bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Type of the Ferroelectric Phase Transition
Authors: Holakovský J. 
Published: July 2007

AbstractIt, is suggested that a ferroelectric phase transition could be triggered by an instability of the crystal with respect to another phase transition parameter η. The spontaneous polarization P and spontaneous η may occur either successively or simultaneously (at the same temperature), the latter case being always a first order phase transition. The necessary condition for the existence of a triggered ferroelectric phase transition (TFT) is that η2 P2 is the lowest order interaction term in the free energy expansion. The symmetry change due to TFT is discussed.
Temperature Dependence of Hall Coefficient and Electrical Resistivity in Sb Single Crystals at Low Temperatures
Authors: Bansal S. K. , Duggal V. P. 
Published: July 2007

AbstractMeasurements of the ideal electrical resistivity of single crystals of pure antimony are given in the temperature range 4.2 to 77 °K. Below 20 °K the resistivity shows a T3 dependence unlike the case of the semi‐metal Bi in which a T2 dependence is observed. The temperature variation of the Hall coefficients from 4.2 to 30 °K is presented. The Hall coefficient R23,1 decreases linearly with temperature from 4.2 to 20 °K whereas the coefficient R12,3 increases monotonously from 4.2 to 20 °K. This is in contrast with the observed behaviour of these coefficients above 55 °K. The possible causes of the observed temperature dependence of the Hall Coefficients are discussed.
Photoconductivity of KCl and KBr with F‐centres
Authors: Hoffmann H. J. 
Published: July 2007

AbstractThe kinetics of the photoconduction in additively coloured KCl and KBr has been investigated experimentally in the temperature range where F'‐centres decay thermally. The experimental results at high F‐ centre concentration and high illumination levels confirm the second‐order model discussed in [1]. At F‐centre concentrations below 1016 cm–3 and very low illumination levels, however, the order of the kinetics changes from second to the first order because of some additional deep traps (presumably α‐centres). Besides the concentration of additional α‐centres in the order of 1011 to 1012 cm–3, the recombination coefficient of the α‐centre and the thermal ionization energy of the F'‐centre (KCl: 0.44eV; KBr: 0.34 eV) have been determined.
Energy bands of copper chloride
Authors: Calabrese E. , Fowler W. B. 
Published: July 2007

AbstractThe techniques developed in a preceding paper have been applied to compute the energy bands of CuCI. Results of calculations using Slater, screened Slater, and empirically modified Slater exchange potentials are presented. The valence bands are relatively sensitive to the choice of potential, but the conduction bands are not. The calculated valence bands agree rather well with various experimental data, and slight empirical modifications are suggested to yield even better agreement. The conduction band effective mass and the band gap deformation potential are also calculated and compared with experiment.
Surface states and ionicity
Authors: Louis E. , Yndurain F. 
Published: July 2007

AbstractA simple model, based on the nearly free electron approximation, is developed in order to calculate the surface state energies in heteropolar compounds using the matching of the Green's function method. The analysis is based on the effect of the crystal ionicity on the surface state energies. The results are compared with experimental data, and general trends are obtained fairly similar to the experimental evidence. Finally, the effect of using a tight‐binding model instead of a nearly free electron model to describe the crystal is studied and only minor differences are obtained.
Valence bands of amorphous and crystalline GeTe determined by X‐ray and UV photoemission
Authors: Shevchik N. J. , Tejeda J. , Langer D. W. , Cardona M. 
Published: July 2007

AbstractThe density of valence states, the energies of the core levels, and the characteristic energy loss spectra of crystalline and amorphous GeTe have been measured by X‐ray (1486.6 eV) and UV (21.2 eV) photoemission spectroscopy. The valence band densities of states of the two GeTe phases are in general similar, but exhibit distinct differences in their detailed structure. That of the amorphous form of GeTe may be approximated by a sum of the densities of states of the elemental forms of amorphous Ge and Te. A model for the valence band density of states is proposed which may be generally applicable to random covalent networks. No difference in the separation of the core level of the Ge and Te atoms is found between the amorphous and crystalline phases, thus indicating that there is no significant ionicity difference in the bonding character of these two phases. In light of the current structural models for the amorphous form, the similarities between the photoemission from the two phases are surprising. The plasma frequencies of the amorphous and crystalline forms are found to be 16.4 and 16.9 eV, respectively.
Large transverse spin component around impurities in an almost saturated ferromagnet
Authors: Muggli J. 
Published: July 2007

