bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation and Decay of Electronic Excitations Localized near Divacancies in Alkali Halides
Authors: Lushchik A. , Lushchik Ch. , Lushchik N. , Frorip A. , Nikiforova O. 
Published: July 2007

AbstractThe thermal quenching or plastic strain of RbCl, KCl, and KBr crystals leads to an increase in the number of associations of anion and cation vacancies. Using the methods of VUV spectroscopy, electronic excitations localized near divacancies are detected at 5 K. The process of radiative and nonradiative decay of these excitations is studied as well as the process of radiational creation of divacancies.
The Condensation and Ferromagnetism of Triplet Frenkel Excitons
Authors: Li Bao‐Xing 
Published: July 2007

AbstractThe problem of coexistence of condensation and ferromagnetism in the triplet excitonic system is studied by using the symmetry‐broken Hartree approximation. It is found that the ground state of the system is the mixed state of both orders. Two kinds of particular cases, pure condensing phase and pure ferromagnetic phase, are discussed. A phase diagram is obtained from the calculation of free energies.
Fermi Surface Properties of Platinum
Authors: Ahuja R. , Solanki A. K. , Auluck S. 
Published: July 2007

AbstractThe extremal areas of the Fermi surface of paramagnetic f.c.c. transition metal platinum are calculated using the linear muffin tin orbital (LMTO) method in the atomic sphere approximation. To see the effect of exchange and correlation potential on the Fermi surface, the calculations are done using various exchange and correlation potentials. The Slater Xα exchange potential with α = 0.815 gives the best agreement with experimental data. Inclusion of relativistic effects also show remarkable improvement over the non‐relativistic calculations for platinum. The Fermi velocity of electrons at the Fermi surface and the mass enhancement factor are also calculated using the Slater Xα (α = 0.815) exchange potential and are compared with the experimental data and recent theoretical calculations.
Collective Behaviour of Photoinjected Plasma in Semiconductors
Authors: Esperidião A. S. , Vasconcellos A. R. , Luzzi R. 
Published: July 2007

AbstractThe spectrum of elementary excitations in the nonequilibrium state of a semiconductor under high levels of continuous photoexcitation is studied. Resorting to a quantum transport theory based on the nonequilibrium statistical operator method, the dynamic dielectric response function of the carrier system in the far‐from‐equilibrium steady state is derived, to calculate the Raman scattering spectrum and from it to analyze the spectrum of elementary excitations. Besides the expected bands due to quasi‐particle and collective plasma excitations, the presence is demonstrated of two additional bands associated to low energy excitations and with a linear dispersion relation, and hence termed acoustic plasma modes. The analysis of these two bands points to an interpretation of them as due to the collective motion of the electrons (the ones higher in energy) and of the holes (the ones lower in energy) interacting through the screened Coulomb interaction. At low temperature their lifetimes are mainly determined by dissipative effects mediated by the interaction of the carriers with the radiation recombination field.
Characteristics of Permanent Magnetic Coercivity with Application to Sintered Hard Ferrites
Authors: Elk K. , Jahn L. 
Published: July 2007

AbstractTo get information on the magnetization processes of permanent magnetic materials the angular dependences of the coercivity Hc, the remanence coercivity HR, and the maximum position H of the total susceptibility are investigated. Considering two competing coercivity mechanisms and two different magnetic prehistories the differences between these three quantities are demonstrated by model calculations and experimental results on hard ferrites. It is shown that HR(θ) is the most suitable measure to describe the irreversible magnetization processes in polycrystalline hard magnets.
The Re‐Entrant Behaviour of the Spin‐One Ising Model
Authors: Kerouad M. , Saber M. 
Published: July 2007

AbstractA spin‐one Ising model with random nearest‐neighbour interactions is studied within the finite cluster approximation (FCA). The application is discussed of FCA to the spin‐one Ising model with random nearest‐neighbour exchange interactions on a honeycomb lattice according to a two‐valued distribution of the random interactions. Re‐entrant phase diagrams are found.
Resonant Cavities for X‐Rays. Dynamical Diffraction of Dipole Radiation at Bragg Angles near π/2
Authors: Caticha A. , Caticha N. 
Published: July 2007

AbstractThe X‐ray field radiated by a classical oscillating point dipole inside a crystal is calculated in a non perturbative way. In the interesting situation in which Bragg's angle is near to π/2 it is shown that the crystal acts as a resonant cavity.
Cohesive and Anharmonic Properties of Some Fluorite Structure Nitrates
Authors: Rao C. N. , Singh R. K. , Hasan S. 
Published: July 2007

