bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence of Two Paramagnetic Defects in WO3‐Doped V2O5
Authors: Gaillard B. , Blanchard C. , Deville A. , Livage J.
Published: July 2007

The nature of paramagnetic defects in crystalline V2O5 can be drastically modified by adding very small quantities of doping impurities. Until now, the semiconducting properties of such crystals are interpreted by using a two level hopping model. Spin–lattice relaxation time measurements show that two kinds of paramagnetic defects exist in WO3‐doped V2O5. One is associated with the doping impurity but the other one is not. It corresponds to the intrinsic paramagnetic defects due to the non‐stoichiometry of V2O5.
Exchange Interaction between Paramagnetic Centers and Valence Band Electrons in Semiconductors with Cubic Lattices
Authors: Semenov Yu. G. , Shanina B. D.
Published: July 2007

A Hamiltonian is derived for the exchange interaction between paramagnetic ions and electrons from the bands Γ6, Γ7, Γ8, that is the result of the splitting Γ′15, Γ′25, by the spin‐orbit interaction of arbitrary intensity Δso in semiconductors with cubic lattices. It is shown that, Δso being sufficiently large, the Hamiltonian of each splitted subzone is of Heisenberg form. Formulas are derived and numerical estimations are carried out for the exchange interaction constants; the relation of the latter to the crystal band structure is discussed. The sign difference which was discovered experimentally earlier for the constants of exchange coupling between 3d ions and electrons of valence and conduction bands in AIIBVI:Mn2+ crystals is explained by the results of the theory.
Crystal Field of Cr3+ Ion in Spinel Lattice: The Effect of High Hydrostatic Pressure
Authors: Ślawska‐Waniewska A.
Published: July 2007

The crystal field parameters of an octahedral Cr3+ ion in normal and inverse spinel lattices are calculated in the point charge model. As an example LiFe5O8:Cr3+ is considered in more detail. For this spinel the spin Hamiltonian parameter and the one‐ion anisotropy constant of Cr3+ are calculated and compared with experiment. The investigations are extended to include the case of the crystal being under high hydrostatic pressure.
Hopping Conduction and Energy Spectrum of Localized States in low‐Doped Intermediate‐Compensated n‐ZnSe
Authors: Timchenko I. N. , Nedeoglo D. D.
Published: July 2007

The temperature dependence of the resistivity of low‐doped n‐ZnSe crystals with intermediate compensation is investigated in ohmic and non‐ohmic regimes. In the temperature interval from about 20 to 7 K hopping conduction is observed with a constant activation energy, but at lower temperatures the conductivity may be approximated by a dependence of the type In ˜ T−1/2, which may be due to a Coulomb gap in the energy spectrum of localized states. It is found from the non‐ohmic hopping conduction data that the effective length of non‐ohmicity is of the order of the mean inter‐impurity distance and is practically independent of the electric field; the temperature dependence of the effective length (or the percolation threshold) corresponds to the energy spectrum of localized states with a Coulomb gap.
d—s, p Resonance and Electronic Structure of Compounds, Alloys, and Solid Solutions
Authors: Domashevskaya E. P. , Terekhov V. A.
Published: July 2007

On the basis of the valence band structure regularities, obtained from combined X‐ray spectral and X‐ray photoelectron studies of electron energy spectra, a model is suggested for the interaction between valence electrons of s, p‐elements and d‐electrons of IIIA, IIB, IB, and transition metals under the formation of compounds, alloys, and solid solutions, the so called d—s, p resonance. The model qualitatively explains different observed manifestations of state interaction: the energy displacements, subband splitting, mixing of states of different symmetry or, vice versa, pushing of s, p‐states out of the energy interval, occupied by d‐band, due to the mutual energy arrangement of d‐ and s, p‐subbands.
Electron Spin Resonance of Doped Glow‐Discharge Amorphous Silicon
Authors: Dersch H. , Stuke J. , Beichler J.
Published: July 2007

The influence of doping on the ESR spectra of glow‐discharge a‐Si:H is systematically investigated in the X‐ and Q‐band for phosphorus‐ and boron‐doped samples up to a high doping level. Whereas for undoped and moderately doped material the well‐known line with g = 2.0055 is observed, for highly boron‐doped samples the broader line at g = 2.01 predominates as does the g = 2.0043 line in the case of high phosphorus doping. The linewidth of the resonance at g = 2.01, due to holes in localized valence band tail states, is mainly determined by a g‐value spectrum. With increasing boron doping the width of this spectrum decreases and its centre of gravity shifts to smaller g‐values. The narrower line with g = 2.0043, due to electrons in localized conduction band tail states, however, broadens with increasing phosphorus doping due to hyperfine interaction with the phosphorus nuclei. From these features it is concluded that the wave function of holes in valence band tail states is much more localized than that of electrons in the conduction band tail. At the same high doping level the spin density for the hole resonance at g = 2.01 is a factor of about 102 larger than for the electron line with g = 2.0043. This difference is explained by a different correlation energy U. Besides these lines a relatively weak resonance at g = 2.0026 is found for boron‐doped samples and for phosphorus‐doped material as well. Measurements on compensated samples indicate that by doping dangling bonds are created.
Mössbauer Study of the 3d5 Shell Deformation of Fe3+ Ions in MnFe2O4
Authors: Ligenza S. , Kucharski Z. , Suwalski J.
Published: July 2007

