bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conduction Electron Spin Resonance in Magnesium
Authors: Bowring C. S. , Smithard M. A. , Cousins J. E. 
Published: July 2007

AbstractMeasurements of the conduction electron spin resonance linewidths and relaxation times of magnesium are presented as a function of temperature and at a frequency of 9.27 GHz. The samples all had dimensions which were large in comparison with the skin depth and a temperature range of 80 to 600 °K was covered. The results are interpreted in terms of a temperature‐dependent intrinsic relaxation mechanism, a temperature‐dependent surface relaxation mechanism and a temperature‐independent impurity one.
Pressure Dependence of Elastic Constants and Crystal Stability of Alkali Halides: NaI and KI
Authors: Barsch G. R. , Shull H. E. 
Published: July 2007

AbstractThe single crystal elastic constants and their first and second pressure derivatives have been measured ultrasonically at 298 °K for NaI and KI. Fair agreement with lattice theoretical data calculated from an interaction potential composed of Coulomb, van der Waals and first and second nearest neighbor repulsive forces is found. On the basis of this model it is possible to explain semi‐quantitatively that the first pressure derivatives of the elastic constants of all alkali halides depend almost exclusively on the cation. The convergence of the Taylor expansion of the elastic constants with respect to pressure is investigated theoretically. On the basis of Born's stability criteria the relations between the pressure dependence of the shear moduli c44 and cS to the B1‐B2 transition and the melting curve are investigated.
Etude I.R. et Raman des vibrations de réseau de AlO3Nd
Authors: Alain P. , Piriou B. 
Published: July 2007

AbstractThe optical phonons of AlO3Nd are studied by measurements of polarized infrared reflexion spectra on single crystals in the range 80 to 30000 cm−1. The Eu‐mode parameters are fitted by classical dispersion theory after performing Kramers‐Kronig analysis. Owing to the small size of single crystal domains, an accurate reflexion spectrum for A‐modes cannot be observed and a peculiar analysis method is used to determine oscillator parameters from a composite spectrum with two standards of mode. The Raman active frequencies measured on single crystals oriented (X, Y, Z) and (X, YZ, YZ) are given. These results, together with crystallographic studies, indicate that the three compounds AlO3Nd, AlO3Pr, and AlO3La are consistent with the space group D3d6.
A Calculation of the Second‐ and Third‐Order Elastic Constants of Aluminium
Authors: Benckert S. 
Published: July 2007

AbstractA calculation of the second‐ and third‐order elastic constants of aluminium has been made by the method of homogeneous deformation. The electronic contributions to the elastic constants are calculated using second‐order perturbation theory, Ashcroft's model potential, and a dielectric function with corrections for exchange and correlation effects, as suggested by Singwi et al. Within this model we have also estimated the difference between the calculated static and dynamic bulk modulus. This difference results from neglecting certain higher order model potential terms in the dynamic approach.
Magnetic Field Distribution Analysis of the Broadened Mössbauer Spectra of Zinc Ferrite
Authors: Varret F. , Gerard A. , Imbert P. 
Published: July 2007

AbstractIn some magnetically ordered compounds, broadened Mössbauer spectra are interpreted as arising from hyperfine field (Hn) distributions. These distributions measured at several temperatures are used to determine both a possible distribution of transition temperatures in the sample as well as the set of curves of Hn as a function of temperature. The method of calculation is applied to ZnFe2O4.
Influence of Quadratic Interactions on Impurity Absorption Bands in Solids
Authors: Levenson G. F. 
Published: July 2007

AbstractGeneral integral relations are derived for the impurity absorption band in the case of arbitrarily strong both linear and quadratic electron‐phonon or electron‐magnon interaction, which are valid also in the presence of weak anharmonic relaxation of normal modes. These relations can be useful as a starting point for the approximate analytic treatment of impurity spectra in the cases when both linear and quadratic terms in the interaction Hamiltonian are important. In particular, the high‐temperature line shape of the absorption band is investigated. Expressions for the low‐temperature shape, bandwidth, and shift of the central line in the electron‐magnon spectra are derived, and formulae for the absorption spectrum of an impurity electron interacting with only one local mode are obtained.
New oxygen centres in KCl single crystals
Authors: Andersen T. , Baptista J. L. 
Published: July 2007

