bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure Derivatives of the Elastic Constants of NaBr and KF
Authors: Koliwad K. M. , Ghate P. B. , Ruoff A. L.
Published: July 2007

The isothermal pressure derivatives of the adiabatic second order elastic constants at 25 °C of NaBr and KF have been measured by the ultrasonic interferometric technique. The results are:
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Here c′αβ = ―ϱ where ―ϱ is the density and Vαβ is the velocity at the given pressure and temperature. These pressure derivatives are analyzed in the framework of the Born model of ionic solids. The pressure derivatives of the second order elastic constants can be expressed in terms of the second and third order elastic constants. The theoretical values of the second and third order elastic constants used in this article were obtained by considering the coulombic interactions of point ions, short range repulsive interactions up to second nearest neighbors, and van der Waals terms. Even though there is qualitative agreement between theory and experiment quantitative agreement is less satisfactory than desired.
The Effect of the E(k)‐Relation on Tunneling through Asymmetric Barriers
Authors: Gundlach K. H. , Heldmann G.
Published: July 2007

The tunneling current through an asymmetric trapezoidal potential barrier depends on the polarity of the applied voltage. The magnitude of this polarity effect depends on (amongst other factors) the relation between the energy E and the attenuation coefficient χ — the imaginary component of the wave number k. In the theory of electron tunneling the free‐electron parabolic E(k)‐relation is usually used. It is not however possible to explain the considerable polarity effect observed in Al‐Al2O3‐Al films by using the parabolic E(k)‐relation. By using an E(k)‐relation which describes the complex band structure of the insulator at least qualitatively good agreement is obtained between theory and experiment.
Influence of Defects and of the Interaction between them on Phonon Scattering in Heavily Doped Ge and Si Crystals
Authors: Arasli D. G. , Aliev M. I.
Published: July 2007

Measurements are made of the thermal conductivity x of highly doped Ge and Si monocrystals. At 300 °K x starts to decrease with increasing impurity concentration for concentrations greater than 1017 cm−3 in Ge and 1018 cm−3 in Si. Heat transfer in these crystals occurs primarily via the phonons and the observed decrease of x as a function of concentration is connected with phonon scattering. An estimate is made of the thermal resistance due to impurities, complexes of atoms of the doping impurity, vacancies, and carriers. Hence, the types of defect which are the main centres of phonon scattering can be determined. It is shown that in p‐Ge the additional thermal resistance ΔW is due to phonon‐scattering by the impurities and carriers, but in n‐Ge phonons are scattered by complexes and vacancies. In n‐Si ΔW is caused primarily by phonon scattering by impurities.
Arrays of Dislocation Dipoles in Cadmium
Authors: Blasdale K. C. A.
Published: July 2007

Symmetrical edge dislocation quadrupoles and linear edge multipoles have been observed by an etch‐pit technique in cadmium single crystals. The observed dimensions of the quadrupoles are in good agreement with the predictions of anisotropic elasticity, but those of the multipoles can be reconciled with theory only if it is assumed that dislocation movement is resisted by a force of frictional type. The required frictional resistance is of the right order of magnitude to account for the observed critical shear stress. For multipoles containing small numbers of dislocations in cadmium and in an isotropic medium, equilibrium configurations and configurations to be expected under small resistive forces have been calculated. Possible mechanisms for producing the multipoles are discussed.
Effect of Donor Impurity Concentration on the Piezoresistance of n‐Type GaSb
Authors: Averous M. , Bougnot G.
Published: July 2007

Measurements are made of the change of resistance under uniaxial stress of several single crystal samples of n‐type GaSb with different carrier concentrations (5.7 × 1017 to 1.6 × 1018 donors/cm3) from 77 to 300 °K. The piezoresistance coefficients as functions of temperature are found to pass through an extremum. This extremum shifts to higher temperatures as Nd increases. It is concluded that the dominant effect of uniaxial stress, in the presence of mixed conduction involving the two conduction band minima (lowest minimum (000) and the next minimum (111)), is to cause a change in the energy separation of these minima.
Time Lag in Heterogeneous Nucleation due to Nonstationary Effects
Authors: Toschev S. , Gutzow I.
Published: July 2007

The basic expression for the time lag in nonstationary nucleation in a homogeneous medium is discussed in some detail. Since heterogeneous nucleation is dominant in phase transitions, formulas may be developed to account for the influence of the substrate on the time necessary to establish a stationary nucleation rate. The following models are considered: isotropic nuclei on a solid substrate, crystalline nuclei on a solid substrate and isotropic nuclei growing by surface diffusion of components previously adsorbed onto the substrate. The analysis shows that the time lag is usually smaller than that of the homogeneous case under the same conditions.
Zur Berechnung der Fehlordnung in Silberhalogeniden
Authors: Müller P.
Published: July 2007

Es wird gezeigt, daß bei der Berechnung der Parameter für die thermische Frenkelfehlordnung in AgBr und AgCl sowohl die Wechselwirkung der Fehlstellen untereinander als auch die 200 grd unterhalb des Schmelzpunktes beginnende verstärkte Volumenausdehnung berücksichtigt werden muß. Es werden quantitative Angaben über den absoluten Fehlordnungsgrad und die Beweglichkeiten der Fehlstellen gemacht.
Theory of Spin‐Lattice Relaxation of Conduction Electrons of Ionic Semiconductors at Extremely High Magnetic Fields
Authors: Kalashnikov V. P.
Published: July 2007