AbstractAround a nonmagnetic impurity in a ferromagnet as e.g. Nd in iron the spin system is strongly disturbed. The magnetic exchange is weakened and the spins interact with the strain through magnetoelastic coupling. It is shown in a simple continuum model that a strong enough strain can cause an instability of the solution with parallel average spin and produce thus a long range disturbed region with a net transverse spin component. The hyperfine field at the defect site makes then an angle to the total magnetization in accordance to experimental results.
A method for computation of dislocation loops in a pile‐up
Authors: Maurissen Y. , Minari F. , Capella L. 
Published: July 2007

AbstractAnalytical methods cannot be applied to problems of dislocation pile‐ups when the number of dislocations is large or when the stress field involved is not uniform. A general method is given of computation based on the decomposition of a dislocation loop into elementary loops. By these one can determine the configuration and the number of dislocations in a pile‐up in the case of every sort of stress field or barrier.
Resonance interband interaction and vibronic coupling in molecular crystals
Authors: Zgierski M. Z. 
Published: July 2007

AbstractA two‐exciton‐band model of a molecular crystal with linear vibronic coupling of different strength in each band is investigated. The possibility of resonance interaction between two exciton bands is taken into account. A formula for the optical absorption coefficient of the lower, less intense band is derived and discussed for the first singlet exciton state of the anthracene crystal. It is shown that the resonance interband interaction is completely responsible for the difference between the relative intensities of the vibronic lines in the absorption spectrum of the crystal and the free anthracene molecule.
The Electronic Structure and Magnetic Moment of Fe, Co, and Ni Atoms
Authors: Galperin F. M. 
Published: July 2007

AbstractA previously suggested new theoretical model for the extension of the charge density of 3d electrons of atoms of ferromagnetic metals of the iron group (in comparison to that in a free atom) and a concept of a neutral atom in metals is considered and on the same basis a calculation has been made for the electronic structure and magnetic moment of Fe, Co, and Ni atoms.
Magnetic Field Effects on the Spin Wave Spectra and Magnon Specific Heat of Antiferromagnetic NtF2
Authors: Deonarine S. , Joshua S. J. 
Published: July 2007

AbstractThe effects of magnetic field on the spin wave spectra, magnon density of states, and the magnon contribution to the specific heat have been calculated for the antiferromagnet NiF2. The results show that the Davydov splitting of the k= 0 magnons decreases with increasing field whilst the zone boundary magnons remain degenerate. The spin wave contribution to the specific heat decreases with increasing field as expected.
Computer‐Generated Structures of Amorphous Ge
Authors: Shevchik N. J. 
Published: July 2007

AbstractSeveral structures for amorphous Ge have been generated on a computer with procedures that are believed to approximate the true deposition process. All of the structures are characterized by rigid bond lengths and 8 to 10° bond angle distortions. The primary differences among the structures are in the distribution of the dihedral angles. For the most physically reasonable assumed deposition process, in which the dihedral angle are unconstrained, the resulting RDF of the cluster agrees best with the experimental RDF. It is shown that the continuous random network model for amorphous Ge can fit even the higher features of the experimental RDF.
Scattering Probabilities for Holes I. Deformation Potential and Ionized Impurity Scattering Mechanisms
Authors: Costato M. , Reggiani L. 
Published: July 2007

AbstractThe integrated scattering probabilities per unit time for the hole‐deformation potential (acoustic and optical) scattering mechanism, and for the hole‐ionized impurity scattering mechanism have been evaluated for a typical two‐band (Ev1 and Ev2)valence band structure, spherical and parabolic. The wave functions of the two bands are mostly p‐like, the first (P3/2, M±1/2), the second (P3/2, M±3/2). The symmetry properties of the valence band wave functions are shown to introduce the following effects: (1) To scale down of about a factor two the transition rate for the acoustic and optical deformation potential scattering mechanisms with respect to the case in which an s‐like symmetry is assumed for the band wave functions. (2) To correct in a non‐trivial manner the transition rate for the ionized impurity scattering mechanism, leading to a decoupling effect of the two bands by increasing the hole energy. This decoupling effect opposes the otherwise strong coupling for the transitions from Ev2 to Ev1 found for the acoustic and optical deformation potential scattering mechanisms.
Study of the Excitation of 4d Electrons in Rare‐Earth Metals by Inelastic Scattering of a High Energy Electron Beam
Authors: Trebbia P. , Colliex C. 
Published: July 2007

