bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unified Perturbation Treatment for Phonons in Metallic Covalent and Ionic Crystals
Authors: Eschrig H. 
Published: July 2007

AbstractAn interpolation formula which interpolates the exact Hartree expression for the electronic part of the dynamical matrix between the limits of strong and weak crystal potentials and which becomes rigorous in the zero wave vector limit is used to avoid to the problems connected with the inversion of the screening tensor. In the ionic part of the dynamical matrix the Gaussian charge densities of the usual Ewald technique are replaced by the true charge densities around each ion in the unperturbed crystal. The arising expressions are transformed in such a way that the compensation with the corresponding terms in the electronic part can be done explicitely. As a result one gets an alternative formula for the dynamical matrix of simple metals, a practicable formula for transition and noble metals and covalent crystals, and a rather simple expression for ionic crystals which has some link to the physical picture of a shell model. It is shown that the given theory describes the qualitatively correct pressure dependence of the phonon frequencies.
Vibronic Interactions and Magnetic Dipole Effects in the Polarized Crystal Spectra of Diaquobismethoxyacetato Co (II)
Authors: Hu P. D. , Companion A. L. 
Published: July 2007

AbstractPolarized absorption spectra of single crystals of diaquobismethoxyacetato Co(II) hare been measured at room and liquid nitrogen temperatures. The temperature dependence of oscillator strengths indicates that both vibronic and magnetic dipole transition mechanisms are operative. Selection rules within the C2t, point group permit assignment of major absorption peaks to transitions from a 4Bg ground state.
Pseudopotential and Lattice Vibrations of Simple Metals
Authors: Prasad B. , Srivastava R. S. 
Published: July 2007

AbstractThe phonon dispersion curves and binding energies of Rb, Cs, and Ba have been calculated using Harrison's modified point ion pseudopotential with two adjustable parameters. The exchange and correlation effects in the Hartree dielectric function have been adequately considered. The theoretical results are found to be in good qualitative agreement with the experimental results.
On the Theory of Phonon Electroreflectance of Light from Semiconductors
Authors: Dmitruk N. L. 
Published: July 2007

AbstractThe influence of a non‐uniform electric field on the reflectance of light by a semiconductor in the reststrahlen band (phonon electroreflectance) is considered. The calculation is carried out using the phenomenological model in which only the linear term of frequency and oscillator strength expansions in the local electric field is used for bulk phonons. The integral and differential phonon electroreflectance (PhER) are calculated for an arbitrary relation between wavelength λ and thickness I of the surface space charge region (SCR). The spectral and field dependence of the PhER is analysed.
Elektronenstruktur und Oberflächeneigenschaften von Übergangsmetallen
Authors: Goryachev Yu. M. , Podchernyaeva I. A. 
Published: July 2007

AbstractNit dem GO LCAO‐Verfahren (tight‐binding‐Näherung) wird das Energiespektrum der Valenzelektronen für die 〈111〉‐ und (110)‐Flächen von Mo‐, W‐ und Re‐Kristallen (mit hypothetischer k.r.z.‐Struktur) für die Analyse der Größenund der Elektronenbesetzung ders‐ und d‐Zustande der Oberflächenatome berechnet. Es wird gezeigt, daß die Anisotropie der Elektronenaustrittsarbeit mit der Besetzung der Elektronenzustände der Oberflächenatome zusammenhängt.
Energy Band Structure for Si and Ge from a Nonlocal Separable Potential Model
Authors: Fock H. 
Published: July 2007

AbstractIf the local potential at each lattice site is replaced by a nonlocal projection operator, the eigenfunctions of the electrons can be eliminated from the Schrödinger equation. The method of Green's functions is utilized and calculation of the energy bands is done assuming projection potentials, which are formed by s‐ and p‐symmetrical Gauss functions. Quantitative agreement is obtained between calculated and observed transition energies, but no parallel bands over a larger range along the A‐axis can be produced. So the curvature of this energy band model which contains four parameters differs from other band calculations.
Application of Vibronic Model to Stress‐Induced Polarization of F‐Centre Emission
Authors: Muramatsu S. 
Published: July 2007

AbstractA vibronic model is applied to the stress‐induced polarization of the F‐center emission, and a comparison of calculations is made with experimental results by Hetrick and Compton [2]. A value obtained for a stress coupling constant with Eg, symmetry is consistent with parameters previously estimated from comparison of a model to experiments of magneticfield induced circular polarization and Stark effect. The temperature dependence of the stress‐induced polarization can be explained by assuming that an odd‐parity internal field changes with temperature.
Effect of Dislocations on Perturbed Angular Correlations in Paramagnets
Authors: Denisenko G. A. , Khaimovich E. P. 
Published: July 2007

