bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Temperature Dependence of the Optical Second Harmonic Generation Coefficientd11of Quartz Homeotypic AlPO4(Berlinite)
Authors: Defregger S. , Engel G. F. , Krempl P. W. 
Published: July 2007

AbstractThe nonlinear optical properties of quartz homeotypic AlPO4(Berlinite) are studied. The second harmonic generation (SHG) coefficientd11is determined experimentally in the range from 296 to 783 K (the upper temperature limit is due to precipitation effects). At higher temperaturesd11decreases (approximately 35% decrease at 783 K). The order parameter associated with the α–β transition (at about 860 K) and derived from the measured temperature dependence ofd11agrees well with the corresponding results derived from previous birefringence measurements. Theoretical calculations using Levines bond charge model are also made at various temperatures up to the α–β phase transition. The strong decrease of the calculatedd11to values near zero about 25 K below the α–β transition is discussed in terms of the mean rotation angles of the AlO4and PO4tetrahedra as deduced from literature X‐ray data.
The Energy of Constrictions in Extended Dislocations
Authors: Püschl W. 
Published: July 2007

AbstractThe shape and energy of screw dislocation constrictions is calculated numerically according to the principles of linear, anisotropic elasticity theory, in contrast to previous treatments which did not correctly take into account all interaction energies. The energy of the whole constriction configuration can be conveniently written as the energy of two isolated half‐constrictions plus the energy of the completely compressed straight piece between them. Suitably normalized, the half‐constriction energy does not depend very strongly on specific material properties. In first approximation, it can be calculated by a simple rule, provided extension width or stacking fault energy are known.
Investigation of the Thermodynamic Properties of Anharmonic Crystals by the Momentum Method. III. Thermodynamic Properties of the Crystals at Various Pressures
Authors: Tang Nguyen , Van Hung Vu 
Published: July 2007

AbstractBy the momentum method established in the preceding papers the thermodynamic properties of strongly anharmonic crystals are considered with face‐centred cubic structure being under action of pressure. In the application properties as the thermal expansion coefficient, the specific heats cv and cp etc. at various pressures are calculated numerically for the inert gas solids and compared with experimental data.
Dynamics of Liquid Na0.5K0.5Alloy
Authors: Jain K. C. , Gupta N. , Saxena N. S. 
Published: July 2007

AbstractAn effort is made to study the motion of effective atoms in liquid Na0.5K0.5alloy in terms of velocity autocorrelation function, power spectrum, and mean square displacement analogous to the single particle motion in liquid metals employing the model developed by Glass and Rice in quasi crystalline approximation. The motions of effective atoms are also studied through the collective excitations by computing the longitudinal and transverse phonon frequencies. The results of collective excitations are in good agreement with the molecular dynamics (MD) results. Besides, results of thermodynamical properties such as isothermal bulk modulus and Debye temperature are also presented. The computed values are in good agreement with the results obtained by other theoretical calculations.
Remarks on the Thermodynamics of Sintering of Ceramics
Authors: Skala L. , Kenkre V. M. , Weiser M. W. , Katz J. D. 
Published: July 2007

AbstractIn the microwave sintering of some materials a rapid increase of their density is observed in a relatively small temperature range of about 100 K. This may be viewed as a transition from a metastable low density state to a more stable state with a density close to the maximum theoretical density. A thermodynamic description of this transition similar to the Landau theory of phase transitions is suggested and applied to the sintering of boron carbide and alumina.
Tight‐Binding Description of Surface States in Semiconductors
Authors: Kasandrov S. Yu. 
Published: July 2007

AbstractA matrix Green's function technique is used to find the surface band structure of the zincblende‐type semiconductors. A crystal is described by a tight‐binding Hamiltonian with interactions between nearest neigbours. The exact analytical expressions for the transfer matrices at the centre of the surface Brillouin zone are obtained and existence conditions of the surface states are discussed.
Collective Charge‐Density Excitations in Generalized Fibonacci Semiconductor Superlattices
Authors: Zhong J. X. , You J. Q. , Yan J. R. 
Published: July 2007

AbstractThe plasmon properties of generalized Fibonacci type I and type II semiconductor superlattices are studied by a dynamical‐map method. It is shown that the plasmon spectra are Cantor‐set‐like, i.e. the spectra are self‐similar and the gaps in the spectra are densely distributed.
Calculation of the Free Energy and the Pair Correlation Functions of Disordered Binary Alloys by the Method of Collective Variables
Authors: Yukhnovskii I. R. , Gurskii Z. A. , Chushak Ya. G. 
Published: July 2007

