bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of atomic relaxation near the (111) 1 × 1 surface of covalent semiconductors: Tight‐binding Green's function approach
Authors: Masuda K. 
Published: July 2007

AbstractThe atomic relaxations near the (111) 1 × 1 covalent semiconductor (C, Si, and Ge) surfaces are calculated using a tight‐binding Green's function approach and compared with the results of LEED experiments as well as those of other theoretical calculations. The present calculation takes into account the repulsive interaction energies between adjacent atomic sites and uses a total energy minimization procedure. It is shown that the change in the topmost interlayer spacing δ0 depends strongly on the material and subsurface relaxation is unimportant. The value of δ0 increases rapidly as going C(≈︁ 1%) → Si(≈︁ 5%) → Ge(≈︁ 13%). Simple physical interpretation for this behaviour is also given.
On the theory of resonance Raman scattering in heavily doped degenerate semiconductors
Authors: Quang Doan Nhat , Esser B. , Keiper R. 
Published: July 2007

AbstractThe influence of the random impurity potential on the dispersion of the one‐phonon resonance Raman scattering of a heavily doped p‐type degenerate semiconductor is investigated. It is proved that a local scattering amplitude representable by the difference of local dielectric functions may be introduced. The local coordinate dependence is due to the fluctuations of the impurity potentia. The resonance scattering cross‐section of the system is shown to be proportional to the modulus square of the difference of configurational averaged dielectric functions. The dispersion curve is dominated by the peaks occurring at the energy of the Burstein‐Moss shift in the real part of the dielectric function.
Quantum transport theory of impurity and electron‐electron scattering resistivity in n‐type semiconductors using the correlation function method
Authors: Röpke G. , Höhne F. E. 
Published: July 2007

AbstractThe quantum transport theory of electrical conductivity of a model system of electrons interacting with fixed ions should unify the usual theories of electrical conductivity of doped semiconductors, liquid metals, and dense ion plasmas. Starting from the method of nonequilibrium statistical operator, the conductivity is expressed by correlation functions which can be evaluated using the Green's function technique. Especially, the influence of electron‐electron scattering on the conductivity is considered. Results are given for arbitrary degree of degeneration and are compared with results obtained from the solution of the Boltzmann equation by standard methods.
Crystal growth, EPR, and luminescence of BaZnF4:Mn
Authors: Recker K. , Wallrafen F. , Büscher R. , Lehmann G. 
Published: July 2007

AbstractPure and doped crystals of BaZnF4, are grown in graphite crucibles using the Bridgman technique. EPR measurements at Q‐band show one center of Mn2+ with b = −301 ± 10; b = −185 ± 20 and A = −88.1 (all in units of 10−4 cm−1). The latter value indicates exclusive occupation of Zn sites. For the first time different values of the intrinsic ZFS splitting parameter \documentclass{article}\pagestyle{empty}\begin{document}$\overline {b_2 }$\end{document} for bridging and nonbridging F−ions are required for the superposition analysis, but both values are close to those for Mn‐F in other systems. For low energy excitations a second low energy emission band is observed. In accordance with previous results it can be explained by the large distortion of the [MnF2F4/2]2− units.
Far‐infrared reflectivity spectra of KH2PO4 between 300 and 400 K
Authors: Brehat F. , Wynckk B. , Hadni A. 
Published: July 2007

AbstractThe far‐infrared reflectivity spectra of a KDP single crystal in the temperature range 300 to 400 K are explained in terms of six lattice modes predicted by group theory and two extra modes: i) for E ‖ c, a lattice mode (ω = 183 cm−1) is coupled to an overdamped extra‐mode (ω1 = 76.5 cm−1), ii) for E ⟂ c, five lattice modes and an overda mped extra mode without any coupling, are needed tolexplain the reflectivity data. The extra‐modes ω1 = 76.5 cm−1 (B2) and Ω1 = 65 cm−1 (E) are probably the proton tunneling modes.
Electron momentum distribution and charge transfer study of FeAl, CoAl, and NiAl
Authors: Manninen S. , Sharma B. K. , Paakkari T. , Rundqvist S. , Richardson M. W. 
Published: July 2007

AbstractCharge transfer and electron momentum distribution of transition metal alloys FeAl, CoAl, and NiAl are studied using the γ‐ray Compton scattering technique. The results support the model where the charge transfer takes place from aluminium to the transition metal. A proper solid state calculation is, however, required in order to explain the details of the electronic properties of these alloys.
Some peculiarities of the temperature dependence of the electronic conductivity in charge‐ordered crystals
Authors: Manakova L. A. , Zemskov B. G. , Ionov S. P. 
Published: July 2007