AbstractThe effect of the elastic fields of dislocations on γ‐ray perturbed angular correlations in paramagnets has been investigated. The γ‐ray directional correlations are perturbed by magnetic hyperfine and nuclear Zeeman interactions. The crystal imperfections cause the hyperfine splittings to vary from ion to ion. The frequency‐averaged perturbation factor taking into account these variations is obtained. For obtaining the frequency distributions a statistical method is used. Numerical calculations are performed for the case of the Er3+ion in CaF2.
The Application of Perturbation Theory and Pseudo Alloy Atom Model to the Cs–Rb and K–Rb Systems
Authors: Tanigawa S. , Doyama M. 
Published: July 2007

AbstractThe pseudopotential theory of metals is applied to the Cs–Rb and K–Rb alloy systems using the pseudo alloy atom model. The total binding energies, bulk moduli, and heats of solution were calculated as a function of alloy compositions. The calculated values of the total binding energies showed reasonable agreement with experimental data. The results predict the presence of a mixture of two phases at low temperatures. It is found that previous pseudopotential approaches are justified only for an alloy in which the electron density is nearly uniform. The present model is not subject to such a limitation.
Pulse Saturation of the O EPR Signal in Some Potassium Halides
Authors: Cornelis E. , Boesman E. 
Published: July 2007

AbstractThe results of spin–lattice relaxation (SLR) measurements of the O oxygen centre in KCl, KBr, and KI are given. The pulse saturation method was used. The results are compared with those of Castner, who used a different experimental technique, and the causes of the differences are briefly analysed. A theoretical calculation of the direct process, different in some respects from previous ones, is also summarized. The results of a numerical calculation for the angular variation of the SLR are given and discussed.
Single‐Phonon Contribution to the Hopping Low‐Field Magnetoresistance of Amorphous Semiconductors and Glasses
Authors: Čáapek V. 
Published: July 2007

AbstractThe change of sign of the low‐field hopping magnetoresistance at low temperatures is shown to be compatible with a previously reported theory of the hopping conduction in magnetic fields. When limiting to the low‐temperature single‐phonon contribution the longitudinal and transversal magnetoresistances are found to be the same in accordance with the experiment.
M center reorientation in CaF2
Authors: Collins W. C. 
Published: July 2007

AbstractThe reorientation efficiency of M centers in CaF2 is found to be directly proportional to the M+ center concentration. The wavelength dependence of the efficiency for optically induced reorientation is also found to agree with the M absorption rather than the MF. We propose that the M centers in CaF2 reorient under ultraviolet excitation by first photoionizing, i.e., becoming an M+ center; this M+ center then absorbs light in the same spectral range and reorients during a nonradiative transition from the excited state. This agrees with the mechanism found previously in the alkali halides.
Magnetic field dependence of the electron‐phonon correlation effects in polar crystals
Authors: Kaetheuser E. P. , Negrete P. 
Published: July 2007

AbstractPolaron properties in magnetic fields of arbitrary strengths are studied in the framework of an improved Landau‐Pekar approach. General expressions of the ground state energy and longitudinal effective mass are given. It is shown that the introduction of the electron‐phonon correlation effects in Landau‐Pekar's approximation leads to a 10% lower value of the longitudinal effective mass. The correlation effects are reduced when a high magnetic field is switched on.
Spin wave amplification in ferromagnetic semiconductors
Authors: Coutinho Filho M. D. , Miranda L. C. M. , Rezende S. M. 
Published: July 2007

AbstractThe damping coefficient of magnons interacting ‐with drifting carriers in ferromagnetics semiconductors for both k l > 1 and k l < 1 regimes is calculated. It is shown that for CdCr2Se4 the amplification factor can be of the order or greater than the losses of spin waves due to other effects.
Dielectric susceptibility of 〈100〉‐type paraelectric defects in varying static bias fields and simulated random stress
Authors: Minor P. C. , Dick B. G. 
Published: July 2007

AbstractThe effect of simulated random stress on the static dielectric susceptibility of 〈100〉‐type paraelectric defects with varying bias electric fields is investigated. The results are applied to the interpretation of measurements of dielectric loss due to OH − defects in K Br by Reymann and Lüty.
Atomistic expression of thermal expansion of metallic elements
Authors: Plendl J. N. 
Published: July 2007

