bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Study of the Electronic Structure of Rare Earth Hexaborides
Authors: Grushko Yu. S. , Paderno Yu. B. , Ya. Mishin K. , Molkanov L. I. , Shadrina G. A. , Konovalova E. S. , Dudnik E. M. 
Published: July 2007

AbstractX‐ray lineshifts of rare earth elements in the hexaborides of La, Ce, Pr, Nd, Sm, Eu, Gd, Yb, and Y relative to the corresponding tri‐ or difluorides are measured by the crystal diffraction method. The experimental shifts are compared with the values obtained in relativistic self‐consistent field calculations in the effective free ion approximation. The hexaborides of La, Ce, Pr, Nd, and Gd are shown to have 4fn‐15d configuration (4d for Y), and those of Eu and Yb, 4fn configuration. The shifts obtained for Sm in SmB6 support the suggestion that Sm is here in an intermediate valence state and is best described by the 4f6−x5dx configuration with x = 0.615 ± 0.007.
Brillouin Zones and Fundamental Regions
Authors: Jones G. A. , Landsberg P. T. 
Published: July 2007

AbstractThe n‐th Brillouin zone is defined to be the set of points in reciprocal space which have the origin as their (not necessarily unique) n‐th nearest lattice‐point. From this definition it is shown that (a) all zones have equal volumes and (b) each zone can be translated into the first zone so as to fill it exactly by translating different pieces of the zone by appropriate reciprocal lattice‐vectors. The argument, being purely geometrical, does not require appeal to periodic boundary conditions, the Schrödinger equation or similar results from the physics of the solid state. A connection with the more general “fundamental regions” is also pointed out.
Calculation of the EEE Parameters at Annealing of the F‐Centres in NaCl Crystals
Authors: Gerasimov A. B. , Merkin M. M. , Tsertsvadze A. A. 
Published: July 2007

AbstractWithin the frames of a previously suggested mechanism an elementary act of exoelectron emission resulting from annihilation of an F‐centre and interstitial negative halogen ion in a NaCl crystal is discussed. The dependence of the EEE parameters on the crystal orientation is studied. Energy spectra and exoemission parameters are obtained for three different crystal orientations. There is good agreement between the theory and experimental results.
Static Polarizability and Dipolar Surface Plasmon of Small Metal Particles
Authors: Bao Tran Thoai Duy 
Published: July 2007

AbstractThe frequency of the dipolar surface plasmon of small metal clusters is calculated using the sum rule techniques due to Lushnikov et al. The effect of surface diffuseness of electron density is included. The screening of the electrons is described within the Thomas‐Fermi approximation. A red shift of the surface plasmon frequency is obtained.
Picosecond Processes of Laser‐Excited Carriers in Silicon on Sapphire
Authors: Bergner H. , Brückner V. , Kerstan F. , Nowick W. 
Published: July 2007

AbstractThe relaxation processes on a ps‐time scale in silicon on sapphire, ion‐beam damaged SOS and hydrogenated ion‐beam damaged SOS are studied by means of time‐resolved reflectivity and photoconductivity measurements. The excitation wavelength is changed to excite the carriers either near to the band edge or into the conduction band. Therefore, it is able to distinguish between different relaxation processes. The results can be explained using a 4‐level model. The influence of the amorphization of samples on the relaxation time is discussed.
Temperature Dependence of Fourth‐Order Elastic Constants of Alkali Halide Crystals
Authors: Varshney R. K. , Shanker J. 
Published: July 2007

AbstractA method for evaluating the temperature dependence of fourth‐order elastic constants (FOEC) of NaCl as well as CsCl‐structure alkali halides is developed on the basis of the phonon‐pressure theory. Eleven distinct values of FOEC for each alkali halide crystal are calculated at 0 K and at room temperature (300 K). The pressure derivatives of second and third‐order elastic constants are calculated at both the temperatures. The method is based on the phonon‐pressure theory incorporating Lundqvist's three‐body potential. The second‐order temperature derivatives of second‐order elastic constants are also evaluated. The results obtained are discussed and compared with other investigations. The importance and significance of temperature contributions to various order elastic constants are discussed.
Investigation of the Equation of State and the Grüneisen‐Anderson Parameters for Fluorite‐Structure Crystals
Authors: Dutt N. , Agrawal G. G. , Shanker J. 
Published: July 2007

