bluuebunny/crossref_metadata_2025_split huggingface dataset:
ESR from boron in silicon at zero and small external stress. II. Linewidth and crystal defects
Authors: Neubrand H. 
Published: July 2007

AbstractObservations of the ESR lineshape of the shallow acceptor centre B in silicon at zero external stress are reported. The broadening of two ΔM = 1 transitions can be well fitted by a Voigt profile. The Lorentzian part of the fit is shown to behave in full accordance with the theory of strain broadening by point defects. From linewidth measurements for different oxygen and carbon content the elastic strengths of oxygen and carbon in silicon are determined. All obtainable elastic strengths for point defects in silicon are collected. The possibility of determining the total amount of substitutional impurities from the Lorentzian broadening of the ΔM = 1 transitions is discussed.
Cross relaxation studies in the Cr3+‐doped magnetically dilute paramagnetic Al2O3–Fe2O3 system. I. Effect of Cr3+ concentration
Authors: Srivastava J. K. , Dale B. W. 
Published: July 2007

AbstractMössbauer measurements are made in undoped and Cr3+‐doped Al2O3–0.04 mol% 57Fe2O3 systems at 4.2 K. The cross relaxation between Fe3+ and Cr3+ ions, dispersed in the diamagnetic Al2O3 lattice, is studied. The spin–spin relaxation time of the Cr3+ ions is reduced with increasing Cr3+ concentration and these faster relaxing Cr3+ spins are found to enhance the Fe3+‐relaxation process, destroying the paramagnetic hyperfine structure observed in the 57Fe Mössbauer spectra of undoped Al2O3–0.04 mol% 57Fe2O3. It is concluded that at higher Cr3+ concentrations, cross relaxation does not take place by the mutual energy exchange between a Cr3+ ion and and Fe3+ ion but a new kind of pair cross‐relaxation process occurs where a Cr3+ ion and an Fe3+ ion first form an exchange coupled pair and then two such pairs cross relax.
Interband optical absorption in semiconductors with one‐dimensional electronic superlattice
Authors: Dubrovskii G. B. , Pavlov S. T. , Vershinin M. S. 
Published: July 2007

AbstractThe shape of the fundamental absorption edge is theoretically analysed for semiconductors with one‐dimensional electronic superlattice. The structure associated with minizone edges is found experimentally in the absorption spectrum of 6H‐SiC crystals. Good agreement with the theoretical predictions is obtained.
Solid silicon selfconsistently with Xα potentials
Authors: Stöhr H. , Bross H. 
Published: July 2007

AbstractThe band structure of solid silicon is selfconsistently determined with the help of local Xα exchange and correlation potentials using the MAPW method. From a detailed comparison with experimental data and regarding the care taken with numerical convergence and approximations one is forced to conclude that the Xα potential at best may only yield a rough understanding of the electronic structure of Si.
Magneto‐Seebeck and Shubnikov‐de Haas effect in n‐type (Bi1−xSbx)2 Te3
Authors: Köhler H. , Ossau W. 
Published: July 2007

AbstractThe magneto‐Seebeck effect in a transverse magnetic field is investigated in n‐type (Bi1−xSbx)2 Te3 mixed crystals (0 ≦ x ≦ 0.5; 20 K ⪅ T ⪅ 130 K) in order to evaluate electronic parameters from the saturation of the thermoelectric power α⟂ (∞) at high magnetic fields. In addition magneto‐quantum phenomena are observed in the Seebeck and Shubnikov‐de Haas effect simultaneously for B ∥ c. The electron concentrations deduced from the saturation value of the Hall constant (−eRH∞)−1 ranged between 1.8 × 1018 and 3.2 × 1019 cm−3. It is shown, that the presence of two types of electrons has to be assumed for the interpretation of the experimental data (α⟂ (∞)), where the energy gap between the two adopted conduction band minima decreases from Bi2Te3 (24.5 meV) towards zero at x ≈ 0.2, re‐opening for x > 0.2 after the different types of conduction band minima have crossed over and therefore the meaning for the lowest and higher conduction bands is substituted compared to x < 0.2.
Electron–phonon coupling constant and critical temperature of some A15 superconducting compounds of Nb and V
Authors: Raychaudhury M. , Chatterjee P. , Chatterjee S. 
Published: July 2007

