Showing papers in "Physica Status Solidi (a) in 1993"

Solving Micromagnetic Problems. Towards an Optimal Numerical Method

Abstract: Various possibilities to improve numerical methods for the solution of micromagnetic problems are studied. Special attention is paid to the computation of the non-local energy part — the stray field energy. The evaluation of a scalar magnetic potential using a FFT algorithm turns out to be the most powerful and reliable acceleration technique. A Landau-Lifshitz-like equation of motion is used to drive the system towards the equilibrium state, where the effective field appearing in this equation is used at the same time to calculate and monitor the system energy during the iteration process. Two classical two-dimensional micromagnetic problems in low-anisotropy materials are solved with the methods described above: the field-induced transition between asymmetric Bloch and Neel walls in a thin film, and the structure of the transition line inside an infinitely extended Bloch wall in a uniaxial material.

The XYZ-Difference Method with Polarized Neutrons and the Separation of Coherent, Spin Incoherent, and Magnetic Scattering Cross Sections in a Multidetector†

Abstract: Equations are derived for the polarization analysis in a multidetector to separate coherent, spin incoherent, and magnetic scattering using three-dimensional analysis or the xyz-difference method. Then the conditions for the magnetic guide fields to rotate the polarization into the three directions x, y, and z are discussed on the basis of the existing instrument D7 at the ILL in Grenoble. Gleichungen fur die Polarisationsanalyse in einem Multidetektor zur Trennung von koharenter, spininkoharenter und magnetischer Streuung mittels dreidimensionaler Polarisationsanalyse oder xyz-Differenzmethode werden abgeleitet. Dann werden die Bedingungen fur die magnetischen Fuhrungsfelder zur Drehung der Polarisation in die drei Richtungen x, y bzw. z diskutiert auf der Grundlage des Instruments D7 des ILL in Grenoble.

Genesis of the cell microstructure in the Sm(Co, Fe, Cu, Zr) permanent magnets with 2:17 type

Abstract: The alloys with composition around Sm11.5Co58.4Fe22.5Cu5.3Zr2.4 (at%) present hard magnet properties when their microstructure consists of a network of cells based on Sm2(Co, Fe)17, limited by boundaries based on Sm(Co, Cu)5 and cut by platelets based on (Sm, Zr)Co3. The genesis of this microstructure is studied by transmission electron microscopy of heat-treated specimens. The fractions and compositions of the phases formed are evaluated from atomic balance equations. The microstructure forms by nucleation growth of ordered R2:17 cells in the 1:7 matrix, then by nucleation of 1:3 platelets on the twin boundaries in R2:17. The processes are likely limited by diffusion. Les alliages de composition voisine de Sm11,5Co58,4Fe22,5Cu5,3Zr2,4 ont des caracteristiques exceptionnelles d'aimants permanents quand leur microstructure est constituee d'un reseau de cellules a base de Sm2(Co, Fe)17, limitees par des parois a base de Sm(Co, Cu)5 et decoupees par des plaquettes a base de (Sm, Zr)Co3. La genese de cette microstructure est etudiee par caracterisation, par microscopie electronique en transmission, d'echantillons traites thermiquement. La composition des phases formees est evaluee a partir d'equations de bilans atomiques. La microstructure se construit par nucleation-croissance de cellules de phase ordonnee R2:17, puis par nucleation de plaquettes de phase 1:3 sur les joints de mǎcles de la phase R2:17. Les reactions apparaissent limitees par diffusion.

On the interpretation of the mössbauer spectra of ordered FeSi alloys

Abstract: Iron–silicon alloys in the concentration range between 13 and 27 at% Si are investigated using Mossbauer spectroscopy. Such alloys are known to have the D03 crystal structure of ordered Fe3Si which exhibits a wide homogeneity range. Non-stoichiometric alloys, however, show complicated Mossbauer spectra with many subspectra due to the various Fe sites which in this case are present in the D03 structure. The aim of this investigation is to improve both the spectral resolution of the Mossbauer spectra obtained for various Si concentrations and the assignment of the subspectra to the Fe sites. Using appropriate binomial distributions, it would then be possible to calculate the silicon content of the alloys from the Mossbauer spectra.

