bluuebunny/crossref_metadata_2025 huggingface dataset:
Local partial al DOS in FeAl and AlAl
Authors: Müller Ch. , Ziesche P.
Published: July 2007

The energy eigenvalue results obtained by a linear KKR method for B2 FeAl and an hypothetical B2 AlAl of the same lattice spacing are used to calculate the local partial DOS (densities of states) as well as the corresponding valence‐electron numbers per muffin‐tin sphere (MTS) of these two systems. The comparison of the two different local partial Al DOS indicates that the Al states in the FeAl compound are strongly affected by the antiresonance effect caused by the presence of the resonant Fe scatterer in the neighbourhood. The charge transfer is also discussed in connection with the antiresonance effect.
Nonlinear excitations in superionic crystals near the nonuniform state transition temperature
Authors: Bondarev V. N. , Kuklov A. B. , Rublyov I. S.
Published: July 2007

The amplitude solitonic solutions are investigated on the phenomenological base applied earlier to the superionic conductor (SC) phase transition into the charge density wave (CDW) state. These solitons ‐ long range CDW modulations ‐ can be produced by an external electric field in the SC symmetrical phase. For sufficiently strong fields such solitons represent the unstability channel with respect to the CDW formation throughout the crystal above the transition point. Due to the additional charge redistribution the mentioned solitons can be observed experimentally.
On the problem of electron localization in a two‐dimensional system
Authors: Bonch‐Bruevich V. L. , Mironov A. G.
Published: July 2007

Renormalization group method is extended to take account of the correlation between the energy levels. It is shown that in a d = 2 system, as contrasted to d = 1 and d = 3, all or not all levels are localized depending upon some dynamical properties of the system.
Temperatur‐ und magnetfeldabhängigkeit einer transversalen schallgeschwindigkeit im tetragonalen paramagneten mit dem gesamtdrehimpuls J = 1
Authors: Ulner J.
Published: July 2007

Im Rahmen der Theorie der rotationsinvarianten magnetoelastischen Wechselwirkungen wird die Temperatur‐ und Magnetfeldabhängigkeit einer transversalen Schallgeschwindigkeit im tetragonalen J = 1‐Paramagneten bestimmt. Dabei wird eine Green‐Funktionsmethode formuliert, die die Eigenschaften des Gesamtdrehimpulses exakt berücksichtigt. Es wird der Fall eines kooperativen Jahn‐Teller‐Überganges diskutiert.
Luminescence of high density electron‐hole plasma in CdS and CdSe in a wide temperature range
Authors: Yoshida H. , Shionoya S.
Published: July 2007

Time‐resolved spectra of the spontaneous luminescence of the high density electron‐hole plasma (EHP) in CdS and CdSe are observed in a wide range of temperature which is surely higher than the calculated critical temperature for electron‐hole liquid formation, in order to carry forward discussion on dynamic nature of the EHP previously observed in 4.2 K experiments. Spectra in the late stage are analyzed, and obtained values of the reduced bandgap energy and chemical potential are compared with those theoretically calculated for higher temperatures. The aspects of the change of the spectral shape in the late stage are hard to understand. Unfortunately, no clear conclusion is drawn on the nature of the EHP produced at 4.2 K. The only thing one can say is that the condensed electron‐hole liquid state, which is in equilibrium with the exciton state, is not realized.
Mean‐square displacement and Lindeman's criterion for melting of alkali metals
Authors: Soma T. , Kagaya H.‐Matsuo , Nishigaki M.
Published: July 2007

The temperature dependence of the mean‐square displacement for alkali metals is quantitatively calculated from first principles. Lindeman's criterion for melting obtained is nearly constant for the five alkali metals. The Debye temperature at higher and lower temperatures is also estimated using Debye's model.
Analysis of the equation of state of lithium and sodium halides
Authors: Shanker J. , Singh K.
Published: July 2007

A theoretical analysis of the equation of state is performed for the halides of lithium and sodium. The variation of volume with pressure is calculated using seven different potential functions for the short‐range overlap repulsive energy. The van der Waals dipole‐dipole and dipole‐quadrupole interactions derived from thevariational method are taken into account. The results obtained are compared with available experimental data. In most of the crystals studied, the Varshni‐Shukla exponential potential for the repulsive energy gives the best agreement with experimental data for the equation of state.
Thermally‐stimulated excitation of electrons from deep traps of insulators in electric fields
Authors: Köster H. , Iassievich I. N. , Hübner K.
Published: July 2007

An analytic expression for the probability of thermal activation of electrons trapped in deep defect states of an insulator is derived taking explicitly into account an electric field and lattice vibrations. From the activation probability a detrapping current intensity is calculated, which is in good agreement with corresponding experimental results obtained, for example, by means of the thermally stimulated electron emission (TSEE). In this way, for the TSEE effect a possible microscopic explanation is found for the first time.
EPR of iron‐boron centres in silicon
Authors: Gehlhoff W. , Segsa K. H.
Published: July 2007

The EPR spectra of one type of iron‐boron centres detected in low‐resistivity B‐doped p‐silicon after iron doping are investigated in detail. The spectra are characterized by a dominating zerofield splitting and a resolved SHF structure due to the interaction with the boron isotopes and arise from interstitially incorporated Fe+ ions adjacent in 〈111〉 directions to B− ions on substitutional sites.
Electronic structure and stability of amorphous PdSi alloys
Authors: Buschow K. H. J. , Eifert H.‐J. , Elschner B.
Published: July 2007