AbstractThe expressions of the free energy and the pair correlation functions for random binary alloys are obtained by means of the method of collective variables. The advantages of a new approach are discussed. The theory is exemplified by numerical calculations of the K‐Cs system properties. The calculated phase diagram is in agreement with the results obtained by other authors and with the experimental data. The analysis of the Fourier transform of the binary correlation function shows that the KcCs1−c alloys are similar to ideal solid solutions at high temperatures (T ≧ 300 K). As the temperature decreases, the deviation from the ideal solution increases. The short‐range order parameter at the first coordinate sphere is calculated.
Effect of Non‐Parabolic Band on the Scattering Rates of Free Electrons in High Purity Semiconductors at Low Lattice Temperatures
Authors: Ghorai A. K. , Bhattacharya D. P. 
Published: July 2007

AbstractThe scattering rates of the free electrons in a semiconductor depend upon the energy band structure of the material. No semiconductor possesses a parabolic energy band. The acoustic scattering rate of the free electrons for a non‐parabolic and band is well known for the high lattice temperatures when the scattering is effectively elastic. But when the lattice temperature is quite low ( <20 K) the scattering process becomes inelastic. The effect of the band non‐parabolicity on the acoustic and the piezoelectric scattering rates of the free electrons is investigated here under the condition when the lattice temperature is low. The same effect on the piezoelectric scattering rates at high lattice temperatures is also obtained here. Numerical calculations are carried out at different lattice temperatures for Si which has a low value for the non‐parabolicity factor and for InSb which has quite a high value for the same factor. The results are interesting and prompt one to take up further investigation.
Far‐Infrared Spectra of Crystalline Antimony Tri‐Iodide and Arsenic Tri‐Iodide
Authors: Anderson A. , Campbell J. A. 
Published: July 2007

AbstractFar‐infrared spectra of SbI3 and AsI3 in both single crystal and powder form at 20 K are reported. Principal features are identified through the predictions of a group theoretical analysis and by comparison with Raman data. Tentative assignments of the six infrared active modes are proposed. Certain anomalies are attributed to a partial breakdown of the molecular interpretation of the spectra and to the importance of interionic effects, especially for SbI3.
Optimal Density of States in the Fourier Space (k‐Space)
Authors: Schulz M. , Handrich K. 
Published: July 2007

AbstractThe orthogonality relations for a crystalline lattice are invalid for an amorphous solid. Therefore it is reasonable to determine a basic set, lying in the neighbourhood of the orthogonal system. A minimum problem, whose solution determines the optimal density of states in thek‐space, is formulated.
Spin Collective Oscillations in Two‐Dimensional Charged Fermi Liquids
Authors: Ahmad M. , Gladysz S. J. 
Published: July 2007

AbstractStarting from the transport equation for spin magnetization the transverse dynamic spin susceptibility is calculated in terms of the Landau two‐dimensional Fermi liquid parameters Bl. The formula allows to estimate the dispersion relation of spin waves with arbitrary l and the oscillator strength of the modes with l = 0, 1. The possibility of experimental determination of the parameters Bl with higher l is discussed.
The Einstein relation in quaternary alloys under different physical conditions
Authors: Ghatak K. P. , Mondal M. 
Published: July 2007

AbstractThe Einstein relation for the diffusivity—mobility ratio of the carriers in quaternary alloys is studied, taking the In1−xGaxAsyP1−y lattice matched to InP, by using the three‐band Kane model in bulk specimens, magnetic quantization, cross‐field configurations, and the low‐dimensional quantum confined structures of the same material under various quantization of band states by formulating the respective electron energy spectra. The same ratio is plotted with different physical variables in all the cases and the theoretical results are in agreement with the suggested experimental method of determining the Einstein relation in degenerate materials having arbitrary dispersion laws. In addition, the corresponding well‐known results of parabolic semiconductors are obtained from our generalized expressions as special cases under certain limiting conditions.
Semi‐ab initio tight‐binding band‐structure calculations of χ(3) (− 3ω; ω, ω, ω) in C, Si, Ge, SiC, BP, AIP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb
Authors: Moss D. J. , Ghahramani E. , Sipe J. E. 
Published: July 2007