AbstractTheoretical calculations are made of the coupling constant, λ, for the A15 compounds Nb3Al, Nb3Sn, V3Si, and V3Ge with the help of the theory of Gaspari and Gyorffy. For this purpose Herman‐Skillman potentials are used for the phase shift calculation, and the density of states and the Fermi energy are taken from the band structure calculations of Mattheiss. Using these values of the coupling constant the Tc's are obtained of these materials. These values of Tc's agree fairly well with the experimental values. Since for the highest Tc material, Nb3Ge, no band structure calculation exists, Tc is plotted as a function of the Fermi energy. From the plot, the experimental Tc of 23.2 K is reached for EF = 1.330 Ryd.
Application of unitary groups for determining tensor components in crystals and selection principles for phase transitions
Authors: Kustov E. F. , Zakharov N. A. , Steczko G. 
Published: July 2007

AbstractThe paper is concerned with compound series of unitary groups, of rotation groups and point groups for classification of various tensor components in crystals, which have various components in relation to a rotation group and a permutation group. For this purpose the following series U[γ]γ ⊃ R[γ]γ ⊃ … ⊃ G is being introduced, where γ represents a vector (a pseudovector); then the number of various branches which end with a unit group G determines the number of various tensor components, which have obvious properties for reduction symmetry. When classifying in this way, a new interpretation of selection principles for phase transitions in crystals can be introduced.
Phonon frequencies in off‐symmetry directions of NaCl determined by neutron inelastic scattering
Authors: Nilsson G. G. 
Published: July 2007

AbstractPhonon frequencies in NaCl at 80 K have been determined using neutron inelastic scattering. 72 off‐symmetry phonons are measured, both in the symmetry plane (110) and in the off‐symmetry plane (301). The experimental frequencies are compared to earlier breathing shell model calculations and found to be in excellent agreement.
An information theoretical method (ITM) applied to the metal–insulator transition of the neutral hubbard model
Authors: Heiner E. 
Published: July 2007

AbstractBy a minimization procedure of the information measure for the single particle spectral weight function (SWF) of fermions a method is found for the approximate calculation of the SWF. Using this method it is possible to overcome the shortcoming of the rigid shape ansatz for the SWF within the moment expansion method. The new method is applied to the neutral Hubbard model and a criterion for the localization of the quasi‐particles is given.
The structure of liquid mercury over a wide range of temperature (−30 to 290 °C)
Authors: Waseda Y. , Miller W. A. 
Published: July 2007

AbstractX‐ray diffraction patterns are obtained from liquid mercury at −30, 20, 120, 220 and 290 °C. The structure factors obtained are insensitive to temperature and applied to the calculation of the electrical resistivity and the thermoelectric power on the basis of the t‐matrix formulation of the Ziman nearly free electron theory. The calculated values show reasonable agreement with the available experimental data.
Influence of the size effect and surface roughness on phonon transport in bounded systems
Authors: Nonnenmacher Th. F. , Wunderle R. 
Published: July 2007

AbstractThe influence of the size effect and of surface roughness on the thermal conductivity x is investigated. The starting point for treating this problem is the relaxation time approximation of the Boltzmann equation for all bulk scattering mechanisms. The boundary scattering mechanism comes into play via the boundary condition for flux conservation with the result that x can be calculated as a function of the thickness d of the crystal and two roughness parameters L and η characterizing the horizontal and vertical widths of the surface defects, respectively. The resulting formula for x is a composition of a pure bulk term and a term containing a mixture of bulk and surface properties.
Temperature and concentration dependence of the knight shift of 115In in liquid In–Hg alloys
Authors: Ploumbidis D. , Sutter T. 
Published: July 2007

AbstractDetailed measurements of the temperature and concentration dependence of the Knight shift of 115In in In–Hg system, in a range of 240 to 510 K and 0 to 100 at% Hg, respectively, are carried out. The temperature coefficient of the 115In Knight shift and its concentration dependence at constant volume is determined using only experimental results. A possible interpretation of the concentration dependence of this coefficient is given in the framework of Mott's pseudogap model.
Isotope effects of diatomic TiH and TiD complexes in FeTi crystals
Authors: Kronmüller H. , Vetter K. 
Published: July 2007

