bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Interaction of Electrons and Holes in a Molecular Crystal
Authors: Jurgis A. , Silinsh E. A. 
Published: July 2007

AbstractA self‐consistent polarization field (SCPF) method is used in the framework of a classical electrostatic model to compute single charge carrier polarization energies and electron‐hole interaction energies in naphthalene and anthracene crystals. The crystal polarization energy Pe‐h of an electron‐hole pair localized on specific sites and the energy of the respective charge transfer (CT) states ECT have been calculated for nearest‐neighbour states in naphthalene and five specific sites in anthracene. The estimated polarization energy of a single charge carrier is 1.27 eV for naphthalene, 0.07 eV below the mean reported experimental value, and 1.52 eV for anthracene, 0.06 eV below the mean experimental value. The energy of the nearest‐neighbour CT state is estimated to be 4.29 eV for naphthalene, 0.09 eV below the reported experimental value, and 3.19 eV for anthracene, 0.26 eV below the reported experimental value. The energy of the first conductivity level for electrons E'C is estimated to be 3.96 eV for anthracene, 0.06 eV above the reported threshold for intrinsic photoconductivity. The validity and perspectives of the SCPF method are discussed.
Transport Relaxation Time for Phonon‐Impurity Scattering
Authors: Altukhov V. I. , Zavt G. S. 
Published: July 2007

AbstractStarting from the Kubo formula the thermal conductivity is expressed by the two‐phonon Green's function. The latter is calculated for a cubic lattice containing a small fraction of impurities with taking into account the change of force constants. It is shown that the procedure of the configurational average introduces a correlated motion of two phonons which is described by the vertex correction. This correction appears to be essential if the impurity generates at least two resonant modes with close frequencies but with opposite parity. In this case the scattering cross‐section is decreased by the vertex correction. The correlation in the phonon motion is expected to be essential in KI: Ag.
Use of Green's Function to s–d Interaction in Ferromagnetism
Authors: Nicoarǎ I. 
Published: July 2007

AbstractThe influence of the s‐d interaction on the ferromagnet with S = 1/2 with nearest‐neighbour exchange interaction has been considered using the double‐time Green's functions. The equations of motion have been obtained for two kinds of Green's functions G(−) and G(+), which are derived using commutator and anticommutator, respectively. Expressions are given for the energy shift and damping caused by the s–d interaction, using the decoupling approximation proposed by Katsura and Horiguchi.
The Influence of Quantum Effects on the Low‐Temperature Creep of Zinc Crystals
Authors: Natsik V. D. , Osetskii A. I. , Soldatov V. P. , Startsev V. I. 
Published: July 2007

AbstractThe creep of single crystals of Zn deformed by simple shear along the basis plane (0001) has been investigated in the temperature range 1.5 to 80 °K. It is shown that the influence of temperature on the creep in the investigated temperature range is weaker than that predicted by the classical theory of thermally activated creep. A peculiar temperature run of parameters describing the creep process has been discovered and proved anomalous as compared with the classical run. A mechanism for the influence of zero‐point vibrations of the dislocation line on its motion through an aggregate of local obstacles is suggested and analyzed. The results obtained in this way show a satisfactory agreement with the experimental data.
On the Theory of Nonradiative Transitions in Polar Media I. Processes without “Mixing” of Quantum and Classical Degrees of Freedom
Authors: Dogonadze R. R. , Kuznetsov A. M. , Vorotyntsev M. A. 
Published: July 2007

AbstractThe probability of radiationless transitions between two multi‐dimensional parabolic terms is calculated. The dependence of transition probability on temperature and heat of the processes is investigated. It is shown that all the degrees of freedom of the system may be divided into “classical” and “quantum” degrees of freedom in dependence of their behaviour during process. The activation dependence of the transition probability on the temperature is associated with the motion along the classical degrees of freedom only. The change of states of quantum degrees of freedom leads to the appearance of an exponential non‐temperature factor in the transition probability. The transition is shown to be of activationless or barrierless character at large values (modulo) of the heat of process for the processes without “mixing” of classical and quantum degrees of freedom.
On the Elasticity of Ionic Compounds under Hydrostatic Pressure
Authors: Vuxcevich M. R. 
Published: July 2007

