bluuebunny/crossref_metadata_2025_split huggingface dataset:
On Anisotropic Hopping Conduction in Thin Amorphous Germanium Films
Authors: Thomas P. 
Published: July 2007

AbstractThe hopping conductivity is calculated for cases where the number of hops on a conducting path between the electrodes is small. This model is applied to transverse conduction in thin films. Using an isotropic distributionof localized states the conductivity shows an apparent anisotropy, which decreases with film thickness. Reasonable agreement with existing experimental data on transverse hopping conduction in thin amorphous Ge films is obtained. It is concluded that the experimentally observed thickness dependence of the anisotropy of the conductivity is not necessarily related to structural inhomogenieties. By fitting the model to the experimental data a reasonable value is obtained for the orbital size of the localized states withoutmaking any assumptions about the density of states.
X‐Ray‐Induced Vacuum Ultraviolet Luminescence from Neon Crystals
Authors: Schuberth E. , Creuzburg M. 
Published: July 2007

AbstractIn the X‐ray‐induced emission spectrum of solid neon excitonic lines are found at 744.2, 741.8, 738, and 733 Å, and broad peaks at 770 and 890 Å of unrelaxed Ne*2 molecules which arebelieved to originate only from exciton relaxation. We also observed a peculiarly strong temperature dependence of the emission intensity which can becaused by changes in the crystal structure that influence the exciton formation.
Unsymmetrized self‐consistent field approximation for a crystal. I. Linear chain
Authors: Zubov V. I. 
Published: July 2007

AbstractIn the unsymmetrized self‐consistent field approximation the second‐order correction to the Helmholtz free energy is derived by statistical perturbation theory. This correction takes into account the effect of the anharn micity of odd orders on the Helmholtz free energy and on the thermodynamic properties of a crystal. The case of the linear chain is studied in more detail. Special attention is paid to the case of strong anharmonicity.
Structure of phonon sidebands of the ν1 vibration absorption band of the NCO− impurity ion in KI:KCl and KBr:KCl mixed single crystals
Authors: Kondilenko I. I. , Tsyashchenko Yu. P. , Zaporozhets V. M. , Pinkevich I. P. 
Published: July 2007

AbstractThe change of the structure due to local vibrations of the perturbed environment is studied at 10°K in the phonon sideband (PS) of the ν1 vibration absorption band of the impurity ion NCO− in mixed KI:KCl and KBr:KCl lattices. It is found that at increased concentration of Cl− ions beginning from 1 wt% the intensity of a high‐frequency structure is sharply decreased and the number and half‐width of the gap‐local‐vibration bands increase; one fraction of these shifts to the high‐frequency side, the other to the long‐wave one. These effects are explained by the different locations of Cl− near NCO− in KI and KBr matrix lattices and, consequently, changes different in sign of the perturbed force constants of the axial interaction of the ν1 stretching vibration with lattice phonons.
Spin–lattice relaxation of Tl2+ ions in K2SO4 single crystals
Authors: Aminov L. K. , Kurkin I. N. , Silkin N. I. , Shlenkin V. I. 
Published: July 2007

AbstractSpin‐lattice relaxation times of Tl2+ ions in potassium sulphate single crystals were measured in the temperature range 1.5 to 25°K at a frequency of about 9 GHz by electron spinecho method. The relaxation is due to direct and Raman processes: T1−1 = 1.0 T + 3.3 × 10−5T7. Deviations from the T ∼ T7 dependence at high temperatures allow to estimate the Debye tempeature of K2SO4 to θ = 120°K. The anomalous temperature dependence of the Raman processes is discussed.
The effect of monovalent impurities on KCl low‐temperature specific heat
Authors: Augst G. R. , Kvavadze K. A. 
Published: July 2007

AbstractAn enhancement of the specific heat of KCl crystals doped with Ag+ and Na+ impurities in the temperature range 5 to 30 K is observed. A comparison of the experimental results with the theory shows that in the case of Ag+ the force constants (FC) are weakened by four times. The established quasi‐local frequency (QLF) is close to that found in experiments of infrared absorption. The anomalous increase of the low‐temperature specific heat of the KCl crystals with light substitutional Na+ impurities are ascribed to the vibration of isolated ions with FC weakened 2.5 times. The results of the investigation of KCl crystals with monovalent impurities show that the curve shape of the specific‐heat excess differs in accordance with FC strengthening or weakening.
Binding energy of wannier excitons interacting with LO phonons in anisotropic polar crystals
Authors: Fock H. , Kramer B. , Büttner H. 
Published: July 2007

