bluuebunny/crossref_metadata_2025 huggingface dataset:
A disorder model of melting
Authors: Vaid B. A. , Sharma K. C. , Syal V. K.
Published: July 2007

A disorder model of melting is proposed which provides a unified description of both the classes of liquids, viz. one contracting on freezing and the other one contracting on melting. In order to accomplish this, a generalization of the well‐known concept of packing fraction is affected and a calculation of thermodynamic quantities is presented which yields better agreement with the data.
More on the F‐Center Decay in Additively Colored NaF:LiF
Authors: Bosi L. , Gagliardelli P. , Nimis M.
Published: July 2007

Accurate measurements of the F‐center lifetime, τ(T), in additively colored NaF:LiF samples are presented as a function of the temperature, starting from 7.6 K. The anomalous behavior of the F‐center decay in NaF is confirmed only as regards the behavior of the relative quantum yield ηr(T): the presence of another decay channel for the F‐center electron, besides the jumping into the conduction band, is evidenced. The disagreement with data obtained by other authors is explained by the presence of aggregate centers in their samples. A τ(T)/ηr(T) behavior contrary to that presented by Stiles, Fontana, and Fitchen is observed. A critical review of models and guesses proposed in the literature is also presented in order to obtain a correct understanding of the nature of the relaxed excited state of the F‐center.
Multipole Theory of the Polarization of Solids by Point Defects. I. Dipole Approximation
Authors: Kantorovich L. N.
Published: July 2007

The electronic structure of solids is investigated where the electronic density is localized on structure elements (atoms, molecules, bonds). For these solids containing point defects the Schrödinger equation is obtained in the framework of a molecular cluster model taking self‐consistently into account the polarization of the rest of the solid outside the cluster. The polarization is considered in terms of multipole moments on structure elements induced by the defects neglecting exchange interactions. In the first part of the paper the general theory developed is applied to ionic crystals in the dipole approximation. The way to use the cluster symmetry in polarization calculations is also analyzed.
Space Distribution of the Chemical Composition of the Thermo‐Grown SiO2SiOxSi System
Authors: Lei Min‐sheng , Wang Zhi‐cheng
Published: July 2007

A simple statistical model for the oxygen distribution in a thermo‐grown SiO2 film on the surface of a silicon single crystal is proposed considering the bond saturation, and the oxygen distribution function of space coordinate for the SiO2‐SiOx‐Si system is deduced. Furthermore the space distribution function of the average chemical composition is obtained. Experimentally some SiO2 samples which are grown at temperatures from 900 to 1200°C, are investigated with AES and SIMS. These experimental results sustain the theoretical model. The SiOx transition region in the SiO2‐SiOx‐Si system is discussed, and the width of the transition region grown by thermal oxidation is ≈4 to 6 nm.
Phonon‐Polaritons in Bilayer Systems. Surface Phonon‐Polaritons
Authors: Wendler L. , Jäger E.
Published: July 2007

Surface phonon‐polaritons in a bilayer system consisting of two dielectric media with local, frequency‐dependent dielectric functions are studied. The dispersion relation for p‐polarized polaritons is derived. The dispersion curves and electric fields of surface phonon‐polaritons are presented for various cases in graphical form.
The Photoacoustic Effect in Semiconductors
Authors: Sablikov V. A. , Sandomirskii V. B.
Published: July 2007

A theory of the photoacoustic effect (PAE) in semiconductors is developed for the region of fundamental absorption, taking into account the generation of free electrons and holes, their diffusion, and recombination. The temperature on the illuminated surface of a semiconductor is calculated in a general form. The PA measurements allow to determine the diffusion length of carriers, the surface recombination velocity, and the bulk lifetime along with the light absorption coefficient. The qualitative difference of the results from the conventional Rosencwaig and Gersho (RG) theory is demonstrated. The problem of interpretating the experiments is discussed.
A Tetrahedron Method for Doubly Constrained Brillouin Zone Integrals Application to Silicon Optic Phonon Decay
Authors: Allen P. B.
Published: July 2007

Integrals over the Brillouin zone with two delta‐functions are considered. Such integrals are constrained to the intersection of two different constant energy surfaces. Following the discussion by Lehmann and Taut for the case of one delta‐function, the tetrahedron method is shown to yield simple analytic results when the energies and weight functions are linearly interpolated throughout a small tetrahedron. The method is illustrated with a calculation of the density of available two‐phonon decay channels of the Q = O optic phonon of Si.
Self‐Consistent Calculations of the Lattice Dynamics and Thermodynamics of Anharmonic Noble Metals
Authors: Malinowska‐Adamska C.
Published: July 2007

The reduced second‐order self‐consistent phonon approximation is applied to the investigation of the dynamic and thermodynamic properties of noble metals using the Morse and Rydberg and Varshni potentials as models of nearest‐neighbour central force interaction. The temperature and pressure dependence of the dynamic and thermodynamic functions of Cu, Ag, and Au in the high and low temperature limits are given and compared with experimental and other theoretical data. The behaviour of the physical quantities in the vicinity of the instability point is investigated, too.
The Semiconduction in the Molten Tl‐CuTlTe2 System
Authors: Uemura O. , Wada Y. , Takahara T. , Satow T.
Published: July 2007

