bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Determination of Enhancement Factors of Solvent Diffusion
Authors: Hagenschulte H. , Heumann Th. 
Published: July 2007

AbstractIn dilute binary f.c.c. alloys of the substitutional type a nonlinear increase of the solvent diffusion coefficient D by alloying solutes with positive excess charge is frequently observed. The formation of vacancy–impurity complexes leads to this increase, which is usually described in terms of the enhancement factors bi in the following manner: D(NB) = D(0) (1 + b1NB + b2NB2 + + b3NB3 + …). The determination of enhancement factors by using this polynomial is critically discussed. From the complex model according to Dorn and Mitchell and more generally according to Bérces and Kovács and its application to solvent diffusion by Hehenkamp et al. it becomes reasonable, that the dependence of the solvent diffusion coefficient on the solute concentration is approximately given by: D(NB) = D(0) exp (b1NB). This relation, which is already known in the literature for a long time, yields an alternative method for the detemination of enhancement factors. Results are presented for many noble metal systems and discussed in the frame of two different estimation methods of the Gibbs free energy of binding δg1 of a vacancy–impurity pair calculated from the enhancement factors b1 and b2.
The Effect of Stress on the Lattice Instability of a TiNi Alloy
Authors: Li D. Y. , Wu X. F. , Ko T. 
Published: July 2007

AbstractThe behavior of the phase transformation in equiatomic TiNi alloy during thermal cycling under applied stresses is studied by measuring the electical resistivity and investigating the diffuse streak diffraction of electron and the X‐ray diffraction. The results show that the stress has a strong effect on the lattice instability. The tensile stress promotes the softening of phonon modes which relate to the nucleations of the R phase and the martensitic phase so that the tensile stress is favourable for the formation of the R phase and martensitic phase, while the compression stress has negative effects. The investigation shows that the effect of stress on 〈111〉 longitudinal phonon mode is larger than that on 〈110〉 transversal phonon mode. The tensile stress enhances particularly the softening of 〈111〉 longitudinal phonon mode which corresponds mostly to the R phase transformation, but the compression stress is unfavourable for it. It is identified that the diffuse streak diffraction patterns of electron associated with more R phase induced by the tensile stress arises from the softening of 〈111〉 longitudinal phonon mode.
A Hamiltonian Model of Liquefaction and Crystallization in Three Dimensions
Authors: Maćkowiak J. 
Published: July 2007

AbstractA model of a classical gas on a three‐dimensional sphere is discussed. The sphere is partitioned into cells, each corresponding to a different particle. The potential of each particle in its own cell is zero and, outside the cell, of order ln n, n being the number of particles. The two‐body interaction between the particles is shown to provoke (in the thermodynamic limit) a gas–liquid phase transition and a liquid–solid transition at a lower temperature. Both transitions are accompanied by a discontinuous drop of entropy.
Dispersion Curves of Phonon‐Plasmon Coupled Polaritons in n‐Type AlxGa1−xAs
Authors: Chang C. P. , Pai K. F. , Fang C. S. , Tse W. S. 
Published: July 2007

AbstractThe dielectric constant method is used to calculate the dispersion curves of phonon‐plasmon coupled polaritons in n‐type AlxGa1−xAs. The method is based on the assumption that the polarisabilities of the ion system and the electron system are additive. The conventional additive form is used for the dielectric function of the lattice. The Lindhard dielectric function is used for the dielectric constant of the electron gas in the system. The polariton‐mode frequencies are derived by equating the total dielectric function to c2q2/ω2, where c2 = 1/μ0ε0, q the wave number, and ω the frequency. The reflectivity spectra of n‐type AlxGa1−xAs are also presented.
Thermodynamics of the Phase Transition Sequence in the Incommensurate Compound (N(CH3)4)2CuBr4
Authors: López‐Echarri A. , Ruiz‐Larrea I. , Tello M. J. 
Published: July 2007

