bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Self‐Consistent Statistical Theory of Anharmonic Effects in Imperfect Crystals
Authors: Zubov V. I. , Rabelo J. N. Teixeira 
Published: July 2007

AbstractThe improved unsymmetrized self‐consistent field method developed in preceding papers is used to study anharmonic effects in imperfect crystals. Various one‐dimensional models of anharmonic crystals with defects are considered: vacancy, free surface, adsorption with taking into account the influence of adatoms on the adsorbent, and substitutional impurities. The formulae for the lattice relaxation near defects, for the effective amplitudes of the anharmonic vibrations of atoms, and for the Helmholtz free energy are obtained. They are expressed in terms of the nearest‐neighbour interaction potentials and their derivatives of several orders at the equilibrium points. A comparison with known results for some harmonic models is made. The decisive role of the anharmonicity in such effects as the temperature dependence of the lattice relaxation and the influence of the imperfections on thermal properties of crystals is emphasized. The possibility of application of the method to three‐dimensional imperfect crystals, as well as of taking into consideration the interactions with next neighbours is noted.
Thermoluminescence of BaFCl:Dy and BaFCl:Cu X‐Irradiated at Room Temperature
Authors: Inabe K. , Utsui Y. , Takeuchi N. 
Published: July 2007

AbstractThree glow peaks around 320, 370, and 410 K are observed for X‐irradiated BaFCl:Dy and BaFCl:Cu. Optical bleaching effects on both glow peaks and F centers suggest that the thermal decay of F(Cl−) centers is not directly related to the 370 and 410 K peaks. Emission spectra indicate that the luminescence centers of these peaks of BaFCl:Dy can be attributed to Dy3+ ions. On the basis of concluding the luminescence centers to be Dy3+, the glow peak reactions are proposed tentatively.
On the Interband Absorption in Disordered Semiconductors
Authors: Arbuzov Yu. D. , Kolenkin M. Yu. 
Published: July 2007

AbstractThe imaginary part of the interband dielectric function ϵ2(ω) of disordered semiconductors is calculated in the case of a Gaussian random field. The corrections to the semiclassical expression for ϵ2(ω) are obtained. The limits of validity of the semiclassical approximation are found.
Nonlinear Propagation of Nanosecond Laser Pulses through Polycrystalline CuCl Layers
Authors: Bigot J. Y. , Frindi M. , Fidorra F. , Levy R. , Hönerlage B. 
Published: July 2007

AbstractA temporal and spectral analysis is made of high intensity nanosecond laser pulses when propagating through polycrystalline CuCl samples of different thickness. The spectral region investigated is around the two‐photon resonance of the biexciton. The dynamical behaviour of the nonlinear transmission is studied when varying the laser incident intensity, its photon energy, and the sample thickness. It is shown that the experimental results can be explained, when calculating the transient dielectric function. The importance of the dynamics of excitons and biexcitons is stressed.
LO‐Phonon Modes Bound to Neutral Impurities in Polar Semiconductors. I. General Theory
Authors: Monecke J. , Cordts W. , Irmer G. , Bairamov B. H. , Toporov V. V. 
Published: July 2007

AbstractThe influence of the Fröhlich interaction between charge carriers bound at impurities and LO‐phonons in polar semiconductors is considered within second‐order perturbation theory taking into account the possibility of degenerate unperturbed electronic ground states. From the general theory presented here changes of the bare electronic excitation energies (bound polaron excitations), Jahn‐Teller like splittings of degenerate ground states and the formation of bound to neutral impurities phonons (dielectric modes) can be obtained. The application of the general theory to special cases and experimental results will be published in a forthcoming paper.
Further Calculations of the F+‐Center Wave Function for Lithium Niobate
Authors: Ho Fat Duen 
Published: July 2007

AbstractThis work is a continuous effort of the F+‐center calculation for lithium niobate. The simplified semicontinuum model developed previously by this author is again used. The polarization effect is taken into account. Although the major procedures follow those developed before, there is one departure in the 2p‐energy‐eigenvalue calculation. It is assumed that the Franck‐Condon principle applies, and that the ions do not move during the absorption process. The transition energies computed here are rather compatible with those values calculated by using the point‐ion‐lattice model. All results are found to be in good agreement with the experimentally observed value.
Localization Effect of Electrons in the InP–SiO2 Interface
Authors: Er‐wang Mao , Hung‐rei Zhang , Wei‐yuan Wang , Liang Ye , Guo‐ping Fang 
Published: July 2007