The deformation of the 3d5 electron shell of iron atoms in an MnFe2O4 spinel is investigated by means of Mössbauer effect measurements with 60 kOe and without an external magnetic field at 4.2 K. An analysis of ME spectra is carried out using neutron spectroscopy data. It is found that the 3d5 shell deformation observed by neutron spectroscopy brings about the quadrupole splitting 23d = −0.040 mm/s. A change of the charge density at 3d5 electron shell is calculated to be about 0.3%. A dipole magnetic contribution to the effective field on iron ions in octahedral sites, HD, is estimated as +17.6 kOe. The magnitude of all other hyperfine interaction parameters of 57Fe nuclei are also given.
Characteristics of Secondary Electrons Ejected from Solid Targets by Multiply Charged Ions with Energy up to 20 MeV/Nucleon
Authors: Akkermann A. F. , Botvin V. A. , Ya. Chernov G.
Published: July 2007

Detailed characteristics of secondary electron emission from silicon after bombardment by multiply charged ions Al, C, O, Ca, Si, Fe with energies up to 20 MeV/nucleon are deduced from Monte‐Carlo simulations. The calculated integral yields η in forward direction to approach the η—Zeff law. The discrepancies between calculated and experimental data for fission fragments are discussed. Limits for ion charge resolution by secondary particle counting are obtained.
Wigner‐Seitz Radius Dependent Model Potential
Authors: Khanna K. N.
Published: July 2007

A model pseudopotential for electron‐ion interaction depending on the Wigner‐Seitz radius is proposed for simple metals. The results of individual contributions of binding energy, liquid metal resistivity, phase stability, and electronic charge density obtained from the proposed model potential agree reasonably well with the experimental results for several simple metals.
A Theory of an Amorphous Ferromagnet
Authors: Kaneyoshi T. , Fittipaldi I. P.
Published: July 2007

A new‐type effective field theory with correlations in an amorphous ferromagnet is discussed. The Curie temperature and a critical percolation concentration in an amorphous ferromagnet are obtained.
Effect of Surface Relaxation on Point Defects in the Vicinity of W (100) Surfaces
Authors: Mhaskar S. P. , Naik P. K.
Published: July 2007

Surface relaxations of W (100) planes and their effect on point defects are computed with the help of a program that can simulate various processes occurring in the bulk of a solid and in the vicinity of the surface. Formation energies of vacancies and divacancies at various depths from the W (100) surface are calculated. Effect of surface on the activation energies of detrapping reaction of helium from HeV is also investigated. It is observed that formation energies of point defects and activation energies of thermal detrapping reactions continue to decrease approaching the surface from the bulk of a solid.
Effect of Magnetic Quantization on the Diffusivity—Mobility Ratio in n‐Cd3As2
Authors: Chakravarti A. N. , Ghatak K. P. , Dhar A. , Ghosh S.
Published: July 2007

An attempt is made to study the dependence of the diffusivity‐mobility ratio on a quantizing magnetic field in degenerate n‐Cd3As2 in the extreme quantum limit according to the Bodnar model which has recently been shown in the literature to be the most valid model for Cd3As2. The results obtained are then compared to those derived on the basis of the Kane model since many authors have continued to use the Kane model for Cd3As2.
Stability Surface for the Blume‐Capel Model
Authors: Taggart G. B.
Published: July 2007

The stability surface for the Blume‐Capel model is obtained in the thermodynamic space of the temperature and densities (order parameters). This surface, which separates thermodynamically stable (metastable) regions from unstable ones, is determined from divergences in the generalized static susceptibility. The susceptibility itself is derived from correlation functions which are calculated from high temperature expansions to the first order beyond the mean field approximation. Consequently the stability surface exhibits lattice‐dependent effects.
Non‐Γ Deep Levels and the Conduction Band Structure of Ga1−xAlxAs Alloys
Authors: Saxena A. K.
Published: July 2007

The electrical properties of the Ga1−xAlxAs alloys are strongly controlled by the emergence of deep levels in crystals which have x values near to the direct—indirect conduction band transition composition. The activation energy of the deep levels and the energy of the L conduction band minima with respect to the lowest energy Γ minimum (0.19 ≦ x ≦ 0.43) and × minima (0.43 < 〈x ≦ 0.61), are determined from the temperature dependence (77 K ⪅ T ⪅ 750 K) of the Hall electron concentration on high‐purity crystals.

It is shown that the lowest energy indirect minima is L in Ga1−xAlxAs for alloy compositions in the range 0.19 ≦ x ≦ 0.37. The variation in the energy separation ΔEΓL at 300 K between the Γ and L minima is best described by the equation ΔEΓL = (0.285 — 0.595x) eV for 0.19 ≦ x ≦ 0.47. The Γ—L cross‐over composition is, thus, determined to be x = 0.47. For x ⪆ 0.25, a deep level dominates the electrical characteristics of the crystals. The activation energy of the deep level with respect to the Γ minimum increases with x, being (0.170 ± 0.005) eV at x = 0.44, but with respect to the L minima remains almost constant with a value of ≤0.200 ± 0.005≤ eV for 0.19 ⪅ x = 0.44. For x > 0.44, the energy of this level below the × minima decreases monotonically reaching a value of (0.106 ± 0.005) eV at x = 0.78. Heavily compensated shallow donor levels are also present in the alloys. Similar measurements on samples with compositions in the range 0.23 ≦ x ≦ 0.32 and under hydrostatic pressure have shown that the deep level is mainly associated with the indirect minima L and × although the Γ minimum is the lowest in energy.
Effective Electron—Electron Interaction in Conjugated Polymers
Authors: Ukrainskii I. I.
Published: July 2007

