bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Thermal Capture of the Acceptor Level of Gold in Silicon
Authors: Morante J. R. , Carceller J. E. , Cartujo P. , Barbolla J. J. 
Published: July 2007

AbstractOn the basis of the quantum‐defect wave function and assuming a linear coupling, a calculus of the Huang‐Rhys factor S and the other matrix elements is made using the theory of non‐radiative multiphonon assisted carrier capture processes at deep levels in semiconductors. A fitting of the temperature dependence of the capture cross‐section of the gold acceptor level in silicon is made also, while pointing out as well the existence of high sensitivity in the absolute values of the capture rate to the S parameter. The number of phonons used is p = 8, whereas the values of the associated Huang‐Rhys factor varies accordingly to the sample.
Numerical Approach to the Band Structure in TCNQ Stack
Authors: Komorowski L. 
Published: July 2007

AbstractParameters of the band structure as given by the Hubbard model are explored to characterize the stack composed of (TCNQ) dimers with −4 ≦ n ≦ 4. The energy gap is found to be drastically modified by the value of the charge n. The semiconducting state of the chain is realized only, with the minimum energy gap EH ≈ 0.20 eV.
Analysis of Temperature Variation of EPR Linewidths for Gd3+ Ion in CeF3 Single Crystals
Authors: Korczak W. , Subotowicz M. 
Published: July 2007

AbstractThe 9.4 GHz electron paramagnetic resonance (EPR) of Gd3+ doped in CeF3 and LaF3 single crystals is studied at temperatures of 120 to 293 K. The g‐values and linewidths of the Gd3+ spectra in the kramers host Ce3+ ions are compared with those for the isostructural diamagnetic La3+ lattice. The observation of resolved Gd3+ spectra in the presence of paramagnetic Ce3+ ions is interpreted in terms of a random modulation of the interaction between the Gd3+ impurity and Ce3+ host ions by rapid spin‐lattice relaxation of Ce3+ ions using the generalized theory of magnetic resonance by Kubo and Tomita. The Debye temperature θD is estimated of the CeF3 single crystal at 193 to 220 K. It is found that the effective host spin‐lattice relaxation time can be written in the following form τ1 ∼ T−n where n ε (1.7 to 2.2) (H ‖ z) for T > θD. Two‐phonon Raman scattering dominates in CeF3 single crystals at temperatures larger than θD.
Sternheimer Quadrupole Factors in Ferric Compounds
Authors: Liverts E. Z. , Zhetbaev A. K. 
Published: July 2007

AbstractExpressions for the quadrupole shielding (antishielding) factors corresponding to various types of electronic charge distributions in a solid complex are obtained by means of Sternheimer's perturbation‐numerical method generalized for the two‐centre case. According to the formulae obtained Sternheimer quadrupole factors in isostructural CuFeO2 and α‐NaFeO2 compounds are calculated which differ significantly from those used earlier. The importance of considering the exchange effects which give rise to anomalous shielding effects for some electronic charge distributions is revealed.
Ultrasonic Investigation of the Acceptor Ground State of Si(B) II. The Distribution of Splittings
Authors: Zeile H. , Lassmann K. 
Published: July 2007

AbstractThe splitting distribution of the acceptor ground state of Si(B) is determined from the frequency dependence of the ultrasonic resonance attenuation and from acoustic paramagnetic resonance. In the purest crystals a residual distribution is found of unknown origin. In crystals containing carbon or oxygen at concentrations above about 1022 m−3 the distribution is broadened in rough accordance with statistical estimates.
Elastic‐Stiffness Constants under Pressure of CsK, CsRb, and RbK Solid Solutions
Authors: Soma T. , Kimura Y. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe shear elastic constants C44 and C′ = (C11 ‐ C12)/2 under pressure of the Cs1‐xKx, Cs1‐xRbx, and Rb1‐xKx systems are investigated theoretically using the pseudo‐alloy atom model and the local Heine‐Abarenkov model potential. The pressure‐derivatives dB/dP, dC44/dP, and dC′/dP have a maximum as function of the atomic fraction x, and decrease under compression from the data at low pressures, especially for shear coefficients.
Effect of Hydrostatic Pressure on the Band Structure of InSb A Pseudopotential Calculation
Authors: Gorczyca I. 
Published: July 2007