A longitudinal spin‐lattice relaxation time T1 is considered for conduction electrons due to optical phonons scattering in a high magnetic field. The temperature and field dependences of T1 are obtained for the quantum limit and for various mutual locations of the Fermi level and the two lowest spin sublevels of the carriers. It is shown that the deviation of the phonon distribution from thermal equilibrium due to the interaction with the spins of the conduction electrons is small, and a phonon bottleneck should not occur, in contrast with the case of spin‐lattice relaxation of localized spins.
Light Absorption and Dispersion by Impurity Centres at High Concentrations
Authors: Lubchenko A. F.
Published: July 2007

An investigation is made of the optical absorption and the shape of the dispersion lines due to impurity centres in a solid for the case of weak electron‐phonon coupling and high impurity concentration. It is shown that the shape of the absorption lines may be Lorentzian or Gaussian depending upon the magnitude of the shift in the electronic levels of the impurities due the interactions between impurity centres.
Field Emission from p‐Type Germanium
Authors: Fursey G. N. , Sokolskaya I. L. , Ivanov V. G.
Published: July 2007

A study is made of the behaviour of field‐emission current‐voltage characteristics in 3.5 Ωcm p‐type Ge emitters, cleaned by field desorption. Nonlinearity of the Fowler‐Nordheim plots, and a contracting field‐emission pattern in the region of slow emission current increase are observed. The dependence of the nonlinear effects on the shape of the emitter and the temperature treatment is studied. The behaviour of the current‐voltage characteristics is also studied for the case where barium and gold films are deposited on the emitter. It is found that coating a field‐emitter with a metallic layer of thickness less than 0.1 monolayers results in the complete removal of the nonlinear effects. A qualitative explanation of these results is given based on the concept of “exhausting” the inversion region near the emitting surface when the emission current is removed.
Peculiarities of the RbMnF3:Nd3+ Crystals Decay Kinetics due to the Migration of Excitation Energy
Authors: Matyushkin E. V. , Kukushkin L. S. , Eremenko V. V.
Published: July 2007

The decay kinetics of the Nd3+ ions luminescence in RbMnF3:Nd3+ crystals are investigated experimentally during excitation into the Mn2+ absorption bands. It is shown that the energy transfer process is preceded by the migration of the excitation energy over the Mn2+ ions in the crystal. A theoretical treatment is given of the diffusion mechanism for this energy migration. The results of the calculation are in quite good agreement with the experimental data.
Wachstum und Struktur dünner, aus schmelzflüssigen Filmen auskristallisierter Germanium‐Kristalle
Authors: Paschoff N.
Published: July 2007

Flüssige Germanium‐Filme lassen sich in Schleifen aus dünnem Wolframdraht aufspannen. Bei der Abkühlung kristallisieren die Filme in dünne polykristalline Kristallfolien, für die die Ausbildung einzelner stark abgedünnter Bereiche charakteristisch ist. Die Struktur dieser Bereiche kann optisch und elektronenmikroskopisch untersucht werden. Die geringe Dicke einzelner Bereiche ermöglicht die elektronenmikroskopische Beobachtung bei der relativ niedrigen Betriebsspannung von 65 kV. Die verwendete experimentelle Anordnung zur Herstellung der Kristallfolien wird beschrieben. Der spezielle Wachstumsvorgang dieser dünnen Kristalle wird im Zusammenhang mit dem Kristallisationsprozeß flüssiger Filme diskutiert. Die Mikro‐ und Versetzungsstruktur wurde licht‐und elektronenmikroskopisch untersucht. Hierzu werden einige Beispiele mitgeteilt.
Feldelektronenmikroskopische Untersuchungen der Quecksilberkeimbildung
Authors: Paunov M.
Published: July 2007

Die Quecksilberkeimbildung aus der Dampfphase wird mit dem Feldelektronenmikroskop untersucht. Die zur Bildung des ersten Keimes not wendigen Zeiten werden bei verschiedenen Temperaturen der Feldemissionsspitze und bei Atomflüssen verschiedener Intensität gemessen. Bei niedrigen Temperaturen der Unterlage, wenn die mittlere Verweilzeit genügend groß ist, nimmt die Übersättigung in der Adschicht stetig zu. Die Keimbildungszeit bestimmt daher die Adatomkonzentration. Für Quecksilber auf Wolfram beträgt letztere etwa 3.2 Monoschichten. Bei genügend hohen Temperaturen der Unterlage ist die mittlere Verweilzeit viel kleiner als die Keimbildungszeit. In diesem Falle ist die Beziehung zwischen Keimbildungsgeschwindigkeit I und Keimbildungszeit τ1 sehr einfach, nämlich I = 1/τ1. Die Versuchsdaten werden in diesem Gebiet qualitativ durch die Volmersche Gleichung beschrieben. Die Aktivierungsenergie für Desorption von einer Mehrschichtbedeckung beträgt 0.6 eV.
Faraday Effect and Spin‐Orbit Interaction of the Lowest Exciton States in Molecular Crystals
Authors: Majerníková E.
Published: July 2007

The spin‐orbit interaction of the lowest excition states of a benzene crystal is calculated with the configuration interaction included. It is shown that the mixing of singlet and triplet exciton states due to the spin‐orbit interaction is negligibly small. The Faraday effect in molecular crystals is investigated taking into account Davydov splitting with application to the lowest singlet exciton states in a benzene crystal. No account is taken here of the interaction involving lattice vibrations and the internal vibrations or of rotations of the molecule as a whole.
Electrical Conduction of Semiconducting Thin Films in Strong Electric Fields
Authors: Licea I.
Published: July 2007

Non‐ohmic electrical conduction in semiconducting thin films is studied using the electron temperature approximation. The longitudinal electrical conductivity arising from warm electrons is calculated for a sufficiently large temperature range taking into account optical mode scattering.
Electroreflectance of CdS and CdSe Single Crystals at the Fundamental Absorption Edge
Authors: Gutsche E. , Lange H.
Published: July 2007

