bluuebunny/crossref_metadata_2025 huggingface dataset:
The Peculiarities of the Electronic Structure of BaTiO3 in the ATiO3 (A = Ca, Sr, Ba) Series
Authors: Nemoshkalenko V. V. , Timoshevskii A. N.
Published: July 2007

The electronic structure of ATiO3 (A = Ca, Sr, Ba) titanates is studied by the APW and Xα‐SW methods. The degree of participation of atom A states in formation of the valence band and the conduction band is shown to grow in this order. The results are confirmed by X‐ray emission and XPS experimental data. The peculiarity of the electronic structure of BaTiO3 is the presence of Ba 5p, 5d, 4f levels in the vicinity of the valence band and the bottom of the conduction band. Due to this fact in the investigated series of the compounds the Ti‐O interaction is weakened in BaTiO3.
F‐Centres in KCl–Tl Crystals
Authors: Nagli L. E.
Published: July 2007

The infrared emission and photostimulated luminescence under excitation in F‐absorption band are investigated in KCl–Tl crystals coloured by X‐ray or by KrF‐laser pulses at 12 or at 290 K. Basing on the concentration, temperature, kinetic, and spectral dependences of these emissions, it is proposed that the main part of the F‐centres is created at distances smaller than 12a from Tl+ and Tl2+ ions.
Electron–Phonon Scattering and Low‐Temperature Thermal Conductivity of Niobium and Tantalum Single Crystals
Authors: Wasserbäch W.
Published: July 2007

The thermal conduction of niobium and tantalum single crystals of different impurity contents is measured below 20 K. The investigation of the lattice thermal conductivity as limited by the interaction of phonons with electrons demonstrates that both, longitudinal and transverse phonon modes are scattered strongly.
The Study of Tl 〈110〉 Centres in NaCl and RbCl
Authors: Nistor S. V. , Schoemaker D. , Ursu I. , Yang B. R.
Published: July 2007

The presence of 〈110〉 oriented Tl centres is confirmed in the ESR spectra of heavily doped NaCl:Tl+ and RbCl:Tl+ crystals following X‐irradiation. This identification is supported by an analysis of the spin‐Hamiltonian parameters as well as by the formation and optical bleaching properties, which are similar to the previously reported optical‐absorption and ESR studies on Tl〈110〉 centres in KCl. An analysis of the spin‐Hamiltonian parameters in the frame of a molecular‐orbital model is presented.
Long‐ and Short‐Range Magnetic Interactions in EuO
Authors: Averous M. , Desfours J. P. , Vellas J. R.
Published: July 2007

In Eu‐rich EuO (EuS), the resistivity versus temperature shows an insulator‐metal transition, and in some cases a shoulder and a peak situated above the Curie temperature when T increases. Especially the shoulder temperature range is studied. It is shown that this region has a De Gennes‐Friedel‐type behavior whereas the peak region exhibits a Fisher‐Langer‐type behavior. The long‐range magnetic interactions in the shoulder temperature range are due to the existence of bound magnetic polarons. These interactions are emphasized either by magnetic field or by increasing of the Eu excess, i.e. bound magnetic polaron concentration.
Empirical Tight‐Binding Band Structure of Wurtzite Semiconductors SiC, ZnSe, and ZnTe
Authors: Tuncay Ç. , Tomak M.
Published: July 2007

The electronic energy band structures in an sp3 tight‐binding model of the wurtzite semiconductors SiC, ZnSe, and ZnTe are reported.
Tensorial Coupling and the Reduced Matrix Elements of One‐ and Two‐Body Operators
Authors: Tuszyński J. A. , Dixon J. M.
Published: July 2007

The reduced matrix elements of products of tensor operators, coupled to form a non‐zero rank, are investigated to emphasize the importance of correctly incorporating all tensorial couplings. It has recently been realized that serious inaccuracies can arise, in some cases, unless the complete many body nature of the full operator and the states involved is properly incorporated. Exact results are presented for one‐ and two‐body operators which include all couplings and compare and contrast them with some approximate methods.
Stimulated Brillouin Scattering of High‐Power Helicon Waves in Longitudinally Magnetized Cubic Piezoelectric Semiconducting Plasmas
Authors: Ghosh S. , Saxena R. B.
Published: July 2007

A detailed analytical investigation is made of the stimulated Brillouin scattering of a high‐power helicon pump wave propagating parallel to the applied magnetic field in an n‐type cubic piezoelectric semiconducting plasma belonging to class 43m. A general dispersion relation is obtained by using the hydrodynamic model of a homogeneous, piezoelectric, one‐component (electron) semiconducting plasma, and the threshold value of the pump electric fields and the initial growth rates of both the excited modes (i.e., in the cases of left‐hand and right‐hand circularly polarized modes) well above the threshold are discussed. The analysis is applied to a specific semiconductor, n‐InSb at 77 K, duly irradiated by a high‐power helicon wave for numerical estimations. The laser field intensities used are in the range of 107 to 1011 Wm−2 which is assumed to be less than the damage threshold of the InSb crystal. The order of wave amplitude is experimentally feasible.
On the Temperature Behaviour of DC Conductivity in One‐Dimensional Conductors above Tc
Authors: Dieterich K. , Wagner M.
Published: July 2007

