bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron‐positron colour centre in alkali halides
Authors: Berezis A. A. , Evakestov R. A. 
Published: July 2007

AbstractThe wave function of the F‐colour centre (i.e. the bound state of positron and F‐centre) in alkali halides is determined by a variational calculation in the rigid polarizable point‐ion lattice approximation. The localization of positron on the F‐centre leads to the contraction of the optical electron cloud of the F‐centre. The function of the angular correlation for the two‐quantum annihilation of the positron with the F‐electron is found using the calculated wave function of the F‐centre. It is shown that the trapping model for the positron leads to a better agreement with the experiment than the model previously considered in [5] which describes the annihilation of the F‐electrons with free positrons.
Induced uniaxial magnetic anisotropy in disordered FeAl alloys
Authors: Steinert J. 
Published: July 2007

AbstractIn Fe‐Al alloys the dependence of the induced uniaxial magnetic anisotropy on concentration, direction, temperature, and time was investigated. The results were compared with a theory given by Néel. The part G of the induced anisotropy is caused by A1–Al atom pairs in nearest neighbour position and F is caused by complexes which consist of more than two substitutional atoms. No any contribution of pairs of next nearest neighbours to F were found. In contrast to a theory by Taniguchi the interaction energy of atom pairs with the direction of magnetization shows a linear dependence on temperature. The formation of the induced anisotropy doesn't follow an exponential function on time and therefore it isn't possible to determine their magnitude and activation energy by usual methods.
Analysis of tracer and nuclear magnetic resonance measurements of self‐diffusion in aluminium
Authors: Seeger A. , Wolf D. , Mehrer H. 
Published: July 2007

AbstractThe various nuclear magnetic resonance techniques used for determining self‐diffusion coefficients and activation energies in aluminium are evaluated critically. The data considered most reliable are analyzed together with the Al26‐tracer measurements of self‐diffusion. From the temperature and the pressure dependence of the self‐diffusion coefficients it is deduced that at high temperatures divacancies contribute appreciably to self‐diffusion in aluminium and that the self‐diffusion activation energy for a monovacancy mechanism is Q1  E + E = 1.28 eV. With the help of measurements on the equilibrium concentration of vacant sites Q1 is subdivided into the formation energy E = 0.66 eV and the migration energy E = 0.63 eV. The difference between migration and binding energies of divacancies is found to be E  E = 0.28 eV. It is shown that the ratio of the self‐diffusion activation volume for monovscancies to the atomic volume is smaller than unity and about equal to 0.9.
High‐frequency conductivity of hot carriers in semiconductors with non‐parabolic dispersion law of energy
Authors: Almasov L. A. , Dykman I. M. 
Published: July 2007

AbstractThe tensor of microwave conductivity in semiconductors with isotropic non‐parabolic band in the presence of applied electric field has been calculated. Various frequency ranges of microwave field have been considered. The splitting of plasma frequencies in a constant field has been determined. It is shown that the tensor anisotropy of the dielectrical permeability obtained is manifested in the electro‐optical Kerr effect, observed in [6].
Charge carrier‐exciton interaction in crystalline tetracene
Authors: Peter L. , Vaubel G. 
Published: July 2007

AbstractInteraction of holes with excitons has been investigated in tetracene crystals at room temperature. It is found that the annihilation of triplet excitons by trapped holes is characterised by a rate constant KT = (1.5 ± 0.5) × 10−10 cm3 s−l. For the rate constant for singlet exciton‐hole annihilation an upper limit of Ks ≤ 1 × 10−7 cm3 s−l is estimated.
Dynamical screening of the wannier exciton
Authors: Zimmermann R. 
Published: July 2007

AbstractAn effective mass equation for the Wannier exciton is derived with a, modified interaction taking dynamical screening due to unbound electron‐hole pairs into account. The binding energies are enhanced which distortes the hydrogenic series formula. In the limit of shallow excitons static screening is justified only in the dominant interaction term whereas the non‐Hermitean splitting terms are substantially affected. The connection with Haken's screening formula with regard to LO‐phonon screening is revealed.
Neutron diffraction by vortex lattlices in superconducting Nb and Nb0.73Ta0.27
Authors: Schelten J. , Ullmaier H. , Schmatz W. 
Published: July 2007