AbstractAs it was shown very recently, the coefficient of the thermal expansion of metallic elements is proportional to the valency which is effective between any two next neighbor atoms within the atomic coordination of crystalline structure, at ambient conditions of pressure and temperature. Presently, the Grueneisen parameter γ is shown to be a function of the atomic coordination number. Combining the two results leads to an expression for the thermal expansion based entirely on absolute constants and atomic parameters. Seventy percent of 48 elements, examined in this way, obey a single atomistic expression. The remaining thirty percent, belonging to group II, subgroup IVB, and to the lanthanides, have, in principle, the same expression, however, with different numerical factors, indicating a relative reduction of the thermal expansion, which increases in that order.
Self‐diffusion in silver at low temperatures
Authors: Lam Nghi Q. , Rothman S. J. , Mehrer H. , Nowicki L. J. 
Published: July 2007

AbstractSelf‐diffusion in silver single crystals was measured at temperatures between 270 and 500 °C. The diffusion coefficients were in the range of 3×10−18 to 2×10−13 cm2/s. The results indicate that the Arrhenius plot is curved owing to a large divacancy contribution and that the activation energy for diffusion by divacancies is temperature dependent due to a partial dissociation of the divacancies. The best values of the parameters for diffusion by monovacancies are Do= 0.041 cm2/s, Q = 1.76 eV.
Effective charges and lattice dynamics of zincblende structure crystals
Authors: Mani K. K. , Singh R. P. 
Published: July 2007

AbstractIn an earlier paper (referred to as I) effective charges for a number of II‐VT and III‐V compounds have been obtained from a model of the chemical bond in these crystals. In the present paper, the dynamics of GaAs is studied using a variety of rigid‐ion models and some empirical rules are deduced regarding their accuracy. These rules are used to evaluate the zone‐boundary phonon frequencies for CdTe, InSb, and AlSb, which have nearly the same effective charges (in the scheme of the present work) as GaAs. Phonon frequencies have also been calculated for ZnS, which is more ionic than the crystals mentioned above. The two and three phonon spectra of AlSb are calculated in order to show a possible way of refining lattice dynamical calculations.
Etude des transitions optiques dans MgO:Ni2+ par dichroïsme circulaire magnétique
Authors: Régis M. , Farge Y. , Fontana M. 
Published: July 2007

AbstractCircular magnetical dichroism experiments, performed in the near infra‐red absorption spectrum of the Ni2+ ion in MgO crystals, at temperatures between 1.8 and 4.2 °K, show that the F3, F4 components of the 3T2g level are split. The presence of a dynamic Jahn‐Teller effect on the F4 component is also deduced.
Intra‐band electron pairing in the presence of a radiation field
Authors: Shankar R. K. , Sinha K. P. 
Published: July 2007

AbstractA semiconductor with almost overlapping conduction bands b and c is considered. It is found that an attractive interaction leading to superconductivity can be induced between electrons in the conduction band b by a strong radiation field of monochromatic photons whose energy differs slightly from the band gap Ebc. The mechanism is the exchange of a photon and a phonon between the interacting electrons and the interaction is found to be proportional to the photon density.
Thermoreflectance spectra and energy band structure of ZnGeP2 crystals
Authors: Raudonis A. , Grigoreva V. S. , Prochukhan V. D. , Šileika A. 
Published: July 2007

AbstractThe thermoreflectance spectra of ZnGeP2 chalcopyrite crystals have been investigated with polarized light in the spectral region 2.0 to 5.0 eV at 120 and 320 °K. Three structures (2.46, 2.53, and 2.59 eV at 120 °K) due to the optical transitions derived from T15 — T1 transitions in sphalerite have been observed by 0.4 eV above the fundamental absorption edge. Crystal‐field and spin‐orbit splittings of the valence band were found to be 0.084 and 0.075 eV, respectively. At higher energies eight thermoreflectance peaks strongly dependent on polarization of light were observed. They were attributed to optical transitions derived mainly from transitions responsible for E1 E1 + Δ1, E0 and E2 structures in the optical spectrum of GaP, the closest binary analogue of ZnGeP2.
Kinetic Phenomena in Semiconductors with Narrow Forbidden Gaps at Resonance Scattering
Authors: Geigin A. P. 
Published: July 2007

