bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiments on Fluctuations in Optically Quenched CdS and CdSe Crystals
Authors: Herczfeld P. R. , van Vliet K. M. , Pai M. D.
Published: July 2007

Measurements of electronic fluctuation spectra in CdS and CdSe crystals, irradiated by primary light, causing excitation, and infrared light, causing quenching, are reported. For the primary light in the tail absorption region, a marked effect is found. Even for moderate quenching, the noise often increases by an order of magnitude; moreover, a characteristic ω−5/2‐spectrum appears, as has not been observed in photoconductors hitherto. At low temperatures the relative variance is close to unity or even sub‐poissonian. At room temperature, thermal quenching presumably may enhance the noise, though in lesser degree than infrared quenching. In the fundamental absorption band, infrared quenching enhances the noise, but does not alter the spectral shape, which generally shows a diffusion behavior signified by an ω−3/2‐dependence. A qualitative discussion of these features is given. A quantitative description, particularly of the ω−5/2‐spectrum is referred to a subsequent article [3].
Electronic Processes and Fluctuations in Optically Quenched CdS and CdSe Crystals
Authors: Herczfeld P. R. , van Vliet K. M.
Published: July 2007

A detailed analysis is given of the electronic fluctuations in a “five‐level” photoconductor, the “levels” being the conduction band, valence band. electron traps, shallow hole traps, and quenching centers. Two recombination paths are open to the electrons, viz. via the deep traps and via the quenching centers. It is assumed that the former process prevails at the surface and the latter mainly in the bulk. As a consequence fluctuations arise from diffusion to the surfaces, in addition to the effects of the electronic transitions. The various effective diffusion constants and lifetimes are complex. The resulting spectra are evaluated with the Green's function method and reveal ω−2‐, ω−5/2‐, and ω−3/2‐contributions. It is shown that the ω−5/2‐term disappears if there is no quenching, and that it is highly unlikely for this spectral dependence to appear in a more simple model than analyzed here. Surface recombination enhances the feasibility of the ω−5/2‐spectrum. The results, in as far as they can be analytically pursued, are in reasonable agreement with the previously described experimental data [1].
Production of Colloidal Calcium by Electron Irradiation of CaF2 Crystals
Authors: McLaughlan S. D. , Evans H. W.
Published: July 2007

After irradiation with 75 keV electrons the optical absorption spectra of differently doped CaF2 crystals show an identical broad band peaking between 515 and 565 nm which is attributed to colloidal particles of calcium. Further evidence for the existence of a colloid is given by an ESR investigation. After irradiation most samples exhibit a narrow isotropic resonance g = 2.006 ± 0.001 which is thought to arise from conduction electron spin resonance in the particles of colloidal calcium.
Stress‐Induced Inhomogeneous Effects of the K‐Absorption in RbCl
Authors: Maier K. , Gebhardt W.
Published: July 2007

The change in the K‐absorption in additively coloured RbCl under applied uniaxial stress is investigated. A new technique with an ac‐stress is applied. The effects are compared with the change in the absorption shape in Ba++ doped crystals. The analysis reveals two components of the K‐absorption, K1 and K2, which behave differently under external perturbations. The K2‐component coincides with the spectral range of high photoconductivity.
Electrical and Optical Properties of Sputtered In2O3 films. II. Optical Properties in the Near Infrared
Authors: Müller H. K.
Published: July 2007

The influence of conduction electrons on the optical properties in the near infrared has been investigated for sputtered In2O3 films. The results are interpreted using the present theories of absorption and dispersion by free carriers. The optical properties in the investigated frequency range are considerably influenced by the anisotropy of the predominant scattering mechanism (scattering at charged defect centres) and by the low mean free time of the electrons (τ ≈ 1.5 × 10−15 s).
Comparative Investigation of the Specific Heat of KH2PO4 (KDP) and KD2PO4 (DKDP) Single Crystals
Authors: Strukov B. A. , Amin M. , Kopchik V. A.
Published: July 2007

The surplus entropy of the phase transition is measured for KH2PO4 and KD2PO4 crystals. The corresponding values are as follows: (0.69 ± 0.02) and (0.96 ± 0.08) for KDP and DKDP, respectively. The temperature dependence of the specific heat of DKDP shows that the phase transition in the crystal is of the first order. For the KDP crystals, the analytic form of the surplus specific heat is approximately Δcσ,E ∼ (Tc–T)−δ, δ = 0.51 ± 0.01. Theoretical estimates and experimental measurements are made of the effect of an electric field on the specific heat.
Attenuation and Amplification of Hypersound by Mott Excitons in Semiconductors with Piezoelectric and Deformational Electron‐Phonon Interactions
Authors: Lipnik A. A. , Ruvinskii M. A.
Published: July 2007

A calculation is made of the attenuation of hypersound by Mott excitons in semiconductors with piezoelectric and deformational electron‐phonon interactions taking into account 1. the complex band structure (anisotropy, many‐valleyness, degeneracy, spin‐orbit interaction); 2. the presence of many sorts of carriers and screening of the electron‐phonon interaction; 3. the possible change in the internal state of the exciton including its dissociation and formation from a pair; 4. the possible degeneracy and Bose‐Einstein condensation of the excitonic gas. It is proved that there is a real possibility of amplification of hypersound both by the excitonic gas, due to its de‐excitation and by the electron‐hole gas, due to the formation an exciton from a pair (at rather low temperatures). The resonant character of hypersonic attenuation by the excitonic condensate may serve as an agent for detecting the latter effect. The measurement of attenuation and emission frequencies allows the exciton binding energy and the main values of its effective mass tensor to be determined.
Schottky Defects in Alkali Halides: Their Creation, Interaction, and Migration
Authors: Rao K. J. , Rao C. N. R.
Published: July 2007

