bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of different approaches to the study of local defects in crystals. II. Substitutional impurities in the tight‐binding approximation
Authors: Pisani C. , Dovesi R. , Ugliengo P.
Published: July 2007

Different approaches to the study of local defects in perfect crystals are compared as applied to the classical problem of substitutional impurities in tight binding (TB) cubic metals. The standard embedding procedure proposed by Koster and Slater (KS) is perfectly suited for this problem and its results are taken as a reference. It is so possible to evaluate the performance of isolated cluster (IC) calculations, and of those “perturbed cluster” approaches which correct the cluster molecular solution by a suitable coupling operator (MLEC schemes). It is shown that while IC results are affected by enormous relative errors at small perturbations even with large clusters, the MLEC approach is very effective in accounting for the presence of the surrounding media and reproducing the correct electronic structure within the cluster.
Positron–annihilation measurements of the Fermi surface of copper‐base solid solutions with gallium, germanium, and nickel
Authors: Steinmetz K.‐H. , Fischer H.‐P. , Martin M. , Nembach E.
Published: July 2007

The {011} cross‐section of the Fermi surface of Cu‐rich solid solutions with Ga, Ge, and Ni is measured by positron annihilation. The “rotating specimen” method is used. The concentrations of Ga and Ge cover the whole range of primary solid solutions; cNi extends up to 22 at%. For all three solutes investigated, the neck radius of the Fermi surface increases monotonously with solute concentration. For a given electron per atom ratio e/a, Ga widens the neck 32% more than Ge does. All three solutes decrease the ratio of maximum to minimum diameter of the Fermi surface. The electronic structure of these solid solutions is not exclusively determined by the e/a ratio, but depends on the specific properties of the solute. The present experimental results do not support the view that the extent of primary solid solutions is mainly governed by the electron structure.
Thermoluminescence and optical absorption studies rubidium bromide doped with barium
Authors: Sastry S. B. S. , Nagarajan S.
Published: July 2007

Thermoluminescence (TL) and optical absorption studies are made on RbBr:Ba2+. An absorption band due to Z1‐centres appears at 1.58 eV on F‐light bleaching subsequent to γ‐irradiation. A TL glow peak attributable to Z1‐centres is identified. TL emission under the main glow peak shows a broad emission at 2.65 eV with a shoulder at 1.95 eV. This 1.95 eV emission is attributed to VM2‐centres which give rise to an absorption band around 4.1 eV. A tentative energy band scheme is suggested explaining the various TL processes.
EPR and luminescence of Mn2+ in distorted tetrahedral symmetry in CaZnF4 crystals
Authors: Heming M. , Lehmann G. , Recker K. , Wallrafen F.
Published: July 2007

Small crystals of CaZnF4 with scheelite‐type structure, doped with about 1% Mn are obtained from the melt by the Bridgman method with subsequent annealing at 725 °C, 50 K below a reversible phase transformation detected by DTA. Mn2+ exclusively occupies Zn sites as evident from the size of the hyperfine splitting constant. The intrinsic zero field splitting parameter of second order obtained from superposition analysis is in the same range as that for [MnF6]4− units. The luminescence spectra do not serve as a critical test for distinction between four‐ and eightfold coordination.
Magnetization and 161Dy mössbauer effect study of DyMn2 and Dy6Mn23 and their ternary hydrides
Authors: Gubbens P. C. M. , Ras W. , Van Der Kraan A. M. , Buschow K. H. J.
Published: July 2007

The compounds DyMn2 and Dy6Mn23 and their ternary hydrides are investigated by means of magnetic measurements and 161Dy Mössbauer spectroscopy. In DyMn2 magnetic ordering disappears after charging with hydrogen gas. In Dy6Mn23 the absorption of hydrogen gas leads to a strong reduction of the bulk magnetization even though the Dy sublattice remains magnetically ordered at low temperatures, with magnetic moments on the Dy atoms close to the free ion values.
Study of the 3D5 Shell Deformation of Fe3+ Ions in Znfe2O4 by High‐Field Mössbauer Spectroscopy
Authors: Ligenza S. , Lukasia M. , Kucharski Z. , Suwalski J.
Published: July 2007

The deformation of the 3d5 electron shell of Fe3+ ions in ZnFe2O4 is investigated by Mössbauer spectroscopy without and with an external magnetic field of 6 T at 4.2 K. It is found that 3d5 shell deformation observed by neutron spectroscopy brings about a quadrupole shift equal to ϵ3d = −0.030 mm/s. The magnitude of all other hyperfine interaction parameters of 57Fe nuclei are also reported. Noncollinear arrangements of Fe3+ spins, inside clusters as well as in their local environments, are observed. Among the Fe3+ ions in the octahedral B‐sites five different magnetic configurations are distinguished.
Low‐Temperature Fluctuational Motion of Dislocations in Crystals II. Manifestations Of Dissipative and Quantum Effects in the Low‐Temperature Plasticity
Authors: Osetskii A. I.
Published: July 2007

