bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Properties of Lattice Vibrations in Molecular Crystals
Authors: Barentzen H. , Schrader B. , Merten L. 
Published: July 2007

AbstractA classical microscopic theory is presented for the optical properties of lattice vibrations in molecular crystals, which are composed of electrically neutral molecules bound by van der Waals forces. It is shown, that Huang's theory, which until now has been applied to ionic crystals only, is also valid for molecular crystals. Finally, oscillator strengths as well as LO and TO frequencies are calculated for thiourea according to the “oriented gas” model. A comparison shows, that the calculated oscillator strengths have the same order of magnitude as those of α‐quartz.
Lattice Dynamics of Lead: A Pseudopotential Approach
Authors: Gupta H. C. , Tripathi B. B. 
Published: July 2007

AbstractThe phonon frequencies, Grüneisen parameters, binding energy, compressibility, spin susceptibility, and the elastic constants of crystalline lead and the electrical resistivity and the thermoelectric power of lead in the liquid state are calculated using a model pseudo‐potential, recently proposed having two adjustable parameters. Kohn anomalies show up in the calculated phonon dispersion and Grüneisen parameter curves.
Lattice Dynamics and Infrared Absorption of Cesium Halides
Authors: Mahler G. , Engelhardt P. 
Published: July 2007

AbstractBased on the Breathing Shell Model dispersion curves and densities of states of CsCl, CsBr, and CsI are calculated. In addition the two‐phonon‐density of states, the damping function, and the shift of the resonance frequency are computed for CsBr and compared with experimental data.
Exact Test of the Adiabatic Approximation for Exciton–Phonon Interactions
Authors: Suna A. 
Published: July 2007

AbstractThe adiabatic approximation, used recently by Davydov to study the deformation of molecular crystals in the presence of electronic excitation, is examined with the aid of a numerically exactly soluble model of an exciton in a deformable dimer. This approximation, valid when the phonon energy is small compared to the exciton–phonon binding energy, gives a generally good upper bound on the ground state exciton energy for this model, but is insufficient to characterize exciton propagation. Delocalization of the exciton wavefunction in this approximation is not necessarily equivalent to free exciton motion but implies a weak exciton–phonon correlation.
Intermolecular Exchange Interaction in Copper (II) Carboxilates
Authors: Gavrilov V. V. , Yablokov Yu. V. , Milkova L. N. , Ablov A. V. 
Published: July 2007

AbstractMonocrystals and powders of some binuclear Cu(II) carboxilates which EPR spectra cannot be described by the usual S = 1 spin Hamiltonian were investigated. It is shown that all the peculiarities of their spectra can be interpreted taking temperature dependent intermolecular exchange into account. The observed effects are discussed assuming that the triplet exciton is able to migrate through the crystal lattice.
A Statistical Treatment of the Free Energy of Binary Non‐Homogeneous Solutions
Authors: Cadoret R. 
Published: July 2007

AbstractA statistical treatment of non‐homogeneous binary solutions is obtained by considering subsystems with a random distribution. The free energy is derived from the partition function corresponding to a given distribution of A and B atoms between the subsystems. Calculations are more precisely performed on the base of nearest neighbour interactions. For cubic lattices, the relation deduced from the general equation obtained is similar to the equation previously given by Cook, de Fontaine, and Hilliard. Cahn and Hilliard's equation appears as an approximation restricted to small composition fluctuations.
Localized Orbitals in Polyatomic Systems (II)
Authors: Kunz A. B. 
Published: July 2007

AbstractPreviously we have developed a technique for obtaining the charge density for closed shell solids in their ground state in the Hartree‐Fock approximation by a transformation to local orbitals. Using this first order local orbitals equation we obtain self‐consistent local orbitals for solid argon. We then use symmetry and equivalence restrictions to extend the technique to open shell systems and obtain the local orbitals for aluminum in its ground state.
Infrared Absorption by Excitons and Their Associates in Silicon
Authors: Ashkinadze B. M. , Kretsu I. P. , Patrin A. A. , Yaroshetskii I. D. 
Published: July 2007

