bluuebunny/crossref_metadata_2025_split huggingface dataset:
Triplet relaxed excited state structure and luminescence of thallium‐doped alkali halides
Authors: Nagirnyi V. , Soovik † T. , Vaino P. , Zazubovich S. , Jaanson N. 
Published: July 2007

AbstractFor the first time a slow component is observed and studied in the decay kinetics of AT emission of TI+ centres in KBr, KI, RbCl, and RbI crystals. The existence is established of a singlet metastable level below the doublet emitting one in each Jahn‐Teller minimum of the triplet excited state of the TI+ centres. It is concluded that for all ns2 ions in alkali halides the structure of the relaxed excited state is qualitatively the same, and it may adequately be described in terms of a theory that considers the Jahn‐Teller effect as a main interaction in the relaxed excited states of the luminescence centres. The nature is discussed of the weak emission bands appearing on excitation in the A absorption band of TI+ centres besides the main AT and AX emission bands, earlier interpreted as hot luminescence of Tl+ centres.
EPR of new platinum‐related complexes in silicon. I. Defects of symmetry C1h formed at intermediate temperatures
Authors: Höhne M. , Gehlhoff W. 
Published: July 2007

AbstractThe variety of Pt‐related complex defects in silicon is enlarged by EPR detection of a new group of defects, each of them containing one Pt ion. They are formed by different annealing procedures, including a step at intermediate temperatures. Two of the new complexes exhibit an EPR spectroscopic peculiarity: Though the angular dependences evidence an apparent monoclinic symmetry, two of the line groups, typical for this symmetry, coincide for any angle of rotation. The condition for this behaviour is discussed.
Investigations of Bijvoet Differences and Anharmonicity in Gallium Phosphide
Authors: Saravanan R. , Mohanlal S. K. , Chandrasekaran K. S. 
Published: July 2007

AbstractPrecise X‐ray diffraction intensity data are collected at 300 K using a perfect single crystal sphere of gallium phosphide. The data are firstly analysed assuming a harmonic thermal vibration of atoms. The refined Debye‐Waller factors for this harmonic model are B(Ga) = 0.446(0.010)× 10−2 nm2 and B(P) = 0.507(0.001) × 10−2 nm2 with the residual index R = 1.2715%. Then anharmonic thermal vibration effects are included in the structure factor expressions. In the anharmonic model, two additional parameters, the individual anharmonic thermal parameters, are also included in the refinement process. The refined values are β(Ga) = −1.201(0.371) × 10−13 J nm−3 and β(P) = 2.002(0.274) × 10−13 J nm−3 with R = 1.2646%. The effect of anomalous dispersion on the structure factor is also analysed. It leads to Bijvoet differences between all odd index inverse reflections. The inclusion of anharmonic effects leads to Bijvoet differences between all even index inverse reflections. The measured Bijvoet ratios are in good agreement with the calculated Bijvoet ratios both in sign and magnitude. The individual Debye‐Waller factors, the Bijvoet ratios, observed and calculated both, for the harmonic and anharmonic models, are reported.
Theory of Macroscopic Local Single‐Particle Charge States in Quasi‐Zero‐Dimensional Structures Surface Local States
Authors: Pokutnyi S. I. , Efremov N. A. 
Published: July 2007

AbstractA theory of macroscopic local single‐particle charge states in quasi‐zero‐dimensional structures is framed. The energy spectrum of charge carriers in a small particle (semiconducting or dielectric) is investigated as well as its dependence on the size of the particle, the effective mass of the charge and relative dielectric constant under conditions when polarization interaction plays an important role. A new type of local states of charge carriers inside a small particle, namely surface states, is predicted.
Microstructural Aspect of Electron Transfer in the Blue and Red Molybdenum Bronzes
Authors: Colaitis D. 
Published: July 2007

AbstractThe electron transfer process is systematically examined in K0.33MoO3 semiconductor red bronze and in K0.30MoO3 metallic blue bronze as a direct consequence of cation‐anion orbital overlaps. The critical interatomic distance below which the overlap occurs is established at about 0.196 nm. In K0.33MoO3, it is shown that closed localized molecular‐type orbitals correlate the rigid units which characterize the MoO3 layers. In K0.30MoO3, the paths for collective electrons are three quasi‐one dimensional Mo–O chains, with occurrence of transverse correlations between the two among them which are equivalent. The third chain connects two staggered rigid‐unit columns. The coupling of the metal–semiconductor transition with the lattice modulation is investigated in correlation with low temperature structural slight rearrangements and atomic displacements. It is shown that a part of collective electrons can condense in collective localized orbitals which close in between two equivalent chains with the modulation periodicity. The extension of transverse correlations towards the third inequivalent chain is discussed in relation with orbital overlaps and with the two‐band states model. Finally a microstructural model is proposed, which can describe in terms of interface modulation the conduction electron modulation and its incommensurability.
EPR of New Platinum‐Related Complexes in Silicon. II. Coexistence of a Tetragonal Jahn‐Teller System and a Nearly Trigonal System in One Pair
Authors: Höhne M. , Gehlhoff W. 
Published: July 2007