AbstractA full band‐structure calculation is made of the dispersion, anisotropy, and magnitude χ(3) for optical third harmonic generation (THG) in C, Si, Ge, SiC, BP, AIP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb. The calculation is performed using a semi‐ab initio tight‐binding band‐structure technique and standard perturbation theory within the random phase approximation and neglect of local field corrections. The sign of χ(3) (0) is positive for all materials, consistent with experimental results from the literature. Trends are investigated in the periodic table in the structure of χ(3), and shown that the structure in most materials is dominated by 3ω resonances with either the E0 or E1 optical peaks, with the E2 critical points typically making a negligible contribution to χ(3).
On Extreme Dynamic Parameters of a Powerful Ion Beam–Metallic Target System
Authors: Boiko V. I. , Kishkin V. P. , Shamanin I. V. 
Published: July 2007

AbstractA model for the interaction of a power ion–beam a metallic target is briefly discussed. It is taken as a base for simulating numerically the interaction of a 1.5 MeV proton beam with an aluminium target at current densities up to 1.5 MA/cm2. The magnitudes of pressure applied to the target and recoil impulse of plasma scattered from the irradiated surface are found to tend to saturation. It is found that a heavy fraction present in the light ion beam diminishes the efficiency of providing the beam energy for a target.
Exciton Effects in the Reflectance Spectra of Mixed Lead Halides PbCl2xBr2(1 −x)
Authors: Certier M. , Erguig H. , Lumbreras M. 
Published: July 2007

AbstractThe reflectance spectra of orthorhombic single crystals of PbCl2xBr2(1 − x) (0 ≦ x ≦ 1) are studied in the spectral range between 3.5 and 4.8eV at 293, 95, and 39K. The strong peaks observed in these isomorphic solid solutions are attributed to cation exciton transitions. The fine structure of these exciton peaks is observed as a function of temperature and solid composition x. The coefficient of temperature dependence varies nearly linearly with composition for PbBr2 (x = 0), PbClBr (x = 0.5), and PbCl2 (x = 1). The variation of the singlet exciton peak with the fractional composition x shows two different regions: one for 0 ≦ x ≦ 0.5 and another one for 0.5 ≦ x ≦ 1.
Space‐Charge‐Limited Currents at High Electric Fields
Authors: Grekov E. V. , Sukhorukov O. G. 
Published: July 2007

AbstractThe steady‐state space‐charge‐limited current at high electric fields in an insulator or high‐resistance semiconductor with traps is analyzed theoretically. Poole‐Frenkel carrier emission from traps is considered. The analysis of the space‐charge centroid yields a current–voltage characteristic in analytical form. These results are compared with experimental data on the conductivity of Si3N4 films. The obtained characteristic gives a good fit to the observed relation between the current and the film thickness. The trap density in Si3N4 is determined to be (5 to 8) × 1018 cm−3.
Superconducting Transition Point in Dilute U and Be Solutions in V
Authors: Tiwari M. D. 
Published: July 2007

AbstractThe Green's function technique is applied to study theoretically the changes in phonon specific heat and transition temperature of V due to introduction of heavy (U) and light (Be) impurities. Changes in force constants (radial and angular), in mass and in volume are taken into account. The anharmonic effects due to large impurity motions are accounted for within the quasiharmonic approximation and the relaxations of the V neighbours of an impurity are also included. The electron–phonon and electron–impurity interactions are discussed. The calculated results are in good agreement with the experimental results for both the properties.
Reorientational Motion of NH4 Ions in (NH4)2SbF5 Quasielastic Neutron Scattering Study
Authors: Mukhopadhyay R. , Goyal P. S. , Rao K. R. 
Published: July 2007

Abstract(NH4)2SbF5 has orthorhombic structure at room temperature. It has two crystallographically inequivalent NH4 ions in the unit cell. Neutron quasi‐elastic scattering study is made of reorientational motion of NH4 ions in this salt. Experiments are carried out at 300, 180, and 160 K in the wave vector transfer region of 10 to 23 nm−1. Measured ratio of elastic to quasi‐elastic intensity as a function of wave vector transfer suggests that the two NH4 ions have similar reorientation times measurable within the time window of the spectrometer namely, in the range of 3 to 75 ps. The average form factor A(Q) and the average reorientation time, τ = (10 ± 3) ps, associated with the two NH4 ions are obtained. Broadening of the elastic peak is not seen at 180 or 160 K. This suggests that at these temperatures the value of τ is more than 75 ps.
Dynamics of Liquid Metals
Authors: Gupta N. , Jain K. C. , Saxena N. S. 
Published: July 2007