AbstractThe pressure derivatives of the elastic constants of CsCl, NaCl, and ZnS lattices were calculated as functions of the difference in sizes of ions and the range of the repulsive forces. General conditions for the negative pressure dependence of the shear constants are examined. The agreement with the experimental results is reasonable, which indicates that the ion‐size difference will have to be taken into account in all future considerations of the elastic properties of compounds.
An Analytical Discrete Lattice Calculation of Vacancy Decay in Dilute Alloys
Authors: Macewen S. R. , Koiwa M. 
Published: July 2007

AbstractA discrete lattice calculation of vacancy annealing in dilute alloys has been performed, and the results are compared with the Damask and Dienes chemical reaction rate formulation. It is shown that the reaction rate scheme overestimates the initial transient vacancy decay rate. However, at long times, after the attainment of chemical equilibrium between solute‐vacancy complexes and f pee vacancies, the discrete lattice and rate theory formulations become identical. The rate of solute‐vacancy complex formation has been calculated using the theory of stochastic processes to determine the expected time required for a vacancy to migrate from a given position in the lattice to a first nearest neighbour position of a solute atom. Good agreement is found with the transient rate constants found from the discrete lattice annealing calculations.
Non‐Linear Theory of Charged Dislocations and Their Surrounding Charge Clouds
Authors: Whitworth R. W. 
Published: July 2007

AbstractThe thermal equilibrium charge on a dislocation is calculated on the assumption that the dislocation is charged by a number of identical point charges at sites on its core. The surrounding charge cloud is treated as a continuum interacting with the dislocation by electrostatic forces only. The non‐linear differential equation of this cloud is solved numerically for cases appropriate to ionic crystals and semiconductors in both the intrinsic and extrinsic regions. The effect on the free energy of electrostatic interactions between nearest‐neighbour charges on the core is taken into account. The force to pull a dislocation from its charge cloud is calculated.
EPR Optical Detection of F Centre Pairs in Alkali Halides I. Pumping Cycle Kinetics and Characteristics of the Resonances
Authors: Ruedin Y. , Schnegg P.‐A. , Jaccard C. , Aegerter M. A. 
Published: July 2007

AbstractThe electron paramagnetic resonance of F centres in the ground and excited states has been optically detected in the following alkali halide crystals: NaCl, KF, KCl, KBr, KI, RbBr, and RbI. A decrease of the radiative quantum efficiency of the F centre luminescence is observed when microwave transitions are induced between the spin levels. The mechanism responsible for this effect is an electronic tunnelling through the crystal field potential; the electron in the relaxed excited state of an F centre (F̃*) is transfered non radiatively to another nearby F centre in its ground state (F0), and leads to the momentary formation of an α and an F′ centre. Such a process is a function of the total spin of the F̃*‐F0 pair. The role played by the paired centres is confirmed by measurements at different F centre concentration. Moreover at high optical excitation pumping rate the population of the intermediate complexes (F′‐α) is large enough to allow an estimation of the rate of the reverse process F′ + α → F0 + F0.
Metal–Insulator Transition and Lifshits Instability in the Hubbard Model
Authors: Weller W. 
Published: July 2007

AbstractThe metal–insulator transition (Mott transition) in the Hubbard model for a half‐filled narrow band is considered by means of the functional integral method. The functional integral is calculated in the static approximation. Higher‐order fluctuations in the exponent of the functional integral are neglected, and a self‐consistent approximation scheme analogous to the coherent potential approximation is used. An instability in the free energy leading to a first order transition is obtained. This instability corresponds to the instability studied by Lifshits in connection with the passing of an energy branch through the Fermi energy.
Raman Effect in Selenium–Tellurium Mixed Crystals
Authors: Geick R. , Steigmeier E. F. , Auderset H. 
Published: July 2007

AbstractThe Raman effect in selenium–tellurium mixed crystals has been studied. Four first order Raman lines have been observed and associated with long wavelength lattice modes of the alloy system. The experimental results together with existing infrared data indicate that the long wavelength modes from three of the six optical branches in these trigonal crystals show “multimode behaviour” while the other three branches show “one mode behaviour”. All the experimental data are compared to and discussed in connection with an existing random‐element‐isodisplacement model calculation of the eigenfrequencies of the lattice modes as a function of composition. The calculated frequencies and the predictions of the model for the behaviour of the long wavelength lattice modes are in, at least, qualitative agreement with the experimental data.
NMR Lineshapes of Magnetic Diluted Systems in Solids
Authors: Freude D. , Schmiedel H. 
Published: July 2007

