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The ternary iron arsenide compound BaFe2As2 exhibits a structural phase transition from tetragonal to orthorhombic at a temperature of about 140 K. The twin lamellae arising below this transition temperature were studied in undoped single crystalline bulk and epitaxial thin film samples using electron backscatter diffraction in a scanning electron microscope equipped with a helium cryostat. Applying this technique on bulk single crystals a characteristic twin lamella size in the range of 0.1 μm up to a few μm was observed. In contrast, in epitaxially strained thin films the phase transition is not observed at temperatures above 19 K.

This chapter is structured into two main parts. Part 1 describes the fundamentals of the atomic (ideal) structure and (real) microstructure arrangement of solid matter. The way in which (metallic) materials are generated from the melt and the resulting phase diagrams for common binary systems are elucidated in the first part of this chapter (Sect. 4.1). In order to understand materials properties, microstructural characterization has to be carried out on various length scales. Therefore, in the second part (Sect. 4.2), the most common preparation steps for microscopy methods used in materialography are given. Next, basic micromethods for the investigation of the local chemical composition and local crystalline structure are outlined. This includes methodologies for the quantification of the complex microstructures in engineering materials.

A CuAg7Zr0.05 alloy was processed by high-pressure torsion (HPT) for 10 revolutions, and subsequent annealing resulted in a fully recrystallized ultrafine-grained (UFG) microstructure. A minimum mean grain size of 117 nm was successfully achieved, which is quite uncommon via conventional deformation and annealing process. Tensile tests indicate that these recrystallized UFG specimens possess ultrahigh yield strength up to 917 MPa and notable ductility of 14%. However, the uniform elongation was sensitive to the grain size, and there was a sharp improvement when the grain size increased from 334 nm to 444 nm. Mechanisms for the sharp transition were explored.

The most ductile rare earth intermetallic compound, YAg, was subjected to an thermal activation analysis at low temperatures down to 4 K. Evaluation of the activation parameters and their dependence on stress and temperature yields strong indication for forest dislocation cutting as the rate-controlling deformation mechanism, similar to face-centered cubic metals. Surprisingly, nil temperature ductility was observed. Together with results of a detailed TEM analysis of the active slip systems it is concluded that, despite of violating the von Mises criterion for the plastic deformation of polycrystalline materials, a low elastic anisotropy and/or low Peierls stress is responsible for the appreciable ductility at low temperatures. This finding may help to search for other ductile systems in the broad class of intermetallic compounds.

We determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calorimetry, cp-measurements are carried out from &minus, 170 &deg, C to the materials&rsquo, solidus temperatures TS. From these experiments, we determined the thermal entropy and compared it to the configurational entropy for each of the studied alloys. We applied the rule of mixture to predict molar heat capacities of the alloys at room temperature, which were in good agreement with the Dulong-Petit law. The molar heat capacity of the studied alloys was about three times the universal gas constant, hence the thermal entropy was the major contribution to total entropy. The configurational entropy, due to the chemical composition and number of components, contributes less on the absolute scale. Thermal entropy has approximately equal values for all alloys tested by DSC, while the crystal structure shows a small effect in their order. Finally, the contributions of entropy and enthalpy to the Gibbs free energy was calculated and examined and it was found that the stabilization of the solid solution phase in high entropy alloys was mostly caused by increased configurational entropy.

The ternary iron arsenide compound BaFe

Copper and its alloys are widely used because of their outstanding conductivity, workability and resistance to corrosion. Selected alloys from the principal groups of copper-based materials are presented, including unalloyed coppers, high-copper alloys, brasses, and bronzes, highlighting the capability of this class of materials. The description of the alloys is presented with a strong focus on physical metallurgy, i. e., basic considerations of the phase equilibria in binary systems are drawn and linked to the mechanical and physical properties of the alloys. This chapter pinpoints the potential of the alloys based upon their properties and includes essential information important for materials selection.