Schottky defect energies of alkali halides are calculated by the force balance method employing a modified Born model with higher than van der Waals terms and appropriately adjusted repulsive terms. The energies for various potassium and rubidium halides of NaCl structure show good agreement with the experimental values. Schottky defect energies of CsCl are calculated for the CsCl and the NaCl structures. The calculated value (≈︁ 1 eV) for the CsCl structure is in excellent agreement with the recent experimental value. The Schottky energy of CsCl in the NaCl structure is about 2 eV. The ground state interaction energy between a positive and a negative ion vacancy is determined with the inclusion of van der Waals terms. The values obtained for various alkali halides are in fair agreement with the previous ones. The migration barriers for single and pairs of vacancies in KCl and RbCl are calculated by an energy minimization procedure. The barrier heights compare nicely with the experimental value and reflect the expected trend in various parameters. The values also show that the activation energies for the migration of double vacancies and single vacancies are nearly the same; this result contradicts the generally accepted statement that migration of pairs is less energetic, but supports the recent proposal of Lidiard who obtained this result by employing different repulsive energy expressions in the different interionic regions.
An Investigation of the Electrical Resistivity of Nickel‐Rich Nickel‐Gold Alloys
Authors: Arajs S.
Published: July 2007

Electrical resistivity of nickel‐gold alloys, containing 0.075, 0.22, 0.45, 0.68, 1.07, and 1.54 at% gold, has been measured at 4.2, 77.2, and 300.0 °K. The resistivity increase at 4.2 °K, due to 1 at% gold in nickel, is (0.33 ± 0.01) μΩcm. This value compares favorably with the result of (0.38 ± 0.02) μΩ cm due to Roberts et al., This finding implies that the disagreement between the measured and the theoretical isomer shifts, calculated by Roberts et al., for 197Au in nickel is not due to the uncertainty in the residual resistivity data. Nickel‐gold alloys exhibit large deviations from the Matthiessen rule. The longitudinal electrical magnetoresistivity at 4.2 °K in presence of an applied field of 60 kOe is positive, rapidly increases with increasing gold concentrations, and then gradually saturates at higher gold contents.
Vibrational Resonance Mode and the Temperature Dependence of Hyperfine Coupling of Mn2+ in BaO
Authors: Žďánský K.
Published: July 2007

The temperature dependence of the hyperfine coupling constant A of Mn2+ in BaO is measured in the temperature range 4 to 300 °K. It is shown that the theoretical temperature dependence of A given by Šimánek and Orbach [5] does not give a good agreement with the measured values. The temperature dependence of A is calculated by assuming that the interaction of the electronic states of the impurity ion with the resonance mode of vibration prevails over the interactions with the continuous phonon spectrum. To explain the discrepancy between the theoretical curve and the experimental data, the effect of anharmonic terms on the temperature dependence of hyperfine coupling is taken into account.
Electrical Conduction in Li‐Doped MnO Single Crystals
Authors: Ali M. , Fridman M. , Denayer M. , Nagels P.
Published: July 2007

A study of the electrical properties including resistivity, Hall effect, and thermoelectric power is made on slightly Li‐doped single crystals of MnO. The temperature dependence of the conductivity is almost completely determined by the charge carrier concentration. From the results of electrical conductivity and thermoelectric power measurements it is concluded that the samples are slightly compensated. When the samples are thermally treated in an atmosphere containing oxygen in excess compared to the equilibrium pressure, more donor centres are introduced resulting in further compensation. The height of the acceptor (Li+Mn+++) level is 0.64 eV while the band gap has a value of 2.6 eV. The calculations of the density of states Nv and the effective mass m* yield a high value. These results indicate that holes move in a narrow band.
Calculation of Properties of Vacancy‐Centered Z1−Center Models in Alkali Halides
Authors: Dick B. G.
Published: July 2007

A simple variational calculation of the ground and excited p‐state energies, wavefunctions, and transition oscillator strengths is carried out for three forms of proposed vacancy‐centered models for Z1−centres in alkali halides. The calculated excitation energies compare well with experiment for NaCl, NaBr, KCl, RbCl, KBr, and KI.
Untersuchungen zum Mechanismus der Elektrolumineszenz von CdS‐Einkristallen
Authors: Hänsch H.‐j.
Published: July 2007

An investigation is made of the spectral distribution of intensity and the intensity‐current density dependence of electroluminescence (EL) of CdS single crystals at 77 °K. In the range of the short wave series of the edge emission good agreement is found between EL and photoluminescence (PL) spectra. Moreover, some short wavelength bands appear in EL, whose intensities increase essentially stronger than the edge emission with increasing current density. Analogously to the PL it is assumed that in the edge emission range the EL is due to a transition within a donor‐acceptor associate. The short wave EL bands are assigned to a radiative annihilation of a bound exciton assisted by longitudinal optical phonons and (presumably) acoustical ones. Although at large current densities the necessary laser condition is fulfilled, no laser action could be observed.
Optical Transitions in the Spectra of the Fundamental Absorption and Reflection of InSe Single Crystals
Authors: Andriyashik M. V. , Yu. Sakhnovskii M. , Timofeev V. B. , Yakimova A. S.
Published: July 2007

