bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of harrison's potential in mixed alkali halide crystals
Authors: Jain G. D. , Shanker J. 
Published: July 2007

AbstractHarrison's overlap repulsive potential is used for evaluating the cohesive energies and bulk modulus of alkali halide mixed crystals. This potential replaces the old and widely used Born‐Mayer repulsive potential in ionic crystals. The Harrison repulsive potential is represented by a quantum mechanical analytical potential form derived from the tight binding theory. The calculations are performed for the mixed crystals of NaCl—NaBr, KCl—KBr, and KBr—KI for the entire range of composition. The results are found in good agreement with experimental data and are better than those predicted from the Born‐Mayer potential.
Study of Cu K edge in some copper (II) octahedral complexes
Authors: Bhattacharya P. , Chetal A. R. 
Published: July 2007

AbstractThe K‐absorption edge of copper in the complexes Cu(LH)2SO4 · 4 H2O, Cu(LH)SO4 · 4 H2O, and Cu(phen) (xant)2 is investigated using a Cauchois‐type bent crystal X‐ray spectrograph. The peaks A, B, and C observed in the edges are explained on the basis of molecular orbital theory. Peak positions are correlated with partial charge on the central metal ion. It is observed that the peak A shifts to the low‐energy side while the peaks B and C shift to the high‐energy side as the partial charge on an absorbing ion in the complex increases.
Effective dynamical coupling constants of the a‐band of Tl+ centers in NaCl, KCl, KBr, and KI
Authors: Oboth K.‐P. , Schmitt K. 
Published: July 2007

AbstractThe temperature dependence of the A‐absorption band of Tl+ centers in NaCl, KCl, KBr, and KI and the stress induced linear dichroism (SLD) are investigated in the region between 4 and 300 K. Moment analysis enables to determine the effective dynamical coupling constants corresponding to the |A〈‐state. The effective phonon frequencies show decreasing values for increasing halogen mass. It turns out that the theory of linear electron—phonon coupling is correct for temperatures up to 200 K in NaCl: Tl+, and KCl:Tl+, and up to 100 K in KBr:Tl+ and KI:Tl+.
Raman study of the phonon halfwidths and the phonon—plasmon coupling in ZnO
Authors: Bairamov B. H. , Heinrich A. , Irmer G. , Toporov V. V. , Ziegler E. 
Published: July 2007

AbstractThe LO‐phonon—plasmon coupling in n‐ZnO single crystals is investigated by Raman spectroscopy at room and liquid nitrogen temperatures. The energy shift and halfwidth broadening of the LO‐phonons relative to the uncoupled modes are analyzed to get the concentration and mobility of the charge carriers. These results are compared with those from electrical measurements. The uncoupled phonon modes are measured in high‐ohmic crystals in which the interaction with the charge carriers can be neglected. For the low energy E2 mode an extreme small halfwidth of 0.3 cm−1 is found. At 77 K with increasing intensity of the exciting continuous laser light (hω = = 2.54 eV < Eg = 3.3 eV, P = 800 mW) nonequilibrium carriers are generated not connected with an increase of the lattice temperature.
Relaxation in the ferromagnetic phase of terbium arsenate (TbAsO4)
Authors: Müller P. H. , Kasten A. , Schienle M. 
Published: July 2007

AbstractBelow Tc = 1.5 K TbAsO4 is an Ising ferromagnet with induced magnetic moments. A superstructure of the magnetic moments found by Schäfer and Will may be explained by very small ferromagnetic domains. A simple estimation of the free energy at T = 0 yields 0.05 μm for the thickness of these domains. In the ordered phase the complex magnetic ac susceptibility is strongly frequency dependent. The relaxation depends on two coupled processes. It is assumed that the process at lower frequencies is due to domain wall shifting and the process at higher frequencies is caused by the internal field. The frequency dependence can be described by an extension of the Debye equation which decouples the two processes. The susceptibility of a system with rigid domain walls is determined in mean field approximation.
Excited states of bound excitons in wurtzite‐type semiconductors
Authors: Puls J. , Henneberger F. , Voigt J. 
Published: July 2007

AbstractExcitons bound to neutral impurities are studied with respect to excited states by means of excitation spectroscopy in CdS single crystals at 1.8 K. The symmetry of the four excited states of the exciton bound to neutral donor (placed energetically below the free exciton) can be deduced from the observed dependence of their optical transitions on the direction of the wave vector and the polarization. Theoretical considerations taking into account the complex valence band structure of wurtzite‐type semiconductors lead to an explanation of these states in terms of excited (p‐ and d‐like) hole states of the bound exciton. With respect to the exciton bound to neutral acceptor only the well‐known I1B‐states are found experimentally arising from the incorporation of a hole from the lower B‐subvalence band in the complex.
Electrical resistivities of the liquid alkali metals
Authors: Canessa E. , Vignolo J. 
Published: July 2007