AbstractA three‐body potential (TBP) model is used to describe the cohesive and anharmonic properties of strontium, barium, and lead nitrates of fluorite structure. This TBP model consists of the long‐range Coulomb and three‐body interactions and the short‐range van der Waals attraction and overlap repulsion effective up to the second neighbour ions. This model reveals a better description of the cohesion, third‐, and fourth‐order elastic constants, and pressure derivatives of the second‐order elastic constants of these nitrates than those obtained by earlier workers. The scope for improvements is also discussed.
Influence of Short‐Range Order on the Electron–Phonon Interaction in Disordered Binary Alloys
Authors: Gurskii Z. A. , Chushak Ya. G. 
Published: July 2007

AbstractA microscopic theory for the investigation of the short‐range order effects on electron–phonon interaction in binary alloys is proposed. An expression for the electron–phonon matrix element is derived. Due to the presence of disorder in alloys, an additional term arises in this matrix element in comparison to the case of pure metal. The influence of pair correlations on the Eliashberg function α2F(ω) and the electron–phonon interaction constant in alloys of the KRb and KCs systems is investigated numerically and is analyzed. The pair correlations are shown to cause an increase of the electron–phonon interaction constant in the vicinity of the phase instability point. Under certain conditions such an increase may be essential.
Thermodynamic Investigations of the Phase Transition in Ferroelastic CoZrF6
Authors: Gorev M. V. , Flerov I. N. , Tressaud A. , Grannec J. , Rodriguez V. , Couzi M. 
Published: July 2007

AbstractThe heat capacity and the pressure dependence of the phase transition temperature of CoZrF6 are measured. The first order phase transition Fm3m → R3 is characterized by large values of both, the entropy change ΔS = (5.8 ± 0.8) J mol−1 K−1 and the rate of increase of the transition temperature T0 with applied hydrostatic pressure, dT0/dp = (340 ± 40) K GPa−1. An analysis of the results is performed in terms of the Landau theory. The parameters of the thermodynamic potential are determined.
E(k) above the Vacuum Level from Low Energy Electron Reflection. ΓK Line of Cu and Ni
Authors: Strokov V. N. 
Published: July 2007

AbstractIncidence angle dependent electron reflection coefficient curves R(E) measured in the 0 to 30 eV range on Cu(111) and Ni(111) surfaces are analysed. With incidence scanning in ΓK azimuth, some extrema of the dR/dE curves are shown to manifest bands along the ΓK line of the Brillouin zone. Comparing the experimental angular dispersion of these extrema with its calculated counterpart, bands along ΓK are mapped. Experimental technique and details of calculation are briefly discussed.
Influence of Intercalation by Metallic Atoms on the Shubnikov ‐de Haas Effect and the Energy Spectrum of Bi2Te3
Authors: Kulbachinskii V. A. , Kovalyuk Z. D. , Pyrlya M. N. 
Published: July 2007

AbstractLi and Ba atoms are intercalated into the van der Waals gaps of Bi2Te3 single crystals of n‐ and p‐types. The resistivity, the Hall effect, and the Shubnikov‐de Haas effect are investigated in host single crystals and after intercalation. It is found that the scattering of carriers is connected preferentially with acoustic phonons and does not change after intercalation. The intercalation of metallic atoms causes a change in the carrier concentration and hence, the Fermi energy. The intercalated samples possess the same six‐ellipsoidal Fermi surface as the host material.
Spin Waves in a Generalized Anderson‐Lattice Model
Authors: Irkhin V. Yu. , Entelis A. M. 
Published: July 2007

AbstractA two‐band model is considered describing, in particular, intermediate‐valence and Kondo systems and high‐Tc superconductors. Spin‐wave and electron spectra in ferro‐ and antiferromagnetic states are calculated both within the generalized Hartree‐Fock approximation and in the limit of strong correlations (with the use of perturbation theory in the fluctuating part of hybridization).
Calculation of the Spin System Correlation Functions in the Frames of the Functional Integration Methol. I. The Ising Model
Authors: Vakarchuk I. A. , Matskevych P. A. 
Published: July 2007