AbstractThere are two well‐known methods for calculating dipolar broadened NMR lineshapes of magnetic diluted spin systems in solids, viz. the “method of moments” and the “statistical theory”. It is shown, that in the case of a two‐dimensional statistical spin distribution the above‐mentioned methods give different results, which can be explained by the arbitrary assumption of a Lorentzian lineshape within the method of moments. An extension of statistical theory by introducing a minimum distance between the spins reveals lineshapes, which converge more rapidly and thus better correspond to real situations. Finally lineshapes of magnetic diluted spin pairs are discussed.
Dependence of Positron Lifetimes on the Temperature and Phase of Some Organic Media
Authors: Thosar B. V. , Laciu R. G. , Kulkarni V. G. , Chandra Girish 
Published: July 2007

AbstractMeasurements of the value τ2 and the intensity I2 of the long component in the life‐time spectra of positrons annihilating in some simple unassociated, polar, and associated organic liquids are reported as a function of temperature. A semi‐empirical free volume model for the formation and quenching of ortho‐positronium atoms is developed for simple molecular materials to explain the correlation between viscosity η, density ϱ, and τ2 observed in unassociated and polar liquids. Such a correlation is not observed for associated liquids in which the presence of hydrogen bonds between molecules apparently influences the annihilation process. The data of positron lifetimes during the solid‐liquid phase transition in some organic systems are discussed in terms of the free volume model.
Dislocation Description of Twin Dynamic Behaviour
Authors: Boiko V. S. 
Published: July 2007

AbstractRelationships are obtained which allow to describe the characteristics of the twin as functions of time and medium constants for dynamic external loads within the framework of the dislocation theory. The case of large velocities is considered when the drag force arising in the dislocation motion is of the viscous friction character and, yet, the relativistic effects may be neglected. Two problems in the dynamic behaviour of the twin are solved, namely the escape of the elastic twin from an unloaded crystal due to the surface tension force and passage across the crystal by the twin in a uniform stress field. The obtained results are compared with experimental data for iron, calcite, and cadmium. It is shown that in the considered case of large velocities the twin motion velocity should be weakly (at least, not exponentially) dependent on temperature. This result is in agreement with available experimental data.
Charge Compensation of Fe3+ Ions in V2 O5 (ESR Measurements)
Authors: Jansen K. , Sperlich G. 
Published: July 2007

AbstractThe ESR spectrum of iron doped V2O5 single crystals shows two different line groups. Analysis of the angular dependence and intensity measurements prove that, contrary to Cr3+ ions, Fe3+ ions occupy lattice sites and tetrahedral sites as well. This is in agreement with published Mossbauer results. Moreover, the influence of the Fe3+ concentration upon the signal intensity of the vanadium 3d1 electron was investigated.
Properties of Pseudoatoms Derived from the Shaw Model Potential
Authors: Paasch G. , Woittennek H. 
Published: July 2007

AbstractA smooth pseudoatom potential is derived from the Shaw model potential for simple metals. The screening by a homogeneous conduction electron density yields nearly the same results as the self‐consistent screening. The minimum perturbation in terms of phase shifts is investigated. The pseudoatom is compared with the Mattheiss potential and with the renormalized atom via the logarithmic derivatives.
Determination of Optical Constants: a‐Si
Authors: Jungk G. 
Published: July 2007

AbstractOptical studies of a‐Si samples are reported. The dielectric function was determined ellipsometrically from 2.0 to 4.0 eV. Different concentrations of slit‐like voids may account for the variation of the optical constants in the investigated films. The depolarization factor L of the voids was estimated to 0.75 5 ≦ L ≦ 0.9. A structure of the optical constants near 3.5 eV indicates an exciton‐like transition. The extrapolation of the hv √ E2eff curves points to a pseudogap of the ideal a‐Si comparable with the indirect gap of the crystalline phase. These pseudogaps increase with increasing void‐concentration.
Temperature Dependence of Half‐Widths and Integral Absorptions of the Impurity Polyatomic Ion Vibration Bands in Alkali‐Halide Crystals
Authors: Tsyashcrenko Yu. P. , Demyanenko V. P. , Pinkevich I. P. 
Published: July 2007