AbstractThe binding energy of an exciton is calculated taking into account its interaction with optical phonons as well as the anisotropy of the band masses and the dielectric constants. For not too large anisotropies one might approximate the exciton–phonon interaction by an isotropic effective potential with averaged material constants. In II–VI compounds the energies calculated with this isotropic potential agree quite well with the experimental results.
The peculiar behaviour of transport coefficients in the presence of inelastic scattering by optical phonons
Authors: Kravchenko A. F. , Kubálková S. , Morozov B. V. , Polovinkin V. G. , Skok E. M. 
Published: July 2007

AbstractA method is developed of calculating galvanomagnetic and thermomagnetic coefficients taking into account successively the inelastic scattering on the polarisation potential of the optical phonons together with the elastic scattering mechanisms. In the approximation of weak magnetic fields, the solution of the Boltzmann transport equation is expanded into a power series of the magnetic field by means of perturbation theory. Numerical computations for n‐GaAs with impurity concentrations of 1012 to 1020 cm−3 in the temperature range of 4.2 to 600 °K are made. The results are given as nomograms which are convenient for experimental data processing. The peculiarities of the behaviour of transport coefficients depending on the impurity concentration are analysed.
Spin‐one heisenberg antiferromagnet with biquadratic exchange
Authors: Micnas R. 
Published: July 2007

AbstractBy a Green's function formalism, an analysis of the collective excitation spectrum and thermodynamical properties of a two‐sublattice uniaxial spin‐one Heisenberg magnet with biquadratic exchange is proposed. The case of antiferromagnetic and quadrupolar ordering is analysed in detail. The results are compared to those of the molecular field theory.
ESR spectra reflecting the motion of ligands in NH4Cl:Cu2+
Authors: Watanabe K. , Abe H. 
Published: July 2007

AbstractThe ESR spectra of doped impurity (centre I in the system of NH4Cl:Cu2+) which reflect the motions of ligands were examined. The frequency (4 to 33 GHz) and temperature (4.2 to 400 K) dependence of the Cu2+ spectrum can be explained at low temperatures by the motion of Cl− ions and at around room temperature, including partial fading‐out of its hfs, by that of reorienting NH4+ tetrahedra for which the activation energy is deduced as 2570 K.
ESR of the 6S‐ions in a trigonal field: Fe3+ in α‐LiIO3
Authors: Martirosyan V. O. , Meilman M. L. , Marov I. N. , Zhukov V. V. , Sevinyan K. T. 
Published: July 2007

AbstractThe ESR spectra of Fe3+ impurity ions localized in positions of trigonal symmetry in α‐LiIO3 single crystals are investigated in the X‐ and Q‐bands at room temperature. The parameters of spin‐Hamiltonian are: g33 = g‖ = 2.0014; g11 = g22 = g⊥ = 2.0080; b = 7.831 GHz; b = −0.133 GHz; b = −0.101 GHz. In X‐band the temperature dependence of the spectra in the interval (−180 to +180°C) is studied. Possible models of active centres in α‐LiIO3 crystals are discussed. The results show that a preferable substitution scheme in the investigated crystals is Fe2+ → Li+. A close connection is obtained between the fine structure parameters of the ESR spectra of iron group ions in crystals of lithium iodate, niobate, and tantalate.
Quantum statistics of an electron–hole plasma
Authors: Kraeft W. D. , Kilimann K. , Kremp D. 
Published: July 2007

AbstractThermodynamic functions of an electron–hole plasma in an optically excited semiconductor are derived in the nondegenerate region. The existence of excitons and the ionization equilibrium are discussed in the ne–T (electron density–temperature) plane. Above the Mott curve (r0 = 0.84 a0, r0 screening length, a0 Bohr's radius) excitons do not exist. Besides the well known electron–hole droplet phase transition the critical point of which lies above the Mott curve, a region of instability is found below the Mott curve which might correspond to a plasma phase transition (weakly ionized plasma → strongly ionized plasma). Outside of this instability region at the Mott curve a diffuse phase transition (Mott‐transition) exists.
Statistical interpretation of lattice response in amorphous semiconductors
Authors: Mitra S. S. , Tsay Y. F. , Paul D. K. , Bendow B. 
Published: July 2007

AbstractA statistical approach to the prediction of lattice response in amorphous solids is presented which emphasizes the role of crystalline‐analogue allowed processes. The method is shown to provide a successful interpretation of the principal features of first‐order Raman and IR spectra in tetrahedrally bonded amorphous semiconductors.
Unsymmetrized self‐consistent field approximation for a crystal. II. Three‐dimensional lattice
Authors: Zubov V. I. 
Published: July 2007