The temperature behaviour of the fluctuation‐dissipative effects is analysed. At sufficiently low temperatures it is controlled by variations in the viscosity coefficients of the phonon and electron gas. Some experimental data are quoted which can be regarded as evidence for the influence of fluctuation‐dissipative effects upon the low temperature plasticity of materials, i.e. change in the activation energy during NS transition, correlation between the activation energy and the phonon gas viscosity, etc. The temperature dependence of such values as the flow stress, activation energy and activation volume, work hardening coefficients, and the relaxation depth of effective stresses are analysed for the range of temperatures where fluctuation‐dissipative effects are essential. The dependences are calculated both, in the framework of the classical approximation and in the fluctuation‐dissipative model, and compared with the data measured with single crystals of lead and zinc at temperatures below the Debye point. As found, many anomalies observed at low temperatures in the temperature behaviour of the plasticity parameters can be satisfactorily explained as manifestations of the impact of dissipation on the velocity of activated dislocation motion through the crystal.
Tight‐Binding Cluster Model for C, Si, and Ge. I. Analytic Solution for s‐States in Diamond Lattice
Authors: Bílek O. , Skála L. , Künne L.
Published: July 2007

Using the tight‐binding approximation an analytic solution of the Schrödinger equation for the s‐states of C, Si, and Ge clusters in the form of a rectangular parallelepiped is found and discussed.
Local Heine‐Abarenkov Potential with Volume‐Dependent Parameters of Al
Authors: Soma T. , Konno Y. , Kagaya H.‐B.
Published: July 2007

A local Heine‐Abarenkov model potential with volume‐dependent parameters is proposed for Al. Two parameters are determined by satisfying the zero pressure condition and the first zero of the empirical pseudopotential interpolated from band calculations. Calculated values of cohesive energy and the equation of state are in good agreement with the experimental data.
Magnetic Symmetry in Several Cubic Compounds
Authors: Luchian H.
Published: July 2007

A well known group theoretical method derived from the Landau theory of the second order phase transitions is applied to several cubic compounds. Only symmetry considerations are taken into account.
Resonant Coherent Energy Transfer. Role of Initial Conditions
Authors: Agabekyan A. S.
Published: July 2007

The dependence of dynamics of coherent resonant energy transfer of electronic excitation between impurity ions in condensed media on the initial conditions of the donor excitation is investigated. Their crucial role in the coherence of the energy transfer process is shown. Validity criteria of different limiting cases of the energy resonant transfer are specified taking into account initial conditions of excitation. The “excitation trapping” effect at the coherent energy transfer is also shown to be present.
Density of States and Optical Conductivity of Ferromagnetic Nickel
Authors: Ahuja A. K. , Auluck S. , Joshi S. K.
Published: July 2007

The density of states and the interband optical conductivity of ferromagnetic nickel are calculated using the energy eigenvalues and the eigenfunctions from the interpolation scheme band structure where the parameters are adjusted to fit the Fermi surface data. The Brillouin‐zone integrations are performed using the special‐direction method. The effects of including optical matrix elements and a phenomenological lifetime broadening are studied. The calculations are in good agreement with the optical data. A comparison is made with the recent angle resolved photoemission data.
The Biexciton Levels and Nonlinear Optical Transitions in ZnO
Authors: Hvam J. M. , Blattner G. , Reuscher M. , Klingshirn C.
Published: July 2007

The controversy about the level scheme of the biexcitons in ZnO is solved by two‐photon reabsorption spectroscopy. Three levels are detected, corresponding to the possible combinations of A and B valence band holes. The diamagnetic shift of these states is below 2 × 10−6 eV T−2 in agreement with the small exciton and biexciton radii. In forward two‐photon Raman scattering, two excitation induced renormalizations of the polariton dispersion are observed, partly involving transitions to the biexciton level. The M‐band luminescence and the resonance structure observed in backward two‐photon Raman scattering are reconsidered in terms of the new level scheme.
Effects of a Transition Layer on Nonlinear Surface Polaritons
Authors: Wendler L.
Published: July 2007

The dispersion relation for nonlinear surface polaritons is derived, for both, p‐ and s‐polarization, which propagate in a system consisting of two semiinfinite media. One of them is characterized by a nonlinear diagonal dielectric tensor. Moreover a transition layer (thickness 20 to 150 Å) between the two media is taken into account.
Impurity Band Conduction in HgTe. II. Theoretical Analysis
Authors: Dziuba Z.
Published: July 2007

The impurity band conduction in HgTe is analysed. The electrical conduction in low magnetic field is described in short mean free path approximation. The impurity concentration is estimated by the analysis of the electrical conduction versus magnetic field. The electrons and holes in the impurity band are qualitatively described as carriers from different parts of the impurity band.
Electronic Relaxation Effects in Core Level Spectra of Surfaces and Interfaces
Authors: Bechstedt F. , Enderlein R. , Reichardt D.
Published: July 2007

The electronic relaxation energy of core hole excitations is calculated for the spatial inhomogeneous system of a solid with a surface or interface. The most important approximations involved in the calculations are the linear expansion of the relaxation energy with respect to the difference of the shielded and bare core hole potentials and, for the treatment of the surface or interface, the neglect of quantum mechanicals interference terms in the polarization function of the system. At a given distance from the interface the relaxation energy of the excited core hole can be expressed in terms of the bulk dielectric function. The general theoretical results are applied to calculate relaxation energies as functions of the distance from the surface or interface for the clean Si surface and for abrupt interfaces of Si with SiO2, GaAs, and metallic Pd. The relaxation energy exhibits notable spatial variations only within a thin layer of about 2 at. units thickness whereas it remains practically constant and shows only small deviations from the bulk value outside of this layer. The conclusion is drawn that core electron binding energies from first layer atoms at a surface or interface are shifted because of spatial changes of relaxation energies by tenths of an eV compared to bulk binding energies. For chemisorbed atoms the relaxation of the electrons in the underlying solid changes core electron binding energies compared to those of free atoms much stronger (several eV).
The Luminescence of K4Bi2Br10 · 4 H2O and Rb3BiBr6 Single Crystals
Authors: Timmermans C. W. M. , Blasse G.
Published: July 2007