There is no method that allows the simultaneous preparation of titanium and aluminum, so that both phases can be investigated by means of scanning electron microscopy (SEM) at the same time. Especially local orientation measurements by electron back scatter diffraction (EBSD) are challenging as they require a very good surface quality. This study deals with the preparation of aluminum/titanium composites, produced by Accumulative Roll Bonding (ARB) as well as with their microstructural analysis emphasing on the metallographic sample preparation. Well established routes of metallographic preparation for aluminum and titanium are facing serious problems such as rounding of edges, arising of deformation layers, blurred layers and oxide layers. This is of particular concern when these routes are applied to Al/Ti multilayered samples without adaption. This study reveals a route for metallographic sample preparation that enables SEM including EBSD analyses of Al/Ti composites for both phases simultaneously.

The use of copper - high nitrogen stainless steel macrocomposites for applications such as pulsed high magnetic field coils is demonstrated in this contribution. The macrocomposite reveal an enhancement of up to 40% in strength when cooling from 300 K down to liquid nitrogen temperature. An ultimate tensile strength of 1.53 ± 0.017 GPa is reached with a 3 mm × 2 mm wire with 52 vol.-% Cu and a logarithmic drawing strain of η = 2.8 at liquid nitrogen temperature. Compared to the low nitrogen stainless steel macrocomposites in use up to now, which have an UTS of 1.02 ± 0.017 GPa and reveal an enhancement of 28% in strength when cooling down, these values related to high nitrogen stainless steel macrocomposites bear great improvements. © 2003 Elsevier Science Ltd. All rights reserved.

The tensile deformation behaviour of an extruded, polycrystalline YCu intermetallic compound was investigated from room temperature down to 77 K. A stress-induced martensitic transformation of the cubic B2 to the orthorhombic B27 phase was observed. The increasing amount of B27 phase with decreasing temperature leads to a decrease in ductility. A drastic decrease sets in at about 160 K when thermally induced martensite is formed, characterizing the brittle-to-ductile transition of YCu. Reasons for the relatively high ductility above 160 K are discussed.

In an austenitic Fe 61.5 Mn 23 Ni 7 Cr 8.5 antiferromagnetic (afm) alloy deformation results in a splitting between magnetisation-vs.-temperature curves measured during field cooling (FC) below the Neel temperature and those measured at the same field after zero-field cooling (ZFC). Furthermore, a thermoremanent magnetisation (TRM) appears that corresponds to the splitting between zero-field and field cooled thermomagnetic measurements for a given cooling field and scales with the degree of deformation. This TRM is attributed to the deformation induced defects which act as a source of uncompensated magnetic moments and interact with the bulk afm moments. This interpretation is also supported by the fact that the net magnetic moments vanish above the Neel temperature. The TRM does not saturate in fields of up to 7 T, applied during cooling, and cannot be switched by fields up to 7 T. Within the investigated field range of −7 T to 7 T the magnetisation-vs.-field curves show a stable shift along the magnetisation axis. Thus, the uncompensated moments appear to be strongly exchange coupled to the afm matrix surrounding them. Within the series of experiments the maximum TRM reached after FC in 7 T corresponds to about 4 × 10 −4 μ B /atom (Bohr magneton) of the maximum deformed afm sample. The Neel temperature decreases due to deformation.

We study low-mobility 2D electron gas in GaAs quantum well in tilted magnetic field up to 45 T. Analyzing the behavior of the Shubnikov-de Haas (SdH) oscillations we obtain the value of g-factor, | g | = 0.9 ± 0.1 , which is noticeably larger than that predicted theoretically and obtained from optical experiments. Possible reasons of the discrepancy are discussed.

The microstructure and mechanical properties of heavily cold-worked CuAgZr alloys are investigated to understand the development of strain in these alloys. Heat treatments increase strain and if applied intermediately between large strains of cold deformation this happens to be valid even for comparable stress levels. This study is focused on the state after the heat treatment in order to show the impact of the microstructure in the mentioned state on the development of the mechanical properties. The microstructure of the samples is inhomogeneous after heavy plastic deformation and also after annealing in the order of the recrystallisation temperature. At this temperature a certain fraction of Ag that has been dissolved during deformation reprecipitates and strengthens the material again. In addition, annealing causes the formation of twins, which is considered as origin of an raised elastic modulus.

