bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic and optical properties of rutile‐structure fluorides in the rigid‐ion approximation
Authors: Striefler M. E. , Barsch G. R.
Published: July 2007

The elastic constants and the infrared and Raman frequencies of the difluorides XF2 with X = Mg, Mn, Fe, Co, Ni, Zn have been calculated for a rigid ion model with an effective ionic charge and with first and second nearest neighbor central force short range interaction. Explicit expressions for the elastic constants are given with the internal strain contributions expressed in terms of the Raman frequencies. The nine parameters of the model are determined from the three equilibrium conditions and from least squares fits over some or all available experimental elastic and optical data. The model is able to account well for the magnitude of the experimental data and for their almost monotonic decrease with increasing cation radius, but the calculated deviations from the Cauchy relations are smaller than the observed values.
Mössbauer effect study of the hyperfine field at the tin site in PtMnSn
Authors: Rao K. R. P. M. , Iyengar P. K.
Published: July 2007

The magnitude of the hyperfine field at the tin site in the PtMnSn alloy has been measured using the Mössbauer effect technique. The observed field is 7 kOe at 293 °K and 33 kOe at 78 °K. The sign of the field has also been determined and found to be positive. Saturation hyperfine field at the Sn‐site has been estimated using the virtual bound state model of Caroli and Blandin for a range of values of the parameters of the model. It is found that the theory is inadequate since it does not predict even the correct sign of the hyperfine field at the tin site. It is suggested that the hyperfine fields observed at the tin sites in various Heusler (L21) and related Clbstructure alloys could probably be understood on the basis of the model of Campbell in terms of the effective impurity potentials present at the Sn‐sites in the various alloys.
Superconductivity in the palladium‐hydrogen system
Authors: Skośkiewicz T.
Published: July 2007

Superconductivity has been investigated in palladium hydride samples prepared electrolytically. At H/Pd ratios higher than 0.77 a strong dependence of the superconducting critical temperature on H/Pd ratio has been observed. The critical temperature of 6.6 K was found at H/Pd = 0.94. Extrapolation of the experimental data up to H/Pd = 1 gave the critical temperature of stoichiometric PdH about 11 K. It is shown that the normal residual resistivity of a sample can be used for an estimation of the hydrogen content. The measurements of the electrical resistance in the magnetic field revealed a linear dependence of the critical magnetic field on temperature. Extrapolation of Hc down to T = 0 gave an Hc(0) value equal to 1800 Oe independent of H/Pd.
Small polaron model of the electron motion in organic molecular crystals
Authors: Vilfan I.
Published: July 2007

The electron mobility in organic molecular crystals, in particular in anthracene, is calculated applying the small polaron model. The fluctuations of the electron polarization energy are considered as the electron‐phonon interaction. The mobility is calculated in two ways, in the first the electron‐hole correlation is neglected. It is shown that the effect of the electron‐hole correlation is to increase the mobility by about 80%. The calculated and experimental mobility values are compared.
The effect of high magnetic fields on the ground state of hydrogen‐like impurities in semiconductors
Authors: Halbo L.
Published: July 2007

A variational calculation has been made of the ground state energy of a semiconductor impurity in the effective mass approximation (EMA), in the presence of high magnetic fields. The field dependence of the computed binding energy and the wave function parameters are presented. The calculation was made for isotropic effective mass as well as for a mass anisotropy corresponding to electrons in germanium. The effect of the many‐valley structure of the conduction band in germanium, and the deviations from the EMA, are discussed.
EPR investigation of paramagnetic centres in β‐rhombohedral boron
Authors: Gewinner G. , Kubler L. , Koulmann J. J. , Jaeglé A.
Published: July 2007

A symmetrical EPR line with a g‐factor of 2.0028 is observed in β‐rhombohedral boron at temperatures above 300 °K. The spin density is measured in the range 300 to 1000 °K. It increases exponentially with the temperature and an activation energy of about 0.40 eV is obtained. The line width exhibits a minimum in the neighbourhood of 450 °K. These results suggest a carrier model with localized wave functions. The number of corresponding electronic states is very large. In the neighbourhood of 300 °K, the line width, line shape, and g‐value are within experimental errors the same as those reported for the EPR line observed under illumination with a radiation of about 0.8 μm. The two EPR spectra may thus be attributed to the same electronic states being occupied either by optical or by thermal excitation. Measurements of line width and spin density for the photo‐induced EPR line between 77 and 300 °K are reported and support this hypothesis.
Ferroelectric phase transition in small crystals of BaTiO3
Authors: Bäuerle D. , Genzel L. , Martin T. P.
Published: July 2007

Infrared absorption measurements show that the depolarization field in small crystals of BaTiO3 prevents the zero wavevector optical mode from becoming soft. Yet the transition temperature is found to be the same for small crystals and bulk. We suggest that the phase transition in small particles is driven by soft modes with nonzero wavevectors.
Mössbauer studies of thermal neutron radiation damage in an ordered alloy
Authors: Simopoulos A. , Vogl G.
Published: July 2007