AbstractA system of localized electrons capable of passing into the charge‐ordered state is found to modify substantially the properties of crystals. In the calculations the finite compressibility of the crystals is taken into account. The lattice parameters are shown to vary under definite conditions, giving rise to a temperature dependence of the electron conductivity differing from that observed in metals. For properly chosen compounds this effect can amount to tens of percents.
LO‐Phonon‐Plasmon Dispersion in GaAs Hydrodynamical Theory and Experimental Results
Authors: Nowak U. , Richter W. , Sachs G. 
Published: July 2007

AbstractMeasurements of the LO‐phonon‐plasmon dispersion in GaAs epitaxial samples are performed in the wave vector range K ≈︁ 0 to 106 cm−1, by using VIS, IR Raman scattering, and FIR reflectivity. For analysis the simple hydrodynamical theory for the free carrier electric susceptibility is used. Good agreement with the experimental data is obtained.
Double Spin Flips in Nuclear Double Resonance Calculated Cross‐Relaxation Rates for the Alkali Halide Structure
Authors: Whitaker M. A. B. 
Published: July 2007

AbstractA general expression for the rate of double spin flips in nuclear double resonance, produced in a previous paper, is evaluated for crystals of an alkali halide structure. A Gaussian approximation is used, and a number of lattice summations performed in order to obtain numerical answers for any given case. Reasonable agreement is found with the experimental values of Kunitomo and co‐workers. A statement by other workers concerning the location of the absolute maximum of the resonance is modified.
Temperature Dependence of the Infrared Absorption Spectrum of P4S3
Authors: Chattopadhyay T. , Von Schnering H. G. 
Published: July 2007

AbstractThe temperature dependence of the infrared absorption spectrum of P4S3 is investigated from 10 to 360 K. The internal mode frequencies have negligible temperature dependence whereas the external mode frequencies show a relatively strong temperature dependence which is almost linear. At the phase transition temperature 314 K the sharp absorption peaks due to the low‐frequency external mode disappear leaving relatively flat features characteristic of the plastic phase.
The Crystal Field in the Hexagonal Compound PrCu5
Authors: Andreeff A. , Goremychicin E. A. , Griesswn H. , Kaun L. P. , Lippold B. , Matz W. , Chistyaeov O. D. , Savitskii E. M. , Ivanitskii P. G. 
Published: July 2007

AbstractCrystal field effects on inelastic neutron scattering, specific heat, and susceptibility are studied in PrCu5. From the neutron scattering experiment the following crystal field parameters are determined: B02 = 0.48 meV, B04 = −8,5 × 10−4 meV, and B06 = 49 × 10−6meV B66 = 14 × 10−4meV. The ground level is a P1 singlet. Using these Bml the specific heat, the susceptibility, and the thermal conductivity of PrCu, are computed and compared with experimental results.
Conversion of F‐HA Pairs into α‐IA Pairs in KBr:Li and KBr:Na X‐Rayed at 80 K
Authors: Dauletbekova A. , Elango A. 
Published: July 2007

AbstractAn optical method is used to investigate the dependence of the number of defects, created by X‐irradiation at 80K (F, α, HA, V4, V4A, and IA, centres), on the impurity concentration in KBr:Li and KBr:Na. It is revealed that the amount of α‐IA pairs in the total anion defect number increases (approximately up to 90%) and the amount of F‐HA pairs decreases with the increase of the impurity concentration. As a reason the tunnel recharge of neutral primary F‐HA pairs into charged α‐IA pairs is considered, the probability of which increases with the decrease of the distance between the partners (i.e. with the enhancement of the impurity concentration).
An Extended Interionic Potential for Alkali Halides
Authors: Murti Y. V. G. S. , Selvarajan T. V. 
Published: July 2007

