bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical bleaching and F → M conversion in doped KCl crystals
Authors: Srinivasan T. M. , Sastry E. V. R. 
Published: July 2007

AbstractUndoped KCl and KCl crystals doped with Co, Ba, and Cd have been irradiated with X‐rays for various periods and bleached with F‐light at room temperature. The resulting decay of F‐centres and changes in the M‐ and R‐centre concentrations were studied. Co‐ and Ba‐doped crystals X‐irradiated into the second stage of coloration have been found to exhibit, when compared to undoped crystals, (1) greater stability of F‐, M‐, and R‐centres against F‐light bleaching, and (2) higher F → M conversion efficiency. Cd‐doped KCl showed a rapid bleaching of F‐centres without any increase in the M‐centre concentration. The role of impurities in the vacancy and electronic processes which control the bleaching and aggregation of F‐centres is discussed.
High temperature phase transitions and metastability in KDP type crystals
Authors: Grünberg J. , Levin S. , Pelah I. , Gerlich D. 
Published: July 2007

AbstractMeasurements of dielectric constants and infrared reflection were carried out on KH2PO4, KD2PO4, and RbH2PO4 single crystals in the temperature range 300 to 500 °K. Both types of measurements show the existence of two distinct phase transitions Tp and T1 in the above range. The Tp transition is associated with a change in the hydrogen bond. At this temperature the crystal structure changes from tetragonal to monoclinic. The crystal remains in the new structure even after cooling back past the transition to room temperature. Below Tp this phase is metastable and mechanical vibration will release the crystal back to the stable state in room temperature. The T1 transition seems to be dependent on the PO1 and the new phase is also methastable below T1.
Theory of positron trapping by F‐ and F′‐colour centres in alkali halides
Authors: Berezin A. A. 
Published: July 2007

AbstractThe trapping energies of the positron to the F‐ and F′‐colour centres are calculated for NaCl, KCl, and KBr crystals. For the field of F′‐centre the Hultéh potential approximation is used. The values of the positron affinity of the negatively charged F′‐centre are found to lie near 3 eV. This is about twice as much as the positron affinity of the neutral F‐centre which is found to be 1.4 eV for NaCl, 1.6 eV for KCl, and 1.7 eV for KBr.
The influence of optical phonons on the seebeck and Nernst‐Ettingshausen effects in CdTe
Authors: Kubálková S. 
Published: July 2007

AbstractDetailed measurements are made of the temperature dependence of four transport effects in CdTe: the electric conductivity, the Hall effect, the thermoelectric Seebeck effect (a), and the transversal Nernst‐Ettingshausen effect. (Q). The first two effects have been used for the determination of theoretical values of α and Q. The great discrepancy between experimental and theoretical values of α and Q is explained using Plâvitu's theory of the phonon drag effect of carriers in ionic crystals.
Diffusion of Ni and Ba in MgO up to 2600 °C
Authors: Harding R. C. 
Published: July 2007

AbstractThe diffusion of Ni2+ and Ba2+ in single crystal magnesium oxide has been studied over the temperature range 1100 to 2500 °C using radio isotopes and a sectioning technique. Results indicate that the enthalpies of motion of these two ions in MgO differ by about 10% only. Below about 1500 °C, segregation of impurities to dislocations has a marked effect on the activation energy for diffusion in agreement with the results obtained in cation self‐diffusion studies previously published. The formation enthalpy of a Schottky pair has also been confirmed.
Low temperature X‐ray diffraction and phase transitions in DyVO4, and DyAsO4
Authors: Göbel H. , Will G. 
Published: July 2007

AbstractCrystallographic phase transitions have been observed in DyVO4, and DyAsO4, at 13.8 and 11.2 °K, respectively by low temperature X‐ray diffraction on powders. These phase transformations coincide with observed anomalies in the temperature dependence of the specific heat. They occur prior to magnetic phase transitions at 3.0 and 2.44 °K, respectively, which were determined by neutron diffraction.
Impurity induced Raman spectra of NaCl and KCl crystals with various monovalent impurities
Authors: Möller W. , Kaiser R. 
Published: July 2007

AbstractImpurity induced Raman spectra have been measured in NaCl:Br, NaCl:I, KCl:I, NaCl:Li, and KCI:Ag. The strongest scattering intensities are caused by A1g vibrations in NaCl:Br, NaCl:I, KCl:I and by Eg vibrations in NaCl:Li, KCl:Ag. No F2g scattering could be found in NaCl:Li and no A1g, scattering was observed in KCl:Ag. The position and in part the shape of the scattering spectra are discussed. The measured scattering intensities are compared firstly with the polarizabilities (for impurities and neighbours) and the overlap and secondly with the calculated intensities for the three vibration types.
Thermodynamics of strongly anharmonic crystals
Authors: Siklós T. , Aksienov V. L. 
Published: July 2007