AbstractThe prototype‐incommensurate‐ferroelectric‐ferroelastic phase transition sequence in (N(CH3)4)2CuBr4 is studied by adiabatic calorimetry in the temperature range 60 to 343 K. The thermodynamic function values assigned to the successive phase transformations permit a comparative study with other tetramethylammonium tetrahalogenmetallates. The enthalpies involved in their phase transition sequences can be related to the packing of the crystal unit cell and to the position of each compound in a common pressure‐temperature phase diagram. In the case of (N(CH3)4)2‥CuBr4, this diagram is correctly described by a simple phenomenological model. A brief discussion on the critical exponents associated to the specific heat (α = α′ = 0.01 for ‖T − T0‖ < 0.2 K) and to the order parameter, for the prototype‐incommensurate phase transition, is also included.
Theoretical Investigation of Ferroelastic Phase Transition of Pure and Mixed Alkali Cyanide Systems by the Elastic Dipole Model. I. The Cubic‐Orthorhombic Phase Transition of Pure Potassium Cyanide
Authors: Yang Zhengju , Luty F. 
Published: July 2007

AbstractThe kinetics of elastic ordering of KCN controlled by a thermally activated process is studied by considering the interaction between elastic CN− dipoles. The lattice constants obtained and reorientational activation energy of dipoles in the elastically ordered lattice agree quantitatively with experiments. The calculation indicates that the orientation ordering of elastic dipoles is induced by the strain field due to ordering alignment of dipoles. The elastic interaction between close neighbors of dipoles has little influence. The first‐order character of the phase transition is obtained, and it is found that an initial degree of order depending on the temperature is necessary to start the ordering process. It is concluded that this corresponds to the nucleation process of the first‐order phase transition.
Electronic Structure and Properties of Boron Phosphide and Boron Arsenide
Authors: Prasad C. , Sahay M. 
Published: July 2007

AbstractThe composite wave variational version of the APW method is used to obtain the electronic band structure of the compounds boron phosphide and boron arsenide at the high symmetry points Γ, X, and L. The tight binding interpolation scheme of Slater and Koster is used to calculate the rest of the band structure. The results show that both these materials are indirect band gap semiconductors. The density of states, and the imaginary part of the dielectric constant is also calculated. The theoretical results are compared with the reported experimental and theoretical data.
The Quadratic Response of a Fermi Gas for Arbitrary Degree of Degeneracy
Authors: Pickenhain R. , Flietner B. , Unger K. 
Published: July 2007

AbstractThe diagonal quadratic response function of a non‐interacting Fermi gas is generalized to arbitrary degrees of degeneracy. The validity of a simplified quadratic response function proposed earlier, is analyzed in detail. Hints to its applications are given.
The Superconductor Glasses (SuG). A Fractal Description
Authors: Giovannella C. 
Published: July 2007

AbstractIt is shown that the value of the 1/Ψ critical exponent measured on sintered high‐Tc granular superconductors (La1.85Sr0.15CuO4−δ and YBa2Cu3O7−δ) can be understood within the framework of a fractal model. Using the fractal cluster model, it is shown that under the hypothesis of ν = 1.33, the fractal dimension of these systems can be always straightforwardly derived. The comparison between the values of the SuG critical exponents and those of the spin glasses (SG) suggests the inclusion of both the ensembles of critical systems in a unique universality class whose definition differs from the usual one.
Electronic Properties of the Defect Perovskite System La1−xLixMO3
Authors: Bahadur D. , Bilas Ram , Murty B. S. R. 
Published: July 2007

AbstractThe systems La1−xLixFeO3 for x values up to 0.5 are synthesised and found to be monophasic with rhombohedral and orthorhombic symmetry, respectively. Unlike for Sr2+ substitution, these samples do not become cubic for higher x values. The electron transport in these systems is discussed in terms of variable valence and spin states and the band picture. Improvements in the magnetisation values in the system La1−xLixFeO3 are attributed to disordering of spins and lowering of symmetry around Fe3+ due to substitution and oxygen vacancy.
Charge Transport in FeCl3‐Doped Polyethylenevinylacetate–Polyoctylthiophene Blends
Authors: Isotalo H. , Laakso J. , Kuivalainen P. , Stubb H. , Österholm J.‐E. , Yli‐Lahti P. 
Published: July 2007

AbstractThe results of an experimental study of the temperature (T) dependent dc conductivity σdc, T‐dependent thermoelectric power (TEP), and electron spin resonance in a new conducting polyethylenevinylacetate–polyoctylthiophene (EVAPOT) polymer blend doped with FeCl3 are presented. For a POT content of 20 wt% σdc (300 K) varies from 10−10 to 1 Ω−1 cm−1 with increasing doping, while σdc(T) fits σdc(T) = σ0 exp [– (T0/T)1/2], especially in highly conducting material. In the most heavily doped samples TEP shows metallic behaviour and the charge transport is described by the granular metal model. In lightly doped samples the T‐dependence of TEP follows the T−1‐law for band conduction in non‐degenerate crystalline or amorphous semiconductors. This is the first time the latter behaviour is found in conducting polymers.
Electron Transport in Quasi‐Two‐Dimensional Systems. Influence of Intersubband Scattering
Authors: Pratsch Chr. , Suhrke M. 
Published: July 2007