AbstractDoping of pure KCl with oxygen in a closed system leads to formation of a new oxygen containing centre. Absorption, fluorescence, and ESR spectroscopy have been used together with chemical analysis to characterise the centre. It is suggested that the centre is an O2−2‐anion vacancy association. The radiolysis of the doped KCl single crystals and the influence of subsequent annealing treatments have been investigated.
Relationship between enthalpy of point defect formation and other thermochemical properties for ionic salts
Authors: Maycock J. N. , Verneker V. R. Pai 
Published: July 2007

AbstractNew measurements of the dc ionic conductance of KBrO3 and KClO4 are presented and the enthalpies of defect formation and migration are derived from these data. A compilation of enthalpy of defect formation values for a series of potassium, lithium, and silver salts has been made. These data have been compared to the respective melting points and entropies of crystal formation. From these comparisons it is clear that linear relationships exist between these thermochemical parameters and the enthalpy of defect formation. This correlation has been used as a basis to explain why salts such as KNO3 and KN3 melt at a much lower temperature than KCl, etc. An enthalpy of defect formation‐melting point temperature equation is also presented.
Vibronic spectra of molecular crystals under totally symmetric vibrations
Authors: Davydov A. S. , Serikov A. A. 
Published: July 2007

AbstractA new theory of the vibronic absorption spectra of molecular crystals, which is a generalization of the usual exciton theory, is suggested. It allows to consider, in principle, both one‐phonon and many‐phonon vibronic excitations. An investigation of the vibronic states corresponding to the combination of the electronic excitation with the intramolecular totally symmetrical vibrations is made for the case of a change of the vibrational frequency and a small variation of the equilibrium of the normal vibrational coordinate during the electronic excitation of the molecule. Expressions for the shape of the vibronic absorption spectra are obtained.
Localized orbitals for polyatomic systems (I)
Authors: Schlosser H. 
Published: July 2007

AbstractAdams and Gilbert independently derived a rigorous generalization of the Hartree‐Fock equation which enables one to obtain localized orbitals in any polyatomic system with closed shells or which may be represented by a single Slater determinant. This generalization is approximately valid in any polyatomic system which one may approximate by a single Slater determinant. Kunz transformed the Adams‐Gilbert equation into another form and analyzed the equation in powers of overlap. We re‐examine the Adams‐Gilbert equation and transform it into a considerably simple form by use of a non Hermitian localization operator. Development in powers of the overlap yields equations identical to those found by Kunz. However our equations are valid in the more general case where the orbitals localized about a given site are non orthogonal. We also develop several perturbation iteration solutions of the Adams‐Gilbert equation.
Chlorine‐35 quadrupole resonance in Ca(ClO3)2·2 H2O
Authors: Kumar U. Vignaneswara , Rao B. D. Nageswara 
Published: July 2007

AbstractThe Cl35 quadrupole resonance of polycrystalline Ca(ClO3)2 · 2 H2O is found to consist of two resonances of unequal intensities. The variation of the resonance frequencies with temperature is studied in the range 77 to 300 °K and the results are analysed on the basis of existing theories. The asymmetry parameter of the electric field gradient is found to be negligible.
The analogy of the elastic and dielectric spherical inhomogeneity for cubic and isotropic media
Authors: Muggli J. 
Published: July 2007

AbstractThe elastic spherical inhomogeneity in an infinite medium is treated in analogy to the dielectric inhomogeneity. In the isotropic and cubic cases the formulas for the homogeneous internal field and the induced dipole are analogous to those for the electric case except for the sign of the polarization. In the isotropic elastic case octopoles are induced in addition to the dipoles, whereas in the cubic case an infinite series of multipoles appears. The electric and elastic Clausius‐Mossotti formulas for polarizable and for reorienting dipoles are very similar. However in the cubic medium the elastic dipoles in the Lorentz sphere contribute always to the strain in the centre.
Lattice modes and phase transition in SbSi
Authors: Balkanski M. , Teng M. K. , Shapiro S. M. , Ziolkiewicz M. K. 
Published: July 2007