Mössbauer effect measurements on Au197 were done to study neutron radiation damage in the ordered alloy CoPt. Pt196 nuclei were irradiated with neutrons to produce unstable Pt197nuclei which β decay to the Au197 Mössbauer nuclei. The average recoil energy of ≈ 30 eV connected with thermal neutron capture led to replacement collisions of Pt197 ions with their neighbours. The Mössbauer results show that by irradiation at 330 K about 40% of the produced Au197 atoms have left their ordered sites with eight Co and four Pt nearest neighbours and ended up in sites with an average of (5.5 ± 0.3) Co and (6.5 ± 0.3) Pt nearest neighbours. This result can be explained by a model of replacement collisions of the recoil atoms with nearest or next nearest neighbours in the 〈110〉 or 〈100〉 directions. The results are fairly in agreement with computer‐simulation predictions for low‐energy recoil in f.c.c. metals.
Hot‐exciton luminescence in CdSe crystals
Authors: Gross E. , Permogorov S. , Morozenko Ya. , Kharlamov B.
Published: July 2007

The emission spectra of CdSe crystals under the excitation in the region of fundamental absorption with the HeNe laser line λ = 6328 Å have been studied at temperatures 4.2 to 300 °K. A set of narrow emission lines shifted by the energies of an integer number of LO phonons to lower energies from the exciting line has been observed in the region of fundamental absorption. No emission line has been observed at the position shifted by l LO. The intensity of LO‐shifted lines drastically decreases with increasing crystal temperature. It is shown that this temperature dependence and the comparable intensity of multiphonon lines cannot be explained on the basis of a resonant Raman scattering model. The observed line emission was assigned to a luminescence of hot excitons. The latter model can explain both thermal quenching of emission and intensity distribution in the spectrum. In the emission spectra of mechanically polished samples a defect activated 1 LO emission line has been observed. This line is due to the indirect exciton transitions without phonon participation in the partially disordered surface layer. Besides the line structure, the continuous emission background has been observed in the region of fundamental absorption. This background forms the high energy exponential tail of the quasi‐equilibrium exciton emission line n = 1 A and can be considered as Urbach region of the exciton emission spectrum.
Magneto‐seebeck effect and Shubnikov‐de Haas effect in n‐type bismuth telluride
Authors: Schröder B. , von Middendorff A. , Köhler H. , Landwehr G.
Published: July 2007

Shubnikov‐de Haas experiments were performed between 1.8 and 4.2 K on n‐Bi2Te3 single crystals with carrier concentrations between 1.4 × 1018 and 8.4 × 1019 cm−3.In addition the magneto‐Seebeck effect was measured between 20 and 100 K in transverse magnetic fields up to 6 T (60 kG). The Hall effect and Shubnikov‐de Haas oscillations were observed in fields up to 10.5 T (105 kG). The results of the different physical phenomena may be explained by a two‐conduction‐band model. The best fit of the data is obtained with a value of ΔE = 20 meV for the energy difference between the two band minima and a density of states mass of md2 = O.9 m0 for the upper conduction band. With this set of parameters and the known masses for the lower band both the Shubnikov‐de Haas and magneto‐ Seebeck data can be quantitatively accounted for. Also, previously measured specific heat data can be explained on the same basis.
Influence of vibronic coupling on the dissociation of Frenkel excitons
Authors: Zgierski M. Z.
Published: July 2007

The influence of vibronic coupling on one‐ and two‐particle dissociation processes of Frenkel excitons is investigated. Special attention is paid to the temperature dependence of dissociation processes, in which quanta of intramolecular vibration coupled with excitons take part. Some remarks on activation energy for photoconductivity of anthracene and metal‐free phtalocyanine crystals are given.
Crystal field studies of some rare earth hydroxides
Authors: Kumar V. , Gupta G. K. , Dass N. , Chandra K.
Published: July 2007

The magnetic susceptibility, μeff, and the Schottky specific heat have been calculated over a temperature range 10 to 300 °K in Er(OH)3, Er3+:Y(OH)3, Dy(OH)3, and Ho3+: Y(OH)3 systems. The spectroscopic splitting factors, Curie constants, and extra entropy associated with the Schottky anomaly were compared to experimental results. By reason of the good agreement it was concluded that the crystal electric field parameters used are significantly accurate.
Dipolar contributions to magnetic hyperfine fields in ErxY1−xFe2 and TbxY1−xFe2 compounds
Authors: Dariel M. P. , Atzmony U. , Lebenbaum D.
Published: July 2007

Mössbauer effect measurements on 57Fe have been carried out in the pseudobinary systems ErxY1−x Fe2 and TbxY1−xFe2 at 4.2, 80, and 300 K. The isotropic part of the hyperfine field acting on the iron nuclei includes a term due to polarization by the localized rare‐earth spin. Magnetic dipolar contributions account only in part for the differences in the magnitude of the hyperfine fields at the inequivalent sites.
Phonon Raman spectra of layer compound GaSe
Authors: Yoshida H. , Nakashima S. , Mitsuishi A.
Published: July 2007

Raman scattering spectra of GaSe were examined at various temperatures (80 to 400 K) and the far‐infrared transmittance was obtained in the energy range from 10 to 30 cm−1. It is shown that the band at 20 cm−1 is both Raman‐ and infrared‐active. Results of the resonant Raman enhancement in GaSe indicates that the Raman band at 250 cm−1 is due to a LO mode. Comparison between the Raman spectrum of GaSe and that of Gas confirms this. These facts can be explained by considering the hexagonal GaSe as the ϵ‐type which lacks inversion centre. Six Raman bands observed in GaSe are assigned to normal modes on the basis of the ϵ‐type. An E′ (TO) mode is degenerated accidentally with an E″ mode at 211 cm−1.
Statistical theory of nuclear magnetic relaxation in the rotating frame
Authors: Yulmetev R. M.
Published: July 2007