The luminescence properties of K4Bi2Br10 · 4 H2O and Rb3BiBr6 are reported. Both compounds show blue luminescence at low temperatures. For Rb3BiBr6 the luminescence is ascribed to the 3P0 → 1S0 transition on the isolated Bi3+ centre, while in K4Bi2Br10 · 4 H2O the luminescence originates from the [Bi2Br10]4− dimers. The energy level diagram of the dimer centre is approached by using simple MO‐theory. The compound K4Bi2Br10 · 4 H2O shows also an emission band in the red, which is ascribed to a charge‐transfer transition. The quenching of the luminescence is caused by energy migration among the dimers in K4Bi2Br10 · 4 H2O, while in Rb3BiBr6 the luminescence is quenched via the charge‐transfer state.
Channeling of Ultrarelativistic Electrons in Crystals
Authors: Muralev V. A.
Published: July 2007

The kinetic equation for axially channeled ultrarelativistic electrons in the energy range of 1 to 55 GeV for Si and W is solved. The results show that the dechanneling lengths for different targets are close. Yet, the Kumakhov radiation power in W is higher than in Si. Therefore, the Kumakhov radiation efficiency in heavy crystals, such as tungsten, can be very high. The present method permits to study the contribution provided to the dechanneling function by electron scattering, thermal vibrations, the density effect etc. It is shown that electron scattering provides the main contributions. The results can be useful in planning experiments on charged‐particle radiation in channeling and in the data analysis, in particular in obtaining the optimal crystal thickness.
Radiation Damage Studies of Co2+ and Ni2+ Doped NH4Cl Crystals
Authors: Rambau B. , Ramasastry C. , Chowdari B. V. R.
Published: July 2007

Results from the radiation damage studies of NH4Cl:Co2+ and NH4Cl:Ni2+ crystals are presented. On X‐irradiation at room temperature the NH4Cl:Co2+ crystals are found to absorb at 270, 345, 585, 900, and 1000 nm. These absorption bands are attributed to the charge transfer transitions between radiation induced hydrazine‐like defect, N2H, and ligands H2O or NH3 which are made available in the crystal along with the divalent impurity. If not all the absorption bands but similar absorption is found on irradiation in Ni2+ doped NH4Cl crystals also. ESR studies of X‐rayed Ni2+ doped NH4Cl crystals reveal the formation of both, Ni+ and Ni3+. Spin‐Hamiltonian parameters for these centers are given.
Central Peak in Ising Model with Transverse Field (II)
Authors: Kashcheev V. N.
Published: July 2007

It is shown that in the hydrodynamic limit the central peak, traced back to the interaction of the pseudospin critical fluctuations with thermal diffusion mode in the Ising model with a transverse field, has the Lorentz form. The critical exponent of the width of this peak is calculated.
Splitting of the 3d Levels of Iron Group Impurities in Crystals with Zincblende Structure
Authors: Biernacki S. W.
Published: July 2007

A new parametrization scheme is presented of the crystal term energies for 3d impurities in ZnS‐ structure crystals. This allows a practical analysis of the optical spectra in these structures. This scheme, unlike the Tanabe‐Sugano scheme, accounts for the different deformations of e‐ and t2‐ orbitals in the tetrahedral crystal field. To avoid the complexity caused by the many unknown parameters which appear when the e‐ and t2‐Orbitale are considered deformed to different degrees, the point charge model of the crystal field and the Slater form of the d‐orbitals are employed. This provides two adjustable parameters for describing the crystal term energies. The results indicate that the energy separation between the crystal terms depends not only on the Racah parameters B and C but also on the Racah parameter A, and it is shown how the Racah parameters for a given impurity depend on the crystal field. The energy separation Δ between the crystal terms A2 and T2 is interpreted to be the sum of two terms: Δcryst the contribution due to the crystal field splitting and Δrep the contribution due to different repulsion energies between the electrons in the two states. As an example of the application of this parametrization scheme, the impurities Ti2+, V2+, Co2+, and Ni2+ in ZnSe are considered.
On the Reflectivity for Oblique Incidence of the Uniaxial Antiferromagnetic Crystals FeF2, CoF2, and MnF2
Authors: Lehmeyer A. , Merten L. , Häussler K. M.
Published: July 2007

By combining the dispersion relations of the refractive index and the boundary conditions in the surface the formulae of reflectivity of the antiferromagnetic crystals FeF2, CoF2, and MnF2 can be derived for oblique incidence. This is performed for two important orientations of the surface, namely for the surface perpendicular to the optical axis and for a surface which contains the optical axis. The results are six different formulae of reflectivity for oblique incidence.
Many‐Electron Hopping
Authors: Gosar P.
Published: July 2007

Correlated hopping of many electrons in the impurity band of the moderately compensated semiconductor is studied. The calculation of the n‐electron cluster transition rate is based on the following assumptions: the one‐electron states in the impurity band are strongly localized, the motion of each electron is restricted to the hopping between two impurity sites, the electrons mutually interact by Coulomb forces, and the deformation‐potential‐type coupling to phonons is used. A statistical approach is applied in the calculation of transition rates for very large clusters.
Effects of Order on the Electronic Structure of Ni3Fe
Authors: Lipiński S.
Published: July 2007