AbstractThe properties of the f.c.c. lattice with nearest neighbour central force interaction are investigated in the case of an arbitrary external pressure. The instability temperature, phonon frequencies, phonon widths, and the thermodynamical properties of the f.c.c. lattice are calculated in the high and low temperature limits.
Hahnsches Echo der magnetischen Resonanz im Festkörper
Authors: Fenzke D. , Freude D. , Müller D. , Schmiedel H. 
Published: July 2007

AbstractBeobachtet man im Festkörper ein Hahnsches Echo, so kann eine Ursache für die Entstehung des Echos die starke magnetische Wechselwirkung der beobachteten Spins mit einer sich außerhalb der Resonanz befindlichen Spinsorte sein. Es wird gezeigt, wie man in diesem Fall Informationen über die geometrische Anordnung der Spins und Korrelationszeiten ihrer Bewegung erhalten kann. An Messungen der Protonenresonanz dekationisierter Zeolithe wird die Effektivität des Verfahrens nachgewiesen.
Diffusion of F‐centers in potassium chloride crystals
Authors: Kuczynski G. C. , Byun J. J. 
Published: July 2007

AbstractDiffusion coefficients of F‐centers in additively colored KCI single crystals have been measured as a function of F‐center concentration [F] and temperature. It has been found that up to a certain critical concentration which decreases with temperature, these coefficients are independent of [F]. Above this concentration, diffusion coefficients decrease with [F]. Presence of divalent cations seems to increase diffusion rates. Theoretical analysis of the experimental data indicates, that at low [F], diffusion of F‐centers is controlled by electrons hopping from one vacancy to another. At high [F], the dominant transport mechanism is diffusion of cation vacancies.
A Mössbauer study of hyperfine parameters of Sn119 in antiferromagnetic and paramagnetic states of FeSn
Authors: Ligenza S. 
Published: July 2007

AbstractMössbauer investigations of Sn119 nuclei in FeSn have been performed at temperatures from 5 to 400 °K. The temperature dependence of the hyperfine field on the tin nuclei on the magnetically ordered (001) planes, of the isomer shift and quadrupole interaction have been studied for two crystallographic sites of Sn nuclei. Different values of the isomer shift and quadrupole parameters were observed in the antiferromagnetic and paramagnetic states of FeSn. It is concluded that in the paramagnetic state the tin atoms on the (001) planes form linear bonds along the c‐axis involving the p, orbitals only, whereas in the antiferromagnetic state the bonds include also the pz and py orbitals which yield the asymmetry of the electric field gradient. On the (002) planes the tin atoms form bonds involving all Px Py Vz orbitals in both the antiferromagnetic and the paramagnetic state of FeSn.
Investigations of the two low lying ground‐level doublets of Dy3+ in YAsO4 by paramagnetic resonance and optical absorption spectrum
Authors: Hillmer W. , Plamper J. , Wappler D. 
Published: July 2007

AbstractParamagnetic resonance at K‐, Q‐, and X‐band frequencies and optical absorption spectrum of trivalent dysprosium have been investigated in single crystals of yttrium arsenate within a temperature range from 1.7 to 15 K. The measurements indicate, that there is a linear Zeeman splitting parallel and a nonlinear Zeeman splitting perpendicular to the c‐axis of the crystal for the two lowest ground‐level doublets. The energetic distance of these doublets at zero magnetic field is ΔW = (1.35 ± 0.03) cm−1. A spin Hamiltonian is given with effective spin S = 3/2, which describes the observed Zeeman effect of the two doublets lying close together.
Lattice dynamics and magnetic ordering in the chalcogenide spinels CdCr2S4 and CdCr2Se4
Authors: Brüesch P. , D'ambrogio P. 
Published: July 2007