Measurements of the electrical conductivity, the magnetic susceptibility, and the thermoelectric power for the molten Tl‐CuTlTe2 system are made in wide temperature and composition ranges. It is observed that the conductivity for the system falls abruptly at the composition of 66.7 mol% Tl and the thermoelectric power changes its sign around this composition. The diamagnetic susceptibility also shows a sharp maximum at the corresponding composition. These anomalies of electronic properties indicate that molten Tl‐CuTlTe2 system gives rise to a metal‐nonmetal transition at the composition of CuTl3Te2. The experimental results of the present work are compared with the previous data of molten Tl‐chalcogenide systems which exhibit a similar electronic behaviour and are discussed using some electron transport theories often employed in amorphous and liquid semiconductors.
Temperature‐Dependent Effective Masses in III‐V Compound Semiconductors
Authors: Sharma A. C. , Ravindra N. M. , Auluck S. , Srivastava V. K.
Published: July 2007

A study is made of the temperature dependence of the effective masses of carriers for some III‐V compound semiconductors essentially based on the model band structures of Kane and Penn. Using the nearly free electron model of Penn, we obtain an analytical expression for the matrix element P appearing in Kane's expression. The material dependence of P is hence explained. It is further seen that the temperature dependent effective mass is accounted, for, to a very large extent by the temperature dependence of the energy gap. This apart, the contribution of the electron‐phonon interaction term to the temperature dependence of the effective mass is shown to be significant.
Optical Absorption and Electronic Structure of NaCl:Ag+. A Multiple Scattering Xα Study of the (AgCl6)5− Cluster
Authors: Pedrini C. , Chermette H. , Goldberg A. B. , McClure D. S. , Moine B.
Published: July 2007

A multiple scattering Xα calculation is performed on the (AgCl6)5− cluster in order to study the electronic structure of the Ag+ impurity center in NaCl. The optical absorption spectrum is compared to theory and new symmetry assigments are made. The temperature dependence of the absorption bands is analysed and the Jahn‐Teller stabilization energy of the Ag+ excited state is measured.
Structure and Bonding in Cubic IV–VI Crystals. II. Instability of the TO(Γ) Mode: Unified Universal‐Parameter Treatment of the Group‐V Semimetals and Cubic IV–VI Semiconductors
Authors: Enders P.
Published: July 2007

The inherent instability of the cubic crystal structure of group‐V semimetals and of AIVBVI semiconductors exhibiting a cubic phase is treated on equal footing using the LCAO‐based approaches by Bersuker and Vekhter and by Volkov and Pankratov. By means of the universal parameter relation for the ppσ‐resonance integral, this instability is founded without adjustable parameters. The stability of the lead chalcogenides is explained on a semi‐quantitative level. The relation to Littlewood's pseudopotential‐based work is discussed.
Investigation of Z Center Conversions in KCl:SrCl2. I. Optical Measurement of the Kinetics of the Thermal Z1 → F, Z2 Decay
Authors: Kessler A. , Kizler P.
Published: July 2007

The absorption caused by a gradual conversion of a Z1 band during a linear heating into an F and Z2 band is obtained and analysed by fitting of rate equations. The results show that the decay proceeds in at least two phases. First F centers are formed and these seem to form with remaining Z1 centers Z2 centers then. Finally, at higher temperatures, the Z2 centers decay into F centers.
Spectroscopic Investigation of the Magnetic Properties of Ho2O2SO4
Authors: Kasten A. , Weschenfelder D. , Hess G.
Published: July 2007

Below Tn ‐ 3.4 K Ho2O2SO4 is antiferromagnetic with canted moments. The magnetic properties are strongly influenced by a crystal field splitting of the two lowest electronic Ho3+ states. The details of the magnetic short‐range order as well as the occurrence of intermediate ferrimagnetic phases in external magnetic fields may be explained within a model which takes into account the crystal field splitting as well as dipole and superexchange interactions up to third‐nearest neighbours.
Two Types of Low‐Temperature Phase Transitions in Uniaxial Ferromagnets with High Single‐Ion Anisotropy
Authors: Kazakov A. A.
Published: July 2007

It is mentioned, that the low‐temperature exchange hybridization of magnon modes in the uniaxial strongly anisotropic crystals with single‐ion anisotropy results in the presence of special points in magnon spectrum, where the energetic gaps become equal zero, and the dispersion mode law is of power character. The physical nature of this peculiarities occurrence is connected with the level crossing. It is shown, that the influence of these points essentially tells on the low‐temperature behaviour of magnetization and its derivatives by field and temperature.
Local‐Density‐Functional Approximation to the Energy Band Structure of TmS Using the Self‐Consistent Relativistic Linearized‐Augmented‐Planc‐Wave Method
Authors: Farberovich O. V. , Nizhnikova G. P. , Vlasov S. V. , Domashevskaya E. P.
Published: July 2007

The self‐consistent relativistic linearized‐augmented‐plane‐wave method is applied to local‐density calculation of electronic structure of TmS. It is found, that thulium monosulphide is a metal with a trivalent state of thulium. The influence of spin—orbital interaction is shown for different symmetry states of electrons. Calculated densities of states are used for the estimation of the electron—phonon coupling constant. And in conclusion it is shown that TmS is a high temperature Kondo‐like system.
The First‐Principles Calculation of the Norm‐Conserving Non‐Local Singular Atomic Pseudopotentials
Authors: Chulkov E. V. , Sklyadneva I. Yu. , Panin V. E.
Published: July 2007