AbstractInvestigations of the equation of state describing the relationship between pressure and volume are presented for seven fluorite‐structure crystals viz., CaF2, SrF2, BaF2, PbF2, Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2. Recently developed interionic potentials, which take into account three‐body interactions also, are used for calculating the compression values corresponding to very high pressures. Calculations are also performed for the Grüneisen parameter and its volume derivative, the Anderson parameters, and the volume thermal expansion coefficient. The results are compared with available experimental data and also with those calculated by other workers. The nitrates are found to be much more compressible than the corresponding fluorides under the effect of high pressure.
Effects of Strains on the Dynamic Effective Charge of III–V Semiconductors
Authors: Anastassakis E. , Cardona M. 
Published: July 2007

AbstractA calculation is made of the anisotropy induced by an external stress on the dynamic effective charge of zincblende‐type semiconductors. This derivation is based on the semiempirical bondorbital model for the effective charge, and on the stress‐induced changes of the latter due to bond deformation and internal lattice displacements. Numerical application to specific materials shows that the effect can be significant. The results are in reasonable agreement with existing experimental information.
Radiative Recombination at Centres in Germanium–Silicon Solid Solutions
Authors: Lyutovich A. S. , Lyutovich K. L. , Popov V. P. , Safronov L. N. 
Published: July 2007

AbstractThe changes occuring in the spectra of exciton‐impurity complexes (EIC) and in the spectra caused by radiation defects (electron‐oscillating series with the head lines of 1.0097 and 1.0186 eV) according to the content of GexSi1−x solid solution in the range of x < 0.1 are studied. Substantial variations of the shift and the width of the spectrum lines of different types of the centres with the solid solution content are found. The problems of GexSi1−x content influence on the luminescence spectra characteristics caused by different recombination mechanisms are discussed. It is concluded that the lines of 1.0097 and 1.0186 eV are conditioned by the internal transition of electrons from an excited state of the active centre into the ground one.
Emission Processes in Luminescence and Thermally Stimulated Luminescence of Ag‐ and Ca‐Doped KCl
Authors: Bhuniya R. C. , Sridaran P. , Ratnam V. V. 
Published: July 2007

AbstractLuminescent emission during X‐ray excitation at room temperature and above as well as during TSL glow is studied for KCl, undoped and doped with Ag and Ca. It is observed that the spectral character of the emission is the same during both the processes in each of the crystals. In all the samples certain emissions occur at the same wavelength region, (I) 540 to 560 nm, (II) 430 to 445 nm, (III) 420 to 430 nm, and (IV) 385 to 410 nm during X‐irradiation and during TSL glow irrespective of the impurities present, which are intrinsic to the lattice. Emissions in the wavelength regions (V) 280 to 290 nm, (VI) 260 to 270 nm, and (VII) 580 to 620 nm are characteristic of Ag impurity. Recombination centres and recombination sites of the different emissions are explained.
An Interpolytypical Transition in NbS2
Authors: McMullan W. G. , Irwin J. C. 
Published: July 2007

AbstractRaman scattering experiments are carried out on single crystals of 2H‐NbS2. From the results it appears that some crystals undergo a transition to the 3R‐polytype as the sample temperature is lowered. The transition is observed to be continuous and reversible. It is postulated that the transition is driven by an incipient charge density wave.
Density Functional Pseudopotential Calculation of the Cohesive Properties of Disordered Solid Alloys of Alkaline‐Earth Metals. Influence of the Ionic Pseudopotential
Authors: González D. J. , Zapata C. M. , Alonso J. A. 
Published: July 2007

AbstractA density functional pseudopotential method is used to calculate the compressibility of alkaline‐earth metals and the cohesive properties of disordered solid binary alloys formed between those metals. Two pseudopotentials are used, namely, the empty‐core model potential and Shaw's pseudopotential. It is found that the results are very similar, although the empty‐core model potential leads to slightly better predictions in comparison with experiment.
The Effect of Spin–Vibrational Interaction in Magnetic Properties of Exchange Tetraclusters
Authors: Polinger V. Z. , Chibotaru L. F. , Bersuker I. B. 
Published: July 2007