An ab‐initio single particle theory is presented for the temperature behaviour of electrical transport in one‐dimensional conductors. The calculation of the conductivity is based on a Kubo‐Moriformalism. The Kohn mode‐softening near the Peierls temperature is taken into consideration in a new approximation step for the calculation of the relaxation time, which is beyond a mean field calculation. For temperatures sufficiently above Tc the T−1 law of the semiphenomenological earlier calculations is obtained, whereas close to the Peierls temperature a high maximum caused by the Kohn anomaly is found. This conductivity peak depends very sensibly on the quotient of the Debye temperature and the Peierls transition temperature. The calculation permits the suggestion that in the commensurate phase at high pressure single particle excitations provide the dominant conduction path far above Tc.
Temperature Dependence of the Elastic Constants of p+ Silicon
Authors: Khan F. S. , Allen P. B.
Published: July 2007

The free hole contribution to the elastic properties of p‐type silicon is investigated. A wide range of doping concentration, from 1017 to 1020 cm−3, and temperature variation, from 100 to 500 K, is considered. Numerical calculations are given for the free hole contribution to the elastic constants. Effects of temperature variation are investigated and numerical results are given for the temperature coefficients of the elastic constants of p+ silicon.
Analysis of the Equation of State of Ammonium Halides
Authors: Agrawal S. C.
Published: July 2007

An analysis of the equation of state is performed for the ammonium halides. The variation of volume with pressure is calculated using interionic potentials including the effect of short range overlap repulsive energy up to next nearest neighbours. The van der Waals dipole‐dipole and dipole‐quadrupole interactions derived from the variational method are also taken into account. The results are discussed and compared with available experimental data.
Structure and Bonding in Cubic IV–VI Crystals. V. Lattice Repulsion. Comparison of Lattice and Vibronic Anharmonicity
Authors: Enders P.
Published: July 2007

Two simple models for the lattice repulsion forces are applied to cubic IV–VI crystals giving semiquantitative results. Nor the lattice nor the vibronic contribution to the anharmonic coefficients of the Landau free energy expansion is negligible in these materials, for what a simple criterion is derived.
Formation of Localized Magnetic Moments in Chromium‐Manganese Alloys
Authors: Aidun R. , Arajs S. , Moyer C. A.
Published: July 2007

The electrical resistivity (ϱ) and magnetic susceptibility (χ) of CrMn alloys containing 2, 8, 10, 13, and 16 at% Mn are studied as a function of temperature (T). Both the ϱ−T and χ−T curves exhibit characteristic anomalies at the Néel temperature (TN). Careful analyses of the χ data by several methods all suggests the existence of a magnetic moment on the Mn impurities below and above TN. These results are discussed briefly from the standpoint of previous investigations and compared with the behavior exhibited by Fe and Co impurity moments in the Cr matrix.
Frequency‐Dependent Conductivity Studies of the Ordered and Disordered Phases of Ag2HgI4 and Cu2HgI4
Authors: Sudharsanan R. , Clayman B. P.
Published: July 2007

Far infrared reflection and transmission properties of Cu2HgI4 are measured in the region 10 to 200 cm−1 for both, α‐ and β‐phases. The TO and LO mode frequencies are obtained from a Kramers‐Kronig analysis of the reflection spectra. Frequency‐dependent conductivity is calculated from the values of ε″ in the region 10 to 200 cm−1 for both phases. The conductivity spectra of α‐Ag2HgI4 and α‐Cu2HgI4 are analysed using the Kostadinov and Vu Thi Binh model. It is concluded that the mobile ions (Ag+ and Cu+) have two different sites ofo ccupation during their conduction process. It is suggested that other than regular tetrahedral sites, the mobile ions may occupy interstitial sites, in good agreement with the observations of Kasper and Browall and the Wiedersich and Geller model for the conduction process in these materials.
Phonon‐Dislocation Scattering and Low‐Temperature Lattice Thermal Conductivity of Niobium and Tantalum Single Crystals Deformed at Low Temperatures
Authors: Wasserbäch W.
Published: July 2007

The thermal conduction of niobium and tantalum single crystals plastically deformed in steps at low temperatures is measured between 0.3 and 20 K. The dislocation arrangement is studied by X‐ray topography and transmission electron microscopy. The thermal resistivity Wd due to the plastic deformation deduced in the temperature range 0.3 K < T < 5 K is found to be proportional to about T−3 after weak deformation. Strong deformation gives rise to a thermal resistivity proportional to T−2. The results are consistent with the model of scattering of phonons by the static distortion field of dislocations.
Influence of Cationic Vacancies on the Mobility of Li+ Ions in Some Cation‐Deficient Materials. An NMR Study
Authors: Latie L. , Villeneuve G. , Cros Ch. , Hagenmuller P.
Published: July 2007

7Li NMR is carried out between 150 and 450 K in Li‐deficient chlorides with LiCl‐type or the related Suzuki‐type structure. Diffusive motion of Li+ ions is observed and the analysis of experimental data for Li1−2xMgxCl with x = 0.01 shows that the introduction of 1% vacancies into the lattice enhances the Li+ mobility by a factor of 30 at 440 K. By increasing the number of vacancies, the activation energy decreases down to 0.38 eV for ordered Li6VCl8 which contains 12.5% vacancies and even to 0.25 eV for the disordered phase corresponding to the same composition.
Some Photoluminescence Properties of Mn2+ in Magnesium Bromide
Authors: Mićić R. , Drašković B.
Published: July 2007