Measurements are presented of the electroreflectance spectra of CdS and CdSe single crystals. Comparison with the photon energies of the interband edges and exciton peaks demonstrates that the low‐energy peak of the spectra is dominated by exciton quenching. At higher energies field‐influenced interband transitions are also important at room temperature.
Theory of Weakly Bound Bloch Electrons in a Magnetic Field. I. Nearly‐Free Approximation
Authors: Fischbeck H. J.
Published: July 2007

The energy spectrum and the wave functions of the Bloch electron in a magnetic field are calculated and discussed in the nearly‐free approximation. The calculation employs a new formulation of the symmetry properties of this problem.
Kinetics of the Thermal Mutual Conversion of F and Z2 Color Centers in KCl:Sr Crystals
Authors: Wolfram G. , Witt V.
Published: July 2007

The thermal equilibrium between F and Z2 color centers in KCl:Sr crystals is studied as a function of the Sr++ concentration c, and the activation energies for the conversion of the centers are determined. For Sr++ molar concentrations between 0.4 × 10−4 and 9 × 10−4 the equilibrium equation is [F]/[Z2] = (2.6/c) exp (− 0.28 eV/kT). The activation energies for the conversions F → Z2 and Z2 → F are qf = 0.76 eV and qr = 1.07 eV, respectively. The results given support the Seitz, model for the Z2 center.
Some Model Problems on the Dynamics of Two‐Component Crystals
Authors: Iosilevskii Ya. A.
Published: July 2007

A study is made of the dynamic problem of superstructures such as ABr−1, with r atoms per a unit cell built up on the basis of the nearest neighbour, central, and non‐central model of a simple rhombic, tetragonal, and cubic Bravais lattice.
Magnetoacoustic Resonance Effects in Metals in Inclined Magnetic Fields
Authors: Kaner E. A. , Falko V. L.
Published: July 2007

A theoretical study is made of the features of magnetoacoustic resonance at high magnetic fields in metals with convex Fermi surfaces. For inclined fields the resonant ultrasonic attenuation lines are due to the drift movement of electrons near the boundary section or elliptical limiting points of the Fermi surface. The shape, width, and angular dependence of the amplitudes of the resonance lines are investigated.
EPR Evidence of Exchange‐Coupled Ion Pairs and of Isolated Ions in Some Chlorosubstituted Cupric Acetates
Authors: Dall'olio A. , Dascola G. , Varacca V.
Published: July 2007

Some chlorosubstituted cupric acetates are studied by EPR (X‐band) in order to examine the effect of different environments on the exchange interactions between the cupric ions. In hydrated and anhydrous tri‐ and dichlorosubstituted cupric acetates only isolated ions are present, while hydrated cupric acetate and monochloroacetate show only exchange‐coupled ion pairs. However, in anhydrous cupric acetate and monochloroacetate both these situations are found to occur. Some possible interpretations of these results are given.
Theory of the Hall Effect in Disordered Systems: Impurity Band Conduction (II)
Authors: Aldea A.
Published: July 2007

A one‐electron quantum‐mechanical formula for the low‐field Hall effect is derived for an ac electric and dc magnetic field. A comparison is made between the adiabatic and stationary approach to this problem. With some simplifying assumptions the formula is applied to two simple density‐of‐states models and the results indicate that the sign of the Hall effect depends on the degree of filling of the bands.
Spontaneous Solid—Vapour Transformation of Negative Crystals in Diphenyl
Authors: Georgieva A. , Nenow D.
Published: July 2007

Observations show a spontaneous transformation at constant temperature of the form of the negative crystals (inclusions) of own vapours within diphenyl crystals. A study is made of the kinetics of this process. The process leads to the creation of inclusions with equilibrium form. The spontaneous transformation of the negative crystals is a very convenient method for studying the growth rates of the crystal surfaces for very small super‐saturations under very pure conditions. It is established at several different temperatures that the normal rate of growth depends linearly on the curvature of the inclusion (i.e. the supersaturation). The activation energy of the transformation process is calculated from the experimental data.
Cyclotron Resonance in Zinc
Authors: Henningsen J. O.
Published: July 2007

Results are given for cyclotron resonance in zinc with the magnetic field in the (1010) and the (0001) planes. Four distinct resonance series are observed and interpreted in terms of the Fermi surface model due to Gibbons and Falicov. The mass values are in agreement with earlier cyclotron resonance measurements by Shaw, Sampath, and Eck, but there is some disagreement over the angular range of observability of one of the resonances. Weak traces of an additional resonance series, not reported earlier, are seen and an h‐resonance, reported by Shaw, Sampath, and Eck, is identified as probably arising from tip effects. Finally, tip effects are investigated systematically for two central resonances and one limiting point resonance, and the results are to some extent interpreted in terms of the theoretical treatment given by Smith.
Mössbauer Study of the FeMn Carbides (Fe1−xMnx)3C and (Fe1.1Mn3.9)C2
Authors: Huffman G. P. , Errington P. R. , Fisher R. M.
Published: July 2007