AbstractNeutron diffraction experiments on flux line lattices in superconducting Nb and NbTa are reported. From experimental data (form factors, lattice parameters, rocking curves etc.) following results are obtained. The microscopic flux distribution of a single flux line in NbTa could be determined. For Nb the form factors are compared with a theory valid in the vicinity of Hc2 A correlation between the flux line lattice and the crystal lattice has been found. Finally the attractive interaction between neighbouring flux lines in Nb has been verified and the resulting maximum lattice parameter compared with the corresponding distance in recent nonlocal calculations.
Statistical perturbation theory of order‐disorder ferroelectrics: First perturbative correction
Authors: Nettleton R. E. 
Published: July 2007

AbstractThe equation‐of‐motion method is used to calculate excitation energies of proton tunneling modes in KD2PO4 using an Ising pseudo‐spin representation of the proton Hamiltonian. The calculation is carried to terms 0 (Z – 〈Z〉) extending an earlier treatment and representing the first perturbative correction in a systematic extension of random‐phase decoupling devised by Wallace. The corrections are small for the deuterated compound, as are the corresponding first‐order contributions to the isotope effect in spontaneous polarization at 0 °K. With increasing temperature, the newly‐calculated terms make a small contribution to the observed decrease in the long‐wavelength excitation energies.
Infrared absorption of SeO and SeO impurity ions in KCl and KBr crystals
Authors: Demyakekko V. P. , Tsyashchenko Yu. P. , Verlan E. M. 
Published: July 2007

AbstractIn the temperature range 120 to 300 °K a study has been made of the infrared absorption spectra of KCl and KBr single crystals doped with SeO and SeO anions. It is shown that the SeO anions in these matrices form complexes SeO · M2+ of symmetry C2V, with cations M2+ (M2+ – Ca2+, Sr2+, Ba2+) similar to the complexes SeO · M2+ and CrO · M2+ observed earlier. A lowering of the local symmetry results in the splitting of V3(F) vibration of the tetrahedral anion SeO. An identification of bands and their fine structure assumed to be isotropic was made in the infrared absorption spectra of the complex SeO · M2+. The existence of similar complexes SeO · M2+ was assumed in KBr and KCI lattices doped with SeO in connection with the quartet structure of infrared absorption spectra in the vibration region V3(E) of the SeO anion.
Paramagnetic resonance and relaxation of Dy3+ and Er3+ in YAsO4 and YVO4
Authors: Schowalter R. 
Published: July 2007

AbstractParamagnetic resonance experiments on Dy3+ ions in (Y, Dy)VO4 (100:1) showed both the transition in the ground doublet and the transition in the first excited doublet. The energy gap between both doublets was estimated by comparing the line intensities at various temperatures. By means of a pulse saturation technique at X‐band frequencies paramagnetic relaxation times have been observed in the temperature range of liquid helium as a function of the angle between the optical axis and the magnetic field, and additionally in the case of (Y, Dy)VO4, as a function of crystal size and concentration 100:1, 20:1, and 5:1).
Hyperfine and transferred hyperfine interaction of Cr3+ in yal and lual garnets
Authors: Valentin R. , Luft H. , Baberschke K. 
Published: July 2007

AbstractThe hyperfine field at the 53Cr nucleus and the transferred hyperfine field at the Al3+ neighbours at the next octahedra sites were measured with ENDOR at Cr3+‐doped YAlG and LuAlG single crystals. The electric field gradient at the octahedrally surrounded lattice sites could be determined by the quadrupole interaction with the 27Al nucleus. From the measured quadrupole splitting of 53C13+ a new value of the 53Cr quadrupole moment of |Q| =0.082 b is derived. The magnetic part of the transferred hyperfine interaction between the Cr3+ ion and the A1 nuclei at the next octahedra sites could be well described assuming a point‐dipole model.
The influence of an electric field on the B, n = 1 ground state exciton line of CdS and CdSe single crystals
Authors: Lange H. 
Published: July 2007

AbstractThe influence of an electric field has been measured for the B. n = 1 exciton line of CdS and CdSe single crystals. The results indicate a quadratic Stark shift in agreement with second‐order perturbation theory and a quadratic field dependence of half‐width.
Validity of the electron energy distribution function for piezoelectric scattering at high electric fields
Authors: Sodha M. S. , Phadke U. P. , Chakravarti A. K. 
Published: July 2007

AbstractA solution of the kinetic equation for the piezoelectric mode of electron‐lattice interaction has been obtained by retaining the higher‐order terms in the orthonormal expansion of the distribution function at high electric fields. It is seen that at low temperatures and moderately high electric fields, the inclusion of the higher‐order terms significantly changes the isotropic part of the distribution function of electrons in piezoelectric semiconductors with low electron densities (for which the analysis is relevant).
Mössbauer study of proton irradiation effects in potassium iron cyanides
Authors: Kisyńska K. , Kopcewicz M. , Kotlicki A. 
Published: July 2007