The spectrum of the fundamental absorption and reflection of n‐type InSe single crystals is studied in the energy region 1 to 5 eV and in the temperature range 293 to 90 °K. In the spectrum an absorption is observed which may be related to direct and indicrect interband transitions. The main parameters characterizing the indirect and direct optical transitions are determined. The fine structure in the absorption spectrum due to excitons is investigated. On the basis of the analysis of the optical absorption and reflection properties in the fundamental region and using selection rules, the character of optical transitions as well as the peculiarities in the energy band structure of InSe single crystals are established.
Effect of Reactor Irradiation on the Conductivity and the Photoconductivity of Hexagonal Selenium Single Crystals
Authors: Tuomi T. O.
Published: July 2007

Radiation damage in selenium is investigated at various temperatures. Fast neutron irradiation is found to decrease the conductivity of a hexagonal selenium single crystal at 310 °K in an exponential manner. According to the barrier model the decrease of the conductivity is a result of the decrease in the hole concentration in the high conductivity regions. The photoconductivity measurements indicate that the fast neutron irradiation does not markedly change the properties of the barriers. At 80 °K the crystals are more sensitive to radiation than at 310 °K, whereas at 20 °K the effect of radiation on the conductivity is of the same order as at room temperature.
Stationary Anode‐Adjacent High‐Field Domains in Cadmium Sulfide
Authors: Böer K. W. , Voss P.
Published: July 2007

It is shown that in n‐type material with negative differential conductivity due to field quenching, stationary cathode‐ or anode‐adjacent high‐field domains occur dependent on electron density at the cathode and applied voltage. Cathode‐adjacent high‐field domains can be observed only with a blocking cathode. Anode‐adjacent high‐field domains occur with a slightly blocking cathode at applied voltages above the range at which cathode‐adjacent domains are observed or as the only domain type possible with an injecting cathode. With different cathode metals evaporated onto the same CdS:Ag, Al crystal the electron density in the conduction band n1(E) for space charge free conditions has been determined as a function of the actual field between 0 and 240 kV/cm.
Computational Evidence for the Transition Point of a Square Ising Lattice with First and Second Neighbour Interactions
Authors: Bitterlich W. , Jelitto R. J.
Published: July 2007

From numerical calculations for a toroidally closed Ising lattice of finite diameter it is seen that it is possible to obtain the transition point of a square Ising lattice with nearest and next‐nearest neighbour interactions to a high degree of accuracy. In the case of a lattice with pure nearest neighbour interactions the curves of the internal energy for all diameters of the torus intersect in one point, which is the transition point of the infinite lattice. When next‐nearest neighbour coupling is present, this is no longer exactly valid, but the dependence of the situation of the different points of intersection on the diameter is so exceedingly weak that a rapid convergence to the Curie point may be assumed with increasing size of the lattice and the transition point can be deduced thereby. The assumptions involved in this method and its consequences are discussed and the result of the investigation is compared with a theory of Vaks et al., which deals with a similar type of interaction.
Innere optische Reflexionen an kubischem ZnS mit eindimensionaler Lagefehlordnung
Authors: Farwer A. , Matossi † F.
Published: July 2007

Die inneren Reflexionen in eindimensional lagefehlgeordnetem kubischem Zinksulfid werden zwischen 350 und 1000 nm Wellenlänge untersucht. Da die Stapelfehler hexagonale Struktur besitzen, ist es möglich, die Verhältnisse der Hauptbrechungsindizes von Wurtzit und Sphalerit sehr genau zu bestimmen. Für 360 nm Wellenlänge ergibt sich nhex, o/nkub  0,980 und nhex, ao/nkub  0,990, wahrend für 850 nm die entsprechenden Werte 0,993 und 1,003 sind. Der mittlere Abstand zwischen den Stapelfehlern kann zu etwa 100 Å abgeschätzt werden.
On the Thermal Conductivity of ZnxHg1−xTe Solid Solutions
Authors: Kelemen F. , Néda A. , Cruceanu E. , Niculescu D.
Published: July 2007

Thermal conductivity measurements are carried out in single crystals of ZnxHg1−xTe solid solutions as a function of composition and temperature between 90 and 450 °K. The temperature dependence of the thermal conductivity in ZnTe may be explained by U‐processes. At the same time, the lattice thermal conductivity measured in these solid solutions is lower than that calculated on the basis of U‐processes and phonon scattering at point defects. Therefore it is assumed that the interaction between acoustical and optical phonons as well as the three‐phonon N‐processes also contribute to the thermal resistivity in these solid solutions. In the light of this assumption, a satisfactory agreement is found between the experimental and the calculated values of the lattice thermal conductivity.
Investigations of Some Properties of Vitreous and Crystalline CdGeP2
Authors: Goryunova N. A. , Ryvkin S. M. , Shpenikov G. P. , Tichina I. I. , Fedotov V. G.
Published: July 2007

Recombination radiation is observed in vitreous and crystalline CdGeP2. Some electric properties of vitreous and crystalline specimens are also studied. n‐ and p‐type crystals with concentrations n = 6 × 1010 to 7 × 1015 cm−3 and p = 7 × 1014 to 4 × 1015 cm−3 at 300 °K and p‐type vitreous CdGeP2 are used. The effect of the recrystallisation of vitreous CdGeP2 as well as the effect of impurities on the recombination radiation of crystalline CdGeP2 is investigated.
On a Certain Type of Instability of Electrical Domains
Authors: Enderlein R.
Published: July 2007