The first‐principles non‐local singular atomic pseudopotentials are constructed for seventy‐five elements of the Periodic Table. The pseudopotentials are calculated with account of norm‐conserving. The energy dependence of the constructed pseudopotentials is studied. They are shown to be energy independent within the energy range which is characteristic of low‐energy electron excitations in solids. The values of the classical turning points of pseudopotential are calculated for all the elements considered.
Shubnikov‐De Haas Effect and Cyclotron Resonance in p‐CdSb
Authors: Cisowski J. , Portal J. C. , Arushanov E. K. , Broto J. M. , Huant S. , Brunel L. C.
Published: July 2007

Shubnikov‐de Haas (SdH) effect and cyclotron resonance (CR) in single crystal samples of p‐CdSb are studied in magnetic fields up to 19 T. The angular dependence of the SdH periods is determined as well as the cyclotron effective mass for different hole concentrations. The hole effective masses along the three crystal axes are obtained and compared with theoretical calculations.
Electron Paramagnetic Resonance Investigation of Pb‐ and Ge‐doped CdTe
Authors: Bilbé R. M. , Nicholls J. E. , Davies J. J.
Published: July 2007

EPR spectra are observed from Pb and Ge ions in CdTe. The spectra are characterized by isotropic g‐values of 2.2055 and 2.1450, respectively, and show strong anisotropic hyperfine interaction with the neighbouring tellurium ions. The resonances result from a hole localized primarily on the tellurium ligands and the results are discussed in relation to group IV ions in other II–VI compounds.
Polarizability of Donors in Polar Semiconductors. Effect of a Weak Magnetic Field
Authors: Cahay M. , Kartheuser E.
Published: July 2007

The electrical polarizability tensor of shallow donors in polar semiconductors is calculated in the presence of a weak magnetic field. A variational treatment of the donor is developed in the framework of the effective‐mass theory, including the effects of interaction between the charge carriers and the longitudinal‐optical (LO) phonons within the static approximation. The effective‐mass Hamiltonian of the donor allows for central‐cell corrections by means of a phenomenological impurity potential. The results are compared with previous theoretical work and experiment in the case of donor impurities in Si. It is shown that the donor polarizability depends strongly on the form chosen for the model impurity potential and undergoes a 30 to 50% decrease due to the electron—(LO)phonon interaction in the case of impurities in III–V and II–VI compounds, respectively.
Stimulated Raman Effect on Plasmons and Longitudinal Plasmon‐Phonons in Simple Cubic Crystals
Authors: Merten L. , Goltsche W.
Published: July 2007

It is shown that Stokes and anti‐Stokes waves anharmonically can couple not only with transverse but also with longitudinal quasi‐particles (stimulated Raman effect). As examples the coupling with plasmons and longitudinal plasmon‐phonons in simple cubic crystals is treated. The dispersion functions can be represented by simple analytic expressions, if the coupling with the anti‐Stokes waves is neglected against the coupling with the Stokes waves. In this approximation one “stimulated region” exist for plasmons and two for longitudinal plasmon‐phonons.
Anharmonic Thermal Atomic Vibrations in the Cubic Phase of Cs2NaNdCl6 Single Crystals
Authors: Makarova I. P. , Misyul S. V. , Muradyan L. A. , Bovina A. F. , Simonov V. I. , Aleksandrov K. S.
Published: July 2007

Thermal atomic vibrations in the cubic phase of Cs2NaNdCl6 single crystal undergoing the structural phase transition (PT) at 138 K are investigated from the data of X‐ray diffraction obtained at 278, 218, and 148 K. A significant anisotropy of thermal vibrations and their deviations from harmonic behaviour are found for the Cl‐atoms of the structure. These atoms displace from their equilibrium positions below PT due to the tilts of the octahedral groups.
Optical Phonons in Amorphous Silicon Oxides. II. Calculation of Phonon Spectra and Interpretation of the IR Transmission of SiOx
Authors: Lehmann A. , Schumann L. , Hübner K.
Published: July 2007

Basing on the theoretical investigations of Part I of this work a simple model for the calculation of the density of vibrational modes and of the IR response function of the geometrically and chemically disordered material SiOx (0 < x ≦ 2) is developed. This model leads for the first time to a theoretical interpretation of LO—TO splittings and of chemical shifts of the minima of IR transmission spectra of thin SiOx films prepared by reactive sputtering.
Thermodynamic Functions of the Electron Fluid for a Wide Density—Temperature Range
Authors: Richert W. , Ebeling W.
Published: July 2007

On the basis of the present knowledge on the analytical behaviour of the thermodynamic functions in three regions: dense degenerate electron‐fluid, low‐density electron gas, and Wigner lattice, Padé approximations are constructed. The proposed formulae cover the entire (non‐relativistic) range of density and temperature and are for T = 0 in good agreement with the points found recently by Monte Carlo calculations.
Resonatorless Optical Bistability Based on Increasing Nonlinear Absorption
Authors: Hennebeger F. , Rossmann H.
Published: July 2007

A new type of optical bistability is presented. Instead of a resonator the intrinsic feedback between the optical excitation of carriers and their recombination is used. Optical bistability appears, if the absorption coefficient increases with growing carrier density. Both propagation effects and carrier diffusion are considered. Analytical model calculations are carried out for an abrupt behaviour of the absorption coefficient. The results explain the hysteresis in the transmittivity of CdS, recently observed.
On the Electronic Structure of Palladium—Hydrogen and Platinum—Hydrogen Systems
Authors: Seifert G. , Fritsche H.‐G. , Ziesche P. , Heera V.
Published: July 2007