AbstractA research on the conductivity of the InP‐SiO2 interface reveals a localization effect related to long‐range fluctuations of the surface potential. The investigation of the negative magnetoresistance effect shows that the inelastic scattering interactions of electron–electron and electron–polar optic phonon play an important role in the InP interface and obviously affect the negative magnetoresistance. Interaction between electrons is decisively important in activated localization conductance and Mott's mobility edge model is the limit of the model obtained by neglecting the interaction.
IR Spectroscopy and Structure of RF Magnetron Sputtered a‐SiC:H Films
Authors: Rübel H. , Schröder B. , Fuhs W. , Krauskopf J. , Rupp T. , Bethge K. 
Published: July 2007

AbstractAmorphous hydrogenated silicon carbide (a‐SiC:H) films are prepared by magnetron sputtering of crystalline silicon in an argon—hydrogen—methane atmosphere. The specific absorption modes (wagging, rocking, deformation, stretching) of the SiC, (CHm)nC/Si(n = 1, 2, 3; m = 2, 3), and SiHm−(m = 1,2) groups are assigned and analyzed. The composition of the films is determined by nuclear reaction techniques. Structural, electrical, and optical properties of the films show characteristic changes near an alloy composition of a‐Si1−xCx:H, x = 0.5 which indicate the transition to a structure with threefold coordinated carbon. For x ⪆ 0.75 in the infrared absorption spectra an absorption band is identified which arises from graphitic constituents.
Effect of Pressure on the Luminescence of Trapped Excitons in Xe Crystals
Authors: Kink R. , Kalder K. , Lôhmus A. , Niedrais H. 
Published: July 2007

AbstractAt 115 to 130 K, where the concentration of vacancies in solid Xe is in thermodynamical equilibrium, the intensities of two luminescence bands at 7.2 (A) and 7.6 eV (B) are investigated for Xe crystals under 70 at pressure or without any excess pressure. The decrease of the band A intensity compared to that of the band B is in reasonable agreement with the decrease of the vacancy concentration under an excess pressure. The results confirm an earlier suggestion that the band A originates from excitons trapped at vacancies, whereas the band B is due to self‐trapped excitons.
Electronic Structure and Optical Properties of Polycrystalline Cubic Semiconductors
Authors: Gavrilenko V. I. 
Published: July 2007

AbstractAn analysis of the electronic energy structure (EES) in ideal cubic semiconductors shows that the values of direct energy gaps E′0 and E′1 are determined by an interatomic interaction primarily in the nearest coordination sphere. This is the reason of their relative stability to external effects (mechanical and electric fields, atomic structure distortions, etc.) which may be observed in the experiments. A method for calculating the EES in polycrystalline cubic semiconductors with regard to the main factors (atomic structure distortions, internal mechanical and electric fields) characterizing the grain boundary effect is proposed. The EES of polycrystalline silicon in dependence on an average size of microcrystallites is calculated. The main conclusions of this study are confirmed by the experimental data available in literature.
Electronic Structure and Magnetism of AFe2 Compounds with C14 and C15 Laves Structures
Authors: Terao K. , Shimizu M. 
Published: July 2007

AbstractThe d‐band densities of states are calculated by the recursion method for the paramagnetic AFe compounds with C14 and C15 structures, where A is occupied by 3d (Se, Ti, V), 4d (Y, Zr, Nb) or 5d (Lu, Hf, Ta) series' elements. The densities of states of the ferromagnetic and antiferromagnetic (Zr1−xNbx)Fe2 compounds with C15 and C14 structures are calculated. The pseudobinary systems are treated within a virtual crystal approximation. The trends of the crystal structures are related to the d electron number around the A site. Magnetic moment and spontaneous volume magnetostriction are calculated on the basis of the Stoner theory.
Fine Structure of the Fast Luminescence Component from BaF2 Crystal Excited by Fast Electrons
Authors: Kubota S. , Kanai N. , Ruan J. 
Published: July 2007

AbstractA fine structure (a new 195 nm band) is found of the fast luminescence component from BaF2 crystal excited by electrons. This band has a decay time of (0.8 ± 0.1) ns and is observed in the case of electron excitation and not in α‐particle excitation. The observed fine structure is explained by the model of Aleksandrov et al.
On the model calculation of the excitonic‐like states and their possible role in autocatalytic processes. I. Application to the formation of autocatalytic NiP Amorphous Coatings
Authors: Demidenko V. S. , Szász A. , Aysawi M. A. , Kuznetsov V. D. 
Published: July 2007

