bluuebunny/crossref_metadata_2025_split huggingface dataset:
Raman Spectra of the Incommensurate and Ferroelectric Phases of Rb2CoCl4 Single Crystals
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Smutný F. , Vaněk P. , Březina B. 
Published: July 2007

AbstractRaman spectra of Rb2CoCl4 (RCC) single crystals, prepared by an improved method, are studied at 90 to 297 K. The results show that the temperature dependence of the spectra of RCC is analogous to that of Rb2ZnCl4 and Rb2ZnBr4. Eigenfrequencies of internal modes v1 and v3 vary with temperature in a manner well describable by a model, which is suggested by Rasing et al. for Rb2ZnBr4. Low‐frequency lines at 20 and 37 cm−1 exhibit a pronounced temperature dependence. The broadness of spectral lines speaks for a high anharmonicity of oscillations in RCC.
The Stress Fields on Secondary Slip Systems Due to a Group of Dislocations in a Stress Gradient
Authors: Hu Xiaoyu , Margolin H. 
Published: July 2007

AbstractResolved shear stress distributions are calculated from the stress fields arising from screw and edge dislocation arrays produced by stress gradients. The resolved shear stress distributions are determined for planes parallel to a primary slip plane which has undergone slip and for other slip systems. For the screw dislocation array largest resolved shear stresses are found on the cross slip plane. For edge dislocation arrays largest resolved shear stresses are found on the conjugate slip system.
Volume Dependence of Short‐Range Force Constant and Dielectric Properties of Alkali Halides
Authors: Pachauri A. K. , Sharma A. K. , Saxena H. C. 
Published: July 2007

AbstractA simple and useful empirical relationship showing the volume dependence of short‐range force constant is investigated. The relation is found to hold well for the variation from one crystal to the other as well as for a given crystal under changing volume. The usefulness of the relationship is demonstrated by calculating the volume derivatives of dielectric constant, and optic mode longitudinal and transverse Grüneisen parameters. The special feature of these calculations is that they do not require the detailed knowledge of the interionic potentials. The results obtained are found in good agreement with experimental data.
In Search of Hydrogen Local Vibrational Modes in CuCl, CuBr, CuI, ZnS, and AISb
Authors: Tatarkiewicz J. , Cardons M. , Breitschwerdt A. , Lin C.‐T. , Grötzschel R. , Witthuhn W. 
Published: July 2007

AbstractA systematic study is made of hydrogen localized vibrational modes in some III–V, II–VI, and I–VII compounds after proton implantation. HCl vibrations are observed in CuCl with an energy of 2585 cm−1, but no CuH vibrations. This is verified by the lack of hydrogen‐related vibrations in CuBr and CuI. In ZnS vibrations of ZnH are observed at 1325 cm−1 and HS vibrations at 2415 cm−1. No hydrogen‐related vibrational modes are observed in AlSb after proton irradiation. For all hydrogen local vibrational modes the measured oscillator strengths are about 0.075. It is found that vibrational energy of HS agrees with that predicted from a simple diatomic molecular bond. ZnH vibrations exhibit much higher energies, and HCl much lower energies, than those calculated from the model. These results are discussed in terms of the ionicity of crystal bonds.
Raman Scattering in Gallium Selenide and Sulfide Films
Authors: Ibragimov T. D. , Kurbanova G. G. , Gorelik V. S. 
Published: July 2007

AbstractThe spectra of Raman scattering (RS) in gallium selenide and sulfide films are investigated. The variation in the intensity of RS peaks with the film thickness is shown to be fairly well described by the theory of light scattering in an absorbing medium. A deviation from this theory is observed at the peak corresponding to the RS‐forbidden A mode of GaSe. It is explained by the contribution of the surface vibrational states to the RS cross‐section at this peak.
Dynamic and Electrooptic Parameters of Monolayers in Ethane Adsorbed on Graphite
Authors: Podoprigora V. G. , Remizov I. A. , Shabanov V. F. , Shmeleva L. V. 
Published: July 2007

AbstractThe vibration spectrum of surface phonons for ordered phases of ethane monolayers adsorbed on graphite is investigated using different potential functions. The average heat motion amplitudes of molecules adlayer, effective molecular polarizabilities, and their derivatives with respect to external coordinates, which determine Raman spectra intensities as well as the section of one‐phonon inelastic neutron scattering from the surface are calculated taking into account the ethane‐substrate dynamic interaction. The last results are compared with experimental ones.
Absence of the Gap in the Optical Excitation Spectrum of TCNQ Salts with Methyl Derivatives of Pyridinium
Authors: Vainrub A. M. , Zavt G. S. , Graja A. 
Published: July 2007