Synthesis and photoluminescence are reported of two phosphors whose basis lattice is MgBr2 · 6H2O. In the first case Mn2+ ions as impurity are introduced in this basis and in the second case Mn2+ and Zn2+ ions. For both the phosphors it is shown that the absorption‐emission center is a manganese Mn2+ ion. In the first case the Mn2+ ion is located in octahedral coordination, reaching this state through an isomorphic substitution of the Mg2+ ion. In the second case, depending on the relative concentration of Zn2+ ions in comparison to Mn2+ ions, the Mn2+ ion may exist in octahedral, tetrahedral, and quasi‐tetrahedral coordination, causing the appearance of three emission bands in its luminescence spectrum. Zn2+ impurities cause two effects: they influence the change of ligands and the site symmetry of the Mn2+ ion and, simultaneously, distort the symmetry of the complex MnCl2+4. It follows that an adequate choice of concentration of ZnCl2 impurities enables one to manage indirectly the emission of Mn2+ in these phosphors.
Magnetic Symmetry in Several Tetragonal Compounds
Authors: Luchian H.
Published: July 2007

All the non‐helical spin arrangements which can be supposed to arise in the sites 4c and 4e in several tetragonal compounds crystallizing in the space group I4/mmm are proposed using a well known group theoretical method derived from the Landau theory of the second order phase transitions. The investigation is based only on black and white symmetry arguments.
1H‐NMR Spectra of Molecular Groups in a Paramagnetic Matrix
Authors: Birczyński A. , Lalowicz Z. T.
Published: July 2007

Proton NMR spectra of molecular groups (NH+4, H2O) in a diluted matrix of paramagnetic spins are presented and compared with experiments. The sensitivity of the spectra to the paramagneticantiferromagnetic transition is discussed. Fits to experimental lines for antiferromagnetic ammonium salts (NH4)2IrCl6, (NH4)2RhCl6, and paramagnetic CoCl2 · 6 H2O are shown. The range of effective local magnetic fields is evaluated.
Adequacy of the Nearest‐Neighbour LCAO Model Hamiltonian for the F.C.C. Transition and Noble Metals
Authors: Smith P. V.
Published: July 2007

The value of model Hamiltonians as interpolation schemes for studying the electronic properties of a wide variety of systems is now well known. In particular, the mixed basis schemes of Hodges et al., Mueller, and Smith and Mattheiss are extensively applied in determining theoretical photoemission spectra for the f.c.c. transition metals, and in studying the role of impurities in these systems. Unfortunately, however, such schemes are not suitable for studying strongly localized defects, bulk elastic properties or surfaces because of the extended nature of their plane wave basis functions. A novel approach to calculating such properties involves the use of the Chadi total energy algorithm which is based on a nearest neighbour LCAO model Hamiltonian description of the host metal bandstructure. The main objective of this present paper is thus to assess the adequacy of the empirical tight‐binding method within the nearest‐neighbour approximation, in describing the electronic structure of the f.c.c. transition and noble metals. Using copper as a prototype system, it is shown that such a simple LCAO representation can indeed yield band structures and density of state curves which are comparable in accuracy with those of the mixed basis sets. The employment of this simple LCAO model within the Chadi scheme for the determination of therelaxation of f.c.c. transition and noble metal surfaces is then discussed.
Zero Energy Gap Conditions and Band Inversion in Superlattices
Authors: de Dios Leyva M. , Gondar J. López
Published: July 2007

Using the envelope‐function approximation and the transfer‐matrix method, for k⟂ = 0, the wave functions, the dispersion relation, and the zero energy gap conditions connected with light particles (electrons and light holes) in GaAs‐AlxGa1−xAs and InAs‐GaSb superlattice are obtained. One of the obtained zero energy gap conditions is a direct consequence of the spatial dependence of the energy gap. Also studied, in detail, are the properties of those states for which the lowest conduction band and the highest valence band touch each other. It is established that with increasing magnitude of the conduction band‐valence band edge discontinuity, or of layer thickness, the band inversion phenomenon occurs. Finally, some numerical results for the InAs‐GaSb superlattice are reported.
A Study of the Electronic Structure of Rare Earth Hexaborides
Authors: Grushko Yu. S. , Paderno Yu. B. , Ya. Mishin K. , Molkanov L. I. , Shadrina G. A. , Konovalova E. S. , Dudnik E. M.
Published: July 2007

X‐ray lineshifts of rare earth elements in the hexaborides of La, Ce, Pr, Nd, Sm, Eu, Gd, Yb, and Y relative to the corresponding tri‐ or difluorides are measured by the crystal diffraction method. The experimental shifts are compared with the values obtained in relativistic self‐consistent field calculations in the effective free ion approximation. The hexaborides of La, Ce, Pr, Nd, and Gd are shown to have 4fn‐15d configuration (4d for Y), and those of Eu and Yb, 4fn configuration. The shifts obtained for Sm in SmB6 support the suggestion that Sm is here in an intermediate valence state and is best described by the 4f6−x5dx configuration with x = 0.615 ± 0.007.
Brillouin Zones and Fundamental Regions
Authors: Jones G. A. , Landsberg P. T.
Published: July 2007

The n‐th Brillouin zone is defined to be the set of points in reciprocal space which have the origin as their (not necessarily unique) n‐th nearest lattice‐point. From this definition it is shown that (a) all zones have equal volumes and (b) each zone can be translated into the first zone so as to fill it exactly by translating different pieces of the zone by appropriate reciprocal lattice‐vectors. The argument, being purely geometrical, does not require appeal to periodic boundary conditions, the Schrödinger equation or similar results from the physics of the solid state. A connection with the more general “fundamental regions” is also pointed out.
Calculation of the EEE Parameters at Annealing of the F‐Centres in NaCl Crystals
Authors: Gerasimov A. B. , Merkin M. M. , Tsertsvadze A. A.
Published: July 2007