AbstractA detailed analysis is presented of the k = 0 phonons of CdCr2S4 and CdCr2Se4 which is based on a simple force model with four adjustable short range parameters. With the help of the derived dynamical matrices for the different symmetry species, the analysis can be performed easily for any compound with the normal spinel structure. From the measured frequencies of the Raman and infrared active phonons of CdCr2S4 and CdCr2Se4 the force constants and eigenvectors of the different normal modes are calculated. We firstly discuss the derived force fields of these two compounds and secondly the coupling between the internal and external lattice vibrations. Finally, with the help of the calculated normal coordinates, the observed influence of the magnetic ordering on the Raman‐ and infrared active phonons of CdCr2S4 and CdCr2Se4 is studied in detail.
The elastic constants of cubic crystals with covalent and partially covalent bonds
Authors: Vukcevich M. R. 
Published: July 2007

AbstractGeneral formulae for the elastic constants of purely and partially covalent cubic crystals are derived. For the mixed covalent‐ionic bond a new model of electron locale‐transition is proposed, according to which the ionicity of a bond depends on the bonding angle. This model can account, qualitatively, for the elastic properties of ZnS‐compounds. Also discussed are some earlier theories, which appear to be in error, and some broader implications of the proposed model.
Lattice absorption of solid and liquid iodine
Authors: Wagner V. 
Published: July 2007

AbstractThe lattice absorption of I2 single crystals was measured with polarized radiation from 20 to 300 cm−1 at 110 and 300 K. Besides the absorption of the ir‐active phonons there is considerable absorption situated near the inactive internal vibration of the molecule. This absorption is due to two‐phonon processes involving an internal vibrational mode. The corresponding selection rules were deduced. The lattice absorption persists in the liquid phase near the melting point. However, it is altered by strong absorption of the internal vibration.
Influence of the mean free path of the conduction electrons on the magnetic properties of Gd intermetallics ith CsCl structure
Authors: Buschow K. H. J. , Oppelt A. , Dormann E. 
Published: July 2007

AbstractThe variation of Curie temperature with number of conduction electrons in compounds GdAg1 − x, Inx, GdAg1 − x Znx, and GdZn1 − x, Inx is interpreted in terms of the RKKY model. Especially, the influence of a nonconstant exchange integral with a cutoff wavenumber is discussed. The Curie temperatures of compounds with a constant number of conduction electrons were determined for GdCd1 − x Znx and GdAg0.5(1 − x)In0.5(1 − x)Znx. It is shown, that the mean free path of the conduction electrons modifies the strength of the indirect exchange interaction, which can explain, that different Curie temperatures are obtained in compounds with equal number of conduction electrons. The variation of the Pauli susceptibility was estimated from determinations of the magnetic susceptibility of the compounds YAg1 − x Inx YAg1 − xZnx, and LaAg0.5(1 − x)In0.5(1 − xZnx.
ESR study of copper doped NaCl
Authors: Fârcas S. I. , Darabant A. , Nicula A. 
Published: July 2007

AbstractThe ESR spectra of NaCl: Cu systems at LNT and RT are studied. In one of the samples a new paramagnetic centre with [100] tetragonal symmetry was found. The principal values of the g tensor are: g∥ = 2.298 ± 4 × 10−3, g∥ = 2.058 ± 4 × 10−3 In a second type of samples the ESR spectrum of Cu2+ was observed. The g and hyperfine tensors have axial symmetry along a [100] axis. From the parameters of the spin Hamiltonian and from the results of optical spectroscopy the value of the spin‐orbit coupling constant of the copper ion was obtained to λ = (−847 ± 20) cm−l. From this result it is supposed that covalency effects between Cu2+ and the chlorine environment in the NaCl lattice are not important when the crystals are not irradiated.
Energy Transfer between Impurity Molecules of a Crystal in the Presence of Relaxation
Authors: Davydov A. S. , Serikov A. A. 
Published: July 2007

AbstractThe time dependence of the probability W(t) of excitation energy transfer from the donor to the acceptor for various values of resonance interaction energy (ħ L), donor excitation energy relaxation time (γ−1), and the relaxation time (λ−1) of the vibrational part of acceptor excitation energy is found using the method of density matrix. It is shown that W (∞) = \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{\lambda \alpha ^2 }}{{(\lambda + \gamma)(1 + \alpha ^2)}}{\rm where } \alpha {\rm = }\frac{{{\rm 2|}L{\rm |}}}{{\sqrt {\gamma \lambda } }} $\end{document}. Thus, W(∞) is proportional to the square of resonance interaction energy at α ⪅ 0.2. However, W(∞) is approximately proportional to α with the values of α satisfying the inequality 0.2 ⪅ α ⪅ 1.7.
Separation of the e1 and E1 Interband Transitions near 2 eV in Germanium by Thermoabsorption
Authors: Kessler F. R. , Dettmer K. 
Published: July 2007