AbstractIt is shown that the dispersion of the real and imaginary parts of the dielectric function of the TCNQ salts with methyl derivatives of pyridinium gives important information about the density of electronic states. It leads to the conclusion that a gap is not present in the optical excitation spectrum of the salts. It is shown that the model of the localized charge oscillations in dimers is inadequate for the salts.
Phase Transition and Padé Approximants for Fröhlich Polarons
Authors: Selyugin O. V. , Smondyrev M. A. 
Published: July 2007

AbstractTo extrapolate the weak‐ and the strong‐coupling expansions into the intermediate‐coupling regime two‐point nondiagonal Padé approximants are used. It is observed that there exist two alternative versions of approximants, leading to upper and lower bounds whose properties differ from those proven for Stieltjes series. Taking the Feynman polaron as an example, its characteristics are calculated in higher orders of the weak‐ and the strong‐coupling expansions and the corresponding Padé approximants are constructed. This makes possible to tighten the gap between the bounds considerably. Applying the method to the actual Fröhlich polaron the exact result are used of three‐loops calculations of its ground state energy (E3 = −0.806070048 × 10−3). The polaron characteristics seem to lie between smooth functions of the coupling constant — the fact that restricts their hypothetic jumps. This indicates the absence of a phase transition at least in those numerical limits where it is suspected to exist.
Reentrant Paramagnetic‐AFM Paramagnetic Phase Transitions in La2CuO4 Theory
Authors: Hudák O. 
Published: July 2007

AbstractStatistical thermodynamic mean‐field theory for 3d AFM ordering in La2CuO4‐δ is presented. Conditions for its existence, reentrant phenomena, effective reduction of magnetic moments, density temperature dependence of magnetic singlets, and isolated 1/2‐spins are the main theoretical results. Their correspondence with experimental results is discussed.
Z2‐Oscillations of the Proton Stopping Maximum in Gases and Solids
Authors: Balashova L. L. , Chumanova O. V. , Kabachnik N. M. 
Published: July 2007

AbstractThe local electron density approximation is used to calculate the position and value of the maximum in the proton stopping cross‐section for gases and solids. The electron density of atoms in gases is calculated using the Hartree‐Fock‐Slater approximation. The electron density of solids is represented by a muffin‐tin model. The calculations show significant variations in the position of the stopping maximum as a function of Z2 and demonstrate a substantial difference in the Z2‐dependences for gases and solids. The calculation results are in qualitative agreement with experimental data.
Relations between Characteristics of Point Defects and Bulk Properties of Solids a Criticism of the Varotsos‐Alexopoulos Model
Authors: Bekf D. L. , Neumann G. , Szabó I. A. 
Published: July 2007

AbstractUsing the similarity of the effective potentials seen by ions in solids general relations between characteristics of point defects (i.e. the volume vi, the entropy si and the energy Qi of formation, migration, and activation) and bulk properties of solids are derived. It is shown that the basic assumption of the Varotsos‐Alexopoulos‐model (VA‐model) is not necessarily valid. Using dimensional analysis the validity conditions of this model are expressed in a form of partial differential equation from which relations “derived” by Varotsos and Alexopoulos are obtained. Their relations are different from the here obtained results because the ratios of vi, si, and Qi are proportional to expressions containing only bulk parameters of the solid, while in the relations obtained by us there are proportionality factors depending on i, i.e. these constants are different for the formation, migration, and activation (formation plus migration) processes. It is also shown that the basic assumption of the VA‐model is not valid for a harmonic solid. Experimental data for f.c.c. metals definitely confirm these results instead of those obtained by Varotsos and Alexopoulos.
Correlation Mechanism to Change Lattice Parameters and Phase Transitions in Compounds with Intermediate Valency
Authors: Manakova L. A. , Ionov S. P. 
Published: July 2007