AbstractThe equations for the spin system correlation functions and Green functions as well as the way of their self‐consistent solution are suggested in the frames of functional integration method. As an example the Ising model is considered. The Curie temperature of this model is calculated from the pole of the pair correlation function. Calculations are performed for the cases of the crystalline and amorphous system. The value of critical temperature in the crystalline case is in good agreement with known data. It is shown that the magnetic order can be destructed by amorphization of the crystal.
EXAFS Study of the CuAsSe Amorphous Alloys
Authors: Gómez‐Vela D. , Esquivias L. , Prieto C. 
Published: July 2007

AbstractSome amorphous alloys of the chalcogenide CuAsSe family are studied by EXAFS spectroscopy. Results are presented, obtained for the two samples Cu8As26Se66 and Cu26As37Se37. The mean coordination number of the three different atoms and their distances to the first coordination sphere are determined in both the alloys. It is found that the copper atoms are fourfold and the arsenic ones are threefold coordinated in both the compounds and the coordination numbers for selenium are 3.8 and 2.2 in Cu8As26Se66 and Cu26As37Se37, respectively.
Setting‐up of a Generalized Clustering Model in Fluorite‐Type Anion Excess Solid Solutions
Authors: Réau J. M. , Wahbi M. , Sénégas J. , Hagenmuller P. 
Published: July 2007

AbstractA model correlating ionic conductivity to short‐range order in fluorite‐type anion excess solid solutions is proposed. It is based on the composition dependence of the number of the fluoride ions appearing to account for the long‐range motions. The validity of this generalized clustering process model is checked by 19F NMR and/or neutron diffraction investigations.
Reference System Approach in the Electron Liquid Theory. II. Ground State Characteristics in the Medium Density Region
Authors: Vavrukh M. , Krokhmalskii T. 
Published: July 2007

AbstractIt is shown that the reference system approach (see part I of this paper), based on the application of n‐particle correlation functions of a degenerate system of noninteracting electrons, proves to be efficient in describing the interacting electron gas in the medium density region. The energetic, dielectric, and structural characteristics of the homogeneous electron liquid ground state are obtained as functions of the coupling parameter rs.
Bulk Photovoltaic Effect in LiTaO3: Fe Crystals
Authors: Karabekian S. I. , Odoulov S. G. 
Published: July 2007

AbstractFour independent components of photovoltaic tensor, responsible for “linear” photovoltaic currents, are measured for the first time for LiTaO3: Fe crystals in the range of photon energy from 2.07 to 3.88 eV. The observed correlation of the spectral dependencies of βs15 and β22 components indicates common origin of the transverse linear photovoltaic currents in this material.
Interplane Cooper Pairing in YBa2Cu3O7 Crystals and Phonon Frequency Softening Below Tc as a Consequence of Electron‐Phonon Interaction
Authors: Liaptsev A. V. 
Published: July 2007

AbstractA model of the YBaCuO crystal based on tight‐binding approximation is considered. The electronic Hamiltonian describes uncoupled plane (layer) bands and chain bands. The vibronic interaction appears due to the overlap of Cu2(d) and O4(pz) orbitals when the nuclei are displaced from their equilibrium positions. This interaction is transformed to the Renner‐type vibronic interaction which is nondiagonal with respect to the indices corresponding to different planes and quadratic in the vibronic coordinates. It is shown that the Renner‐type interaction can cause interplane pairing of electrons and phonon frequency softening below Tc. Some estimates are obtained and compared with experimental data.
X‐Ray Double and Triple Crystal Diffractometry of Silicon Crystals with Small Defects
Authors: Holý V. , Kuběna J. 
Published: July 2007

AbstractIntensities of X‐ray diffraction and X‐ray diffuse scattering are calculated on the basis of the kinematical approximation of the statistical dynamical diffraction theory for crystals with randomly distributed small defects. Various approaches are derived for defect parameter determination (the density, size, and strength of defects) and some of them are compared with previously published X‐ray methods. The theoretical results obtained for two various defect models are proved by double and triple crystal diffractometry measurements.
Size Changes of Lattice Parameters in Small Particles of Hexagonal Crystals
Authors: Gamarnik M. Ya. 
Published: July 2007

