bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Nonlinear Light and Sound Absorption in Materials with Weakly Bound Atoms
Authors: Bonch‐Bruevich V. L. , Kakhlishvili T. Z. 
Published: July 2007

AbstractSome optical and acoustical effects are studied which are due to the anharmonicity of vibrations of weakly bound atoms. Discontinuities are calculated of the sound absorption coefficient and of the real and imaginary parts of the differential dielectric permeability. Amplitudes are estimated of the vibrations corresponding to the nonlinear resonances at the frequencies ω = ω0/2 and ω = ω0/3, ω0 being the eigenfrequency in the linear regime.
Far‐Infrared Dielectric Function of Zincblende ZnS
Authors: Memon A. , Tanner D. B. 
Published: July 2007

AbstractThe complex dielectric response function of zincblende ZnS is determined at 300 K by dispersive Fourier transform spectroscopy. The frequency range studied, 150 to 450 cm−1, spans the frequency of the q = O transverse optic (TO) phonon mode. The frequency dependence of the anharmonic self‐energy function Γ(ν) of the q = 0 TO phonon is calculated from these data. The features observed in the spectrum of Γ(ν) are satisfactorily assigned to multi‐phonon processes by comparison to theoretical lattice dynamics calculations for cubic ZnS.
Structural Disorder Model of Amorphous Semiconductors Thermodynamics of a‐As
Authors: Vaid B. A. , Sharma K. C. 
Published: July 2007

AbstractThe structural disorder model of amorphous semiconductors, near the amorphous to crystalline transition, recently proposed, is generalized for triply coordinated As. The model is able to explain at least qualitatively the change in enthalpy and the configurational entropy during transition.
Static and Thermophysical Properties of Mixed Crystal Systems
Authors: Gupta B. R. K. 
Published: July 2007

AbstractAn analysis of the interionic potential is performed to study the static and thermal properties of KClKBr and KBrKI mixed crystals for the entire range of composition. The interionic potential consists of the long‐range Coulomb and three body interaction, the short‐range van der Waals attraction, and the overlap repulsion, effective up to the second neighbour ions. Instead of using the BM‐type short‐range potential the Hafemeister and Zarht (HZ)‐type repulsive potential is considered between the nearest as well as between the next nearest neighbours. The three body charge transfer parameter f(r) and repulsive hardness parameters are evaluated using respectively the Cochran formula and overlap integrals. The van der Waals interaction coefficients are determined using the Slater‐Kirkwood variational approach. The calculated values of cohesive energy, bulk modulus, and the pressure derivatives of bulk modulus for the mixed crystals under study agree fairly well with available experimental data. The results achieved by previous investigators are also shown for the sake of comparison with the present and experimental investigations.
Correlation and Spectral Properties of Individual Particles of Molecular Crystals with Isolated Point Imperfections
Authors: Vikhrenko V. S. , Kulak M. I. 
Published: July 2007

AbstractThe analogue of the dynamical equations for a crystal lattice is used to calculate the momenta time correlation functions and vibrational spectral densities of individual particles in heavy rare gas solids with defects. Some peculiarities in the behaviour of particles near a vacancy and light or heavy substitutional imperfections are discussed.
Some Comments and Corrections on the Defect Diffusion Models of Dielectric Relaxation
Authors: Bozdemir S. 
Published: July 2007

AbstractAn attempt is made to improve the “defect‐diffusion model” initially proposed by Glarum. Some of the basic ideas underlying the model and assessing its success and rationality as applied to polymer relaxation are discussed. The model is generalized by developing a new one‐dimensional “molecular chain‐defect diffusion model”, namely, extending the single dipole relaxation to a linear chain molecular system. A dipole correlation function derived from this new model under various physical conditions, appears in the form of the Williams‐Watts empirical decay function φ(t) = exp [−(t/τ)γ] with 0 < γ ≦ 1. The results obtained lead to a molecular interpretation of this “universal” non‐exponential decay function.
Anomalous High‐Temperature EPR Linewidths in the Spinel Solid Solution Cu2xCr2xSn2−2xS4
Authors: Colombet P. , Glaunsinger W. S. 
Published: July 2007