Within the frames of a previously suggested mechanism an elementary act of exoelectron emission resulting from annihilation of an F‐centre and interstitial negative halogen ion in a NaCl crystal is discussed. The dependence of the EEE parameters on the crystal orientation is studied. Energy spectra and exoemission parameters are obtained for three different crystal orientations. There is good agreement between the theory and experimental results.
Static Polarizability and Dipolar Surface Plasmon of Small Metal Particles
Authors: Bao Tran Thoai Duy
Published: July 2007

The frequency of the dipolar surface plasmon of small metal clusters is calculated using the sum rule techniques due to Lushnikov et al. The effect of surface diffuseness of electron density is included. The screening of the electrons is described within the Thomas‐Fermi approximation. A red shift of the surface plasmon frequency is obtained.
Picosecond Processes of Laser‐Excited Carriers in Silicon on Sapphire
Authors: Bergner H. , Brückner V. , Kerstan F. , Nowick W.
Published: July 2007

The relaxation processes on a ps‐time scale in silicon on sapphire, ion‐beam damaged SOS and hydrogenated ion‐beam damaged SOS are studied by means of time‐resolved reflectivity and photoconductivity measurements. The excitation wavelength is changed to excite the carriers either near to the band edge or into the conduction band. Therefore, it is able to distinguish between different relaxation processes. The results can be explained using a 4‐level model. The influence of the amorphization of samples on the relaxation time is discussed.
Temperature Dependence of Fourth‐Order Elastic Constants of Alkali Halide Crystals
Authors: Varshney R. K. , Shanker J.
Published: July 2007

A method for evaluating the temperature dependence of fourth‐order elastic constants (FOEC) of NaCl as well as CsCl‐structure alkali halides is developed on the basis of the phonon‐pressure theory. Eleven distinct values of FOEC for each alkali halide crystal are calculated at 0 K and at room temperature (300 K). The pressure derivatives of second and third‐order elastic constants are calculated at both the temperatures. The method is based on the phonon‐pressure theory incorporating Lundqvist's three‐body potential. The second‐order temperature derivatives of second‐order elastic constants are also evaluated. The results obtained are discussed and compared with other investigations. The importance and significance of temperature contributions to various order elastic constants are discussed.
Investigation of the Equation of State and the Grüneisen‐Anderson Parameters for Fluorite‐Structure Crystals
Authors: Dutt N. , Agrawal G. G. , Shanker J.
Published: July 2007

Investigations of the equation of state describing the relationship between pressure and volume are presented for seven fluorite‐structure crystals viz., CaF2, SrF2, BaF2, PbF2, Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2. Recently developed interionic potentials, which take into account three‐body interactions also, are used for calculating the compression values corresponding to very high pressures. Calculations are also performed for the Grüneisen parameter and its volume derivative, the Anderson parameters, and the volume thermal expansion coefficient. The results are compared with available experimental data and also with those calculated by other workers. The nitrates are found to be much more compressible than the corresponding fluorides under the effect of high pressure.
Effects of Strains on the Dynamic Effective Charge of III–V Semiconductors
Authors: Anastassakis E. , Cardona M.
Published: July 2007

A calculation is made of the anisotropy induced by an external stress on the dynamic effective charge of zincblende‐type semiconductors. This derivation is based on the semiempirical bondorbital model for the effective charge, and on the stress‐induced changes of the latter due to bond deformation and internal lattice displacements. Numerical application to specific materials shows that the effect can be significant. The results are in reasonable agreement with existing experimental information.
Radiative Recombination at Centres in Germanium–Silicon Solid Solutions
Authors: Lyutovich A. S. , Lyutovich K. L. , Popov V. P. , Safronov L. N.
Published: July 2007

The changes occuring in the spectra of exciton‐impurity complexes (EIC) and in the spectra caused by radiation defects (electron‐oscillating series with the head lines of 1.0097 and 1.0186 eV) according to the content of GexSi1−x solid solution in the range of x < 0.1 are studied. Substantial variations of the shift and the width of the spectrum lines of different types of the centres with the solid solution content are found. The problems of GexSi1−x content influence on the luminescence spectra characteristics caused by different recombination mechanisms are discussed. It is concluded that the lines of 1.0097 and 1.0186 eV are conditioned by the internal transition of electrons from an excited state of the active centre into the ground one.
Emission Processes in Luminescence and Thermally Stimulated Luminescence of Ag‐ and Ca‐Doped KCl
Authors: Bhuniya R. C. , Sridaran P. , Ratnam V. V.
Published: July 2007

Luminescent emission during X‐ray excitation at room temperature and above as well as during TSL glow is studied for KCl, undoped and doped with Ag and Ca. It is observed that the spectral character of the emission is the same during both the processes in each of the crystals. In all the samples certain emissions occur at the same wavelength region, (I) 540 to 560 nm, (II) 430 to 445 nm, (III) 420 to 430 nm, and (IV) 385 to 410 nm during X‐irradiation and during TSL glow irrespective of the impurities present, which are intrinsic to the lattice. Emissions in the wavelength regions (V) 280 to 290 nm, (VI) 260 to 270 nm, and (VII) 580 to 620 nm are characteristic of Ag impurity. Recombination centres and recombination sites of the different emissions are explained.
Calculation of Lattice Sums
Authors: Kozarzewski B.
Published: July 2007

A fast converging method of treatment of the lattice sums is presented. The method covers wide class of sums appearing in different solid state problems.
An Interpolytypical Transition in NbS2
Authors: McMullan W. G. , Irwin J. C.
Published: July 2007