AbstractThe magnetic properties are considered of cubic crystals of tetrahedral copper tetraclusters of the type Cu4OX6L4, in the case when each copper ion is orbitally nondegenerate, under the assumption of strong spin‐vibrational interaction with E‐type cluster distortions. It is shown that within this model for all possible values of the exchange parameters the temperature dependence of the effective magnetic moment of the system is monotonous, and hence the four‐centre (pseudo) Jahn‐Teller effect is concluded to be the most probable reason of the anomalous magnetic properties of the copper tetraclusters.
Determination of Effective Indirect Exchange Interaction Integrals in Ferrimagnets
Authors: Sidorov A. A. , Suetin V. P. , Pokazaniev V. G. , Karpenko B. V. 
Published: July 2007

AbstractIn terms of a collinear two‐sublattice ferrimagnet a statistical method of estimating exchange interaction integrals is developed. Using the Mössbauer spectroscopy data for the temperature induced variation of the spontaneous magnetization of tetra‐ and octahedral sublattices and the temperature dependence of inverse susceptibility the stable and unambigious estimates of exchange integrals for Y3Fe5O12 and Li0.5Fe2.5O4 are developed.
The General Theory of the Dynamic Susceptibility in Thin Ferromagnetic Films
Authors: Świrkowicz R. 
Published: July 2007

AbstractThe transverse dynamic susceptibility of thin ferromagnetic films is calculated within the framework of RPA by using of the method of equation of motion. A representation in which the general multiband Hamiltonian is diagonal in the Hartree‐Fock approximation is consequently used in all calculations. The expression, obtained in the paper for the dynamic susceptibility of thin films represents a generalization of the formula obtained by Cooke for bulk crystals. Certain approximations which allow to deal with this general formula are also discussed.
Optical and Magnetic Investigations of Some NiAs‐Type Transition Metal Compounds
Authors: Neitzel U. , Bärner K. 
Published: July 2007

AbstractThe reflectivity and the logarithmic derivative of the reflectivity is measured as a function of quantum energy (1.3 eV < ħω < 4.7 eV) and temperature (10 K < T < 300 K) for several NiAs‐type compounds: NiAs, NiSb, MnAs, MnSb, Ni0.95Mn0.05As, Ni0.8Mn0.2As, and Ni0.5Mn0.5As. The optical constants are consistent with existing bandstructure calculations for the nonmagnetic compounds NiAs and NiSb. This is not so for the ferromagnetic compounds MnAs, MnSb, and for the mixed crystals; in particular, for the mixed crystals the magnetic susceptibility indicates that Mn builds up a local moment.
Optical Properties of β′‐AuZn by Wavelength‐Modulated Derivative Spectroscopy
Authors: Stearns R. , Braunstein R. , Muldawer L. 
Published: July 2007

AbstractDerivative spectra of the optical properties of β′‐AuZn are obtained using wavelength‐modulated spectroscopy between 1.5 and 5.1 eV. Assignments are made for the interband transition at the M point of the Brillouin zone which fix the transition energies with an accuracy previously unattained.
Energy Transfer Mechanisms in the NaCl:Pb++, Mn++ System along Aggregation Processes
Authors: Capelletti R. , Manfredi M. , Solzi M. 
Published: July 2007

AbstractThe non‐radiative energy transfer mechanisms between Pb++ (donor) and Mn++ (acceptor) ions in NaCl:Pb++, Mn++ system are examined at different aggregation stages of the impurities. Mn++ ions are characterized by a series of absorption bands partially overlapping the emission bands of Pb++ aggregates peaking at 380, 430, and 500 to 530 nm. The energy transfer mechanism connected with Pb++‐380 nm emission band is based on a resonant single pair interaction, while the transfer process connected with 430 nm and 500 to 530 nm emission bands can be explained on the basis of a fast energy migration within the donor system followed by a final transfer, donor–acceptor, that is resonant for the transfer connected with 430 nm band and phonon assisted for the transfer connected with the 500 to 530 nm band.
The Resistance of a One‐Dimensional System with a Stationary Random Potential which is a Markov Process
Authors: Potapenko S. Yu. , Satanin A. M. 
Published: July 2007

AbstractThe zero‐temperature de resistance of a one‐dimensional disordered system with a random potential which is a Markov process is investigated. A universal expression for the probability distribution for the logarithm of the resistance in the weak scattering limit is obtained. Disordered systems with typical random non‐Gaussian po tentials are considered.
Temperature Dependences of Conductivity at Small Electron Mean Free Path
Authors: Katsnelson M. I. , Shcherbakov A. S. 
Published: July 2007