We have performed Mössbauer experiments on FeMn carbides having the cementite structure (Fe1−xMnx)3C, where x ranges from 0 to 0.6, and on a Hägg carbide with the Pd5B2 structure, (Fe1.1Mn3.9)C2, over the temperature range from 12 to 500 °K. Above the Curie temperature, the spectra exhibit a quadrupole interaction ranging from about 0.20 to 0.28 mm/s and the contributions from Fe atoms in the two types of cementite lattice sites can be identified. It is found that Mn atoms have a slight preference for “general” over “special” lattice sites in cementite. The specimens containing 0 to 20% Mn all become ferromagnetic at low enough temperatures, and the effective field decreases with Mn concentration very rapidly, extrapolating to 0 at about 34% Mn. Below Tc, the quadrupole splitting decreases drastically to less than 0.05 mm/s. Most of the results seem to be consistent with a donor theory in which C donates both of its 2p electrons to the metal d‐band, giving the Fe in cementite an average electron configuration of approximately 3d7.66 4 s1.
Role of γ‐Radiation Intensity on the First Stage of the Room‐Temperature F‐Colouring in NaCl
Authors: Agulló‐López F.
Published: July 2007

An investigation is made of the effect of γ‐ray intensity (within the range 500 to 30000 R/min) on the first stage of room‐temperature F‐colouring in NaCl. In accordance with recent work, the first stage is found to consist of two different components (fast and slow), both of which are observed to be approximately exponential. The saturation value for the fast component seems to be independent of intensity whereas that for the slow component increases with intensity in the same way as the total saturation level. The observed growth rates are not monotonic over the entire intensity range. However, for intensities ≧ 1000 R/min the growth‐rate for both the fast and the slow processes appears to be a decreasing function of γ‐radiation intensity. A brief qualitative discussion of these results in terms of a simple model is presented.
Energy Band Structure of Germanium
Authors: Morgan D. J. , Galloway J. A.
Published: July 2007

The energy bands of Δ7‐type symmetry in the (100) direction in the first Brillouin zone are calculated for germanium by diagonalizing a k · p Hamiltonian matrix referred to basis functions at k = 0 which transform according to the extra irreducible representation Δ7 of the double group of the wave vector k (1, 0, 0). Effective masses at k = 0 are used to calculate the magnitudes of the relevant parameters. It is found that the relative signs of the matrix elements of momentum between the basis functions at k = 0 have a marked effect on the computed energy band structure.
Single Crystal Growth of Calcium Pyroniobate
Authors: Graves P. W.
Published: July 2007

Single crystals of calcium pyroniobate, Ca2Nb2O7, have been grown from the melt by the Czochralski method. Crystal growth along a 〈OVW〉 direction is easy, being characterized by the formation of large area mirror facets, which under certain conditions leads to the growth of thin ribbon crystals. Growth along [100] is difficult and rates of less than 0.4 cm/h have to be used to obtain crack free crystals. Growth defects such as inclusions and cavities were found to be absent in the crystals, and no evidence was found for the presence of impurity striations.
Neutron‐Diffraction Study of Antiferromagnetism in USb2 and UBi2
Authors: Leciejewicz J. , Troć R. , Murasik A. , Zygmunt A.
Published: July 2007

The magnetic ordering in polycrystalline USb2 and UBi2 is studied by means of neutron diffraction. It is found, that the magnetic unit cell of USb2 is twice the size of the chemical cell along the c‐axis, with alternating ferromagnetic sheets in the sequence + − − + …︁. In the case of UBi2 the magnetic and chemical unit cells are identical. The sequence of ferromagnetic sheets is + − + − …︁ in the direction of the c‐axis. In both cases magnetic moments are parallel to the c‐axis and their magnitudes are (0.94 ± 0.03) BM for USb2 and (2.1 ± 0.1) BM for UBi2.
Epitaxial Growth of Vacuum‐Evaporated Co on NaCl. II. Analysis of Diffraction Patterns
Authors: Otsuka K. , Wayman C. M.
Published: July 2007

The existence of long streaks in 〈111〉 directions must be taken into consideration in order to consistently explain diffraction patterns from f.c.c. films in (001), (110), (111), and (211) orientations. In orientations other than (110) the apparent streaks correspond to the projection of 〈111〉 reciprocal lattice vectors onto the plane normal to the electron beam, and these are ascribed to buckling. The (110), (111), and (211) orientations are not thought to be truly epitaxial and appear to be associated with substrate irregularities. The epitaxially grown films are substantially f.c.c. containing many microtwins rather than f.c.c. films with h.c.p. regions which have transformed on {111} planes, indicating a suppression of the f.c.c. → h.c.p. martensitic transformation in thin films.
An Interpretation of the Dislocation Velocity‐Stress Exponent
Authors: Evans K. R. , Bailey D. J. , Flanagan W. F.
Published: July 2007

A thermal‐activation model of deformation has been used to analyze the dislocation velocity‐stress exponent, m*, from the relationship v ∝ τ* m* where τ* is the effective stress acting on a mobile dislocation. It is shown that m* is directly related to the retarding‐force profile of the rate‐controlling obstacles to dislocation motion and may be quantitatively evaluated from temperature and strain‐rate sensitivity measurements. Values of the dislocation velocity‐stress exponent reported in the literature, which are based on the applied stress, are shown to be structure sensitive and are not uniquely characteristic of the material.
Epitaxial Growth of Gold on Cadmium Iodide
Authors: Persson B. , Norden H.
Published: July 2007

The epitaxial growth of gold on (0001) surfaces of cadmium iodide is studied by transmission electron microscopy. A method for the preparation of suitable substrates is given. Dark field studies of different stages of film growth show that the deposit nucleates with a particular orientation, and during further growth this orientation changes by 30°. The diffraction pattern contains many extra twin and double diffraction spots which arise from twins and double position boundaries introduced during island coalescence.
Magnetic After‐Effect in Deformed Cobalt Single Crystals
Authors: Gerward L.
Published: July 2007