The electronic densities of states for partially ordered Ni3Fe are calculated within the framework of the Hartree‐Fock and coherent potential approximations. The four‐sublattices Hubbard model with an ansatz simplifying the hopping part of the Hamiltonian is used.
Phase diagram of a spin glass of EupSr1 − pS
Authors: Katsura S. , Matsuno A.
Published: July 2007

EupSr1 − pS is modeled as a site‐diluted Ising model with first and second neighbor interactions (J > 0, J' < 0) between Eu atoms, on a lattice with square coordination number zc. By use of the reducibility of the four‐body density matrix to the one‐body density matrix, an integral equation for the distribution function for the effective field is obtained. The integral equation for the case J' = − J/2 is solved exactly at T = 0 in the case of zc = 2 and the three solutions for the paramagnetic, ferromagnetic, and the spin glass states are obtained. The boundary between the ferromagnetic and spin glass state is given by pFG = 0.545 and the phase diagram shows a reentrant behavior.
Direct luminescence evidence for the degenerate electron—hole plasma formation in AIIBVI semiconductors
Authors: Brodin M. S. , Bandura V. M. , Matsko M. G.
Published: July 2007

The emission spectra of ZnTe and ZnSe crystals are investigated at T = 4.2 K at high excitation densities by a Coumarin 30 and 120 dye laser. It is shown that for excitation densities Rexc > > 0.1 MW/cm2 the emission spectrum of ZnTe exhibits the P‐band due to inelastic exciton‐exciton scattering. For Rexc > 6 MW/cm2 the emission of a degenerate electron—hole plasma (EHP) is observed. These emission bands may be differentiated by scanning the exciting quanta energy in the short‐wavelength tail region.
The theory of magnetic polarons in antiferromagnetic semiconductors
Authors: Egorov B. V. , Timofeev B. B.
Published: July 2007

The electron states in antiferromagnetic semiconductors with large atomic spins S and an arbitrary relation between the band width ΔE and the spin—electron interaction A are considered. It is shown that in the mean‐field approximation of atomic spins the spin—electron interaction in case of AS ≧ ΔE leads to essential transformations in the electron spectrum, while the interactions of electrons with the spin deviations from the average values (at T = 0 with virtual magnons) leads to a polaron‐type quasi‐particle formation: the antiferromagnetic polaron (AFP). With the help of the diagram technique at T = 0 the AFP Green function and its spectrum are obtained.
Biexcitons in crystals with large ortho—para‐exciton splitting
Authors: Bobrysheva A. I. , Moskalenko S. A.
Published: July 2007

It is shown that in a system of ortho‐ and para‐excitons two ortho‐excitons with total spin S = 0 interact attractively and biexcitons can be formed. The interaction potential of two ortho‐excitons is approximated by a generalized Morse potential depending on the electron—hole mass ratio σ. On this basis the energy of vibrational and rotational levels of the biexciton is obtained. The binding energy of the biexciton ground state is estimated for all values of σ.
Analysis of the dielectric properties of mixed alkali halide crystals
Authors: Shanker J. , Jain G. D.
Published: July 2007

The electronic and static dielectric constants, longitudinal and transverse optic mode frequencies, effective charge parameters, optic mode Gruneisen parameters, and volume derivatives of dielectric constants are calculated for the entire range of composition of mixed NaCl—NaBr, KCl—KBr‐and KBr—KI crystals. The calculations are performed using the knowledge of interionic potentials. The results are discussed and compared with available experimental data.
A scattering matrix calculation of very low energy electron reflection intensities for barium and magnesium oxides
Authors: Lynch D. F. , Smith A. E.
Published: July 2007

Results of calculations are presented for electrons incident on barium and magnesium oxide crystals with energies in the respective ranges 0.5 to 15 eV and 0.5 to 30 eV. Comparisons are made between these computations based on a simple pseudopotential scattering matrix approach and data from LEED and total current experiments. It is concluded that the good agreement can be explained on the basis of the dominance of the crystallography of the specimen over the precise description of the individual scattering events. The coincidence of low order kinematical Bragg reflection conditions with the features is also commented upon.
NMR study of the charge‐density‐wave state in VSe2
Authors: Skripov A. V. , Stepanov A. P. , Shevchenko A. D. , Kovalyuk Z. D.
Published: July 2007

The 51V NMR lineshape, Knight shift, quadrupole interaction, spin—lattice relaxation time and magnetic susceptibility in a single‐crystalline VSe2 are studied in the temperature range 4.2 to 300 K. Above the charge‐density‐wave (CDW) onset temperature T0 ≈ 110 K the linear temperature dependence of the quadrupole coupling constant and the pretransitional line broadening are found. The temperature dependence of the CDW amplitude is determined from the width of electric‐field‐gradient distribution at nuclear sites below T0. Combining the experimental data on NMR properties and magnetic susceptibility the effective electron—electron interaction parameter, J = 0.29 eV, is estimated and the density of electron states at the Fermi level. The latter is found to decrease from 2.05 to 1.60 states/eV spin V at the phase transition into the CDW state.
Crystal field splitting in NdAl3 studied by inelastic neutron scattering
Authors: Alekseev P. A. , Goremychkin E. A. , Lippold B. , Mühle E. , Sadikov I. P.
Published: July 2007

Inelastic neutron scattering experiments are performed in polycrystalline NdAl3 to determine the crystalline electric field parameters for the Nd3+ ion in its hexagonal environment. The parameters obtained are checked with the results of other measurements related to the crystalline electric field, such as magnetic susceptibility, heat capacity, and electric resistivity.
Carrier Mobility in Doped Nondegenerate Semiconductors
Authors: Khamidullina N. M.
Published: July 2007