Raman scattering experiments are carried out on single crystals of 2H‐NbS2. From the results it appears that some crystals undergo a transition to the 3R‐polytype as the sample temperature is lowered. The transition is observed to be continuous and reversible. It is postulated that the transition is driven by an incipient charge density wave.
Density Functional Pseudopotential Calculation of the Cohesive Properties of Disordered Solid Alloys of Alkaline‐Earth Metals. Influence of the Ionic Pseudopotential
Authors: González D. J. , Zapata C. M. , Alonso J. A.
Published: July 2007

A density functional pseudopotential method is used to calculate the compressibility of alkaline‐earth metals and the cohesive properties of disordered solid binary alloys formed between those metals. Two pseudopotentials are used, namely, the empty‐core model potential and Shaw's pseudopotential. It is found that the results are very similar, although the empty‐core model potential leads to slightly better predictions in comparison with experiment.
The Effect of Spin–Vibrational Interaction in Magnetic Properties of Exchange Tetraclusters
Authors: Polinger V. Z. , Chibotaru L. F. , Bersuker I. B.
Published: July 2007

The magnetic properties are considered of cubic crystals of tetrahedral copper tetraclusters of the type Cu4OX6L4, in the case when each copper ion is orbitally nondegenerate, under the assumption of strong spin‐vibrational interaction with E‐type cluster distortions. It is shown that within this model for all possible values of the exchange parameters the temperature dependence of the effective magnetic moment of the system is monotonous, and hence the four‐centre (pseudo) Jahn‐Teller effect is concluded to be the most probable reason of the anomalous magnetic properties of the copper tetraclusters.
Determination of Effective Indirect Exchange Interaction Integrals in Ferrimagnets
Authors: Sidorov A. A. , Suetin V. P. , Pokazaniev V. G. , Karpenko B. V.
Published: July 2007

In terms of a collinear two‐sublattice ferrimagnet a statistical method of estimating exchange interaction integrals is developed. Using the Mössbauer spectroscopy data for the temperature induced variation of the spontaneous magnetization of tetra‐ and octahedral sublattices and the temperature dependence of inverse susceptibility the stable and unambigious estimates of exchange integrals for Y3Fe5O12 and Li0.5Fe2.5O4 are developed.
The General Theory of the Dynamic Susceptibility in Thin Ferromagnetic Films
Authors: Świrkowicz R.
Published: July 2007

The transverse dynamic susceptibility of thin ferromagnetic films is calculated within the framework of RPA by using of the method of equation of motion. A representation in which the general multiband Hamiltonian is diagonal in the Hartree‐Fock approximation is consequently used in all calculations. The expression, obtained in the paper for the dynamic susceptibility of thin films represents a generalization of the formula obtained by Cooke for bulk crystals. Certain approximations which allow to deal with this general formula are also discussed.
Optical and Magnetic Investigations of Some NiAs‐Type Transition Metal Compounds
Authors: Neitzel U. , Bärner K.
Published: July 2007

The reflectivity and the logarithmic derivative of the reflectivity is measured as a function of quantum energy (1.3 eV < ħω < 4.7 eV) and temperature (10 K < T < 300 K) for several NiAs‐type compounds: NiAs, NiSb, MnAs, MnSb, Ni0.95Mn0.05As, Ni0.8Mn0.2As, and Ni0.5Mn0.5As. The optical constants are consistent with existing bandstructure calculations for the nonmagnetic compounds NiAs and NiSb. This is not so for the ferromagnetic compounds MnAs, MnSb, and for the mixed crystals; in particular, for the mixed crystals the magnetic susceptibility indicates that Mn builds up a local moment.
Optical Properties of β′‐AuZn by Wavelength‐Modulated Derivative Spectroscopy
Authors: Stearns R. , Braunstein R. , Muldawer L.
Published: July 2007

Derivative spectra of the optical properties of β′‐AuZn are obtained using wavelength‐modulated spectroscopy between 1.5 and 5.1 eV. Assignments are made for the interband transition at the M point of the Brillouin zone which fix the transition energies with an accuracy previously unattained.
Energy Transfer Mechanisms in the NaCl:Pb++, Mn++ System along Aggregation Processes
Authors: Capelletti R. , Manfredi M. , Solzi M.
Published: July 2007

The non‐radiative energy transfer mechanisms between Pb++ (donor) and Mn++ (acceptor) ions in NaCl:Pb++, Mn++ system are examined at different aggregation stages of the impurities. Mn++ ions are characterized by a series of absorption bands partially overlapping the emission bands of Pb++ aggregates peaking at 380, 430, and 500 to 530 nm. The energy transfer mechanism connected with Pb++‐380 nm emission band is based on a resonant single pair interaction, while the transfer process connected with 430 nm and 500 to 530 nm emission bands can be explained on the basis of a fast energy migration within the donor system followed by a final transfer, donor–acceptor, that is resonant for the transfer connected with 430 nm band and phonon assisted for the transfer connected with the 500 to 530 nm band.
The Resistance of a One‐Dimensional System with a Stationary Random Potential which is a Markov Process
Authors: Potapenko S. Yu. , Satanin A. M.
Published: July 2007

The zero‐temperature de resistance of a one‐dimensional disordered system with a random potential which is a Markov process is investigated. A universal expression for the probability distribution for the logarithm of the resistance in the weak scattering limit is obtained. Disordered systems with typical random non‐Gaussian po tentials are considered.
Temperature Dependences of Conductivity at Small Electron Mean Free Path
Authors: Katsnelson M. I. , Shcherbakov A. S.
Published: July 2007