AbstractThe temperature and electron concentration dependence of the electron mobility is calculated for single quantum wells considering two occupied electron subbands. The results for the different scattering mechanisms and their interplay in the total mobility are changed with respect to those of other theoretical approaches which neglect multisubband coupling. The influence of the intersubband scattering is analyzed and the results are in agreement with experimental data.
Anomalous Behavior of the Low‐Temperature Spin Disorder Resistivity in PrH2+x Compounds
Authors: Daou J. N. , Burger J. P. , Vajda P. 
Published: July 2007

AbstractPure PrH2 dihydride presents an antiferromagnetic transition at 3.35 K; above TN, a decrease of the resistivity ϱ(T) is observed which can be explained by a Kondo effect but also by crystal field effects if the first non magnetic excited state Γ1 it situated very near to the magnetic Γ5 ground state. Magnetic ordering and the resistivity minimum disappear in PrH2+x compounds when x ≫ 0.08; this can be explained if there is an inversion of the Γ5 and Γ1 states or if there is a splitting of the triplet Γ5 state due to a tetragonal deformation of the lattice. Anomalous values of the low temperature slope dϱ/dT seem to correlate with the occurrence of this cubic‐tetragonal transformation of the host lattice.
ESR Studies of Single Crystals of Bis(ethylenedithio)tetrathiafulvalene‐Based Conductor with Octaiodinemercurate Anion (BEDT‐TTF)4Hg3I8
Authors: Firlej L. , Graja A. , Wolak J. , Lyubovskaya R. N. , Goldenberg L. M. 
Published: July 2007

AbstractThe electron spin resonance g‐value, linewidth, and spin susceptibility of single crystals of bis‐(ethylenedithio)tetrathiafulvalene‐based conductor with octaiodinemercurate anion, (BEDT‐TTF)4Hg3I8, are found to show pronounced temperature dependences in the T‐range from 20 to 300 K. A first‐order phase transition of the type semiconductor–semiconductor is observed at 265 K; it is associated with ordering of HgI4 tetrahedra in the crystal lattice. Discussion of the line‐shape and other ESR parameters is given.
Electromagnetic Wave Scattering in Inhomogeneous Media with Spatial Dispersion
Authors: Fokin A. G. , Shermergor T. D. 
Published: July 2007

AbstractThe problem of electromagnetic wave scattering on inhomogeneities of the dielectric permittivity tensor εij  εij(r) is considered. It is shown that effects caused by the coordinate dependence of εij can be studied by means of analyzing properties of the Fourier transform of the effective dielectric permittivity tensor ε(k). This fact makes it possible to develop a unified approach to solving the problem of electromagnetic wave attenuation and phase an group velocity variations caused by the scattering. The scattering index γ, phase velocity ν, and group velocity c are calculated within the framework of the Bourret approximation in all ranges of wavelengths. Asymptotic expressions for γ, ν, and c are obtained in the long (as compared to sizes of scatterers), short, and ultra‐short wavelength ranges. In the latter case the results can be obtained only when taking into account the spatial dispersion.
Application of Statistical Mechanics Using Asymmetric Electrolytes. Model Evaluation of Structural Properties of Ionic Gold—Cesium Melts
Authors: Rao R. V. Gopala , Satpathy A. 
Published: July 2007

AbstractTreating the gold—cesium as an ionic melt around 50 at% of Cs, Blum's generalized equations of asymmetric electrolytes are used to compute the partial structure factors and the total structure factors. The partial and total pair correlation function and coordination numbers are calculated from the computed structure factors. It is found that the agreement between the calculated total structure factors and the experimental values is excellent. The value of the generalised Γ parameter is found to be similar to that of fused salts. The coordination numbers of like ions is much higher than the close packed value and is analogous to that found in fused salts. Further in the case of unlike ions the coordination number as in salt is less. It is very gratifying to note that the present method requires just two parameters namely the ionic diameters of gold and cesium.
Continuous Evolutions which Connect Quasilattices with Lattices
Authors: Torres M. , Pastor G. , Jiménez I. , Fayos J. 
Published: July 2007