The statistical theory of the nuclear magnetic relaxation of the spins in a rotating frame has been developed by the theoretical functional method of projecting operators (PO). This method of PO was used for finding the kinetic equation for the spin TCF. A general expression for the relaxation rates in the case of slow and fast thermal motion in the spirit of the well known Kubo‐Tomita theory is determined from the structure of these kinetic equations.
The role of reservoirs of dipole‐dipole interactions in cross‐relaxation
Authors: Skrebnev V. A.
Published: July 2007

The possibility of introducing a reservoir of interactions responsible for cross‐relaxation with the inverse temperature βcr is considered for magnetic samples containing two kinds of spins. It is shown that, despite the nonsecular character of such interaction, the rate of the change of temperature β−1cr can be much smaller than the rate of establishment of equilibrium in the various magnetic sub‐systems of a sample. Solutions of the equations for inverse temperatures of the magnetic sub‐systems are given in the case of a strong coupling with lattice vibrations of one of the Zeeman reservoirs. A comparison with experiment has been carried out.
The linear jahn‐teller effect for an orbital triplet
Authors: Bersuker I. B. , Polinger V. Z.
Published: July 2007

The results of a Jahn‐Teller vibronic problem investigation for an orbital triplet linearly coupled to both a tetragonal e‐ and trigonal tz‐vibration are given, the e‐type vibroni ccoupling constant being taken arbitrary, while the tz one is assumed to be small. All the second order perturbation seria are summarized exactly. The ground and several excited state energies and wave functions as well as the reduction factors are calculated. The latter seems to be very sensible to the variation of the coupling constants.
Magnetic susceptibility of pure boron
Authors: Kubler L. , Gewtnner G. , Koulmann J. J. , Jae ´glé A.
Published: July 2007

The magnetic susceptibility of various β‐rhombohedral boron samples has been measured between 4 and 1300 °K. An unusual paramagnetic component, with an experimental number of centres dependent on the temperature of the form N = 2 N0 exp { ‐ E/kT}, is observed above 500 °K. The obtained experimental values are: ΔE≈ 0.41 eV, N0≈ ss 1.0 X 1022 cm−3. ΔE is assumed to be the consequence of a gap of about 0.82 eV between two narrow bands which do not seem to contribute to the conductivity at least for high temperatures (T > 500 °K). Moreover a second contribution is observed increasing linearly above 300 °K with rising temperature and becoming less diamagnetic. The slope of the second signal versus temperature is 2.8 x 10−11 cm3 g−1 deg−1. A Curie paramagnetic contribution appears below 77 °K, which can be accounted for by a part (5 ppm) of the residual impurities.
Strong coupling between proton and phonon in KDP
Authors: Pak K. N.
Published: July 2007

The correlation function for the proton‐phonon coupled system has been obtained b means of the retarded Green's function. The dynamic susceptibility and the internal energ are evaluated in a random phase approximation. Some discussion has been made on tb results by comparison with those obtained previously by others, in which the emphasis ha been laid on the isotope effects. As a result, it is found that the proton‐phonon couplin is very large and then responsible for the isotope effects as well as the lattice instability.
The effect of a line potential parallel to an external magnetic field on electronic eigenstates
Authors: Ortenberg M. V.
Published: July 2007

The energy levels for an quasi‐free electron is calculated in the presence of a short‐range Gauss potential of a dislocation line parallel to an external magnetic field and the conserved quantum numbers are discussed.
X‐ray emission study of the electronic structure of aluminium‐gold and aluminium‐copper alloys
Authors: KÄllne E.
Published: July 2007

The Al K emission spectra for aluminium‐gold and aluminium‐copper alloys have been measured and compared with emission spectra obtained from pure metal as well as with photoelectron and Mössbauer spectra. The alloy spectra indicate a charge transfer from aluminium to gold. The alloy Al K band spectra show a low energy peak which is interpreted as transitions from noble metal d‐states admixed with Al 3p‐states to the inner Is core level. The satellite lines Al Kα3α4 also shift besides showing a complex structure in the alloys.
Binding energy of excitonic molecules in isotropic semiconductors
Authors: Huang Wei‐Teh
Published: July 2007

The solution of the Schrödinger equation of the excitonic molecule system has been expanded using Feynman's path integral method, in order to determine the binding energy of the excitonic molecules. For the numerical treatment the Monte‐Carlo method was used. The results show that for the case of comparable mass size of electron and hole the method used is more general and satisfactory than the calculations up to the present time. Good agreement with experimental observations is obtained for the complexes in Cu Br, CuCl, CdS, Cu2O, CdSe, Ge, and Si.
Optical absorption by free polarons in CdO
Authors: Finkenrath H. , Fricke W. , Uhle N.
Published: July 2007

The optical constants of degenerate CdO films were measured at about 10 K in the spectral range around the LO lattice frequency (5 to 24 μm). Besides the free carrier absorption and a tail of the lattice absorption an additional absorption is found above the LO frequency which can be explained by the theory of free polarons. At higher frequencies it is superimposed by further absorption processes with noticeable structure which are unexplained until now.
Optical spectra and electroabsorption of CdP2 and CdP4 single crystals
Authors: Radautsan S. I. , Syrbu N. N. , Teslevan V. E. , Chumak I. V.
Published: July 2007

The anisotropy of the absorption and electroabsorption spectra of CdP2 and CdP4, single crystals has been investigated. A number of interband gaps has been determined and specified. The energies and the type of phonons involved in direct and indirect transitions have been determined. Proceeding from group‐theoretical calculations of the band structure, the transitions in CdP4 have been localised and some regularities of the phonons in CdP2 have been revealed.
The Susceptibility of HoAsO4 near the Magnetic Phase Transition
Authors: Becher W. , Kalbfleisch H.
Published: July 2007