AbstractFor compounds with intermediate valency (IV) a microscopic mechanism of changing the parameters of crystal lattice depending on the impurity concentration (or pressure) and temperature is suggested. The mechanism is based on the exact account of the Coulomb correlation and hybridization between f‐ and d‐electrons. For that the “non‐Fröhlich” terms in the electron—phonon interaction proportional to the first and second derivatives of the Coulomb interactions and overlapping integrals of f‐ and d‐electrons are considered. These terms in the electron—phonon interaction contain an explicit dependence on the interatomic distance and cause additional (as compared to the termal) shifts of the lattice sites on account of the Coulomb correlations. The corresponding additions for the lattice parameter depend on the concentration of the impurities x (or pressure) and temperature T. The dependences of the lattice parameter on x and T are obtained for both, the semiconductor and metallic phase. The equation for the transition temperature into the state with IV and the existence condition of this state with concentration are obtained. A comparison of the dependences with experimental ones obtained on the basis of the correlation mechanism is made on the example of the solid solutions Sm1−xRS (R3+ is a rare earth element for instance Gd, Y etc.).
Collective Excitations in Microcrystal Aggregates and Composites
Authors: Monecke J. 
Published: July 2007

AbstractThe optical properties of aggregates of microcrystals are dominated by surface excitations. The Raman and ir absorption spectra of polar microcrystals show, however, peaks at the bulk TO‐phonon frequencies, too, the occurrence of which depends on the sample preparation, i.e. on the aggregate microstructure. A recently developed theory for the dielectric function of composites of different topologies is applied to the calculation of the phonon spectra. It is shown that this theory explains the occurrence of bulk TO‐phonon peaks in appropriate microstructures.
Theoretical Investigation of XPS, UPS, and BIS in Rare‐Earth Compounds — Thulium Monochalcogenides
Authors: Nizhnikova G. P. , Farberovich O. V. 
Published: July 2007

AbstractThe investigation of electron spectra in thulium monosulphide and monoselenide is based on the calculations of relative intensities for multiplet transitions fN → fN±1 in the intermediate coupling using the results of self‐consistent band calculations as a zero approximation of perturbation theory. Correct interpretation of all experimental data in rare‐earth compounds is shown to be actual only in the framework of the common calculational model of excitations from highly localized 4f‐states to delocalized band states.
Polariton Theory of Light Propagation in Crystals II. Crystal Optics Approximation
Authors: Koinov Z. G. , Glinskii G. F. 
Published: July 2007

AbstractUsing the method of successive integrations first over rapidly varying photon fields and then over slowly varying photon fields a new tensor ϵαβ(Q, ωv) is defined that provides both, the equation for obtaining the polariton spectra ωv(Q) and the relation between the displacement D(Q) and the electric field E(Q) corresponding to the (v, Q) normal mode in crystals.
Optical Studies of Electronic Transitions of Mn2+ Ion in Na2Mn3Cl8 Single Crystals
Authors: Talapatra D. , Mukherjee R. K. 
Published: July 2007

AbstractLow temperature polarised absorption, and emission as well as excitation spectra of Mn2+ in Na2Mn3Cl8 single crystals are reported. Eight d—d bands are observed in the optical spectra with some additional fine features. Analysis of the spectra indicates octahedral site symmetry around the hexacoordinated Mn2+ ion. The general features of the spectra are analysed quite satisfactorily within the framework of the strong field scheme of Tanabe and Sugano including Trees' correction. The finer spectral details are accounted for by invoking vibronic interactions involving different sites.
Electronic Properties of Vacancy‐Induced Structures in AlAs/GaAs Superlattices
Authors: Wang En‐Ge , Zhang Li‐Yuan , Wang Huai‐Yu 
Published: July 2007

AbstractFor the first time a detailed description is presented of electronic properties in (AlAs)n/(GaAs)n (n = 1, 3) superlattices with different vacancies. The local‐ and partial‐DOS of the vacancy neighbor atoms are calculated within the tight‐binding approximation including nearest and next‐nearest neighbor interactions. The shift of the band‐edge in the point‐defect structures is about 0.14 eV, which is very similar to that of bulk GaAs material and confirm that the top of the valence‐band of these kind of thin superlattices is derived from the As anion p states, and the bottom of the conduction‐band from the Ga or Al cation. Also a negative center is found around a group‐III atom vacancy in the bulk and a local field, which is similar to that of an acceptor impurity, across the interface. A comparison with AlAs/GaAs superlattices with and without impurities is given.
Hole Velocity in an Electric Field for Valence Bands Degenerate at k = 0
Authors: Dargys A. 
Published: July 2007

AbstractIn p‐type semiconductors having spherical constant energy surfaces and parabolic dispersion law the velocity of the hole immersed in an electric field F, as known, is described by the simple formula Ft/mh,1, where t is the time and mh,1 the effective mass of heavy or light holes. The paper shows that inclusion of intervalence tunneling between heavy and light mass subbands leads to a more complicated time dependence of the hole velocity, especially near the point of degeneracy, where the wave vector k = 0. The curves of the time dependence of hole velocity for parameters typical to p‐Ge and for some values of the electric field and initial hole wave vector are presented. The paper also demonstrates how the theory of angular momentum can be adapted to the problems of hole dynamics in valence bands degenerated at k = 0.
Theory of the Residual Resistivity Dipole Diffusion of Non‐Interacting Particles Around a Fixed Point Scatterer
Authors: Lenk R. 
Published: July 2007