AbstractIn order to investigate the phase transition in terms of lattice dynamics, the symmetry modes of the para‐ and ferroelectric phases of the semiconductor SbSI are analysed by means of group theory. Starting from the simplified C22h space group with two formula units per unit cell, the symmetry modes in the different phases are deduced and their correlation from one phase to another is also established. Raman scattering measurements of the crystal in the two phases and in the phase transition region were obtained. These results are compared with available IR and Raman data. On the basis of the proposed model which takes into account the accidental degeneracies of the modes, the main features of the observed IR and Raman spectra are satisfactorily explained; the assignment of observed frequencies to determined symmetry coordinates is performed. An effort is also made to identify the temperature dependence of the mode frequencies in the vicinity of the ferroelectric transition temperature. An optical band whose frequency is strongly temperature dependent is observed in the Raman investigation and is in agreement with earlier works.
The relation between the isotope effect for diffusion and the correlation factor in systems lacking a two‐fold symmetry around the tracer jump vector
Authors: Bakker H. 
Published: July 2007

AbstractIt is investigated under which conditions the isotope effect, E, and the correlation factor, f, for diffusion by means of complex lattice defects (lacking a two‐fold symmetry around the tracer‐defect jump vector) are connected by E = f ΔK. In particular it is shown, that the conditions are fulfilled for (impurity) diffusion by divacancies and for diffusion by vacancy‐impurity pairs in f.c.c. metals.
Quasi‐free rotation of the ammonium ion in crystalline NH4ClO4
Authors: Janik J. A. , Janik J. M. , Mayer J. 
Published: July 2007

AbstractThe frequency distribution function g(ω) was measured by IINS in three series of experiments. The resolution Δω/ω in the ω region 15 to 120 cm−1 was about 6% in two of them and in the third one about 15%. The peaks obtained are interpreted as arising from quasi‐free rotation of ammonium ions in the crystal. Their positions and distances agree with those calculated assuming B = 6.30 cm−1 for the rotational constant of NH4. Their existence may be treated as a proof of a very low rotational barrier of the NH4 groups in NH4ClO4.
The method of lattice statics for excess electron defects with non‐harmonic lattice distortionx
Authors: Vail J. M. 
Published: July 2007

AbstractThe method of lattice statics (Kanzaki method) as extended by Stoneham to determine the lattice distortion, electronic state, and energy of an excesselectron defect in a crystal, is developed in detail to include the case where the defect region, region I, contains non‐harmonic lattice distortion. General expressions are derived for the energies of states in which the lattice is relaxed, and in which it is unrelaxed, leading to evaluation of Franck‐Condon‐type electronic transition energies and the Stokes shift. Details of the method of solution are included, in a unified general formulation.
On the theory of excitons in semiconductors
Authors: Makarov V. P. 
Published: July 2007

AbstractThe excitons in semiconductors with arbitrarily complex band structure are investigated within the framework of the effective mass approximation. The influence of homogeneous external fields on excitons is studied. The formulas for the coefficient of one‐photon and two‐photon absorption in the presence of homogeneous fields are derived. Some particular cases are considered. The theory developed is applied to the explanation of one‐photon and two‐photon absorption spectra in CuCl crystals.
The yttrium‐stabilised electron‐hole centres in anhydrite
Authors: Bershov L. V. , Martirosyan V. O. , Marfunin A. S. , Speranskii A. V. 
Published: July 2007

AbstractEPR has been used to study yttrium‐stabilised electron‐hole centres of natural anhydrites. Geometrical models have been constructed by measuring the main directions of the tensors of the spectroscopic constants accurately and by correlating them with the crystal structure. Hyperfine splitting constant and thermal stability of the centres have been shown to vary as the localization of the unpaired electron density at the yttrium ions which replace calcium of the initial lattice.
Photon‐phonon interaction in radiative recombination by the impurity centre in ZnS:Mn
Authors: Beserman R. , Balkanski M. 
Published: July 2007

AbstractAnalysis of light emission spectra obtained by cathodoluminescence shows a phonon‐assisted process. In order to determine the nature of the participating phonon, light scattering experiments are presented. The results show clearly that the phonon participating in the radiative recombination in ZnS:Mn is a resonant impurity breathing mode whose frequency is 297 cm−1.
Lokalisierte Funktionen als Verallgemeinerung der Wannier‐Funktionen im Vielbandfall
Authors: Kögel G. 
Published: July 2007