AbstractA quantitative study has been made of the temperature dependence of the half‐widths Avlp and integral optical densities A of the vibration bands v2 and v3 of the impurity anion NCO− in CsI crystals, of the vibrations v1 and v2 of NCS− in CsI, of components of the v3 triplet of the complex SO. Ba2+ in KCI (in the temperature range 100 to 500 °K); and of the vibrations v2 and vg of the anion NO in CsI (in the temperature range 100 to 700 °K). It is shown that the integral absorption remains practically constant for all the bands over the whole temperature range while the half‐widths increase sharply with increasing T. In the representation Δvl/2(T) = Δv1/2(0) + α Tn at rather high T (T > 300 °K) the effective ñ for different bands are calculated with the purpose of determining a preferable mechanism of anharmonic interaction of corresponding intramolecular vibrations (local vibrations in the crystal‐matrix) with lattice phonons. The results obtained agree with existing theoretical views of the role of dissociation and modulation mechanisms of the local vibration band temperature broadening.
Paramagnetic Resonance of a Cu(II) Ion in a Distorted Tetrahedral Environment
Authors: Voronkova V. K. , Zaripov M. M. , Kogan V. A. , Yablokov Yu. V. 
Published: July 2007

AbstractElectron paramatic resonance has been studied in polycrystalline undiluted samples of several salicylaldimine derivatives of known crystal structure. In two studied compounds (bis (N‐isopropylsalicylaldiminato) Cu and bis (N‐t‐butylsalicylaldiminato) Cu) the structure of the nearest environment is intermediate between tetrahedral and square coplanar. The obtained values and signs of anisotropy of the g‐factors show the essential difference between the properties of the copper ion in these two compounds and that in the case of the planar complex. On the basis of a theoretical analysis it is found that the electronic properties of the copper (II) ion in bis (N‐isopropylsalicylaldiminato) Cu and bis (N‐t‐butylsalicylaldiminato) Cu can be explained by consideration of the nearest environment symmetry as a elongated tetrahedron with d p ground state and taking into account the admixture of upper 4p and 4s states into the 3d wave functions. The values of the covalency and admixtures of the 4p and 4s states are estimated for bis (N‐isopropylsalicylaldiminato) Cu. A suggestion is made about the variation of these values under the transition to the more distorted structure in bis (N‐t‐butylsalicylaldiminato) Cu.
Tenfold d‐Electron Degeneracy in the Hubbard Model and Transition‐Metal Magnetism. II. The Antiferromagnetic‐Paramagnetic and Antiferromagnetic‐Ferromagnetic Transitions
Authors: Siegel E. J. 
Published: July 2007

AbstractIntrasite d‐d electron interactions are included in the Hubbard model, replacing the simplified s‐electron picture of Penn [5]. The technique is identical with an earlier paper by Siegel and Kemeny [1] on the ferromagnetic‐paramagnetic transition. Choosing k‐space correlation functions to represent the paramagnetic, ferromagnetic, and antiferromagnetic states, the tenfold degenerate eigenvalue problem is solved and free energies are self consistently calculated for various combinations of the three parameters: d‐band filling, direct interaction Coulomb constant divided by one third the d‐bandwidth, and exchange interaction constant divided by one third the d‐bandwidth. The antiferromagnetic‐paramagnetic and antiferromagnetic‐ferromagnetic phase boundary surfaces are plotted a t near zero and finite temperatures with the third dimension being the exchange interaction constant divided by one third the d‐bandwidth (J/4T). The near zero temperature trend shows that the inclusion of exchange, as expected, enhanced the antiferromagnetic region at the expense of the paramagnetic region. This antiferromagnetic region enhancement over the para‐magnetic region is exactly the opposite of the nondegenerate. t‐matrix result of Caron and Kemeny [7]. Finite temperature calculations for the antiferromagnetic‐paramagnetic transition show the same trend with increasing exchange, but shift the phase boundary so as to decrease the antiferromagnetic region relative to that at near zero temperature for the same value of exchange interaction constant, J. The antiferromagnetic‐ferromagnetic phase boundary shift as a function of increasing d‐d exchange interaction constant, J, is much harder to calculate since two ordered magnetic spin states are in competition. Within the scatter of the calculated free energy values, it is seen that the ferromagnetic region is enhanced at the expense of the antiferromagnetic region, but just barely. This enhancement is much less than that of ferromagnetic over paramagnetic. in [1], or of antiferro‐magnetic over paramagnetic, here, where strongly spin ordered magnetic spin states are compared to a spin disordered state. For the slight ferromagnetic region enhancement over the antiferromagnetic region, again the trend is opposite to the t‐matrix result, which enhances the antiferromagnetic region at the expense of the ferromagnetic region relative to Penn's [5] nondegenerate calculation. But again, since Penn's [5] calculation is good only to direct Coulomb interaction constant K = 0.25, while Caron and Kemeny's [7] is good rigorously down to K = 0.0, nothing can be said abont, how the calculation compares with Penn's [5] for K < 0.25.
Nichtlineare optische Suszeptibilitäten von Zinkblende‐ und Wurtzit‐Kristallen
Authors: Hübner K. 
Published: July 2007