AbstractThe band structure of InSb is computed by the empirical pseudopotential method (EPM) including a nonlocal correction. The pressure dependence of energy gaps and wave functions for InSb is then calculated. The pressure coefficient of the momentum matrix element between valence and conduction band is found to be very small as is usually assumed. The pressure coefficients of the parameters of electron scattering on short‐range potential centres associated with ionized impurities in InSb are also given in comparison with experimental estimations.
Soliton Magnetoelastic Excitation in the Heisenberg Ferromagnetic Chain
Authors: Izyumov Yu. A. , Laptev V. M. 
Published: July 2007

AbstractThe Heisenberg ferromagnetic chain of spins interacting with the atomic displacement by exchange interaction modulation is considered. The soliton solution of the nonlinear equation for the amplitude of the spin deviations is obtained in the limit of small velocities (which is equivalent to the limit of large soliton localization size). The nonlinear term of the equation is caused by the spin‐lattice interaction and is formed by the spatial derivatives of the amplitude. The soliton energy is higher than the linear spin wave one.
Recombination Processes at Temperatures Lower than 20 K in Hg0.8Cd0.2Te
Authors: Calas J. , Allèggre J. 
Published: July 2007

AbstractMeasurements of photoconductivity lifetime τ in the range 2 to 20 K are reported for Hg0.8Cd0.2Te. A strong increase of this parameter (from 10 to 800 μs) is observed. This effect is attributed to Auger band‐to‐band recombination according to Gerhardts' theory. Another sample of the same ingot, after a long time bromine etching, shows a rapid decrease of the photoconductivity signal (τ ≈ 30 μs) at 2 K which agrees well with the three bands of Casselman's theory of Auger recombination processes. These results prove the existence of an inversion n‐type layer around the p‐type bulk in the annealed samples, according to Scott and Hager's hypothesis.
Ligand Field Theory of the Magnetic Behaviours of Neodymium Ethylsulphate Nonahydrate
Authors: Nath A. , Ghosh U. S. 
Published: July 2007

AbstractAn attempt is made to examine to what extent the set of parameters deduced by Gruber and Satten from their optical absorption experiment is consistent with the g‐values and magnetic susceptibility data of neodymium ethylsulphate nonahydrate. The intermediate coupling scheme and different J‐mixing under the crystal field of D3h symmetry is used in the calculation. It is found that in order to interpret the g‐values and magnetic behaviour Gruber and Satten's parameters are more or less satisfactory needing slight changes in some of their values and a very small covalency reduction is introduced of the orbital angular momentum which is assumed to partake of the symmetry of the complex.
Estimation of Fermi Surface Parameters from the One‐Dimensional Fourier Transform of the Positron Annihilation Angular Correlation Curves
Authors: Gerber W. , Hoppe W. , Brümmer O. , Dlubek G. 
Published: July 2007

AbstractThe advantage of the use of the Fourier transformation in analysing angular correlation curves of 2γ‐positron annihilation radiation is studied on the simple metals Al, Mg, and Li. It is observed that the values for the Fermi momentum estimated from the first and from the second zero of the one‐dimensional Fourier transform of angular correlation curve show systematic differences. This discrepancy may be resolved by taking into account the electron‐positron correlation using a momentum dependent enhancement factor. The estimated values for the Fermi momentum have an accuracy of 0.5 to 1% and agree excellently with the calculated free electron gas values.
Electronic Properties of the Molten Tl‐AgTlS2 System
Authors: Nakajima T. , Uemura O. , Satow T. , Yagihashi T. 
Published: July 2007

AbstractThe electrical conductivity, the magnetic susceptibility, and the thermoelectric power of liquid Tlx(AgTlS2)1‐x alloys are measured as a function of composition in the temperature range from the melting point to 900 °C. The behaviour of these electronic properties is qualitatively the same as the previous result of liquid Tlx(AgTlTe2)1‐x alloys except for the differences mentioned below. A main difference is that the value of conductivity minimum at x ≈ 2/3 for the sulfide system is considerably smaller than that for the telluride system. Corresponding to the conductivity result, the thermoelectric power becomes as large as 250 μ V/K around this composition. Secondly, for x ≈ 2/3, the conductivity is almost independent of composition in the sulfide alloys, whereas the conductivity of the telluride alloys depends strongly on composition. Furthermore, the anomalous change of electronic properties around x ≈ 2/3 becomes less rapid in sulfide alloys compared with the case of telluride alloys. Discussions on the electron localization for liquid Tlx(AgTlS2)1‐x are made in terms of current electron transport theories for liquid semiconductors using the present data.
Spin Glass of the Site‐Random Ising Model with First and Second Neighbor Interactions
Authors: Katsura S. , Konishi K. 
Published: July 2007