Amorphous alloys Pd1−xSix near x = 0.2 doped with small amounts of Gd are prepared by melt spinning. The g‐shift, the residual linewidth, and the thermal broadening of the EPR linewidth are determined. Doped and undoped amorphous alloys are also investigated by means of differential scanning calorimetry. Values are reported for the glass temperatures, crystallization temperatures, heat of crystallization, and heat of activation. It is shown that electronic properties of amorphous alloys are unlikely to exert much influence on the thermal stability of these alloys.
Divacancy binding energy in F.C.C. metals
Authors: Kornblit L.
Published: July 2007

Divacancy binding energies Eb2V in f.c.c. metals are calculated with aid of an atomistic‐continual model used earlier for single vacancy formation energy calculations. The main part of Eb2V stems from the first nearest‐neighbor (Inn) atomic environment of the divacancy. The outer region which is treated as an elastic continuum contributes a relatively small part.
The use of an iteration method for calculating the potential energy of nonhomogeneous dielectrics
Authors: Fokin A. G.
Published: July 2007

A method of solving linear boundary‐value problems is developed, based on the interpretation of the problems in terms of functional analysis. The potential energy is presented in the form of the functional, which can be generally expanded into a series. The boundaries are obtained, enclosing the exact value of the potential energy.
Diffusion of Frenkel excitons in anisotropic crystals
Authors: Glushko E. Ya. , Efremov N. A.
Published: July 2007

The temperature dependence of the diffusion tensor Dik(T) of coherent excitons in anisotropic molecular crystals is considered. The influence of such exciton energetic band peculiarities as effective mass tensor anisotropy and nonanalyticity of exciton energy on the dependence Dik(T) is analyzed. It is shown that the dependence D ∼ T−1/2, which is characteristic of isotropic crystals, is retained only at weak anisotropy of the effective mass tensor mmax/mmin ≈︁ 1 with no regard for nonanalyticity. At the same time, at great values of the nonanalytic part of the exciton energy the diffusion tensor component dependences vary from Daa ≈︁ Dcc ∼ T−1 ≪ Dbb ∼ T−2 at weak anisotropy of the effective mass tensor to Daa ≈︁ Dcc ≈︁ const ≪ Dbb ∼ T−3/4 at strong anisotropy.
The 3/2 kT problem in the low‐temperature polaron mobility theories
Authors: Peeters F. M. , Devreese J. T.
Published: July 2007

The linear de mobility of Fröhlich polarons is studied in the limit of small electron‐phonon coupling and low temperature. The well‐known discrepancy with a factor of 3/2kT/hωLO between the results appearing in the literature is understood in the light of an interchange of the limits limits lim lim.
Impurities and electron localization in V2O5 crystals
Authors: Grunin V. S. , Patrina I. B. , Zonn Z. N.
Published: July 2007

V2O5 crystals doped with different impurities of the Mn+ (n = 1 to 6) type are investigated by the EPR method. It follows from the experiment that all the paramagnetic defects are connected with the impurities present in the crystals. The main paramagnetic centre in V2O5 is an electron localized on two 51V nuclei. There is no local compensation of its charge and so it easily destroys in the course of oxidation. It is shown by hyperfine structure investigation that the electron states are localized in a wide temperature range (4.2 to 290 K). The substitutional impurity tends to occupy the vanadium positions near the VV pair. A complex paramagnetic centre is created with electron density distribution dependence on the donor‐acceptor characteristics of the cations. This results in the nonequivalence of the electron interactions with different vanadium atoms, in different values of the HFS constants for differently doped crystals, and in different valency of the impurity cations. Centres of this type are locally compensated and therefore stable to oxidation or reduction.
Second‐order quadrupole shift in the incommensurate structures of Rb2ZnBr4 and Rb2ZnCl4
Authors: Aleksandrova I. P. , Grande S. , Moskvich Yu. N. , Krieger A. I. , Koptsik V. A.
Published: July 2007

The angular dependences of second‐order 87Rb (1/2 → −1/2) shift in the incommensurate phases of Rb2ZnBr4 and Rb2ZnCl4 are interpreted and EFG‐tensors at the special points of the displacement profile are determined. The EFG‐tensor of I‐structure is described in the approach of perturbance theory: Vij{S} = V{S} + ΔV{S} where the EFG‐tensor of the paraelectric phase is taken as zero‐approximation. It is most important that the form of “modulation correction” tensor ΔVij is not arbitrary. The symmetry properties of one‐dimensional incommensurate modulated atomic chain determine the selection rule for the non‐zero components of the tensor of modulation corrections. The existence of supersymmetry for structurally incommensurate systems follows from the presented NMR‐experiments. The abstract symmetry conservation law at commensurate‐incommensurate transition seems to be demonstrated in this experiment.
Effect of varying the orientation of a quantizing magnetic field on the effective electron mass in degenerate tetragonal semiconductors
Authors: Chakravarti A. N. , Ghatak K. P. , Ghosh K. K. , Mukherjee H. M.
Published: July 2007

An attempt is made to investigate the effects of varying the orientation of a quantizing magnetic field on the effective mass in tetragonal semiconductors. It is found, taking n‐Cd3As2 as an example, that the crystal‐field splitting results in different effective masses at the Fermi level corresponding to different magnetic sub‐bands. These effective masses are found to be significantly influenced by the orientation of the magnetic field with respect to the c‐axis. This behaviour is further noted to be strongly dependent on the carrier concentration but is relatively much less sensitive to changes in the magnetic field strength.
On the theory of the nonlinear acousto‐optical effect in semiconductors
Authors: Cam Hoang Ngoc , Van Hieu Nguyen , Tan Ha Vinh
Published: July 2007