AbstractIn ferromagnetic b.c.c. FeTi alloys (2at%, 10at%Ti) the magnetic relaxation spectrum of diatomic TiH and TiD complexes is studied in the temperature range from 10 to 180 K. The relaxation spectra of both the types of complexes are composed of two overlapping relaxation maxima which may be attributed to different relaxation modes of the diatomic complexes. A significant isotope effect can be detected for the activation energies whereas in the case of the pre‐exponential factors no significant isotope effect can be observed.
Distribution of the perturbation potential and the density of states in high‐doped semiconductors
Authors: Breitenstein O. , Unger K. 
Published: July 2007

AbstractTo calculate the potential distribution and density of states for a set of randomly distributed potentials the Laguère integration method is used. The method substitutes the inverse Laplace transformation by a finite sum. Application is given to the broadening of the density of states under the influence of screened Coulomb potentials in high‐doped semiconductors. The screening of the single potentials is taken according to the density of states, resulting from the statistical superposition of these potentials in a self‐consistent way.
Spin reorientation in HoIG investigated by means of faraday effect
Authors: Bałanda M. , Nizioł S. 
Published: July 2007

AbstractFaraday rotation measurements in pulsed magnetic fields up to 160 kOe and in low dc fields are carried out for Ho3Fe5O12 near the compensation point. Transition to the canted phase is observed and the temperature dependence of the critical field determined. From the holmium sublattice magnetization and Hcr versus. T gradient, values of the two molecular field coefficients are determined.
Temperature shift of the maximum of neutron critical scattering from an iron polycrystal. A test for the dynamie scaling theory
Authors: Ciszewski R. , Milczarek J. 
Published: July 2007

AbstractIt is found, from neutron critical scattering measurements, that the well‐known temperature shift of the maximum of scattering depends not only on the scattering vector, but also on the wavelength of the incoming neutrons. The results obtained are compared with the predictions of the dynamic scaling theory and a new test for the validity of this theory based on the estimation of the critical index v is proposed.
Size effect, valency factor, and point defect interactions in dilute alloys
Authors: Prakash S. , Lucasson P. 
Published: July 2007

AbstractA simple but realistic physical model is suggested to analyse the capture radii and wipe‐out numbers in dilute alloys of copper and aluminium. The valency of impurity is decided according to Friedel criterion and the size effect is included according to Blatt. It is found that the capture radii and wipe‐out numbers are proportional to the magnitude of perturbation caused by both the realistic valence difference and size effect. It is shown that the size effect is dominating in copper alloys while the valence effect is dominating in aluminium alloys. The deduced linearity relations may be quite useful for predicting the capture radii and wipe‐out numbers for new experiments.
Dynamical exchange effects on the plasmon dispersion in aluminum
Authors: Devreese J. T. , Brosens F. , Lemmens L. F. 
Published: July 2007

AbstractIn the dielectric function, obtained from the dynamical exchange decoupling method, exchange effects are described by a frequency‐dependent local field correction G(q, ω). From the behaviour of G(q, ω) in the static limit ω = 0, it follows that the compressibility sum rule is satisfied, and that the pair correlation function g(r) equals 1/2 at the origin. Also, in the static limit, G(q, 0) shows a sharp peak near q = 2kF. The dynamical behaviour of G(q, ω) at high frequencies fulfills the condition imposed by the third frequency moment sum rule, and it also implies that g(0) = 1/2. The same g(0) thus derives from both the static and the dynamical behaviour of G(q, ω), in contrast to earlier theories. The influence of the dynamical exchange effects on the plasmon dispersion is examined. It is found that, compared to RPA, the plasmon is almost unaffected by exchange outside the continuum, but that in the particle‐hole excitation region exchange effects drastically lower the peak position of the structure factor. This tendency has been experimentally observed in Al, where the RPA peak positions at finite wave vector are found at too large frequencies, but where the dynamical exchange decoupling method yields relatively good agreement with the experimental data.
Interband absorption and the Γ‐point band structure parameters in HgSe
Authors: Szuszkiewicz W. 
Published: July 2007