AbstractA discussion of the calculation of electrical resistivity of liquid alkali metals is presented. The electrical resistivity is revised for these metals from various model potentials using experimental as well as theoretical structure factors. The over‐all agreement between Ziman's theory and experiment is reasonably satisfactory though not in detail. Most of the discrepancies are explained by the behaviour of the structure factor, and in other cases by the validity of the screened pseudopotential employed.
Variation of phonon dispersion curves with temperature in indium arsenide measured by X‐ray thermal diffuse scattering
Authors: Orlova N. S. 
Published: July 2007

AbstractA study of the temperature dependence of the X‐ray thermal diffuse scattering intensity distribution from the (100), (110), (111) planes in indium arsenide single crystals is carried out in the temperature range 80 to 750 K. The data obtained are analysed and yield the phonon frequencies in all three principal symmetry directions at different temperatures. An average decrease in the acoustic mode frequencies is found to about 10 to 12% while for optic modes it is of about 6% with increasing temperature over the temperature range above mentioned.
Magnetic relaxation in dysprosium phosphate (DyPO4)
Authors: Schienle M. , Kasten A. , Müller P. H. 
Published: July 2007

AbstractDyPO4 is a three‐dimensional Ising antiferromagnet with a Néel temperature of TN = 3.39 K. The temperature and field dependence of the relaxation time is investigated by means of magnetic ac susceptibility measurements in the frequency range from 5 Hz to 3 MHz. Above 9.3 K a spinlattice Orbach process via the first excited crystal field state of Dy3+ is dominant. Spin—spin processes contribute only at low temperatures and the relaxation becomes temperature independent, but depends strongly on the magnetic field strength. The relaxation is fast where the external field compensates the nearest‐neighbour interaction, e.g. for vanishing local magnetic field. The magnetically diluted system (Y0.09, Dy0.1)PO4 depends strongly on the properties of the coolant surrounding the crystal, which could be understood quantitatively by a heat conduction model.
Electron paramagnetic resonance of Mn2+ and VO2+ in Ba2Zn(HCOO)6 · 4 H2O single crystals
Authors: Jain V. K. , Seth V. P. , Malhotra R. K. , Yadav S. K. 
Published: July 2007

AbstractElectron paramagnetic resonance of Mn2+ and VO2+ in dibarium zinc formate tetrahydrate is studied at X‐band and at 298 K. The ions substitute for the Zn2+ sites in the lattice. A correlation is found to exist between the V—O and Zn—O bond directions. The spin‐Hamiltonian parameters are evaluated. Forbidden hyperfine transitions Δm = ± 1 and Δm = ± 2 are observed for Mn2+ and their doublet separations are found to be in agreement with calculated values. The angular variation of the intensities of the allowed and forbidden hyperfine transitions of Mn2+ is also studied and is found to be in good agreement with the theory.
A disorder model of melting
Authors: Vaid B. A. , Sharma K. C. , Syal V. K. 
Published: July 2007

AbstractA disorder model of melting is proposed which provides a unified description of both the classes of liquids, viz. one contracting on freezing and the other one contracting on melting. In order to accomplish this, a generalization of the well‐known concept of packing fraction is affected and a calculation of thermodynamic quantities is presented which yields better agreement with the data.
More on the F‐Center Decay in Additively Colored NaF:LiF
Authors: Bosi L. , Gagliardelli P. , Nimis M. 
Published: July 2007

AbstractAccurate measurements of the F‐center lifetime, τ(T), in additively colored NaF:LiF samples are presented as a function of the temperature, starting from 7.6 K. The anomalous behavior of the F‐center decay in NaF is confirmed only as regards the behavior of the relative quantum yield ηr(T): the presence of another decay channel for the F‐center electron, besides the jumping into the conduction band, is evidenced. The disagreement with data obtained by other authors is explained by the presence of aggregate centers in their samples. A τ(T)/ηr(T) behavior contrary to that presented by Stiles, Fontana, and Fitchen is observed. A critical review of models and guesses proposed in the literature is also presented in order to obtain a correct understanding of the nature of the relaxed excited state of the F‐center.
Multipole Theory of the Polarization of Solids by Point Defects. I. Dipole Approximation
Authors: Kantorovich L. N. 
Published: July 2007