Abstract4d electron excitations have been investigated in several rare‐earth metals (Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) by means of electron energy losses of a high energy (75 keV) electron beam. Experiments were made with a transmission electron microscope modified by the adjunction of a Castaing‐Henry dispersive system. The results of the measurements lying in the energy range between 120 and 190 eV agree rather well with X‐ray photoabsorption spectra and oscillator strengths calculated in an atomic model.
EPR Study of Impurity—Vacancy Aggregates in NaCl Containing Both Mn2+ and Other Divalent Cations
Authors: Ikeya M. , Crawford J. H. 
Published: July 2007

AbstractSeveral aggregation products involving divalent cation—cation vacancy complexes in NaCl have been studied using the EPR of Mn2+ which is present as a minor constituent. As the probability that the aggregation product contains more than a single Mn2+ is small, the EPR spectrum of the Mn2+ should be indicative of the symmetry of the aggregates. The principal axes of aggregates produced by an anneal were detected with EPR and compared with those calculated for possible models. Three spectra newly found were identified tentatively as a dimer with 〈100〉 symmetry, large aggregates probably in {111} planes, and a Mn2+ occupying a cubic site in a second‐phase precipitate.
Analytical derivation of spin configuration and intrinsic coercive field of a narrow domain wall
Authors: Hilzinger H. R. , Kronmüller H. 
Published: July 2007

AbstractIn ferromagnetic materials with narrow domain walls the wall energy depends periodically on the position of the wall centre with respect to the crystal lattice. This gives rise to an intrinsic coercive field. The spatial variation of the wall energy is determined by methods previously applied by Seeger and Schiller to the Peierls potential of dislocations. It is found that the oscillations of the wall energy depend sensitively on the precise spin structure of the domain wall. Therefore an improved micromagnetic treatment of the domain wall was required taking into account fourth‐order terms in the exchange energy.
First and second order Raman scattering of monocrystalline CuCl
Authors: Prevot B. , Sieskind M. 
Published: July 2007

AbstractA detailed study of the first and second order Raman effect in CuCl is presented using either He–Ne or Ar‐ion laser beam. The spectrum is observed at room and liquid N2 temperature. For the first time, at room temperature a pronounced polarization effect on the 65 cm−1 line was observed when looked either at the Γ15 component of the spectrum or at the Γ1 and Γ12 ones. In the lower part of the Raman shift, the Γ15 spectrum is the strongest, whereas the Γ1, Γ12 contributions become more visible beyond 200 cm−1 but weaker by an order of magnitude. Using recent neutron scattering data (slightly corrected for optical phonons) the major peaks are explained by superimposed lines rather than by isolated processes. The most parts of the features are well interpreted. The lines at 162 and 199 cm−1 are shown to have a similar temperature shift while the 123 cm−1 one behaves quite different.
Mössbauer frequency shift in spin‐ordered systems
Authors: Shukla G. C. 
Published: July 2007

AbstractConsidering the displacement of magnetic ions up to cubic terms the temperature‐dependent Mössbauer shift has been calculated for a crystal of monoatomic lattice containing exchange coupled magnetic ions. The expression for the second order Doppler shift (SOD) is derived in the low‐ and high‐temperature limits.
The role of spatial dispersion in a quadrupole light absorption
Authors: Davydov A. S. , Eremko A. A. 
Published: July 2007

AbstractThe phenomenological Maxwell equations are used to investigate the passage of light through a crystal in a frequency range that corresponds to an isolated band of exciton states of the quadrupole type. The conditions are found under which the singularities connected with the wave‐vector dependence of the exciton frequency and an oscillating dependence of the light transmission coefficient on the crystal width may occur (when the width is small). The calculated results are compared with the Gorban‐Timofeev experiment with Cu2O in the quadrupole exciton absorption region when λ = 6125 Å.
Fine structure details in the LMM Auger spectra of germanium
Authors: Lindau I. , Ribbing C. G. 
Published: July 2007