AbstractOptical absorption in HgSe crystals is measured in a wide energy range (0.04 to 0.9 eV). Transmission experiments are carried out at seven temperatures from 10 to 295 K. Very thin samples with electron concentration ranging from 4 × 1017 to 2 ± 1018 cm−3 at helium temperature are used (the absorption coefficient is measured up to 3 × 104 cm−1). Direct optical transitions Γ → Γ, manifesting themselves as a „step”︁ on the absorption curve, are observed at low temperatures. The relationship between the value of the negative energy gap E0 and the value of the spin–orbit splitting Δ is determined from the energy of the front of the „step”︁ as a function of temperature. The absorption coefficient for HgSe is calculated numerically using Kane's formulae for the inverted band structure. The finite value of the spin–orbit splitting Δ and the parameters describing the interactions with „higher bands”︁ are taken into account. A new set of band structure parameters (E0, dE0/dT, P, Δ, A′, L′, M, L – M – N) is obtained. This set can explain the data measured as well as previous experimental results.
U centres in alkali iodides
Authors: Sebastian R. , Raj G. A. Savari , Haridasan T. M. 
Published: July 2007

AbstractExact changes in force constant due to H− substitution (U centres) in alkali iodides are systematically analysed using Green's function technique. NaI:H−, KI:H−, RbI:H−, and CsI:H− systems are considered. There is a weakening of the force constant varying from 50% to 63% depending on the mass of the neighbour in the host lattice.
Effect of ordering on the OH Raman bands of K4Fe(CN)6 · 3 H2O
Authors: Savatinova I. , Anachkova E. 
Published: July 2007

AbstractA first detailed Raman study is made of the OH stretching modes of KFCT. The analysis of the spectra is based on a comparison with those of the deuterated compound. Polarized Raman spectra of KFCT in all scattering geometries at both sides of Tc are obtained. The measurements do not reveal any gaining of inversion centre in the paraelectric phase of the crystal. All bands observed in the ferroelectric phase continue to be strong above Tc with the only exception of the 3510 cm−1 band. A correlation between the intensity of this band and the long‐range order parameter m is reported. The influence of the phase transition on the frequencies and bandwidths of the OH spectrum is investigated. As the temperature is lowered down to 80 K the bandwidths narrow drastically. It is shown that this effect is associated with the temperature dependent potential barrier restricting the reorientations of the water trimers.
Nuclear‐acoustic‐resonance determination of the core polarization contribution to the knight shift and hyperfine fields in single‐crystal tantalum
Authors: Schanz G. , Müller V. , Unterhorst E. J. 
Published: July 2007

AbstractBy quantitative evaluation of the nuclear acoustic resonance shift, the temperature dependence of the Knight shift in tantalum is determined for the first time. The experiments are performed in the temperature range of 20 to 300 K. The s‐, d‐ and orbital contributions to the Knight shift, the magnetic susceptibility and the hyperfine fields are specified.
Investigations of EPR superhyperfine structure for the cubic Gd3+ center in CdF2
Authors: Gehlhoff W. , Kreissl J. 
Published: July 2007

AbstractA critical investigation is made of the superhyperfine (SHF) structure in the EPR spectra of the cubic Gd3+ center in CdF2, which arises from the interaction of the Gd3+ ion with its eight nearest‐neighbor 19F nuclear spins. Contrary to previous EPR investigations it is found that the hyperfine splitting produced by the gadolinium isotopes 155Gd and 157Gd cannot be neglected and that the width of the individual SHF line is dependent on the fine‐structure transition. This linewidth behavior is discussed.
Calculation of the broadening of donor–acceptor pair lines due to the potentials of ionized impurities
Authors: Breitenstein O. , Unger K. 
Published: July 2007

AbstractThe broadening of DAP lines under the influence of perturbation potentials from ionized impurities is calculated in the Thomas‐Fermi approximation. The exact treatment is only numerically solvable, but for physically interesting DAP distances less than half the screening length a simple potential well approximation is introduced, leading to analytical results.
On the deformation model of the carrier spectrum for bismuth‐type crystals I. Electrons
Authors: Jung T. , Braune W. 
Published: July 2007

AbstractTwo methods of parameter determination for a complicated dispersion relation of electrons in bismuth are applied. The dispersion relation employed is obtained by Abrikosov and Falkovskii on the basis of a deformation theory. Discrepancies remaining with respect to energy dispersion in the direction of elongation of the electron part of Fermi surface are analysed and compared with k · p‐model considerations. An extended form of the Abrikosov‐Falkovskii model is presented, which should provide a more precise description of the topology of the electron Fermi surface.
The effects of magnetic field and direct interaction between impurities in the Anderson model resistivity
Authors: Zieliński J. 
Published: July 2007