AbstractThe electronic structure of solids is investigated where the electronic density is localized on structure elements (atoms, molecules, bonds). For these solids containing point defects the Schrödinger equation is obtained in the framework of a molecular cluster model taking self‐consistently into account the polarization of the rest of the solid outside the cluster. The polarization is considered in terms of multipole moments on structure elements induced by the defects neglecting exchange interactions. In the first part of the paper the general theory developed is applied to ionic crystals in the dipole approximation. The way to use the cluster symmetry in polarization calculations is also analyzed.
Space Distribution of the Chemical Composition of the Thermo‐Grown SiO2SiOxSi System
Authors: Lei Min‐sheng , Wang Zhi‐cheng 
Published: July 2007

AbstractA simple statistical model for the oxygen distribution in a thermo‐grown SiO2 film on the surface of a silicon single crystal is proposed considering the bond saturation, and the oxygen distribution function of space coordinate for the SiO2‐SiOx‐Si system is deduced. Furthermore the space distribution function of the average chemical composition is obtained. Experimentally some SiO2 samples which are grown at temperatures from 900 to 1200°C, are investigated with AES and SIMS. These experimental results sustain the theoretical model. The SiOx transition region in the SiO2‐SiOx‐Si system is discussed, and the width of the transition region grown by thermal oxidation is ≈4 to 6 nm.
Phonon‐Polaritons in Bilayer Systems. Surface Phonon‐Polaritons
Authors: Wendler L. , Jäger E. 
Published: July 2007

AbstractSurface phonon‐polaritons in a bilayer system consisting of two dielectric media with local, frequency‐dependent dielectric functions are studied. The dispersion relation for p‐polarized polaritons is derived. The dispersion curves and electric fields of surface phonon‐polaritons are presented for various cases in graphical form.
The Photoacoustic Effect in Semiconductors
Authors: Sablikov V. A. , Sandomirskii V. B. 
Published: July 2007

AbstractA theory of the photoacoustic effect (PAE) in semiconductors is developed for the region of fundamental absorption, taking into account the generation of free electrons and holes, their diffusion, and recombination. The temperature on the illuminated surface of a semiconductor is calculated in a general form. The PA measurements allow to determine the diffusion length of carriers, the surface recombination velocity, and the bulk lifetime along with the light absorption coefficient. The qualitative difference of the results from the conventional Rosencwaig and Gersho (RG) theory is demonstrated. The problem of interpretating the experiments is discussed.
A Tetrahedron Method for Doubly Constrained Brillouin Zone Integrals Application to Silicon Optic Phonon Decay
Authors: Allen P. B. 
Published: July 2007

AbstractIntegrals over the Brillouin zone with two delta‐functions are considered. Such integrals are constrained to the intersection of two different constant energy surfaces. Following the discussion by Lehmann and Taut for the case of one delta‐function, the tetrahedron method is shown to yield simple analytic results when the energies and weight functions are linearly interpolated throughout a small tetrahedron. The method is illustrated with a calculation of the density of available two‐phonon decay channels of the Q = O optic phonon of Si.
Self‐Consistent Calculations of the Lattice Dynamics and Thermodynamics of Anharmonic Noble Metals
Authors: Malinowska‐Adamska C. 
Published: July 2007

AbstractThe reduced second‐order self‐consistent phonon approximation is applied to the investigation of the dynamic and thermodynamic properties of noble metals using the Morse and Rydberg and Varshni potentials as models of nearest‐neighbour central force interaction. The temperature and pressure dependence of the dynamic and thermodynamic functions of Cu, Ag, and Au in the high and low temperature limits are given and compared with experimental and other theoretical data. The behaviour of the physical quantities in the vicinity of the instability point is investigated, too.
The Semiconduction in the Molten Tl‐CuTlTe2 System
Authors: Uemura O. , Wada Y. , Takahara T. , Satow T. 
Published: July 2007

AbstractMeasurements of the electrical conductivity, the magnetic susceptibility, and the thermoelectric power for the molten Tl‐CuTlTe2 system are made in wide temperature and composition ranges. It is observed that the conductivity for the system falls abruptly at the composition of 66.7 mol% Tl and the thermoelectric power changes its sign around this composition. The diamagnetic susceptibility also shows a sharp maximum at the corresponding composition. These anomalies of electronic properties indicate that molten Tl‐CuTlTe2 system gives rise to a metal‐nonmetal transition at the composition of CuTl3Te2. The experimental results of the present work are compared with the previous data of molten Tl‐chalcogenide systems which exhibit a similar electronic behaviour and are discussed using some electron transport theories often employed in amorphous and liquid semiconductors.
Temperature‐Dependent Effective Masses in III‐V Compound Semiconductors
Authors: Sharma A. C. , Ravindra N. M. , Auluck S. , Srivastava V. K. 
Published: July 2007