The modulation of the dielectric susceptibility of direct band gap semiconductors due to the interaction with sound waves is considered up to second order of the deformation tensor. The role of the Coulomb interaction between electrons and the holes, i.e. that of exciton states with discrete and continuous energies, is taken into account.
On the Brillouin zone integration
Authors: Reser B. I.
Published: July 2007

A brief and simple description is given of three new methods of integration in the Brillouin zone: direct, ray, and hybrid tetrahedron, proposed by Chen, McDonald et al. These methods are analyzed in detail in application to the calculation of the density and number of states of s.c., b.c.c., and f.c.c. crystals using tight‐binding and empty lattice models. It is shown that all the methods considered exhibit a high accuracy: several hundred initial k points in the irreducible part of the Brillouin zone with not very complicated dispersion relations make it possible to calculate such a quantity, as the density of states, with an average error of less than 1%. The hybrid tetrahedron method is proved to be simpler and many times more effective than the other two methods. Only with dispersion relations close to isotropic is the ray method preferable.
Thermal expansion coefficient of alkali metals
Authors: Soma T. , Kagaya H.‐M. , Kimura Y.
Published: July 2007

The thermal expansion of alkali metals is investigated using a local Heine‐Abarenkov model potential in the perturbational method. The mode Grüneisen parameters and the temperature‐dependence of both the mean Grüneisen constant and the thermal expansion coefficient are calculated, and the obtained results are quantitatively in good agreement with the experimental data.
Thermoelectric properties of GeTe at high hydrostatic pressure up to 8.5 GPa and its valence‐band structure
Authors: Khvostantsev L. G. , Sidorov V. A.
Published: July 2007

The thermopower and the relative electrical resistance of rhombohedral α‐GeTe and orthorhombic γ‐GeTe polycrystalline samples with hole density between 3.9 × 1020 and 2 × 1021 cm−3 are measured under hydrostatic pressure up to 8.5 GPa at room temperature. The phase transition of α‐GeTe to the cubic rocksalt structure (β‐GeTe) reported earlier at 3.5 GPa under nonhydrostatic pressure is not observed up to 8.5 GPa. Orthorhombic γ‐GeTe also exhibits no phase transition. The pressure dependences of the thermopower provide support for the multiple valence‐band model of GeTe.
Nonlinear magneto‐optical phenomena of the third harmonic in semiconductors
Authors: Stramska H.
Published: July 2007

The calculations are carried out starting from the Boltzmann equation. The Faraday rotation and ellipticity of the third harmonic in the current density, are associated with the energy dependence of the momentum relaxation time for a parabolic band and with the nonparabolicity of the band for a constant relaxation time. The present results predict a large enhancement due to resonance at high magnetic fields. It is shown that the magneto‐optical effects have an oscillatory region.
Satellite structure of ZnO and Zn(II) halides studied by X‐ray photoelectron spectroscopy
Authors: Scrocco Marisa
Published: July 2007

The satellite structure in the X‐ray photoelectron spectra of Zn(II) halides and ZnO is examined, particular attention being paid to the 3p, 3s metal subshells and the valence region. The nature of the phenomena giving rise to these satellites and their relative importance in each spectral region, is discussed with reference to known theoretical results.
A binary ferromagnetic alloy with magnetic moments dependent on local environment. I. The Jaccarino‐Walker Model in the effective field approximation
Authors: Zaborov A. V. , Medvedev M. V.
Published: July 2007

A binary ferromagnetic alloy, in which the magnetic moments depend on their local chemical environment in a step‐like manner (the Jaccarino‐Walker model), is considered. It is assumed that Heisenberg exchange interactions of the nearest neighbours are responsible for the ferromagnetic ordering of these magnetic moments. Both, the Curie temperatures versus concentration and the percolation thresholds of the existence of the long‐range magnetic order are investigated for different variants of dependences of both the magnetic components on their local environments. The spin‐wave spectrum is analyzed as well.
Stimulated Brillouin scattering of transversely polarized electromagnetic waves in magnetoactive moderately piezoelectric semiconductor plasmas
Authors: Ghosh S. , Khan S.
Published: July 2007

An analytical investigation is made of the stimulated Brillouin scattering of a large amplitude, transversely polarized, electromagnetic pump wave produced by both, an electron‐plasma wave and acoustical phonon vibrations in a magnetoactive n‐type moderately piezoelectric semiconductor. Using the hydrodynamical model of plasma, the general dispersion relation is obtained in the presence of a large magnetostatic field applied at an arbitrary angle θ to the direction of propagation of the pump wave. The analysis is applied to both the cases of isotropic (B0 = 0) and magnetoactive (B0 ± 0) plasmas. The threshold electric field necessary for the onset of Brillouin instability and the growth rate of the unstable Brillouin mode well above the threshold are studied. It is concluded that the threshold pump amplitude as well as the growth rate are strongly dependent on the orientation of the magnetostatic field with respect to the directions and magnitudes of the wave vectors k and k1 of the acoustic and scattered electromagnetic waves, respectively.
Theory of interimpurity transitions in condensed medium
Authors: Christophorov L. N. , Kharkyanen V. N.
Published: July 2007