The temperature dependence of the drift and Hall mobilities in compensated semiconductors at low temperatures (4 to 100 K) within the range of impurity concentration of (1013 to 1016 cm−3) is examined. Under these conditions the Born approximation for the charged impurity scattering of the charge carriers is incorrect. Therefore when calculating the mobility thee xact scattering amplitudes are used. In semiconductors with a density of states of the conventional type ϱ(E) ∼︁ √E, the curves of mobilities and Hall‐factor are obtained taking account the simultaneous charged impurity and acoustic phonon scattering; for semiconductors with a smooth random field a comparison of all scattering mechanisms is carried out and mobilities curves are obtained taking the simultaneous smooth random field and charged impurity scattering into account.
Spinless Anderson Model with a Local Phonon Mode
Authors: Kowalska J. , Zieliński J.
Published: July 2007

The electron‐phonon coupling in the spinless Anderson model is considered within the perturbation theory. The second‐order theory including the finite lifetime for phonons leads to some narrowing of the density of states for higher values of the ratio of the electron‐phonon coupling constant and virtual level halfwidth, λ/Δ ≈ 1. The simplified fourth‐order theory (V = 0) shows that very pronounced narrowing is expected (λ/Δ < 1) and there is no change in the height of the central peak.
Optical Phonons in GaS1‐xSex Layer Mixed Crystals
Authors: Gasanly N. M. , Goncharov A. F. , Melnik N. N. , Ragimov A. S.
Published: July 2007

Measurements are made of polarized Raman scattering and infrared reflection spectra of twenty two compositions of GaS1‐xSex layer mixed crystals grown by the Bridgman method. Besides the usual one‐mode and two‐mode behaviours of phonon modes, a number of more complex dependences characterized by the appearance of additional bands in the spectra of mixed crystals are observed. Their appearance is accounted for by the uncovering of the Brillouin zone due to the disturbance of the periodicity of the crystal lattice of mixed crystals. Specifically, for modes with a low dispersion in the Brillouin zone the additional modes are interpreted as vibrations of cells having mixed compositions. A number of anomalies are revealed in the concentration dependences of intensities and frequencies of optical phonons, which are attributed to the β → γ and γ → ϵ polytype transformations at x ≈ 0.6 and x ≈ 0.97, respectively.
Theoretical Calculations of the Curie Temperature for Gd1−xRExAl2 Alloys
Authors: Witański K.
Published: July 2007

The intermetallic compounds Gd1‐xRExAl2 (RE = Dy, Ho, Er) are considered as being disordered alloys. An indirect exchange between localized spins via narrow‐band electrons is assumed. The deviation from a linear relation between the Curie temperature and the concentration for the compounds considered is explained by a small variation of the band structure. Molecular field and Hartree‐Fock approximations combined with the coherent potential approximation are used.
The Influence of Hydrostatic Pressure on the Effective Concentration and Cyclotron Mobility of Electrons in Semiconducting Bi1‐xSbx Alloys
Authors: Požera R. , Sutkus A. , Tolutis R.
Published: July 2007

Rf electromagnetic magnetoplasma technique is used to study the influence of hydrostatic pressure (up to 1.0 GPa) on the effective concentration and cyclotron mobility of electrons in the binary plane in semiconducting pure and Te‐doped Bi1‐xSbx alloys (0.076 ≤ x ≤ 0.15) at 77 K. The pressure derivative of the energy gap at the L‐point does not depend on Sb concentration and is close to the known value at 4.2 K. The pressure and concentration dependences of electron cyclotron mobility indicates the importance of acoustic phonon scattering of electrons. An additional scattering which depends on the Sb concentration must also be taken into account in undoped samples.
Hydrostatic Pressure and Uniaxial Stress Dependence of the Silicon (222) X‐Ray Reflection Power
Authors: Pietsch U.
Published: July 2007

The hydrostatic pressure dependence of the silicon (222) X‐ray reflection power is calculated by means of a molecular‐theoretic model of the bond charge. The experiment, published by Yoder‐Short is explained by the variation of the s‐like portion of a/s + sp3> ‐ like model valence orbital. Furthermore, the uniaxial stress dependence of the “forbidden” reflections are calculated. Such experiments indicate the p‐like amount of the model valence orbitals in a direct manner.
Zone Edge Phonons in Gallium Phosphide
Authors: Pödör B.
Published: July 2007

The energies of zone edge phonons at the critical points X, L, W and along the line ∑ in GaP are deduced from an analysis of infrared absorption and Raman scattering measurements. An assignment scheme for the observed lines, based on X, L, W, and ∑ phonons is given.
The Spin‐Wave Theory of Electron and s‐f‐Exchange Magnetostriction in the Rare Earth Metals
Authors: Sadreev A. F. , Sandalov I. S. , Podmarkov A. N.
Published: July 2007

The magnetostriction phenomena are considered in anisotropic rare earth metals. Two mechanisms of the phenomena are investigated. The first is the s‐f‐exchange due to a distortion of the conduction electron wave functions relative to the localized f‐functions. The second is caused by a change of the single‐electron energy. It is shown for kT « Δa, gμBh, where Δa is the anisotropy energy and gμBh the Zeeman energy, that the electron striction is important to give a linear dependence on the external magnetic field. Otherwise the usual exchange striction can be used. The second mechanism is affected by the change of the single‐electron energy.
Effect of Magnetic Field on the Decay Kinetics and Polarization of the AT Emission of KCl:Tl and KI:In Crystals at 0.4 to 0.7 K
Authors: Bragina L. , Hizhnyakov V. , Liidya G. , Nagirnyi V. , Soovik T. , Zazubovich S. , Janson N.
Published: July 2007