Using a simple but nevertheless sensitive experimental arrangement the ac susceptibility of HoAsO4 was studied near its paramagnetic to antiferromagnetic phase transition at TN = 0.559 K. By these measurements concerning with the temperature and the magnetic field dependence of the susceptibility Fisher's theory connecting the specific heat and the reduced susceptibility of an antiferromagnet could be verified. Both the exchange and dipolar fields are given.
A Note on Percolation Probabilities
Authors: Maschke K. , Overhof H. , Thomas P.
Published: July 2007

A bond percolation analysis similar to that recently proposed by Pollak is presented. In contrast to Pollak's work part of the bond correlation is taken into account. This leads to an estimate for the onset of percolation in three‐dimensional random networks. Comparison is made with Monte Carlo and series expansion data for bond percolation on crystalline lattices.
First Excited Librational States for 〈100〉‐, 〈110〉‐, and 〈111〉‐Type Paraelectric Defects in Cubic Crystals
Authors: Dick B. G.
Published: July 2007

First excited librational eigenstates and energy eigenvalues are deduced in the tunneling approximation and listed for 〈100〉‐, 〈110〉‐, and 〈111〉‐oriented paraelectric defects sites of cubic symmetry. These supplement the existing listings for the librational ground states.
External Multi‐Photon Photoeffect from Impure Semiconductors and Dielectrics
Authors: Freydkin E. S. , Kovarskii V. A.
Published: July 2007

The external multi‐photon photoeffect of impure crystals is analysed by the method of kinetic equations. The role isshown that is played by localized states of the electron mteracting with phonons in forming the energetic distribution of the escaped photoelectrons. An explanation is given of the experiments carried out by Logothetis and Hartman [4]. The recombination effect on the external photocurrent is considered.
Diagram Technique for the Green Function of a Heisenberg Ferromagnet with Arbitrary Spin
Authors: Haberlandt H. , Kühnel A.
Published: July 2007

The diagram technique previously developed by one of the authors for the Green's function of a Heisenberg ferromagnet with spin 1/2 is generalized to arbitrary spin. The summation of diagrams is the main problem in the present paper. The diagrams split into two classes; one of them may be summed with help of Dyson's equation, the other cannot be treated as a contribution to the mass operator. The latter class of diagrams is found to be the series expansion of 〈Sz〉 and 〈S S〉. The resulting spin wave energy corresponds in successive approximations to the results of MFA, of Tyablikov's decoupling, of Dyson, and of the decoupling due to Mubayi and Lange, and Kenan, respectively. The low temperature magnetization is calculated directly from the Green's function and agrees with Callen's result in the highest approximation worked out.
Isoelectronic Broadening of the Yellow Exciton Quadrupole Absorption Line of Cuprous Oxide
Authors: Schwab C. , Goltzene A. , Meyer B. , Nikitine S.
Published: July 2007

Experimental results of high resolution absorption measurements of the yellow exciton 1S absorption line of Cu2O single crystals, characterized by chemical and crystallographic analysis are reported. After correction of internal strain effects, a line broadening proportional to the silver content is observed, whereas the oscillator strength remains constant. Finally, these data are discussed in terms of diffusion and radiative recombination life times in order to estimate the possibility of observing the spin‐electron resonance of these excitons.
Change of the Order of a Phase Transition by the Influence of an External Parameter
Authors: Benguigui L.
Published: July 2007

It is investigated how, in a phase transition, the order of the transition may be changed from second to first or vice versa by the influence of a parameter Y. It is supposed that the free energy can be written as the sum of four terms: G1(η) a function only of the order parameter η; G2(X) a function only of X, the conjugate of Y; G3(X, η) a coupling function, and G4 = − YX. Some different examples are examined choosing a simple form for G2(X), and of G3(X, η). Also the case of two external parameters coupled to the order parameter is investigated. The results are discussed in connection with different materials like BaTiO3, PbTiO3, and improper ferroelectrics.
A New Superconducting State
Authors: Fink H. J.
Published: July 2007

In long one‐dimensional superconductors, such as whiskers and thin wires, new current‐carrying states above the critical current were found that are due to spatially periodic solutions of the modulus of the order parameter and spatially periodic super and normal transport currents in parallel. The order parameter is zero a t certain points in the whisker, thereby permitting the phase of the order parameter to slip in time of one singly‐connected superconducting region with respect to the adjacent, the consequence of which is a dc potential difference between the separate singly‐connected superconducting regions. In this model the modulus of the order parameter is time‐independent, the phase is time‐dependent and the difference of the pair electrochemical potentials between adjacent singly‐connected superconducting regions is an integer fraction of the total voltage difference across the whisker. These solutions lead to voltage steps in the dc voltage‐current characteristic of thin whiskers. The upper critical current is derived at which the superconductor becomes completely normal conducting. This current is much larger than the current at which the first voltage step occurs. Agreement with experiments is good.
Resonance Raman Scattering at the Critical Points of Zincblende Crystals
Authors: Jain K. P. , Choudhury Gayatri
Published: July 2007

The results of a calculation of the one‐phonon Stokes‐Raman scattering cross‐section are presented for InAs, GaAs, and InSb using an empirically determined joint density of electron states. These clearly indicate a correlation between the structure in the energy‐dependent Raman cross‐sections and the Van Hove critical points. The broad essential features of light scattering near the M1 edge are brought out by the results. These are large resonance enhancements at the saddle points, deep minima between the resonances and large absolute cross‐sections. The theory is compared with available experimental data.
Effect of Uniaxial Stress and Doping on the One‐Phonon Raman Spectrum of GaP
Authors: Balslev I.
Published: July 2007