AbstractThe results of the Mössbauer study of potassium iron cyanides K4[Fe(CN)6] · 3 H2O and K3[Fe(CN)6] irradiated with 1.5 MeV protons are reported. The observed changes in the Mössbauer spectra are interpreted as a result of radiation damage effects and thermal disintegration processes of the compounds. The formation of metallic iron in the superparamagnetic state was observed.
Covalency reduction factors in C4v and D3h and estimation of bonding parameters from magnetic data
Authors: Majumdar D. , Ghosh U. S. 
Published: July 2007

AbstractThe covalency effect in the complexes of the iron group reduces the orbital angular momentum and the spin‐orbit coupling constant from their respective free ion values. Recent interest in penta‐coordinated complexes suggested the derivation of the expressions for the orbital and spin‐orbit coupling reduction factors in complexes of D3h and C4v symmetry. With the help of these expressions and using Slater functions for the radial integrals involved therein the bonding parameters representing the degree of covalency have been estimated from the available magnetic data in the two cases.
Galvanomagnetic effects in many‐valley semiconductors for strong magnetic and heating electric fields
Authors: Mitin V. V. 
Published: July 2007

AbstractThe effect of the heating of electrons on the conductivity of many‐valley semiconductors in strong (but not quantitizing) transverse magnetic fields is studied. It is shown that at low temperatures the current‐voltage characteristic is of S‐type, when the main mechanism of the intervalley scattering of the hot electrons is the emission of inter‐valley phonons. The anisotropy of conductivity is not only reduced but also changes its sign when the electric field grows. The conductivity in strong magnetic fields can be greater than σ0 (σ0 is σ for H ≡ 0, Ex → 0) within a certain region of the electric field strength. All these effects take place as a result of the influence of the Hall field on the heating of electrons and their redistribution with respect to the valleys.
Propriétés magnétiques des composés équiatomiques terres rares rhodium TRh (T  Tb, Dy, Ho, Er)
Authors: Chamard‐Bois R. , Van Nhung Nguyen , Pierre J. 
Published: July 2007

AbstractLes composés équiatomiques TbRh et DyRh présentent un ordre ferromagnétique, alors que HoRh et ErRh s'ordonnent selon des modes antiferromagnétiques du type (II00). Les moments dans l'état ordonné ont des valeurs réduites en accord avec les résultats d'un calcul de champ cristallin.
Conductivity and hall effect of heavily doped semiconductors at low temperatures in a weak magnetic field
Authors: Van Cong H. , Mesnard G. 
Published: July 2007

AbstractThe transport coefficients of electrons at low temperatures in a weak magnetic field are calculated from a simplified model of heavily doped semiconductors. The treatment is based on the Green function methods, through Feynman path integral formulation, applied to disordered systems and developed already in two previous papers. Two typical cases concerning the relation between the carrier concentration and the donor one are discussed.
An EPR study of an S = 3/2 defect in CaWO4
Authors: Weightman P. , Henderson B. , Dugdale D. E. 
Published: July 2007

AbstractAfter n‐irradiation of CaWO4 up to a dose of 3 × 1019 nvt a spectrum consisting of 12 narrow lines is observed. The angular variation of the spectrum shows that a centre with S = 3/2 located at four magnetically inequivalent sites in the structure is involved. The data are consistent with a spin Hamiltonian ℋ︁ = β S · g · B + S · D. · S, where g and D are noncoincident with principal values gz = 2.048, gy = 2.007, gx = 2.004, D1 = 4.32 × 10−4 cm−1, D2 = 0.31 × 10−4 cm−1 and D3 = −4.63 × 10−4 cm−1. Possible intrinsic lattice defects which might account for this spectrum are discussed.
Electron spin resonance and relaxation of tetrahedrally coordinated copper(11) in some complex halides
Authors: Vaughan R. A. 
Published: July 2007