Sensitization of Luminescence of CaSO4: Dy

Abstract: The increase in photoluminescence and thermoluminescence of CaSO4: Dy TLD phosphor by co-doping with Ce or P is described. Cerium is found to sensitize the PL but not the TL. P doping helps incorporation of Dy in higher concentration. PL increases by 150% while the increase in TL is about 50%. It is claimed that the CaSO4: P, Dy phosphor thus prepared is a suitable replacement for CaSO4: Dy currently in use in TLD and personnel monitoring. Der Verstarkung der Photo- und Thermolumineszenz des CaSO4: Dy-Phosphors durch Kodotierung mit Ce und P wird beschrieben. Ce sensitiviert PL, nicht jedoch TL. P-Dotierung unterstutzt den Einbau von Dy in hohen Konzentrationen. Der hier beschriebene CaSO4: Dy, P-Phosphor scheint ein geeigneter Ersatz fur das als TLD gebrauchliche CaSO4: Dy zu sein.

Dependence of AC electrical parameters on frequency and temperature in zinc phthalocyanine thin films

Abstract: Measurements are made of the ac properties of thermally-evaporated thin films of zinc phthalocyanine using ohmic gold electrodes. These are performed over a frequency range of 100 Hz to 20 kHz at temperatures in the range 90 to 470 K, sufficient to initiate a phase transition from the α-form to the β-form. The ac conductivity σ(ω) is found to vary with angular frequency ω as ωs, where the index s ≦ 1, suggesting a dominant hopping process at lower temperatures and higher frequencies. At higher temperatures and lower frequencies free band conductivity with activation energy approximately 0.29 eV is observed. A decrease in conductivity at all frequencies is observed at temperatures above 430 K suggesting a partial α- to β-phase transition. Capacitance and loss tangent are found to decrease with increasing frequency and increase with increasing temperature, in good qualitative agreement with existing equivalent circuit models assuming ohmic contacts. After prolonged heat treatment both conductivity and capacitance diminish, particularly when the phase transition temperature is exceeded. This behaviour is ascribed to the desorption of oxygen acceptors by the heat treatment, as also observed in both the dc and ac conduction behaviour of copper phthalocyanine films.

Structure and phase-change phenomena in evaporated thin films of cobalt phthalocyanine

Abstract: The structures of thin films of cobalt phthalocyanine (CoPc) which have been deposited onto glass substrates at room temperature are investigated. Films of thickness 0.1 μm are primarily of the α-form and show a single Bragg peak indicating a strong preferential orientation in either the [001] or [200] directions, depending on whether the structure is tetragonal or orthorhombic. Films of thickness 1 μm show a slight decrease in the degree of preferential orientation, with the appearance of several additional peaks. After annealing at approximately 300 °C much of the material undergoes a phase transition to the stable β-form, preferentially oriented in the [001] direction, while annealing at lower temperatures produces a mixture of the α- and β-phases. The mean crystallite grain size increases systematically with maximum annealing temperature from approximately 30 nm without annealing to a maximum of approximately 100 nm when annealed at 315 °C.

Dislocation Patterning during Multiple Slip of F.C.C. Crystals. A Simulation Approach

Abstract: A three-dimensional simulation of dislocation dynamics and interactions is applied to the question of the formation of cell structures in single crystals oriented for multiple slip. The numerical conditions selected are those of a [100]-oriented aluminium single crystal tested in constant total strain rate with a high initial applied stress. The dislocation configurations obtained after deformations of the order of 10−3 are examined under load and after unloading. Thin foils extracted from the simulated configurations show evidence for organized structures which can be considered as preliminary stages of cell formation. These results are critically and prospectively discussed. Une simulation tridimensionelle de la dynamique des dislocations et de leurs interactions est appliquee au probleme de la formation de structures cellulaires dans des monocristaux orientes pour le glissement multiple. Les conditions numeriques choisies sont celles d'un monocristal d'aluminium d'orientation [100] teste avec une vitesse de deformation totale imposee et une forte contrainte initiale. Les configurations de dislocations obtenues apres des deformations de l'ordre de 10−3 sont examinees sous charge et apres decharge. Des lames minces extraites des configurations simulees montrent l'existence de structures organisees qui peuvent ětre considerees comme un stade preliminaire de la formation de cellules. Ces resultats sont discutes de maniere critique et prospective.