The excitation energies of charge carriers and neutral excitons in polyacetylene and polydiacetylene are calculated taking into account the electron correlation effects. The singlet exciton band is shown to split off a conduction band if and only if the electron‐electron repulsion on the neighbouring carbon atoms differs from zero. The value of this repulsion is found to be about 3 eV.
Studies by UV and IR Absorption of Particular Motions of NO in Single Crystals of NaNO2
Authors: Jumeau D.
Published: July 2007

The polarization states of the ν2 IR absorption band of NO (ν2 ≈ 828 cm−1 at 20 °C) and of the zero‐phonon line ν00 of the UV electronic transition of NO (ν00 ≈ 385 nm at 10 K), are studied between 10 and 300 K. When the temperature increases, the ν2 (‖b) and ν00(‖a) absorption lines are no longer perfectly polarized along the b‐and a‐axes, respectively, and this depolarization is strongly dependent on the orientation of the wave vector q of the incident light (q ‖ a, b or c). This result may be explained by the NO interaction with low‐frequency waves.
Line Broadening and Line Displacement of EPR Transitions Produced by Inhomogeneous Plane Stresses in a Two‐Layer System
Authors: Gehlhoff W. , Segsa K. H.
Published: July 2007

The strain induced changes of lineshapes and line positions of EPR transitions in a film‐substrate system with elastic cubic symmetry are analysed. Thereby it is assumed, that the distributions of stresses and strains in the two‐layer system are induced by inhomogeneous plane stresses developed in the film.
The Effect of Short‐Range Order on the Vibrational Spectra of 3:2 Coordinated Chalcogenide Glasses. Analysis of the Vibrational Spectra by Using Pyramidal Structural Units
Authors: Giehler M.
Published: July 2007

Infrared reflection and Raman spectra of 3:2 coordinated chalcogenide glasses are analysed by fitting the optical spectra using a dielectric function consisting of four oscillator terms. The obtained frequencies and infrared intensities of the major infared and Raman vibrational bands are studied within the framework of one aspect of the short‐range order of 3:2 glasses—pyramidal structural units. It is shown that in this model the frequencies of the major vibrational modes (with the exception of As2O3) of all 3:2 chalcogenide glasses can be well explained if one takes into account chemical trends (i) in the force constants (in such a way that the stretching force constant is inversely proportional to the third power of the bond length) and (ii) in the bond angle of the apex atom of the pyramid (in such a way that an increasing electronegativity of the apex atom with respect to that of the chalcogen atom causes mostly an increase of the bond angle at the apex atom). For an understanding of the major vibrational properties of As2O3 glass the vibrational coupling of the pyramidal stuctural units with each other especially due to the high electronegativity and the light mass of the oxygen atom) must be taken into account. The Penn gap energies and ionicities of 3:2 coordinated chalcogenide glasses are determined within the approximation that each pyramidal structural unit contributes eleven valence (including lone‐pair) electrons to the chemical bonding. The chemical trend in the intensities of the major infrared vibrational bands characterized by the effective charges is explained as due to a trend in the ionicities of the studied glasses.
Jahn‐Teller Effect in Narrow‐Band Cubic Crystals with E‐Type Ground State
Authors: Mironov V. S. , Ionova G. V. , Groznov I. N. , Ionov S. P.
Published: July 2007

The cooperative Jahn‐Teller effect in narrow‐band three‐dimensional crystals of cubic symmetry perovskite (AMX3) or ReO3‐type structure is considered. A transition metal ion with E ground state in a crystal field of cubic symmetry is treated. The number of band electrons per ion ranges between 0 and 4. The electronic correlations are neglected. The static Jahn‐Teller distortions of the crystal at T equals; 0 K as well as the electronic structure and possible types of orbital ordering are determined. The cooperative Jahn‐Teller effect in band crystals is shown to lead to charge order (besides orbital order). This orbital‐charge ordering is not connected with electronic correlation.
Phonon Widths in RbBr at 80, 290, and 370 K from Neutron Measurements
Authors: Nilsson G. G.
Published: July 2007

Neutron inelastic scattering experiments are performed on RbBr at 80, 290, and 370 K and the experimental phonon widths are determined. Very little broadening with temperature is observed except for certain longitudinal optical modes which are broad at all temperatures and also show a marked temperature dependence in the width. A comparison is made with infrared data where measurements on the fundamental absorption peak yield information about the phonon width.
Analysis of Interionic Potentials in II‐VI Chalcogenide Crystals with NaCl Structure
Authors: Jain V. K. , Shanker J.
Published: July 2007

An analysis of interionic potentials in 45 chalcogenide crystals is performed. New values of van der Waals coefficients derived from the variational formulae are used in the present calculations. The Born‐Mayer repulsive interactions between nearest neighbours as well as between next nearest neighbours are treated by considering the repulsive hardness parameter as an ionic property. This eliminates the well‐known assumption in the Born model according to which one takes a common hardness parameter for different pair interactions. Values of cohesive energies, bulk modulus and its pressure derivative are calculated and compared with other investigations.
Optical and Polarized Luminescence Studies on RbI:Pb2+ at Liquid Helium Temperatures
Authors: Sapru S. , Sastry S. B. S.
Published: July 2007