AbstractA study is made of the temperature dependence of the effective masses of carriers for some III‐V compound semiconductors essentially based on the model band structures of Kane and Penn. Using the nearly free electron model of Penn, we obtain an analytical expression for the matrix element P appearing in Kane's expression. The material dependence of P is hence explained. It is further seen that the temperature dependent effective mass is accounted, for, to a very large extent by the temperature dependence of the energy gap. This apart, the contribution of the electron‐phonon interaction term to the temperature dependence of the effective mass is shown to be significant.
Optical Absorption and Electronic Structure of NaCl:Ag+. A Multiple Scattering Xα Study of the (AgCl6)5− Cluster
Authors: Pedrini C. , Chermette H. , Goldberg A. B. , McClure D. S. , Moine B. 
Published: July 2007

AbstractA multiple scattering Xα calculation is performed on the (AgCl6)5− cluster in order to study the electronic structure of the Ag+ impurity center in NaCl. The optical absorption spectrum is compared to theory and new symmetry assigments are made. The temperature dependence of the absorption bands is analysed and the Jahn‐Teller stabilization energy of the Ag+ excited state is measured.
Structure and Bonding in Cubic IV–VI Crystals. II. Instability of the TO(Γ) Mode: Unified Universal‐Parameter Treatment of the Group‐V Semimetals and Cubic IV–VI Semiconductors
Authors: Enders P. 
Published: July 2007

AbstractThe inherent instability of the cubic crystal structure of group‐V semimetals and of AIVBVI semiconductors exhibiting a cubic phase is treated on equal footing using the LCAO‐based approaches by Bersuker and Vekhter and by Volkov and Pankratov. By means of the universal parameter relation for the ppσ‐resonance integral, this instability is founded without adjustable parameters. The stability of the lead chalcogenides is explained on a semi‐quantitative level. The relation to Littlewood's pseudopotential‐based work is discussed.
Investigation of Z Center Conversions in KCl:SrCl2. I. Optical Measurement of the Kinetics of the Thermal Z1 → F, Z2 Decay
Authors: Kessler A. , Kizler P. 
Published: July 2007

AbstractThe absorption caused by a gradual conversion of a Z1 band during a linear heating into an F and Z2 band is obtained and analysed by fitting of rate equations. The results show that the decay proceeds in at least two phases. First F centers are formed and these seem to form with remaining Z1 centers Z2 centers then. Finally, at higher temperatures, the Z2 centers decay into F centers.
Spectroscopic Investigation of the Magnetic Properties of Ho2O2SO4
Authors: Kasten A. , Weschenfelder D. , Hess G. 
Published: July 2007

AbstractBelow Tn ‐ 3.4 K Ho2O2SO4 is antiferromagnetic with canted moments. The magnetic properties are strongly influenced by a crystal field splitting of the two lowest electronic Ho3+ states. The details of the magnetic short‐range order as well as the occurrence of intermediate ferrimagnetic phases in external magnetic fields may be explained within a model which takes into account the crystal field splitting as well as dipole and superexchange interactions up to third‐nearest neighbours.
Two Types of Low‐Temperature Phase Transitions in Uniaxial Ferromagnets with High Single‐Ion Anisotropy
Authors: Kazakov A. A. 
Published: July 2007

AbstractIt is mentioned, that the low‐temperature exchange hybridization of magnon modes in the uniaxial strongly anisotropic crystals with single‐ion anisotropy results in the presence of special points in magnon spectrum, where the energetic gaps become equal zero, and the dispersion mode law is of power character. The physical nature of this peculiarities occurrence is connected with the level crossing. It is shown, that the influence of these points essentially tells on the low‐temperature behaviour of magnetization and its derivatives by field and temperature.
Local‐Density‐Functional Approximation to the Energy Band Structure of TmS Using the Self‐Consistent Relativistic Linearized‐Augmented‐Planc‐Wave Method
Authors: Farberovich O. V. , Nizhnikova G. P. , Vlasov S. V. , Domashevskaya E. P. 
Published: July 2007