AbstractThe spinel spin‐glasses Cu2xCr2xSb2−2xS4 are studied by electron paramagnetic resonance in the temperature range 4 to 560 K. The linewidths at high temperatures are much larger than expected from magnetic measurements, and for 0.25 ≦ x ≦ 0.50 the linewidths are effectively dipolar although the lineshape is Lorentzian. The experimental and estimated exchange‐narrowed line‐widths at high temperatures are then compared for ferromagnetic‐antiferromagnetic and predominantly antiferromagnetic insulating spin‐glasses in which the magnetic ions occupy face‐centered‐cubic lattice sites or B‐sites of the spinel structure.
Umbrella‐Type Magnetic Structures in Diluted Ordered Lithium Ferrospinels
Authors: Maltsev V. I. 
Published: July 2007

AbstractA symmetry analysis of ferrimagnetic structures is carried out in spinels that are isostructural with ordered lithium ferrite. The decrease of crystal symmetry due to the formation of atomic superstructure is shown to be a condition for realization of umbrella‐type magnetic structures in compounds of this class. The neutron diffraction data for lithium‐aluminium and lithium‐gallium ferrospinels are given which confirm the results of the theoretical treatment.
Specific Heat and Magnetocaloric Effects in TbPO4 1. Experiments
Authors: Üffinger G. , Kasten A. 
Published: July 2007

AbstractAt low temperatures TbPO4 undergoes two successive phase transitions. Antiferromagnetic ordering along the tetragonal c‐axis at TN1 = 2.28 K is followed below TN2 = 2.13 K by a structure of lower symmetry where the moments are tilted off the c‐axis by about 20°. The B‐T phase diagram (B along c) is determined down to 1 K by means of specific heat, adiabatic and isothermal field sweeps. In applied field there is an additional spin‐flop phase (between Bc1 = 0.61T and Bc2 = 1.06T in the limit T → 0).
Free Energy of the Amorphous Ferromagnets with Heisenberg Exchange Interaction and Liquid‐Like Disorder
Authors: Vakarchuk I. A. , Rudavskii Yu. K. , Ponedilok G. V. 
Published: July 2007

AbstractA continuous integration method is used for the investigation of the Heisenberg quantum model with structure disorder. The free energy of such system is obtained as the perturbation theory series of the inverse cube of effective exchange interaction radius for arbitrary temperature and spin value. The contribution of magnetic and structure fluctuation effects to the thermodynamics, magnetization of the system, and temperature of the ferromagnetic phase transition is investigated. Numerical calculations on the base of model systems show that the change of critical temperature and low temperature magnetization at the amorphization of a crystal are in qualitative agreement with experimental results.
The Influence of Correlation and Band Structure Effects on an Exciton Weakly Bound to an Isoelectronic Impurity
Authors: Geistlinger H. , Weller W. 
Published: July 2007

AbstractA variational method for the ground state of an exciton bound to an isoelectronic impurity is developed. In contrast to the HTL model the correlation between the electron and the hole is taken into account for the first time, using instead of the hole coordinates the relative electron‐hole coordinates. In this way it is possible to describe the whole region from strong exciton binding, where the HTL model is a good approximation, to the free‐exciton limit, impossible to reach in the HTL model. Furthermore, the method predicts a small potential region (≈ 10 meV) above the threshold for electron binding, where the exciton is still bound. Because the impurity potential is short‐ranged instead of the effective‐mass‐approximation a band structure parametrization of the lowest conduction band is used. As a numerical example the case of GaP:N is considered.
Electrical Properties of Grain Boundaries in InSb Bicrystals
Authors: Herrmann R. , Kraak W. , Nachtwei G. 
Published: July 2007