The Raman spectrum of long‐wave optical phonons in n‐type GaP is investigated under the presence of uniaxial stress. The splitting ofthe LO‐phonon is found to be doping‐dependent for (001)‐stress and is explained by phonon—plasmon coupling in connection with repopulation of the electrons. At zero stress the 2 LO‐phonon cut‐off in the second order spectrum does not follow the doping‐induced shift of the LO (k  O) phonon. This indicate avery flat LO‐dispersion curve.
Calculation of the X‐Ray K and L Emission Bands in AlSb and GaP
Authors: Topol T. , Leonhardt G. , Unger K. , Hess E.
Published: July 2007

Using an EPM‐k · p method the K and L emission bands in AlSb and GaP have been calculated based on the corresponding band structures. The results are in good agreement with experimental data in particular for the K bands. For the L bands there is a larger sensitivity with regard to the quality of the valence‐band wave‐functions used. Due to the influence of the transition probability marked differences between the spectra of the A and B components both for K and L emission are obtained. The antisymmetric form factors of the pseudopotential influence the value of the antisymmetric gap such that they may be tested or corrected with the help of X‐ray spectra.
Peculiarities of Raman Scattering by Polaritons and Polar Optical Phonons in Anisotropic Crystals
Authors: Strizhevskii V. L. , Yashkir Yu. N.
Published: July 2007

The theory of the gain factor of the stimulated Raman scattering by polaritons in biaxial crystals is carried out in the fixed stationary pump field approximation. By sufficient length of the polariton wave vector the polariton scattering turns into the scattering by polar optical phonons which may be regarded as quasilongitudinal electromagnetic field quanta. Typical features of scattering by anisotropic polar phonons whose energy depends on the wave vector direction are investigated. Mixing of different symmetry mechanicalvibrations is analysed in anisotropic crystals. The Fermi resonance of polar mechanical phonons is studied in detail. Numerical calculations made for some particular cases agree with available experimental data.
Cluster Theory of a Dilute Antiferromagnet. Application to the Mn1–cZncF2 System
Authors: Dzyub I. P.
Published: July 2007

A cluster theory of a dilute antiferromagnet which simultaneously takes into account the fluctuations in the longitudinal and transverse part of the exchange interaction is proposed. The present theory allows to describe the dependence of the line shapes of the spin excitation spectrum on the nonmagnetic atom concentration and the wave vector. A comparison with experimental results indicates that the predictions of the theory are valid in a wide range of concentrations when the long‐range order persists. It is pointed out that the coherent wave approximation accounts for the gross behaviour of the spin excitation spectrum. It is demonstrated that the results of the cluster theory are close to those of the coherent potential approximation, but more transparent and more suitable for comparison with experiment.
ENDOR Investigation of Cu++ Centres in NH4Cl I. Experimental Results
Authors: Boettcher F. , Spaeth J. M.
Published: July 2007

Two Cu++ centres in NH4Cl single crystals grown from acid (I) and neutral (II) aqueous solution were investigated by ESR and ENDOR at 4.2 °K. From the superhyperfine and quadrupole data obtained for several shells of neighbour nuclei the following centre models are proposed: in both centres Cu++ is at an interstitial site with 2 NH4+ vacancies along [001] at both sides of the Cu++. In centre I the vacancies are filled by H2O, in centre II by NH3. The precise configuration of the H2O and NH3 molecules could be determined.
On the Influence of the Transition Probability on the Shape of X‐Ray Emission Spectra of AIIIBV Semiconductors
Authors: Topol I. , Unger K. , Leonhardt G. , Hess E.
Published: July 2007

Exactly computed transition probabilities governing the X‐ray emission spectra of cubic AIIIBV semiconductors are analyzed. They show remarkable dependences of the energies as well as of the k vector involved. It is demonstrated that the K influence yields different spectra for the two components of the same compound due to the nocks and nodes of the valence wave functions at X1, X3 in the planes where the atoms of the different components are located. Different inner wave functions of the components furnish mainly a shift of the spectra, however, they have only little influence on their shape.
Effect of Irradiation on Impurity–Vacancy Dipoles in KBr Crystals Doped with Strontium
Authors: Muccillo R. , Rolfe J.
Published: July 2007

The concentration of impurity–vacancy dipoles in potassium bromide crystals doped with strontium bromide was measured using the ionic thermocurrent (ITC) technique. The parameters of the dipole relaxation are: fundamental relaxation time 4 × 10−14s, activation enthalpy 0.66 eV. The effect of 60Co γ‐irradiation at room temperature was to reduce the number of dipoles and to increase the number of trapped holes and electrons, but the number of trapped holes and electrons, measured by optical absorption, was about 30 times smaller than the number of dipoles destroyed. It is proposed that the effect of irradiation is to increase the rate of aggregation of dipoles, primarily into trimer aggregates, through temporary electron trapping by strontium ions.
Influence of the Electron‐Phonon Coupling on Energy States of Wannier Excitons
Authors: Mahler G. , Schröder U.
Published: July 2007