Optical Properties of Annealed Tin(II) Oxide in Different Ambients

Abstract: Tin (II) oxide powder is coated at room temperature onto transparent glass substrates by direct thermal evaporation. The films have high transparency (more than 80%) in the visible and near-infrared regions of the electromagnetic spectrum. In the region between 300 and 1300 nm interference fringes are sharp and well defined. The interference fringes are used to calculate the thickness of the amorphous as-prepared film (≈ 722 nm) and the refractive index is found to be 1.84 at 700 nm. The absorption coefficient of this film ≈ 6 × 10−3 cm−1 at 355 nm. The thickness of the film thus measured was compared with results obtained from the Tolansky method. The optical band gap calculated from the simple power law was found to be 3.3 eV. The films are annealed in either O2 or N2 atmosphere for 1 h at various temperatures between 250 and 400 °C. It is found that the film is quite stable until about 400 °C, beyond which the optical band gap reduces to 2.7 eV (in N2 atmosphere) and increases to 3.4 eV (in O2 atmosphere). At higher temperature the films annealed in nitrogen ambient do not show the interference fringes, whereas in the oxygen atmosphere the interference fringes are still observed.

Preparation and Characterization of the K3Na(SO4)2: Eu Phosphor

Abstract: A new phosphor in the system K2SO4 Na2SO4 doped with Eu is reported. This is shown to be at least thrice as sensitive as the conventional CaSO4: Dy phosphor used in the thermoluminescence dosimetry of ionizing radiations. Characterization of this phosphor using XRD, PL, and TL techniques is described.

Growth and characterization of undoped and doped Bi12 TiO20 crystals

Abstract: Single crystals of B12 TiO20 are grown from solutions containing an excess of Bi2O3 by the TSSG (“top-seeded solution growth”) technique. Doping with iron, manganese, aluminium, and chromium is performed by adding the oxides to the melt. Measurements of dielectric constant, refractive indices, optical activity, absorption, light-induced absorption, and dark conductivity are performed. Bi12TiO20-Einkristalle werden aus Losungen mit einem Uberschus an Bi2O3 unter Verwendung der TSSG (“top-seeded solution growth”)-Technik gezuchtet. Dotierung mit Eisen, Mangan, Aluminium und Chrom erfolgt durch Beimischung der entsprechenden Oxide zur Schmelze. Messungen der Dielektrizitatskonstanten, der Brechungsindizes, der optischen Aktivitat, der Absorption, der lichtinduzierten Absorption sowie der Dunkelleitfahigkeit werden durchgefuhrt.

Variation in the effective richardson constant of metal—GaAs and Metal—InP contacts due to the effect of processing parameters

Abstract: The value of experimental Richardson constant (A*) is found to be a function of metal film thickness, type of the metal, method of deposition, and condition of semiconductor prior to metal deposition. In the case of Al and W on GaAs, the value of A* is found higher than the theoretical value. However, as the film thickness increases, the value of A* decreases. The larger value of A* is related to electrically active defects at the interface produced during sputtering. Filament evaporation results in smaller values for A*. In the case of WSi0.6 the presence of Si affects the value of A*. For InP, the value of A* is found smaller than the theoretical value. For both GaAs and InP, the value of A* increases when the semiconductor is annealed prior to metal deposition. This increase is significant in the case of InP.