AbstractThe corrections to the Helmholtz free energy, equations of state, and thermodynamic properties of strongly anharmonic crystals are considered in the second order of the statistical perturbation theory. As a zeroth‐order approximation the unsymmetrized selfconsistent field method is used. In this case the statistical perturbation theory is applicable up to the melting temperatures. The thermodynamic properties of the solid noble gases are calculated. For Ar the pair potentials of Barker‐Bobetic and of Barker‐Fisher‐Watts were used. For Kr calculations for the Barker‐Bobetic pair potential are made. The threebody forces of Axilrod‐Teller‐Muto are included. For Xe the Lannard‐Jones pair potential is used. The results are compared with Monte Carlo calculations.
N4,5 excitations in metallic cesium. Single‐electron behaviour and collective effects
Authors: Petersen H. 
Published: July 2007

AbstractThe N4,5 excitation spectrum of Cs is measured with yield spectroscopy from the onset of transitions at 77 to 180 eV photon energy. Synchrotron radiation served as a light source. A broad maximum due to delayed transitions to f‐symmetric continuum states is the dominating feature of the spectrum. An indication for existence of localized f‐symmetric final states is found. Above the N4,5 edges at (77.1 ± 0.1) and (79.3 ± 0.1) eV photon energy transitions to p‐symmetric extended metal states are observed. Their qualitative agreement with APW band structure calculations is discussed. EDC's obtained with photon energies 75 and 111 eV are presented. The observed asymmetric shape of the 4d photoemission maxima in the EDC's and the shape of the N5 edge are discussed with regard to the final state interaction theory by Mahan, Nozieres, and de Dominicis.
Millimeter wave and far‐infrared investigation on KDP with asymmetric interferometers
Authors: Gauss K. E. , Happ H. , Rother G. 
Published: July 2007

AbstractThe complex dielectric constant in KDP is determined at ω = 4.62 cm−1 (Δ = 2.16mm) for E ‖ c and E ⊥ c between 100 and 295 K by measurement of the complex reflection coefficient using a Michelson interferometer. At room temperature the complex dielectric function (ω) is determined for E ‖ c and E ⊥ c in the far infrared using an asymmetric Fourier spectrometer. The data for E ‖ c, T > TC are discussed with the model of modemode coupling. The soft mode frequency of this model is found to vary as ω = A(T‐117.7)/(T + 155) with temperature. For E ⊥ c a heavily damped mode is found below 80 cm−1 which might be due to a proton E‐mode.
Phonon calculation in Nb–Ta and Pd–Pt alloys in the coherent potential approximation
Authors: Sacchetti F. , Spinelli M. C. 
Published: July 2007

AbstractThe phonon dispersion relations of Nb–Ta and Pd–Pt alloy systems are calculated in the framework of the coherent potential approximation. Though only a few experimental data are available to be compared with the theory, the satisfactory agreement obtained, indicates the necessity of further experimental and theoretical effort in the study of alloy phonon dispersion relations.
Zone‐centered phonons in AIBIIIS2 chalcopyrites
Authors: Koschel W. H. , Bettini M. 
Published: July 2007

AbstractThe spectra of the zone‐centered phonons in five compounds of the AIBIIIS2 chalcopyrite (ch) family are completed by IR absorption and Raman scattering measurements. The ch extended Keating model is applied to these phonons. The experiments and calculations clarify the assignments of the Γ3‐modes and the low‐energy modes which originate from the transverse acoustic zincblende (zb) phonons. The central force constants between nearest neighbours αBS of the homopolar bonds are very large corresponding to the small bond lengths. On the other hand, the strong heteropolar A–S bonds yield very low αAS‐values. The model parameters, which are determined by optical phonon fitting, also reproduce in a zb approximation the elastic moduli of AgGaS2.
Magnetic interactions in NiSO4
Authors: Scheerlinck D. , Peetroons C. , Speybrouck P. , Hautecler S. , Michel K. 
Published: July 2007

AbstractThe energy distributions of neutrons scattered by NiS04 in its paramagnetic state are measured by means of a time‐of‐flight technique. Restricting the range of the exchange interactions to the first and second nearest‐neighbours, the relation (J1/kB)2 + 2(J2/kB)2 = = (149±7) °K2 is obtained from the second moment of these energy distributions. A second relation between the two exchange parameters is obtained from a computation of the Néel temperature in the Green's function approximation. From the two relations J1/kB = = (8 ± 0.8) °K and J2/kB = (−6.5 ± 0.6) °K are derived. Taking properly into account a temperature‐independent contribution to the susceptibility, no experimental indication is found that there are other significant exchange interactions.
Molecular cluster approach to magnesium and calcium oxide crystals. I. Perfect crystals
Authors: Ermoshkin A. N. , Kotomin E. A. , Evarestov R. A. 
Published: July 2007