AbstractA ten‐parameter interionic potential is developed for the alkali halide crystals of rocksalt structure within the framework of the shell model for ionic crystals. This potential is an extension of the traditional Born‐Meyer form and takes into account the additional coupling between the repulsive overlap force and dispersion force. The analytical form of the proposed short‐range interaction potential is suggested by the coupled Drude oscillator model: Φii(r) = Bii exp (−r/σii) + Aii[(1/σii)2 − 2/σiir] Bii exp (−r/σii) − Cii/r6 for like ion pairs and Φij(r) = Bij exp (−r/σij) for unlike ion pairs. The four like ion parameters (Bii, σii) are determined by recourse to the Thomas‐Fermi electron gas model. The unlike ion repulsion parameters (Bij, σij) are fixed by the requirement of consistency with the equilibrium lattice constant as well as with the dielectric data as in the shell model. The van der Waals coefficients Cii and the coupling parameters Aii are treated to be crystal‐independent. A common set of these parameters is deduced by fitting to the elastic constants over the family of sixteen crystals. The resulting van der Waals coefficients are found to be generally large for both, cations and anions. The effect of input data on the constructed potentials is studied.
Phase Transition and Spatial Correlation of Localized States in the Falicov‐Ramírez‐Kimball Model
Authors: Lazo E. , Röessler J. , Moraga L. A. 
Published: July 2007

AbstractThe Falicov‐Ramirez‐Kimball model is solved by means of the two‐atom cluster Caron‐Pratt approximation. Metallic and insulating phases according to the value of an order parameter Δ are obtained, and both second‐ and first‐order phase transitions between them. Two kinds of insulating solutions (ordinary and mixed valence) and a variety of metallic states with different inter‐ionic degrees of correlation are obtained. These results are found to be inqualitative accord both with experiments and former theoretical treatments.
Dynamics of Two‐Spin Cluster in Spin Glass: I. Simple Model Calculation for Remanent Magnetization
Authors: Nara S. , Freudenhammer A. , Heber G. 
Published: July 2007

AbstractThe dynamics of a two‐spin system in a magnetic field is investigated. This system can be regarded as the most dominant two‐spin clusters in some spin glass in the first approximation of cluster expansion theory. Two Heisenberg spins are considered with one‐ion anisotropy in a magnetic field. The spin quantum number is taken as S1 = S2 = 1. The field may be regarded as the superposition of external field and molecular field created by the other clusters. The result of quantum version is briefly compared with the previous work of classical treatment. Assuming that the two spin clusters are in some metastable state due to frustration effects of spin glass, a possible interpretation of an experimental fact is presented — the field dependance of remanent magnetization, which indicates one common dynamical property for several kinds of spin glasses.
Self‐Trapped Exciton Luminescence after Tunnelling of Vk and Nao Centers in CsI:Na Crystals
Authors: Imanaka K. , Kayal A. ‐H. , Mezger A. C. , Rossel J. 
Published: July 2007

AbstractTunnelling recombination luminescence in CsI :Na crystals is studied by means of linear polarization, magnetic circular polarization, and optical detection of ESR either under or after X‐ray irradiation. Results are well interpreted in terms of a self‐trapped exciton (STE) scheme as the final emitting state of tunnelling recombination; here, in the present case with tunnelling, the population for each STE sublevel is derived from the thermal equilibrium spin populations of trapped electrons (NaO) and holes (Vk) instead of the usual creation rate in UV light excitation case.
Simple Spectral Density Approach to the Problem of Mixed Valency
Authors: Nolting W. , Olés A. M. 
Published: July 2007

AbstractA simple spectral density approach is proposed for the extended Falicov‐Kimball model to describe the phenomenon of mixed valency observed in 4f‐compounds. The general influences of typical model parameters, as for instance the Coulomb interaction g between localized f‐ and itinerant s‐electrons or the s‐f hybridization V, on characteristic properties of intermediate valence compounds are calculated and discussed. Depending on the parameters g and V the theory predicts both first‐and second‐order transitions as found for the Sm chalcogenides.
Critical Anomaly of the Electron Spin‐Lattice Relaxation in X‐Irradiated Rochelle Salt
Authors: Völkel G. , Müller H.‐E. , Flohrer W. 
Published: July 2007

AbstractUsing the electron spin‐echo technique the spin‐lattice relaxation time T1 of a free radical in X‐irradiated Rochelle salt and in the solid solution NaK0.985(NH4)0.015C4H4O6 · 4 H2O are determined in the temperature range from 90 to 300K. In the close vicinity of the upper and lower phase transitions of both crystals a critical behaviour of the longitudinal relaxation can be detected. Several ways of analysing this behaviour are discussed. They all reveal a critical increase of T1. Measurements of crystals irradiated with different X‐ray doses show that the anomaly in T1 is shifted simultaneously with the phase transition temperatures. The observed anomaly is explained by the influence of an increasing phonon damping at the ferroelectric phase transition on the spin‐lattice relaxation time.
On the Luminescence of Sm3+, Gd3+, and Dy3+ in Yttrium Aluminium Borate
Authors: Kellendonk P. , Blasse G. 
Published: July 2007