The magnetic after‐effect of deformed cobalt single crystals is investigated in the temperature region −120 to + 95 °C. Over the entire temperature region a weakly temperature‐dependent relaxation is found which obeys a logarithmic time law. Above room temperature another after‐effect is superimposed. This is interpreted as a diffusion aftereffect due to point defects. The annealing of the defects takes place at the same temperature, and obeys a first‐order rate equation. Methods of measurement are developed which take the annealing into account.
Planar Hall and Nernst Effect in Ferromagnetic Metals
Authors: Ky Vu Dinh
Published: July 2007

The planar Hall and Nernst effects due to spin‐orbit interaction between conduction electrons and d‐spin system are considered. Experimental data are obtained for the planar Nernst effect in Ni‐Fe alloys.
Magnetic Susceptibility of Face‐Centered Cubic Iron‐Rhenium Alloys
Authors: Arajs S.
Published: July 2007

Mass magnetic susceptibility of iron‐rhenium alloys containing 0.6, 1.6, 3,2, and 7.2 at% rhenium have been studied in the f.c.c. phase up to 1500 °K. Their magnetic behavior cannot be described by the Curie‐Weiss law. The 1/(χT) vs. 1/T plots, where χ is the magnetic susceptibility and T the absolute temperature, reveal indirectly that the antiferromagnetic character of f.c.c. iron is not altered by alloying with rhenium.
On the Classical Theory of the Optical Properties of Free Carriers in Semiconductors
Authors: Kosinskaya A. I. , Uritsky S. I.
Published: July 2007

Magneto‐optical effects are studied in the infrared and microwave region for carriers in a doubly degenerate band (heavy and light holes in Ge). The treatment is based on the classical kinetic equation. The dependences of the magneto‐optical effects on frequency and magnetic field are found for the low and high frequency regions and for the classical regions of low and high magnetic fields. Some of these effects may be due to the light holes under certain conditions. It is shown that under these conditions, plane‐polarized light may become circularly polarized when it passes through the crystal.
Conduction Band Structure of HgTe from Thermomagnetic Measurements
Authors: Szymańska W.
Published: July 2007

The electron effective mass in n‐type HgTe is found for concentrations between 5 × 1017 and 6 × 1018 cm−3 by measurements of the thermoelectric power in a magnetic field. The effective mass is strongly dependent on the electron concentration. This dependence can be explained by using Kane's model with the parameters mn/m0 = 0.018, ε0 = 0.21 eV. In the investigated samples the dominant electron scattering is due to ionized impurities.
Galvanomagnetic Effects in PbTe
Authors: Tovstyuk K. D. , Voronyuk P. I.
Published: July 2007

An experimental and theoretical study is made of galvanomagnetic effects in PbTe. The theory takes into account the nonparabolicity of the bands and the departure of the constant energy surfaces from the ellipsoidal form.
Sum Rules for Effective Masses in Energy Band Theory
Authors: Morgan D. J. , Galloway J. A.
Published: July 2007

Sum rules are obtained for the effective masses of energy bands whose Bloch functions transform according to one particular irreducible representation of the group of the wave vector on a symmetry axis inside the first Brillouin zone. The application of these sum rules to the energy band structure of germanium is discussed.
Electroluminescence of AgCl Crystals Excited by Short Field Pulses
Authors: Vacek K.
Published: July 2007

An investigation is made of the electroluminescence excited by short electric field pulses in pure and doped (0.01 mol% TlCl or 0.01 mol% MnCl2) AgCl crystals. The majority of the results obtained (dependence of electroluminescence on voltage and pulse duration; threshold exciting voltage) are similar to electroluminescence phenomena in ZnS. Illumination of the electroluminescence cell by red light, and by UV light, respectively decreases and increases the electroluminescence brightness. Attempts to interpret the data in terms of a bipolar field emission model prove satisfactory under the assumption that the luminescence centres are cation vacancies.
ESR on UV Irradiated Lead Halides at 80° K
Authors: Arends J. , Verwey J. F.
Published: July 2007

Results are presented of electron spin resonance measurements on uv irradiated single crystals of PbCl2, PbBr2, and PbI2 at liquid nitrogen temperature. Both pure single crystals and PbBr2 crystals doped with Tl+, Ag+, Cu+, and Bi+++ ions are studied. The ESR spectra indicate that Pb+ ions occur as an initial step in the photochemical decomposition. These ions are probably present in clusters of two or three and coagulate to metallic lead particles. The ESR signals due to the conduction electrons of these small lead particles are studied. Some hole centres which are formed during the irradiation are also described. The experiments show that the ambient conditions of the crystals are much more important in the photolysis process than the presence of foreign ions.
Point Defects in Neutron‐Damaged Silica Glass
Authors: Lungu S.
Published: July 2007

A point defect structure for neutron‐damaged silica glass is postulated. Pease's formula as tested by Monte Carlo calculations using a special closed model of a silica glass lattice is applied to the experimental volume compaction data, by considering SiO2 point defects. Some new experimental data, which are presented here, are used to compute the threshold energies.
The Orientation of Crystallites in ZnTe Thin Films
Authors: Spinulescu‐Carnaru I.
Published: July 2007

The orientation and size of the crystals in ZnTe thin films are studied as a function of the stoichiometric and growth conditions using electron diffraction and X‐ray techniques. The conditions governing the growth of relatively large crystals in the texturised ZnTe thin films are established.
The Equilibrium Position of an Orientation Junction of an Edge Dislocation Dipole
Authors: Knésl Z.
Published: July 2007

Using a linear isotropic theory of elasticity, a calculation is made of the energy and the equilibrium position of an orientation junction of an edge dislocation dipole. The junction is approximated by segments of straight lines and the calculation shows that the junction is highly localized.
Magnetic Susceptibilities of Sodium Neodymium Tungstate and Sodium Terbium Tungstate
Authors: Wang F. F. Y. , Kestigian M.
Published: July 2007