Optical absorption, luminescence, and polarized luminescence studies are made on RbI:Pb2+ from 4.7 to 50 K. It is found that the charge compensating vacancy is predominantly in the next‐nearest neighbour sites at these temperatures. The B‐band shows a splitting and the emission under B‐band excitation disappears around 20 K. Possible crossing of 3T2u and 3Eu levels with 1A1g is suggested to explain the behaviour.
Density of States in Multilayer Sandwiches
Authors: Dubovskii L. B.
Published: July 2007

The density of states of finite metal—semimetal system is considered in the case of boundary conditions that assure the damping of electronic states at infinity. The density of states of the transition region metal‐semimetal is investigated which is found to be strongly dependent on the shape of the transition layer. Special attention is paid to the case when in one part of the system, in the metal, the coherence of the motion of the electron is broken, while in the other part, in the semimetal, the electron moves coherently. Under this condition, the oscillations of the density of states of systems consisting of a metallic film covered on both sides with the semimetal, and systems consisting of two metallic films with a semimetallic interlayer are considered. Within the model described, one can understand the experimentally observed behaviour of Tc (the temperature of the superconducting transition) at small thicknesses of the semimetallic layer.
Infrared and Raman Spectra of Germanium Dichalcogenides I. GeS2
Authors: Popović Z. V. , Stolz H. J.
Published: July 2007

The polarized IR reflectivity and transmission spectra as well as the polarized Raman spectra of single crystalline GeS2 are measured. From a comparison with a factor group analysis most of the expected 141 optically active phonons are identified with their symmetry type. From the observation of rigid layer modes and from the Davydov splitting a force constant anisotropy of about 100 between interlayer and intralayer forces is deduced.
The Mn2+ Ion Spectra in PbxSn1−xTe Alloys
Authors: Hejwowski T. , Subotowicz M.
Published: July 2007

Electron paramagnetic resonance (EPR) and Hall coefficient are measured for Mn2+ ‐doped PbxSn1−xTe alloys at temperatures of 77 and 300 K. A rapid change in the HFS constant A and the g‐factor is observed in the range 0.9 ≦ x < 1. In addition, some results for Mn2+‐doped PbTe alloys are presented to confirm the hypothesis of the inhomogeneous distribution of the atoms (Mn, Sn, Pb) in the alloys investigated.
Lattice Dynamics and Some Related Thermal Properties of Body‐Centred Cubic Metals
Authors: Ramji Rao R. , Rajput A.
Published: July 2007

A phenomenological model is developed for the calculation of the lattice dynamics and thermal expansion of a homogeneously strained body‐centered cubic (b.c.c.) crystal in which both two‐and three‐body interactions are assumed to operate. The phonon dispersion curves and lattice heat capacity of the four alkali metals Li, Na, K, and Rb, and of the three transition metals α‐Fe, Mo, and W are computed employing four second order parameters in each case. The second‐order elastic constants of these metals are also evaluated. The model is then applied to the four alkali metals to calculate their generalised Grüneisen parameters for various normal mode frequencies and hence the temperature dependence of their effective Grüneisen functions. The results of calculations are in good agreement with the corresponding experimental data wherever the latter exist.
A New Method for Detecting the Wannier‐Stark Ladder in a Semiconductor in a Strong Electric Field
Authors: Berezhkovskii A. M. , Ovchinnikov A. A. , Suris R. A.
Published: July 2007

A new method for detecting the Wannier‐Stark ladder in a semiconductor in a strong electric field is proposed. The method is based on the measurement of the interband absorption coefficient in strong parallel magnetic and electric fields at frequencies less than the energy gap.
Order Parameter Symmetry for the β–γ Transition in Pb3(VO4)2
Authors: Hatch D. M.
Published: July 2007

The 100 °C phase transition in Pb3(VO4)2 is theoretically described. The description is in terms of the Landau group theoretical formulation as extended by Birman and Jari°C. Representations from the F point are constructed from which the representation that induces the transition is identified. It is found that this representation satisfies the necessary conditions for a continuous transition. The free energy form consistent with the phase of higher symmetry is constructed as a function of the order parameter and elastic strain.
Infrared Studies of Defects in ZnS Crystals Double‐Doped with Li and Al, Ga, and In
Authors: Król A. , Nazarewicz W. , Gluziński L. , Kozielski M. J.
Published: July 2007

Infrared absorption (360 to 500 cm−1) is studied in ZnS crystals doped with both, lithium and a group IIIA dopant. The dominant bands in the obtained absorption spectra can be ascribed to the localized vibrational modes of two types of defects: 1) unassociated Li on a Zn site, Li−Zn, and 2) pairs comprising substitutional Li on a Zn site and substitutional group IIIA impurity on the nearest Zn site, M+Zn‐Li−Zn (M = Al, Ga, or In). Li in ZnS is found to have a considerable effect on atomic interactions in the neighbouring region and, therefore, cannot be regarded as a pure mass defect.
Low‐Temperature Heat Capacities of Pd–Al Alloys at Low Al Contents
Authors: Glugla M. , Severin H. G. , Sicking G.
Published: July 2007

The heat capacities of Pd–Al alloys up to 15 at% Al content were measured in the temperature range between 1.5 and 12 K. The results are discussed in terms of a band‐filling model. In this picture Al admixtures behave like Ag admixtures to Pd but contribute about three electrons to the host instead of one. Conclusions are drawn concerning the superconducting transition temperature in Pd–Al hydrides.
Electrical Conductivity of Superionic AgI between 18 and 26.5 GHz
Authors: Luther G. , Roemer H.
Published: July 2007