The stability of the Riemann solution in the theory of electrical domains with respect to variations of the boundary conditions is investigated. Both the drift and the recombination non‐linearities are considered. The Riemann solution is found to be stable under certain conditions of experimental interest.
Elastic Constants and Tensile Strength of NaCl‐Type Alkali Halides
Authors: Szomor P. O.
Published: July 2007

The second‐order elastic constants and tensile strength of NaCl‐type alkali halides are calculated on the basis of the Born‐Mayer model of the lattice energy of ionic solids. The repulsive parameters which include the contribution of the second nearest neighbours in the expression of the repulsive energy are obtained from the equation of state of static solids and its volume derivative. For determining the elastic constants and the tensile strength a procedure similar to Zwicky's procedure is chosen. The comparison of the calculated elastic constants and the available experimental results show that the basic radii obtained by the Huggins‐Meyer procedure are not accurate enough in the case of certain ions.
The Electronic Structure of CdO I. The Energy‐Band Structure (APW Method)
Authors: Maschke K. , Rössler U.
Published: July 2007

The energy‐band structure of CdO was calculated along the high symmetrical axes of the Brillouin zone by use of the APW method. This method seems to be more suitable for the rocksalt lattice than for the zincblende structure. The resulting energy bands are similar to the bands of silver halides.
EPR and Thermoluminescence Measurements on CaWO4 Crystals
Authors: Born G. K. , Grasser R. J. , Scharmann A. O.
Published: July 2007

After irradiation with X‐rays in the energy range 50 to 150 keV at the temperature of liquid air paramagnetic centres are created in single crystals of CaWO4. The centre with a spectroscopic splitting factor slightly higher than g = 2 originates from a hole stably trapped between two tungstate tetrahedrons. The signal of the corresponding electron is broad and rather difficult to detect. The concentration of these centres depends linearly on the dose of irradiation. The decrease of the EPR signal of the hole and electron centres with temperature is correlated with the thermoluminescence intensity.
Hall Effect and Magnetoresistance in Copper Single Crystals at Low Temperatures
Authors: Saeger K. E.
Published: July 2007

The Hall coefficient and transverse magnetoresistance of copper single crystals of different purity are measured in dependence on the magnetic field strength, temperature, and crystal orientation. For high magnetic fields and low temperatures, Kohler's rule is valid for both effects in pure samples for all crystal orientations investigated. Departures from Kohler's rule occur for increasing temperatures and impurity contents. The investigation of the temperature dependence of the Hall coefficient shows that the maximum in the Hall coefficient versus temperature curves recently found by several authors is due to anisotropic electron‐phonon scattering. The results of the present investigation indicate that the temperature dependence of the low field Hall coefficient differs significantly from that previously assumed to be valid.
Electron Irradiation and Recovery of Tungsten
Authors: Neely H. H. , Keefer D. W. , Sosin A.
Published: July 2007

Damage rates and recovery of 99.99% pure tungsten have been investigated after electron irradiation near 4 °K by means of electrical resistivity. The damage rate data tend to a value of T0 = 38 to 42 eV. The recovery of the residual electrical resistivity shows three major stages: Stage I from 4.2 to 100 °K, Stage II from 100 to 500 °K, Stage III from 500 to 1000 °K. Stage I is dominated by only one major peak at 70 °K. An analysis based on second‐order kinetics yielded a good fit to the data through 95% of the recovery. The energy derived was 0.17 eV. Only ≈︁ 26% recovery is seen in Stage I and we propose that the suppression is due to interstitial trapping by impurities. Stage III accounts for about 40% recovery of the induced resistivity and has a center temperature of 760 °K. The stage was analysed assuming second‐order kinetics; this analysis gave an energy of 1.1 eV.
On Transverse Electrical Conductivity of Metals
Authors: Kishore R.
Published: July 2007

With the help of the Kubo formula an expression for the transverse electrical conductivity of metals is obtained within the Hartree‐Fock approximation using the method of the double‐time temperature‐dependent Green's function. It is observed that the expression is the same as that obtained by Leribaux with the help of perturbation theory using the Feynman diagram technique if the change in the energy of the electrons due to electron‐phonon interaction is neglected.
Thermal Quasi‐Equilibrium of Vacancies, Divacancies, and Impurities in Platinum
Authors: Polák J.
Published: July 2007

The change in the electrical resistivity of platinum quenched in air and in water is measured. The transient phenomenon at the very beginning of the isothermal annealing at a temperature of about 250 °C is observed. The possible interactions of point defects in quenched platinum are analysed. Various interactions are quantitatively compared with the measured data and the probable interpretation of the results is discussed.
Calculation of the Point Lattice Potential of a Bounded Crystal
Authors: Vendik O. G.
Published: July 2007

The eigenfunctions of the electrostatic potential in a rectangular box were used for the calculation of the potential of a point lattice of an ionic crystal. The potential within the bounded crystal and in its surface region was found. The final result was obtained in the form of an expansion in spherical harmonics referred to coordinates whose origin could be at any lattice point of the crystal. The method was used to explain an experiment [8] dealing with electron diffraction from the surface layers of BaTiO3.
Injection of Current Carriers in Anisotropic Semiconductor Plates and the Magnetodiode Effect
Authors: Gribnikov Z. S. , Lomova G. I. , Romanov V. A.
Published: July 2007