AbstractBy thermoabsorption of Ge thin films (thicknesses 300, 500, and 520 Å, modulation frequency 12.5 Hz, modulation depth δT ≤ 4 K) the interband transitions e1 and E1 in the spectral range near 2 eV are investigated including the transitions with spin–orbit splitting. It is possible to separate these transitions on account of their significantly different temperature dependences: de1/dT = −(5.47±0.02) × 10−4eV/K and dE1/dT = −(3.89±0.02) ×× 10−4 eV/K. The spectral shift divergence overcompensates the Lorentz broadening of the peaks so that their resolubility becomes better at higher mean temperatures. The energies for the transitions extrapolated to 295 K and corrected as to give bulk results are e1 = 2.107 eV, e1 + Δ = 2.294 eV, E1 = 2.134 eV, and E1 + Δ1 = 2.314 eV.
Infrared Absorption in Small Ionic Crystals
Authors: Genzel L. , Martin T. P. 
Published: July 2007

AbstractThe infrared transmission of 0.1 μm crystals of MgO has been measured in the region of fundamental lattice absorption. In particular, the effects of anharmonicity and particle density on the transmission have been observed. These effects have also been calculated using a continuum model applicable to spheres very much smaller than the wavelength of light. In agreement with these calculations, the frequency of the fundamental infrared absorption of small particles was found to decrease with increasing particle density. In addition, it was observed that the frequency dependent damping function of massive MgO must be increased by a factor of about eight in small crystals in order to fit the experimental data.
Lattice Dynamics of MgO Microcrystals
Authors: Genzeland L. , Martin T. P. 
Published: July 2007

AbstractThe eigenvalues and eigenvectors of the modes of vibration of small MgO crystals were calculated using a rigid ion model. The infrared absorption by microcrystals composed of 48 ions was calculated and the infrared transmission of small 0.2 μm cubes was measured. Both the experiment and the calculation exhibit three absorption bands, one weak band at the reststrahl frequency and two more bands at higher frequencies. The calculated density of states of microcrystals composed of 64 and 180 ions is found to resemble closely the density of states obtained using a rigid ion model and cyclic boundary conditions. In addition, the calculated density of states of microcrystals is in good agreement with the measured density of states obtained from inelastic neutron scattering of powder samples.
Pseudopotential Calculation of Binding Energies, Structures, and Lattice Constants of Simple Metals
Authors: Hafner J. , Nowotny H. 
Published: July 2007

AbstractThe nonlocal pseudopotential formalism of Harrison is applied to the problem of binding energies, structures, and lattice constants of nine simple metals. The formulation of the crystal potential is similar to that given by Harrison, but the Kohn‐Sham approximation is used for the description of the core‐valence exchange interaction and the effect of the orthogonalization hole on the core energies is computed by a weighted average scheme. Exchange and correlation between the conduction electrons are taken into account using the modified dielectric function proposed by Kleinman and Langreth. The correct structure is predicted in all cases and the binding energies, equilibrium atomic radii, and axial ratios are obtained with good accuracy.
Optical Anisotropy of β‐Rhombohedral Boron from 0.4 to 16 μm
Authors: Werheit H. , Hausen A. , Binnenbruck H. 
Published: July 2007

AbstractIn the intrinsic range the anisotropy of the reflectivity amounts to about 2% while the dichroism is very small at high photon energies and can only be measured when α ⪅ 2 × × 103cm−1. Especially distinct is the anisotropy of the lattice vibrations. Similar to polycrystalline boron two indirect interband transitions occur; the energy gaps are 1.561 and 1.39 eV with E ∥ c and 1.541 and 1.34 eV with E ⟂ c. The edge tail is dominated by an absorption band, which is possibly caused by C or Si impurities.
Dislocation Jog and Kink Interactions in Ionic Crystals
Authors: Brækrus J. , Lothe J. 
Published: July 2007

AbstractJogs and kinks on dislocations in ionic crystals interact both elastically and electrically. In cubic crystals the electrical interaction can be calculated by simple isotropic theory. Anisotropic calculations of the elastic interaction have been performed for a number of ionic crystals of the NaCl type in order to decide whether the net interaction is attractive or repulsive and whether neutral superjogs tend to form.
Intermolecular Triplet Energy Transfer in Naphthalene–Pentacene Mixed Crystals via Higher Excited Triplet States
Authors: Vaubel G. , Peter L. 
Published: July 2007