The structure of emission and excitation spectra as well as the decay kinetics and polarization of the AT luminescence are investigated for Tl+ and In+ centres in KCl:Tl and KI:In at 80 to 0.4 K. The effect of a magnetic field up to 2 T on the decay times, intensities, and polarization properties of the emission occurring from the metastable tetragonal minima of the triplet excited state is studied at 0.4 to 0.7 K. The parameters of the centres are determined. Good agreement between the experimental results and theory is obtained.
Optical Properties of Molecular Crystals Phenomenological Approach
Authors: Botvich A. N. , Podoprigora V. G. , Shabanov V. F. , Shestakov N. P. , Vtyuren A. N.
Published: July 2007

The ability to calculate the optical properties of molecular crystals is shown in terms of the polarizability theory. The main factors to be taken into account for such calculations are analyzed. The applicability of the method is illustrated by calculations of refractive indices and Raman and second harmonics intensities for the m‐chloronitrobenzene crystal.
Deformational Phase Transitions and Periodic Structures in a Magnetic Field
Authors: Kochelap V. A. , Sokolov V. N.
Published: July 2007

An instability theory of the homogeneous distribution of current carriers and lattice deformations in semiconductors with electron‐phonon interaction via deformation potential in a quantizing magnetic field is developed. It is shown that the instability takes place in a number of regions on the concentration‐temperature plane, their mutual position being connected with the alternation of electron state density peaks in a magnetic field. Each isolated region is characterized by its own maximum temperature point depending in power‐law fashion on the electron‐phonon interaction constant. At lower temperatures the Peierls‐type instability sets in. Phase diagram peculiarities associated with various types of the instability are considered. Characteristic inhomogeneity periods are calculated and their dependences on carrier concentration and temperature are investigated.
Spin Fluctuations in Alloys with Random Transfer
Authors: Fehske H.
Published: July 2007

The local spin fluctuation theory proposed by Hasegawa is extended to binary alloys with random transfer of the additive type. Spin fluctuations and alloy disorder are treated within an extended coherent potential approximation (ODCPA). The dc conductivity σ, including CPA vertex corrections, is derived via density‐density susceptibility from the functional integral scheme. In the paramagnetic region model calculations are presented for the averaged local moment, σ, density of states, and the distribution function of spin fluctuations.
Correlation Function Method for the Thermoelectric Power of Metals
Authors: Goedsche F. , Richter R. , Wegener H. , Röpke G.
Published: July 2007

A general linear response theory of the thermoelectric transport is developed on the basis of Zubarev's approach to non‐equilibrium statistical thermodynamics. In the weak‐scattering limit electrical resistivity and thermopower are related to generalized dynamical susceptibilities. It is shown that the Mott formula for the thermopower is approximately correct in two cases, first in the case of elastic scattering, and furthermore, in the presence of inelastic scatterers at high temperatures. At low temperatures Mott's formula is shown to be no longer valid. The correction terms due to the inelasticity of the scattering are derived systematically and estimated for a Debye model of electron‐phonon scattering. For the same reason the Nordheim‐Gorter rule must be generalized at low temperatures. The theory is extended to homogeneously disordered systems. The phonon drag is briefly discussed.
An Analytical Theory of FMR in Bulk Metals (Parallel Configuration). II. Penetration Depths
Authors: Fraitová D.
Published: July 2007

The general formulae for the penetration depths of the three waves, which are excited in a bulk ferromagnetic metal in the ferromagnetic resonance (FMR) region, are evaluated for parallel configuration and compared with the antiresonance skin‐depth expression. The concept of the FMR “effective skin‐depth” is introduced.
Exoemission of Pyroelectrics
Authors: Rosenman G. I. , Pechorskii V. I. , Chepelev Yu. L. , Boikova E. I. , Issakova L. E.
Published: July 2007

The investigation of the current density, the angular and energy distributions, as well as the field dependence of the exoemission arising under the pyro‐ and piezoeffect conditions, shows that the electron emission occurs from a dielectric layer on the ferroelectric surface. The effect of exoemission depletion is found. The mechanism of the exoemission phenomenon is examined. The calculations of the barrier permeability show that the exoemission represents the tunnel electron emission from the polaron band or from the bottom of the conduction band.
Localized Magnetization Arising from Spin‐Dependent Impurity Potentials in the Wolff Model
Authors: Liu K. C. , Lam Kai‐Shue , George Th. F.
Published: July 2007

The Wolff model for localized magnetic moments in dilute alloys is extended to include spin‐dependent impurity potentials. Two virtual levels emerge, corresponding to different spin states of the conduction electrons. As a result of this removal of degeneracy, there always exists a more favorable spin polarization for the spin state with the more attractive impurity potential, even in certain circumstances where the original Wolff model yields no magnetization. The results are obtained graphically for various situations. The physical pictures entailed can also be interpreted in terms of the Anderson model.
Asymptotic Solutions for the Differential Equation Describing Solute Drag by Dislocations
Authors: Fuentes‐Samaniego R. , Hirth J. P.
Published: July 2007