The magnetic susceptibilities of sodium neodymium tungstate Na0.5 Nd0.5 WO4 and sodium terbium tungstate Na0.5 Tb0.5 WO4 were measured from 10 to 800 °K. They were found to become antiferromagnetic at 20 and 39 °K, respectively. Their magnetic behaviors suggest the existence of clustering of magnetic ions.
On the Isotope Effect in Interstitial Diffusion III. Quantum Corrections
Authors: Pegel B. , Lepski D.
Published: July 2007

A one‐dimensional Prigogine‐Bak model of interstitial diffusion which has been discussed classically in two earlier papers, is treated quantum mechanically. By means of S‐matrix theory an energy transport equation is established for the diffusing particle. By solving this equation with the appropriate Prigogine‐Bak boundary condition, the quantum corrections for the frequency factor of the diffusion constant are obtained. It is found that the classical isotope effect is generally reduced by these corrections which are important for small interstitial masses and/or low temperatures.
Recoil Effects in the Polaron Problem
Authors: Porsch M. , Röseler J.
Published: July 2007

A general formalism for diagonalizing quadratic forms of boson operators [7], is used to obtain a translationally invariant variational ansatz which is suitable for calculating the polaron self‐energy, effective mass, and energy momentum relation in both coupling limits. The self‐energy and effective mass are calculated in the weak‐coupling limit. The strong coupling limit shows the wellknown α2‐dependence of the self‐energy. Diagonalizing the quadratic part of the recoil term gives rise to an additional self‐energy contribution to the cutoff.
Optical Absorption of an Interstitial Alkali‐Earth Cation in an Alkali‐Halide Crystal
Authors: Wang S.
Published: July 2007

Using both the concepts of the polaron model of the electron‐excess color center and the valence‐electron model of atoms introduced in this paper, we have formulated a method to compute the optical absorption energy of an interstitial alkali‐earth cation contained in an alkali‐halide crystal. The numerical results are given for the interstitial ion Ca+ in KCl and KBr. The possibility of Kojima's model for the Z2 and Z3 bands is also discussed in this work.
Electronic States of the MA‐Centers in KCl
Authors: Wang S.
Published: July 2007

The electronic states of the MA‐center in a potassium‐chloride crystal containing sodium are theoretically investigated on the basis of the Schneider model. The method is formulated by using both the polaron model and the quasi‐continuum model of electron‐excess centers. The impurity potential is treated by the valence‐electron model of atoms introduced in the preceding paper. We have used our theoretical results to discuss the origin of the MA bands reported by Schneider.
Effect of Strong Electric Fields on Magneto‐Resistivity and Hall Coefficient in Semiconductors
Authors: Kolodziejczak J.
Published: July 2007

A calculation is made of the effect of high electric fields on the magneto‐resistance and Hall coefficients of semiconductors with parabolic energy bands. Three scattering mechanisms are considered i.e. acoustic, nonpolar optical, and polar optical.
Atomie Arrangement in the Homogeneity Range of the Laves Phases ZrFe2 and TiFe2
Authors: Brückner W. , Kleinstück K. , Schulze G. E. R.
Published: July 2007

The Laves phases ZrFe2 (MgCu2 type) and TiFe2 (MgZn2 type) have a homogeneity range of several atomic percent (mainly on the side rich in iron). An investigation is made of the modifications to this type of AB2 lattice which result from an excess of B‐atoms. X‐ray and neutron diffraction measurements show that for both ZrFe2 and TiFe2 the excess B‐atoms are associated with the sites of A‐atoms. The concentration variation of the lattice constants confirms these results.
The Influence of Vacancies and Impurities on the Damage Production in Platinum Electron‐Irradiated at 90 °K
Authors: Duesing G. , Hemmerich H. , Meissner D. , Schilling W.
Published: July 2007

In platinum foils of 99.999 and 99.9% purity different vacancy concentrations are frozen in by quenching. The foils are then irradiated with 3 MeV electrons at 90 °K. The difference between the radiation damage build‐up in these foils and the damage built‐up in annealed foils which are irradiated simultaneously is investigated up to electron doses corresponding to induced resistivities of 3 × 10−7 Ωcm. It is found that 1. pre‐quenching can reduce the initial damage rate by a factor of more than 20; 2. the initial damage rate of the annealed samples is independent of their purity; 3. with further irradiation, the rate of decrease of the damage rate for the annealed samples increases with the purity of the samples; 4. for large damages the dose dependence of the damage lies between Δϱ ∼ φ and Δϱ ∼ φ1/2;. The results can easily be explained by interstitials which migrate freely at 90 °K and are either annihilated by vacancies or converted into another interstitial configuration at impurities. The direct production of immobile interstitials at 90 °K can be excluded.
A Quasi‐Harmonic Calculation of Lattice Dynamics for Na
Authors: Ho P. S. , Ruoff A. L.
Published: July 2007

We have applied a phenomenological model for a quasi‐harmonic calculation of the lattice dynamics for Na. The lattice potential is separated into the electrostatic energy, the ion‐core exchange repulsion and the screened electron‐ion potential. The ion exchange term is taken to be the Born‐Meyer type potential. The model pseudopotential suggested by Heine and Abarenkov is used for the screened potential. The model parameters are determined from the elastic constants. First we calculate the dispersion curves at 90 °K which agree very well with the neutron scattering data. Then the calculation is extended to the temperature and pressure dependences of dispersion curves. Our result indicates that the phonon frequencies are almost inversely proportional to the volume, a fact which is needed in the Grüneisen equation of state for solids. The martensitic transformation of Na is discussed according to the temperature dependence of the [1110] shear waves along [110] direction. Some related electronic properties such as the Fermi surface distortion and the liquid metal resistivity have also been calculated as a function of pressure.
Coupling of Magnons and Phonons at High Frequencies
Authors: Lord A. E.
Published: July 2007