On the origin of EBIC defect contrast in silicon. A reflection on injection and temperature dependent investigations

Abstract: Available data about the dependence of EBIC contrast c of extended defects on sample temperature T and beam current Ib are analysed. Two main types of behaviour are distinguished characterized by negative c(Ib)/positive c(T) slope and positive c(Ib)/negative c(T) slope, respectively. The former is attributed to defect charging (deep states) and the latter to shallow centres. Further, chemomechanical polishing is shown to influence the defect recombination activity. Die verfugbaren Daten zur Abhangigkeit des EBIC-Kontrastes ausgedehnter Defekte von Proben-temperatur T und Strahlstrom Ib werden analysiert. Zwei Haupttypen des Kontrastverhaltens – positiver Anstieg der c(Ib)-Kurve/negativer Anstieg der c(T)-Kurve oder aber negativer Anstieg fur c(Ib)/positiver Anstieg fur c(T) – konnen unterschieden werden. Wahrendersterer auf geladene Defekte (tiefe Zustande) zuruckgefuhrt wird, wird letzterer der Wirkung flacher Zentren zugeschrieben. Weiterhin wird gezeigt, das durch chemisch-mechanisches Polieren die Rekombinationsaktivitat der Defekte beeinflust wird.

EBIC investigations of dislocations and their interactions with impurities in silicon

Abstract: The applicability of the EBIC technique for studying the gettering of impurities to dislocations and other extended defects is discussed, including how quantitative values for the energy level position and concentration of the resulting electronic states can be determined when the Wilshaw model of recombination is obeyed. New experimental results from “clean” dislocations deformed at 900°C are presented along with evidence of the existence of a band of states at dislocations. In addition, EBIC measurements of nickel decorated dislocations show recombination behaviour that may be described in terms of a mixture of Wilshaw's recombination model and another type of mechanism. Finally, a new effect termed “electron beam induced activity” has been discovered, whereby the electron beam increases the electrical activity observed.

Microplasticity during High Temperature Indentation and the Peierls Potential in Sapphire (α‐Al2O3) Single Crystals

Abstract: The temperature dependence of the Vickers hardness is measured on the basal (0001) plane of single crystal α-Al2O3 (sapphire) from room temperature to 1273 K. The plastic zone surrounding the indents is investigated using selective chemical polishing and etching, optical microscopy, and transmission electron microscopy (TEM). Indentation was accompanied by three competitive damage processes: fracture, twinning, and dislocation plasticity. At room temperature, cracking predominates, and the presence of dislocations and/or twins could be revealed only by TEM. At intermediate temperatures (673 to 1073 K), extensive rhombohedral twinning is observed, while at higher temperatures, prismatic slip bands on {1120} dominates the microstructure. TEM observations reveal that the dislocation substructure at the vicinity of the indents consists of fairly straight dislocations lying in basal and/or prism planes and aligned along the 〈1010〉 and 〈1120〉 directions. The details of the glide dissociation of perfect 〈1010〉 screw dislocations into three collinear 1/3 〈1010〉 partials on the prism plane, the mechanism of the microplasticity of sapphire single crystals, and details of the Peierls potential for α-Al2O3 are discussed. Die Temperaturabhangigkeit der Vickers Harte wird auf der Basalebene (0001) in Saphireinkristallen im Temperaturbereich von Zimmertemperatur bis 1273 K gemessen. Die die Eindrucke umgebende plastische Zone wird durch selektives chemisches Polieren, Atzen, optische Mikroskopie und Transmissionselektronenmikroskopie (TEM) untersucht. Die Identierung wird von drei dominanten Schadensprozessen begleitet: Bruch, Verzwillingung und Versetzungsplastizitat. Bei Zimmertemperatur dominiert der Bruch; nur mit Hilfe der TEM kann das Vorhandensein von Versetzungen und/oder Zwillingen nachgewiesen werden. Im mittleren Temperaturbereich (673 bis 1073 K) werden rhomboedrische Zwillingslamellen mit Hilfe von selektivem Atzen auf (0001) gefunden. Bei hoheren Temperaturen dominieren prismatische Gleitbander auf {1120}-Ebenen die Mikrostruktur. TEM Beobachtungen der Hochtemperaturfolien zeigen, das die Versetzungsstruktur im Bereich der Eindrucke aus relativ geraden Versetzungen entlang 〈1010〉 und 〈1120〉 auf der Basal- und/oder den prismatischen Ebenen gebildet wird. Die Details der Gleitaufspaltung von perfekten 〈1010〉-Schraubenversetzungen in drei kollineare 1/3 〈1010〉-Partialversetzungen auf der prismatischen Ebene und der Mechanismus der Mikroplastizitat von Saphireinkristallen werden diskutiert.

