively that a DC consists of a vacancy‐rich core surrounded by a distribution of self‐interstitial atoms (SIAs) — the latter are predominately created by RCSs. Recent results on the application of MD to the behavior of 5 keV cascades in copper are presented. Some of the results of the application of field‐ion microscopy to the study of DCs in tungsten are reviewed, and compared with the MD results.
Eigenstates of Kinked Dislocations in Crystals
Authors: Mann E. 
Published: July 2007

AbstractIn a first contribution, the unstable equilibrium configuration of a dislocation with a kink pair at high effective stresses is established and the small‐amplitude eigenvibrations on it are derived. The contribution of the eigenfrequencies to the entropy is calculated in both the high‐ and the low‐temperature approximation. The second part deals with the influence of small effective stresses on the breather oscillations. The homogeneous solution of the perturbed Enneper (sine‐Gordon) equation is found in general form by virtue of Bäcklund transformations. The inhomogeneous initial‐value problem is reduced to a system of two integral equations, a special solution of which is obtained by asymptotic expansion.
Electronic Properties of Glassy Metals
Authors: Krey U. , Ostermeier H. , Zweck J. 
Published: July 2007

AbstractElectronic properties of glassy metals, including transport properties, are studied by numerical calculations for realistic structural models. For the Fe1‐xBx and Cu1−Zrx system results are presented for total and partial densities of states and the electrical resistivities. For Cu0.65Zr0.35 also the Hall constant is calculated. The results agree with recent experiments. The projections of the densities of states on the B‐p‐bands give the possibility to distinguish between different structural models with similar radial distribution function.
A Reexamination of the Continuum Approach to the Calculation of Lattice Sums
Authors: Mohazzabi P. , Behroozi F. 
Published: July 2007

AbstractThe continuum approach of Born and his collaborators to the calculation of simple lattice sums, originally suggested for large‐inverse‐power interatomic potentials in cubic crystals, is reexamined. Explicit calculations show that the model is an effective approximation not only for large powers of the inverse interatomic potential, but for all powers as low as n = 4. Furthermore, the method is shown to be applicable to any solid regardless of its crystal structure. The hexagonal close‐packed case is considered as an example. The model is expected to be useful for amorphous solids and liquids.
Electronic Spectra of Radiation‐Induced CrO in 3 CdSO4 · 8 H2O Crystals
Authors: Murthy T. S. N. , Salagram M. 
Published: July 2007

AbstractThe optical absorption spectra of 3 CdSO4 · 8 H2O crystals doped with different concentrations of CrO impurity are analysed at different stages of X‐irradiation. The products of radiation damage are identified to be SO and a new species formed out of CrO impurity. The ligand‐field (LF) nature and the charge transfer (CT) nature of the optical peaks suggest that the new species is a CrO ion. The assignment of the bands indicate that the approximate site symmetry of CrO ion in the lattice is D2d. The radiation damage mechanism for the formation of CrO ion in the lattice is discussed.
The Model Description of Neutron Scattering by Quasilocal Vibrations and Phonons in Glasses
Authors: Plakida N. M. , Stamenković S. , Vujičić G. M. 
Published: July 2007

AbstractIn the frame of an appropriate dynamical model of glasses the differential cross sections for inelastic neutron scattering by quasilocal vibrational excitations (QVE) and phonons are evaluated. It is shown that at low energies (E ≦ 10 meV) these cross sections are of the same order and could explain the corresponding experimental results.
Structural Phase Transition of Alkali Halides Using a Modified Interaction Model
Authors: Kumar M. , Hans D. , Sharma A. K. , Shanker J. 
Published: July 2007

AbstractA new interionic potential model is developed by taking into account (i) the effect of three body interactions, (ii) the recent values of van der Waals (vdW) potentials estimated from Kirkwood‐Muller formula, (iii) the repulsive hardness parameters evaluated from the overlap integrals using the exchange charge model, and (iv) the effect of coupling between overlap repulsive and van der Waals forces in terms of the Drude oscillator model. The modified potential model is capable of predicting correctly the relative stability of two structures viz. NaCl and CsCl structures. The calculated values of transition pressure are found to present close agreement with experimental data.
The Influence of the Compression Effect on the Phase Diagrams of Si–Ge System
Authors: Kagaya H.‐Matsuo , Soma T. 
Published: July 2007