AbstractA spectroscopic peculiarity of two Pt‐related complex defects is interpreted for both of them by assuming one Pt ion in a crystal field, which is tetragonal, though another defect is trigonally coordinated. This coexistence is discussed in the framework of a static Jahn‐Teller effect. Wave functions, compatible with the g‐values, are sketched.
Temperature Variation of EPR Linewidth of Gd3+ and Estimation of Spin–Lattice Relaxation Time of Nd3+ in NdF3 Single Crystals
Authors: Korczak W. , Paradowski M. L. , Misiak L. E. 
Published: July 2007

AbstractEPR (X‐band) linewidths of the Gd3+ ion in NdF3 and LaF3 single crystals in the temperature range 140 to 510 K are investigated. The mechanism of spin–lattice modulated narrowing is adapted to explain the temperature dependence of the Gd3+ EPR linewidths in the presence of the Kramers host Nd3+ ions (4f3, 4I9/2). The spin–lattice relaxation time (τ′1) of the host ions Nd3+ in Gd3+‐doped NdF3 single crystal is calculated, using the equation for crystals containing two different species of paramagnetic ions.
Energy Band Structure Calculation of CdGeAs2 by Pseudopotential Method with Spin–Orbit Interaction
Authors: Madelon R. , Paumier E. , Hairie A. 
Published: July 2007

AbstractThe electronic energy bands of CdGeAs2 are calculated at symmetry points and along symmetry directions of the Brillouin zone, using the empirical pseudopotential method and taking into account the spin–orbit interaction. The introduction of the spin–orbit interaction improves the correspondence between calculated and measured values of transition energies. The symmetry properties of the wave function are determined with and without spin–orbit interaction: this study confirms the level order and the transition polarization dependence of levels, in particular around the gap which is a direct one.
Electrical Properties of Alkaline Earth Fluorohalide Crystals
Authors: Ayachour D. , Sieskind M. , Geist P. 
Published: July 2007

AbstractThe ionic conductivity of undoped BaFCl, BaFBr, BaFI, SrFCl, and SrFBr single crystals is measured. The activation energies for a variety of anion vacancy mechanisms and the Schottky energy are defined. They are found to be in good agreement with Baetzold's theoretical data. Partial measurements of the static dielectric constant point out that these materials show an important dipolar contribution which is connected with their antiferroelectric character.
Processes of Hot Electrons and Lattice Relaxation in Ion Implantation
Authors: Mazzone A. M. 
Published: July 2007

AbstractThe relaxation processes of a hot electron gas formed under bombardment with particles of energy in the MeV and GeV range are described by using molecular dynamics simulation methods based on a classic representation. The calculations lead to a noticeable lattice disorder whose features and mechanisms of formation differ from the ones of a Coulomb explosion or of a thermal spike.
Multifractal Properties of Diffusion‐Limited Aggregates and Random Multiplicative Processes
Authors: Canessa E. 
Published: July 2007

AbstractThe multifractal properties are considered of irreversible diffusion‐limited aggregation (DLA) from the point of view of the self‐similarity of fluctuations in random multiplicative processes. In particular the breakdown of multifractal behaviour and phase transition associated with the negative moments of the growth probabilities in DLA are analysed.
Fourth‐Order Adiabatic Linear Compressibilities for Non‐Cubic Solids
Authors: Delannoy‐Coutris M. , Toupance N. , De Belloy J. Boistel 
Published: July 2007