AbstractConcentration quenching of the luminescence in Y1−xRExAl3B4O12 (RE = Sm, Gd, Dy;0 < x ≦ 1) is examined. In the case of gadolinium compound the quenching is due to energy migration among the Gd3+ ions to quenching centres. From the decay curve of GdAl3B4O12 a lower limit for the diffusion constant at 300 K is derived. The quenching of the Sm3+ and Dy3+ ion emission can be ascribed to resonant cross‐relaxation. The interaction between the ions is probably of the electric dipole‐dipole type. The critical concentrations for the transfer processes are given.
Effect of Magnetic Field on the Susceptibility and the Specific Heat of Spin Glasses
Authors: Das S. K. , Joshi S. K. , Tripathi R. S. 
Published: July 2007

AbstractThe susceptibility and the specific heat of spin glasses in the presence of an external magnetic field are calculated within the frame of Edwards' and Andersons theory. The quantum Heisenberg Hamiltonian is used with exchange interactions distributed randomly about a positive mean. The field dependence of the susceptibility and the specific heat are compared with the experimental data near the spin glass transition temperature.
Effect of Size Quantization on the Einstein Relation in Ultrathin Films of n‐Cd3As2
Authors: Chakravarti A. N. , Ghatak K. P. , Ghosh K. K. , Ghosh S. , Mukherjee H. M. 
Published: July 2007

AbstractAn attempt is made to investigate the effects of size quantization on the Einstein relation for the diffusivity‐mobility ratio in ultrathin films of n‐Cd3As2. It is found that the ratio increases, at a given electron concentration, with decreasing film thickness and also increases with increasing electron concentration corresponding to a given film thickness. For extremely thin films, the influence of size quantization becomes increasingly prominent with decreasing values of the electron concentration.
Semiempirical Calculations of Defect Properties in LiF Crystal
Authors: Shluger A. L. , Kotomin E. A. 
Published: July 2007

AbstractTo obtain the electronic structure of both, perfect and imperfect ionic crystals the standard calculation scheme of the INDO semiempirical method is modified in order to consider the interaction of valence electrons with ionic cores more accurately than it has been done so far. The INDO parameters are optimized to reproduce a number of experimentally observed properties of a perfect LiF crystal. The parameters derived permit to reproduce quite well the distinctive properties of free F02, F−2, LiF molecules which is necessary for reliable calculations of the properties of intrinsic hole defects.
Evidence of the Conduction–Valence Band Overlap Induced by a Magnetic Field in Zero‐Gap Hg1–xMnxTe
Authors: Sandauer A. M. , Byszewski P. 
Published: July 2007

AbstractExperimental evidence and theoretical results are given of the conduction–valence bands overlap induced by an exchange interaction in zero‐gap Hg1–xMnxTe. The Fermi level as well as the concentration of electrons and holes strongly depend on the magnetic field in the region where the overlap exists.
The Vibrational Entropy Change Associated with the Disordering of a Two‐Dimensional Binary Alloy Using a Model of Nearest‐ and Next‐Nearest‐Neighbour Interactions
Authors: Bakker H. 
Published: July 2007

AbstractIn a model of harmonic central forces, acting between nearest and next‐nearest neighbours the change of vibrational entropy due to disordering of a completely ordered binary alloy is calculated numerically. The crystal structure is the two‐dimensional square lattice. The temperature is well above the Debye temperature. A comparison is made with results obtained previously using a different model. It turned out that the values of the entropy change are not too much model dependent in the examples investigated. Again it appears that the change of the vibrational entropy is of a similar magnitude as that of the configurational entropy.
On the Susceptibility of the Periodic Anderson Model
Authors: Elk K. 
Published: July 2007

AbstractThe periodic Anderson model is studied as a simple model describing intermediate valence compounds. In this model a strong electron–electron correlation is taken into account. The correlation term is decoupled using the alloy analogy approximation, which yields a two‐peak structure of the density of states of the f‐electrons. Then the isothermal longitudinal susceptibility χ can be obtained by means of the Green function technique. Restricting the effective coherent potential to the atomic limit the temperature dependence of χ is computed. It is found that caused by the strong correlation χ diverges atT→ 0, in contrast to the Pauli behaviour observed experimentally in intermediate valence compounds. On the other hand, the strong dependence of χ on the electron densityncan be explained.
Investigation of Superhyperfine Interactions of Mn2+ in α‐LiIO3 and Evaluation of Lithium Quadrupolar Interactions
Authors: Daraselia D. M. , Bräer A. 
Published: July 2007