The problem is investigated of the quantum particle transfer between impurities imbedded in a condensed medium via the states of the latter. The kinetic equation containing explicitly no medium indices (the role of medium is taken into account by effective constants found from “free” medium properties) is obtained. The two‐impurity case (the donor‐acceptor transfer) is considered in detail for an one‐dimensional model of a crystal.
Peculiarities of phase transitions and physical properties in (NH4)2SbF5
Authors: Avkhutskii L. M. , Davidovich R. L. , Zemnukhova L. A. , Gordienko P. S. , Urbonavičius V. , Grigas J.
Published: July 2007

The dynamics of the (NH4)2SbF5 crystal lattice showing the superionic phase transition is studied in a broad temperature interval by NMR and NQR methods, together with electrophysical and calorimetrical properties. The investigations establish the ionic state of the axial fluorine atom in relation to equatorial atoms in the [SbF5]2− complex. The successive phase transitions are revealed and the mechanism of phase transitions is elucidated. The phase transitions are caused by the reorientation movements of NH4 and [SbF5]2− groups. The paper also describes the influence of water solution inclusions in the crystal on the superionic phase transition.
Local partial DOS and experimental Al K spectra of transition metal aluminides charge transfer trend
Authors: Müller Ch. , Blau W. , Ziesche P.
Published: July 2007

For the B2‐type compounds VAl, CrAl, MnAl, FeAl, CoAl, and NiAl the local partial DOS (densities of states) and the corresponding integrated DOS are determined on the basis of a linear KKR‐method. The calculated local partial DOS are directly compared to experimental SXE (soft X‐ray emission)‐spectra. The integrated local partial DOS provide the valence charge distributions per unit cell. The latter are used to estimate the charge transfer in the intermetallic compounds. The calculated results are in good agreement with the experimental observed trend.
Energy losses in crystalline and amorphous solids in the intermediate energy region
Authors: Kührt E. , Wedell R.
Published: July 2007

Using the classical theory for two moving charged particles the electronic stopping power of amorphous and random oriented crystalline solids is calculated. It is shown that in the intermediate energy region, where the stopping is maximized, motion of the target electrons must be considered. The specific problems of energy losses in crystals are discussed and directional effects are taken into account. Calculated values of the stopping power agree well with experimental results for protons in the random as well as in the channeling regime.
Charged‐particle stopping in crystals
Authors: Khodyrev V. A. , Sirotinin E. I.
Published: July 2007

The energy loss by a charged particle moving along a given path in the crystal lattice is calculated in terms of quantum perturbation theory. In calculating the contribution of excitations with lowenergy transfer, the sum rule is used. The highly‐excited states are described in a quasi‐classical approximation. The results obtained with these approximations coincide in the intermediate region of excitation energy. The results obtained allow the electrons of the core and the valence electrons to be treated from a unified standpoint. The averaging of the obtained expression for ΔE(b) over the random impact‐parameteri distribution leads to the Lindhard‐Scharff formula. The calculated dependence of the mean relatve proton‐energy loss upon the dechanneling depth is compared with available experimental data.
Volume dependence of the melting temperature for alkali metals with Debye's model
Authors: Soma T. , Kagaya H.‐Matsuo , Nishigaki M.
Published: July 2007

Using the volume‐dependence of the Grüneisen constant at higher temperatures, the volume effect on the melting temperature of alkali metals is studied by Lindeman's melting law and Debye's model. The obtained melting curve increases as function of the compressed volume and shows the maximum of the melting point at the characteristic volume. The resultant data are qualitatively in agreement with the observed tendency for alkali metals.
On the theory of singlet and triplet charge‐transfer excitons
Authors: Schmid B. J. , Reineker P. P.
Published: July 2007

A many‐particle Hamiltonian for electrons which takes into account their energy in a periodic potential and in an external magnetic field, as well as their Coulomb and spin—spin interaction energies is specialized for charge‐transfer excitons on a linear chain with one donor and one acceptor molecule in the unit cell. The Hamiltonian decomposes into a part for singlet excitons, which is diagonalized exactly, and a part for triplet excitons, whose diagonalization is reduced to wave vector dependent eigenvalue problems of the dimension of the unit cell. The fine‐structure tensor is expressed explicitly in terms of electronic matrix elements.
Observation of dispersion on magnetic polaritons
Authors: Häussler K. M. , Brandmüller J. , Merten L. , Finsterhölzl H. , Lehmeyer A.
Published: July 2007

Far‐infrared reflectivity measurements on uniaxial antiferromagnetic CoF2 display a characteristic dispersion of the magnetic reststrahlenbands if the wave vector components of the radiation are varied by choosing different angles of incidence. Thus the expected dispersion behaviour of the socalled magnetic polaritons is demonstrated experimentally in a direct manner for the first time. The simulation of the infrared reflectivity spectra based on a generalized formula for anisotropic magnetically ordered insulators shows good agreement with the experimental results and can be used to predict even weak polariton dispersion effects.
Photoinduced absorption spectra of ZnS:Fe crystals
Authors: Zimmermann H. , Boyn R. , Nagel N.
Published: July 2007

Photoinduced absorption (PA) spectra of ZnS:Fe crystals are measured between 0.3 and 3.6 eV by means of a modulation technique. Transitions related to the charge states Fe3+ and Fe+, which have been detected by EPR a long time ago, are believed to be seen in these spectra. In particular, the processes Fe3+ → Fe2+ + h and Fe2+ + Fe3+ + e are identified, the latter manifesting itself most clearly in the excitation spectrum of the PA band due to the former transition. The shapes of the photoneutralization and photoionization spectra are discussed, and the position of the Fe+ ground state in the forbidden gap is estimated.
Emission of free and bound excitons in layered gase crystals
Authors: Gnatenko Yu. P. , Kovalyuk Z. D. , Skubenko P. A. , Zhirko Yu. I.
Published: July 2007