AbstractSingle particle motion and collective excitations for group IIA elements (Mg, Ca, and Sr) are presented at their respective melting temperatures. The theory developed by Glass and Rice in static harmonic well approximation is applied for the study of the dynamical variables. Three independent theories viz. theory of amorphous solid, Hubbard and Beeby approach, and a model approach given by Bhatia and Singh are applied to study the collective excitations in terms of longitudinal and transverse phonon frequencies in these metals. Besides, some thermodynamic properties are computed. It is observed that the theories of Takeno and Goda and Hubbard and Beeby describe collective excitations in these liquid metals in close agreement whereas the model approach of Bhatia and Singh underestimates the phonon frequencies.
Investigation of the Role of Excited States in the Impurity Breakdown Development
Authors: Danilchenko B. A. , Komirenko S. I. , Rozhko S. Kh. 
Published: July 2007

AbstractI–U characteristics of n‐Ge:Sb samples with impurity concentrations of Nd = 2 × 1016 cm−3 are of S‐shape at the temperature of liquid He. The depth of the NDC‐region increases with lowering the temperature and with application of uniaxial stress along the 〈111〉 direction. This fact is explained within the framework of the “three‐level” mechanism of the impurity breakdown. Nonequilibrium ballistic phonons ionise excited states of impurity atoms abundantly populated in pre‐breakdown fields, and cause the development of breakdown, that approves the model discussed.
Ground State Energy of an Exciton Coupled to Acoustic Phonons in 2D Nonpolar Crystals
Authors: Xiao Jing‐Lin 
Published: July 2007

AbstractSome properties of an exciton both, strongly and weakly coupled with acoustic phonons via the deformation potential in 2D nonpolar crystals are studied. The effective Hamiltonian of the surface exciton is obtained by the method of a linear‐combination operator and a simple unitary transformation. The self‐trapping energy and the effective electron–hole interaction potential of an exciton may be written as a series α(α), the first term being proportional to α1(α2) the coupling constant.
Structural and Dynamical Properties of Solid Solutions of BaF2 and GdF3. An EPR Study
Authors: Den Hartog H. W. 
Published: July 2007

AbstractResults of EPR experiments on solid solutions of barium and gadolinium fluoride in the temperature range 300 to 900 K are presented. At room temperature the Gd‐ions are located predominantly at trigonal sites. If the temperature is increased, the interstitial fluoride ions are found to dissociate from the dipolar complexes, and cubic Gd‐centers are formed. The transition of the Gd‐ions from the trigonal symmetry to the cubic one occurs in qualitatively the same temperature region for GdF3 concentrations between 0 and 4 mol%. For low Gd‐concentrations and moderate temperatures the widths of the cubic EPR lines vary only slightly with increasing temperatures. The widths of these lines increase rapidly with T at high temperatures. The increasing linewidths are associated with the increasing avarage mobility of the interstitial fluoride ions present in the crystals. For heavily doped samples the distance between the Gd‐centers is small. Consequently, the EPR lines of the cubic Gd‐ions are broadened due to the rapid jumps of the highly mobile interstitial fluoride ions of nearby dipoles.
Spin‐1 Random‐Bond Transverse Ising Model with Competing Interactions
Authors: Yang Chuan‐Zhang , Zhong Jia‐Lin , Jiang Xue‐Fan 
Published: July 2007

AbstractThe longitudinal magnetization, the transverse magnetization, and the order parameter y of the spin‐1 random‐bond transverse Ising model with competing interactions on a diamond lattice are discussed within the framework of the effective‐field theory. The phase diagrams of the system are obtained. The possible reentrant phenomena displayed by the system and the influence of random parameters α and p̄ on the behavior of the system are investigated.
An Extended Polarizable Point Ion Model for Schottky Defects
Authors: Banhatti R. D. , Murti Y. V. G. S. 
Published: July 2007

AbstractThe polarizable point ion model for Schottky defects is extended to include the effects of induced quadrupoles in region 1. Schottky defects in AgCl are studied using this model. It is found that it is important to include induced quadrupole moments in any theoretical treatment of charged point defects in ionic crystals. Quadrupolar deformations make sizable contribution to the defect energy which ranged from −0.2 to −0.4 eV in the case of the cation vacancy over the range of anion quadrupole polarizabilities studied. The work further points to the relative significance of chlorine ions in respect of the quadrupole distortions.
γ‐Fe Precipitation in Cu97Fe3 and Cu75Au24Fe1
Authors: Klein J. , Campbell S. J. , Aubertin F. , Gonser U. , Schneeweiss O. 
Published: July 2007