It is shown that the current‐voltage characteristics in of plate‐ or filament‐shaped long diodes are essentially different for the isotropic and anisotropic cases. For the effective lifetime of excess carriers in anisotropic case is inversely proportional to the external electric field, the direct current through such a diode increases slower than I ∼︁ U2, that is “ohmically” I ∼︁U. As a result of such difference the characteristics of the isotropic plate‐shaped diodes strongly depend on pressure and magnetic field (the effect of a small magnetic field may be considered to be equivalent to the effect of pressure). This indicates that significant tensodiode and magnetodiode effects take place. A satisfactory agreement of the experimental data with the theory has been obtained.
A Dynamical Treatment of the Stress‐Induced Dissociation of Triangular Frank Dislocation Loops in F.C.C. Metals
Authors: Humble P. , Forwood C. T.
Published: July 2007

The problem of the dissociation of triangular Frank dislocation loops to form stacking fault tetrahedra during the plastic deformation of f.c.c. metals is reconsidered. It is pointed out that since this process involves the movement of dislocations, any consideration of the energy balance of the defect must take into account the kinetic energy of the moving dislocations. The problem is reformulated in terms of the total energy of the system where terms in the kinetic energy, the work done by the stress, and the energy dissipated are included, as well as the energy due to dislocation interactions and stacking faults. Using this formulation and the observations of Loretto et al. [3], it is deduced that the values for the stacking fault energy of silver, copper, and gold are (19 ± 3), (62 Melbourne 9), and (47 ± 7) erg cm−2, respectively.
Absolute Thermoelectric Power and Electrical Resistivity of Chromium‐Rich Chromium–Nickel Alloys
Authors: Schröder K. , Baum N. P.
Published: July 2007

The absolute thermoelectric power S and resistivity ϱ of chromium‐nickel alloys with up to 10 at% nickel were measured between 100 and 600 °K. Both ϱ and S were linear functions of the temperature above room temperature. Alloys with less than 4 at% nickel showed at lower temperatures a maximum in ϱ and S, which was attributed to antiferromagnetic ordering. The Néel temperature decreases about 100 °K/at% Ni.
Infrared Lattice Absorption of Silicon and Germanium
Authors: Kress W. , Borik H. , Wehner R. K.
Published: July 2007

The two‐phonon absorption bands of silicon and germanium are calculated taking into account the second‐order dipole moment up to second‐nearest neighbours. The agreement between the calculated and measured bands shows that the shell model used in our calculations gives quite good phonon dispersion curves. The detailed analysis of the remaining deviations between measured and calculated frequencies indicates that in some points of the Brillouin zone the shell model should be corrected.
Change in Electron Affinity of a Semiconductor due to Different Forms of Chemisorption
Authors: Ahmad L.
Published: July 2007

A model has been proposed for the calculation of the variation in electron affinity, with the changes in the degree of surface coverage, for the case where different forms of a given gas species are chemisorbed on a semiconductor surface. This model embodies two parameters, which can be selected to fit the experimental results. It has been applied to the problem of oxygen chemisorption on the deformed (100) BaTiO3 surface. Neutral and ionic forms of chemisorption are postulated. The dipole moment associated with the neutral form, the higher attainable coverage, and the corresponding change in the electron affinity were found to be ≈ 3.1 D, ≈ 0.54, and ≈ 3.2 eV, respectively.
Interpretation of Self‐Diffusion and Vacancy Properties in Gold
Authors: Seeger A. , Mehrer H.
Published: July 2007

Measurements of the self‐diffusion coefficient and the high‐temperature equilibrium concentration of vacant lattice sites in gold are reanalysed in a critical manner. The analysis takes into account divacancy contributions and temperature dependences of the activation energies and entropies. A consistent set of self‐diffusion and vacancy parameters is derived. Previous interpretations, in particular those of Stoebe and Dawson [25] and Wang, Seidman, and Balluffi [20], are criticized.
Untersuchung der magnetischen Nachwirkung in Nickel nach Neutronenbestrahlung und plastischer Verformung
Authors: Walz F.
Published: July 2007

Die Nachwirkung der Anfangssuszeptibilität in Ni‐Einkristallen nach Neutronenbestrahlung und plastischer Verformung wird zwischen −180 und s+150 °C eingehend untersucht. Bei − 128, − 100, − 80, − 38 und − 21 °C werden ausgeprägte Nachwirkungsmaxima beobachtet, die durch einfache Relaxationsprozesse beschrieben werden können. Zwischen 0 and +150 °C tritt – auch nach plastischer Verformung – ein wenig strukturiertes Relaxationsgebiet auf, das bei +50 °C ein breites Maximum besitzt. In Übereinstimmung mit zusätzlich durchgeführten Koerzitivkraftmessungen und Erholungsexperimenten werden die beobachteten Relaxationsprozesse der Umorientierung kleiner anisotroper Komplexe aus Eigenfehlstellen bzw. Eigenfehlstellen und Fremdatomen, zugeschrieben.
On the L‐Bands and the First Exciton Bands in the Photoemission Spectra of Alkali Iodides
Authors: Petrescu P.
Published: July 2007

The photoemission spectra of NaI, KI, RbI and CsI are investigated experimentally. Besides the bands already revealed by optical absorption measurements and confirmed by photoemission studies, the L1–L4‐bands in Nal, the L4‐band in RbI, and the fine structure of the E1‐bands in KI and RbI are observed. In CsI electron emission is detected corresponding to the first exciton band in the absence of F‐centres. The very intense “extra”‐bands occurring in the absorption spectra are not found.
A Phase Transition and the Photoemissive Quantum Yield at Low Temperatures in Cs3Sb Films
Authors: De'Munari G. M. , Giusiano F. , Mambriani G.
Published: July 2007