The interaction of hydrogen with palladium and platinum is studied on the basis of cluster calculations using the SW‐Xα method in a semirelativistic variant. Energy level spectra, density‐of‐states curves, and charge distributions are represented and discussed with respect to other theoretical and experimental investigations. The dominant role of covalent bond between hydrogen and palladium/platinum is illustrated. The results of the calculations show that for a heavy element as platinum relativistic effects can influence the bonding between atoms in a qualitative way. The less stability of the hydrogen—platinum system — compared with the PdH system — is explained as a relativistic effect.
Scattering by Ions near Interfaces
Authors: Gerlach E.
Published: July 2007

Using the “energy loss method” the resistivity is calculated due to scattering by an ion being inside or outside a conducting film (placed between two insulating materials). As examples a half‐space and a thin film are studied.
Geometry and Energy of Disclinations in Topologically Disordered Systems
Authors: Richter A. , Romanov A. E. , Pompe W. , Vladimirov V. I.
Published: July 2007

A model for the description of topologically disordered structures is proposed which is characterized by structural units that are odd‐ and even‐member rings in covalently bound materials. The energy of such a system can be calculated by the introduction of line defects, disclinations, and dislocations. Several arrangements of disclinations and their relations to the geometry of the disordered structure are discussed. The calculation of the elastic strain energy is performed in terms of screened disclination elements which are disclination dipoles, disclination quadrupoles, and disclination loops combined with dislocations. The main contribution to the strain energy of the system is given by the self‐energy of these screened elements. Interactions between them are taken into account and result in negligible correction terms if the distance between the screened units is larger than their size. Structural averages over the disordered defect structure are performed by the introduction of short‐range order parameters.
Thermal Conductivity of Rare‐Earth Orthoferrites at Reorientation Phase Transitions
Authors: Barilo S. N. , Ges A. P. , Soshnikov L. E. , Smirnova T. V.
Published: July 2007

The dependence of thermal conductivity on temperature is measured for the first time for three compositions of rare‐earth orthoferrites (REO): SmFeO3, Sm0.4Gd0.4FeO3, and Sm0.65Er0.15Tb0.2· ·FeO3 in the spin reorientation region (SRR). Characteristic anomalies are found on curves λ(T) at temperatures of reorientation phase transitions. Presence and form of the anomalies are associated with the summary effect of the changes of the specific heat, averaged free‐path length of phonons, and their averaged velocity of propagation. The behaviour of the averaged velocity of the phonon propagation at magnetic phase transitions is studied on the basis of the temperature dependence of the velocity of the shear sound wave. An interpretation is given by using the phenomenological model conformably to the case of REO. The values of the four‐fold anisotropy Kb = 7.97 × 103 J/m3 and magnetoelastic coupling B55 = 4.472 × 106 J/m3 constants are estimated for the compound Sm0.6Gd0.4FeO3. The temperature dependence of two‐fold anisotropy constant Ku(T) in the spin‐reorientation region and its ranges are calculated by way of example of a samarium–gadolinium orthoferrite.
Effective Charges and Their Pressure Dependence in α‐LiIO3
Authors: Cerdeira F. , Lemos V. , Melo F. E. A. , Cardona M.
Published: July 2007

A simple static charge model is formulated for the zone‐center optical modes of α‐LiIO3 which are simultaneously Raman and ir‐active. The model predicts successfully the experimental values of the oscillator strengths for all but one mode (E1‐librational) and serves to clarify previous discrepancies in mode assignments resulting from Raman and ir‐reflectivity measurements. From previously reported experimental data the pressure dependence is calculated of the effective charges and the angle between the I‐O bond and the C3v axis of the IO pyramids. The self‐consistency of these results is discussed using simple arguments based on rigid spheres and ionic radii.
Heat Conductivity of the Cooperative Vibronic System TmVO4
Authors: Daudin B. , Mutscheller W. , Wagner M.
Published: July 2007

TmVO4 thermal conductivity is measured between 80 mK and 50 K for H = 0 and 70 kOe. It is found that a large phonon scattering is present at H = 0 compared to the H = 70 kOe measurement. Using a Mori‐Zwanzig formalism, a theoretical analysis may explain the general behaviour in the temperature region below the phase transition temperature.
The Frustration of Antiferromagnetic Bonds in the Screw Dislocation
Authors: Nakamura T. , Kawamura K.
Published: July 2007

The influence of a screw dislocation on the antiferromagnetic ordering is studied in the mean field theory. The topological disorder of a dislocation is exclusively taken into account. A formulation, which has been developed previously in the electron problem, is applied.
Plasmon and X‐Ray Chemical Shifts in Some Copper Systems
Authors: Chattopadhyay T. , Chetal A. B.
Published: July 2007

X‐ray chemical shifts in the systems CuCl, CuBr, CuI, CuSe, Cu2S and Cu2Te are studied using a Cauchois‐type X‐ray spectrograph. The shifts are correlated with the plasmon shifts. It is observed that as the chemical shift increases the plasmon shift also increases. It is also observed that as the partial charge on the copper ion increases both, the chemical shift and plasmon shift increase, except in Cu2S.
ESR and ODMR of ZincVacancy‐Associated Defects in ZnSe
Authors: Schrittenlacher W. , Nelkowski H. , Pradella H.
Published: July 2007