New insights into the microscopic motion of dislocations in covalently bonded semiconductors by in‐situ transmission electron microscope observations of misfit dislocations in thin strained epitaxial layers

Abstract: By in-situ annealing of metastably strained (Si)/GexSi1−x/Si heterostructures in a transmission electron microscope, it is possible to directly observe and measure misfit dislocation propagation velocities. These measurements correspond to different regimes than conventional measurements of dislocation velocities in bulk Ge and Si, as in the present experiments motion at extremely high resolved applied (lattice-mismatch) shear stresses, of the order 1 GPa, and very low propagating dislocation lengths, 10 to 100 nm, is studied. This typically ensures that dislocation motion in the kink non-collision regime is observed, as opposed to the kink collision regime generally assumed in bulk measurements. By variation of the GexSi1−x/Si interface orientation, it is also possible to study the motion of total versus partial dislocations.

Dislocation dynamics and mechanical behaviour of elemental and compound semiconductors

Abstract: Experimentally observed stress-strain characteristics in yield deformation of Si, GaAs, and InP crystals are discussed in terms of the dynamic processes of dislocations on a microscopic scale. It is shown that experimental observations are satisfactorily reproduced by calculation on a theoretical model using empirical velocity equations of individual dislocations and taking into account the activities of dislocations of the primary and secondary slip systems.

Recombination Activity of Misfit Dislocations in Silicon

Abstract: A study of misfit dislocations in Si using the techniques of electron beam induced current (EBIC) and cathodoluminescence (CL) is presented. The dislocation recombination properties are found to depend on contamination. Dislocations in clean, as grown samples without D-band luminescence have very low recombination activity, with an EBIC contrast c of about 0.3% at T = 80 K and without detectable contrast at 300 K. Ni contamination is shown to increase the dislocation contrast markedly and to lead to pronounced dark spots at 300 K. A negative c(T) slope is observed for dislocations, which is attributed to shallow centres. Another contrast mechanism acting at the dark spots is ascribed to charged Ni silicide particles. Dark CL dislocation contrast is observed at 5 K when using the substrate luminescence, caused by dislocation-related reduction of exciton density. CL and EBIC correlate in a semi-quantitative manner for all samples studied, suggesting that the same centres might be responsible for the CL and EBIC contrasts. Es werden Untersuchungen von Fehlanpassungsversetzungen in Silizium mittels elektronenstrahlinduziertem Strom (EBIC) und Kathodolumineszenz (CL) vorgestellt. Es erweist sich, das die Rekombinationseigenschaften der Versetzungen vom Grad der Verunreinigung abhangen. Versetzungen in sauberen Proben ohne D-Band-Lumineszenz sind nur in sehr geringem Mase rekombinationsaktiv. Ihr EBIC-Kontrast c erreicht Werte von etwa 0,3% bei T = 80 K und ist bei 300 K nicht mehr nachweisbar. Verunreinigung durch Nickel fuhrt zu einer deutlichen Erhohung des Versetzungskontrastes und zu ausgepragten, dunklen, punktartigen Kontrasten, die bereits bei 300 K zu beobachten sind. Fur die Versetzungen wird ein negativer c(T)-Anstieg gefunden, der flachen Zentren zugeschrieben wird. Ein anderer Kontrastmechanismus, der am Ort der dunklen punktartigen Kontraste wirksam ist, wird auf geladene Nickelsilizid-Teilchen zuruckgefuhrt. Dunkler CL-Kontrast an Versetzungen, der aus einer Reduzierung der Exzitonendichte resultiert, ist bei 5 K zu beobachten, wenn die Substratlumineszenz genutzt wird. Fur alle untersuchten Proben stimmen CL- und EBIC-Ergebnisse halbquantitativ uberein. Das gibt Anlas zu der Vermutung, das CL- und EBIC-Kontrast durch die gleichen Zentren hervorgerufen werden.