AbstractElectrical properties of n‐ and p‐type InSb bicrystals with tilt angles of θ = 6° and θ = 13° and carrier concentrations p = NA ‐ ND = 1.5 × 1015 to 3 × 1017 cm−3 are investigated in the temperature range from 77 to 293 K. From the experimental date it is found that in the vicinity of the grain boundary in p‐InSb bicrystals with p < 5 × 1015 cm−3 a pronounced potential barrier (ΦB ≈ 200 meV at T = 150 K) exists. For samples with p > 5 × 1015 cm−3 the height of the potential barrier strongly decreases with increasing carrier concentration p = NA ‐ ND. The dependence of the barrier height on the applied voltage is evaluated numerically, a remarkable decrease of the barrier height with increasing voltage occurs for U > 1 V. The conduction mechanisms through the potential barrier at various temperature intervals are discussed.
Neutron Spin Precession and Spin Dichroism of Nonmagnetic Unpolarized Single Crystals
Authors: Baryshevskii V. G. , Cherepitsa S. V. 
Published: July 2007

AbstractIt is shown that a spin‐orbit interaction of neutrons with crystal nuclei leads to a new phenomenon: neutron spin precession in nonmagnetic unpolarized single crystals and spin dichroism. The spin of the diffracted neutrons with a wavelength of 0.15 nm is rotated by 1.2 rad after transmission of neutrons through a tungsten carbide crystal (WC) of thickness 1 cm, set in exact symmetric Laue diffraction position (211). The neutron spin is rotated in the diffraction plane.
Pair‐Correlation Functions for Liquid Noble Metals through Percus‐Yevick Theory
Authors: Bhattacharya T. , Ghosh A. K. 
Published: July 2007

AbstractPair‐correlation functions for liquid Cu, Ag, and Au are calculated via a numerical iterative solution of the Percus‐Yevick equation using solid‐state pair potentials derived from first‐principles resonant model potential theory. Results are compared with experimental data and theoretical values obtained via the optimized random phase approximation.
Giant Moment, Superparamagnetic, Spin‐Glass, and Quasiferromagnetic Properties of Dilute PtFe Alloys
Authors: Kiymaç K. 
Published: July 2007

AbstractUsing an RF‐SQUID magnetometer, the temperature‐dependent magnetic susceptibility of dilute Pt‐Fe alloys containing 10.5 ppm Fe, and 0.87 and 0.99 at% Fe is measured in the temperature range 1 to 4.2 K and in de‐fields between 0.5 and 15 Oe. For 10.5 ppm Fe, the susceptibility obeys the Curie law, and the saturation magnetic moment μsat is ≈ 9.3μB/Fe. The Pt‐0.87 at% Fe and −0.99 at% Fe alloys are spin‐glass and quasiferromagnetic, respectively, and both show superparamagnetic properties at temperatures between transition temperature Tt and ≈ 2Tt. Furthermore, the susceptibility of these alloys, around and below Tt, is field dependent, decreasing in magnitude with increasing field.
Energy Spectrum and Light Absorption Coefficient for Bound Electron‐Exciton States in One‐ and Two‐Dimensional Molecular Crystals
Authors: Grigorchuk N. I. 
Published: July 2007

AbstractThe energies of bound charge carriers and Frenkel excitons in one‐ and two‐dimensional molecular crystals are calculated in the nearest‐neighbour approximation. The band width of the bound states is found to decrease with increasing interaction potential between these particles. The formulae for the light absorption coefficients with excitation of these states are derived. In the case of narrow electron bands and high temperatures it is shown, that the absorption edge is described by the Urbach rule, and the corresponding peaks in the band have van Hove nature.
Electron–Phonon Interaction as Effective Electron–Electron Interaction
Authors: Enders P. 
Published: July 2007