A calculation is given describing the coupling of magnons and phonons, for a general wave vector, in a simple cubic ferromagnetic lattice. The source of magnetoelastic coupling is taken as the strain (or displacement) dependence of the magnetic dipole‐dipole energy, or Van Vleck's pseudodipolar energy. Particular solutions of the secular equation, describing the dispersion relation, are given for k ‖ z, z being the direction along which the spins are aligned.
Fine Structure of Weak Kinematical Electron Diffraction Beams for a Foil Containing Stacking Fault or Anti‐Phase Boundaries ‐ Two‐Beam Case
Authors: Gevers R. , van Landuyt J. , Amelinckx S.
Published: July 2007

A calculation is made of the fine structure of weak kinematic electron diffraction spots arising from small areas containing stacking faults. It is assumed that the illumination conditions are such that there are only two strong beams, i.e. the transmitted beam and a scattered beam. The calculation allows for the fact that the electrons propagating in the weak beam directions originate from these two beams at all depths below the entry surface. The anomalous absorption is considered in the usual phenomenological manner. The analysis leads to four satellites for every weak beam occurring for the two‐beam situation. The intensities of the satellites can, however, vary considerably due to the anomalous absorption. It is then apparent why only a single satellite is usually observed which is in agreement with the simple one‐beam kinematic treatment, which is strictly speaking incorrect. Observations on stainless steel foils are discussed and it is shown that in fact, under good two‐beam situations, there are more complicated satellite configurations as predicted by the refined kinematic treatment.
Estimation of the Peierls Stress in Alkali Halides
Authors: Gutmanas E. Yu. , Nadgornyi E. M.
Published: July 2007

The data obtained for the velocities of individual dislocations and for the mechanical properties of “pure” NaCl and LiF crystals indicate that the effect of small impurity is very great whilst the effect of temperature is small. Examination of the results on the basis of a double kink mechanism shows that this mechanism cannot describe the dislocation motion in the crystals under consideration at screw dislocation velocities greater than about 10−3 cm/s. Therefore, the upper limit of the Peierls stress in the crystals may be estimated to be not more than some tens of p/mm2.
Electrode‐Limited to Bulk‐Limited Conduction in Silicon Oxide Films
Authors: Stuart M.
Published: July 2007

The current‐voltage behaviour of evaporated silicon oxide films, several microns thick, have been investigated. At low voltages conduction is determined by contact barriers at the electrodes. At high voltages conduction is bulk‐limited and obeys a modified Poole‐Frenkel equation.
Akzeptorbildende Gitterdefekte im Tellur
Authors: Hörstel W. , Kretzschmar G.
Published: July 2007

Aus Abschreck‐ und Ausheiluntersuchungen an Tellureinkristallen ergibt sich die Gleichgewichtskonzentration thermischer Akzeptoren zwischen 380 und 550 °K zu [V′Te] = 7 × 1024 exp (−0,8 eV/kT) cm−3 ± 50%. Unter Zugrundelegung eines Zweibandmodells mit konstanten effektiven Massen und konstantem Beweglichkeitsverhältnis folgt daraus, daß thermische Akzeptoren bei etwa 580 °K eine „anomale”︁ Vorzeichenumkehr des Hallkoeffizienten bewirken müßten. Die Wanderungsenthalpie der eingefrorenen thermischen Akzeptoren wird zu (0,31 ± 0,02) eV bestimmt. Während des Ausheilens der thermischen Akzeptoren scheinen sich größere Assoziate zu bilden.
Growth of Zinc and Cadmium Whiskers from the Vapour Phase on a Single Crystal Substrate of the Same Material
Authors: Nanev Chr. , Iwanov D.
Published: July 2007

A determination is made of the crystallographic orientation of zinc and cadmium whiskers grown on single crystal substrates of the same substances which have well‐formed faces, edges and tips. Zinc and cadmium whiskers grown in this way in the presence of hydrogen or argon are oriented as 〈1120〉, however zinc whiskers grown in vacuum have the orientation 〈1123〉. These are in fact the directions of the screw dislocations in the lattice. These and other results indicate that the whiskers grow preferentially via a screw dislocation mechanism. Some cases are observed in which zinc “whiskers” grow at large supersaturations without involving a surface diffusion mechanism as required by the classical theory of whisker growth. Possible causes for the appearance of whiskers on a single crystal substrate are discussed, as well as the factors which determine their orientation.
De Haas‐van Alphen Effect in White Tin
Authors: Stafleu M. D. , de Vroomen A. R.
Published: July 2007

The de Haas‐van Alphen effect in white tin is measured using the field modulation technique. The results contain much more detail than those reported by Gold and Priestley. The smaller parts of the Fermi surface can be constructed directly from the measurements; the construction of the larger parts will be described in a separate paper.
Fermi Surface and Pseudopotential Coefficients in White Tin
Authors: Stafleu M. D. , de Vroomen A. R.
Published: July 2007

The de Haas‐van Alphen measurements previously reported are used to determine the shape of the Fermi surface in white tin, and to calculate the pseudopotential coefficients. The present results give much better agreement with the model potential of Animalu and Heine than does the recent band calculation by Weisz.
Influence de l'organisation en domaines du titanate de baryum sur sa température de transition
Authors: le Traon A. , le Traon F. , le Montagner S.
Published: July 2007