AbstractThe absorption of light, Λ = 1.4 μm, has been investigated in undoped silicon at T < 30 °K under powerful laser light with hω = 1.21 eV. Under these conditions the absorption modulation pulse shows two distinct decay times with τc 0.4 μs and τex. ≈ 5 to 7 μs, the proportion of either of the two components being strongly dependent on temperature and excitation intensity. The results are discussed in terms of the formation of a condensed exciton phase having a short lifetime of τc 0.4 μs. In specimens immersed in liquid He absorption oscillations induced by laser light have been observed.
Small Polarons in Conducting Barium Titanate Crystals
Authors: Bursian E. V. , Girshberg Ya. G. , Starov E. N. 
Published: July 2007

AbstractThe light absorption and concentration dependence of the thermopower in BaTiO3 conducting single crystals were investigated. The absorption peak at Λ = 2 μm is interpreted as due to small polaron absorption. A quantitative comparison is made between theory and experiment.
On the Calculation of the Narrow Band Width in Solids
Authors: Perrot F. 
Published: July 2007

AbstractUsing the APW method for the crystal states description, an upper bound to the band width of the tight bound core states in solids can be obtained from the calculation of two particular solutions of the Schrödinger radial equation with respect to the crystal muffin‐tin potential and the dominant angular momentum in the band. An analytical expression of the dominant logarithmic derivative calculated as a function of energy at the APW sphere radius is then derived, which saves much computer time if different points in the band have to be exactly computed. A numerical test is performed on the 1s state in solid lithium.
Paramagnetic Resonance of Er3+ and Dy3+ in Natural Single Crystals of Zircon
Authors: Ball D. 
Published: July 2007

AbstractThe paramagnetic resonance of two rare‐earth ions Er3+ and Dy3+, not previously reported in the literature, was observed in natural single crystals of zircon. The spectra were observed at 4.2 °K at 9 and 35 GHz. For both ions well‐resolved hyperfine structure was observed corresponding to the natural isotopic abundances of both ions. In particular for Er3+ in the perpendicular direction forbidden Δm = ±2 lines were observed, from which an accurate value of P was calculated. The spectra were fitted by a spin‐Hamiltonian containing electronic Zeeman, hyperfine, and nuclear quadrupole terms for Er3+ and electronic Zeeman and hyperfine terms for Dy3+.
Kinetics of Localized Exciton Recombination in CsI
Authors: Lamatsch H. , Rossel J. , Saurer E. 
Published: July 2007

AbstractTwo absorption peaks situated on the long‐wavelength tail of the excitonic bands in thick films and bulk crystals doped with divalent cations are reported. Calculations using a Born‐Haber cycle show that these peaks are due to excitons localized on cationic vacancy‐divalent cation complexes as previously proposed. The decay time of the corresponding emission is determined and the kinetics of localized exciton recombination is discussed.
Local Orbital Equations for Excited States
Authors: Kunz A. B. 
Published: July 2007

AbstractPreviously, we have developed computationally tractable, local orbitals techniques for computing the charge density of the ground state of a crystal in the Hartree‐Fock limit. In the present paper, we extend our previous concepts to the question of the virtual orbitals of a Hartree‐Fock system. Such orbitals may become useful in constructing the states of excitons, excited states of impurity centers or for LCAO calculations of energy bands. These orbitals also provide a convenient basis for performing configuration interaction calculations. This is demonstrated in a simple case, that of the helium atom. Finally we develop equations for the virtual orbitals which are correct to first order in interatomic overlap.
Impurity Concentration Broadening of Acceptor Lines in Indium‐Doped Silicon
Authors: Bhatia K. L. 
Published: July 2007

AbstractIndium external acceptor states in Si(In) are experimentally studied as a function of increasing indium impurity concentration. The halfwidth of the observed indium external absorption line 2, is determined in Si(In) samples of impurity concentrations 6 × 1015 to 5 × 1017 atoms/cm3. The species dependent behaviour of the indium external line 2 is attributed to the changes produced in both, the ground state and the excited state wave functions, by the deviation of indium core potential from that of a simple point charge.
Magnetic Field Dependence of Even Hall Effect in n‐Ge
Authors: Baranskii P. I. , Baidakov V. V. , Dakhovskii I. V. , Samoilovich A. G. 
Published: July 2007