AbstractThe scattering of current carriers in degenerate semiconductors with narrow forbidden gap has been considered for the case when the scattering at the ion core potential predominates. To obtain the scattering probability the Green's function method has been used. The calculation of relaxation time due to the narrow forbidden gap and the short range nature of the potential has been carried out in a two‐band model. It is shown that taking into accound the second band leads to the renormalization of the ion core potential. The resonance scattering of carriers at small width virtual level has been discussed. Conductivity, thermopower, and longitudinal magnetoresistance have been calculated. It is shown in particular that the magnetoresistance in the case of resonance scattering is negative and anomalously great.
Properties of CsBr Derived from the Phonon Density of States
Authors: Daubeet J. , Jex H. , Müllner M. 
Published: July 2007

AbstractDetailed calculations are presented for the one‐ and two‐phonon density of states in CsBr. These densities are based on models fitted to phonons determined by inelastic neutron scattering. Most of the 800 phonons are in off‐symmetry directions. The densities and physical properties of CsBr derived from integrals over the frequency distribution are compared with optical measurements (infrared absorption, Raman scattering, infrared absorption from U‐centers) with caloric data (specific heat, frequency moments), and with elastic scattering experiments (Debye‐Waller factors, Debye temperatures).
Einfachgleitung in Natriumchlorid auf {110}‐ und {100}‐Ebenen
Authors: Franzbecker W. 
Published: July 2007

AbstractEine Schubapparatur wurde entwickelt zur Verformung von NaCl‐Kristallen mit konstanter Geschwindigkeit. Es wurden quantitative Schubverfestigungskurven auf (110)‐Ebenen aufgenommen. Bei Fassungsabständen Δ < 3 mm erfolgte bis 25% Einfachgleitung. Die Verfestigung war nur wenig geringer als im Bereich I druckverformter Proben. Ebenso konnte die Schubverfestigung auf (100)‐ (aber nicht auf (111)‐)Ebenen bei verschiedenen Temperaturen gemessen werden. Die Gleitebenen wurden durch Elektronen‐mikroskopie von Oberflächenabdrücken ermittelt. Die Ergebnisse werden im Zusammenhang mit Verfestigungstheorien von Hesse und Frank diskutiert. τ0auf (100) wird mit elektrostatischer Wechselwirkung zwischen (100)‐Versetzungen und Ca2+‐Verunreinigungen erklärt. Fur τ0 auf (111) wird aus Druckverformungen eine untere Grenze angegeben.
NMR and NQR Properties of Liquid In
Authors: Halder N. C. 
Published: July 2007

AbstractThe pseudopotential method in the theory of liquid metals and the experimental atomic interference functions have been used to investigate the temperature dependence of the Knight shift Ks and nuclear spin relaxation rate 1/T1 in liquid In. From this study, a value for the uniform exchange enhancement factor η = 1.65 has been predicted which agrees well with that estimated by Dupree and Seymour η = 1.58. With this η, K have been determined which are found to be in good agreement with the experimental data of Warren and Clark. These results seem to suggest that the core polarization contribution to Ks could be 25% of the direct shift and the exchange enhancement could be as large as 39% of Kstheo. From the present study the magnetic and quadrupolar contributions to Tl turn out to be T1 m = 0.538ms and T1 q = 0.960 ms, respectively, at 170°C.
Optical Absorption and Luminescence of I‐Centers in KBr
Authors: Takahashi M. , Saidoh M. , Itoh N. 
Published: July 2007

AbstractOptical absorption and luminescence of interstitial ion centers, the I‐, IA(Na), and IA(Li) centers in KBr are studied. Two optical absorption bands associated with each center are identified around 230 nm and the separations of the two bands for the I‐, IA(Na), and IA(Li) centers are 0.31, 0.39, and 0.35 eV, respectively. These two bands are ascribed to the transition to the spin‐orbit doublet, E5/2 and 63/2, and the increase in the width of the lower energy band in the order of the I‐, IA(Na), and IA(Li) centers is ascribed to the removal of the degeneracy of G3/2 in the C3 v symmetry. On the basis of the similarity of the I‐center luminescence and recombination luminescence, it is suggested that the I‐center luminescence is essentially caused by the recombination of (Br + e)*. The relaxation processes from the excited Br− at the interstitial site to the (Br + e)* at either the singlet or triplet states are discussed.
Ferroelectric Transitions in KH2PO4 and KD2PO4 Studied by Infra‐Red Polarized Reflection
Authors: Levin S. , Pelah I. , Wiener‐Avnear E. 
Published: July 2007