It is demonstrated by consideration of available experimental data that the unusual temperature dependence of the conductivity σ(T) = σ0 + A exp [–B/T1/(1 + d)], d being the dimension, is typical for different disordered systems with a small electron mean free path. A possible explanation of this dependence is proposed in the framework of a model with two kinds of weakly hybridized electron states, taking into account phonon‐induced transitions between them. It is assumed that such dependence σ(T) is a characteristic one for systems near the Mott transition.
Unambiguous Determination of Interatomic Force Constants of Crystals by Coherent Inelastic Neutron Scattering
Authors: Kohl H.
Published: July 2007

The interatomic force constants in a crystal can be obtained experimentally by measuring both the frequency and a corresponding eigenvector of each phonon mode. The measurement of the double differential cross section does not generally suffice to determine the eigenvector unambiguously. It is shown that by orienting the crystal near a Bragg position it is possible to obtain additional information on the eigenvector. An experimental procedure is proposed which should yield unambiguous values for the force constants.
The Phase Diagram of TbPO4 Measured by Linear Optical Birefringence
Authors: Becker P. J. , Kahle H. G. , Keller K.
Published: July 2007

Measurements of the linear optical birefringence are used to determine the B–T phase diagram of TbPO4 down to 1.5 K for two principal field directions. There are three ordered phases, a simple antiferromagnetic one with the moments along the tetragonal c‐axis below TN1 = 2.28 K, a further colinear antiferromagnetic one with the moments tilted off the c‐axis and a lower crystal symmetry below TN2 = 2.13 K, and a spin‐flop‐like phase in a certain field range for B along c.
Monte Carlo Simulation of the Production of Charge Carriers in NaCl Crystals by XUV Irradiation
Authors: Kikas A. , Elango M.
Published: July 2007

A Monte Carlo simulation of the number as well as energy and spatial distribution of the electron‐hole pairs created in NaCl crystals by irradiation with photons of 20 to 250 eV is carried out by using a simplified band scheme and the random‐k approximation. It is shown that the low‐energy parts of the carrier bands are populated preferentially. The computed mean pair‐creation energy is in reasonable agreement with the experimental value (13.4 to 16.7 eV) if the inelastic electron‐electron scattering threshold energy is chosen in the interval 1.2 to 1.5Eg (Eg is the band‐gap energy). The mean distance of the electron‐hole pair creation events from the photon absorption site is 50 to 60 Å.
The FH(H−) Center Energy Parameters and the Nature of the F Center Unrelaxed Ground State in KCl
Authors: Salomatov V. N. , Parfianovich I. A. , Kristoffel N. N.
Published: July 2007

The FH(H−) center energy parameters in KCl are calculated within the framework of the perturbation theory. A comparison of theoretical and experimental results leads to the following conclusion: the F center unrelaxed ground state as well as the relaxed excited state has a diffuse spatial distribution. A possibility to identify the F center unrelaxed ground state‐conduction band transition by the picosecond laser spectroscopy, is mentioned.
Some Remarks on Thermodynamics of Stress‐Induced Martensitic Transformations
Authors: Kato Masaharu , Pak H‐R.
Published: July 2007

The thermodynamics of stress‐induced martensitic transformations is re‐examined based on the recently developed formulation of thermodynamics of stress‐induced first‐order solid‐solid phase transformations. The tacit assumptions to derive the Clausius‐Clapeyron equation for the Ms temperature are revealed and the effects of different elastic constants for martensite and parent phases on thermodynamic aspects of the transformation are discussed. Previous approaches on the stress effects on martensitic transformations are also re‐investigated.
Uniaxial Stress Dependence of the Static Dielectric Constant of Some Alkali Halides
Authors: Barth M. , Lorke W. , Mohler E.
Published: July 2007

A sensitive method to measure the strain derivatives of the static dielectric constant of uniaxially stressed crystals is described. With stress modulation and phase‐sensitive detection, changes as small as 5 × 10−7 of the sample's capacitance can be detected. The piezodielectric and electrostrictive tensor components of LiF, NaCl, and KCl are given. The experimental results are compared with theoretical estimates of these coefficients based on lattice dynamical models.
Structure and Bonding in Cubic IV‐VI Crystals VII. On the Influence of Defects on the Stability of the Cubic Structure
Authors: Enders P.
Published: July 2007

The influence of defects (vacancies) on the phase transition is qualitatively treated within the framework of simple one‐dimensional models. Generalizing Gömez‐Santos' and Ynduráin's treatment to a diatomic chain, their stabilizing the cubic phase rôle can be explained as destroying the coherence of the electronic charge density wave driving the Peierls instability. The degree of coherence destroying necessary to suppress the phase transition can be quite small due to the extrinsic Peierls gap (ionic energy).
Mechanisms of Diffusion of a Small Impurity in Noble Gas Crystals
Authors: Eletskii A. V. , Stepanov E. V.
Published: July 2007

Mechanisms of diffusion of fluorine in noble gas crystals are analyzed. By numerical simulation of the fluorine atom interstitial diffusion jump in a crypton crystal the profile of the system potential energy is obtained along the jump coordinate. The most energy‐beneficial way for the fluorine atom transition between neighbouring octahedral interstices is shown to pass through a tetrahedral interstice in which the position of fluorine atom is unstable (the octa‐tetra‐octa jump). The theory of such transitions is developed, taking into account the change in phonon spectrum of a disturbed crystal in the process of diffusion jump. The fluorine atom diffusion coefficient is obtained.
Displacement Spike Annealing in α‐Iron Irradiated by PKA in the Energy Range 20 to 100 keV
Authors: Melker A. I. , Romanov S. N. , Tokmakova V. S.
Published: July 2007