The high frequency ionic conductivity σ of the solid electrolyte α‐AgI was measured at temperatures up to 520 K in the microwave K‐band (18 to 26.5 GHz). In contrast to a structure of σ(ω) with a distinct minimum at 20 GHz reported in the literature, a frequency dependence cannot be detected and the same values of σ are measured as are well known from static measurements. The results are in a accordance with a simple “hopping model”.
The Exact Solution of the Curie‐Weiss‐Néel Model Ferrimagnet
Authors: Bowers R. G.
Published: July 2007

An analogue for ferrimagnetism, of the Curie‐Weiss ferromagnet is introduced. The complete thermodynamics of the resulting Curie‐Weiss‐Néel model is obtained. The exact solution of the model is essentially identical with the results of mean‐field theory. Attention is focused on the Néel point and associated critical phenomena. Novel features of critical phenomena in ferrimagnets are considered. Theroretically the staggered magnetization and staggered fields are important whilst experimentally the total magnetization and uniform fields are employed. It is shown that, within the present context, corresponding staggered and uniform properties have identical critical exponents.
The Electron Mobility and Thermoelectric Power in InSb at Atmospheric and Hydrostatic Pressures
Authors: Litwin‐Staszewska E. , Szymańska W. , Piotrzkowski R.
Published: July 2007

First, theoretical calculations of electron mobility and thermoelectric power in n‐type InSb are reported at liquid nitrogen and room temperatures. All the scattering mechanisms of importance in InSb are taken into account. The calculations based upon a variational solution of the Boltzmann equation are compared with experimental results over the whole available range of electron concentrations. Good agreement between theoretical and experimental results is obtained using the value of deformation potential constant C = 14.6 eV. Secondly, both, experimental and theoretical investigations are made of mobility in InSb under hydrostatic pressure at 77 K within a wide range of electron concentrations. The smallest electron concentrations obtained by freezing the conduction electrons on the metastable states are of order of 1 × 1012 cm−3. Also for those smallest concentration it is possible to describe theoretically the dependence of mobility on the hydrostatic pressure using the same set of parameters as previously, and assuming some compensation of donors by acceptors.
Composition Dependence of the Anisotropy of the Cyclotron Masses in n‐Type Semiconducting Bi1‐xSbx
Authors: Fellmuth B. , Krüger H. , Rudolph R. , Herrmann R.
Published: July 2007

The anisotropy of the band‐edge cyclotron masses of n‐type Bi1‐xSbx (0.07 ≦ x ⪅ 0.16) in the binary plane is determined by investigating the wave propagation in the Voigt configuration B ⟂ C2 ‖ k. At low antimony concentrations (x ≤ 0.10) the anisotropy is independent of x. For x > 0.10 a strong change is observed, where at x ≈ 0.15 a distinct maximum is achieved. These peculiarities can be described by a great variation of the model parameters which determine the energy dispersion in the direction of elongation of the Fermi surface.
Origin of Radiative Transitions from Metastable Minima of the Excited State of Sn2+v−c Centres in Alkali Halides
Authors: Hizhnyakov V. , Soovik T. , Zazubovich S.
Published: July 2007

The dependence of electronic wave functions on the coordinates of not totally symmetric vibrations and the hyperfine interaction are considered theoretically as the possible reasons of the radiative decay of the metastable minima of the sp excited state of Sn2+ vc centres in KCl crystals. It is shown that the dependence of electronic wave functions on the coordinates of not totally symmetric vibrations, which leads to the dynamical lowering of symmetry and removal of forbiddenness for radiative transition from metastable minima (deviation from the Condon approximation), is the main reason of the radiative decay. Taking into account also the mixing of the functions of the radiative and metastable minima by the hyperfine interaction, a 1 to 10% shortening of decay time τ is expected at the transition from natural tin (containing 16% of Sn119) to pure isotop Sn119. A comparison of the decay times is performed which are measured at 2 and 4.2 K for AT luminescence of Sn2+ vc centres in KCl crystals doped with tin having different isotopic abundance. The values of τ in KCl:SnCl2 and KCl:119SnCl2 crystals are shown to differ to about 4%, whereas in KCl crystals doped with the isotope 119Sn the decay time is always shorter than that in KCl with natural tin. This result, being the first experimental observation of the influence of the hyperfine interaction on luminescence decay kinetics of impurity centres in the crystals, is in good agreement with the theory.
Relaxation Time and Effective Masses for Charge Carriers in Semimetallic BiSb Alloys versus Alloy Composition
Authors: Braune W. , Straubel U. , Kubicki N. , Lebech J. , Saermark K.
Published: July 2007

Recent investigations on the propagation and damping of magnetoplasma waves in semi‐metallic BiSb alloys allow for the conclusion that the effective masses of the holes and the tilt angle of the electron ellipsoids of the Fermi‐surface do not vary in the semimetallic region of the alloy system. The variations of the effective masses for the electrons with alloy composition can be deduced from magnetoplasma wave data and are in good agreement with cyclotron resonance‐ and quantumoscillation experiments. Observation of the wave damping for different measuring configurations indicates, that the relaxation time for the holes decreases more strongly with increasing Sb‐concentration than the relaxation time for the electrons does.
Adequacy of Local‐Exchange Excitation Hamiltonias in Insulators
Authors: Trickey S. B. , Ray A. K. , Worth J. P.
Published: July 2007