AbstractA new exciton‐like excitation mechanism is suggested for the formation of amorphous NiP coatings based on the special spatial bonds of hydrogen ions on the surface.
Study of elastic properties and their pressure dependence of zincblende structure semiconductors
Authors: Singh R. K. , Singh Sadhna 
Published: July 2007

AbstractA three‐body force potential is used to derive the correct expressions for third‐order elastic constants and pressure derivatives of second‐order elastic constants for the zincblende structure semiconductors following the lines of Sharma and Verma. These corrected expressions are used for the first time to study the elastic properties and their pressure dependence of ZnS, ZnSe, and ZnTe. It is found that the inclusion of the corrections and the van der Waals interactions yield more reasonable values of the third‐order elastic constants and the pressure derivatives of second‐order elastic constants than those obtained by earlier workers from their somewhat erroneous expressions.
Representation of Energetical and Low‐Field Magnetic Properties of J = 5/2 Rare Earth Ion States in Tetragonal Crystal Fields
Authors: Fischer G. , Herr A. 
Published: July 2007

AbstractThe effect of a tetragonal crystal field on a J = 5/2 rare earth ion is calculated and is presented in a graphical form giving a complete description of the energy, the individual magnetic moment, and Van Vleck susceptibility of each doublet resulting from the crystal field splitting, as a function of two dimensionless parameters and a scale factor. These magnetic properties, which correspond to terms in H and H2 in the development of the energy in presence of a perturbating magnetic field, are given for both the cases, when H is either parallel or orthogonal to the c axis. The results are applied to the compound CeRu2Si2.
Multiple Scattering Study for CI K XANES of KCl, SrCl2, and CsCl Crystals
Authors: Kitamura M. , Muramatsu S. , Sugiura C. 
Published: July 2007

AbstractA method for constructing crystal potentials which explicitly includes Madelung corrections due to charge transfer is presented for multicomponent crystals. In two‐component crystals, this correction is systematically taken into account by the use of a reduced Madelung constant. On the basis of the crystal potentials obtained with this method including self‐consistent field calculations, Cl K XANES of KCl, SrCl2, and CsCl crystals is studied by a multiple scattering theory within the muffin‐tin approximation. It is found that the overall profiles of experimental spectra are well explained by the calculations.
Raman Spectra and Directional Dispersion in LiNbO3 and LiTaO3
Authors: Yang Xichen , Lan Guoxiang , Li Bing , Wang Huafu 
Published: July 2007

AbstractRaman spectra of ordinary and extraordinary phonons in LiNbO3 and LiTaO3 are recorded under a set of angles between wave vector and optic axis with the same backward scattering geometry, which makes all of the extraordinary phonons to appear in one directional‐dispersion spectra series, and the directional dispersion is reliably determined. The symmetry and the number of polar phonons in both the crystals are found to be the same, 4A1T + 4A1L + 9ET + 9EL. The directional dispersion of extraordinary phonons has thirteen branches with similar coupling in LiNbO3 and LiTaO3.
Optical Bleaching of the F+ Optical Absorption Bands in ZnS Crystals
Authors: Matsuura K. , Kishida S. , Yoshida K. , Tsubumi I. 
Published: July 2007

AbstractThe optical bleaching of the 2.3 and 2.9 eV bands related to the F+ centers in the electron‐irradiated and Zn‐treated ZnS crystals are measured from 25 K to room temperature under illumination of light from 395 to 702 nm. It is found that the 2.9 eV band is bleached in exactly the same manner as the 2.3 eV band and that under illumination of light around 2.9 eV, these bands are bleached with a decay constant independent of temperature, while under illumination of light around 2.3 eV, they are bleached by two stages, where the first stage has a decay constant independent of temperature and the second stage has a decay constant with an activation energy of (49 ± 5) meV. These bands are confirmed to be due to the same defects. It is deduced that the 2.3 eV absorption band is due to the transition of electrons from the ground state to the lower excited state located (49 ± 5) meV below the conduction band, while the 2.9 eV band is due to the transition to the higher excited state located in or closely below the conduction band.
Electron Paramagnetic Resonance of Titanium in GaP
Authors: Kreissl J. , Gehlhoff W. , Ulrici W. 
Published: July 2007

