bluuebunny/crossref_metadata_2025 huggingface dataset:
New Temporary Infrared Absorption Bands in the Alkali Halides
Authors: Borms F. , Jacobs G.
Published: July 2007

New temporary infrared absorption bands are observed in several alkali halides. In NaCl a short‐lived centre with a transition at 4 μm is formed by excitation of the electron excess centres at low temperatures. Decay times have been measured simultaneously in the M, F, and 4 μm band. They indicate a bimolecular decay with the same time constant for the three bands. The 4 μm band is attributed to a transition of an electron in a shallow trap. Simultaneous absorption measurements were made in the F, M, and 4 μm band after ruby laser excitation in the F band, and in the F, F', and 4 μm bands after laser excitation in the F' band. From these measurements it was concluded that the shallow trap is the F centre. This implies the existence of a metastable form of the F' centre. A triplet state is postulated. Absorption bands analogous to the 4 μm band in NaCl have been observed in KCl at 6 μm, in NaF at 2.4 μm, in KBr, and KI.
Best Localized Symmetry‐Adapted Wannier Functions of the Diamond Structure
Authors: Teichler H.
Published: July 2007

By application of proper unitary matrices the four Bloch functions of each bandgroup with equal wave vector k are transformed into modified Bloch functions in such a way that the resulting four sets of Wannier functions are adapted to the tetrahedral symmetry of the lattice. The Wannier functions behave like the “equivalent MO's” of the tight‐binding approximation (but with vanishing non‐orthogonality integrals). Furthermore, we give explicitely those phases of the Bloch functions that lead to best localized Wannier functions. Values of energy matrix elements between these functions are determined for Ge and Si.
Electron Spin Polarization due to the s‐d Exchange Interaction
Authors: Kishore R. , Joshi S. K.
Published: July 2007

An expression for the electronic spin polarization p(r) due to s‐d exchange interaction between the conduction electrons and the localized impurity of spin 1/2 in a dilute magnetic alloy is obtained by using the one particle Green function approach. For large distances p(r) is found to exhibit exponentially damped behavior. This feature of p(r) was also predicted earlier by Bose, Tanaka, and Halow by using the method of cluster variation of the co‐operative phenomena.
The Relationship between the Work‐Hardening of B.C.C. and F.C.C. Metals
Authors: Šesták B. , Seeger A.
Published: July 2007

The paper develops and supports in some detail the hypothesis that the well‐known “three‐stages work‐hardening” curve of b.c.c. metals is closely analogous, beyond its inflexion point, to stage‐III work‐hardening of f.c.c. metal single crystals. The basic reason for this correspondence is that in both cases screw dislocations may cross‐slip easily. A qualitative picture for stage‐III hardening in f.c.c. metals and for the work‐hardening of b.c.c. metals based on the internal stresses originating from dislocation sheets parallel to the primary glide plane (or the glide plane of maximum shear stress) is proposed.
Approximate Theoretical Treatment of Weak‐Beam Dislocation Images
Authors: De Ridder R. , Amelinckx S.
Published: July 2007

A simple approach is reported allowing to deduce the well‐known approximate criterion which relates the strain field of a dislocation to its image position in a weak beam. The proposed approximations also permit to make predictions about the width of the image peaks and the image contrast. The obtained results are compared with the intensity profiles calculated by performing the kinematical integral. It is shown that the mentioned position criterion, deduced within the one‐beam kinematical theory, can easily be adapted for a more realistic many‐beam theory, e.g. the two‐beam kinematical theory.
Elastic Constants of Argon at 4.2 °K from Phonon Measurements
Authors: Dorner B. , Egger H.
Published: July 2007

Phonon measurements with inelastic neutron scattering have been analysed carefully, by use of the resolution ellipsoids of the three‐axis spectrometer. The slopes of the dispersion curves at the low frequency phonons are taken to be the sound velocities. From these sound velocities the elastic constants are calculated: C11 = (3.67 ± 0.14).1010 dyn cm−2, C12 = (1.74 ± 0.17).1010 dyn cm−2, C44 = (2.34 ± 0.11).1010 dyn cm−2. Theoretical calculations with an accurate pair potential in the self‐consistent phonon approximation give the best agreement for a model without anharmonicity and without three‐body forces.
Local Mode Broadening by Impurity‐Impurity Interactions
Authors: Harrington J. A. , Walker Ch. T.
Published: July 2007

Concentration and temperature dependences of the bandwidth of the Raman and infrared active local mode for H− in BaF2 have been determined. The bandwidth is observed experimentally to vary as the square root of the impurity concentration, and as T1.5 at high temperatures. This concentration dependence is in qualitative accord with the theoretical predictions of Dawber and Elliott.
Conduction Electron Spin Resonance in Magnesium
Authors: Bowring C. S. , Smithard M. A. , Cousins J. E.
Published: July 2007

Measurements 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

The 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

The 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

A 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

In 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

General 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

Doping 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

New 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

A 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

Adams 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

The 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

The 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

In 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

It 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

The 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

The 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

The 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

EPR 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

Analysis 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

Für 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

Mössbauer 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

Es 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.
Rigid ion model lattice dynamics of cuprite (Cu2O)
Authors: Carabatos C. , Prevot B.
Published: July 2007

The rigid ion model theory of crystal dynamics is applied to cuprite structure. The general force system involving interactions between first neighbour atoms is derived. Central forces between oxygen second neighbours are also included. Discussion and comparison are made with experimental data.
Dislocations dans les cristaux piézoéectriques
Authors: Saada G.
Published: July 2007

On 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

Magnetic 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

The 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

The 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

The 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

The 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

The 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

The 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

Careful 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.
Optical Properties of Lattice Vibrations in Molecular Crystals
Authors: Barentzen H. , Schrader B. , Merten L.
Published: July 2007

A 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

The 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

Based 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

The 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

Monocrystals 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

A 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

Previously 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

The 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

The 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

Using 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

The 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

Two 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

Previously, 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

Indium 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

The 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

An “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

Experimental 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

Paramagnetic 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

The 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

The 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

The 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

To 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

The 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

Magnetic 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

On 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

The 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

Some 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

The 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

The 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

Nous 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

Using 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.