The local‐density (Xα) calculation of insulator band gaps is re‐examined. Both new and extant data show the calculated gaps to be systematically small by substantial percentages (35 to 50%) while cohesive energies, valence band widths, and PV curves are in satisfactory agreement with experiment. The Slater transition state cannot be invoked directly to resolve the dilemma and its periodic generalization is unsuccessful. The simple periodic excitation calculation of ΔESCF can be interpreted usefully in terms of the first exciton absorption, a fact we illustrate in f.c.c. Ar. It is argued that the numerical results indicate strongly that Xα calculations of metal‐insulator transition pressures yield lower bounds to that pressure.
Lattice Sums for Zinc Sulphide Structure Crystals
Authors: Chatterjee S. , Ghosh S. , Basu A. N.
Published: July 2007

Following the procedure due to Born and his co‐workers a method is developed for evaluating the lattice sums for cubic crystals without a centre of symmetry. For the zinc sulphide structure crystals the like particle sums can be worked out with Born et al. 's formulae but these are not applicable to the unlike particle sums. Further Jacobi's imaginary transformation adopted by Born et al. for the primitive lattices cannot be used in these sums for the evaluation of the integrals. Instead convergence is achieved by the use of Ewald's θ transformation. Finally the explicit formulae for the lattice sums – both, static and periodic – applicable directly to diamond and zinc sulphide structures are deduced.
Electronic Absorption Spectrum of Rb2MnCl4 Single Crystals
Authors: Ghosh B. , Mukherjee R. K.
Published: July 2007

The polarized electronic absorption spectra of Rb2MnCl4 single crystals are studied down to 77 K in the 15 000 to 45 000 cm−1 spectral region. The observed spectral features can be satisfactorily explained by invoking the four‐parameter (B, C, Dq, and α) ligand field model which indicates the octahedral site symmetry around the Mn2+ ion. Two higher energy bands are found to be due to double‐exciton transitions.
Cyclic and dihedral point groups as subgroups of the limiting groups
Authors: Sivardière J.
Published: July 2007

Irreducible representations of cyclic and dihedral point groups are deduced from those of the limiting groups ∞ and ∞2. The method is equivalent to that of crystal quantum numbers and gives immediately a classification of spherical harmonics according to the representations of each group. Results are applied to the determination of crystal field splittings and of tensorial invanants and covariants.
A cooperative model of stress relaxation in solids
Authors: Högfors Ch. , Kubát J. , Rigdahl M.
Published: July 2007

The process of stress relaxation in solids is discussed in terms of a two‐level system where stimulated emission of phonons may occur. There is no a priori information on field equations or interaction Hamiltonian but the physically reasonable statistical assumption about the phonon distribution, that they are bosons, is enough in order to describe the macroscopic behaviour qualitatively. With certain approximations, the equation for the stress rate may be solved with analytical methods. Comparison with experiments reveals that this proposed mechanism for stress relaxation might be correct.
X‐ray investigation of thermal expansion and atomic thermal vibrations of tin, indium, and their alloys
Authors: Wołcyrz M. , Kubiak R. , Maciejewski S.
Published: July 2007

Thermal expansion and anisotropic thermal vibrations are investigated for pure tin, indium, and their intermetallic compounds : In3Sn and InSn4, below and above room temperature. Measurements are performed with spherically shaped single crystals. The dependences of the lattice parameters on temperature are measured by using the high precision Bond‐type diffractometer. Sets of reflection intensities are taken and anisotropic temperature factors were calculated in the structure refinement process. An analysis of the formula concerning the bonding energy of the crystals discussed is carried out. The theoretical thermal expansion coefficients are compared with experimental ones.
Recombination processes in 3 to 5 μm HgCdTe
Authors: Calas J. , Allègre J. , Fau C.
Published: July 2007

An analysis of the decay of the excess majority carriers created by a photon beam with an energy higher than the energy gap is given. The recombination processes as well as the radiative process and also the Auger process are studied for Hg1−xCdxTe when x is nearly equal to 0.30, and their range of validity versus temperature is defined. From the continuity equations, the change of ne versus time is deduced when the recombination takes place in deep levels for a given injectpion rate ne0. The capture cross section NRτn0 of a given level at weak injection rate and at low temperature is obtained from the slope of In(ne(t)). At higher temperature, the population of the re‐ combination level and the ionisation enefgy with respect to the valence band are determined from the slope of ne(t) at high injection rate and from the slope of In(ne(t)) at weak injection.
Excitation induced renormalization effects of the excitonic polariton dispersion in CdS
Authors: Kempf K. , Schmieder G. , Kurtze G. , Klingshirn C.
Published: July 2007

The investigation of the excitonic polariton dispersion curve of highly excited CdS platelets reveals some modifications of the dielectric function ϵ˜(ω, k). Considering the real part of ϵ˜(ω, k), the renormalization effects introduced by an intense laser can be qualitatively described by adding to ϵ˜ appropriate resonance terms. These additional resonances are partly situated at the spectral position of the incident laser, partly their position is correlated to the energy of the biexciton. Furthermore, a weak shift is observed of the excitonic eigenenergy at high excitation. The techniques used to investigate the above‐mentioned anomalies are two‐photon Raman scattering and the study of Fabry‐Perot interferences.
Masse effective des électrons et Eg(x) dans la solution solide CdIn2 (Se1−xTex)4
Authors: Chizhikov V. I. , Panyutin V. L. , Ponedelnikov B. E. , Rozenson A. E.
Published: July 2007