AbstractExpressions for the linear adiabatic compressibilities of an at least orthorhombic crystal and their pressure derivatives are derived in terms of the second‐, third‐, and fourth‐order elastic constants within a finite‐strain theory which includes thermal effects according to the quasi‐harmonic approximation of lattice dynamics. The expressions are derived in terms of the Lagrangian strain tensor and the frame‐indifferent analogue of the Eulerian strain tensor. Numerical applications are given for three hexagonal metals: cadmium, magnesium, and zinc, namely the temperature variations of the linear adiabatic compressibilities and their pressure derivatives, including recent estimations of the combinations of fourth‐order elastic constants appearing in the present work. When possible, the comparison with experimental data shows a rather good agreement with the compressibilities calculated within the present theory using the Green‐Lagrange strain measure of the deformation. About the variations of the first pressure derivatives of the adiabatic compressibilities with temperature, the present work provides us with theoretical values in the lack of experimental data.
Alloy Broadening of Semiconductor Impurity Lines Second‐Neighbor Effects
Authors: Ochi Carmen Lucia C. , Koiller Belita 
Published: July 2007

AbstractThe alloy broadening of impurity lines in ternary semiconductor alloys is investigated using a tight‐binding Hamiltonian with nearest‐neighbor interactions and the cluster ‐ Bethe‐lattice approach. A 17‐sites cluster connected to the alloy Bethe‐lattice effective medium within a one‐orbital per site diagonal disorder model is used for the study of a single impurity and of impurity pairs. The method is applied to InxGa1‐xP doped with Ge, and it is found that broadening occurs for the impurity on the same sublattice as the group‐III species, i.e., second neighbor to the occupationally disordered sites. This result is interpreted in terms of the cluster statistics and of the spacial distribution of the wavefunctions associated to the localized impurity states.
Electronic Structure of Bi2Sr2CaCu2O8 Doped by Sulphur in the Cluster Approximation
Authors: Kalinkin A. N. , Skorikov V. M. , Soldatov A. A. , Yu. Dobretsov V. 
Published: July 2007

AbstractThe electronic structure of SrBi4Cu4O4+9, SrBi4Cu4O5S4+4 clusters in the high‐Tc superconductor Bi2Sr2CaCu2O8 doped by sulphur is calculated using the relativistic self‐consistent Xα‐SW method. The effective charges of atoms and electronic densities of states are obtained. The substitution O → S in Cu‐O sheets is shown to result in hole doping and the improvement of hole hopping that may increase Tc.
Schrieffer‐Wolff Transformation of the p–d Model for Oxide Superconductors Charge Fluctuation Regime
Authors: Lovtsov S. V. , Yu. Yushankhai V. 
Published: July 2007

AbstractTo describe low‐energy properties of the CuO2 plane in oxide superconductors the effective interactions up to the fourth order in the p–d hybridization amplitude, V, are derived systematically by the Schrieffer‐Wolff transformation. Contrary to other analogous derivations the value of V is assumed to be comparable to the charge transfer gap, V ≈ Δ = ϵp − ϵp, that corresponds to the charge fluctuation (not spin fluctuation, V < Δ) regime in the system. Among the variety of relevant phenomena only a particular problem of magnetic frustrations in the system of Cu‐spins is examined.
Hysteresis of the Microwave Absorption in High‐Tc Superconductors
Authors: Czyzak B. , Stankowski J. 
Published: July 2007

AbstractHysteresis of Josephson microwave absorption (JMA) in the magnetic field by means of standard EPR methodology in ceramic superconducting YBa2Cu3O6.9 is investigated. The hysteresis of JMA strongly depends on 100 kHz modulation amplitude of the external magnetic field and the external magnetic field sweep rate. For a small amplitude (Bm < 1 G) of the 100 kHz modulation a fast dissipative process, independent on the sweep rate is observed. For Bm higher than 1 G Josephson‐like dissipation occurs. The hysteresis behavior of the JMA disappears for slow enough sweep rate. It disappears also for the magnetic field sweep range lower than ±25 G. A phenomenological model for explanation of the observed phenomena is proposed.
Molecular Orbital Explanation of Surface Magnetism of α‐Fe
Authors: Li Zhiqiang , Luo Helie , Lai Wuyan , Zheng Qingqi 
Published: July 2007

AbstractThe electronic structure and magnetic properties of bulk and surface of α‐Fe are studied by a SCF‐LCAO‐MO method within the local density functional theory. The enhancement of surface magnetic moment is observed and attributed to the decrease of overlaps of atomic orbitals on the surface, which is related to the coordination number and the occupation of localized antibonding orbitals near the Fermi level. The vacancies on the surface are found to increase the magnetic moment of the adjacent atom.
Monte Carlo Simulations for Pure and Site‐Diluted Simple Cubic Classical Heisenberg Systems
Authors: Jochims M. , Holey T. , Fähnle M. 
Published: July 2007