AbstractThe site‐random Ising mixture of atoms A and B, of which the first and second neighbor interaction energies are J1AA. J1BB, J1AB J2AA J2BB, J2AB, is considered. The second neighbor interactions are treated along the line of Hüller. For the mixtures where J1AA > 0 (ferromagnetic) and J1BB < 0 (antiferromagnetic), the Curie, Néel, and spin glass transition temperatures are calculated and the phase diagrams are obtained. The severe situation for the appearance of the spin glass state in the site‐random Ising model with only first neighbor interactions (possible region of J1AA, J1BB, and J1AB for the spin glass is very narrow) is much improved by the introduction of the proper choice of the second neighbor interactions which enhances the frustration.
Effect of γ‐Irradiation on Eu2+ Ions in KCl Crystals
Authors: Opyrchał H. , Nierzewski K. D. , Macalik B. 
Published: July 2007

AbstractOptical absorption and emission, EPR, ITC, and thermoluminescence spectra of RT γ‐irradiated KCl:Eu2+ crystals are examined. ITC and EPR measurements of heavily irradiated samples point to the lack of any I.V. Eu2+ dipoles. Examination of optical properties permits to exclude the presence of Eu+ and Eu3+ ions. On the other hand, the examination of thermal annealing effects in heavily irradiated samples reveals the lack of any correlation between the recovery of original europium dipoles and the decay of colour centres. The results obtained can be understood by assuming radiation field induced aggregation of europium dipoles.
Two Types of Tetrahedral Sites in the Mixed {Ca2Na} [Mg2] (V3)O12 Garnet
Authors: Wójcik M. , Le Gall H. , Desvignes J. M. 
Published: July 2007

AbstractThe untypical quadrupolarly split NMR spectrum, from 51V in the tetrahedral sites (d), of mixed {Ca2Na} [Mg2] (V3)O12 single crystal is investigated. The EFG distribution in the (d) sites, associated with the random distribution of the Ca2+ and Na+ ions over the nearest neighbour dodecahedral sites in garnet, is calculated. On ground of the theoretical results, the observed NMR lines are indentified as arising from the two types of (d) centres: calcium‐type and sodium‐type, characterized by a different EFG tensor.
Optical Investigation of Ag+ Centers in Cesium Halides
Authors: Pfalzgraf B. , Roder O. , Spaeth J.‐M. 
Published: July 2007

AbstractIn Ag+ doped CsCl and CsBr single crystals several absorption bands are found in the far UV region which strongly depend on crystal growth conditions. By means of a special thermal treatment two different monomer Ag+ centers could be produced reproducibly. From optical absorption, fluorescence emission, and radiative lifetimes as well as optical bleaching experiments it is concluded that the optical properties of these centers are due to bound excitons.
Calculation of Binding Energies of Small Vacancy Clusters in B.C.C. Transition Metals
Authors: Masuda K. 
Published: July 2007

AbstractThe binding energies Ebin of vacancy‐type lattice defects in b.c.c. transition metals are calculated using a tight‐binding type electronic theory and compared with available experimental results. The present calculation takes into account the Born‐Mayer repulsive energies and uses a total energy minimization procedure. It is shown that atomic relaxation around the lattice defects (small vacancy clusters) plays a dominant role in determining the binding energies Ebin: in general, Ebin depends strongly on the configuration of vacancies. Detailed information on the local d‐electron density of states (near the defects) is also given.
Temperature Dependence of the Electrical Conductivity of the Periodic Anderson Model
Authors: Elk K. 
Published: July 2007

AbstractThe temperature dependence of the electrical conductivity σ of the periodic Anderson model is investigated using a modified version of the model of Chen, Weisz, and Sher, describing the electron‐phonon scattering by a temperature dependent stochastic potential. The correlation term of the Anderson model is decoupled in the framework of the alloy analogy approximation taking into account strong electron‐electron interaction. Then the electrical conductivity can be obtained using the Kubo‐Greenwood formula. By numerical methods the density of states and the temperature dependence of σ are calculated. For σ(T) a pronounced minimum is obtained at low temperatures T, whereas at higher temperatures σ increases with T.
Lattice Mechanics of Molecular Solid Sodium Nitrate
Authors: Singh R. K. , Chaplot S. L. 
Published: July 2007