AbstractIt is demonstrated by consideration of available experimental data that the unusual temperature dependence of the conductivity σ(T) = σ0 + A exp [–B/T1/(1 + d)], d being the dimension, is typical for different disordered systems with a small electron mean free path. A possible explanation of this dependence is proposed in the framework of a model with two kinds of weakly hybridized electron states, taking into account phonon‐induced transitions between them. It is assumed that such dependence σ(T) is a characteristic one for systems near the Mott transition.
Unambiguous Determination of Interatomic Force Constants of Crystals by Coherent Inelastic Neutron Scattering
Authors: Kohl H. 
Published: July 2007

AbstractThe interatomic force constants in a crystal can be obtained experimentally by measuring both the frequency and a corresponding eigenvector of each phonon mode. The measurement of the double differential cross section does not generally suffice to determine the eigenvector unambiguously. It is shown that by orienting the crystal near a Bragg position it is possible to obtain additional information on the eigenvector. An experimental procedure is proposed which should yield unambiguous values for the force constants.
The Phase Diagram of TbPO4 Measured by Linear Optical Birefringence
Authors: Becker P. J. , Kahle H. G. , Keller K. 
Published: July 2007

AbstractMeasurements of the linear optical birefringence are used to determine the B–T phase diagram of TbPO4 down to 1.5 K for two principal field directions. There are three ordered phases, a simple antiferromagnetic one with the moments along the tetragonal c‐axis below TN1 = 2.28 K, a further colinear antiferromagnetic one with the moments tilted off the c‐axis and a lower crystal symmetry below TN2 = 2.13 K, and a spin‐flop‐like phase in a certain field range for B along c.
Monte Carlo Simulation of the Production of Charge Carriers in NaCl Crystals by XUV Irradiation
Authors: Kikas A. , Elango M. 
Published: July 2007

AbstractA Monte Carlo simulation of the number as well as energy and spatial distribution of the electron‐hole pairs created in NaCl crystals by irradiation with photons of 20 to 250 eV is carried out by using a simplified band scheme and the random‐k approximation. It is shown that the low‐energy parts of the carrier bands are populated preferentially. The computed mean pair‐creation energy is in reasonable agreement with the experimental value (13.4 to 16.7 eV) if the inelastic electron‐electron scattering threshold energy is chosen in the interval 1.2 to 1.5Eg (Eg is the band‐gap energy). The mean distance of the electron‐hole pair creation events from the photon absorption site is 50 to 60 Å.
The FH(H−) Center Energy Parameters and the Nature of the F Center Unrelaxed Ground State in KCl
Authors: Salomatov V. N. , Parfianovich I. A. , Kristoffel N. N. 
Published: July 2007

AbstractThe FH(H−) center energy parameters in KCl are calculated within the framework of the perturbation theory. A comparison of theoretical and experimental results leads to the following conclusion: the F center unrelaxed ground state as well as the relaxed excited state has a diffuse spatial distribution. A possibility to identify the F center unrelaxed ground state‐conduction band transition by the picosecond laser spectroscopy, is mentioned.
Some Remarks on Thermodynamics of Stress‐Induced Martensitic Transformations
Authors: Kato Masaharu , Pak H‐R. 
Published: July 2007

AbstractThe thermodynamics of stress‐induced martensitic transformations is re‐examined based on the recently developed formulation of thermodynamics of stress‐induced first‐order solid‐solid phase transformations. The tacit assumptions to derive the Clausius‐Clapeyron equation for the Ms temperature are revealed and the effects of different elastic constants for martensite and parent phases on thermodynamic aspects of the transformation are discussed. Previous approaches on the stress effects on martensitic transformations are also re‐investigated.
Uniaxial Stress Dependence of the Static Dielectric Constant of Some Alkali Halides
Authors: Barth M. , Lorke W. , Mohler E. 
Published: July 2007

AbstractA sensitive method to measure the strain derivatives of the static dielectric constant of uniaxially stressed crystals is described. With stress modulation and phase‐sensitive detection, changes as small as 5 × 10−7 of the sample's capacitance can be detected. The piezodielectric and electrostrictive tensor components of LiF, NaCl, and KCl are given. The experimental results are compared with theoretical estimates of these coefficients based on lattice dynamical models.
Structure and Bonding in Cubic IV‐VI Crystals VII. On the Influence of Defects on the Stability of the Cubic Structure
Authors: Enders P. 
Published: July 2007