AbstractFür eine beliebige Gruppe von m entarteten Bändern gibt es m + l „lokalisierte Funktionen”︁, die asymptotisch exponentiell abfallen und, im Gegensatz zu den Wannier‐Funktionen, im wesentlichen in einer Gitterzelle lokalisiert sind. Sie stellen Basisfunktionen irreduzibler Darstellungen der Punktgruppe des Gitters dar und spannen den Hilbert‐Raum aller Bloch‐Funktionen dieser Bänder auf. Die Zahl l wird durch die Art der Atomfunktionen bestimmt, aus denen die Bänder hervorgehen. Ein quantitatives Maß für die Lokalisierung läßt sich aus einer Analyse der Bandstruktur gewinnen. Bei der Untersuchung von Punktfehlern läßt die Formulierung mit „lokalisierten Funktionen”︁ verstehen, warum auch bei entarteten Bändern die herkömmliche Entwicklung nach Wannier‐Funktionen die richtige Grobstruktur der Lösungen ergibt.
Contribution of the lattice energy to the stability of aliovalent iron species formed after 57Co decay in CoX2 (X = F, Cl, Br, Oh)
Authors: Cruset A. , Friedt J. M. 
Published: July 2007

AbstractMössbauer emission spectra of 57Co in β‐Co(OH)2 and CoBr2 are reported. The proportion of ferric ions stabilized after 57Co electron capture increases with increasing lattice energy along the series of cobaltous compounds; a thermodynamical model is suggested to explain the stability of aliovalent ions after 57Co EC in cobalt compounds with simple ligands.
Statistische Theorie der Haftkraft von Flußliniensystemen in harten Supraleitern. I. Eigenschaften des statistischen Kraftfeldes
Authors: Kornfeld G. , Kronmüller H. 
Published: July 2007

AbstractEs werden die mathematischen Eigenschaften des zufälligen Kraftfeldes FP(r) behandelt, dem das Linienelement einer Flußlinie auf Grund der Wechselwirkung mit statistisch verteilten Defekten unterliegt. Mit der Voraussetzung einer linearen Wechselwirkung zwischen Flußlinie und Defekt folgt aus dem zentralen Grenzwertsatz, daß FP(r) normalverteilt ist. In diesem Fall ist die vollständige, statistische Information über FP(r) in der Korrelationsmatrix B(a) enthalten, aus der wir die mittlere Amplitude, die mittlere Wellenlänge und die Anisotropie des Zufallsfeldes FP(r) erhalten. Die Korrelationsmatrix sowie die genannten Parameter werden für Stufenversetzungen parallel zu den Flußlinien explizit berechnet, und zwar auf Grund eines Wechselwirkungsmechanismus, der auf dem sogenannten Volumeffekt beruht. Für genügend hohe Versetzungsdichten (ϱ ≦ 1/ξ2) ist die Wellenlänge lP unabhängig von ϱ (lP ≈ 2 π ξ), während die mittlere Amplitude (Streuung) proportional zu ist.
Dislocations dans les cristaux piézoéectriques
Authors: Saada G. 
Published: July 2007

AbstractOn donne une méthode exacte pour calculer le champ de déformation et de contraintes, le champ électrique et l'énergie emmagasinée dans un cristal piézoélectrique contenant une dislocation. Le cas du cristal à large bande interdite est traité rigoureusement, puis les résultats sont étendus au cas de cristaux à bande interdite étroite. Des applications numériques au cas du quartz et du tellure permettent de préciser les points suivants: 1. Le champ de déformation est peu affecté par le couplage piézoélectrique. 2. Le champ de contrainte est fortement affecté par le couplage piézoélectrique. Le champ électrique peut ětre très élevé. Ces deux champs sont fortement effectés par la charge du coeur. 3. L'énergie de ligne n'est pas sensiblement affectée par la piézoélectricité pour une dislocation à coeur neutre. Elle peut ětre très sensible à la charge du coeur. 4. Les interactions dislocations‐porteurs de charge sont très fortes; une compréhension complète nécessite toutefois l'étude des effets d'écran. 5. Dans les semi‐conducteurs à faible bande interdite les dislocations piègent préférentiellement les porteurs d'un signe; on montre que celà peut contribuer à expliquer la conductivité du tellure. De plus les dislocations peuvent contribuer à créer des barrières.
Magneto‐optical effects in the U2 band in alkali halides
Authors: Ingels J. , Jacobs G. 
Published: July 2007

AbstractMagnetic circular dichroism was measured in the U2 bands in KCl, KBr, KI, RbBr, RbI, and CsI. By an analysis of the data using the method of moments the spin‐orbit splitting of the excited states was determined. Absorption spectra of the U2 centres in RbBr, RbI, CsBr, and CsI and some of the optical properties of these compounds are also reported.
Dielectric function for alkali halide crystals
Authors: Lipari N. O. 
Published: July 2007