Par la méthode du pseudopotentiel empirique, nous avons effecté un calcul de l'évolution de la bande interdite et de la masse effective des électrons en fonction de la composition de la, solution solide CdIn2(Se1−x,Tex)4. L'accord obtenu avec les résultats expérimentaux est satisfaisant.
Study of optical second harmonic generation in ferroelectric liquid crystal
Authors: Vtyurin A. N. , Ermaeov V. P. , Ostrovskii B. I. , Shabanov V. F.
Published: July 2007

Second harmonic generation in the ferroelectric smectic C phase of i‐amyl‐4‐[4‐decyloxybenzylideneamino]‐cinnamate (DOBAMBC) is studied. Its dependences on temperature and external electric field are measured. A considerable effect of orientational fluctuations is pointed out.
Optical measurements of the surface plasmon of copper
Authors: Robusto P. F. , Braunstein R.
Published: July 2007

The optical properties of the noble metal copper are determined by computer fitting the experimentally obtained attenuated total internal reflection (ATR) spectra of its surface plasmon in the visible spectral region (0.42 to 0.63 μm). The dispersion curves of the surface plasmon resonance of copper are determined; they show that the resonance exists on the steep absorption edge of ϵ2 at 2.16 eV. This absorption edge, which is due to the d‐band to Fermi level transition, causes the large shift in the location of the surface plasmon excitation from ϵ1(ωs) = −1 to ϵ1(ωs) = −4.7 and causes the true resonance to occur in the complex frequency plane.
Luminescent analysis of an impurity in the near‐surface layer of thermally evaporated silicon
Authors: Safronov L. N. , Aleksandrov L. N. , Lovyagin R. N.
Published: July 2007

A low‐temperature (T = 6 K) photoluminescence of surface silicon layers undergoing thermal evaporation in a high vacuum at 1300 to 1350 °C has been studied. It is found that irrespective of the impurity concentration of the initial samples the bands are observed in the luminescence spectra of the surface region of thermally treated plates, which are due to annihilation of excitons bound with: 1) single non‐ionized boron atoms in substitutional positions of the silicon lattice; 2 ) pairs and clusters of substitutional boron atoms in a layer about 1 μm thick. The processes resulting in the formation of a narrow concentration profile of boron atoms near the surface of a silicon plate are discussed. Boron is accumulated due to a considerable difference (by a factor of about 102) between the rates of evaporation of boron and silicon atoms under non‐steady‐state diffusion.
The model of the phase transition in squaric acid
Authors: Schneider V. E. , Tornau E. E.
Published: July 2007

A statistical model of phase transition in squaric acid (C4H2O4 and C4D2O4) crystals is proposed. The thermodynamical properties of the transition are investigated by a five‐particle cluster approximation not taking into account the tunneling motion of protons. It is shown that the phase transition in the analysed model can be of both first and second order. A comparison with recent experimental data is carried out.
Band calculation of copper by an interpolation scheme based on recent pseudopotential methods
Authors: Yamada Y.
Published: July 2007

The interpolation scheme for f.c.c. copper, which is based on the empirical or model‐pseudo‐potential method, is formulated without using Slater‐Koster matrix elements. It is based on the fact that the pseudopotential is separable into the local and nonlocal parts. Consequently, in contrast to the previous methods, the parameters in the d‐d matrix elements do not depend upon the crystal structure and their number is small. The present scheme is applicable to other crystal structures. It is devised so as to give the same condition in the expansion of the Bloch function in terms of plane waves over the first Brillouin zone. The calculated band structures are compared with those obtained by other methods.
On the influence of fluctuations on the Peierls transition of the quasi‐one‐dimensional Fröhlich model with a nearly half‐filled band
Authors: Puff H.
Published: July 2007

The influence of fluctuations on the Peierls transition of the quasi‐one‐dimensional Fröhlich model with a nearly half‐filled band is investigated within a renormalized random phase approximation. In the limit of weak interchain coupling, the stability limit of the normal phase with respect to the formation of a commensurate charge‐density wave is calculated.
Unified study of metals on pseudopotential theory: Lead
Authors: Sen D. , Sarkar S. K.
Published: July 2007

A comprehensive unified study of lattice‐mechanical and electronic properties of lead using the Heine‐Abarenkov model potential and Harrison's two‐parameter model potential is made. Screening functions proposed by Taylor and by Vashishta and Singwi, coupled with the two pseudopotentials are used in order to make a comparative study of their effectiveness. Properties studied include cohesive energy, equilibrium lattice parameter, second‐order elastic constants, pressure derivatives of second‐order elastic constants, equation of state (at T = 0), and phonon dispersion relation of crystalline lead and the resistivity and thermoelectric power of the liquid metal. Inspite of its excellence in reproducing one set of properties, Harrison's potential is found to be inadequate for a unified study. The Heine‐Abarenkov potential, on the other hand, is found to be better suited for the purpose. The liquid metal resistivity, however, is found to be much lower than the experimental value. In fact, it is pointed out that this is a common feature of all unified studies with pseudopotentials.
Group‐theoretical study of light‐induced electron‐spin polarization at the Γ‐point of cubic crystals
Authors: Wöhlecke M. , Borstel G.
Published: July 2007