AbstractHigh resolution LMM Auger spectra of germanium are reported showing fine structure not previously observed and interpreted. The Auger spectra were obtained by X‐ray excitation and analyzed under high resolution with an electrostatic analyzer. The observed fine structure for the LMM transitions L3M23M45, L3M45M45, and L2M23M45 can not be interpreted within the j‐j coupling model but fits better into the pure L‐S coupling scheme of the final vacancies of the Ge atom.
Antiferromagnetic properties of NiO and CoO. II. Paramagnon symmetries and magnon dispersion relations
Authors: Joshua S. J. , Morgan F. D. 
Published: July 2007

AbstractAn investigation is made of paramagnons and mognons in NiO and CoO. In particular, the possible paramagnon symmetries for NiO and CoO are derived and the magnon dispersion relations calculated along all the important symmetry directions of the antiferro‐magnetic Brillouin zone of NiO and CoO. The latter are found to agree well with the group theoretical predictions reviewed in paper I.
Lattice vibrations of lithium on model pseudopotential
Authors: Kushwaha S. S. 
Published: July 2007

AbstractA two parameter model pseudopotential is used to calculate the phonon frequencies along the symmetry directions for lithium. The calculated frequencies are in good qualitative agreement with the experiment, except the observed crossing of the longitudinal and transverse branches along the [100] direction. Grüneisen parameter, compressibility, and binding energy have also been calculated and compared with available experimental results.
Variational calculation of the three‐phonon umklapp resistivity
Authors: Singh D. P. , Verma G. S. 
Published: July 2007

AbstractA variational method is used to calculate the three‐phonon umklapp resistivity in Ge, Si, NaCl, and KCl where the expressions are used for the three‐phonon scattering strengths, derived previously for a simple cubic crystal. The temperature ranges, considered for Ge, Si, NaCl, and KCl are 400 to 1000 °K, 400 to 1600 °K, 30 to 80 °K, and 40 to 100 °K, respectively. The present calculations show that for the semiconductors Si and Ge the calculated umklapp resistivities are half as great as the experimentally observed values. This suggests that the three‐phonon normal processes are quite important for Si and Ge even for temperatures greater than 400 °K. For alkali halides the agreement between theory and experiment is reasonably good. It is also found that the contribution due to T + T ⇌ L processes towards the umklapp resistivity is greater than that of the T + L ⇌ L processes for all the materials at all temperatures.
On the theory of metamagnet transitions
Authors: Mitsek A. I. 
Published: July 2007

AbstractThe domain structure in the region of the metamagnet transition is considered and the magnetic susceptibility, magnetostriction, and ΔE‐effect are calculated. It is shown that the appearing domain walls may be of two types: discrete walls having the smaller energy, where an activation energy is necessary to displace them and continuous walls whose energy is greater, but which can be displaced elastically. Two nucleation mechanisms are considered.
Minority carrier magnetophonon resonance in p‐InSb and in p‐GaSb–InSb mixed crystals
Authors: Byszewski P. , Walukiewicz W. 
Published: July 2007

AbstractMeasurements of longitudinal magnetoresistance have been made on p‐InSb and p‐GaxIn1−xSb over the range of temperature from 77 to 300 K. The magnetophonon effect on the minority carriers was observed. Theoretical discussion of the position of observed minima enables the determination of transitions contributing to the oscillations and parameters of the conduction band of mixed compounds.
Dielectric relaxation of Ca++–vacancy dipoles in KCl + KBr mixed crystals
Authors: Robert R. , Barboza R. , Ferreira G. F. L. , de Souza M. Ferreira 
Published: July 2007

AbstractUsing dielectric loss and ionic thermo‐current (I.T.C.) techniques the dielectric relaxation of KCl + KBr mixed crystals doped with Ca++ was measured. It was found that the activation energy, H, for dipole reorientation decreases as the Br− minority anion concentration increases in the KCl + KBr:Ca++ mixed crystal. In KBr + KCl:Ca++ (Cl− as a minority anion) the activation energy for dipole reorientation increases as the Cl− minority anion increases. In addition to the relaxation peak that displaces with the minority Cl− anion concentration, another one was found in KBr + KCl:Ca++, but not in the KCI + KBr:Ca++ system where Br− is the minority anion. The experimental results are explained, for minority anion concentration not higher than 10%, in terms of lattice parameter change and of the local effect of the minority anion.
The surface density of the acoustical phonon states
Authors: Iosilevskii Ya. A. 
Published: July 2007

