bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractBasing 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

AbstractOn 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

AbstractA 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

AbstractThe 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.
Geometry and Energy of Disclinations in Topologically Disordered Systems
Authors: Richter A. , Romanov A. E. , Pompe W. , Vladimirov V. I. 
Published: July 2007

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractTmVO4 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

AbstractThe 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

AbstractX‐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

AbstractESR 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

AbstractA 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

AbstractAmorphous 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

AbstractTheoretical 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

AbstractThe 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

AbstractElectronic 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

AbstractThe 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

AbstractElectroreflection, 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

AbstractThe 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

AbstractAn 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

AbstractBelow 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

AbstractUsing 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

AbstractThe 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

AbstractA 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

AbstractNormal 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractIn 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

AbstractPhase 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

AbstractCohesive 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

AbstractThe 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.