AbstractEmploying a superposition representation of the microcanonical density matrix the perturbation of the stationary diffusion process by a fixed point scatterer is treated approximately. The primary dipole distributions of carrier and current density are calculated and interpreted without additional assumptions. The stationarity of the current is shown explicitly. The primary dipole is localized in a region limited by the mean free path. The classical diffusion process which follows removes this localization, the electrostatic screening by the ensemble of all electrons restores it. The ideas of Landauer are confirmed within a coherent theoretical scheme.
Spin‐Canting Effect and Magnetic Moment of LiZn Ferrite
Authors: Zhang Shouye , Fong Guangyao , Mao Ming 
Published: July 2007

AbstractThe magnetic moment at 0 K of zinc‐substituted lithium ferrite is calculated, based on the spin‐canting model, for an accurate relationship between the moment and the substituent level of zinc. A modified computational plan is adopted in the calculation in contrast with those of recent publications so that a hitherto optimal fitting between the theory and experiment is realized. A generalization is also made to the case of double‐substituted LiTiZn ferrite.
NMR of 167Er and Magnetic Structure of Er3Fe5O12 Garnet
Authors: Savosta M. M. , Doroshev V. D. , Novák P. , Veltruský I. 
Published: July 2007

AbstractNMR of 167Er in Er3Fe5O12 garnet is studied at temperatures 2.1 to 4.2 K using the spin echo method. Two spectra centered at 448.5 and 691 MHz are observed and an unambiguous correspondence between them and two inequivalent positions of Er3+ ions is established. With raising temperature the relaxation time of the spectrum at 448.5 MHz decreases rapidly and at 4.2 K its detection is difficult. The magnitudes of the magnetic moments of the Er3+ ions are determined and the resonance frequencies are discussed within the framework of the crystal field theory and isotropic exchange approximation for the Er3+ ion.
Optical Studies on Europium Doped K2SO4
Authors: Kumar V. S. Kishan , Sastry S. B. S. , Acharyulu B. S. V. S. R. 
Published: July 2007

AbstractOptical absorption (OA), fluorescence, and thermoluminescence are studied on γ‐irradiated K2SO4:Eu crystals. The OA spectrum shows a prominent peak around 5.33 eV which is identified as due to europium ions in their divalent state (Eu2+). On irradiation, the population of Eu2+ is found to increase. Fluorescence shows the characteristic Eu2+ emission around 3.05 eV. The glow curve consists of an intense peak around 365 K with two weaker ones around 415 and 435 K. The emission under all these glow peaks is the same and consists of a single band around 3.06 eV attributable again to the characteristic emission of Eu2+ ions.
The Quantum Theory of the Optical Activity of Ionic Dielectric Crystals
Authors: Kotsur S. S. , Stasyuk I. V. 
Published: July 2007

AbstractIn the frames of the field theoretical approach an analytical expression for the dielectric permeability tensor of ionic dielectric crystals, containing the contributions of higher multipole momenta, is obtained, taking into account the spatial dispersion. The expression for the tensor describing optical activity is separated; its analysis is performed. The Hubbard operator formalism and the two‐time Green's function method are used.
Effects of Correlated Rotation of Linear Molecules in the Low‐Temperature Dynamics and Thermodynamics of Weak Molecular Solutions
Authors: Kokshenev V. B. , Zholonko N. N. 
Published: July 2007

AbstractThe paper proposes a pseudospin approach to describe low‐temperature dynamics and thermodynamics of weak molecular solutions of linear molecules in atomic cryomatrices. On the basis of a microscopic Hamiltonian, a direct analogue of a weak ortho‐parahydrogen solution, the characteristics energies of various types of intermolecular interactions are estimated, i.e. the direct quadrupole‐quadrupole one and the indirect ones, dynamic and static, which involve phonons. The thermodynamic characteristics (specific heat, thermal expansion, and the Grüneisen parameter) of the rotational subsystem of the 14N2‐Ar solution are calculated with consideration of longrange correlations in the molecule rotation. A comparison with experimental data on the specific heat of 14N2‐Ar is made.
Gap Modes and Local Density of States of Impurities in RbCl and KBr
Authors: Rath B. K. , Ram P. N. 
Published: July 2007