AbstractThe polarized infra‐red reflection spectra (250 to 4000 cm−1) of single crystals of KH2PO4 and KD2PO4 were measured at various temperatures above and below the ferroelectric Curie temperature. The results were compared with previous absorption measurements and allow better assignment of the infra‐red active modes. The existence of strong coupling between certain PO4 modes and low frequency hydrogen modes is deduced from the abrupt spectral changes on crossing the ferroelectric phase transition. This coupling results from the extremely anharmonic nature of the potential wells along the hydrogen bonds, as is also demonstrated by the KD2PO4 results. The build‐up of the line strength of the transverse hydrogen mode was related to the establishing of the spontaneous polarization below Tc. The two phase transitions observed in the KD2PO4 reflection spectra lead to the conclusion that KH2PO4 crystalline nucleation exists on the surface of KD2PO4 single crystals.
Photoelectric Properties of the Lead Chalcogenides
Authors: Cardona M. , Langer D. W. , Shevchik N. J. , Tejeda J. 
Published: July 2007

AbstractThe energy distribution spectra of electrons photoemitted from the lead chalcogenides by 48.4, 40.8, and 21.2 eV photons have been measured. Both the valence band and the 5d electrons of Pb are observed in these spectra. The valence band portions exhibit considerable structure which is compared with theoretical calculations and with recent X‐rays photoemission work. The d‐electrons spectra are extremely sharp (line width 0.5 eV). They are also compared with theoretical predictions (OPW, KKR, and pseudopotential calculations), with the result of X‐ray photoemission, and with the corresponding spectra of pure Pb. A discussion of the relative intensities of the valence and d‐electron energy distribution spectra is presented.
High‐Field Transport: Collision Integrals for Small Band Gap Semiconductors
Authors: Stokoe T. Y. , Cornwell J. F. 
Published: July 2007

AbstractCollision integrals are derived for polar optical, acoustic, and intervalley phonon scattering, ionised impurity scattering and carrier—carrier scattering. The full effects of band structure non‐parabolicity are taken into account.
Anisotropic Spin‐Orbit Coupling Contribution to the Zero‐Field Splitting of 3d5 Ions
Authors: Lowther J. E. 
Published: July 2007

AbstractThe crystal field potential contributes directly to the spin‐orbit interaction. Effective Hamiltonians describing this interaction are used to calculate the magnitude of this effect in the ground state splitting of 3d5 ions. Numerical results are given for ZnF2:Mn2+.
NMR Study of the Low‐Temperature Insulating State in the One‐Dimensional “Conductor” K2Pt(CN)4Br0.3·3H2O
Authors: Niedoba H. , Launois H. , Brinkmann D. , Brugger R. , Zeller H. R. 
Published: July 2007

AbstractNMR experiments from 1.2 to 110 °K in the one‐dimensional conductor K2Pt(CN)4Br0.3·3H2O are presented. The observation of a single quite narrow NMR line, with a temperature independent position that is typical for chemical shifts of such compounds suggests that the compound is a band insulator in its ground state. The T1 data obtained at liquid helium temperature support this hypothesis. This insulating state would be due to a Peierls instability.
An EPR Study of Divacancy Centres in CaWO4
Authors: Weightman P. , Henderson B. , Dugdale D. E. 
Published: July 2007

AbstractTwo paramagnetic defects with spin S = 1/2 have been identified in CaWO4 after neutron irradiation. The EPR spectra of these defects fit the spin‐Hamiltonian ℋ = β S g̃ B + SÃ (I1 + I2) with g1 = 1.811, g2 = 1.785, g3 = 1.497 and g1 = 1.766, g2 = 1.774, g3 = 1.429. The hyperfine structures for both centres are identical, arising from the 14% abundant 183W isotope at two equivalent sites. The hyperfine tensors have components A‖ = 167.4 × 10−4 cm−1 and A⊥ = 87.4 × 10−4 cm−1 with I1 = ±1/2 or 0 and I2 = ±1/2 or 0. The detailed analysis of the spectra, magnitude of the spin‐Hamiltonian parameters and tensor axes are consistent with the two spectra arising from different charge states of oxygen divacancy centres located on adjacent WO complexes.
Proton Spin‐Lattice Relaxation Time of TCNQ NH
Authors: Alizon J. , Berthet G. , Blanc J. P. , Gallice J. , Robert H. 
Published: July 2007

AbstractProton spin‐lattice relaxation time T1 of tetracyanoquinodimethan‐ammonium salt (TCNQ NH) has been studied as a function of temperature. In this material, the shape of the T1 curve is quite different of that observed in simple alkaline M‐TCNQ salts. It is shown that the reorientation of the NH4 ion must be taken into account.