The short time annealing of the displacement spikes initiated by primary knock‐on atoms (PKA) with an energy E = 20, 50, and 100 keV in α‐iron is studied. The interstitital distributions got are in good agreement with the theoretical ones found by the stationary approximation method suggested. The vacancy cluster distribution remains practically unchanged during a short‐time annealing and therefore is completely determined by creation processes of athermal vacancy clusters.
Charge Transfer in Chromium‐Transition Metal Alloys
Authors: Kulakowski K. , Maksymowicz A. Z.
Published: July 2007

The average T‐matrix approximation is applied for calculations of charge transfer of 3d‐electrons in transition metal alloys. In the dilute limit for Cr‐based alloys the transfer of electrons from Cr produces a surplus of about 1.1 electrons on V sites. Manganese lacks 1.1 3d‐electrons and Fe gives away 2.2 electrons. The values are in reasonable agreement with experimental data. For a concentration c = 0.5 the transfers are about half of the values for the dilute cases: 0.5, —0.5, and —1, respectively. Atomic short range order has only slight influence on the charge transfer. Atomic long range order plays a considerable role and may even change the sign of the transfer when compared with the chaotic alloy case.
Gap Shift in Doped Semiconductors at Finite Temperatures
Authors: Thuselt F. , Rösler M.
Published: July 2007

The interaction part to the chemical potential in doped semiconductors which is well‐suited to describe the gap shrinkage is calculated in the random‐phase approximation (RPA). The numerical results are compared with several approximate formulas to be approached within certain ranges in the density‐temperature plane. The numerical calculations are performed for n‐doped Si and GaAs being representatives of typical indirect and direct materials. Both behave completely different: in the former the gap shift is nearly independent of temperature due to the dominance of short‐wavelength screening, where in direct semiconductors the long‐wavelength screening leads to a strongly temperature‐dependent gap shift. The fraction of the impurity contribution to the total gap shrinkage behaves different in both types of materials, too.
Magnetoconductance in Metallic Granular Gallium Films
Authors: Sood B. R.
Published: July 2007

An expression for the magnetoconductance in metallic granular gallium films is obtained by modifying McMillan's conductivity expression which was derived by a phenomenological scaling theory that included localization, correlation, and screening. McMillan's result for the conductivity is modified so as to include the magnetic field dependences of the correlation gap parameter and of the localization length parameter. The magnetic field dependence of the correlation gap parameter observed by the author in granular gallium films is used, whereas for the magnetic field dependence of the localization length parameter an expression obtained by equating the length scale to the Landau orbit radius is used. The expression for the magnetoconductance contains a critical field parameter and is valid for magnetic field values greater than this critical field. It is expected that the expression for the magnetoconductance holds for other materials also with an appropriate value of the critical field. The predicted results compare very well with recent results on granular aluminium films.
Defect Formation in LiF by Low Energy Ion Implantation
Authors: Afonso C. N. , Ortiz C. , Clark G. J.
Published: July 2007

The defect formation is studied in LiF by 100 to 290 keV 1H, 4He, 11B, 16O, and 20Ne ion implantation. Room temperature optical absorption is used to study the F‐center aggregates as well as colloid formation. 2 K optical absorption is performed to analyse the zero phonon lines (ZPL) associated with the higher aggregates. The induced damage versus the ion mass, energy, and dose is studied. The influence of impurities such as Ni and Co, as well as pre‐existing defects due to γ irradiation is analysed. It is observed that the induced damage decreases as the implanted ion mas increases and that negatively charged aggregates such as R' and M' are not formed by ion implantation.
Magnons in an Anisotropic Ferromagnetic Heisenberg Chain with One Static π‐Kink
Authors: Fischer K. G. , Heber G.
Published: July 2007

A ferromagnetic Heisenberg spin chain with an anisotropic exchange interaction of the easy axis type is considered. The chain has a π‐kink structure. The energy of one‐magnon‐states and their localization is calculated, depending on the relative anisotropy, for nearest neighbour interactions in the continuum approximation.
The Refractive Index and the Exciton Transition Oscillator Strength of CdSe Single Crystals
Authors: Terekhova S. F. , Onishchenko N. A. , Talenskii O. N. , Pendur S. A.
Published: July 2007

The dependences of the refractive index and the group velocity of light on the photon energy are obtained near the exciton transitions of CdSe single crystals at 5 K by the method of twobeam interferometry. The independence of the oscillator strength on the sample thickness is determined for the exciton transitions in CdSe. The results are compared with the data obtained by other's methods in recent papers.
Stimulated Raman Scattering and Raman Instability of an Intense Helicon Wave in Longitudinally Magnetized n‐Type Piezoelectric Semiconducting Plasma
Authors: Ghosh S. , Dixit S.
Published: July 2007

A detailed analytical investigation is made of the Raman instability of the Stokes component of the scattered helicon wave in longitudinally magnetized n‐type nondegenerate cubic piezoelectric semiconductor crystal belonging to the class 43m. The general dispersion relation is obtained by using coupled mode theory and considering that the scattering is due to both the molecular vibrations produced due to the pump wave at a frequency equal to that of the transverse optical phonons and the electron plasma wave. The dispersion relation is solved for both the cases of scattered helicon waves (i.e. in the cases of left‐hand and right‐hand circularly polarized waves). The threshold value of the pump amplitude necessary for the onset of instability and the growth rate well above the threshold are obtained analytically for both the modes. The analysis is applied to a specific semiconductor, n‐InSb at 77 K duly irradiated by a high‐power helicon wave for numerical estimations. The laser wave intensities used are in the range of 109 to 1012 Wm−2 which is assumed to be less than the damage threshold of the InSb crystal. The order of wave amplitude is feasible presently.
Evaluation of Suitable Mean‐Field (Hartree‐Fock) Representations for Perturbational Studies of Disordered Solids
Authors: Böhm M. C.
Published: July 2007