The differential equation describing the drag of a Cottrell atmosphere by a dislocation appears in a number of other physical moving‐frame‐of‐reference problems related to line sources of vector fields, such as vortices in fluid flow and line sources of heat. It reduces to the so‐called modified Mathieu equation. This equation is solved and the asymptotic behavior of the modified Mathieu functions is determined in the limiting situations of small velocity and small or large distance from the line source. A specific asymptotic form of the function of the second kind is found to behave like a K‐Bessel function in the limit of the argument z approaching ∞ and like an I‐Bessel function in the limit z → ∞. The solution can be used to obtained analytical results for the Cottrellatmosphere problem.
Electron—Phonon Interaction in Transition Metals. Results of Relativistic APW Band Structure Calculations
Authors: John W. , Nemoshkalenko V. V. , Antonov V. N. , Antonov Vl. N.
Published: July 2007

The Hopfield parameter η of the electron—phonon coupling is calculated for twelve transition metals (Rh, Pd, Ag, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au) in the rigid muffin‐tin approximation. Using relativistic APW band structure data and a generalized Gaspari‐Gyorffy formula the influence of relativistic effects is completely taken into account. It is found that η may be calculated in remarkably good approximation using spin‐weighted averages of phase shifts and density matrix coefficients. The theoretical results for the electron—phonon parameter λ and the electronic specific heat are compared with the experimental data.
Symmetry Breaking in Organometallic Polymers Due to Interchain Interactions
Authors: Böhm M. C.
Published: July 2007

The electronic structure of the tetrathiosquarato nickel (II) polymer 1 is studied in the framework of an extended crystal orbital (CO) formalism where the interchain coupling between adjacent organometallic stacks is taken into account. The theoretical approach is based on the combination of a semiempirical INDO CO model for intrachain interactions with a self‐consistent‐electrostatic‐field approximation for the interchain coupling. The band structure of 1 is studied as a function of the strength of the interchain interaction for two different solid state geometries (rhombic and monoclinic lattice models). Symmetry‐broken solutions of the charge density wave type are predicted for the monoclinic solid in the case of an enhanced interstack coupling. The electrostatic potential between the one‐dimensional Ni backbones leads to a condensation of double and single bonds in the C4S4 moieties.
Localization of Electronic States in Disordered Tight‐Binding Systems. II. Mobility Edges
Authors: Unger H.‐J.
Published: July 2007

The model of a “partially disordered semi‐infinite chain” for disordered real systems which was obtained from first principles in a foregoing paper is further investigated. The existence of mobility edges in the spectrum is shown if the recursion coefficients tend to constant limiting values. The convergence of the sequence of recursion coefficients is discussed. Interesting relations to the theory of critical phenomena and to the percolation theory are found. The physical picture behind converging recursion coefficients, i.e. the existence of short‐range order, is cleared up. A theoretical foundation for the Mott‐CFO‐model is given. Within the framework of the recursion method the dependence of the degree of localization on the dimensionality is discussed.
On the Percolation Approach to the Hopping Conduction in Strong Electrical Fields
Authors: Böttger H. , Wegener D.
Published: July 2007

The non‐Ohmic hopping behaviour on random lattices is studied by solving the percolation problem by computer simulation. The dimensional “invariants” Bc (average number of open bonds per site) and vc (critical volume fraction) are shown to be not suitable for an investigation of this problem, because they are field dependent. Furthermore the field dependence of the “returns” in the percolation paths and the decrease of the conductivity at sufficiently low fields are studied.
The Morin Point as Degenerate Critical Point
Authors: Kuleshov V. S. , Popov V. A.
Published: July 2007

The notion of the degenerate critical point (DCP) of phase transitions is introduced. The theory of antiferromagnet properties near such points is developed. Various instances are given of realization of the Morin point as a DCP and its modifications resulting from symmetry breaking due to inclusion of new internal and external interactions. Phase diagrams show lines of zero‐order phase transition critical points.
Magnetic States of a Binary Ferromagnetic Alloy with Competition of Easy‐Axis and Easy‐Plane Single‐Ion Anisotropies
Authors: Lukanin A. I. , Medvedev M. V.
Published: July 2007

The magnetic phase diagrams of a binary ferromagnetic alloy with positive nearest‐neighbour exchange interactions and competing easy‐axis and easy‐plane single‐ion anisotropies are investigated in the molecular field approximation, especially the possibility of random asperomagnetic and fan states at low temperatures. The spontaneous magnetization vectors for these states are aligned along the crystallographic axes and the transverse projections of atomic spins are frozen in an incoherent spin‐glass like manner.
Valence Bands of the Cu—III—VI2 Chalcopyrites Studied by Photoemission Spectra, X‐Ray Emission Spectra, and Electronic Structure Calculations
Authors: Neumann H. , Bullett D. W. , Sommer H. , Tomlinson R. D. , John W.
Published: July 2007

Ultraviolet and X‐ray excited photoemission spectra and Cu Kβ5 X‐ray emission spectra are used to measure the valence band density of states in CuGaTe2 and CuInTe2. In both compounds the density of states exhibits five structures which are ascribed to Cu 3d—Te 5p hybridized states, Ga 4s/In 5s—Te 5p bonding states, and Te 5s states. The valence band density of states of all Ga‐and In‐containing Cu—III—VI2 is calculated in an atomic orbital basis with the noble metal d states explicitly included. The agreement between theory and experiment is good for CuGaTe2 and except the In 5s—VI p bonding states also for the CuInVI2 chalcopyrites. Larger discrepancies between theory and experiment are found for CuGaS2 and CuGaSe2.
Kinetics of the Decay of Surface γ‐Conductivity of Magnesium Oxide
Authors: Wysocki S.
Published: July 2007