The emission spectra of GaSe single crystals of ϵ‐modification doped with Co of 0.001 to 0.5 wt% concentration are investigated at different temperatures (T = 4.2 to 35 K) using polarized light. It is shown that the wide emission band with energy 2.031 eV is due to structural defects while the other wide bands of 2.039 and 2.008 eV are due to indirect exciton transitions with radiation of TO‐phonons. The narrow emission lines correspond to the decay of direct excitons bound on different defects and to their phonon sattelites involving phonons of (14.5 ± 0.5) meV. The temperature dependence of a doublet structure of the free exciton emission line, which is thought to be due to the peculiarities of the GaSe crystal band structure, namely the splitting of the valence band by inter‐layer interaction is investigated.
Temperature dependence of the wannier‐stark level width in a semiconductor in a strong electric field
Authors: Berezhkovskii A. M. , Ovchinnikov A. A.
Published: July 2007

Analytical expressions for the level width of the Wannier‐Stark ladder caused by an electron‐phonon interaction are derived. They allow to investigate the dependence of the width on temperature, external field, and semiconductor band parameters. It turns out that with increase in temperature the width associated with acoustic phonons is drastically increased whereas the width associated with optical phonons rises much more slowly. It seems that almost all experiments for finding the Wannier‐Stark ladder had been carried out at too high temperatures when the interaction of an electron with acoustic phonons eliminates the ladder.
Optical conductivity in the impurity band of doped semiconductors
Authors: Gryko J.
Published: July 2007

A formula for the optical conductivity is derived from the Kubo relation in a framework of tightbinding approximation using a method due to Matsubara and Toyozawa. The derived formula is applied to the calculation of the optical conductivity and optical absorption in the far IR of doped semiconductors at low temperatures. The calculated values of the optical absorption obtained using different approximated Green's functions are compared with the experimental data for Sb doped germanium.
Hartree‐fock exchange and LCAO approximation in the band structure calculations of solids
Authors: Evarestov R. A. , Lovchikov V. A. , Tupitsin I. I.
Published: July 2007

It is shown that the use of the simple cubature formula for the approximate calculation of the density matrix Qrr in the non‐local Hartree‐Fock exchange for crystals leads to a non‐physical divergence of the lattice sums. To overcome this difficulty it is proposed to introduce a weight function in the cubature formula for the numerical integration over the Brillouin zone in calculating non‐local exchange. It is discussed the simple way to choose the nodes of the numerical integration which is based on the large unit cell transformation in the direct and reciprocal lattices. This choice allows to extend the special point technique of the Brillouin zone integration to the non‐local exchange calculation.
Phase Segregation in Tellurium‐Saturated GeTe
Authors: Vengalis B. , Valatska K.
Published: July 2007

Regions with different free hole concentrations and different lattice distortions are assumed to explain the specific heat, electrical resistivity, and IR reflectivity data for annealed GeTe crystals with 50.4 to 50.8 at% Te. The phase segregation is explained taking into account free hole redistribution between the twelve Σ‐valleys of the material.
Dispersion of Optical Constants in Cdp2
Authors: Babonas G. , Korets N. S. , Marcinkevičius S.
Published: July 2007

Spectral dependences of the gyration tensor components g11, g33, refraction indices and birefringence of tetragonal CdP2 are investigated at 300 K. The optical activity of the crystal is found to be determined by both the crystal and the molecular contributions, the latter being due to the distortion of the tetrahedral symmetry of the structural elements. The dispersion of the refractive indices is discussed on the basis of a single‐effective‐oscillator model. The ionicity of CdP2 is equal to 0.56 and is close to the values of AIIBVI compounds and the ionicity of CdP bond in AIIBIVC semiconductors. The dispersion of the spectroscopic properties of CdP2 is concluded to be mainly determined by the CdP bound.
Band‐Gap Narrowing in n‐Type Moderately Doped Silicon at 300 K
Authors: Vancong H.
Published: July 2007

The band‐gap narrowing at 300 K in n‐type moderately doped silicon is investigated, basing on a second‐order Thomas‐Fermi model which was first developed by Friedel and recently by Van Cong et al. There are three contributions to band‐gap narrowing: (1) Δg,opt (rigid‐band effect), (2) Γn (non‐rigid band effect), and (3) ΔEg,FD (Fermi‐Dirac statistics effect), where ΔEg,FD is negligible because of large negative values of the Fermi energy. ΔEg,opt is a major contribution, while Γn only takes an effect at sufficiently high donor concentrations; they increase with increasing doping. It is suggested that the numerical results of ΔEg, opt and ΔEg, elec ≈︁ (ΔEg, opt + Γn) are in good agreement with optical measurements of Balkanski et al., and with electrical measurements of Mertens et al., respectively. Finally, the present results of ΔEg,opt and Γn are also compared with a recent theory of Lanyon and Tuft, and with that of Dhariwal and Ojha, respectively.
The Interband Interaction and the Tunnel Level Width of the Wannier‐Stark Ladder in a Semiconductor Subject to a Strong Electric Field
Authors: Berezhkovskii A. M. , Ovchinnikov A. A.
Published: July 2007

It is shown that the interband interaction does not lead to the disappearance of the Wannier‐Stark ladder.
Comparative Studies of Fast Recombination Processes in Amorphous Silicon Films
Authors: Bergner H. , Brückner V. , Kerstan F. , Nowick W.
Published: July 2007