AbstractA newly modified projection method is developed in order to generate continuous transformations which connect quasilattices with lattices. The evolution and collapse of a 2D octagonal quasilattice, a continuous evolution of the 3D Penrose tiling which leads to a cubic primitive lattice on a side and to an f.c.c. vertices arrangement on the other side and, finally, the evolution and collapse of the historical 2D Penrose tiling are studied in detail. Applications of these quasiperiodic tiling evolutions to quasicrystal—crystal transitions and to atomic decorations of quasicrystalline phases are suggested.
Interatomic Forces and Pseudopotential Parameterization
Authors: Meyer A. , Young W. H. 
Published: July 2007

AbstractIt is shown that the calculated interatomic forces in a metal are sensitive to the pseudopotential postulated, even if the principal (“atomic”) node in the form factor is kept fixed. Much less sensitivity is displayed when the pseudopotential core is fixed with respect to low energy s‐ and p‐scattering.
Description of Interdiffusion Processes in Multicomponent Systems by the First Fick's Law
Authors: Slyusarenko E. M. , Soldatov V. S. 
Published: July 2007

AbstractA new approach, based on Fick's first law, is proposed for the theoretical description of interdiffusion processes in multicomponent systems. In distinction to the well‐known model, where interdiffusion in an n‐component system is characterized by (n2 – n) partial (intrinsic) diffusion coefficients, in the model of independent fluxes n coefficients are used. To determine the analytical dependence of partial diffusion coefficients Di = Di(C1, C2, …︁, Cn) it is unnecessary to investigate the Kirkendall effect with the help of markers.
Kinetics of an Ensemble of Jogs on the Edge Dislocation for Inefficient Capture of Point Defects by Jogs
Authors: Borodin V. A. , Ryazanov A. I. 
Published: July 2007

AbstractThe kinetics of an ensemble of jogs on a straight edge dislocation is investigated for a material supersaturated with vacancies and interstitials. The concentration of jogs is determined in a selfconsistent manner under the assumption of low efficiency of absorption of point defects by dislocation jogs. The range of validity of the results obtained is discussed.
Particle Size Effects of Ion Crystallites
Authors: Fritsche H.‐G. 
Published: July 2007

AbstractThe cohesive energy of cubes (NaCl) N (4 ≦ N ≦ 500) is optimized, changing the uniformly assumed size‐dependent nearest‐neighbour ion pair distance, by means of summation of pair potetials. Formulae of particle size effects of energy‐dependent quantities – compressibility, surface energy, surface tension, pressure, and chemical potential – are derived analytically. Despite of the longrange order of the Coulomb interaction of ions, all the investigated size effects are dominated by the topology of the particles.
On Concentration Dependences of the Band Parameters in AIIBVI Solid Solutions with Structural Phase Transitions
Authors: Areshkin A. G. , Suslina L. G. , Fedorov D. L. 
Published: July 2007

AbstractThe connection between the structure of solid solution and its spectroscopic and band parameters is discussed on the example of ZnxCd1−xSe and Zn1−xMgxS systems with the structure phase transition: zinc blende (ZB)‐wurtzite (W). It is shown that if the Eg(x) dependence is parabolic for the ZB and W pure structure ranges, it is linear in the phase transition range (for the Zn1−xMgxS system). Eg(x) is always higher for the anisotropic crystals (with stacking faults (SF) and W) than for the ZB ones depending on the more ionic character of their chemical bond. The influence of the disorder potential due to composition x and SF concentration fluctuations on the exciton and band parameters of the solid solutions is considered.
Non‐Zero Momentum Pairing and Peierls Order in One‐Dimensional Systems
Authors: Fazakas A. B. , Pitis R. 
Published: July 2007

AbstractA one dimensional solid of the kind which may undergo a Peierls transition is considered in the mean field approximation. The electrons in a half‐filled tight‐binding band interact via the soft or softening phonons. It is found that, for reasonable values of the interactions parameters, electron pairs with the momentum equal to that of the phonons condense at low temperatures, coexisting with the Peierls order. The transition temperatures are discussed.
The Conduction Band Parameters and Scattering Mechanisms in Solid Solutions Based on Bi2Te3
Authors: Kutasov V. A. , Lukyanova L. N. 
Published: July 2007