AbstractThe model of the molecular cluster (MC) is used to determine the properties of the perfect crystals MgO and CaO (the widths of the valence bands and forbidden gap, the effective charges of ions). The effective charges in the perfect crystal are shown to be ±1.6 in MgO and ±1.8 in CaO, which indicates high degree of covalency effects of the chemical bonding in these crystals. The obtained band widths are in reasonable agreement with the results of the other band structure calculations. The best results are obtained when the MC simulating the perfect crystal is chosen in the form of the LUC, that means that even the indirect consideration of the translational symmetry turns to be more important than that of the point symmetry.
On exciton absorption, band structure, and phase transformation of GaSe under pressure
Authors: Panfilov V. V. , Subbotin S. I. , Vereshchagin L. F. , Ivanov I. I. , Molchanova R. T. 
Published: July 2007

AbstractThe spectra of the absorption coefficient (α) of GaSe at the photon energy range 1.94 to 2.64eV and at pressures between 1 bar and 12 kbar are investigated at 295°K. Data at 1 to 4360 bar confirm that the edge exciton of GaSe is the direct allowed one. The pressure coefficient of the band gap (dEg/dP = −6.2 × 10−6eV bar−1), one of the Rydberg exciton constant (dR/dP = −0.6 × 10−6eV bar−1), and one of the exciton effective mass [(1/μ) (dμ/dP) = −2.4 × 10−5 bar−1] are approximately determined. It is supposed that two interband exciton transitions at 2.001 and 3.25eV give the contribution into the α spectrum above 2.1eV. The assignment of these transitions is discussed in connection with the band structure calculation of Schlüter. At 5280 bar a discontinuous jump of the absorption edge shape is observed for GaSe, with a change of the sign and a value for dEg/dP of +2.0 × 10−6eV bar−1 within the range of 5280 to 11780 bar. This effect is interpreted as the transformation of one GaSe polytype into another, i.e. as a possible phase transformation close to that of second kind.
On the Theory of Mössbauer Emission Relaxation Spectra
Authors: Afanasev A. M. , Gorobchenko V. D. 
Published: July 2007

AbstractBy utilizing a method previously developed, an expression is derived for the shape of the Mössbauer emission spectrum in the presence of relaxation. The final formula coincides with that of Hartmann‐Boutron, but the derivation is much simpler.
Strain‐Associated Band Tailing Effect in Semiconductors
Authors: Leyral P. , Bois D. , Pinard P. 
Published: July 2007

AbstractIn order to explain the band tails experimentally observed in undoped semiconductors especially in GaAs, a model for band tails associated with inhomogeneous strain fields has been developed. An analytical law for the optical absorption edge is deduced and compared with experimental results obtained in bulk or epitaxial GaAs samples. Two cases are considered: spherical and cylindrical strain fields. The origin of such strain fields, dislocations or precipitates, is discussed.
Self‐Consistent Local Orbitals for Silver Halide Crystals
Authors: Mickish D. J. , Kunz A. B. 
Published: July 2007

AbstractSelf‐consistent local orbitals are reported for the crystals AgF, AgCl, and AgBr. The formalism of Adams and Gilbert, expanded to first order in overlap, is used. All relativistic effects are neglected. Only small changes in the Ag+ one‐electron wavefunctions are found in going from the ion to the solid‐state local orbitals but large changes are observed in the halide wave functions. Changes in the ion local orbitals and the surrounding environment are traced during the self‐consistency process.
Interband‐Current Theory for Esaki Diodes
Authors: Wünsche H.‐J. , Henneberger K. 
Published: July 2007

AbstractA new theoretical concept for calculating diode characteristics is presented, using the splitting of the total current into an intraband and interband part. The direct calculation of the interband current inside the junction leads to results, which agree considerably better with experimental data, than the results of the traditional theory. Furthermore, the formalism allows to consider many‐body effects without of conceptual difficulties.
Local‐Mode Absorption of H− and D− in SrCl2:RE and SrF2:RE Single Crystals
Authors: Timans J. W. J. , Den Hartog H. W. 
Published: July 2007