AbstractThe magnetic field dependences of the coefficient R̃ determining the even Hall effect are theoretically calculated and experimentally measured in n‐Ge at j ∥︁ [111] and H ∥︁ [110] in the magnetic field interval 0 ≦ H ≦ 35 kOe and in the range of dominant phonon scattering (at 77.4 °K). The results of the calculations are in quantitative agreement with experimental data. For the conditions of dominant phonon scattering it is shown theoretically and experimentally that the relation G = Ū(H)/UU = f(H) (where Ū(H) is the voltage of the even Hall effect and UH⟂ is the voltage determining the specific resistance of an investigated crystal in a transverse magnetic field of the same strength) is completely saturated in magnetic fields ≧ 15 kOe. This saturation is directly connected with the anisotropy parameter K. The saturation magnetic fields have considerably lower values than those (approximately 50 to 100 kOe) which are necessary for the saturation of the function M = ϱH∥︁H→∞(H). This fact advantageously distinguishes the proposed method of measurement of K from a formely known one, where M is used for this purpose.
A transport equation for electrons in simple liquid metals
Authors: Gilbert R. , Morgan G. J. 
Published: July 2007

AbstractAn “equation‐of‐motion method” is used for calculating the one‐particle density matrix. In this way an exact electron transport equation is derived in terms of the Green function of the Liouville equation. Approximations are developed which are applicable to simple liquid metals when the “mean free path” is comparable with the atomic spacing.
Multiple scattering of lithium ions with energies from 10 to 50 keV in various target materials
Authors: Schwabe S. , Stolle R. 
Published: July 2007

AbstractExperimental results are reported regarding the multiple scattering of lithium ions with energies from 10 to 50 keV in carbon, aluminium, silicon, vanadium, chromium, iron, cobalt, and germanium. The targets consisted of thin self‐supporting foils 150 to 700 Å thick. The results of the scattering measurements agree satisfactorily with Meyer's theory of multiple scattering with regard to the dependence on the energy of the ions, foil thickness, and the form of the scattering distribution.
Paramagnetic resonance of Er3+ and Yb3+ in YAsO4
Authors: Plamper J. 
Published: July 2007

AbstractParamagnetic resonance of trivalent erbium and ytterbium in single crystals of yttrium arsenate has been observed at K‐band frequencies and temperatures of 4.2 and 1.6 K. Spin‐Hamiltonian parameters have been determined and the ground state eigenfunctions are discussed.
Multiple scattering of thermal neutrons by a perfect crystal. II. Calculation of approximate values for the information quantities
Authors: Solbrig H. 
Published: July 2007

AbstractThe general method of part I of this work is developed further to get explicit approximate solutions for the information parameters Q and X(Q) of this theory in the quasi‐optical case, the symmetrical Laue case, and the symmetrical Bragg case. Starting from a formally exact method for computation of Q and X(Q), which is equivalent to that following from a theory using a differential equation, the basic approach of part I is introduced. The resulting equations are, in principle, equivalent to those of the Laue theory for X‐rays.
The chemical potential for interstitials in solid solution
Authors: Buck H. , Alefeld G. 
Published: July 2007

AbstractThe configurational entropy and the chemical potential in the molecular‐field approximation are derived for interstitials in solids applying the following model: The host lattice is divided into cells of such a size that at maximum concentration each cell is occupied by one interstitial. Within each cell the interstitial may occupy n distinguishable positions. For n = 1 the results of the lattice gas model are reproduced whereas n ≫ 1 yields the van der Waals isotherms.
A contribution to the theory of electromagnetic analogy for the field of moving dislocations
Authors: Minagawa S. 
Published: July 2007

AbstractThe conception of the source and sink of a dislocation line is introduced, and the creation of dislocations by the movement of the source is treated. The theory of the electromagnetic analogy for the field of moving dislocations is extended to a version which includes the terms related to the source. Finally the force acting on a source is discussed.
Numerical solution of the Born‐Green equation for the pair potential
Authors: Waseda Y. , Suzuki K. 
Published: July 2007

AbstractTo derive the pair potential from observed structural data the Born‐Green equation has been numerically solved by a linearized simultaneous equation method without any initial function. Liquid Cs has a long‐range oscillatory potential, whereas liquid Ar has a Lennard‐Jones type potential. Problems such as truncating the infinite integral at a finite upper value in computing the pair potential have been discussed by means of numerical analysis.
Hall mobility of holes in α‐sulfur
Authors: Seager C. H. 
Published: July 2007