AbstractRadiationless intermolecular host‐guest and guest‐host triplet energy transfer involving a hot triplet state of pentacene embedded in a crystalline naphthalene matrix has been observed. The latter process gives rise to delayed fluorescence which increases with the fourth power of the intensity of optical excitation.
Pseudodislocational Interactions in the System Germanium–Arsenic
Authors: Rozhanskii V. N. , Aresenteva I. P. , Zakharov N. D. , Govorkov V. G. , Voinova N. N. 
Published: July 2007

AbstractThe interaction of arsenic pseudodislocations with each other and with dislocations of a germanium lattice is analyzed. The nature of the interaction depends largely on the directed diffusion processes. Interaction between pseudodislocations and gliding dislocations results in a dispersion strengthening of the system.
The Dynamical Behaviour of Silver Chloride with Modified Shell Model
Authors: Singh R. K. , Upadhyaya K. S. 
Published: July 2007

AbstractA detailed study is presented of the dynamical behaviour of silver chloride using the modified shell model, developed by Verma and Singh, which accounts for the deformation of electron shells introducing three‐body interactions. The results obtained are in fair agreement with the experiments on phonon dispersion. Debye temperatures, second‐order Raman scattering, and infrared absorption spectra of the solid under consideration.
On the Influence of Screening on the Ferroelectric Curie Point
Authors: Nattermann Th. 
Published: July 2007

AbstractA simple model of a uniaxial ferroelectric photoconductor is considered in which the influence of the electronic system is described by an appropriate expression for the dielectric function. On the basis of the Hamiltonian of the soft optical vibration mode the theory of the thermodynamical Green's function is used to derive an equation for the temperature of the ferroelectric phase transition. From this, the shift of the transition temperature and the change of the spontaneous polarization, caused by an excitation of valence band electrons, can be calculated. Under certain conditions the results are shown to be in agreement with those obtained by other authors.
An Elastic‐Modulus Effect Calculation of the Interaction of Point Defects with Extended Dislocations in F.C.C. Metals
Authors: Bapna M. S. , Meshii M. 
Published: July 2007

AbstractA generalized calculation was carried out on the interaction energy and interaction force of point defects with extended dislocations due to the elastic‐modulus effect. It was shown that the maximum interaction does not occur at the middle of two partials. The results obtained were used to estimate the maximum interaction energy between a vacancy and an extended dislocation and the hardening coefficient, αv, for vacancy‐dislocation interaction. These results were examined in the light of experimental results in gold. Further, it was noted that asymmetry in the sign of the interaction above and below the slip plane will not occur when the interaction between an edge dislocation and a point defect is predominantly of the elastic‐modulus type rather than an elastic‐misfit type.
EPR of the Four‐Copper‐Ion Complex with Spin S = 2 in Triglycine Fluoroberylate Monocrystal
Authors: Stankowski J. , Maćkowiak M. 
Published: July 2007

AbstractEPR study of Cu2+ in TGFB revealed at high temperatures isolated complexes with square coordination decreasing in number with lowered temperature to yield four‐ion aggregates. In describing the aggregate spectrum, a spin Hamiltonian with effective spin S = 2 is used; its parameters are determined to gz = 2.12, gy = 2.15, gx = 2.08, D = 0.108 cm−1, E = 0.030 cm−1, c = 0.009 cm−1, α = −0.003 cm−1. The hyperfine structure constant of the aggregate is four times smaller than that of the isolated centre. The strong dependence on temperature and high pressure is related with NH3 group rotation in the TGFB crystal.
Résonance électronique de spin et susceptibilité magnétique des composés GdCu et GdAg
Authors: Burzo E. , Urzu I. , Pierre J. 
Published: July 2007

AbstractNous avons étudié par R.P.E. les composés GdCu et GdAg. La valeur de l'interaction d'echange Jsf déduite de ces mesures est négative. Elle est comparée à celles déduites de mesures magnétiques et de R.M.N.
Electron Images of Two‐Dimensional Domain Walls
Authors: Hothersall D. C. 
Published: July 2007

AbstractThe out‐of‐focus electron images of the two‐dimensional 180° Bloch‐wall model of Hubert are calculated using a wave optical formulation. The asymmetry of the calculated images is established and qualitative comparison is made with experimental domain wall images from walls in thin sections of Fe and Co. The experimental image of a 1800 wall in a foil of FeSi is compared with theoretical profiles calculated in two ways; the first using a one‐dimensional wall model with a linear rotation of the magnetization, and the second using the two‐dimensional wall model. As a result of these comparisons the electron imaging effects of the two wall models can be tentatively related.