AbstractThe self‐consistent relativistic linearized‐augmented‐plane‐wave method is applied to local‐density calculation of electronic structure of TmS. It is found, that thulium monosulphide is a metal with a trivalent state of thulium. The influence of spin—orbital interaction is shown for different symmetry states of electrons. Calculated densities of states are used for the estimation of the electron—phonon coupling constant. And in conclusion it is shown that TmS is a high temperature Kondo‐like system.
The First‐Principles Calculation of the Norm‐Conserving Non‐Local Singular Atomic Pseudopotentials
Authors: Chulkov E. V. , Sklyadneva I. Yu. , Panin V. E. 
Published: July 2007

AbstractThe first‐principles non‐local singular atomic pseudopotentials are constructed for seventy‐five elements of the Periodic Table. The pseudopotentials are calculated with account of norm‐conserving. The energy dependence of the constructed pseudopotentials is studied. They are shown to be energy independent within the energy range which is characteristic of low‐energy electron excitations in solids. The values of the classical turning points of pseudopotential are calculated for all the elements considered.
Shubnikov‐De Haas Effect and Cyclotron Resonance in p‐CdSb
Authors: Cisowski J. , Portal J. C. , Arushanov E. K. , Broto J. M. , Huant S. , Brunel L. C. 
Published: July 2007

AbstractShubnikov‐de Haas (SdH) effect and cyclotron resonance (CR) in single crystal samples of p‐CdSb are studied in magnetic fields up to 19 T. The angular dependence of the SdH periods is determined as well as the cyclotron effective mass for different hole concentrations. The hole effective masses along the three crystal axes are obtained and compared with theoretical calculations.
Electron Paramagnetic Resonance Investigation of Pb‐ and Ge‐doped CdTe
Authors: Bilbé R. M. , Nicholls J. E. , Davies J. J. 
Published: July 2007

AbstractEPR spectra are observed from Pb and Ge ions in CdTe. The spectra are characterized by isotropic g‐values of 2.2055 and 2.1450, respectively, and show strong anisotropic hyperfine interaction with the neighbouring tellurium ions. The resonances result from a hole localized primarily on the tellurium ligands and the results are discussed in relation to group IV ions in other II–VI compounds.
Polarizability of Donors in Polar Semiconductors. Effect of a Weak Magnetic Field
Authors: Cahay M. , Kartheuser E. 
Published: July 2007

AbstractThe electrical polarizability tensor of shallow donors in polar semiconductors is calculated in the presence of a weak magnetic field. A variational treatment of the donor is developed in the framework of the effective‐mass theory, including the effects of interaction between the charge carriers and the longitudinal‐optical (LO) phonons within the static approximation. The effective‐mass Hamiltonian of the donor allows for central‐cell corrections by means of a phenomenological impurity potential. The results are compared with previous theoretical work and experiment in the case of donor impurities in Si. It is shown that the donor polarizability depends strongly on the form chosen for the model impurity potential and undergoes a 30 to 50% decrease due to the electron—(LO)phonon interaction in the case of impurities in III–V and II–VI compounds, respectively.
Stimulated Raman Effect on Plasmons and Longitudinal Plasmon‐Phonons in Simple Cubic Crystals
Authors: Merten L. , Goltsche W. 
Published: July 2007

AbstractIt is shown that Stokes and anti‐Stokes waves anharmonically can couple not only with transverse but also with longitudinal quasi‐particles (stimulated Raman effect). As examples the coupling with plasmons and longitudinal plasmon‐phonons in simple cubic crystals is treated. The dispersion functions can be represented by simple analytic expressions, if the coupling with the anti‐Stokes waves is neglected against the coupling with the Stokes waves. In this approximation one “stimulated region” exist for plasmons and two for longitudinal plasmon‐phonons.
Anharmonic Thermal Atomic Vibrations in the Cubic Phase of Cs2NaNdCl6 Single Crystals
Authors: Makarova I. P. , Misyul S. V. , Muradyan L. A. , Bovina A. F. , Simonov V. I. , Aleksandrov K. S. 
Published: July 2007

AbstractThermal atomic vibrations in the cubic phase of Cs2NaNdCl6 single crystal undergoing the structural phase transition (PT) at 138 K are investigated from the data of X‐ray diffraction obtained at 278, 218, and 148 K. A significant anisotropy of thermal vibrations and their deviations from harmonic behaviour are found for the Cl‐atoms of the structure. These atoms displace from their equilibrium positions below PT due to the tilts of the octahedral groups.