AbstractExperimental weak‐field galvanomagnetic data are used to determine some conduction band parameters (the ratios of the effective mass tensor components mi/mj, the tilt angle of the principal axes of the constant energy ellipsoids, and the degeneracy parameter) using the many‐valley model of the band structure for n‐Bi2Te3 and its solid solutions. The charge carrier scattering mechanism is discussed. It is shown that the scattering parameter is not equal to −0.5, e.g. the value specifies for the acoustic scattering mechanism. The effective scattering parameter reff is calculated and its temperature and concentration dependences are found.
Critical Behaviour of n‐ZnSe Parameters in the Vicinity of the Metal—Insulator Transition
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N. 
Published: July 2007

AbstractThe critical behaviour of the parameters of n‐ZnSe is studied near the metal—insulator (M–I) transition obtained by variation of compensation degree or concentration of shallow donor impurity. It is found that the localization radius of the electron wave function, dielectric permittivity, density of states at the Fermi level as well as several other parameters characterizing the conductivity at the dielectric side of the transition are continuously varied over the critical region of the transition according to the scaling theory of localization. It is shown, that the critical concentration and critical indices for the M–I transition obtained by doping have somewhat lower values than that for the transition produced by compensation. The compensation smeares out the M–I transition and makes the concentration dependences of the system parameters in the critical region less abrupt. The symmetry of the M–I transition formed by doping is established as opposite to the slightly asymmetric transition induced by compensation. In the case of M–I transition obtained by doping replacement of electron localization on individual impurity centres by the Anderson localization is observed in the critical region while approaching the transition.
Piezomagnetoresistance Anisotropy of n‐Ge in Strong Magnetic Fields near the Metal–Insulator Transition
Authors: Matveev G. A. , Tsidilkovskii I. M. , Lonchakov A. T. 
Published: July 2007

AbstractOver the temperature range 2 to 77 K longitudinal and transverse magnetoresistance (MR) measurements are performed on Ge:Sb crystals in magnetic fields up to 200 kOe. The crystals used are uniaxially compressed along the 〈111〉 axis and have electron concentrations between 0.82 × 1017 and 6.2 × 1017 cm−3. A large MR anisotropy is found to arise chiefly from the anisotropy of the energy gap between the Fermi level and the mobility edge. A correlation is shown to exist between the temperature dependences of the negative and positive MR's in high magnetic fields. From an analysis of the concentration and temperature dependences of the MR anisotropy, it is inferred that for n > nc there exist certain regions of electron concentrations and temperatures where, despite the metallic character of conduction, effects show up which are typical of impurity band charge carriers. Put another way, the electron states in these regions are intermediate between band states, for which the scattering is weak, and virtually localized states, for which the scattering is strong.
Electronic Degeneracies, Inelastic Processes, and Bohm‐Aharonov Magnetoresistance Oscillations in Ordered Normal‐Metal Rings
Authors: Dunne L. J. 
Published: July 2007

AbstractA model is presented for magnetic flux dependent inelastic scattering processes in cyclic systems. This goes beyond previous work which assumes flux independent scattering processes. It is suggested that the model is of relevance to the interpretation of magnetoresistance oscillations which are observed in ordered normal metal rings. Electron scattering processes become more effective at flux values corresponding to degeneracies in the ring electronic states, and this manifests itself by oscillations in the magnetoresistance.
First‐Order Quantum Corrections to the Diffusivity and Current‐Induced Density Fluctuations in the Three‐Dimensional Bulk
Authors: Lenk R. 
Published: July 2007

AbstractEmploying a superposition representation of the density matrix for a fixed energy, the first order quantum corrections to the diffusivity are calculated for independent charge carriers scattered by uncorrelated point‐like scatterers. It is shown how fluctuations in carrier density, especially those which are caused by the current itself, contribute to the quantum corrections.
Electroreflectance Lineshape of Step‐Like Doped GaAs Structures
Authors: Goldhahn R. , Röppischer H. 
Published: July 2007

AbstractFor a semiconductor structure consisting of a homogeneously doped layer on a lower‐doped substrate of the same material the electroreflectance lineshape at the fundamental absorption edge is studied by model calculations. With the electric field penetrating into the substrate a characteristic superposition of the two partial spectra arising from the differently doped semiconductor regions is found. The change of the lineshape simulated for a GaAs structure in dependence on the modulation conditions and layer thickness is confirmed by electroreflectance measurements using successive layer removal. From the applied voltage producing first spectrum modification the thickness of the top layer can be estimated.