Theen ergies of Wannier excitons are investigated taking into account the electron‐phonon coupling described by the Fröhlich‐type interaction. The energies of the ground and the first excited states are calculated by a variational treatment. The exciton is treated as an interacting polaron pair, the electron‐phonon coupling of which is mutually disturbed. The expansion in terms of the particle momenta reproduces in the first order the effective potential derived by Haken. The following terms can be interpreted as additional mass renormalizations depending on the exciton radius. These terms are found to improve the agreement with experiment.
Schottky Defects in Sodium and Potassium Chloride
Authors: Roy D. , Sen S. K. , Manna A.
Published: July 2007

The energy of formation of Schottky defects, the binding energy of the Schottky pair in the ground state and the entropies of formation of isolated vacancies and vacancy pairs for NaCl and KCl have been computed assuming an elastic displacement in the form proposed by Boswarva and Lidiard. In the calculation of the displacement of the ten immediate neighbours of the vacancy pair, the relaxation of the distant neighbour was also considered. The calculations show a reasonable agreement with the recent experimental values.
NGR, EPR, and Optical Characteristics of Sn Centres in CaS
Authors: Jaek I. , Realo E. , Seman V. , Mürk L.
Published: July 2007

NGR, EPR, and optical spectra of Sn centres in CaS have been measured. An established correlation between the NGR and optical data enabled to identify the luminescence centres in CaS host containing Sn2+ and Sn4+. A preliminary interpretation of the optical spectra for the Sn2+ centres is proposed using the MO method. Paramagnetic Sn3+ centres have been found by EPR spectroscopy and their identification has been made on the basis of the differences in the nuclear characteristics of Sn isotopes. Some aspects of covalent bonding between different Sn centres and their ligands are discussed.
Trigonal Centre of Gd3+ in CdS Investigated by Variable‐Frequency EPR
Authors: Urban W. , Siegel E. , Hillmer W.
Published: July 2007

For the new axial centre of Gd3+ in hexagonal CdS, reported recently, a more detailed analysis of results obtained by variable‐frequency EPR is carried out, establishing trigonal symmetry and giving spin‐Hamilton parameters b = + 1853 × 10−4cm−1,b = (±)2.6 × 10−4 cm−1. The model of Newman and Urban has been applied to estimate b for various local arrangements and these are compared with the experimental values of all three axial centres reported so far for Gd3+ in CdS.
Proton Spin–Lattice Relaxation in the Hydrogen‐Bonded Ferroelectrics Colemanite, KFCT, and TGS
Authors: Brosowski G. , Buchheit W. , Müller D. , Petersson J.
Published: July 2007

The nuclear spin–lattice relaxation time T1 of protons in single crystals of the hydrogen‐bonded ferroelectrics colemanite, KFCT, and TGS is measured between 8 and 60 MHz and between +80 °C and −100 °C by applying 90°‐t −90° pulse sequences. In all crystals there are several contributions to the relaxation rate T. Near the ferroelectric transition a ferroelectric contribution appears which is superimposed on a general behaviour according to one or two BPP type curves from which the corresponding activation energies are estimated. In colemanite and KFCT the ferroelectric relaxation rate shows a. frequency independent logarithmic singularity whereas in TGS a more complicated behaviour is observed. With respect to colemanite and KFCT these results are interpreted by applying established theories whereas for describing the behaviour of TGS several models are discussed.
On Variable Range Hopping near the Fermi Energy. Two‐Dimensional Systems
Authors: Maschke K. , Overhof H. , Thomas P.
Published: July 2007

Results of a computer study on variable range hopping in two‐dimensional systems are presented. A 2D system was chosen to allow for a treatment of models of considerable size with modest computational effort. The convergence properties of the results with respect to the model size have been carefully examined. It is found that an extrapolation to quasi‐infinite samples is possible. The results are discussed in connection with percolation results. Conditions for a strict T−1/3(T−1/4) law of the conductivity in 2D (3D) systems are derived. The influence of a non‐constant density of states is discussed.
Optical Phonon Analysis in the AVBVICVII Compounds
Authors: Teng M. K. , Balkanski M. , Massot M. , Ziolkiewicz M. K.
Published: July 2007

The Raman spectra of SbSBr, BiSI, SbSeI, and BiSeI are investigated and compared with those of SbSI. Following the analysis of each observed mode from one substituted compound to another, a set of normal mode functions is proposed to account for the overall spectral feature of these compounds. The results are then tentatively interpreted in terms of the mass change based on a semi‐ionic model. It is shown that the agreement with experimental data is excellent for the system SbSBrSbSIBiSI. In the contrary, a serious discrepancy exists in the SbSeIBiSeI system suggesting that the binding of sulfur and neighbouring atoms is substantially affected by the SSe substitution in these compounds.
Local Magnetic Field near Mn Atoms in CuMn Dilute Alloys
Authors: Tompa K.
Published: July 2007

A satellite line shifted in the direction to lower internal fields as compared with the main line has been observed in the NMR spectrum of 63Cu in CuMn alloys diluted to 0.5 or 2.5 at% Mn. The shift of the satellite is independent of the Mn concentration but varies with the applied field and the temperature as H/T. This indicates that the satellite is due to the spin density perturbation around the localized magnetic moment. The experimental data suggest that the satellite originates most probably from the 63Cu nuclei on the first coordination shell of the Mn atoms. The NMR spectrum of the same nuclei shows no second order quadrupole effect within the experimental error.
Secondary Electron Emission from Some Aromatic Hydrocarbons
Authors: Ya. Bubnov L. , Frankevich E. L.
Published: July 2007