AbstractAfter rederiving the tight‐binding electron–phonon Hamiltonian for a diatomic chain with special emphasis on the dispersion of the coupling constant the linear electron–phonon interaction is transformed into an effective Electron–Electron one following Chatterjee and Mitra (CM). The subsequent Hartree‐Fock decoupling with inclusion of anomalous averages allows for a simple treatment. Within the one‐mode approximation (keeping q = 0‐phonons only), Bogolyubov's method of approximating Hamiltonian leads to the mean‐field result, therefore, CM's “opposite Born‐Oppenheimer approximation” cuts off the kinetic phonon energy.
Electron Nuclear Double Resonance of the Trapped Hole Center in α‐Al2O3:Mg2+
Authors: Duvarney R. C. , Niklas J. R. , Spaeth J.‐M. 
Published: July 2007

AbstractThe superhyperfine (shf) interactions of trapped hole centers with 27Al neighbor nuclei in α‐Al2O3 doped with Mg2+ are resolved with electron nuclear double resonance (ENDOR). The hole is localized at an O2− ion. With electron nuclear triple resonance (double ENDOR) it could be established that one of the two next nearest neighbor Al3+ ions is missing, but no ENDOR lines due to a Mg2+ impurity can be identified. The isotropic shf interaction constants of the nearest and next nearest Al3+ neighbors are negative. The shf interactions are quantitatively interpreted by taking into account transferred exchange polarization at the oxygen ion. From this, it seems more likely than not that the Al3+ vacancy is filled by a Mg2+ ion.
Radiative Energy Transfer Process in the KCl:Pb++, Eu++ System
Authors: Capelletti R. , Cywiński R. , Manfredi M. , Solzi M. 
Published: July 2007

AbstractMeasurements of emission spectra, time decay scheme, and time resolved spectroscopy, in the temperature range 80 to 300 K, show the existence of an energy transfer process in the KCl:Pb++, Eu++ system at low concentrations of the dopants. The experimental results – in particular time decay scheme both of donors and acceptors – indicate that the transfer is of radiative type; the same conclusion is obtained from the comparison between the transfer probability estimated as if the transfer is supported by a non‐radiative mechanism and the intrinsic decay probability of the donors.
Nonlinear Thomas‐Fermi Dielectric Function in Semiconductors
Authors: Zhang Kaiyi , Chao K. A. 
Published: July 2007

AbstractA nonlinear Thomas‐Fermi dielectric function is derived for semiconductors in the framework of the Resta model. When the concept of an effective impurity charge is introduced to ensure the correct screening radius, the analytical dielectric function agrees excellently with the exact numerical solution.
On the Frequency‐Dependent Small‐Polaron Conductivity in the High‐Temperature Regime
Authors: Loos J. 
Published: July 2007

AbstractUsing the Matsubara‐Green functions the small‐polaron conductivity problem at high temperatures is formulated without making any restricting assumptions concerning the dispersion of the lattice vibrations. All the results obtained within this framework remain finite and meaningful for arbitrary external‐field frequency and for arbitrary phonon bandwidth. Also the dc conductivity deduced as the zero‐frequency limit has no singularities.
Effective Masses in Monatomic and Diatomic Crystals and the Transfer‐Matrix Notion
Authors: Detcheva V. , Metodieva M. , Kandilarov B. D. 
Published: July 2007

AbstractThe effective masses of the electrons in monatomic and diatomic crystals are derived on the basis of one‐dimensional models and in the framework of a relevant transfer matrix. From the general expression thus obtained the particular cases corresponding to all possible band edges of models with δ‐function potentials are deduced. In certain special cases the effective mass characterizing the diatomic crystal may be expressed throughthe effective masses in the two monatomic crystals.
Photostimulated Electron Redistribution between F and F+ Centres in Corundum
Authors: Atabekyan R. R. , Ezoyan R. K. , Gevorkyan V. A. , Vinetskii V. L. 
Published: July 2007