AbstractElectron spin resonance and relaxation measurements are reported for some copper salts in which the Cu2+ ion has tetrahedral coordination. For the CuCl42− ion in Cs2CuCl4, the results are in some respects at variance with those previously reported [1]. The crystallographic cell parameters for [(C4H9)4N]2CuBr4 have been measured, and in this material a single broad asymmetric ESR line is reported, about 145 G wide at X‐band, having principal g‐values of 2.068, 2.053, and 2.220. Spin‐lattice relaxation times measured by both pulse and continuous saturation methods yielded values of T1 in the range 60 μs at 4.2 K to 140 μs at 1.7 K. These are compared with the much larger values predicted for copper in other tetrahedrally coordinated materials [2]. The ESR spectra of CuCl42− and CuBr42− ion adsorbed on an ion exchange resin are compared with those from powdered samples of the above two complexes. Measurements of T1 for the CuBr42− ion on the resin yielded values of 100 μs at 4.2 K and 280 μs at 1.86 K. It is concluded that the complex halides are not a suitable system in which to study relaxation behaviour of Cu2+ in a tetrahedral crystal field.
Hydrogen in palladium–silver in the neighbourhood of the critical point
Authors: Buck H. , Alefeld G. 
Published: July 2007

AbstractThe chemical potential and the concentration of dissolved hydrogen in Pd0.9Ag0.1have been measured along fifteen isotherms near the critical point. The critical exponent γ, describing the temperature dependence of the lattice gas compressibility, was determined to 1.02 ± 0.04. For the temperature range investigated ((T–Tc)/Tc> 0.01) the isotherms can very well be fitted by Landau's theory. Quantitative arguments are given in favour of the interpretation that the attractive interaction is the long range elastic dipoledipole interaction. From the critical data the dipole strength is found toP= 3.5 eV. The validity of the mean field approximation so close to the critical point is consistent with the assumption of long range interaction.
Energy shift in the resonant absorption of γ‐rays due to disordering of the lattice
Authors: Srivastava B. P. , Sharma H. N. K. , Bhattacharya D. L. 
Published: July 2007

AbstractA theoretical expression for the energy shift of the resonant absorption of γ‐rays by a disordered lattice has been derived using the double‐time Green's function and taking a simplified model of a vacancy and an interstitial pair in the lattice. Considering only nearest‐neighbour interactions in the harmonic approximation it has been found that in addition to the energy shift due to the second‐order Doppler effect there is an additional shift due to the disordering of the lattice which depends on the position coordinate of the interstitial atoms, the changed force constant of this atom, and the temperature.
Thermal‐electric alignment and stark effect of Z1 centers in KCl
Authors: Jain V. K. , Lüty F. 
Published: July 2007

AbstractThe experimental results of detailed electro‐optical studies on Z1 centers in KCl doped with Ca, Sr, and Ba are reported. For randomly oriented Z1 center systems an isotropic quadratic Stark effect is measured, with a spectral dependence (close to a third derivative of the Z1 absorption) markedly different from that of F centers. The equality of the Z1 center orientations can be disturbed by the application of de fields (about 104 Vcm−1) above 120°K, leading to the development of a linear Stark effect. The spectral dependence and characteristic anisotropy of this linear Stark effect are determined. Quantitative pulse annealing experiments under applied de field show that the Z1 centers reorient with an activation energy of ≈0.4 eV. This process is attributed to jumps of the cation vacancy among equivalent lattice sites within the Z1 complex and will be discussed on the basis of a vacancy‐centered model proposed earlier [1].
On the spectrum of acoustical phonons of a plane‐parallel plate
Authors: Iosilevskii Ya. A. 
Published: July 2007

AbstractBy a method based on the Dyson equation and on the interpretation of boundaries as extended defects in an infinite solid, the phonon Green function of a plane‐parallel elastically isotropic plate of arbitrary thickness is found in a closed analytical form in the acoustical frequency region. The effect of the boundary conditions on the local density of the phonon states is analysed. This effect is found to be spread over a rather considerable distance relaxing mainly as \documentclass{article}\pagestyle{empty}\begin{document}$\frac{c}{{2\omega x}}\sin \left({\frac{{2\omega x}}{c}}\right)$\end{document} where c is the characteristic velocity of sound.
Monte‐Carlo calculations of the blocking effect
Authors: Ryabov V. A. 
Published: July 2007

AbstractThe angular distribution of fast charged particles originating at the lattice sites is studied by computer simulation. Multiple scattering effects were found to be necessary for agreement with the experiment in the planar case. The dependence of the intensity of multiple scattering on crystal thickness and temperature is discussed. Detailed calculations of the blocking pattern are performed for the [100] and [111] directions of a simple lattice (b.c.c.). It is shown that in case of emitting nucleus displacement from the lattice site the most sensitive parameter of the distortion is the value of the originating planar shoulder near a lowindex direction. The distortion of the blocking pattern is calculated as a function of the compound nucleus lifetime.
Absorption spectra of Ti(d2), V(d3), and Cr(d4) ions in CdTe
Authors: Slodowy P. A. , Baranowski J. M. 
Published: July 2007