AbstractThe models of two types of paramagnetic centres in manganese‐doped LiIO3 are determined by means of the radiofrequency discrete saturation method (RFDS) and ENDOR, which measure the superhyperfine interactions of the centres with the neighbouring 7Li nuclei. Manganese is arranged at lithium sites and charge compensation results from a vacancy at a lithium site. The measured quadrupolar splitting parameters of the 7Li nuclei are calculated with good agreement in point charge approximation on the basis of the models determined.
Kr and Xe Guest Atoms in Ar Matrix: Emission Spectra, Excitation Spectra, and Lifetimes
Authors: Hahn U. , Haensel R. , Schwentner N. 
Published: July 2007

AbstractEmission bands of isolated Kr and Xe atoms in solid Ar matrices are assigned to atomic 3P1 and 1P1 states on the basis of excitation and emission spectra. The temperature and concentration dependence of these spectra is used to sort out emission from distorted sites. The dependence of the lifetimes on temperature reflects the competition between radiative and nonradiative decay.
Investigation of EPR and Thermoluminescence Glow‐Curves of X‐Irradiated KCl:CrO, Ca2+ Crystals
Authors: Alybakov A. A. , Toichiev N. , Akchalov Sh. 
Published: July 2007

AbstractKCl crystals doped with CrO and Ca2+ are studied. It is shown that in these crystals there are impurity centres being the complexes CrO with anion vacancy and CrO with Ca2+. As a result of X‐irradiation, the Cr6+ ions in these centres turn into the paramagnetic pentavalent state and show EPR spectra of two types lettered A1 and A2. The A1 spectrum is interpreted as to be due to Cr5+ ions generated in the complexes with anion vacancy; the A2 spectrum is assigned to the Cr+5 ions generated in the complexes with Ca2+. A comparison with the results of thermoluminescence study shows, that heating results in the destruction of paramagnetic centres. A thermoluminescence peak at 436 K corresponds to the A1 centre destruction and a peak at 486 K corresponds to the A2 centre destruction.
Transport Properties of PrNi5 at Low Temperatures
Authors: Reiffers M. , Flachbart K. , Jáoš Š. , Beznosov A. B. , Eska G. 
Published: July 2007

AbstractThe temperature dependence of the electrical resistivity and thermal conductivity of PrNi5 is investigated. In the electrical resistivity at temperature around 10 K a slight anomaly indicating the crystal‐field effect on the resistivity is observed. The thermal conductivity shows a linear temperature dependence in the temperature range 0.5 to 20 K.
Luminescence Accompanying the Recombination of Electrons with VF Centres in KCl Crystals
Authors: Egemberdiev Zh. , Zazubovich S. , Seeman V. , Nagirnyi V. 
Published: July 2007

AbstractProcesses of an optical production of VF centres (holes localized near cation vacancy) are investigated by absorption, ESR, and thermoluminescence methods. It is established that VF centres are most effectively produced in KCl: PbCl,2 crystals X‐irradiated at 80 K and subsequently heated up to 270 K, at the recombination of optically released electrons with V2z(Pb2+) centres (molecular Cl ions associated with Pb2+ ions). After an optical production of VF centres, the stimulation in the electronic absorption bands (K or L2) results in the appearance of luminescence with a peak at 3 eV and band half‐width equal to 0.75 eV. If VF centres are previously oriented by polarized light, the 3 eV emission becomes polarized in the directions perpendicular to the molecular axis of the oriented VF centres. The 3 eV emission quenches rapidly at 237 K and its depolarization occurs at 111 K. The same emission is observed in undoped KCl crystal. It is concluded that the 3 eV emission is caused by the recombination of electrons with VF centres. The same spectrum must have the triplet emission of a self‐trapped exciton perturbed by a cation vacancy.
Electron Paramagnetic Resonance of Gold in Silicon. II. Cluster Centres
Authors: Höhne M. 
Published: July 2007

AbstractThe interpretation of the EPR spectrum suggests two alternative models: five gold atoms or three gold atoms with two boron atoms, respectively, form a cluster occupying lattice sites and adjacent interstitial sites. This cluster tends to further precipitation. Both of the paramagnetic gold‐related centres – that with one gold atom and the cluster – are assumed to belong to the group of acceptor levels in Si:Au.