AbstractAuf der Basis der semiempirischen Theorie für die lineare optische Suszeptibilität von Phillips und Van Vechten und eines Ladungstransportmodells von Tang und Flytzanis wird ein Modell ohne freie Parameter für die Suszeptibilität 2. Ordnung aafgestellt, das außer den Valenzelektronen explizit Rumpf‐d‐Elektronen berücksichtigt. Das Modell liefert für die untersuchten 29 IV–IV–, III–V–, II VI– und I–VIT–Verbindungen mit tetraedrischer Koordination numerische Ergebnisse in guter Übereinstimmung mit experimentellen und theoretischen Werten anderer Autoren und erklärt das anomale nichtlineare Verhalten von ZnO und ähnlichen Verbindungen ohne wesentliche Zusatzannahmen. Es wird eine Beziehung zwischen dem Miller‐Koeffizienten und der effektiven Ionenladung von Szigeti hergestellt.
Low‐Field Transport Properties of a Polar Semiconductor in a Quantizing Parallel Magnetic Field
Authors: Magnusson B. 
Published: July 2007

AbstractLow field momentum distribution functions and magnetoresistance in a quantizing magnetic field have been calculated numerically for a semiconductor with a parabolic conduction band. The shifting of maxima and minima in the magnetoresistance versus magnetic field curves and the detailed behaviour around the first magnetophonon resonance point are investigated. A second resonance series is noticed for higher lattice temperatures.
Zero‐Phonon Lines in the Luminescence Spectra of Impurity Organic Crystals and Electron–Phonon Interaction
Authors: Sapozhnikov M. N. 
Published: July 2007

AbstractThe temperature dependences of the shapes, widths, positions, and intensities of the zero‐phonon lines in the fluorescence spectra of 1.12‐benzperylene and coronene in a normal hexane matrix are investigated experimentally. The results obtained are discussed in terms of the theory of the electron‐phonon interaction in the impurity crystals. Thestrength of the impurity‐matrix coupling in the systems studied is shown to he very small. At high temperatures the zero‐phonon linewidth is a result of the Raman seattering of the lattice phonons by the impurity molecule. The estimation of the change in normal mode frequencies upon the phototransition in the impurity molecule and the mixing of the initial state normal modes of the crystal show that those values are small. The anharmonicity of the crystal vibrations in the “soft” organic crystals in contrast to the “hard” inorganic crystals is shown to play an important role and to determine considerably the zero‐phonon line characteristics.
Energy Bands of Copper Chloride I. Theory
Authors: Calabrese E. , Fowler W. B. 
Published: July 2007

AbstractA calculation of the energy bands of CuCl has been performed in which several innovations and refinements were made to previous procedures. In this paper the method used in the calculation is described. The combined plane‐wave tight‐binding (“mixed‐basis”) method of Kunz was adapted to the zinc blende lattice. Tight‐binding functions were truncated so as not to overlap one another, as suggested by Deegan and Twose. Overlap between these functions and the short‐range potential (which was not truncated) of neighboring ions was significant and so was included. A semiempirical approach was devised which involved adding a square‐well potential of adjustable strength to each ionic potential. In order to obtain coefficients of p‐like and d‐like contributions to a given eigenfunction, a technique was devised for projecting these from the plane waves.