AbstractThe absorption spectra of divalent impurities Ti(d2), V(d3), and Cr(d4) in cadmium telluride are presented. From the spectra values of the crystal field parameter Δ and Racah parameters B and C are derived and discussed.
Anisotropy of the dielectric constants of trigonal selenium and tellurium between 3 and 30 eV
Authors: Bammes P. , Klucker R. , Koch E. E. , Tuomi T. 
Published: July 2007

AbstractThe reflectivity of Se and Te single crystals has been measured at near normal incidence for photon energies between 3 and 30 eV with the electric field vector lying parallel and perpendicular to the c‐axis of the crystals. The measurements were made using the polarized continuum of the synchrotron radiation of DESY. A Kramers‐Kronig analysis gave the optical constants for both directions of polarization. For both substances electron energy loss measurements are reported. Comparison with optical data gives satisfactory agreement. Even at high energies considerable anisotropic behaviour and several new spectral features are observed. They are discussed in terms of recent band structure calculations.
Conversion and equilibrium between F‐ and F2‐centers in X‐irradiated KCl. I. Slow warm up experiments
Authors: Seager C. H. , Welch D. O. , Royce B. S. H. 
Published: July 2007

AbstractMeasurements are reported in which the number of F2‐centers produced by warming crystals previously X‐irradiated at liquid nitrogen temperatures is studied as a function of temperature and crystal purity. These data are analysed in terms of a diffusion model in which the energy of migration and the initial F+‐center distribution are adjustable parameters. It is shown that the best fit is obtained with an energy of motion of negative ion vacancies (F+‐centers) of 0.66 eV and a vacancy distribution such that the F+‐centres tend to be within five nearest neighbor distances of the F‐centers.
A comparison of the long wave optical phonons in trigonal Se and trigonal Te
Authors: Lucovsky G. 
Published: July 2007

AbstractThe frequencies of the long wave optical phonons in trigonal Se and Te are compared. Differences in the relative frequencies of the A1 and A2 modes, and in several of the elastic constants as well, are attributed to differences in the intra‐ and inter‐chain bonding. These comparisons are made quantitative by defining reduced lattice dynamical properties in which the nearest and second nearest neighbor distances are used as scaling parameters respectively for the intra‐ and inter‐chain properties. The comparison is extended to the optic mode frequencies of amorphous Se and Te.
Electron transport in PdNi alloys with Ni concentration above the critical concentration
Authors: Leger M. G. , Muir W. B. 
Published: July 2007

AbstractThe electrical and thermal resistivities and thermopowers of three palladium‐nickel alloys have been measured between 2 and 77 °K. The alloys had nickel concentrations slightly higher than the critical concentration necessary for low temperature ferromagnetism. The electrical resistivity results indicate that both the electron‐electron and electron‐phonon terms change with composition. The electron‐electron term decreases with increasing nickel concentration and has been attributed to nickel‐nickel interactions which decrease the effective enhancement. The greatly reduced electron‐phonon term in two alloys near 3 at% nickel does not seem to be related to a similar reduction in the coefficient of the T3 term in the specific heat. The thermopower has been observed to change character between 3.1 and 4.3 at% nickel. This effect is similar to previous results on Pd‐Ni alloys which are as yet unexplained.
Dynamique d'un cristal d'urée
Authors: Lefebvre J. 
Published: July 2007

AbstractLa dynamique d'un cristal d'urée est faite dans le cadre de la théorie moléculaire. Un potentiel d'interaction simplifié comportant les potentiels dǔs aux liaisons hydrogène et au moment dipolaire de la molécule permet de calculer l'énergie cristalline (‐27,2 kcal/mol), les constantes élastiques (C11 = 2,37; C33 = 5,12; C44 = 0,648; C66 = 0,058; C12 = ‐1,04 et C13 = 0,79 en 1011 dyn/cm2), les fréquences principales (53; 54; 79; 149 et 219 cm−1), les déplacements quadratiques moyens dǔs à l'agitation thermique et le spectre de fréquences. Ces valeurs théoriques sont ensuite confrontées avec les déterminations expérimentales chaque fois que cela est possible.