AbstractA series of isothermal and isochronal heat treatments (300 to 800 °C; 0 to 92 h) is used to compare the precipitation of f.c.c. γ‐Fe in Cu97Fe3 with that in Cu75Au24Fe1 as determined by room temperature Mössbauer spectroscopy. The precipitation process is similar in both systems with up to 90% and 70% of the Fe in Cu97Fe3 and Cu75Au24Fe1, respectively, being precipitated in the form of γ‐Fe. Low temperature measurements (15 K) in zero and applied magnetic fields (5.3 T) on γ‐Fe in the Cu75Au24Fe1 sample show magnetic behaviour similar to that of the familiar low moment, low atomic volume γ1‐state of Fe rather than the high moment γ2‐state expected of this matrix of high atomic volume.
Magnetophonon Resonance on Three Types of Carriers in p‐InSb
Authors: Ugrin Yu. O. , Sheregii E. M. 
Published: July 2007

AbstractFor the first time in a single experiment the magnetophonon resonances of three types of carriers in p‐InSb are investigated: light holes (MPR1), heavy holes (MPRh), and electrons (MPRe). From the temperature shift of the ground series (most intensive ones) of MPR1 and MPRh the valence‐band parameters of the band structure as function of temperature are calculated. The investigation completed allows for the first time to identify nonearlier observed two‐phonon transitions in p‐InSb, alongside with an additional series of peculiarities: a satellite of the main MPRh series peaks at weak magnetic fields. The comparison of MPRh of two samples with different mobilities of heavy holes lead to the observance of a distortion in the period of the transverse field of the main MPRh series in the sample of less mobility of heavy holes.
Neutron Scattering Studies of C6H12 and C6D12 Cyclohexane under High Pressure
Authors: Mayer J. , Urban S. , Habrylo S. , Holderna K. , Natkaniec I. , Würflinger A. , Zajac W. 
Published: July 2007

AbstractThe results of inelastic neutron scattering (INS) and neutron diffraction (ND) studies of both, C6H12 and C6D12 cyclohexane under hydrostatic pressure (up to 3.7 × 108 Pa) and in the temperatures down to 160 K, are reported. All the solid phases (three in C6H12 and four in C6D12) are well seen in the INS and ND experiments. The lattice vibration spectra strongly depend on the crystal phase, on the applied pressure, and on the isotopic substitution. In view of the complementary Raman spectroscopy results (under atmospheric pressure) it is concluded that the molecular dynamics plays a decisive role in the mechanism of the consecutive phase transitions in cyclohexane.
Band Structure and Nonlinear Optical Susceptibilities of Proustite (Ag3AsS3)
Authors: Dovgii Ya. O. , Kityk I. V. 
Published: July 2007

AbstractTheoretical and experimental investigations are made of the band structure of proustite (Ag3AsS3). The calculation is performed using the tight‐binding method. As scale factors in the corresponding secular equation the experimental results of VUV‐reflection are used in the spectral region 2 to 30 eV. The contribution of different electronic states to the electronic bands are obtained. From the calculated band energy structure and infrared spectra the influence of the cluster vibrations on the nonlinear susceptibilities is estimated and the contribution of the electronic and ionic part to the electrooptical tensors is separated.
Phonon‐Polaritons in Isotropic Ferromagnets II. Polaritons Due to Magnon‐Phonon Excitations
Authors: Dimitriev O. P. , Lozovskii V. Z. , Getsko O. M. 
Published: July 2007

AbstractThe possibility of phonon‐ and magnon‐polaritons coupling in the volume and on the surface of a polar ferromagnetic isolator is theoretically investigated. Conditions under which excitations of new type waves, magnon‐phonon polaritons, occur are found. It is shown that the properties of these waves may be efficiently guided by applied magnetic fields, which can be used to make new devices in the infrared.
Magnetic Properties and Structure of (CrxAl1‐x)2O3 Solid Solutions
Authors: Viktorov V. V. , Evdokimov I. V. , Fotiev A. A. 
Published: July 2007

AbstractStatistical homogenity of (CrxAl1‐x)2O3 solid solutions is investigated. It is shown, that there may be distinguished the region of statistical regularities and regions where prevail the clusters of two, three, and four chromic ions (III). The formation mechanism of solid solutions mentioned is proposed.