AbstractThe role of particle size in the change of lattice parameters is theoretically and experimentally studied. A monotonous increase of the lattice parameters a and c with decreasing particle size is established by means of X‐ray analysis for a series of fine‐dispersed powder samples of quartz obtained by fractionation. It is shown that the effect cannot be explained by impurity or intrinsic defects in the small quartz particles. Analytical expressions are obtained to calculate the size changes of the lattice parameters in crystals with hexagonal syngony and external shape of a hexagonal prism. The expressions derived are based on the size dependence of the internal stress – the intracrystalline pressure stipulated by the interaction of the elements of the crystal charge lattice. Calculations made for the ion charge lattice of quartz evidence the monotonous increase of the lattice parameters with decreasing particle size and agree with the results of the X‐ray experiment.
Microhardness of AN−1 BN + 1 C Chalcopyrite Semiconductors
Authors: Kumar V. , Prasad G. M. , Chandra D. 
Published: July 2007

AbstractMicrohardness of AN−1 BN + 1 C28−N (N = 2, 3) tetrahedrally coordinated chalcopyrite semiconductors are calculated using plasma oscillation theory of solids. The calculated values are in fair agreement with the values reported by several workers and the experimental values.
Green's Functions for Tight‐Binding Electrons on a Square Lattice in a Magnetic Field
Authors: Thamm R. , Kolley E. , Kolley W. 
Published: July 2007

AbstractTight‐binding electrons on a two‐dimensional lattice with a uniform magnetic flux per unit plaquette are described by the method of Green's functions. In analogy to Harper's equation for the energy dispersion a matrix equation for the Green's function is given. Analytical and numerical results for the Green's functions are presented at two special fluxes.
Practicable Method for Estimating Thermal Depths from Phonon‐Broadened Photoexcitation Cross‐Section Bands. II. Analytical Representation for Neutralized Centres
Authors: Pässler R. 
Published: July 2007

AbstractThe zero‐phonon threshold behaviour of thermally broadened absorption cross‐sections σ (hv, T) is examined for processes of photoexcitation of electrons and holes from deep acceptor and donor levels into unperturbed Bloch states of nearly parabolic conduction or valence band edge regions, respectively. In terms of parabolic cylinder functions, analytical descriptions are given for alternative photon energy dependences of the transformed excitation curves ϱ (hv, T) ≡ exp (− hv/2kT) σ (hv, T). Their vertex positions hv′ (T) are found to be shifted with respect to the thermal depths J (T) in question by amounts of about (1 + f) 2kT, where f = 0 or 1, for allowed or forbidden transitions. A remaining uncertainty up to ∓ kT, at maximum, is due to possible variations of the electron–phonon coupling from an extremely weak (vanishing) up to an extremely strong one. From our assessment of optical electron excitation data given by Wang et al. for the B level in GaAs and by Kullendorff et al. for the CuB level in InP we conclude that 1. both transitions are allowed (f = 0) in dipole approximation, 2. both levels are located at low temperatures by about 0.1 eV below the middles of the respective forbidden gaps, and 3. the actual distances of both levels from the respective conduction band edges decrease by about (0.08 ± 0.01) eV when the temperature increases from very low up to room temperature. This “depth shrinkage effect” is pointed out to have important consequences for theoretical interpretations of thermal electron capture properties on the basis of the nonradiative multiphonon (NMP) capture mechanism. The complementary processes of optical hole excitation at both centres appear to be markedly affected by Rydberg‐like states extending up to several dozens of meV above the respective valence band edges.
Effect of a Tilted Magnetic Field on Energy Quantization and the Einstein Relation in Quantum Wires of Semiconductors
Authors: Das N. R. , Chakravarti A. N. 
Published: July 2007

AbstractA perturbational approach is used to investigate the effect of a tilted magnetic field on the energy eigenvalues and the diffusivity‐mobility ratio (the Einstein relation) of the electrons in a quantum wire (a quasi‐one‐dimensional structure) of an n‐type wide‐gap semiconductor having a rectangular cross‐section. The results computed corresponding to the temperature 4.2 K are presented, taking degenerate n‐GaAs as an example.
Optical Destruction and Restoration of {F, In2+} Pairs in KBrIn Crystals
Authors: Braslavets P. F. , Kalniņš A. , Pļaviņa I. , Popov A. I. , Rapoport B. I. , Tāle A. 
Published: July 2007

AbstractUsing photostimulated luminescence of {F, In+} defect pairs in KBr‐In crystals, their F‐light optical destruction under excitation has been investigated. It is shown that the effective absorption cross‐section of F centers manifests itself in the kinetics of photostimulated luminescence of {F, In2} pairs under constant F‐stimulation. It is shown also that the resulting products ‐ {va+, In+} pairs ‐ may be again converted to {F, In2+} under C‐absorption band illumination.
TEM and DLTS Investigations of the Electrical Activity of Σ17 and Σ41 Grain Boundaries in Germanium
Authors: Wang N. , Haasen P. 
Published: July 2007