Comparative studies of recombination processes of laser‐induced charge carriers in the picosecond range are performed in amorphous silicon films prepared by glow discharge technique, UHV evaporation, and sputtering. By means of time‐resolved reflectivity and conductivity measurements a two‐step relaxation process is obtained, where the time of the fast recombination process decreases with increasing defect density. Some semiconductor parameters (recombination constant, capture cross‐section, carrier mobility) are estimated using experimental results.
Experimental Investigations of Electron‐Hole Plasma in Tellurium‐Doped Gap
Authors: Schwabe R. , Streit I. , Thuselt F. , Unger K.
Published: July 2007

Photoluminescence spectra are measured for GaP doped with tellurium in the density range of 2 × 1017 to 5 × 1018 cm−3 at low temperatures. At low doping concentrations and high excitation an electron‐hole liquid is observed only weakly influenced by the impurities. An obvious feature that emerges in intermediately doped samples is the coexistence of two plasma‐like phases, in qualitative agreement with theoretical expectations. The results obtained from the spectra are supported by decay measurements. Further, from the decay times also Auger coefficients are determined.
Effective Debye Temperature of the (110) Ni Face for Different Azimuths
Authors: Mróz S. , Mróz A. , Grudniewski A. , Bąk E.
Published: July 2007

The effective Debye temperature θeff for directions normal to the (110) Ni face and with an angle of about 54° to the normal is measured by LEED for different azimuths, for electron energies of 70 to 100 and 130 to 160 eV, respectively, and for the incidence angle of a primary beam of about 60°. Under such conditions the primary electron beam is diffracted mainly on the first layer of atoms and averaging over an azimuth angle should eliminate the multiple scattering effects. Therefore, the averaged effective Debye temperature θ should describe the vibrations of atoms in the first layer. Values of θ⟂ = (218 ± 20) K and θ54° = (287 ± 20) K are obtained. A dependence of θeff,54° on the azimuth angle is not found, in contradiction to the theoretical prediction for the face investigated. The ratio 〈u2⟂〉 / 〈u〉 calculated by applying our results is equal to 3.37, in good agreement with calculations based on quasi‐harmonic and anharmonic approximations.
Electronic Spectrum of the Co(II) Ion in the Columbite CoNb2O6 Host Lattice at 4.2 K
Authors: Borromei R. , Cavalli E. , Ingletto G.
Published: July 2007

The polarized absorption spectrum of the Co(II) ion in CoNb2O6 at 4.2 K in the range 5000 to 28000 cm−1 with the electric vector E parallel to all three crystallographic axes is reported. After a careful examination of the excited states and of the site symmetry, the bands are assigned as “ligand field bands”. As far as the intensity is concerned, the most contribution is due to the effect of the local distortion, but the effects of the spin–orbit coupling and vibronic interaction are also taken into consideration. The assignments are confirmed from the behaviour of the intensity of the polarized bands and from a ligand field calculation that fits the band energies very well.
Influence of a Strong Electric Field on the Carrier Capture by Nonradiative Deep‐Level Centers in GaAs
Authors: Prinz V. Ya. , Rechkunov S. N.
Published: July 2007

The techniques of capacitance spectroscopy are used to measure directly electron and hole capture cross‐sections of deep levels in a neutral material at zero electric field and in the depletion layer with a strong electric field. The data show that if at zero electric field the electron capture cross‐sections onto the centers are thermally activated and described by the theory of nonradiative multiphonon capture, then in a strong electric field (F ≈ 104 V/cm) the capture cross‐sections increase to the limiting large value (σ ≈ 10−14 to 10−12 cm2) and are only little dependent on temperature. It is shown that an electric field causes a simultaneous increase of the electron and hole capture cross‐sections of the level EL2 by five orders of magnitude at low temperatures (T ≈ 90 K).
Thermally Stimulated Depolarization of AsO Centres in Alkali Halide Crystals
Authors: Pilatus U. , Fischer F.
Published: July 2007

A TSD band below LNT attributed to the AsO centre is observed in several alkali halide crystals. In KI:AsO by annealing at 150 °C the 60 K band can be decreased while a 19 K band appears. NaI:AsO has a band at 11 K. Measured dipole moments of the AsO centre are between 0.9 and 1.2eÅ depending on the off‐centre displacement of the ionic charge.
The Metallic and Ionic Contributions to Lattice Vibrations of III–V Covalent Crystals
Authors: Soma T. , Kagaya H.‐Matsuo
Published: July 2007

The binding force, which includes partially ionic contributions in addition to covalent interactions based on the pseudopotential formalism, is proposed for III–V tetrahedral compounds. Numerical calculations on the phonon dispersion curves are performed for GaAs, GaSb, InAs, and InSb. The resulting ones are qualitatively in good agreement with the observed data in spite of no introducing of adjustable parameters except for the optical phonon‐frequency splitting in the long wavelength limit.
Statistics and Transport Behaviour of Electrons in SiO2
Authors: Köster H. , Hübner K.
Published: July 2007

An analytical expression for the statistical distribution function of conduction electrons in SiO2 is derived by taking into account static electric fields of different strengths and various types of electron‐phonon interaction (i.e. scattering of electrons due to longitudinal‐optical, transversaloptical, and acoustic modes). Electronic energy balances and critical electric field strengths as well as the threshold and runaway behaviour of conduction electrons are derived from their distribution function, the time and field dependence of which is analysed quantitatively.
Covalency as Source of Intensity for d‐d Transitions in Octahedral Complexes
Authors: Malakhovskii A. V. , Vasilev G. G.
Published: July 2007