AbstractThe method of functional derivatives is applied to investigate the Anderson model. It is shown that the presence of magnetic field and the direct interaction between impurities lead to the same form of the low‐temperature resistivity per impurity in arbitrary order of the perturbation series in the symmetric case of the Anderson model. The formal expressions for the first‐ and second‐order (with respect to intraatomic Coulomb interaction) contributions to the d‐electron Green function are given and in the limit of vanishing field (or interaction) the results obtained by Yamada and Yosida are derived. Explicit expressions for the proper self‐energy of the d‐electron are obtained up to the second order and the temperature dependence of the imaginary part of the conduction electron t‐matrix at the Fermi surface is presented.
Influence of crystal lattice defects on the ferroelectric dispersion of triglycine sulphate
Authors: Pawlaczyk Cz. , Luther G. , Müser H. E. 
Published: July 2007

AbstractThe influence of radiation defects and doping on the ferroelectric dispersion in triglycine sulphate (TGS) single crystals is studied. The Cole–Cole plots, temperature dependence of the distribution angle of relaxation times, as well as the temperature dependence of the static dielectric permittivity and the relaxation frequency are given for γ60‐Co irradiated TGS crystals. Deviation from the Debye‐type dispersion in the vicinity of the Curie point is found. The temperature region of this deviation is found to increase with the defect concentration.
Separation of angles in the problem of an exciton bound to an ionized donor in the case of anisotropic effective masses and dielectric constant
Authors: Munschy G. , Stauffer L. 
Published: July 2007

AbstractThe anisotropic exciton–ionized donor complex is studied within the effetive mass approximation. The quantum mechanical formulation of the ground‐state requires a six‐dimensional configuration space, but the problem is reducible from six to three dimensions after separation of the Eulerian angles. It remains only to solve three‐variable wave equations depending on the distances between particles.
Experimental observation of the fermi surface–Brillouin zone interaction in pure zinc by means of X‐ray photoelectron spectroscopy
Authors: Mizutani U. , Kondow T. , Uda M. 
Published: July 2007

AbstractThe 4s–4p valence band of pure zinc is studied by means of X‐ray photoelectron spectroscopy. A fine structure is revealed near the Fermi edge and interpreted in terms of the van Hove singularity due to the Fermi surface–Brillouin zone interaction. The observed peak is attributed to the Fermi surface contacts with the {10.1} zone planes, combined with the electron overlaps across the {10.0} zone planes. This supports the model proposed in the interpretation of the trends of the electronic specific heat coefficients in the h.c.p. Hume‐Rothery alloy phases.
Elastic properties of polytypes
Authors: Geilikman M. B. 
Published: July 2007

AbstractThe elastic moduli of polytypic modifications of close‐packed crystals are calculated. A microscopic calculation of the elastic moduli is made for close‐packing of atoms of the same kind and for tetrahedrally coordinated structures of ZnS‐type crystals. A new variant of a phenomenological approach is suggested, where the requirements of the general theory of internal stresses in crystals are taken into account. Two independent approaches, a microscopic and phenomenologic one, reveal a similar dependence of the elastic moduli on the polytype structure. The elastic energies of various polytypes in stressed states are compared.
Exciton reflection spectra of tetracene single crystals
Authors: Kolendritskii D. D. , Kurik M. V. , Piryatinskii Yu. P. 
Published: July 2007

AbstractThe exciton reflection spectra of free tetracene single crystals and those in optical contact with different substrates (quartz, glass, muscovite) are measured in polarized light at temperatures ranging from 300 to 4.2 K. Peculiarities in the reflection spectra of a free crystal are due to a phase transition in the crystal at 160 K. The phase transition is shown to result from an increase of the crystal internal pressure due to the crystal stress with lowering temperature and leads to the change of the crystal symmetry. The b‐polarized reflection spectra of free and in‐contact crystals show a structure which is related to the exciton effect in the surface region. A weak exciton‐phonon coupling in tetracene is concluded.
Band structure and electronic properties of transition metal hydrides
Authors: Kulikov N. I. 
Published: July 2007

AbstractA calculation of band structures, densities of states, and Fermi surfaces for 3d‐element hybrides is made. The results of this calculation are compared with the APW calculation by Switendick and the experimental measured values of electronic specific heat, magnetic susceptibility, and optical absorptivity. By using the Gaspari‐Gyorffy theory values of the electron‐phonon coupling constant andTcare calculated. High critical temperatures of superconductivity are predicted for chromium and nickel dihydrides.