AbstractEPR and photo‐EPR experiments are reported performed on LEC‐grown GaP:Ti with different Fermi‐level positions. An isotropic signal with g = 1.952 and a linewidth of 20.0 mT is assigned to Ti. The position of the Ti/Ti acceptor level is located at (0.5 ± 0.1) eV below the conduction band minimum.
Thermal Vibrations in Substoichiometric Vanadium Nitrides. Dynamical Deformation Effect
Authors: Čapková P. , Smrčok L. , ŠIma V. , Valvoda V. , Chalupa B. , Ettmayer P. 
Published: July 2007

AbstractThermal parameters BV and BN in substoichiometric vanadium nitrides are studied by means of X‐ray and neutron diffraction without separation of Debye‐Waller factor into dynamic and static parts. With increasing vacancy concentration in N‐sublattice the decrease of BV and increase of BN are observed. This unusual behaviour of B parameters can be explained introducing the static displacements of V atoms adjacent to N‐vacancies. The observed significant differences between BN values determined by X‐ray and neutron diffraction are interpreted as the difference between shell and core vibrations known as dynamical deformation effect.
Carrier Drift Mobilities in Some Organic Solids A Search for Organic Photovoltaic Materials. II. Charge Transport Calculations in s‐Tetrazine and 4 Phenylazoazobenzene
Authors: Kumar B. 
Published: July 2007

AbstractExcess electron and excess hole mobilities of S‐tetrazine and 4‐phenylazoazobenzene are calculated using the tight binding approximation with SCF‐AO's as a basis set. The applicability of the band model in these organic solids is discussed in the light of Munn and Siebrand's theory of charge transport in organic solids. The results show that these two organic solids may be good candidate materials for organic photovoltaic devices.
Interaction between Localized and Delocalized States Indicated from Temperature‐Dependent ESR Study of Submetallic P‐Doped Si
Authors: Stesmans A. 
Published: July 2007

AbstractA K‐band electron spin resonance (ESR) analysis has been carried out on submetallic Si:P powders containing (1.7 ± 0.1) × 1018 P atoms cm−3. As expected, only one signal, generally referred to as the central pair line (CPL), is observed. Accurate data of the peak‐to‐peak linewidth ΔBpp and g‐value are presented for the temperature range 1.6 K ≦ T ≦ 300 K. Unlike previous results, g shows up to be T‐dependent in the range T ⪅ 100 K, g varying from g = 1.99860 + 0.00002 at T ≈ 15 K to g = 1.99890 ± 0.00003 at T = 100 K. The implication of the experimental results regarding the physical model of the P‐in‐Si behaviour is discussed. In the range T ⪅ 4.2 K, comparison to other data reveals the existence of a significant different T dependence of g and ΔBpp between the high and low observational‐frequency situations. In the higher T range, the data are indicative of the presence of an s‐d like interaction between localized donor spins and delocalized electrons, which gradually increases with T. In that sense, it may explain the apparent “single line” behaviour of the CPL over the whole range 1.6 K ≦ T ≦ 300 K.
Atomic Level Stresses in Solids and Liquids
Authors: Vitek V. , Egami T. 
Published: July 2007

AbstractIn condensed matter systems there are, in general, stresses at atomic level which are related to local incompatibilities. Only in perfect crystals in which all the atoms are equivalent such incompatibilities do not exist but they are present in ordered structures with non‐equivalent atoms and in any disordered structure. In this paper evaluation of these stresses in the framework of the local density functional approximation, embedded atom method, and central force interactions is first described. The usefulness and physical significance of this concept in the description of the local atomic structure of liquids and glasses is then demonstrated using as examples atomistic studies of microscopic processes involved in structural relaxation and glass transition. Finally, it is argued that the concept of atomic level stresses provides a general means for describing atomistics of complex structures, both, ordered and disordered.
A Relationship between Prefactor and Activation Energy for Diffusion
Authors: Kirchheim R. , Huang X. Y. 
Published: July 2007

AbstractVery often a relationship is observed between activation energies, Q, of diffusion and the corresponding prefactors, D0. Contrary to the Zener‐Wert relation, where activation energy and prefactor of different species migrating in the same matrix are compared, one species diffusing in a matrix with different defects or slightly varying composition is considered. It is shown that a linear relationship between In D0 and Q very often exists due to the special form of the Arrhenius equation. The slope of the corresponding graph is close to 1/kTa, where Ta is the average temperature of the range covered by the experiments. Experimental results are compiled and compared with this prediction.
Diffusion of H and D in Lutetium
Authors: Völkl J. , Wipf H. , Beaudry B. J. , Gschneidner K. A. 
Published: July 2007