AbstractThe density of the acoustical phonon states of an elastically isotropic solid is found with allowance for its surface. The difference is discussed between the surface “thermodynamic” density of states and the local one describing the spectral distribution of vibrations of the individual atoms. The surface lattice heat capacity and the Kapitza thermal resistance are considered as the characteristic applications of the formalism developed.
Note on the debye temperature of palladium
Authors: Brown J. S. 
Published: July 2007

AbstractThe results of the calculation of the 0 °K equivalent Debye temperature of f.c.c. Pd are given, based on an elegant iterative approach due to Fedorov. The results of Fedorov's first and second approximations are presented for Pd along with their correlation with earlier theoretical results and with elastic and calorimetric experimental determinations.
ESCA studies of some AIIIBv compounds with Ga and As
Authors: Leonhardt G. , Berndtsson A. , Hedman J. , Klasson M. , Nilsson R. , Nordling C. 
Published: July 2007

AbstractElectron spectra have been recorded from the AIIIBV compounds GaP, GaAs, GaSb, and InAs as well as from Ga203, As2O3, Ga, and As. Binding energy values, determined b; careful energy calibrations, are reported for the Ga and As 3d electrons. The bindin energy shifts for the AIIIBV compounds suggest a charge transfer from A to B.
Resonance raman scattering in group Vb semimetals: As, Sb, and Bi
Authors: Renucci J. B. , Richter W. , Cardona M. , SchÖstherr E. 
Published: July 2007

AbstractThe dependence of the Raman scattering cross section of As, Sb, and Bi on the energy of the exciting laser was measured in the region from 1.6 to 2.7 eV. The shape of the resonance curve agrees reasonably well with the squared magnitude of the derivative of the dielectric constant with respect to frequency. Discrepancies are only seen at low frequencies for Sb and As. They are attributed to variations of the electron‐phonon interaction through the Brillouin zone. From these measurements, relative values of several average electron–phonon interaction constants are derived.
Anisotropic electron scattering by interstitial hydrogen impurities in copper
Authors: Dye D. , Lowndes D. H. , Lengeler B. 
Published: July 2007

AbstractMaps of the scattering rate anisotropy for Cu(H) have been obtained using two different representations, one based upon ß phase shift analysis, and the other using a symmetrized Fourier series. The partial wave analysis indicates that p wave scattering is heavily dominant, although the analysis does not account entirely for the large scattering rates observed on the Neck and Dogsbone orbits. The dominance of p wave scattering suggests that the screening of the interstitial proton is carried out primarily by electrons in conduction states derived from orbitals with p‐like symmetry.
Interface and surface polaritons of semiinfinite biaxial crystals
Authors: Borstel G. 
Published: July 2007

AbstractInterface and surface polaritons of an arbitrary semiinfinite crystal cut of biaxial symmetry are investigated. It is shown that regular interface modes can occur only for certain orientations of the propagation vector or special crystal cuts. From energy flow considerations it is found that ordinary interface modes can exist only if the two‐dimensional propagation vector (kx, ky) is along a principal axis of the dielectric tensor. In uniaxial crystals two different types of interface polaritons are found to occur. The first is a regular and real interface mode whose dispersion relation depends neither on the crystal cut nor on the direction of propagation. The second is a generalized interface mode which may have real or virtual character.
The phonon drag in wurtzite‐type semiconductors
Authors: Bulat L. P. 
Published: July 2007

AbstractThe formula for the phonon drag part of the thermoelectric power tensor α in wurtzite structure semiconductors has been received. The comparison between theory and experiment as well as the analysis of various possible mechanisms of phonon relaxation enable to conclude that the phonon drag effect is associated with the piezoelectric interaction between electrons and acoustic phonons, with the phonon relaxation stemming from the phonon‐phonon scattering. Calculation of Kα = α/α for a number of compounds has been performed, where the piezoelectric potential and the dielectric and phonon spectrum anisotropy are taken into account.