On propose de compléter, dans le cas d'un ferroélectrique du type BaTiO3, l'expression de l'enthalpie libre, pour tenir compte de facteurs propres aux domaines de polarisation: on en déduit une formule reliant la température de transition para‐ferroélectrique à un paramétre caractéristique de cette structure en domaines. Les températures généralement données pour BaTiO3 correspondraient alors à des domaines de dimensions moyennes supèrieures à 0,2 μm.
Electronic Structure of F‐Centers in Alkaline Earth Fluorides
Authors: den Hartog H. W. , Arends J.
Published: July 2007

The isotropic hfs constants of F‐centers in alkaline‐earth fluorides and the g‐shift in CaF2 are calculated using various published wave functions. The computed results of these calculations are then compared with experiment in order to assess the validity of the wave functions. The wave functions studied give the correct order of magnitude for the isotropic hfs constants of the first shell of F− ‐ions surrounding the vacancy. For the second shell of F−‐ions a few wave functions give values in agreement with experiment.
A New Type of X‐Ray and Electron Diffuse Scattering and Corresponding Strain Contrast on Electron Microscopic Images
Authors: Khachaturyan A. G. , Usikov M. P.
Published: July 2007

A kinematic theory is developed for electron elastic diffuse scattering by static distortions, caused by coherent particles in the new phase. It is suggested that the lattice of the new phase differs from the matrix lattice in an arbitrary way. The theory is valid in cases when the matrix and the particles are elastically anisotropic and possess equal moduli. The values of the elastic displacements determining the diffuse scattering are obtained from anisotropic elasticity theory. The isodiffuse surface cross‐sections of the reciprocal lattice planes are calculated for the anisotropic ageing alloy CuBe and the isotropic alloy TaO. These alloys show the precipitation of tetragonal and rhombic phases respectively. The isodiffuse surface sections are in good agreement with the structure of the reciprocal lattice points, obtained on the diffraction patterns; the scattering in these cases also differs considerably from Huang scattering which arises when particles are dilatation centres. A kinematic theory is also developed for the strain contrast caused by the distortions in a solution due to the new phase particles. When the particles are not only centres of dilatation but also centres of an arbitrary deformation, the strain contrast differs from Ashby contrast to the same extent as the diffuse scattering differs from Huang scattering. A comparison is made between the contrast calculated theoretically and that obtained on the micrographs of the alloy TaO.
Group‐Theoretical Classification of Electronic States in Crystals Composed of Pairs and Complexes of Bound Impurity Ions
Authors: Vonsovskii S. V. , Cherepanov V. I. , Men A. N. , Nikiforov A. E.
Published: July 2007

A group‐theoretical method is suggested for determining allowed type states of pairs and complexes of impurity ions in ionic crystals. Two cases are discussed in detail. In the first case the energy of the electrostatic interaction Veint between electrons of different impurity ions is greater than that of the internal magnetic interactions Hm0 and in the second case Veint is less than Hm0. For both cases Veint is assumed to be smaller than the total energy of the internal electrostatic interactions and the energies of a crystal field produced by the remaining ions of the crystal. As an example the I—V order pairs of the equivalent ions Cr3+ in corundum are examined.
Transient Behaviour of Space‐Charge‐Limited Currents in p‐Type Silicon
Authors: Lemke H. , Müller G. O.
Published: July 2007

Calculation of the leading transients of space‐charge‐limited currents, neglecting diffusion, predict a “cusp”‐type behaviour which until now has only been confirmed on low mobility materials under optical excitation. On Si samples with p+‐contacts and on Pt‐contacted uncompensated (trap‐free) 60 kωcm crystals it is possible to obtain quantitative agreement at least after the first few ns. This provides a good method for measuring majority carrier mobilities. The origin of an order of magnitude deviation for times small compared with the transit time seems uncertain.
Ferromagnetische Hochtemperaturnachwirkung an Eisen‐Silizium‐Legierungen bei gleichzeitiger plastischer Verformung
Authors: Krings F. J.
Published: July 2007

Durch plastische Verformung wird in Eisen und Eisenlegierungen mit einigen Gew‐% Si unterhalb 400 °C eine starke magnetische Nachwirkung erzeugt. Der Aufbau der Defekt‐konzentration wird während der Verformung gemessen. Meßparameter sind die Temperatur (275 bis 360 °C), die Verformungsgeschwindigkeit (2,8 × 10−7 bis l,0 × 10−5 s−1) und der Si‐Gehalt (0,1,1,2,4 und 3,3 Gew‐%Si). Das Erholungsverhalten der Defekte wird untersucht. Die Ergebnisse lassen sich mit einem Modell deuten, bei dem die Nachwirkung durch Einzelleerstellen hervorgerufen wird, deren Erholung über Doppelleerstellen abläuft. Eine Deutung durch Umorientierung von Si‐Paaren erscheint nicht möglich.
Magnetoconductivity of Trigonal Selenium Single Crystals
Authors: Mell H. , Stuke J.
Published: July 2007

Six of the eight magnetoconductivity components of trigonal Se are measured up to 30 kG over the temperature range 83 to 300 °K. Unlike the Hall mobility, which increases exponentially with temperature, the magnetoconductivity mobility decreases with rising temperature and, at high temperatures, is approximately proportional to T−3/2. At 300 °K a value of 28 cm2/Vs is obtained for the mobility in the chain direction, whilst the Hall mobility at the same temperature is only about 0,2 cm2/Vs[1]. This discrepancy can be explained by assuming a strongly inhomogeneous hole concentration. The directional dependence of the magnetoconductivity is interpreted using a six‐ellipsoidal model. From this the ratio of the mobilities parallel and perpendicular to the chain direction is about 3.5.