By means of a recently developed method the photoemissive quantum yield (Y) of Cs3Sb films is measured as a function of temperature at very low light intensities. A strong evidence for the existence of Cs3Sb in two phases one of which (phase II) is the known “state” with high Y is found. The other phase (I) has a much lower Y which depends strongly on the light intensity. Phase I exists only below (260 ± 2) °K: above this temperature it transforms to phase II. The existence of phase I up to now was not noticed because it is very sensitive to the absorbed light energy which easily can convert it to phase II. We suggest for phase I the regular body‐centred cubic structure and for phase II the pseudo‐body‐centred cubic structure found at room temperature by Jack and Wachtel. Moreover, we propose for Cs3Sb an energy band structure with a split valence band. The observed dependences of Y on temperature and light intensity are discussed in this framework. Even other Cs3Sb properties seem to fit rather well the proposed energy band and crystal structure.
Deformation Modes of the Intermediate Phase NiAl
Authors: Pascoe R. T. , Newey C. W. A.
Published: July 2007

The deformation modes of single crystal NiAl deformed in compression in the range 77 to 1000 °K were found to be dependent on orientation and temperature. The preferred slip direction was confirmed as 〈001〉, but this may be constrained geometrically to allow kinking, or slip in 〈111〉 or 〈011〉 directions, depending on temperature. When 〈001〉 slip occurred, the slip plane was invariably {110} at 77 °K but was dependent on orientation at higher temperatures. The slip planes were also sensitive to temperature when slip occurred in other directions. The von Mises criterion for polycrystalline ductility can be satisfied by combinations of the observed slip systems.
A Deformable Shell Model for the Alkali Halides
Authors: Basu A. N. , Sengupta S.
Published: July 2007

The simple shell model which takes account of the polarizability of the ions is improved by including the effect of deformations of the electron shell during the vibrations of the ions. The deformability is introduced in a phenomenological way and it is shown that this ultimately leads to three body interactions between like particles. Because of the inclusion of many body effects the elastic constants do not satisfy in general the Cauchy relation C12 = C44. The theory is applied to the calculation of the dispersion curves for NaI and the result is compared with the simple shell model curves and with the curves obtained by neutron diffraction experiments. Definite improvement of the agreement for the deformable shell model is noticed.
Energy Loss of 〈110〉 Channelled α‐Recoil Atoms in Gold
Authors: Ibel K. , Sizmann R.
Published: July 2007

Using time‐of‐flight technique, the differential energy loss of channelled Pb‐208 (169 keV), Pb‐210 (146 keV), and Tl‐208 (116 keV) recoil atoms along the 110 direction in gold is investigated. The results are − dE/dz = (34.7 ± 3.5), (35.1 ± 3.1), and (36.8 ± 8.3) eV/Å at transverse energies of the aligned motion to the string direction of 140, 120, and 105 eV, respectively. Theoretical considerations based on Lindhard's string treatment and Firsov's impact parameter dependent electronic energy transfer relation strongly suggest that the measured stopping powers of the aligned motion are predominantly electronic; in random motion nuclear energy loss is preponderating.
The Structure and Properties of the Semiconducting Compound ZnSnP2
Authors: Vaipolin A. A. , Goryunova N. A. , Kleshchinskii L. I. , Loshakova G. V. , Osmanov E. O.
Published: July 2007

The position of the P‐atom in the ordered structure of chalcopyrite type ZnSnP2 is determined: X = 0.239. Crystals with various degrees of ordering are obtained by varying the cooling rate of the melt during growth. The partly ordered crystals show a mosaic structure and consist of blocks having chalcopyrite or sphalerite structure. The dependence of the degree of ordering on the cooling rate is established. From measurements at room and liquid nitrogen temperature the Debye temperature is found to be the same for crystals with different degree of ordering. The mean‐square displacements of atoms as well as the microhardness increase with disordering, and may be related to defect formation. A decrease in the Hall mobility of holes is directly connected with the degree of disordering.
Stability of the Dislocation Dipole in Half‐Space
Authors: Bacon D. J.
Published: July 2007

The stability of an edge dislocation dipole of infinite length lying parallel to the free surface of an isotropic, semi‐infinite medium has been investigated by determining the dipole orientation for which the stress on both poles is less than a chosen dislocation friction stress. It is found that the effects of the surface are considerable, despite the fact that the stress field of the dipole is short‐ranged. In particular, the surface can induce orientations of stability which are not expected from the infinite body behaviour. Similar results are likely to arise for prismatic dislocation loops in bounded media. Some aspects of the effect of an applied shear stress on the dipole are also studied.
Anisotropy of High‐Field Helicon Propagation in PbTe
Authors: Schilz W.
Published: July 2007

The anisotropy of the helicon propagation in PbTe has been investigated theoretically using the anisotropic magneto‐conductivity tensor for static magnetic fields directed along the [100] and [110] axes of the crystal, the wave vector being rotated in a [110] plane. Experiments have been performed with flat samples of p‐ and n‐type PbTe single crystals. In the experiments, the wave vector was directed along the [100], [110], and [111] axes of the crystal. A marked dependence of the resonance frequency and the Q‐value of the helicons on the direction of the wave vector with respect to the magnetic field direction and the crystal axes has been observed.
Hyperfine and Quadrupole Interactions of the F‐Centre in KCl as Measured by ENDOR
Authors: Kersten R.
Published: July 2007