A pair‐vibrational mechanism is suggested for inducing of spin‐forbidden d‐d transitions in centrosymmetric complexes. Only the vibrational part of this mechanism appeared to be sufficient to account for the observed strong difference in intensity of the corresponding d‐d transitions (spinforbidden included) in different crystals with analogous magnetic properties. This phenomenon is proved to be due to the difference in the degree of covalency of the metal‐ligand bonds and not to the difference in the value of crystal fields in the compounds. Experimental results obtained on the crystals RbMnF3, CsMnF3, and RbMnCl3, (in hexagonal and cubic modifications) are in agreement with the drawn deductions.
Magnetic Properties of the Ising Model with a Free Surface
Authors: Tamura I. , Sarmento E. F. , Fittipaldi I. P. , Kaneyoshi T.
Published: July 2007

The magnetic properties in a semi‐infinite ferromagnetic Ising model with enhanced surface couplings are studied by means of a new type of correlated effective field theory. For suitably enhanced surface exchange couplings Js = J(1 + Δ) there are surface orderings. A phase diagram, magnetization curves for surface and bulk, and short‐range order parameters are calculated.
Thermal Conductivity of LiF Containing Dislocations at Low Temperatures
Authors: Kumar A. , Sinha A. K. , Ansari M. A.
Published: July 2007

The thermal conductivity at very low temperatures of LiF crystals containing dislocations are analysed by using the Callaway model, Callaway's approximations, and approximations suggested by Kumar and Joshi. It is found that the contribution of the effective phonon‐dislocation scattering processes to the lattice thermal conductivity can be calculated by suitably combining the static and the dynamic phonon‐dislocation scattering processes.
Dynamics and Thermodynamics of Anharmonic Crystals near the Instability Point
Authors: Malinowska‐Adamska C.
Published: July 2007

Using the self‐consistent phonon theory based on the thermodynamic double‐time Green's function method the dynamics of crystal lattice and the thermodynamics of the anharmonic cubic crystals in the vicinity of the instability point are investigated. The results of calculations for the instability temperature Ts, relative displacements of atoms, anharmonic contributions to the free energy, and free Gibbs energy as well as the isothermal elastic constants are given and compared with experimental and other theoretical data for potassium, sodium, and rubidium.
Phonon Polaritons in the Presence of a Magnetic Field
Authors: Regiński K.
Published: July 2007

The problem of propagation of phonon polaritons in the presence of an external magnetic field is investigated on the basis of equations of motion derived previously. First the dispersion relations for diatomic ionic crystals in the absence of a magnetic field are derived. Then the indices of refraction of right and left circularly polarized waves are found in the case of the Faraday configuration of the system. The Faraday rotation as a function of frequency is determined. Numerical calculations are performed for NaI.
Effect of Crystal‐Field Splitting on the Einstein Relation in Tetragonal Semiconductors
Authors: Chakravarti A. N. , Ghatak K. P. , Ghosh K. K. , Mukherjee H. M.
Published: July 2007

An attempt is made to study the effect of crystal‐field splitting on the Einstein relation for the diffusivity‐mobility ratio of the carriers in tetragonal semiconductors, taking inherently degenerate n‐Cd3As2 as an example. It is found on the basis of the Bodnar model, which has recently been demonstrated in the literature to be the most valid model for Cd3As2, that the above ratio increases with increasing carrier concentration as expected for degenerate semiconductors. It is also shown that the tetragonal crystal‐field effectively reduces the ratio with increasing amount of reduction with increasing carrier concentration.
Use of harrison's potential in mixed alkali halide crystals
Authors: Jain G. D. , Shanker J.
Published: July 2007

Harrison's overlap repulsive potential is used for evaluating the cohesive energies and bulk modulus of alkali halide mixed crystals. This potential replaces the old and widely used Born‐Mayer repulsive potential in ionic crystals. The Harrison repulsive potential is represented by a quantum mechanical analytical potential form derived from the tight binding theory. The calculations are performed for the mixed crystals of NaCl—NaBr, KCl—KBr, and KBr—KI for the entire range of composition. The results are found in good agreement with experimental data and are better than those predicted from the Born‐Mayer potential.
Study of Cu K edge in some copper (II) octahedral complexes
Authors: Bhattacharya P. , Chetal A. R.
Published: July 2007

The K‐absorption edge of copper in the complexes Cu(LH)2SO4 · 4 H2O, Cu(LH)SO4 · 4 H2O, and Cu(phen) (xant)2 is investigated using a Cauchois‐type bent crystal X‐ray spectrograph. The peaks A, B, and C observed in the edges are explained on the basis of molecular orbital theory. Peak positions are correlated with partial charge on the central metal ion. It is observed that the peak A shifts to the low‐energy side while the peaks B and C shift to the high‐energy side as the partial charge on an absorbing ion in the complex increases.
Effective dynamical coupling constants of the a‐band of Tl+ centers in NaCl, KCl, KBr, and KI
Authors: Oboth K.‐P. , Schmitt K.
Published: July 2007

The temperature dependence of the A‐absorption band of Tl+ centers in NaCl, KCl, KBr, and KI and the stress induced linear dichroism (SLD) are investigated in the region between 4 and 300 K. Moment analysis enables to determine the effective dynamical coupling constants corresponding to the |A〈‐state. The effective phonon frequencies show decreasing values for increasing halogen mass. It turns out that the theory of linear electron—phonon coupling is correct for temperatures up to 200 K in NaCl: Tl+, and KCl:Tl+, and up to 100 K in KBr:Tl+ and KI:Tl+.
Raman study of the phonon halfwidths and the phonon—plasmon coupling in ZnO
Authors: Bairamov B. H. , Heinrich A. , Irmer G. , Toporov V. V. , Ziegler E.
Published: July 2007