ESR and ODMR of halogen‐free and iodine‐doped ZnSe single crystals are investigated. In the case of the halogen‐free samples four distinct associated centres are detected by ESR. The iodine‐doped crystals contain only one type of acceptor centres attributed to a zinc vacancy associated with an iodine ion. The g‐tensor components of this centre are g1 = 1.955, g2 = 2.192, g3 = 2.221 with a tilting angle of 2°. The g‐values and tiltings of the acceptor centres are discussed in a model previously developed for similar centres in ZnS, although this model cannot account for the finer structures. From the close similarity of the ESR and ODMR anisotropies and from the conformity of emission, ODMR acceptor, and ODMR donor resonance in their dependence on optical energy the participation of these centres in the donor‐acceptor emission process is concluded. The 77Se hyperfine splitting is observed, and in addition for the first time a ligand hyperfine structure of a selfactivated centre in ZnSe is identified (of 127I). Finally, arguments are given for the existence of a deep iodine‐associated donor complex.
Lattice Dilatation in High‐Concentration Binary Solid Solutions
Authors: Maiti S. N. , Roy D.
Published: July 2007

A simple extension of Huang's theory of lattice dilatation for low concentration is found to reproduce Retger's law of additivity of molar volume. Deviation from the law is accounted for by considering the elastic strength of the defect to be concentration dependent and an attempt is made to calculate the elastic strength of the defect from the parameters of the perfect crystal. The method is then used to predict the concentration dependence of volume over the entire concentration range of eight alkali halide solid solutions and two metallic alloys and fairly good agreement is obtained.
Short‐Range Order and Magnetic Properties in Amorphous Heisenberg Ferromagnets
Authors: Maksymowicz A. Z.
Published: July 2007

Amorphous AcB1−c alloys of magnetic A‐and non‐magnetic B‐atoms are considered. Effects of atomic short‐range order, difference 〈ZA〉 – 〈ZB〉 of the average coordination numbers, and fluctuations of ZA are discussed. Fluctuations in the exchange integral are not taken into account. Calculations based of the Bethe‐Peierls‐Weiss mean‐field model are compared with results for the Ising model, S = 1/2, with spin‐spin correlations included. As expected, the critical concentration for the onset of magnetism is increased while the Curie temperature and susceptibility are decreased due to magnetic correlations. The same, yet much stronger tendency is induced by the atomic short‐range order favouring A‐B pairs or by fluctuations of ZA when the effect is rather weak. Opposite tendency is observed when 〈ZB〉 < 〈ZA〉. Deviations from the Curie‐Weiss law lead to an upward curvature of 1/X against T, yet the effect is too small to explain a strong upward curvature as observed in experiment, especially near TC.
The Magnetic Behaviour of the Pseudobinary Compounds Gd2AuxAuxAl1−x
Authors: Brédimas V. , Gamari‐Seale H. , Papatriantafillou C.
Published: July 2007

Theoretical calculations and experimental results are presented on the magnetic behaviour of Gd2AuxAuxAl1‐x x ϵ [0, 1]. While the theoretical calculations using the mean field approximation and RKKY theory for indicate antiferromagnetic ordering for x < 0.2 and ferromagnetic ordering for x > 0.2, susceptibility measurements indicate a rather complicated situation with two transitions in the vicinity of 200 and 25 K (dependent on x). Cluster formation is observed and shape effects are present.
Low‐Temperature FMR and FMAR Measurements of Metal Single Crystals. I. General Consideration, Experimental Techniques
Authors: Půst L. , Frait Z.
Published: July 2007

The method of evaluating of FMR and FMAR parameters in cubic metal crystals using the solution of resonance equations is discussed based on the precise measurement of the local demagnetizing field by means of EPR of the free radical DPPH. The temperature dependence of the effective g‐factor of DPPH is determined between 3.5 and 300 K and a great influence of the DPPH sample shape is found.
Electronic Processes in Electrode Materials of AxMX2‐Type
Authors: Molenda Janina
Published: July 2007

Electronic processes taking place during intercalation in AxMX2‐type electrode materials (A  Li, Na; M = transition metal; X = O, S) are discussed. It is shown that for cobalt bronze, NaxCoO2−y, taken as representative of the electrode materials under consideration, the variation of Co‐Co interactions, accompanying the intercalation process, leads to the modification of band structure of the cathode material bringing about the Mott transition of metal‐non‐metal type. The experimental results indicate close correlation between the electronic structure of the cathode material and its potential.
Ellipsometric Determination of the Optical Constants of ZnIn2S4
Authors: Logothetidis S. , Ves S. , Spyridelis J.
Published: July 2007

The optical constants n ⟂, k⟂, n∥ and k∥ of the uniaxial layered compound ZnIn2S4(III) are determined in the fundamental absorption edge region 1.8 to 3.4 eV (0.683 to 0.365 nm) using ellipso‐metric measurements only on a plane perpendicular to the optical axis. The method is based on an efficient and suitable algorithm. Using band structure calculation it is possible to explain the different behaviour of k⟂ and k⟂ in this region as well as to assign Eg(⟂) = 2.90 eV and Eg(∥) ≈ 3.05 eV to the corresponding interband transitions.
Detection of Manganese Photoionization in Cd1−xMnxTe Solid Solutions
Authors: Sokolov V. I. , Chernyaev V. V.
Published: July 2007