The isotropic and anisotropic hyperfine constants of the nuclei surrounding the F‐centre in KCl were newly determined by electron nuclear double resonance (ENDOR) in a region within the distance of three lattice constants around the centre (up to nuclei 003). Quadrupole interactions of nuclei 002, 102, and 112 could be measured.
PEM Effect with Short‐Circuited Dember Voltage
Authors: Pfleiderer H.
Published: July 2007

Short‐circuiting of the Dember voltage affects the PEM effect. This is shown by simple phenomenological considerations. Under certain conditions, especially when the recombination due to the contact surfaces is not too strong, the application of Dember short circuits may increase the PEM effect. This is demonstrated by calculated values for intrinsic samples of InSb at room temperature.
Low‐Temperature Elastic Constants and Specific Heats of F.C.C. Nickel–Iron Alloys
Authors: Bower D. I. , Claridge E. , Tsong I. S. T.
Published: July 2007

The elastic constants of some single crystal specimens of nickel and f.c.c. nickel‐iron alloys have been measured at 4.2 °K and used to calculate values of the Debye temperatures. It is shown that by using these to re‐analyse some earlier specific heat measurements values of the spin‐wave contributions to the specific heats are obtained that are in good agreement with estimates made on the basis of small‐angle neutron scattering measurements of the exchange stiffnesses.
Contrast Asymmetries in Lang Topographs of Crystals Strained by Thin Films
Authors: Meieran E. S. , Blech I. A.
Published: July 2007

Causes of contrast asymmetries between (h k l) and (h k l) Lang topographs of crystals strained by thin films are discussed. The images of film edges are approximated by direct and dynamical components, and experimental separation of these components is illustrated. The direct component, dominant for low μ t, is identical in (h k l) and (h k l) topographs, while the dynamical component, dominant for larger μ t, is asymmetrical and is responsible for the Lang topograph asymmetries. The asymmetries are due to the anomalous absorption or Borrmann effect, where waves belonging to one branch of the dispersion surface undergo less than normal absorption, while waves belonging to the other branch undergo more than normal absorption. It is shown that the absorption properties of these two branches can be reversed by suitable reflections from some crystals, leading to image asymmetry reversal.
The Study of Slip Bands on the Surface of Mo Single Crystals
Authors: Veselý D.
Published: July 2007

Single crystals of molybdenum, with the orientation of the tensile axis in the middle of the stereographic triangle, were deformed at 293 and at 400 °K, to different degrees of plastic deformation at a strain rate ε = 6 × 10−5s−1. The slip bands on the cylindrical surface of the crystals were studied by optical microscopy. At room temperature, at the beginning of deformation, a large number of slip systems with all four Burgers vectors are found to be operative. It is found that the slip planes do not correspond to those with maximum resolved shear stress, but rather to planes perpendicular to the surface. The slip bands belonging to the planes with maximum resolved shear stress are more pronounced, when the temperature and flow stress are increased; at 400 °K, in the region I, the primary slip system is dominant. These observations are explained assuming that screw dislocations have a low mobility, which can change under the influence of temperature and stress.
High Resolution Study of Crystal Field Lines in the Far Infra‐Red
Authors: Howell R. G. , Newman D. J.
Published: July 2007

We report the use of high resolution Fourier transform spectroscopy in the far infra‐red to study the lowest crystal field transitions in praseodymium ethyl sulphate and the double magnesium nitrates of cerium, praseodymium, neodymium, and samarium. The spectrometer employed is a Grubb Parsons Michelson interferometer with a Putley‐type indium antimonide detector at 2 °K. The observed line positions, intensities, and strengths are discussed in terms of conventional theories.
Phonon‐Assisted Exciton Transitions in AIIBVI Semiconductors
Authors: Dillinger J. , Koňák Č. , Prosser V. , Sak J. , Zvára M.
Published: July 2007

In CdS, CdSe, and CdTe investigations of both reflectivity – by polarimetric methods – and transmission are made in the spectral region of energies higher than the exciton ground state. An additional structure at energies of approximate Eex + ELO is explained by indirect exciton transitions with phonon emission and compared with simple second‐order perturbation theory taking into account ground exciton states only. The observed shift towards lower energies can be ascribed to the configuration interaction.
Die kritische Schubspannung mit zweiwertigen Kationen dotierter Alkalihalogenide II. Fremdion‐Leerstellen‐Dipol‐Agglomerate und fremdionenreiche Ausscheidungen
Authors: Frank W.
Published: July 2007

Bei Alkalihalogeniden, welchen genügende Mengen zweiwertiger Kationen zugesetzt sind, führt hinreichend langsames Abkühlen zur Ausscheidung fremdionenreicher Partikel. Sind die Ausscheidungen klein, so stellen sie Agglomerate von Fremdion‐Kationleerstellen‐Paaren dar. Es wird gezeigt, daß die kritische Schubspannung τ0 solcher Proben dadurch bestimmt ist, daß diese Partikel die Versetzungsbewegung behindern. Aus der Temperaturabhängigkeit von τ0 sowie aus seiner Abhängigkeit vom Fremdionengehalt werden quantitative Schlüsse über die mittlere Zahl zweiwertiger Kationen pro Ausscheidung gezogen. Es stellt sich heraus, daß die kleinsten Agglomerate drei Fremdion‐Kationleerstellen‐Paare enthalten. Lediglich in NaCl:Ca2+ treten auch Doppelpaare auf. Andererseits enthalten die Ausscheidungen in langsam abgekühltem LiF:Mg2+ einige hundert Mg2+‐Ionen. Die Untersuchungen dieser Arbeit erlauben eine qualitative Deutung der Abschreckver‐ und ‐entfestigung, welche bei mit zweiwertigen Kationen dotierten Alkalihalogeniden auftreten.
The Measurement of the Anisotropy Constant of Antiferromagnetic FePO4 by Means of the Mössbauer Effect
Authors: Beckmann V. , Bruckner W. , Fuchs W. , Ritter G. , Wegener H.
Published: July 2007