Electrical and Photovoltaic Properties of Tetrapyrydilporphyrin Sandwich Cells

Abstract: Electrical and photovoltaic effects observed with a thin film of 5,10,15,20-tetra(4-pyrydil)21H,23H-porphine (TPyP) sandwiched between indium-tin oxide (ITO) and Al electrodes are explained in terms of the n-type semiconducting behaviour of the organic film and its formation of a blocking contact (Schottky barrier) with ITO. Under low forward bias (ITO electrode positive) Ohm's law is followed with a thermally-activated electron concentration of n0 ≈ 3 × 109 cm−3, an electron mobility μ0 ≈ 6 × 10−4 cm2/Vs, and a room temperature electrical conductivity σ0 ≈ 3 × 10−13 Ω−1 cm−1. At high applied voltage there is a space-charge-limited conductivity (SCLC) controlled by a single trap level. The derived trap level parameters are: the total trap concentration Nt, = 1.7 × 1014 cm−3 and the depth of the trap level Ec — Et = 0.78 eV. Under reverse bias currents are identified with Schottky emission over a potential barrier of approximate height 0.7 eV and thickness varying with temperature in the range (193 to 50) nm. At illumination through an ITO electrode with monochromatic light of 32 μ/cm2 at 440 nm, the typical cell parameters are determined. The action spectra are explained in agreement with the proposed energy band model for the ITO/TPyP/Al diodes. Les effets eletriques et photovoltaiques observe avec une couche mince de TPyP place entre les deux electrodes du ITO et Al, sont expliquees par la conduction de type-n, au TPyP et par le fait que le couche de TPyP forme une barriere de Schottky avec ITO. Dans le regime des faibles tensions appliquees il y a une conduction ohmique avec la concentration des electrons n0 ≈ 3 × 109 cm−3, la mobilite μ0 ≈ 6 × 10−4 cm2/Vs et la conductibilite σ0 ≈ 3 × 10−13 Ω−1 cm−1. Dans le regime des fortes tensions appliquees il y un courant limite par la charge d'espace controlle par un seul niveau des trapes. Les parametres des trapes sont: la concentration des trapes Nt = 1.7 × 1014 cm−3 et leur position dans la bande interdite du semiconducteur organique Ec — Et = 0.78 eV. Dans le regime des tensions appliquees dans le sens inverse, le courant est limite par haute de 0.7 eV et l'epaisseur qui varries avec le temperature dans le domain (193 a 50) nm. Quand la cellule a ete illumine avec la lumiere monochromatique de 32 μW/cm2 et 440 nm, les parametres photovoltaiques ont ete determine. Les spectres d'action ont ete explique avec l'aide du diagramme energetique propose pour les diodes ITO/TPyP/Al.

Surface Preparation of FeS2 via Electrochemical Etching and Interface Formation with Metals

Abstract: The effect of passing cathodic currents at potentials of hydrogen evolution through differently pretreated n-type pyrite (FeS2) electrodes is studied by XPS It is shown that hydrogen evolution results in an etching of the crystal via dissolution of FeS2 Surfaces that are destroyed through sputtering or polishing are restored through this etching procedure (100) and (111) surfaces behave similar to each other When depositing gold onto the electrochemically etched surface in ultrahigh vacuum no change of the band bending of the clean surface (650 meV) is observed An abrupt interface with FeS-like defects in the pyrite is formed Deposition of platinum yields a ternary PtFeS interlayer between pyrite and metallic Pt The band bending is reduced by 200 meV during contact formation Concerning the chemical composition and the electronic structure the etched surfaces behave nearly identical to clean (100) cleavage planes of pyrite Die Wirkung kathodischer Strome bei Potentialen der Wasserstoffentwicklung auf unterschiedlich vorbehandelte n-Pyritoberflachen (FeS2) wird mit XPS untersucht Es kann gezeigt werden, das die Wasserstoffentwicklung ein Atzen des Kristalls mittels Auflosung von FeS2 bewirkt Oberflachen, die durch Ionenatzen oder Polieren zerstort wurden, werden durch das elektrochemische Atzen wiederhergestellt (100)- und (111)-Oberflachen verhalten sich dabei nahezu identisch Bei der Bedampfung der elektrochemisch behandelten Oberflachen mit Gold im Ultrahochvakuum bleibt die ursprungliche Bandverbiegung von 650 meV erhalten Es wird eine scharfe Grenzflache gebildet, auf der Pyritseite entstehen dabei FeS-artige Defekte Die Bedampfung mit Platin resultiert in einer ternaren PtFeS-Zwischenschicht zwischen Pyrit und metallischem Pt Die Bandverbiegung wird um 200 meV reduziert In Bezug auf die chemische Zusammensetzung und die elektronische Struktur verhalten sich die geatzten Oberflachen wie saubere (100)-Spaltflachen von Pyrit