The kinetics of surface γ‐conductivity of MgO are investigated and discussed in terms of the tunnelling mechanism assuming the creation of donor—acceptor pairs by Fs‐centres. It is shown that experimental results are consistent with this mechanism.
Position Dependence of Channeling Stopping Power
Authors: Pathak A. A.
Published: July 2007

The position dependence of energy loss rates of MeV α‐particles along (110) and (111) planar channels of silicon single crystals is calculated. The effective electron density responsible for stopping power is estimated by averaging the spherically symmetric radial charge densities corresponding to individual shells of atoms along the relevant planes. This averaging procedure is similar to that adopted in finding the continuum potential, using superposition of interatomic potentials; except that here each individual shell is considered and the contribution is added after planar averaging. The results thus obtained are compared with the recent experimental results of Moak et al.
A Correlation between the Spectral Location of the Absorption Bands Due to the Localized Centers and the Lattice Constant in Alkali Halide Crystals. Anionic Impurity Centers with S2‐Configuration and F Center which Have Cubic Symmetry
Authors: Shimanuki S. , Nishimaki N.
Published: July 2007

For four anionic impurity centers with S2‐configuration (H−, Cu−, Ag−, and Au− centers) and the F center in alkali halides, a correlation between the peak energy, E, of the absorption band concerned and the lattice constant, d is extensively investigated. All the results indicate that the Smakula (STSN) relation, E = ad−n, holds for every alkali family (a and n are adjustable parameters). The values of exponent, n, derived from the analysis for all centers treated show a systematic variation with the defect center, the absorption band, and the alkali ion. It seems that the factor n expresses a degree of the lattice relaxation. In fact, a relation between the n‐value and the Stokes‐shift ΔE concerned, is very simple. An empirical relation, ΔE = bnk, roughly holds and the constants b and k depend only on the crystal structures of the alkali halides.
ESR and Magnetic Investigation of Lithium Intercalated VSe2
Authors: Watanabe Y.
Published: July 2007

X‐band ESR spectra are examined during the Li intercalation process of VSe2 in n‐butyllithium solution. The formation of V2+ ions at an early stage of reaction and their subsequent partial disappearance are ascertained in the case of solutions where Li contents are totally deficient for the production of Li2VSe2. The temperature‐dependence of the width of V2+ ESR lines exhibits a broad minimum around 150 K. This is interpreted in terms of effects of the interaction of V2+ ions with other vanadium ions in some different valence states.
The Simulation and Interpretation of the EPR Powder Spectra of Gd3+‐Doped LaAlO3
Authors: Koopmans H. J. A. , Perik M. M. A. , Nieuwennuijse B. , Gellings P. J.
Published: July 2007

The EPR powder spectra of Gd3+ doped LaAlO3 are simulated for a number of temperatures between 4 and 800 K by means of the usual spin‐Hamiltonian. Values are found for the zero field splitting parameters B(n, 0) only, which agree with single crystal measurements. For an accurate simulation of the axial powder spectra a variable linewidth has to be introduced, because an inhomogeneous broadening of the resonances in the xy plane is observed. This broadening is successfully described by a variable B(2, 2) parameter. This indicates that the Gd3+ ion does not fit within the LaAlO3 lattice, because GdAlO3 is not isostructural with LaAlO3. Crystal field calculations support this assumption.
Thermoelectric Power and Electrical Resistivity of Fe2Nb3Se15
Authors: Bansal C. , Surendranath K.
Published: July 2007

Seebeck coefficient and resistivity of a new Fe‐substituted NbSe3 compound of stoichiometry Fe2Nb3Se15 are studied in the temperature range 77 to 300 K. It is found to show a charge density wave transition followed by a metal‐insulator transition at lower temperatures.
Conductivity of an Electron Gas in a Low‐Frequency Electric Field Due to Large‐Scale Fluctuations
Authors: Radunović J. B.
Published: July 2007

An expression for the conductivity of an electron gas in a low‐frequency electric field (ω < ωL) is derived. The collision integral which accounts for both, the electron‐electron (e‐e) and the electron‐phonon (e‐p) type of interactions is represented in the ν‐approximation. Furthermore, the electron gas is assumed to be a state close to equilibrium. The results are expected to be of interest for the studies of the static electron conductivity.
Structural Disorder Model of Amorphous Semiconductors: Ge and Si
Authors: Vaid B. A. , Sharma K. C.
Published: July 2007

A structural disorder model for the amorphous semiconductors, Ge and Si, is proposed in terms of dangling bonds which are treated as point defects. Generalizing the well‐known concept of packing fraction and exploiting the strong correspondence between the crystalline and amorphous phases near the transition temperature, the contribution of dangling bonds to various thermodynamic quantities is shown to be very important. Its importance and new features are also discussed.
Theory of Compression in Ionic Crystals
Authors: Shanker J. , Narain J. , Rajauria A. K.
Published: July 2007

A theoretical method based on interionic potentials is developed for evaluating the compression of alkali halide crystals corresponding to different values of pressure. The short range overlap repulsive interactions between first neighbours as well as between second neighbour ions are taken into account. The traditional Born method for determining the repulsive parameters is replaced by a more plausible method due to Decker. Recent values of the van der Waals dipole‐dipole and dipole‐quadrupole interaction coefficients derived from the Kirkwood‐Muller formula are used in the present calculations. Pressures are calculated corresponding to different values of compressions. The results are found to compare well with available data.