AbstractThe kinetics of electron redistribution between F and F+ centres in corundum during photoexcitation with 6.05 and 4.86 eV quanta is investigated. Empty anion vacancies V(0) are found in corundum after irradiation with 50 MeV electrons at a dose ≈ 1018 electrons/cm2. The concentrations of these vacancies and of other (non‐vacancy) traps S are calculated. The ratio of the F and F+ centre oscillator strengths is defined to fF:f = 3.9:1.A phenomenological theory of the investigated processes is proposed under the assumption that the photoexcited electrons of F and F+ centres execute jumps between different charge states of the anion vacancies. Theory parameters as well as the values of ratios of the electron jumping probabilities are defined.
Optical Absorption of Cr4+ in GaAs:Cr
Authors: Ulrici W. , Kleinert P. 
Published: July 2007

AbstractOptical absorption experiments are reported on p‐type GaAs:Cr:Zn from which the spectral shape of the absorption due to stable Cr4+ is derived in the energy region from the onset at about 0.4 eV up to the GaAs absorption edge. This absorption is interpreted as due to the photoionization transition Cr4+ + hv → Cr3+ + holevb superimposed by the simultaneously occurring transition Cr3+ + hv → Cr2+ + holevb. Its spectral shape at T = 78 K can well be fitted by a calculated one taking into account the uppermost three valence bands, the 4T1(F) ground state of Cr3+ and the 5T2 ground state of Cr2+ located within the gap, and the electron‐phonon coupling of these localized states. The fit yields the optical threshold energy E3 = 0.68 eV and the broadening parameter Γ3 = 0.24 eV of the Cr4+ → Cr3+ transition indicating a strong coupling of the 4T1(F) state of Cr3+ with TA phonons.
Electron Paramagnetic Resonance of Mn2+ in Double Nitrate Crystals
Authors: Seth V. P. , Jain V. K. , Bansal R. S. 
Published: July 2007

AbstractElectron paramagnetic resonance of Mn2+ in Ce2Mg3(NO3)12 · 24 H2O and Ce2Co3(NO3)12 · 24 H2O single crystals is studied in X‐band at 290 and 90 K. Mn2+ substitutes for Mg and Co sites. The spin‐Hamiltonian parameters are evaluated. The broadening of the resolved spectra of Mn2+ doped in Ce2Co3(NO3)12 · 24 H2O on lowering the temperature is discussed in terms of host spin‐lattice relaxation narrowing. An analysis in terms of the superposition theory shows that the intrinsic second order parameter for the ligand oxygen atoms of the site I probably falls within the normal range of oxygen.
Point Defects in Sn‐Doped Sb2Te3 Single Crystals
Authors: Horák J. , Lošťák P. , Matyáš M. 
Published: July 2007

AbstractSingle crystals of Sb2Te3 doped with 0 to 1.0 at% Sn are prepared and the Hall coefficient, Seebeck coefficient, and plasma resonance frequency of the crystals are determined. The incorporation of one Sn atom into the Sb2Te3 crystal corresponds to an origin of ≈ 2.2 to 3.0 holes. Such an increase in the concentration of holes is explained in terms of a decrease in the bond polarization due to the incorporation of negatively‐charged Sn'Sb defects into the Sb sublattice which is favourable for the formation of antisite defects in Sb2Te3. The observed increase in the hole concentration corresponds to the sum of created Sn'Sb defects and newly formed Sb'Te antisite defects in Sn‐doped Sb2Te3.
On Binding and Superconductivity in Isotypes of Cr3Si
Authors: Schubert K. 
Published: July 2007