Luminescence associated with the presence of dislocations in silicon

Abstract: A brief account is given of some recent investigations of the luminescence associated with the presence of dislocations in silicon. These investigations show that transition metal contamination is necessary for dislocation related luminescence to be observed in plastically-deformed float-zone silicon and in material containing epitaxial and oxidation-induced stacking faults. Cathodoluminescence spectroscopy and imaging measurements, and photoluminescence measurements on material with low densities of grown-in dislocations, imply that the D3 and D4 luminescence features originate in the dislocation cores, whereas the D1 and D2 features are associated with point defects trapped in the strain fields of dislocations.

The Density of Tunneling and Vibrational States of Glasses within the Soft-Potential Model†

Abstract: Numerical calculations of the density of tunneling and vibrational states of glasses within the soft-potential model (an extension of the tunneling model to include soft vibrations) are reported and compared to analytical approximations. Using a specific assumption on the asymmetry of the soft potentials, one is able to describe the anomalous features of the specific heat Cp and the thermal conductivity of glasses over the entire low temperature range, up to and including the peak in Cp/T3 and the second rise of the thermal conductivity above the plateau. Es wird uber numerische Rechnungen zum Modell weicher Potentiale berichtet (eine Erweiterung des bekannten Tunnelmodells fur Glaser auf eine gemeinsame Beschreibung von Tunnelzustanden, weichen Schwingungen und Relaxationen). Die Ergebnisse werden mit analytischen Naherungen verglichen. Eine spezielle Annahme uber die Asymmetrieverteilung der weichen Potentiale ermoglicht eine Beschreibung der Glasanomalien der spezifischen Warme Cp und der Warmeleitung im gesamten Tieftemperaturbe-reich, einschlieslich des Maximums in Cp/T3 und des erneuten Anstieges der Warmeleitung oberhalb des Plateaus.

On the influence of tin on the formation of the σ‐phase in the FeCr system

Abstract: The influence of tin on the formation of the σ-phase, caused by an isothermal annealing at 700°C, in FeCr alloys with near equiatomic compositions was studied by means of 57Fe and 119Sn Mossbauer spectroscopy. It was shown that the addition of up to 5.5 at% Sn to the FeCr alloys retards the formation of the o-phase significantly. The kinetics of the transformation follows the Johnson-Mehl equation. The evidence was found that tin precipitates on the grain boundaries if its nominal concentration exceeds ≈ 2 at%. For a given nominal concentration of added tin the size of grains was found to be the same in the α and σ-phases, but it was smaller for samples with higher Sn content. The composition of the σ-phase remains constant at a value of 46.7 at% Cr and 1.4 at% Sn, regardless of the nominal tin content. L'influence de l'etain dans la formation de la phase σ provoquee par un recuit isothermique a 700°C, a ete etudiee pour les alliages FeCr avec des compositions presque equiatomiques par spectroscopie Mossbauer du 57Fe et du 119Sn. On a verife que l'addition d'etain jusqu'a 5,5 at% aux alliages FeCr retarde significativement la formation de la phase σ. La cinetique de la transformation suit l'equation de Johnson-Mehl. On a aussi observe que l'etain precipite sur les joins de grains quand sa composition nominale est superieure a 2 at%. Pour chaque concentration nominale d'etain additional, les grains gardent la taille dans les deux phases: α et σ, cependant leur taille diminue quand la concentration d'etain augmente. On a aussi verifie que la composition de la phase σ est toujours 46,7 at% Cr et 1,4 at% Sn, quel que soit la concentration nominale d'etain.