Results of the investigation of secondary electron emission from polycrystalline films of tetracene and pyrene and from both amorphous films and single crystals of anthracene are reported. The determination of the relative number of true secondary electrons which lose their initial energy by exciting intramolecular vibrations (≈︁60%) and excitons (≈︁40%) has permitted an estimation of ranges of energy loss in these two processes: more than 70 Å in the former and from 50 to 150 Å in the latter process. The former group of electrons is named subexciting electrons. The mean distance covered by the subexciting electron while it still has sufficient energy to excite intramolecular vibrations is estimated to 200 to 500 Å. All these estimates are essentially new as compared to those used at present. Comparison of secondary electron emission coefficients in anthracene single crystals and amorphous films leads to the conclusion that motion of subexciting electrons in the anthracene crystal is not diffuse. Experimentally obtained range of subexciting electrons, as related to angular scattering (greater than 70 Å), is large in comparison with lattice constant and indicates that in contrast to assumptions of the “compressed gas” model in molecular crystals angular scattering is a relatively rare phenomenon.
A Point Charge Model for the Ferroelectric Transition in Ammonium Sulphate
Authors: Jain Y. S. , Bist H. D.
Published: July 2007

In ammonium sulphate the distortion of the SO42− ion, which has almost tetrahedral symmetry in its paraelectric phase, occurs in a narrow region near the ferroelectric transition temperature Tc = 223 °K. A point charge model has been used to compute the spontaneous polarization (P) due to NH and SO ions in the crystal. The computed value of P (0.42 μC/cm2) agrees well with the experimentally reported ones. The nature of phase transition has also been discussed.
Bound Small Polaron Optical Absorption in V−‐Type Centres in MgO
Authors: Schirmer O. F. , Koidl P. , Reik H. G.
Published: July 2007

A theory, based on the method of moments, is described which predicts exact lineshapes for the optical absorption of bound small polarons. This theory explains the position, large width, and high oscillator strength of the optical absorption of the V centre in MgO and the polarisation of V− in MgO, which has been observed under uniaxial stress.
Calculation of Phonon Dispersion Curves and Mode Grüneisen Parameters in RbI
Authors: Kress W.
Published: July 2007

The phonon dispersion curves of RbI are calculated using the breathing shell model, allowing for the force constants of the isotropic deformation to be unequal to the shell‐core force constants. The model is extended to include the proper third order anharmonic contributions. The mode Grüneisen parameters are calculated within this model using first order perturbation theory. The parameters entering the calculation of the mode Grüneisen parameters are the isothermal pressure derivatives of the harmonic breathing shell model parameters and are obtained from the pressure derivatives of the long wavelength measurements in a similar way as are the harmonic parameters. Using this model the specific heat and the linear thermal expansion coefficient as functions of temperature are calculated.
A General Cluster Expansion and the Definition of Self‐Consistent n‐Site Approximations in the Theory of Disordered Systems
Authors: Fischbeck H. J.
Published: July 2007

A general cluster expansion of the averaged transition operator of a disordered system in terms of the distribution functions of its constituents is given. Self‐consistent n‐site approximations are defined by requiring that a truncated version of this series should be zero in an effective medium. In the alloy case these are shown to be equivalent to previously derived approximations. For amorphous systems a new type of n‐site approximations is obtained.
Jahn‐Teller Effect on Excited Orbital Triplet States of 3dn Ions in Eightfold Cubic Coordination. Co2+ and Fe2+ in CdF2
Authors: Ulrici W.
Published: July 2007

The ions Co2+ and Fe2+ can be substitutionally incorporated on Cd2+ sites in CdF2. The optical absorption bands of the transitions 4A2g → 4T1g(F), → 4T1g(P) and 5Eg → 5T2g are no single bands but exhibit a pronounced triplet structure measured up to 500 K. The splittings increase linearly with \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt T $\end{document} at high temperatures. These results are explained as due to a strong dynamical Jahn‐Teller effect (interaction with τ2g modes) on the excited orbital triplet states based on the theory by Toyozawa and Inone [3]. The frequencies of the τ2g modes and the coupling constants (Jahn‐Teller energies) are determined. The doublet structure of the 4A2g → 4T2g absorption band and additional fine structures of the → 4T1g(F) band at low temperatures are discussed as probably being caused by the simultaneous action of first order spin‐orbit coupling and strong T ⊗ τ2g coupling.
Diffuse Scattering and Surface‐Plasmon Generation by Photons at a Rough Dielectric Surface
Authors: Elson J. M. , Ritchie K. H.
Published: July 2007

First‐order perturbation theory has been employed to compute the scattering and conversion to surface plasma oscillations of photons incident normally on a nearly planar vacuum‐dielectric surface. The calculation proceeds through a classical solution of Maxwell's equations. Transformation to a non‐orthogonal system of coordinates is effected. The Green function tensor for the Hertz vector potential appropriate to the plane surface geometry is found and applied to a determination of the scattered fields. The results are valid for arbitrarily large damping of fields due to electronic transitions in the dielectric.
Kondo Effect in the Transport Properties of the CsCl‐Type Compounds Fe1−xTi1+x. I. Their Anomalous Behaviors in the Titanium‐Rich Compositions
Authors: Ikeda K.
Published: July 2007

A resistance minimum at 30 to 60 °K and a negative and giant valley of the thermoelectric power near 47 °K were observed in the CsCl‐type compounds, Fe1−xTi1+x, with titanium‐rich compositions. This anomalous behavior of the transport phenomena, which are distinct from those of the stoichiometric compound showing an ordinary temperature dependence of the resistivity and a positive and monotonically increasing thermoelectric power, have features similar to the Kondo effect in dilute magnetic alloys. It is suggested that such anomalous phenomena may be caused by the existence of the iron atoms occupying the wrong atomic sites in a slightly disordered CsCl‐type lattice.
The Masses of Free Holes and Electrons in Tellurium
Authors: Lutz M. , Stolze H. , Grosse P.
Published: July 2007