AbstractThe influence of defects (vacancies) on the phase transition is qualitatively treated within the framework of simple one‐dimensional models. Generalizing Gömez‐Santos' and Ynduráin's treatment to a diatomic chain, their stabilizing the cubic phase rôle can be explained as destroying the coherence of the electronic charge density wave driving the Peierls instability. The degree of coherence destroying necessary to suppress the phase transition can be quite small due to the extrinsic Peierls gap (ionic energy).
Mechanisms of Diffusion of a Small Impurity in Noble Gas Crystals
Authors: Eletskii A. V. , Stepanov E. V. 
Published: July 2007

AbstractMechanisms of diffusion of fluorine in noble gas crystals are analyzed. By numerical simulation of the fluorine atom interstitial diffusion jump in a crypton crystal the profile of the system potential energy is obtained along the jump coordinate. The most energy‐beneficial way for the fluorine atom transition between neighbouring octahedral interstices is shown to pass through a tetrahedral interstice in which the position of fluorine atom is unstable (the octa‐tetra‐octa jump). The theory of such transitions is developed, taking into account the change in phonon spectrum of a disturbed crystal in the process of diffusion jump. The fluorine atom diffusion coefficient is obtained.
Displacement Spike Annealing in α‐Iron Irradiated by PKA in the Energy Range 20 to 100 keV
Authors: Melker A. I. , Romanov S. N. , Tokmakova V. S. 
Published: July 2007

AbstractThe short time annealing of the displacement spikes initiated by primary knock‐on atoms (PKA) with an energy E = 20, 50, and 100 keV in α‐iron is studied. The interstitital distributions got are in good agreement with the theoretical ones found by the stationary approximation method suggested. The vacancy cluster distribution remains practically unchanged during a short‐time annealing and therefore is completely determined by creation processes of athermal vacancy clusters.
Charge Transfer in Chromium‐Transition Metal Alloys
Authors: Kulakowski K. , Maksymowicz A. Z. 
Published: July 2007

AbstractThe average T‐matrix approximation is applied for calculations of charge transfer of 3d‐electrons in transition metal alloys. In the dilute limit for Cr‐based alloys the transfer of electrons from Cr produces a surplus of about 1.1 electrons on V sites. Manganese lacks 1.1 3d‐electrons and Fe gives away 2.2 electrons. The values are in reasonable agreement with experimental data. For a concentration c = 0.5 the transfers are about half of the values for the dilute cases: 0.5, —0.5, and —1, respectively. Atomic short range order has only slight influence on the charge transfer. Atomic long range order plays a considerable role and may even change the sign of the transfer when compared with the chaotic alloy case.
Gap Shift in Doped Semiconductors at Finite Temperatures
Authors: Thuselt F. , Rösler M. 
Published: July 2007

AbstractThe interaction part to the chemical potential in doped semiconductors which is well‐suited to describe the gap shrinkage is calculated in the random‐phase approximation (RPA). The numerical results are compared with several approximate formulas to be approached within certain ranges in the density‐temperature plane. The numerical calculations are performed for n‐doped Si and GaAs being representatives of typical indirect and direct materials. Both behave completely different: in the former the gap shift is nearly independent of temperature due to the dominance of short‐wavelength screening, where in direct semiconductors the long‐wavelength screening leads to a strongly temperature‐dependent gap shift. The fraction of the impurity contribution to the total gap shrinkage behaves different in both types of materials, too.
Magnetoconductance in Metallic Granular Gallium Films
Authors: Sood B. R. 
Published: July 2007

AbstractAn expression for the magnetoconductance in metallic granular gallium films is obtained by modifying McMillan's conductivity expression which was derived by a phenomenological scaling theory that included localization, correlation, and screening. McMillan's result for the conductivity is modified so as to include the magnetic field dependences of the correlation gap parameter and of the localization length parameter. The magnetic field dependence of the correlation gap parameter observed by the author in granular gallium films is used, whereas for the magnetic field dependence of the localization length parameter an expression obtained by equating the length scale to the Landau orbit radius is used. The expression for the magnetoconductance contains a critical field parameter and is valid for magnetic field values greater than this critical field. It is expected that the expression for the magnetoconductance holds for other materials also with an appropriate value of the critical field. The predicted results compare very well with recent results on granular aluminium films.