AbstractThe wave‐vector dependent dielectric function for LiCl, LiBr, LiI, NaCl, NaBr, Nal, KCl, KBr, and KI is calculated using a model originally proposed by Fry. An approximate analytical expression for the screened Coulomb potential is also given.
Tunneling in a distortable double well
Authors: Cohan N. V. 
Published: July 2007

AbstractThe tunneling probability W is investigated in an asymmetric double well in which the asymmetry varies with time as the particle “starts to tunnel”. A relaxation time is introduced to account for this variation of the double well, and it is found that W is always larger than in the corresponding rigid double well. This model should apply to several phenomena in which an ion or small molecule changes position through tunneling in a crystal.
The green function method in the theory of magnetic thin films. II. Calculation of the curie temperature for ferromagnetic thin films
Authors: Brodkorb W. 
Published: July 2007

AbstractThe ferromagnetic Curie temperature and the paramagnetic Curie temperature in the first and second approximation of iteration are calculated for the layer magnetizations starting from the implicit system of equations given in [1]. The dependence of these Curie temperatures as a function of the number of layers, n, for several lattice structures and surface orientations is discussed.
Antiferromagnetism in an oxide semiconducting glass
Authors: Friebele E. J. , Wilson L. K. , Dozier A. W. , Kinser D. L. 
Published: July 2007

AbstractThe magnetic structure of a 55 mol% FeO–45 mol% P2O5 semiconducting glass containing various relative concentrations of Fe3+ and Fe2+ has been studied by ESR techniques over the temperature range −190 to 300 °C. It was determined that the iron ions in the glass matrix are antiferromagnetically coupled in Fe3+–Fe2+ ion pairs. The isolated Fe3+−Fe2+ ion pairs. The isolated Fe3+ ions were found to be in orthorhombic crystalline fields with λ = 1/3 and 0.23 < D < 0.8 cm−1, where D and λ are constants in the spin Hamiltonian. Heat treatment of the glass samples caused precipitation of Fe3+‐rich crystalline phases, and it was determined that the Fe3+ ions in these phases were antiferromagnetically aligned.
Anharmonic interactions in diamond‐type crystals
Authors: Jex H. 
Published: July 2007

AbstractThe potential energy of diamond, Si, and Ge crystals has been expanded in a double power series of the infinitesimal strain parameters and phonon coordinates. Third and fourth order expansion coefficients have been fitted to give reasonable agreement with the Grüneisen parameters of the individual modes of vibration, the mean Grüneisen parameters and thermal expansion coefficients, the third order elastic constants and the temperature dependence of the elastic constants. Calculations have been made for the mass operators of normal mode spropagating in the [100] and [111] directions. The relative renormalization of the low energy TA modes in Ge and Si is of the order of 10% while it is one order of magnitude less for phonons of the other branches.
Helicon dispersion and damping in aluminium
Authors: Larsen P. K. , Greisen F. C. 
Published: July 2007

AbstractThe transmission of helicons through Al slabs has been investigated experimentally and numerically for q ∥ B ∥ [100] and [110]. In the former case oscillations are observed, for B smaller than the cut‐off field for helicons which might be of the Gantmakher‐Kaner type. Finally, the Landau damping for B not parallel to q is investigated. For comparison with the theory the non‐local magnetoconductivity tensor is calculated from Ashcroft's Fermi surface model and the helicon dispersion relation is solved numerically. This leads to a good overall interpretation of the experiments.
Optical Properties of α‐TiCl3 at the Magnetic Transition Temperature
Authors: Cavallone F. , Pollini I. , Spinolo G. 
Published: July 2007

AbstractCareful optical absorption measurements of α‐TiCl3 crystals in the energy range 1.2 to 4.2 eV, at various temperatures (down to 4.2 °K), have revealed a noticeable change both in the crystal field and charge transfer spectrum, around Tt = 217 °K. The results found in the crystal field region (1.2 to 2.10eV) have been explained taking into account both the trigonal perturbation of the crystal field and the Jahn‐Teller effect of the electronic energy levels. The charge transfer spectrum (2.10 to 4.2 eV) seems to be more influenced by the lattice parameter discontinuity present at Tt rather than by the magnetic order below TN = 265 °K. Reflectivity measurements in the energy range 1.20 to 5.50 eV, at 300 and 55 °K are also reported. A discussion of the electronic transitions with relations for the optical properties in the energy region from 2.1 to 5.5 eV is given.