AbstractIR studies on localized vibrations of hydride ions in SrCI2 and SrF2 are reported. In hydrogenated and deuterated samples doped with trivalent rare earth ions two different axially symmetric complexes giving rise to two doublets are observed. For SrCI2:RE3+, H− the positions of the absorption lines can be predicted with reasonable accuracy. Lattice relaxations appear to play more important role for C4v oscillators in SrF2 than in SrCI2 and thereforeit is more difficult to give a theoretical description of these tetragonal complexes.
α‐Oxygen Doublets II. Experiment
Authors: Gaididei Yu. B. , Loktev V. M. , Prikhotko A. F. , Shanskii L. I. 
Published: July 2007

AbstractExperimental results of two‐exciton light absorption in α‐O2 at T = 1 K are presented. On the basis of a theory which was previously developed, the interpretation of the doublet structure of the observed absorption is proposed. The effect of resonance interaction on the formation of the vibronic bimolecular bands and the importance of the excited collective states are discussed.
The Formulation of the Formation Energy of a Vacancy as an Alloy Problem
Authors: Tanigawa S. , Doyama M. 
Published: July 2007

AbstractThe formation energy of a vacancy E is studied as an alloy problem. For this purpose, the pseudopotential formalism for binary random substitutional alloys of simple metals is developed and the expression of the total energy of such alloys is given. In the present approach, a vacancy is taken as a solute atom which has the valency of zero and an atomic volume equal to the formation volume of a vacancy. It was found that (a) the expression derived for E is the same as that of Harrison's approach, in which the formation volume was assumed to be zero, (b) E can be properly evaluated both by the constant volume and by the constant pressure cycle, and (c) E does not depend an the formation volume of a vacancy under equilibrium conditions at zero pressure. This seems to arise from the neglect of the lattice relaxation around a vacancy.
EPR Investigation of the Very High Zero‐Field Splitting of Gd3+ in La2O3 Single Crystals
Authors: Vivien D. , Kahn A. , Lejus A. M. , Livage J. 
Published: July 2007

AbstractSingle crystalsof lanthanum oxide doped with Gd3+ are grown by the flame fusion method and studied by ESR. The very high zero‐field parameter B (0.131 cm−l) is of the same order of magnitude asthe energy quantum of X‐band radiation. This gives an abnormal spectrum which has been resolved by computer. These crystals may find interesting applications in solid state masers.
EPR Investigations of a Structural Phase Change in RbCaF3, RbCdF3, and TlCdF3
Authors: Rousseau J. J. , Rousseau M. , Fayet J. C. 
Published: July 2007

AbstractEPR investigations of the structural phase change which occurs in the compounds RbCaFa: Mn2+, TlCdF3:Fez+, and RbCdF3:Fe3+ were made. For RbCdF3 we have determined the critical index and measured the order parameter using two different probes, namely the Fe3+ ion and the Vk center.
Electron Paramagnetic Resonance in Anisotropic Magnets
Authors: Hùber D. L. , Seehra M. S. 
Published: July 2007

AbstractElectron paramagnetic resonance in anisotropic magnets is analyzed. The resonance field at fixed frequency is shown to be a function of the principal values of the external susceptibility tensor and hence can be temperature dependent. The predictions of the theory are compared with data on the temperature dependence of the resonance field in CrBr3. Excellent agreement is obtained.
Electron Spin Resonance Study of Cr3+ and Fe3+ in Alums
Authors: Fǎrcas S. I. , Darabant A. , Nicula A. 
Published: July 2007

AbstractThe angular dependence of the electron spin resonance spectrum of Cr3+ and Fe3+ ions in diluted ammonium alum has been measured, and the spin Hamiltonian parameters have been derived. In addition to the allowed fine structure lines some small‐intensity lowfield lines have been observed. These lines were identified as forbidden fine structure transitions due to Cr3+ and Fe3+ in alum. A good agreement between the theoretical angular dependence with that experimentally found confirmed the lines and the local symmetry of the ions to be correctly determined.
Polariton Scattering and Formation of Exciton Luminescence Spectrum in Anthracene Crystals
Authors: Brodin M. S. , Dudinskii M. A. , Mariscva S. V. , Myasnikov E. N. 
Published: July 2007

AbstractThe exciton luminescence spectrum of anthracene crystals with different thickness has been studied within the temperature range 30 to 1.6 K. The formation of this spectrum was analyzed from a polmiton viewpoint taking into account exciton–photon mixing. It is shown that inelastic (combination) polariton scattering processes on lattice and intra‐ molecular phonons are the most significant ones in the formation of the exciton lumines‐ cence spectrum.