AbstractThe lattice mechanics of sodium nitrate with calcite structure is investigated by means of a rigid molecular ion model of the molecular solids employing the external mode formalism. The phonon dispersion curves calculated are in good agreement with those recently measured from the technique of neutron inelastic scattering. The values of the eigenvectors and the cohesive energy obtained for sodium nitrate also appear to be reasonably correct. The possibilities of further improvement and extension of the model are also discussed.
High Energy Distribution Function in an Electric Field and Electron Impact Ionization in AIIIBV Semiconductors
Authors: Dmitriev A. P. , Mikhailova M. P. , Yassievich I. N. 
Published: July 2007

AbstractA calculation method of the exponential dependence of the high‐energy distribution function in an electric field E is proposed for polar semiconductors. It is shown that in many‐valley semiconductors with complicated conduction band structure a strong anisotropy of the electron impact ionization coefficient α(E) will be obtained. In the case of E ∥ (100) or E ∥ (110) a ballistic transport in the Γ‐valley can occur and the dependence of In α vs.(E01/E) holds. If E ∥ (111) the ballistic transport in the Γ‐valley is impossible and the high‐energy distribution function is always formed due to electron scattering from X‐valleys. Then the dependence of In α vs.(E02/E)2 will be realized for a wide range of fields. The characteristic fields E01 and E02 are connected with the intervalley coupling constants for Γ—X and X—X scattering, respectively. Impact ionization processes are considered in detail for InSb, GaAs, and InP. The results are compared with accessible experimental data.
Phonon Scattering by Paraelectrical Centers in Crystals II. Lowest Order Approximation
Authors: Akhmadullin I. Sh , Saburova R. V. 
Published: July 2007

AbstractOn the basis of formalism developed in a previous work, a theoretical study of the dynamic of paraelectric centers interacting both, with each other and with lattice vibrations is presented. Spectrum and damping of collective excitations are calculated. Frequency and center concentration dependences of phonon lifetime are analysed. An application of the results obtained from the analysis of thermal conductivity is discussed. A new thermal conductivity mechanism is proposed.
Electron States Associated With Partial Dislocations in Diamond
Authors: Persson A. 
Published: July 2007

AbstractElectron states associated with 30° and 90° partial dislocations in diamond are examined by the use of Slater‐Koster parameters evaluated form first principles. The partial dislocations give half‐filled bands in the lower half of the band gap. A possible reconstruction of the 90°‐partial is also considered but found to be unlikely. Including non‐spherical parts of the crystal potential in the calculation of the matrix elements for the atoms with a dangling bond did not appreciably alter the result for the 90° partial.
Temperature Dependence of the Linewidth of First‐Order Raman Spectrum for CdF2 Crystals
Authors: Sato T. , Tateyama S. 
Published: July 2007

AbstractThe first‐order Raman spectrum of CdF2 crystal is measured at temperatures from 4.2 to 469 K. From these experiments, the values of the linewidth at these temperatures are obtained. On the other hand, the linewidth is calculated quantitatively theoretically under consideration of only the cubic anharmonic term of the Coulomb and repulsive forces of the crystal potential. A comparison of the experimental and theoretical results shows good agreement.
Statistical Mechanics of the Random Anisotropic Planar Heisenberg Model. Discussion on the Spin Glass
Authors: Katsura S. , Shirakura T. 
Published: July 2007

AbstractThe classical (S = ∞) and the quantum (S = 1/2) planar model with random anisotropic exchange energy, of which the Hamiltonian is given by —βℋ = σKij(Sjx + ηSiySjy) + σ(CixSix + CiySiy), are discussed by the method of the pair approximation. The high‐temperature uniform and spin glass susceptibilities are obtained. The magnetic phase diagrams of the short ranged binary mixture (±J model), the short ranged mixture with the width ΔJ, and the infinitely long ranged Gaussian mixture are obtained from the divergences of the susceptibilities. In the classical case the spin glass transition is realized in the whole range of 0 ≦ η ≦ 1 while in the quantum case the spin glass is not realized in the range of η > ηc (in particular in the isotropic case η = 1).
Theory of Interionic Forces in Alkali Halide Crystals
Authors: Narayanan R. S. , Shankar J. , Gupta H. C. , Tripathi B. B. 
Published: July 2007

AbstractThe widely used Born‐Mayer potential in the classical theory of ionic crystals is replaced by a quantum mechanical analytical potential form following the recent tight binding theory developed by Harrison. It is found that the crystalline data on interionic distance, separation energies, isothermal bulk modulus, and its pressure derivative for all the alkali halides can be fitted to a very good extent by taking the Madelung energy and Harrison's overlap potential form. It is emphasised that Harrison's overlap potential can be a useful tool for studying the properties of ionic crystals within the framework of conventional approach based on Madelung's energies.
Temperature and Pressure Dependence of the Electric Field Gradient at the Br Sites in PbBr2 and SnBr2
Authors: Bastow T. J. 
Published: July 2007