AbstractThe Hall mobility of holes in orthorhombic sulfur has been measured by a modified Red‐field technique over the range 230 to 330 K. The average room temperature value of the three samples measured was 6.6 cm2/Vs, which is quite similar to previously reported values of the room temperature drift mobility. As has been reported in the case of the drift mobility, the temperature dependence of μH appears to be steeper than the normal T−3/2 power law expected for single phonon acoustic scattering. The significance of these results is discussed with regard to band‐like transport of holes in α‐sulfur.
Magnetic circular dichroism of resolved vibronic lines in Cs2ZrCl6:U4+
Authors: Piepho S. B. , Dickinson J. R. , Schatz P. N. 
Published: July 2007

AbstractMagnetic circular dichroism (MCD) measurements at liquid helium temperature are reported for several resolved f–f vibronic lines of U4+ centres in Cs2ZrCl6. Though these lines are too broad for Zeeman measurements, both the signs and magnitudes of the g‐values are determined from the MCD data using first‐order theory. Some assignments are also suggested on the basis of these data.
Champ cristallin et effet Mössbauer dans le composé DyNi3
Authors: Yakinthos J. , Rossat‐Mignod J. , Belakhovsky M. 
Published: July 2007

AbstractOn a testé la validité d'un calcul de charges ponctuelles dans le composé intermétallique DyNi3 par comparaison avec des résultats obtenus par effet Mössbauer sur le 161Dy. On a pu ainsi interpréter la structure magnétique obtenue par diffraction neutronique.
Calculation of activation energy for dislocation movement
Authors: Greenberg B. A. 
Published: July 2007

AbstractThe thermally activated transformation of a certain initial dislocation configuration into a final one is considered. Various possible final dislocation configurations, viz. those formed by two glissile dislocations or by two dislocations of which one is glissile and the other sessile, as well as some other configurations have been investigated. The activation energy of the processes considered is calculated in a single scheme. The activation energy is determined by solving a variational problem with so‐called mobile boundaries.
Dependence of the activation energy of conductivity on the compensation degree in germanium
Authors: Shlimak I. S. , Emtzev V. V. 
Published: July 2007

AbstractSome changes of the activation energy ϵ1 of the conductivity of Ge which are produced by variations of the compensation ratio K are studied in the region of temperatures where the conductivity is related to electrons released from shallow donors into the conduction band. A substantial increase of ϵ1 is found for shallow donor concentrations of about 1 × 1016 cm−3 and 1 – K → 0. This finding is in good quantitative agreement with the theory of Shklovskii and Efros.
The concept of centro‐frequency and the density in Mössbauer studies of solid krypton
Authors: Mahesh K. , Kapil S. V. 
Published: July 2007

AbstractThe concept of the centro‐frequency of the lattice vibrational spectra has been found useful in determining the Mössbauer characteristic temperature of solid krypton. The calculated zero‐point energy is in agreement with experiment and alternative theoretical treatments. The density of the solid exhibits a definite correlation with the Mössbauer parameters and acts as a significant link in the linear correlation between the recoilless strength lg f and the Mössbauer energy shift. The lattice anharmonicity parameter as evaluated from the experimental data is seen to compare favourably with the product of the temperature dependent Grüneisen parameter and the volume expansion coefficient. A simple correlation of the anharmonicity parameter with the Mössbauer characteristic temperature is indicated which seems to be useful for the determination of the former.
The EPR spectrum in CdxHg1–xSe mixed crystals
Authors: Leibler K. , Giriat W. , Wilamowski Z. , Iwanowski R. 
Published: July 2007

AbstractThe paramagnetic resonance spectrum of divalent manganese has been measured in solid solutions of CdxHg1–xSe (0 ≦ × ≦ 0.6). A dependence of the spectroscopic splitting factor g and the hyperfine structure constant A on the composition parameter has been observed. At transition from semiconducting crystals to semi‐metallic states, with inverted band structure, the value of the g‐factor clearly decreases. The parameters of the EPR spectrum and their relations to the other physical properties are discussed.
Combinaisons linéaires symétrisées d'ondes planes et d'orbitales atomiques pour les cristaux ayant la symétrie du groupe spatial D
Authors: Albert J. P. , Jouanin C. , Gout C. 
Published: July 2007