AbstractThe anisotropy and isotope dependence of H (and D) diffusion in h.c.p. LuH0.05 and LuD0.05 is investigated in Gorsky‐effect measurements (380 K < T < 540 K). In spite of the hexagonal lattice structure, no anisotropy in the diffusion behavior can be established within experimental accuracy. The nearly isotropic diffusion can be understood from a consideration of possible atomistic jump processes. The present results are compared with previous studies on H(D) diffusion in h.c.p. metals.
Calculations of the Polarization Energy of a Complex in Alkali Halide Crystals from Zero to Fourth Order
Authors: Cardenas‐García D. , López‐Tellez E. R. , Ruíz‐Mejía C. 
Published: July 2007

AbstractThe polarization energy of a complex is calculated for all alkali halides crystals containing Eu++ impurities. Up to 48 nearest neighbors of the complex are considered, and assumed that the field on each dipole is the one produced by the charge of the complex and by the field produced by the other induced dipoles. The results show that there are no significant changes in all alkali halides when going from second to fourth‐order. Therefore, it is not necessary to take into account a large number of neighbors when calculating the polarization energy. This is a very important result since a low symmetry defect is considered.
Effect of Thermal Expansion on Absorption Band Shift of the F‐Center in Alkali Halides
Authors: Bosi L. , Nimis M. 
Published: July 2007

AbstractIt is shown that the thermal expansion effect in the absorption band shift of the F‐center in alkali halides is more active than the electron lattice interaction effect. This statement is based on the analysis of detailed experimental data concerning the changes in lattice parameter as a function of temperature. The results substantially confirm those obtained in the past (but disregarded in literature) by Jacobs as well as by Brothers and Lynch.
Alloy Analogy for the Multi‐Band Hubbard Hamiltonian
Authors: Kotrla M. , Drchal V. 
Published: July 2007

AbstractA systematic derivation of the alloy analogy for the multi‐band Hamiltonian of the Hubbard type is given. The formalism, of the Hubbard atomic operators is used and the decoupling procedure is applied to the double‐time Green functions. The solution is equivalent to the coherent potential approximation for a set of effective multi‐component alloys and in the single‐band case it is identical to the Hubbard III solution. The theory is valid both, for crystals and for disordered alloys. It is applicable also for the translationally non‐invariant ground state corresponding e.g. to an arbitrary magnetic ordering.
The Regularities in Ground‐ and Excited‐State Absorption Spectra of Impurity Ions of the Iron Group in Crystals
Authors: Veremeichik T. F. 
Published: July 2007

AbstractThe excited‐state absorption spectra (ESS) of crystalline materials doped with ions with dn‐shells are studied theoretically. The method is used of comparison of the ESS with the ground‐state absorption spectra (GSS). Classification of the ESS into three types is made using the electron distribution in the t2 and e subshells of the strong crystal field and the spin values and the regularities for each type are determined. Comparative diagrams of the transition frequencies from the excited states and from the ground states versus Dq/B are drawn. The cases are determined in which the oscillator strengths of the broad band transitions from the excited states can be calculated in the parameters which are determined using the GSS and the oscillator strengths are estimated. The results show that the GSS of the impurity ions with unfilled d‐shells can be used to evaluate the ESS characteristics.
Optical Transitions of Jahn‐Teller Local Centres
Authors: Perlin Yu. E. , Polyanovskii V. M. , Alifanov O. V. 
Published: July 2007

AbstractThe multiphonon optical transitions between degenerate electronic local states are considered taking into account a strong interaction of the local centre (LC) with dynamic Jahn‐Teller active lattice vibrations. The results of numerical evaluation of the band shape are listed at different values of Stokes' loss constants for T ⊗ (a + e) → E ⊗ (a + e) transition of the cubic LC.
Monte Carlo Determination of Short‐Range Parameters for Multicomponent Solid Solutions
Authors: Dimitrov V. I. 
Published: July 2007

AbstractPartial atom distribution functions and short‐range order parameters are calculated for multicomponent (ternary) alloys on the face‐centered cubic lattice. The Monte Carlo method is used to obtain estimates for these quantities for the first five coordination shells. The results are compared with those predicted by an approximate short‐range order theory of multicomponent solid solutions and good agreement is observed between them.