AbstractA nearest‐neighbour defect model is employed to calculate the local density of states of substitutional impurities K+ and Br− in RbCl and Rb+ and Cl− in KBr. A detailed investigation of resonance condition is made and possible resonance modes are identified. Contrary to earlier assumption of gap modes in all the systems, resonance modes are identified except in KBr:Rb+ in which a gap mode is found.
Quantum‐Chemical‐Calculations of Models for Surface Defects in Dehydroxylated Silica
Authors: Lygin V. I. , Serazetdinov A. D. , Chertikina O. I. , Ryabenko E. A. 
Published: July 2007

AbstractA quantum‐chemical analysis is made of surface defects formed during dehydroxylation of silica. Calculations are made using the MNDO method with optimization of geometric parameters of silica clusters. The results obtained show that surface dehydroxylation leads mainly to the formation of siloxane bridges with different rates of strain. The formation of other types of defects can occur only at high rates of dehydroxylation.
Densities of Interstitial Electrons in Pd(Ni)Noble Metal Alloys
Authors: Dębowska E. , Rudzińaska‐Girulska J. 
Published: July 2007

AbstractThe ion core radii rc and interstitial electron densities nint for Pd, Ni, Ag, and Cu and for binary random alloys of these metals throughout the concentration ranges have been calculated on the basis of positron annihilation data. The differences in rc and nint for pure metals are suggested to be the main reason of different electronic structure of Pd–Cu and Pd(Ni)–Ag(Cu) alloys being the representatives of VCA and split‐band alloys, respectively.
Correlation Effects of the Antiferromagnetic Phase in the Hubbard Model
Authors: Wel G. Z. , Nie H. Q. , Zhang K. Y. 
Published: July 2007

AbstractUsing series expansion of local approach, the electron coupling between nearest‐neighbour sites is considered to investigate the electron correlation effect in the Hubbard model. The results show that when the off‐diagonal elements of the density matrix are considered in the calculation, it leads to an enhancement of double occupancy and are duce of the formation of the local moments.
Ab Intio Calculations on the Adsorption of H, O, and CO atop Cu2+ on MgO(001)
Authors: Bacalis N. C. , Kunz A. B. 
Published: July 2007

AbstractThe adsorption of hydrogen, oxygen, and carbon monoxide atop Cu2+ in a Mg‐vacancy on the MgO(001) surface is studied in a cluster Hartree‐Fock approximation. The H atom binds slightly atop Cu2+ with binding energy of 0.05 eV. The O atom binds with Cu2+ in a quartet spin state with binding energy of about 0.12 eV. In the doublet state it does not bind to Cu2+. The CO molecule in a Cu2+CO geometry perpendicular to the surface binds to Cu2+ with binding energy of about 0.2 eV. In the Cu2+OC geometry it binds directly with Cu2+ with about 0.33 eV. In both geomtrie, the atom of CO closer to the Cu2+ has some more electronic charge near the surface, than in free space. In all three substances, mutual exchanges of electrons occur between z‐directed orbitals. It seems that the adsorption of CO is rather electrostatic in nature (via the dipole moment) than covalent, where a donation and a back donation occurs. In both geometries the donation is mainly from the 5σ CO orbital. The back donation from Cu2+ occurs mainly with the 2σ* CO orbital in the Cu2+OC geometry. In the Cu2+CO geometry it occurs mainly with a σ orbital.
The Enrgy Transfer between Free Excitons, Bound Excitons, and the 3d‐Shell of Mn2+ in Zn1−xSe Mixed Crystals and the s–d Type Exchange Interaction
Authors: Stutnbäumer U. , Gumlich H. ‐E. , Zuber H. 
Published: July 2007

AbstractExcitation spectra of the Mn2+ emission band 4T1 → 6A1 of Zn1−xMnxSe and their dependence on the crystal temperature and the manganese concentration (x ≦ 0.016) gives evidenve of an excitonic energy transfer from free and bound excitons to the 3d‐shell of Mn2+. Reflection spectra and the comparison of excitation maxima of free and bound excitons reveal some steps of the transfr of excitonic energy to the luminescence centre Mn2+ in Zn1−xMnxSe. The full spinsplitting of bound excitons which is not determined by former luminescence experiments is observed (up to 90 meV at B = 5 T) in excitation spectroscopy of the Mn2+ emission band and the s–d exchange constant relation in Zn1−xMnxSe is determind to β/α = −5.5 ± 0.6.