The transverse effective hole masses of tellurium samples with p = 1016 to 1018 cm−3 have been determined from Faraday rotation measurements at 10, 90, and 300 K. The comparison of the experimental values with the calculated Faraday masses enables to prove the validity of various band models for large k. The model presented by Bangert gives the best fit. Thus the strong temperature dependence of the hole mass determined from transport measurements by many authors is shown to be due to the nonparabolicity of the valence band. At higher temperatures (300 to 400 K) also the free electrons contribute to the Faraday effect. This rotation could be explained by Bangert's model, too.
On the Theory of an Impurity Molecule. II. The Born‐Oppenheimer Method
Authors: Liapzev A. V. , Kiselev A. A.
Published: July 2007

A nonlinear impurity molecule is considered. The molecule is assumed to show almost free rotations about one axis which can librate. The Born‐Oppenheimer method is applied to solve the Schrödinger equation transformed from cartesian coordinates to coordinates defined by the Eckart conditions and describing the vibrations and rotations. The Hamiltonian, the eigenvalue, and eigenfunction are expanded in power series in the Born‐Oppenheimer parameter and these expansions are inserted in the Schrödinger equation. The eigenfunction and eigenvalue expansions are calculated up to the first and the fifth terms, respectively. Some kinetic corrections caused by the libration are shown to appear in the first order term of the eigenfunction expansion and in the fourth order term of the eigenvalue expansion.
Investigation of Magnetoplasma Wave Dispersion in Pure and Doped Bi92Sb8 at Liquid Nitrogen Temperature
Authors: Brazis R. , Požela J. , Tairov B. , Shakhtakhtinskii M.
Published: July 2007

The bulk magnetoplasma wave dispersion and its relation to peculiarities of the energy band structure in Bi92Sb8 are investigated. The electron mobility tensor components and the carrier cyclotron mobilities are estimated in pure single crystals and those doped with tin and tellurium.
Magnetische Bereichsstrukturen in Typ‐I‐Dünnschichtsupraleitern. II. Der zweidimensionale Mischzustand
Authors: Lischke B. , Rodewald W.
Published: July 2007

Die Flußquantenstrukturen in dünnen supraleitenden Schichten (Pb) in senkrechten Magnetfeldern wurden durch die Dekoration mit Eisenteilchen sichtbar gemacht. Die Dekorations‐ Technik wird mit der Elektronenmikroskopie dünner Schichten kombiniert. Diese „Dekorations‐Mikroskopie”︁ erlaubt es, die Wechselwirkung von Flußlinien mit Korngrenzen direkt zu beobachten. Der Übergang von den Strukturen des Zwischenzustands in die des zweidimensionalen Mischzustands erfolgt unterhalb einer kritischen Schichtdicke, die mit theoretischen Ergebnissen verglichen wurde.
Asymptotic and Pre‐Asymptotic Region of Charge Density Oscillation around Impurities in Dilute Copper‐Based Alloys
Authors: Serfőző G.
Published: July 2007

Comparison of the wipe‐out numbers for the first and second order quadrupole effects in the magnetic resonance of matrix nuclei shows that Friedel's asymptotic charge density perturbation formula is not valid for the near‐region around the impurity. On the basis of Alfred's and Van Ostenburg's pre‐asymptotic theory, wipe‐out numbers characteristic of the second order quadrupole effect are calculated for Cu‐Zn, Cu‐Ga, and Cu‐Ge dilute alloys and good agreement with the experimental results is found. I n spite of this success this theory is unable to describe adequately, the field gradients measured a t the first and second coordination shells near the impurity.
LCAO Calculations for the Boron and Nitrogen Interstitial in the Diamond Lattice
Authors: Weigel C. , Peak D. , Cobbett J. W. , Watkins G. D. , Messmer R. Y.
Published: July 2007

LCAO‐MO cluster calculations based on the extended Hückel theory are carried out for boron and nitrogen atoms in various interstitial configurations in the diamond lattice. The results favor the (100) split interstitial configuration for both the boron and nitrogen interstitial and suggest a change of the energy minimum configuration with charge state.
Optical Phonons in Small Crystals of ABO3, Perovskites
Authors: Bäuerle D.
Published: July 2007

The infrared absorption spectra of SrTiO3 and KtaO3 powders are compared with calculated spectra. The influence of dielectric surrounding, particle size, and retardation is discussed.
The Interaction between s‐n‐Domain Walls and Lattice Defects in Type‐I Superconductors
Authors: Riedel H. , Kronmüller H.
Published: July 2007

The interaction between crystal dislocations and sn‐walls in type‐I superconductors is treated on the basis of the micromagnetic equations of superconductors. The elastic properties of the sn‐walls are described by quasi‐dislocations and the interaction force with the dislocations is derived from a generalized Peach‐Koehler formula. A statistical analysis of the total force exerted by randomly distributed dislocations on sn‐walls yields characteristic differences between the δV‐effect and the nonlinear elastic effects (δE‐, P‐effect) concerning the mean wavelength of the field of force and the dependence on the dislocation density. The relative changes of the magnetization curve caused by wall pinning due to dislocations are shown to amount to 5 to 15% for large plastic deformations.