AbstractDetailed measurements are made of the 79,81Br NQR frequencies in PbBr2 and SnBr2 at temperatures between 77 and 350 K. Pressure coefficients at up to 250 MPa are measured for these frequencies at room temperature. The assumption that the NQR frequency shift with temperature is a linear function of the mean square atomic displacement, which in turn is described by the quasi‐harmonic theory, is shown to provide a satisfactory account of the observed power law (Tn) temperature dependences.
Calculation of Excess Free Energy of Mixing and Analysis of Phonon Spectra With Clustering Parameter in III—V Pseudobinary Alloys
Authors: Yamazaki S. , Kishi M. , Katoda T. 
Published: July 2007

AbstractThe excess free energy of mixing, ΔGex, is calculated and the phonon spectra for III—V pseudobinary alloys A1–xBxC are analyzed on the basis of a cluster model. ΔGex is a function of the clustering parameter β which represents the deviation from the random atomic distribution. The value of β giving the minimum excess free energy, βs, takes the maximum value at x = 0.5 and it increases with increase in the relative difference of lattice constants, \documentclass{article}\pagestyle{empty}\begin{document}$ \Delta a\sqrt a $\end{document}. The value of β giving the best agreement between the measured phonon frequencies and the calculated ones, βph, takes the maximum value also at about x = 0.5 in systems exhibiting the phonon spectra of partly‐two mode type. The value of βs at x = 0.5 and βph over the entire composition range is zero for two‐mode systems, such as (AlGa)—V.
Monte‐Carlo Calculation of Density of States and Localization in Alloys Including Short‐Range Order
Authors: Brouers F. , Franz J. 
Published: July 2007

AbstractThe alloy density of states calculated with a Monte‐Carlo technique is compared to that calculated with a small cluster approximation. It is shown that the use of small clusters imbedded in an effective medium can give rise to spurious structure in the density of states while the two methods give the same results in the limit of large clusters. The conditions are determined for localization in such systems and some conjectures concerning the nature of localized states observed in real liquid alloys are made.
The Semiconductor—Metal Transition in Liquid Tellurium
Authors: Rokhorenko V. Yaw. , Sokolovskii B. I. , Alekseev V. A. , Basin A. S. , Stankus S. V. , Sklyarchuk V. M. 
Published: July 2007

AbstractThe conductivity and thermoelectric power of liquid tellurium up to 1750 K and its density up to 1500 K are measured. Furthermore, all the parameters are measured at 50 K supercooling. A σ(T) maximum in the region of 1100 K is obtained. The thermoelectric power being positive does not vary in the wide temperature range. The ϱ(T) dependence displays a maximum at the normal crystallization point. The results obtained are interpreted by the approximation of metal character of the conductivity and the double‐structural near order of liquid tellurium.
Self‐Trapping of Polaritons
Authors: Hizhnyakov V. V. , Sherman A. V. 
Published: July 2007

AbstractThe self‐trapping of the exciton component of the polariton is considered in the adiabatic approximation. The possibility of the coexistence of self‐trapped (STP) and coherent (CP) polaritons is demonstrated. Such coexistence is possible even for a large effective mass of the exciton component, if the exciton—photon coupling is sufficiently strong, as it is in the case of core polaritons. The self‐trapping barrier of polaritons depends essentially on the frequency of the exciting source, the character of relaxation processes, and some other factors. The shape of the adiabatic surfaces obtained allows one to suggest an explanation of a number of peculiarities observed in the optical spectra of NaI crystals in which the coexistence of STP and CP has been established previously.
The Initial and Final States for UPS Optical Transitions in Cd0.2Hg0.8Te Crystal
Authors: Orlowski B. A. 
Published: July 2007

AbstractAn UPS experiment is performed to investigate the density of states distribution in the valence and conduction bands of a Cd0.2Hg0.8Te crystal. The crystal is cleaved in UHV (p = 5 × 10−11 Torr) and the EDCs are taken at 300 and 77 K and for UV photon energy hv values very close to each other in the range 8.7 eV ≦ hv ≦ 11.9 eV. A comparison of the measured positions of the EDC peaks with the calculated band structure leads to the conclusion that they originate from the peaks of the density of states in the valence and conduction bands at the L and X points and the σ axis of the Brillouin zone.