The LO‐phonon—plasmon coupling in n‐ZnO single crystals is investigated by Raman spectroscopy at room and liquid nitrogen temperatures. The energy shift and halfwidth broadening of the LO‐phonons relative to the uncoupled modes are analyzed to get the concentration and mobility of the charge carriers. These results are compared with those from electrical measurements. The uncoupled phonon modes are measured in high‐ohmic crystals in which the interaction with the charge carriers can be neglected. For the low energy E2 mode an extreme small halfwidth of 0.3 cm−1 is found. At 77 K with increasing intensity of the exciting continuous laser light (hω = = 2.54 eV < Eg = 3.3 eV, P = 800 mW) nonequilibrium carriers are generated not connected with an increase of the lattice temperature.
Relaxation in the ferromagnetic phase of terbium arsenate (TbAsO4)
Authors: Müller P. H. , Kasten A. , Schienle M.
Published: July 2007

Below Tc = 1.5 K TbAsO4 is an Ising ferromagnet with induced magnetic moments. A superstructure of the magnetic moments found by Schäfer and Will may be explained by very small ferromagnetic domains. A simple estimation of the free energy at T = 0 yields 0.05 μm for the thickness of these domains. In the ordered phase the complex magnetic ac susceptibility is strongly frequency dependent. The relaxation depends on two coupled processes. It is assumed that the process at lower frequencies is due to domain wall shifting and the process at higher frequencies is caused by the internal field. The frequency dependence can be described by an extension of the Debye equation which decouples the two processes. The susceptibility of a system with rigid domain walls is determined in mean field approximation.
Excited states of bound excitons in wurtzite‐type semiconductors
Authors: Puls J. , Henneberger F. , Voigt J.
Published: July 2007

Excitons bound to neutral impurities are studied with respect to excited states by means of excitation spectroscopy in CdS single crystals at 1.8 K. The symmetry of the four excited states of the exciton bound to neutral donor (placed energetically below the free exciton) can be deduced from the observed dependence of their optical transitions on the direction of the wave vector and the polarization. Theoretical considerations taking into account the complex valence band structure of wurtzite‐type semiconductors lead to an explanation of these states in terms of excited (p‐ and d‐like) hole states of the bound exciton. With respect to the exciton bound to neutral acceptor only the well‐known I1B‐states are found experimentally arising from the incorporation of a hole from the lower B‐subvalence band in the complex.
Electrical resistivities of the liquid alkali metals
Authors: Canessa E. , Vignolo J.
Published: July 2007

A discussion of the calculation of electrical resistivity of liquid alkali metals is presented. The electrical resistivity is revised for these metals from various model potentials using experimental as well as theoretical structure factors. The over‐all agreement between Ziman's theory and experiment is reasonably satisfactory though not in detail. Most of the discrepancies are explained by the behaviour of the structure factor, and in other cases by the validity of the screened pseudopotential employed.
Variation of phonon dispersion curves with temperature in indium arsenide measured by X‐ray thermal diffuse scattering
Authors: Orlova N. S.
Published: July 2007

A study of the temperature dependence of the X‐ray thermal diffuse scattering intensity distribution from the (100), (110), (111) planes in indium arsenide single crystals is carried out in the temperature range 80 to 750 K. The data obtained are analysed and yield the phonon frequencies in all three principal symmetry directions at different temperatures. An average decrease in the acoustic mode frequencies is found to about 10 to 12% while for optic modes it is of about 6% with increasing temperature over the temperature range above mentioned.
Magnetic relaxation in dysprosium phosphate (DyPO4)
Authors: Schienle M. , Kasten A. , Müller P. H.
Published: July 2007

DyPO4 is a three‐dimensional Ising antiferromagnet with a Néel temperature of TN = 3.39 K. The temperature and field dependence of the relaxation time is investigated by means of magnetic ac susceptibility measurements in the frequency range from 5 Hz to 3 MHz. Above 9.3 K a spinlattice Orbach process via the first excited crystal field state of Dy3+ is dominant. Spin—spin processes contribute only at low temperatures and the relaxation becomes temperature independent, but depends strongly on the magnetic field strength. The relaxation is fast where the external field compensates the nearest‐neighbour interaction, e.g. for vanishing local magnetic field. The magnetically diluted system (Y0.09, Dy0.1)PO4 depends strongly on the properties of the coolant surrounding the crystal, which could be understood quantitatively by a heat conduction model.
Electron paramagnetic resonance of Mn2+ and VO2+ in Ba2Zn(HCOO)6 · 4 H2O single crystals
Authors: Jain V. K. , Seth V. P. , Malhotra R. K. , Yadav S. K.
Published: July 2007

Electron paramagnetic resonance of Mn2+ and VO2+ in dibarium zinc formate tetrahydrate is studied at X‐band and at 298 K. The ions substitute for the Zn2+ sites in the lattice. A correlation is found to exist between the V—O and Zn—O bond directions. The spin‐Hamiltonian parameters are evaluated. Forbidden hyperfine transitions Δm = ± 1 and Δm = ± 2 are observed for Mn2+ and their doublet separations are found to be in agreement with calculated values. The angular variation of the intensities of the allowed and forbidden hyperfine transitions of Mn2+ is also studied and is found to be in good agreement with the theory.