AbstractThe pressure effect on the phase diagrams of the Si–Ge system are studied using an electronic theory based on pseudopotentials and considering lattice vibrational contributions. A region of phase mixture is increased under pressure, and the top of phase mixture rises at a rate of about 6 K per 109 Pa. The melting curves under compression show a drop in temperature.
Self‐Consistent MAPW Calculation with a Warped Muffin‐Tin Potential. II. The Electronic Structure of Li and Its Pressure Dependence
Authors: Bross H. , Stryczek R. 
Published: July 2007

AbstractThe electronic structure of lithium is self‐consistently evaluated in the b.c.c. and f.c.c. phase on a wide range of the lattice parameter, using a formalism which allows the incorporation of the leading warped‐muffin‐tin correction. With increasing compression the band structure exhibits rather peculiar modifications. At high compression the conduction band has its lowest energy at the N‐point whereas the Γ‐point is shifted above the Fermi level. With this information the free‐energy per Wigner‐Seitz‐cell at zero‐temperature and the equation of state are straightforwardly derived. Using the Hedin‐Lundqvist expression for exchange and correlation the b.c.c. phase is found to be more stable for all pressures up to 2 × 1011 Pa, contrary to recent investigations. However, a final conclusion about the stability of the phases is not possible as long as no similar investigations for the h.c.p. phase have been performed.
Localized Electron Levels in Isotopically Ordered Crystals (Isotopic Quantum Wells)
Authors: Berezin A. A. 
Published: July 2007

AbstractAn infinite defect‐free crystal lattice with large‐scale variations of isotope distribution is considered. It is shown that a sufficiently large “isotopic island” could form a potential well with localized energy levels. An example is given for CaO lattice with isotope 40Ca constituting a “host” part into which a spherical region with 48Ca is incorporated without any lattice misfits. The critical radius of such region which is able to act as an electron trap with a localized electron level is estimated as about 5 nm.
Nonlinearities in Excitonic Luminescence of Direct‐Gap Semiconductors under Very Low Optical Excitation Levels
Authors: Brodin M. S. , Gushcha A. O. , Khotiaintsev V. N. , Shevel S. G. , Taranenko L. V. , Tishchenko V. V. 
Published: July 2007

AbstractThe dependences of peak luminescence intensity Ilum for free and bound excitons on the level Iexe of the above‐gap optical excitation are studied in direct‐gap semiconductors PbI2 and CdSe within a wide range 1011 ≦ Iexe ≦1019 quanta cm−2 s−1 which included the never explored region below ≈ 1016 quanta cm−2 s−1. The experimental dependences Ilum = f(Iexe) are well represented by nonlinear power law Ilum ∼ I, 1 ≦ γ ≦ 1.75. The degree of nonlinearity (i.e. the value of γ) increases gradually with the decrease of Iexe and also becomes higher with increasing of temperature. Linearity (γ = 1) is sometimes observed only at sufficiently high Iexe above 1016 quanta x x cm−2 s−1. A phenomenological theoretical model is proposed which accounts for non‐radiative surface recombination and non‐uniform spatial distribution of the excited carriers and provides satisfactory qualitative agreement with the experimental findings.
Structure Factors of Liquid Zn, Cd, and Hg
Authors: Zou Xian‐Wu , Jin Zhun‐Zhi , Tian De‐Cheng 
Published: July 2007

AbstractThe structure factors a(Q) of liquid metals, Zn, Cd, and Hg are calculated by using the hard sphere cluster model. The calculated concentration and relative sizes of the two kinds of hard spheres, which correspond to the two kinds of clusters, respectively, coincide with the characteristics of solid structures.
On the Mechanisms of Photoreflectance in Multiple Quantum Wells
Authors: Enderlein R. , Jiang Desheng , Tang Yinsheng 
Published: July 2007

AbstractMechanisms of photoreflectance of MQW structures are studied. The photomodulation of the built‐in surface electric field is analysed. It is argued that in MQW structures unlike to bulk crystals the electric field does not result in a Franz‐Keldysh‐effect but rather in a Stark effect of subbands and excitons and a corresponding change of wavefunctions and oscillator strengths. The photoreflectance line shape is not of third derivative but of first derivative type in the case of MQW structures. Experimental photoreflectance spectra are reported which confirm these conclusions and allow the derivation of sublevel energies, broadening parameters, and exciton binding energies.