AbstractA fully‐vectorized Monte Carlo programme is developed to investigate the critical behaviour of pure and site‐diluted classical Heisenberg systems on a simple cubic lattice of 323 spins. The finite‐size effect is much larger than that for the corresponding Ising model. It therefore must be suspected that the asymptotic critical regime could not be penetrated. An effective exponent of β = 0.33 for the root mean square magnetization is found both, for the pure and the site‐diluted case. The attempt to improve the efficiency of the computer programme by a discretization of the continuous Heisenberg model fails because of the very slow convergence with respect to the number of allowed spin orientations.
Radiative Core–Valence Transitions in Alkali‐Halide Crystals
Authors: Rodnyi P. A. , Terekhin M. A. 
Published: July 2007

AbstractUsing pulse X‐ray and synchotron radiation, the spectral and kinetic characteristics of a new type of fundamental luminescence in RbF, CsF, CsCl, and CsBr crystals are analyzed. On the basis of the experimental results obtained, a generalized consideration of the mechanism of this type of luminescence is carried out in alkali‐halide crystals, taking into account the known spectra of photoelectron emission, absorption spectra, and band structure calculations.
The Separable Potential Method A Unified Approach to Various Lattice Models
Authors: Idiodi J. O. A. 
Published: July 2007

AbstractThis work proposes the separable potential method (SPM) as a unified treatment of a class of lattice models. The richness in structure of the unified approach is demonstrated through contact with some of the most important lattice models in the literature, the embedded‐atom method (EAM) being one of such models. As a practical application of SPM some fairly extensive results for f.c.c. metallic copper are reported.
Atomic Hydrogen Centres in LiF–H− and LiF–H−, Mg2+ Crystals
Authors: Egranov A. V. , Otroshok V. V. , Chernyago B. P. 
Published: July 2007

AbstractAtomic hydrogen centres in LiF–H− and LiF–H−, Mg2+ are studied by optical and ESR techniques. X‐irradiation of these crystals at 80 K leads to the formation of the H‐centres which are thermally stable up to 110 K. After thermal annealing of the H‐centres in LiF–H−, Mg2+ crystals a new atomic hydrogen centre is observed which is interpreted as an interstitial hydrogen atom stabilized by a complex of the Mg2+ ion and a positive ion vacancy (H(Mg)‐centre). Thermal decay of the (H(Mg)‐centres occurs at 430 K and leads to the formation of a hydrogen atom in the cation vacancy (H(Mg)‐centre).
Structural Phase Transformation (F.C.C. → B.C.C.) in Ag, Pt, and Sr and Their Stability on the Path of Transformation
Authors: Seyoum K. Belay , Thakur K. P. , Jha D. 
Published: July 2007

AbstractTheoretical calculations are made to locate the stress‐free b.c.c. phase in three f.c.c. metals (Ag, Pt, and Sr). Internal energies corresponding to the unstressed b.c.c. and f.c.c. phases, and the required stress and energy changes for f.c.c. → b.c.c. transformation in these crystals are presented. To determine the range of stability (G stability) the Born criterion is used by calculating the values of corresponding elastic moduli on the line of deformation connecting the stress‐free b.c.c. and stress‐free f.c.c. phases of the crystal. The Morse potential model is used to carry out these calculations.
Chaotic Dynamics of Nonlinear Schrödinger Soliton nteracting with an Oscillating Impurity
Authors: Abdullaev F. Kh. , Abdumalikov A. A. 
Published: July 2007

AbstractThe problem of nonlinear Schrödinger soliton interaction with an oscillating impurity is considered. The regimes of soliton motion for the cases of periodic and random oscillations of the impurity near an equilibrium point are investigated. As shown in the first case there exist regions of parameters under which a soliton dynamics becomes chaotic. The comparison of statistic characteristics of chaos in the region of dynamic and standard stochasticity is carried out. The coefficient of the soliton diffusion is found.
On the Theory of Soliton Lattice Melting in Three‐Dimensional Incommensurate Cystals
Authors: Veshchunov M. S. 
Published: July 2007

AbstractThe transition into the normal phase, associated with the melting of the soliton lattice in the incommensurate phase of a three‐dimensional crystal, is theoretically studied. It is shown, that in barium−sodium niobate (BSN) crystals this transition can take place in two steps.
Experimental Quasi‐Harmonic and Leading‐Order Anharmonic Coefficients of Ag, Al, Au, Cu, Fe
Authors: Quareni F. , Mulargia F. 
Published: July 2007