AbstractNous avons calculé les fonctions de base (sous forme de combinaisons linéaires symétrisées d'ondes planes et d'orbitales atomiques) pour les différentes représentations irréductibles du groupe du vecteur d'onde en quelques points et lignes de symétrie de la première zone de Brillouin des cristaux possédant la structure du rutile (D).
The ϵ2‐spectrum of trigonal Te (pseudopotential calculation)
Authors: Maschke K. 
Published: July 2007

AbstractUsing the pseudopotential method the ϵ2‐spectrum of trigonal Te was calculated. To get further insight into the origin of the structures the contributions from various regions of the BZ were calculated separately. The influence of the oscillator strengths is discussed by comparing the calculated joint density of states with the calculated ϵ2‐spectrum.
Spin magnetic moment and spin resonance of conduction electrons in α‐Sn‐type semiconductors
Authors: Kacman P. , Zawadzki W. 
Published: July 2007

AbstractThe magnetic energy levels in a symmetry‐induced zero‐gap semiconductor of α‐Sn‐type are calculated in the three‐level model. An analytical expression for the g‐factor of conduction electrons is derived and shown to be in good agreement with existing experimental data on HgTe and HgSe. The electron wave function for the conduction band is found explicitly and the optical absorption due to electric dipole transitions between spin states of the same Landau level (electric spin resonance) as well as that due to combined transitions (electric combined resonance) is calculated.
Résonance paramagnétique électronique de l'ion Nd3+ en symétrie cubique dans un monocristal de CaO
Authors: Wasiela A. , D'aubigné Y. Merle 
Published: July 2007

AbstractL'ion Nd3+ dans l'oxyde de calcium a été étudié par résonance paramagnétique électronique. Le spectre observé est dǔ au quadruplet fondamental Γ8 et l'Hamiltonien de spin correspondant peut ětre caractérisé par deux paramètres P = 0,1085 ± 0,0015; Q = = 2,637 ± 0,0015. On en a déduit les valeurs des paramètres définissant le champ cristallin cubique B4 = −195 × 10−3 cm−1; B6 = −131 × 10−5 cm−1. Les résultats expérimentaux sont comparés à ceux calculés suivant différents modèles de champ cristallin.
Temperature dependence of the bounds on thermal resistance due to U‐process
Authors: Srivastava G. P. , Verma G. S. 
Published: July 2007

AbstractTemperature dependence of the first two bounds χ and χ on the thermal transport coefficient χ due to three‐phonon umklapp processes is obtained. The results, both in the high‐temperature and low‐temperature approximations, are in agreement with Benin's calculations for solid argon.
On the optical absorption of free polarons at weak coupling
Authors: Devreese J. , Huybrechts W. , Lemmens L. 
Published: July 2007

AbstractThe optical absorption of Frohlieh polarons as a function of the frequency of the incident light is calculated within the Lee‐Low‐Pines formalism. A simple calculation, which is developed here in full detail, gives a result for the absorption coefficient which is exact in order a. Gurevich et al. [1] had obtained this perturbation result using involved calculations based on Green's functions. This result is also extracted here from the “dissipation” calculation of Feynman ct al. [2]. An analytical expression for the optical absorption between 0 < α < 1 is proposed. For α = 1 the main correction to the perturbation result is e decrease of about 15% around the maximum of the absorption. This seems to explain the difference between the experimental absorption detected in CdO (α = 0.75) by Finkenrath et al. [14] and the perturbation result. The effect of a static electric field on the optical absorption coefficient is examined. For low temperatures a shift towards lower frequencies of the threshold for absorptiou is predicted. This shift depends on the mobility and effective mass of the polaron.
Mössbauer effect of Fe57 nuclei in doped A2B4C type semiconductors
Authors: Yarmarkin V. K. , Ikochukhan V. D. , Gricoreva V. S. 
Published: July 2007

AbstractThe Mössbauer spectra of Fe57 nuclei of 1 at% iron impurity atoms are investigated in some compounds of A2B4C type. The isomeric shift and the quadrupole splittings have been determined in the temperature range from −200 to +200 °C. It follows from the comparison with EPR data that in all cases the impurity atoms of Fe have the electron configuration 3d6‐x 4sJ (0 < x, y < 1) and substitute the elements of the I1 group. It has been found that the Mossbauer parameters depend cssentially on the nature of the anion and some cations. An assumption is necessary to compare data on the degree of bond ionicity in the compounds, using Mössbauer parameters.