Electroreflection, photoconductivity, and Electroabsorption spectra are studied of Cd1‐xMnxTe crystals with 0.0005 ≦ x ≦ 0.6 at 4.2 K at energies less than the free exciton line (FEL) energy in electric fields from 0.5 to 20 kV cm−1. The peculiar form of the spectra and their field dependence enables the conclusion that the observed peaks are associated with the type (d5 + hω → d6) photoionization of Mn2+ ions.
Photoelectromagnetic Effect and Photoconductivity in Quantizing Magnetic Fields
Authors: Knap W. , Kossut J. , Mycielski J.
Published: July 2007

The photoelectromagnetic effect (PEM) and photoconductivity (PC) are considered in a semiconductor in a quantizing magnetic field in the case of intraband excitations (e.g. cyclotron resonance). It is shown that although one is dealing with carriers of the same sign of charge the PEM effect is possible to be observed if the diffusion constants for lower and upper Landau levels are different. The formula for the diffusion constant is derived as a function of the energy of a carrier. Its value is estimated and shown to enable the observation of intraband resonances in PEM in real crystals. A possibility of determination of the Landau level lifetime from simultaneous measurements of the PC and PEM effects is discussed.
Atomic Operators in the Theory of Narrow‐Band Magnetic Semiconductors
Authors: Erukhimov M. Sh. , Ovchinnikov S. G.
Published: July 2007

An exact equivalence of s—dexchange model and the degenerate Hubbard model is shown using the atomic operator representation. The analogy of exact Nagaoka's theorem is proved for a narrowband semiconductor with one carrier and infinite exchange interaction. Using the diagram technique for the Hubbard operators the energy of acoustic and optical magnons is calculated in linear approximation on carrier concentration with allowance for both, kinetic energy and intersite Heisenberg exchange interaction.
Magnetic Properties of Tb2O2SO4
Authors: Kasten A. , Hess G.
Published: July 2007

Below TN = 3.9 K Tb2O2SO4 is antiferromagnetic with canted moments. In the ordered phase, two of the four neighbouring moments are antiparallel and two nearly perpendicular to that of a central ion. The angular dependence of magnetisation, magnetic susceptibility, and spectroscopic Zeeman effect is analysed and the interaction constants (dipole and superexchange) are derived. The crystal field splitting of the two lowest Tb3+ states seems to be vanishingly small. Mean field calculations for applied external fields yield a variety of ferrimagnetic phases with various fractions of the saturation magnetisation, depending on temperature and field direction.
On the Dielectric Function of Three‐Level Systems under High Excitation. II. Exciton—Biexciton Transitions and Population Effects in CuCl
Authors: Hönerlage B. , Bigot J. Y.
Published: July 2007

Using the dielectric function calculated for a three‐level system in the presence of two coherent light fields, renormalization effects are discussed due to a finite level population, to two‐photon transitions, and to exciton—biexcition transitions for CuCl.
Recursion Method with Plane Wave Basis for Band Structure Calculations
Authors: Brüstel U. , Unger K.
Published: July 2007

The recursion method of Haydock et al., being well suited for the determination of local densities of states using a basis set of localized functions, is transferred to band structure calculations with a plane wave basis set. This method, which is applicable to an arbitrary Hamiltonian matrix, turns out to be a fast procedure for the determination of energetically low lying eigenvalues and exhibits some advantageous features leading to a reduction of computational effort, compared with other methods.
Low‐Density Approach to RPA Self‐Energies
Authors: Thuselt F.
Published: July 2007

A low‐density approach to RPA quasiparticle energies including carrier—impurity interaction in second Born approximation at T = 0 is derived. These energies depend essentially on the “plasma cut‐off vector” q* ∼ (nnme + nhmh)1/4 time sprefactors that depend only on the mass ratio memh. Common plasmon‐pole models lead to the same results. It comes out that the approach presented here can be used with success for electron—hole plasmas and most of the highly‐doped semiconductors.
Dispersion of Exciton Polaritons in a Monoclinic Cyanine Dye Crystal. Evaluation of the Reflectivity on Arbitrary Faces
Authors: Hayne Th. , Weiser G.
Published: July 2007

Normal incidence reflectance spectra of the optically biaxial dye bis(N‐ethyl‐thiazoline‐2yl)‐trimethin cyanine iodide are studied on various crystal faces. The spectra vary considerably because the mixing of different electronic transitions by the electromagnetic wave depends on the orientation of the wavevector k. The polarization of the excited polariton modes rotates in the absorbing region if k is not parallel or perpendicular to a symmetry axis. Strength and position of the optical resonances may deviate strongly from the properties of the underlying excitonic transitions. The spectra agree well with the solutions of the Fresnel equation using a model dielectric tensor which approximates the excitonic transitions as Lorentz oscillators.
Resonant Energy Transfer between Localized Excitations in a Linear Polymer Chain
Authors: Čabrič B. , Ristovski Lj. M.
Published: July 2007

A linear molecular polymer chain formed by replacing two host molecules by two identical impurities is investigated. Applying a particular theoretical approach the energies of localized excitations appearing in the system are determined and the dependence of these energies on the distance between the impurities is discussed. The theoretical approach is formulated in a way that reduces the problem to the analysis of an ideal polymer chain with some extra off‐diagonal terms in the Hamiltonian. These extra terms are considered as an interaction caused by the nonideality of the polymer chain.
About the Low‐Temperature Dependence of Activation for Capture Cross‐Sections of Charge Carriers in Semiconductors with Persistent Photoconductivity
Authors: Kovarskii V. A. , Chernysh L. V. , Belousov A. V.
Published: July 2007