In a uniaxial antiferromagnet the anisotropy energy −K (cos2 ϑa + cos2 ϑb)/2 forces the atomic spins in the magnetic sublattices a and b parallel (K > 0) or perpendicular (K < 0) to the symmetry axis. An external magnetic field changes the spin directions. For iron atoms this spin rotation can be detected by means of the Mössbauer effect of 57Fe. The intensities of the six hyperfine structure lines depend on the direction of the internal magnetic fields, which are parallel to the atomic spins. Therefore a spin rotation causes a change of the line intensities. Further, in the presence of an electric field gradient at the iron nucleus the spin rotation affects the electric quadrupole shift in a way, which depends on the sign of K. We have investigated a polycrystalline probe of calcined FePO4. The substance is antiferromagnetically ordered below 25 °K. At 4.2 °K we obtained K = = +(4.6 ± 0.5) × 105 erg/cm3.
Energy Band Structure of ZnxHg1−xTe Solid Solutions
Authors: Dziuba E. Z. , Niculescu D. , Niculescu N.
Published: July 2007

From electrical and optical data, the energy gap versus composition for ZnxHg1−xTe system is given. The deviation from the linearity is explained as an effect of the change of the covalent radii of the Zn, Hg, and Te atoms.
Magnetic Properties of Some Co‐Rich Erbium Cobalt Intermetallic Compounds
Authors: Buschow K. H. J. , Fast J. F. , van der Goot A. S.
Published: July 2007

The magnetization for the ferrimagnetic compounds Er2Co17, ErCo6, and Er2Co7 has been studied in the temperature range 4.2 to 1250 °K and at field strengths up to 30 kOe. The Curie temperatures and the saturation magnetizations at 4.2 °K have been determined. For all compounds a maximum has been observed in the magnetization versus temperature curves. Er2Co7 shows a compensation point at 140 °K. For this compound changes in the crystalline anisotropy were observed near the compensation point. The values of the coercive force obtained by mortar grinding samples of Er2Co17, ErCo6, Er2Co7, and ErCo3 are compared with the variation of the lattice parameters for these compounds.
Temperature Dependence of Hyperfine Interactions in Near‐Stoichiometric FeS I. Experiment
Authors: Thiel R. C. , van den Berg C. B.
Published: July 2007

Mössbauer measurements as a function of temperature are presented for three synthetic 57Fe‐enriched polycrystalline samples of FeS in the composition region near stoichiometry. The independence of the Morin and α‐transitions, previously concluded from neutron diffraction measurements, has been verified. A low‐temperature transition has been found near 200 °K. It appears necessary to postulate the existence of a reversible, crystallographic two‐phase region between the α‐transition and about 200 °K in order to explain the Mössbauer measurements. This hypothesis also seems to provide a logical explanation of several anomalies in FeS.
Fault Structures in Ti2O
Authors: Jostsons A. , McDougall P. G.
Published: July 2007

The structure of Ti2O can be described in terms of a hexagonal close packed arrangement of titanium atoms (c/a = 1.637) in which oxygen atoms are ordered so that they occupy every second layer of octahedral interstices normal to the c‐axis. The nature of possible antiphase domain boundaries and stacking faults in this ordered structure is discussed and compared with transmission electron microscope observations of fault boundaries. – Direct evidence is presented showing that cast specimens, which are ordered at room temperature, contain a high density of growth faults (1 (Δ) faults) at which neighbouring (0001) planes of octahedral interstices are either both occupied by oxygen atoms or both vacant. The (0001) faults are eliminated by high temperature annealing which gives rise to an antiphase domain structure with a morphology of the „Swiss‐cheese”︁ type. The antiphase vector is (c/2 + Δc) [0001] where Δc is a term indicating the presence of lattice strains parallel to [0001] direction at the antiphase boundary. – From the microstructural changes it is concluded that Ti2O solidifies as a disordered c.p.h. structure containing a high density of low energy growth faults which are modified by oxygen ordering during cooling to room temperature.
Perfect Dislocations in the Wurtzite Lattice
Authors: Osipiyan Yu. A. , Smirnova I. S.
Published: July 2007

A detailed analysis has been made of hypothetically possible types of perfect dislocations in the wurtzite structure. A possible electrical activity of the dislocations, depending on the number of broken bonds and atomic polarity of the core is discussed and possible dislocation reactions are pointed out. The energetic balance of the reactions is estimated considering only the change of their elastic energy, determined by squares of their Burgers vectors.
Anharmonic Broadening of Resonant Modes
Authors: Timmesfeld K. H.
Published: July 2007

In order to describe the strong temperature dependence of the infrared absorption of Cu+ in NaCI a model is investigated in which the Cu+ is coupled to its nearest neighbours by harmonic and cubic anharmonic forces. The problem is solved by means of retarded Green's functions solving a Dyson equation with a mass operator of second order in the cubic anharmonicity. The pure crystal is described by a Debye model because the impurity‐induced absorption takes place in the very far infrared (ωR ≈ 1/10 Debye frequency). By iterating the mass operator a good agreement between theory and experiment is reached.