A unitary transformation scheme in Hartree‐Fock (HF) space is derived allowing for the definition of a “mixed” representation of the mean‐field operator which forms a suitable self‐consistent‐field (SCF) HF basis for perturbational studies of disordered solids and polymers. The transformed HF operator contains only a small number of off‐diagonal Lagrange multipliers (i.e. coupling terms) between properly defined “defect state(s)” in the filled or empty HF space and the remaining one‐particle functions of the Fermion system which are collected into a prediagonalized subspace. The unitary transformation scheme requires two numerical operations; in the first one the canonical one‐electron functions are transformed into a set of localized valence‐bond‐type orbitals. This one‐particle representation is then transferred into a mixed basis via elementary matrix diagonalizations and multiplications. The relevant theoretical steps are outlined in a few simple examples.
The Behavior of Active Centers in a Laser Host. A Crystal Field Investigation on Nd3+ and Er3+ in LaF3 Single Crystals
Authors: Neogy D. , Purohit T.
Published: July 2007

The effects of the well known laser host, LaF3, on the triply ionized rare earth (RE) ions, Nd3+ and Er3+, are studied in detail theoretically. The theoretical results deduced with a field of D3h symmetry obtained from absorption spectra, are in good agreement with available experimental results on the magnetic susceptibilities of these two ions in similarly constituted compounds with identical nearest neighbor environments. The effective Hamiltonian which includes the crystal field and spin‐orbit interactions is diagonalized in the complete basis of the 4I term which inherently includes J‐mixing; intermediate coupling effects are also considered. Hyperfine properties arising from nuclear level splitting under the influence of the crystal field are worked out.
Physical Properties of Ion‐Implanted Laser Annealed n‐Type Germanium
Authors: Contreras G. , Tapfer L. , Sood A. K. , Cardona M.
Published: July 2007

An investigation is made of the impurity distribution and carrier concentration in n‐type germanium layers doped with P, As, and Sb by ion implantation and recrystallized by laser annealing. The impurity distribution is determined with SIMS. The electron concentration is obtained from Hall effect and from ir reflectivity measurements. Impurity concentrations as high as 2 × 1021 cm−3 are reached, with carrier concentrations Ne as high as 2.4 × 1020 cm−3, much higher than in bulk doped samples (Ne ≦ 4 × 1019 cm−3). For the P‐doped samples the implanted layers are found to have a lattice constant larger than the substrate for small implantation doses and smaller for larger doses. An analysis of these data leads to the conclusion that most of the ions are implanted substitutionally and, at high concentrations, they are compensated by pairing defects, probably vacancies. With this hypothesis it is also possible to interpret the dependence of the strength of the phosphorus local mode on implantation dose, as found with Raman spectroscopy. The softening of the Raman phonon with dose observed experimentally is also compatible with this hypothesis. A softening of the acoustic phonons with dose found with Brillouin spectroscopy is also reported and discussed.
The Nature of Two Intense Si–H IR Stretching Bands in FZ‐Si:H
Authors: Shi T. S. , Xie L. M. , Bai G. R. , Qi M. W.
Published: July 2007

Based on the isotope effect, two H‐defect complexes: tetrahedral interstitial silane (SiH4)Td and hydrogenated 〈100〉 split interstitials (Isp · 2 H) are proposed to account for the two strong Si–H IR stretching bands in FZ‐Si grown in H atmosphere (2210 cm−1, 1946 cm−1). A series of experimental facts, including the vibration frequency, the correlation with Si–H IR bands in the bending‐wagging region, the temperature dependence of band‐width and the annealing behaviour are presented, which support the proposed model. The results coincide with the view that the self‐interstitial is the dominate thermal defect in crystalline silicon at high temperature.
Secondary Emission Spectra and Energy Relaxation of Polaritons in Layer Polar Semiconductors
Authors: Brodin M. S. , Blonskii I. V. , Gushcha A. O. , Tishenko V. V.
Published: July 2007

The main processes of energy relaxation of polaritons in dependence on their initial energy and temperature are determined for the layer polar semiconductors 2H‐PbI2 and red HgI2. It is shown that thermalization of the polaritons is reached due to the “thermal barrier” effect.
Charge Self‐Consistent Tight‐Binding Parameters. Application to III‐V Compound Semiconductors
Authors: Strehlow R. , Hanke M. , Kühn W.
Published: July 2007

The description of defects (impurities, surfaces, etc.) in the framework of empirical tight‐binding method (ETBM) suffers from the drawback that already the TB parameters of the unperturbed crystal are not uniquely defined when obtained from pure fitting to existing band structures. Such an uncertainty enters the defect model via both, the unperturbed problem itself and the defect potential. It is suggested to overcome these difficulties by determining the diagonal TB parameters and orbital populations always self‐consistently. In the present paper and as the first step a method is developed to construct such charge self‐consistent TB parameter sets for the pure crystal within the framework of a special fitting procedure including up to second‐nearest neighbour interactions. With this additional self‐consistency requirement band structures are obtained being even better than those calculated from other parameter sets. The method is applied to the III‐V compound semiconductors GaP, GaAs, GaSb, InP, InAs, and InSb. Chemical trends are discussed.