A calculation is made for the capture cross‐section of charge carriers on the local centres in semiconductors taking into account the anharmonicity of highly excited states of the ground electron—vibrational term. Near the cross‐over point of the terms the anharmonic potential is approximated by a linear term that gives the decay of the excited electron—vibrational state into the continuum of states. A quantum‐statistical calculation of the multiphonon radiationless capture probability is performed with the help of the coherent states method. It is shown that activation temperature dependence for the capture cross‐section can be obtained for the low‐temperature region: k0T < hω (ω the optical phonon frequency). The developed theory is compared qualitatively with experimental data.
On the Proton Conductivity Mechanism in Systems Containing Hydrogen‐Bonded Chains
Authors: Krasnogolovets V. V. , Tomchuk P. M.
Published: July 2007

The transfer of charge defects (excess protons or proton holes) along the hydrogen‐bonded chains of a series of systems is considered by use of the small polaron model. An expression is derived for the proton electric conductivity, taking into account the strong coupling of the deffect with longitudinal optical polarizational phonons and with the longitudinal acoustic phonons renormalized due to phonon—phonon interaction. The space‐charge‐limited proton current is considered. A comparison with experiments is made.
Mathematical Modeling of the Orientation Distribution Function by the Vector Method of Quantitative Texture Analysis
Authors: Schaeben H.
Published: July 2007

In contrast to metallurgy, where quantitative methods of texture analysis are frequently used to check for certain types of preferred orientations as generated by well‐defined processes of production, in geosciences the same methods are applied in order to reconstruct the history of deformation the sample has undergone. More detailed, the reproduced orientation distribution function (ODF) should be translated back in terms of deformation processes, which match with the entire geological situation. Within this concept, problems of the uniqueness of the reproduced ODF become essential. As the vector method provides certain advantages in comparison to the harmonic method for applications of texture analysis in geosciences, the numerical procedure of solution involved in it is mathematically analysed with special emphasis laid on problems concerning the non‐uniqueness of the solution provided by the vector method in its original form. Finally, the problem is mathematically restated in a well‐posed form, which leads to both, an improved solution and numerical algorithm.
Phase Transition and Soft Mode Behaviour in Superionic Copper Halides
Authors: Ghosh S. , Chatterjee S. , Basu A. N.
Published: July 2007

Phase transitions of superionic conductors are studied extensively at present. Here the lattice dynamical aspect is considered of both the temperature and pressure induced phase transition of such crystals. A study of the lattice dynamics of superionic Cu halides in the quasi‐harmonic approximation shows that it is possible to predict the onset of a phase transition in these crystals. This onset is indicated by an instability in the equation of state and by the softening of one or more phonon modes.
Study of Cohesion, Harmonic and Anharmonic Elastic Properties of CaF2—SrF2 Mixed Crystals
Authors: Singh R. K. , Agnihotri Neeta , Suryanarayana S. V. , Sanyal S. P.
Published: July 2007

Cohesive and harmonic and anharmonic elastic properties are investigated of CaF2—SrF2 mixed crystals using a three‐body interaction potential which consists of the long‐range Coulomb and three‐body interactions and short‐range van der Waals‐attraction and overlap repulsion, effective upto the second neighbour ions. This two parameter model potential successfully predicts the cohesive energy, the higher order elastic constants, and the pressure derivatives of the second order elastic constants of CaF2—SrF2 mixed crystals.
Lattice Dynamics of Al
Authors: Soma T. , Itoh T. , Kagaya H.‐Matsuo
Published: July 2007

The experimentally observed phonon curves for Al are reproduced using second‐order perturbation theory and the local Heine‐Abarenkov model potential with volume‐dependent parameters. The effect of different forms of exchange and correlations on the phonon frequency, the compressibility problem, and the contributions from the third‐order perturbation term are investigated.
Electron—Phonon Interaction in Ferromagnetic Semiconductors
Authors: Wesselinowa Julia M.
Published: July 2007

A Green's function technique is used to study the effects of the electron—phonon interaction in the s—d model. The renormalized energy, the polarization, and the damping of the electrons are obtained and numerically calculated taking parameters for CdCr2S4. The phonon spectrum and damping are discussed, too.
The Electronic Structure of Octahedral Platinum and Iridium Clusters (Pt6, Ir6). A Comparison between Xα‐SW and EHT Calculations
Authors: Bartel H.‐G. , Scholz G. , Neumann R. , Schmidt W.
Published: July 2007

MO calculations are performed using the Xα‐SW and the EHT methods. The calculated DOS profiles of Pt6 and Ir6 show a good coincidence with those from relativistic bulk band structure calculations (RAPW). The use of a 5d/6s basis set with VSIP's from HFS SCF calculations allows a sufficiently good coincidence of the EHT eigenvalue spectrum with the corresponding Xα‐SW spectrum. Therefore a further adjusting of EHT parameters on Xα‐SW results is not necessary.
Polarized Positron Annihilation and Enhancement Effects in Ferromagnetic Iron
Authors: Šob M. , Szuszkiewicz S. , Szuszkiewicz M.
Published: July 2007

By comparison of the independent particle model calculation of the positron annihilation spectra with the spin‐polarized angular correlation results in iron, the polarization of positrons before annihilation is determined to be 0.21 ± 0.05. The character and magnitude of the differences between the independent particle model and experiment is not influenced by the presence of the magnetic field. The explanation of these deviations could be a crucial test for recent treatments of the electron‐positron interaction in metals.
Low‐Temperature Absorption Spectrum of Ni2+ Ion in Single Crystals of Ni2NbBO6
Authors: Borromei Renate , Cavalli E.
Published: July 2007