AbstractThe electronic defect states of near Σ17 and Σ41 tilt grain boundaries (GBs) in germanium are determined by means of deep‐level‐transient spectroscopy (DLTS). The results indicate energy levels Ec − 0.56 ± 0.02 eV and Ec − 0.38 ± 0.02 eV for the Σ17 and Σ41 GBs, respectively. The structure of these GBs is further studied by transmission electron microscopy (TEM). Because of a small twist component of the misorientation in the Σ17 bicrystal, GB dislocations have jogs. These jogs may create dangling bonds which are considered to be at the origin of the electrical activity of the Σ17 GB. No structural feature has been found which may create jogs or dangling bonds in the small angle Σ41 GB.
Balance Equations for Hot Electron Transport in an Arbitrary Energy Band
Authors: Lei X. L. 
Published: July 2007

AbstractBy distinguishing the center‐of‐mass momentum from its velocity the hot‐electron balance‐equation transport theory developed by Lei and Ting for a parabolic band is extended to carriers moving in a single arbitrary energy band. An ensemble averaged inverse effective mass tensor is introduced to describe the collective response of the Bloch electrons to an external electric field. This allows to use a two‐parameter (the center‐of‐mass momentum and the electron temperature) description of nonlinear carrier transport in a uniform electric field. The resulting effective force and energy balance equations turn out to be so succinct that one can perform any hot‐carrier‐transport calculation for a realistic energy band with only a little more numerical effort than that in the parabolic band cases.
Temperature Dependence of the Acoustic Deformation Potentials in CuInSe2 and CuInTe2
Authors: Rincón C. , Fernández B. 
Published: July 2007

AbstractFrom the analysis of the variation of the energy gap with temperature and pressure in the chalcopyrite semiconducting compounds CuInSe2 and CuInTe2, the valence and conduction band acoustic deformation potentials are calculated as a function of temperature between 50 and 300 K. It is found that these parameters increase with temperature for both compounds. The results indicate, specially for CuInTe2, that the variation is important enough to be taken into account in the fit to the mobility data.
Low‐Temperature Dependence of the EPR Spectra of Gd0.5RE0.5Ba2Cu3O7−δ Compounds in the Tetragonal Phase
Authors: Guskos N. , Likodimos V. , Londos C. A. , Windsch W. , Metz H. , Koufoudakis A. , Mitros C. , Gamari‐Seale H. , Niarchos D. 
Published: July 2007

AbstractThe EPR spectra of perovskite ceramics of Gd0.5RE0.5Ba2Cu3O7−δ type (RE  La, Pr, Nd, Sm, Eu, Dy, Ho, Y, Er, Tm, Yb, and Lu) in tetragonal (non‐HTC) phase are investigated as a function of temperature in the range 40 to 3 K. A signal arising from the isotropic exchange interaction of coupled pairs of Cu2+ ions is detected. The intensity of this signal is strongly dependent on the RE ions and its g‐factor varies with temperature. Magnetic measurements show the existence of ferromagnetic anomalies at these low temperature. In the orthorhombic phase, these materials exhibit a superconducting phase transition in the range of 85 to 95 K, apart from the samples with La ions where a TC ≈ 69 K is found and the samples with Prions where a superconducting state can not be observed.
Optical Properties of (F)H Centers in NaCl:SH− Crystals
Authors: Casalboni M. , de Viry D. , Grassano U. M. , Luci A. , Palummo M. , Scacco A. 
Published: July 2007

AbstractThe optical properties of the (F)H center are investigated in NaCl: SH−. The negative sulfur ion stabilizes the center in the same way as the oxygen ion does in the better known system NaCl: OH−. The spectral properties, absorption, emission, and excitation spectra, in the two cases are quite similar, but in NaCl: SH− the F centers are more easily bound to the sulfur ion and this fact yields a greater stability to these centers.
The Effect of Fractal Dimensionality on Self‐similar Grain Growth
Authors: Streitenberger P. , Förster D. 
Published: July 2007

AbstractThe modified LSW‐theory of second phase particle coarsening for irregularly shaped particles recently presented is extended to fractal‐like grain growth in polycrystalline solids, where the grain boundaries can be characterized by a fractal dimensionality D. It is shown that a fractal dimension D > 2 leads to a considerable broadening of the scaled grain size distribution function in the pure‐drift approximation.