AbstractAn electron count which permitted previously the interpretation of Raub's rule, that certain homeotypes of Cr3Si occur at certain values of the average group number of the periodic system of elements, is applied to Matthias' rule for a high transformation temperature Tc to the superconductive state in dependence of the average group number. It is inferred that a b ensemble of electrons (b correlation) exists energetically above the ensemble of the d electrons of the first component (e correlation). A completely occupied b correlation with simple commensurability to e is favourable for a high Tc and this rule opens a useful method to find new alloys with high Tc. It appears that the present model for the dependence of superconductivity on binding is compatible with superconductivity theory, so that the confidence into the model for the binding is increased by the easy explanation of high Tc.
Directional Dispersion of the Phonon Modes in Optically Uniaxial Solids, Far‐Infrared Reflection Spectra, Dielectric and Optic Constants, Dynamic Effective Ionic Charges of the Defect Chalcopyrites CdGa2S4, CdGa2Se4, HgGa2S4, and HgGa2Se4
Authors: Haeuseler H. , Wäschenbach G. , Lutz H. D. 
Published: July 2007

AbstractThe polarized far‐infrared reflection spectra of single crystals of the defect chalcopyrites CdGa2S4 CdGa2Se4, HgGa2S4, and HgGa2Se4 grown by vapour phase transport technique are presented in the range from 40 to 600 cm−1. The spectra reveal ten reststrahlen bands as predicted by group theoretical treatment. The oscillator parameters εα∞, ωαf, ωαf, and γαf, the transverse and longitudinal optical phonon frequencies ωTO and ωLO, and the dynamic effective ionic charges are calculated using classical oscillator fit method. The high‐frequency dielectric constants εα∞ show an anisotropic behaviour, the effective charges (Szigeti charges), however, are approximately scalar quantities. From the obtained oscillator parameters the directional dispersion of the extraordinary polar phonons is determined. The reflection spectra calculated for oblique phonons are discussed and compared to those of pellets hot‐pressed from polycrystalline samples.
The Ionic Gyration and Electrogyration in Dielectric Crystals
Authors: Stasyuk I. V. , Kotsur S. S. 
Published: July 2007

AbstractExplicit expressions are obtained for the ionic components of the gyration and electrogyration tensors for dielectric crystals. The symmetry aspects of the ionic gyrotropy and electrogyration are considered. The procedure of calculation of ionic contributions to the electrogyration is illustrated by the model example of the Pb2+ ion in crystalline fields of S4 and C3i symmetry.
Aggregation of Mn2+‐Cation Vacancy Dipoles in KCl Matrix
Authors: Cywiński R. , Mugeński E. , Nowy‐Wiechuła W. , Wiechuła J. 
Published: July 2007

AbstractThe aggregation kinetics of Mn2+‐cation‐vacancy dipoles in the KCl matrix is examined by ESR and photoluminescence methods at room temperature. In dependence on the annealing (aging) conditions four different Mn2+ aggregation products appear in the crystal: luminescent dipole aggregates (no ESR line) formed during short annealing at room temperature, two non‐luminescent Mn2+‐rich microprecipitates (K4MnCl6 and MnCl2) yielding distinct ESR lines, and a non‐luminescent aggregation product not yielding any detectable ESR line. The activation energies obtained for the Mn2+ emission decay at higher temperatures suggest that after a rapid, initial phasetransition like process (0.1 eV) the further slow decay is conditioned by Mn2+ diffusion (0.6 eV).
Resonance LO Phonon‐Assisted Luminescence and Light and Heavy Excitons in NaI Crystals
Authors: O'connel‐Bronin A. A. 
Published: July 2007

AbstractThe resonance multiphonon luminescence spectra of NaI single crystals are investigated experimentally in the temperature region of 4.2 to 65 K. A detailed investigation of the temperature dependence of peak energies and the intensities of the components of the luminescence spectrum as well as a theoretical analysis reveal an unknown component in the region of the zero‐phonon line. This component is interpreted in the framework of the model of light and heavy excitons. On the basis of experimental data for NaI the energy Δ, induced by the short‐range part of exchange interaction, is evaluated. Peculiarities of resonance luminescence in alkali iodides are analysed by using the theory of resonance multiphonon luminescence developed in the studies of semiconductor crystals.