Polarized absorption spectra of single crystals of Ni2NbBO6 in the range 5000 to 28000 cm−1 are measured at liquid‐helium temperature. The bands are interpreted in terms of “ligand field transitions” with a site perturbation expressed as the sum of two contributions, one major connected to a reduction of symmetry Oh → C3v and one minor connected to C3v → Cs. By assuming that most of the intensity derives from the static low symmetry distortion a full explanation of the intensity behaviour of the bands with the polarisation of the light is given.
SERS from Ag Colloids in Alkali Halide Crystals
Authors: Reimer H. , Fischer F.
Published: July 2007

Surface‐enhanced Raman scattering is investigated on NaCl, KCl, KBr, and KI crystals doped with Ag. By stepwise annealing the controlled formation and growth of Ag colloids out of Ag− centres can be performed. Raman scattering and optical absorption at 20 °C under comparable conditions allow the conclusion that “active sites” at the colloid surface are responsible for the increase and decrease of the SERSspectrum. Comparative SERS at LNT show the preferred excitation near the upper limit of the crystal phonon spectrum.
Stochastic Self‐Oscillations in a Two‐Temperature Electron—Hole Plasma in a Semiconductor
Authors: Bonch‐bruevich V. L. , Ky Le Vu
Published: July 2007

The nonstationary states are studied of an electron—hole plasma generated and heated by an interband light absorption in a direct gap semiconductor. Account is taken of phonon and/or radiative as well as of interband impact recombination processes; adiabatic approximation (“slow recombination”) is not employed. Explicit conditions are stated underwhich the system sustains regular (periodic) or stochastic self‐oscillations of the concentration and temperature of the charge carriers.
On the Determination of Pseudopotential Parameters and the Comprehensive Study of Metallic Properties
Authors: Gohel V. B. , Acharya C. K. , Jani A. R.
Published: July 2007

The practical usefulness of the method of determination of pseudopotential parameters due to Senoo et al. and Soma is examined. It is found that this method is useful for the comprehensive study of electronic und atomic properties of simple metals. The wave vector q0, where the form factor becomes zero, plays a vital role and its correct determination is highly desirable. The present work deals with such study, calculations of band energies at major symmetry points, evaluation of electrical resistivity, and thermoelectric power of aluminium (liquid and solid phases).
The Auger Spectra from Alloys Effect of Partial Long‐Range Order
Authors: Drchal V. , Kudrnovský J.
Published: July 2007

The intraatomic core—valence—valence Auger spectra from partially ordered alloys characterized by the long‐range order parameter S are investigated. The combined effect of disorder and electron correlations is studied for the case of a filled valence band using the coherent potential approximation to treat disorder and the local ladder approximation for the two‐particle Green function that determines the Augerspectrum. The theory is illustrated numerically on a simplified model of analloy.
Local Optical Centers in Rare Gas Crystals
Authors: Ratner A. M. , Tarasova E. I.
Published: July 2007

A comparison between microscopic calculated data and experimental results permits to suggest the character of crystalline surroundings of a local center and to differentiate between surface and bulk centers. The deformation of an excited atomic state is investigated which reduces due to lattice deformation. The analysis of a site exciton state provides some informationon the resonance contribution to the energy.
Luminescence Decay in NaI:Pb
Authors: Baltog I. , Mihuţ L.
Published: July 2007

The dependence of the photoluminescence spectra of NaI:Pb excited in the A absorption band region on crystal temperature and dispersion state of the impurity is studied. The luminescence decay time measurements are performed for each emission band. Two lifetime components can be resolved for the AX emission, the slow component value being temperature independent. Two life‐time components independent of the temperature are observed also for the emission band of the precipitated state. The luminescence of the precipitated state is supposed to be of excitonic type due to a new phase as a result of the aggregation of the impurity. The decrease of the lifetime values of each component towards the higher energy side of the spectrum is explained by modification of the potential energy surface of the luminescent centre by the lowering of symmetry.
On the Theory of Relaxation for Systems with “Remnant” Memory
Authors: Nigmatullin R. R.
Published: July 2007

The investigation of the universal response of an electromagnetic, acoustic, and mechanical force indicates the existence of relaxation processes with memory. It is shown that the form of the polarization current I(t) ∼︁ (ωpt)−(1+m) for (ωpt ≫ 1) can be explained on the basis of a dipole relaxation with a “remnant” memory. In accordance with theexperimental data a memory function is found which describes in one case the exponential decay I(t) ∼︁ exp (—λt) which is equivalent to the absence of memory and in the another case it transforms into a harmonic oscillator equation (full memory). From this theory theexistence of a “superslow” relaxation process also follows, in which the changing of polarization is slower than its first derivative. Such processes are also observed experimentally and are described by linear differential equations in fractional derivatives. The relationship between the experimental exponent m and the derivative exponent λ is found.
On the Calculation of the Residual Resistivity of Precipitates
Authors: Gläser U. H.
Published: July 2007

The change in the residual resistivity of alloys due to clustering is calculated by means of the t‐matrix and without adjusting any free parameter. A criticism of the widely used scattering potentials is given. Basing on isotropic free electron transport the applicability of the theory is limited to small clusters. An initial increase in the residual resistivity due to the formation of Guinier‐Preston zones is found for AlZn and AlCu. The different local Fermi momenta in the matrix and in the clusters have an important influence on the resistivity.