Selection rules are calculated for the excitation of light‐induced spin‐polarized electrons at the center of the Brillouin zone of cubic crystals. The derivation of such rules is based on an application of the generalized Wigner‐Eckart theorem and tabulated coupling coefficients for unitary point groups. For almost all transitions a net electron‐spin polarization less than 50% is achieved. This is mainly due to the existence of bases which are linear combinations of spin‐up and spin‐down states. Tables are presented for the groups Oh, O, and Td. The connection of the results for Γ to those of the high‐symmetry lines is discussed.
Theoretical description of planar channeling process at small depths
Authors: Kührt E. , Wedell R.
Published: July 2007

A model for the description of planar channeling processes on the basis of the solution of the Fokker‐Planck equation is developped. It is applied for the calculation of the backscattering yield of protons and He‐ions in planar channels of several single crystals. The results are compared with recent measurements.
Green functions, power spectra, and Raman scattering of thin film polaritons
Authors: Oliveira F. A. , Cottam M. G. , Tilley D. R.
Published: July 2007

Linear response theory is used to evaluate Green functions for the electric field fluctuations in a general three‐layer system. The Green functions provide a description of the bulk polaritons, surface polaritons, and guided bulk polaritons. Particular consideration is given to polaritons arising from coupling of photons to optical phonons. The results are illustrated with dispersion curves and power spectra for different materials and geometries. The theory of light scattering by the excitations is then presented. A general formalism is developed to express the scattering cross‐section in terms of the Green functions. The full result contains a description of light scattering from bulk polaritons, guided bulk polaritons, and surface polaritons. However, the discussion is concentrated mainly on scattering from the localised surface modes.
Ellipticity effects in spin‐wave spectrum of thin magnetic films
Authors: Duda A.
Published: July 2007

The microscopic and resonance properties of the elliptic spin‐wave polarization are analysed for a Heisenberg ferromagnet thin film with an internal dipolar anisotropy and uniaxial surface anisotropy. The general case of arbitrary oriented external magnetic field is considered. It is found that the bulk and surface sources of the ellipticity influence distinctly the resonance spectrum of spin waves.
Compaison of the s band structure of face centred cubic and hexagonal close packed solids. I. The common zone approach
Authors: Betteridge G. P.
Published: July 2007

The relationship between electron energy levels and atomic environment is investigated by comparing the band structures of the two closely related structures, f.c.c. and h.c.p. Analytical expressions for the energy bands are obtained for a single s electron per lattice site in each structure, using a simple tight binding Hamiltonian incorporating interactions out to third nearest neighbours. A procedure is developed whereby both band structures are expressed in the same zone, thus enabling direct k space comparison. When viewed in this way the band structures for both crystal structures are shown to be very similar, the main deviations occurring over the boundary faces of this common zone.
Estimation of Covalency Effects in the Optical Spectra of Crystals Containing Iron Group Ions (II)
Authors: Kustov E. F. , Uskova L. I. , Klinchikov S. A.
Published: July 2007

In the first part of the paper the general matrices were derived for taking into account covalency effects. However, the solution of these matrices in an analytical form is difficult even for cluster with two electrons (holes). In this paper the covalency effects are taken into account and the parameters σ, Dq, E0, λe, λt, for some compounds with ions Ni2+, Cr2+, and Co2+ are calculated, using the restandardization of state functions of the central ion.
Water Vibrations in Ferroelectric K4Fe(CN)6 · 3 H2O
Authors: Anachkova E. , Ratajczak H. , Savatinova I.
Published: July 2007

Raman and infrared studies are performed of water vibrations of KFCT crystal in the region of 300 to 1700 cm−1. Spectral changes are followed in the temperature interval from room temperature down to 30 K. Special attention is paid to the band at 325 cm−1 whose temperature behaviour is typical for hindered rotation modes. Its frequency change is consistent with the change of the potential barrier restricting the water motion which was reported before.
Theoretical Analysis of Some Ground State and Optical Properties of Impurity F Centers
Authors: Harker A. H. , Vail J. M.
Published: July 2007

Comparisons with experimental data are used to assess calculations on F‐type centers, based on an approximate pseudopotential model, using flexible symmetry‐adapted variational wave functions. Moderate success is obtained for optical absorption of the linear FB center in KCI:Na and RbCI:Na, and for the triangular FB center in KCI:Na. Satisfactory results for nearest‐neighbor isotropic hyperfine interactions of the FA center ground state in KBr:Li are obtained only from point‐ion wave functions, although to describe adequately optical absorption of the F and FA(Li) centers in KBr requires that the ion‐size correction must be included. Luminescence from the type II FA center in KCI:Li is also found to require the point‐ion approximation, including angular momentum components l > 1.
Energy Levels of Intrinsic and Extrinsic Stacking Faults in Silicon
Authors: Marklund S.
Published: July 2007

The electronic interface states of ideal intrinsic and extrinsic stacking faults are calculated using an empirical pseudopotential. The results show two occupied bands above the valence band top (≈︁ Ev + 0.1 eV) for both the faults. No localised states near the conduction band are found which contradicts experimental results for the extrinsic faults interpreted as levels at ≈︁ Ec − 0.1 eV.
Static and Dynamic Structure Factors of Classical Plasma in Weak and Intermediate Couplings
Authors: Dubey G. S. , Chaturvedi D. K.
Published: July 2007

Using the sum rule arguments a self‐consistent scheme is utilized to calculate the short‐range correlations in classical one‐component plasma. The results are used to obtain the static and dynamic structure factors in a unified framework, which are found to be in reasonably good agreement with the available molecular dynamics data in the domain of weak and intermediate couplings ( Γ < 20). The longwavelength limit, where thermodynamic functions are related to the static structure factor, is also analyzed.