AbstractThe recently developed procedure of estimating the leading order anharmonic coefficients (third and fourth order in the Hamiltonian) from available thermodynamic data is applied to five metals: silver, aluminium, gold, copper, and iron. Stable estimates are obtained, yielding that the leading order anharmonic contributions are comparable with the electronic ones. The quasi‐harmonic coefficients are also estimated.
Calculation‐ of Some Defect Parameters in F.C.C. Metals
Authors: Ghorai A. 
Published: July 2007

AbstractThe lattice statics model together with the atomistic continuum model is used for the calculation of relaxation due to a vacancy, the vacancy formation energy and divacancy binding energy in the case of some f.c.c. metals whose phonon dispersion curves are available. Using the measured phonon dispersion relations and the elastic constants as constraints the dynamical matrix is derived considering interactions up to the eighth nearest neighbouring shell. The calculation shows that in all the cases the first twelve nearest neighbours relax towards the vacancy and the magnitude of the displacements of the distant neighbours decreases systematically. The available experimental values of the monovacancy formation energy and divacancy binding energy whereever available, show fairly good agreement. Relations among monovacancy formation energy, melting temperature, and activation energy for self‐diffusion are proposed.
Replica‐Trick Study of Vibrational Properties of Dilute Scalar‐Force Networks
Authors: Böttger H. , Freyberg A. 
Published: July 2007

AbstractVibrational properties of two‐dimensional triangular bond‐percolation systems with scalar forces are studied by means of the replica trick, which allows a self‐consistent effective medium to be derived. The vibrational density of states is calculated and compared with results obtained by means of other methods. The replica‐trick approach can also be extended to models with central and bondbending forces.
Resonant Tunneling in a Symmetrical Rectangular Triple‐Barrier Structure
Authors: Yamamoto H. , Kanie Y. , Taniguchi K. 
Published: July 2007

AbstractResonant tunneling is studied theoretically in a symmetrical rectangular triple‐barrier structure. Analytical expressions for the transmission coefficient and the resonance conditions are derived. It is found that resonant tunneling with transmission 1 and resonant tunneling with transmission < 1 can occur in the symmetrical triple‐barrier structure. It is confirmed that transmission < 1 at resonance may occur when the outer barrier width is less than about one half of the central barrier width.
The Lifetime of Excited O, S, Se, and Te Centres
Authors: Hessmann W. , Fischer F. 
Published: July 2007

AbstractThe decay of photoluminescence of these chalcogen centres in alkali halides is purely exponential. The lifetimes being constant at low temperatures are strongly reduced as the temperature is raised above certain limits. Activation energies for thermal quenching are obtained and discussed within the frame of an anharmonic Franck‐Condon model.
Raman Spectra of [N(CH3)4]2ZnCl4 Single Crystals. III. Activation of Acoustic Phonons in Raman Spectra of the Commensurately Modulated Phases
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Rabkin L. M. , Durnev Yu. I. 
Published: July 2007

AbstractLow‐frequency (v < 50 cm−1) polarized Raman spectra of TMATC‐Zn crystals are studied in the temperature range between 300 and 100 K that covers the range in which the structural phase transitions of this compound occur. The appearance of lines with frequencies below 17 cm−1 is observed in commensurately modulated low‐symmetry phases. These lines correspond to the phonons of transverse acoustic branches in the Γ–Σ–X direction of the normal phase which transfer to the zone center as a result of the unit cell multiplication. A sharp drop in the relaxational contribution to the scattering spectrum is found for frequencies below 20 cm−1 in phases V and VI which is thought to be associated with ordering processes in the crystal lattice.
Diffraction of Neutrons by Superlattices in the Presence of an Alternating Magnetic Field
Authors: Goliney I. Yu. , Rudko V. N. 
Published: July 2007

AbstractThe peculiarities of neutron diffraction by multilayer structures, which are used in neutron monochromators and polarizers, are investigated in the presence of an alternating magnetic field. Deviations from the mirror reflection law take place due to the appearance of neutrons with a normal component of momentum equal to \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt {\chi ^2 \pm 2m\omega /\hbar}$\end{document}, where ω is the frequency of external field and χ the normal component of an incident particle. Expressions for respective reflection and transmission coefficients, R± and T±, that characterize processes with change of neutron energy, are obtained and analysed.
Low‐Temperature Heat Conduction of Disordered Crystals in the Case of Vibrational Spectrum Cross Splitting
Authors: Zhernov A. P. , Salamatov E. I. , Chulkin E. P. 
Published: July 2007

AbstractA model of a crystal with nondiagonal disorder is considered. The regions of quasi‐particle localization are found. The low‐temperature heat conduction behavior is analyzed.