Low temperature deformation results in a considerable refinement of the microstructure of polycrystalline copper by extensive deformation twinning in the case of cryogenic wire drawing. In order to improve the thermal stability of the obtained microstructure, we investigate the deformation of CuZr alloys with up to 0.21 at% (0.3 wt%) Zr by drawing in liquid nitrogen up to a true strain of 2.4. An ultimate tensile strength of 625 MPa in combination with an electrical conductivity of about 60%IACS was found for an initially solution annealed CuZr0.21 alloy. For an initially precipitation treated CuZr0.21, a slightly lower ultimate tensile strength of 600 MPa at about 86%IACS was observed in the as-deformed state. Deformation twinning could be identified in all investigated materials, leading to a refinement of the microstructure. Thermal stability of microstructure as well as electrical and mechanical properties can be significantly improved by the addition of Zr. For cryo-drawn copper the drop of hardness due to recovery and recrystallization occurs between 200 °C and 225 °C for an annealing duration of 30 min. Small recrystallized grains are already identified at 175 °C. In CuZr0.21, a stable microstructure is found up to 350 °C for the solution annealed material while small recrystallized grains are found already at 300 °C in the precipitation treated material. By annealing a homogenized and subsequently cryo-drawn CuZr0.21 at 350 °C for 30 min, ultimate tensile strength can be further increased up to 635 MPa while electrical conductivity is enhanced significantly to 70%IACS by partial precipitation of Cu 5 Zr. Dynamic resistivity measurements indicate that this heat treatment subsequent to cryo-drawing does not affect the thermal stability of the prepared material.

A novel method to manufacture a refractory metal three phase Mo–2.7%Nb–8.9%Si–7.7%B at.% silicide alloy with mechanical alloying as the crucial processing step is presented. After consolidation a triplex ultra-fine grained microstructure with the average sizes of the Mo solid solution and both intermetallic compounds Mo3Si and Mo5SiB2 (T2 phase), respectively, ranging clearly in the sub-micrometer range was obtained. Tensile tests revealed structural superplasticity with strain to failures as high as 400% and temperatures as low as 1300 °C. Due to the extraordinary thermal stability of the microstructure isothermal annealing at 1700 °C for 10 h was needed for significant coarsening of the microstructure. A comparative assessment of the compressive creep properties of both microstructures in the temperature range between 1050 and 1315 °C showed an increase of the creep resistance of the coarsened microstructure by more than one order of magnitude in strain rate compared with the material in the as-processed condition.

We study the strong effect of a small concentration (1 part per 1000) of randomly distributed N-resonant scatterers on the quantized Landau level states of a GaAs quantum well. Our magneto-tunneling spectroscopy measurements allow us to probe the resonant and non-resonant component of the N-related scattering potential.

Magnetostriction gives an insight into the interactions between the electronic and the lattice system of solids. Because only macroscopic methods can be used in fields above 20 T, miniaturized capacitive dilatometers were adapted to the strongest magnets. We performed experiments up to the highest available steady fields of 45 T and in 50 T pulsed field systems. The power of magnetoelastic investigations is illustrated by measurements at two 4f-intermetallics: SmCu2 is an antiferromagnet below 23 K with a nearly compensated magnetic moment and, the monopnictid GdSb orders antiferromagnetically at 24 K. Both materials show magnetic transitions at applied fields of about 30 T when the ferromagnetic state is induced.

GdCo9−xSi4+x (x = −0.2 to x = 0.2) and TbCo9Si4 exhibit the tetragonal LaFe9Si4 structure (space group I4/mcm). Magnetically these samples are ferrimagnetic with ordering temperatures close to 50K. The ferrimagnetic magnetization is found to decrease with decreasing Si content, thus, revealing an increasing cobalt sublattice magnetisation. The antiparallel coupling of the Gd- and Co-sublattice magnetisations breaks up at lower critical fields Hl well above 20 T. From the lower critical field Hl as well as from the slope ΔM/ΔH for fields above Hlthe inter-sublattice molecular coefficient can be determined which is approximately constant within this solid solution.

The high thermal stability of a nanocrystalline mechanically-alloyed Cu–Nb alloy was studied by means of isothermal annealing at high temperatures. The structure of the Cu matrix remains nanocrystalline with a grain size of about 50nm even after annealing at 1000°C for 10h. The copper grain growth is described with the help of kinetic analyses. The activation energy of the copper grain growth in Cu-10at.% Nb is about 0.98eV and the grain growth exponent is 4. The enhanced stability of the nanocrystalline Cu microstructure is attributed to the diffusion of Nb atoms along the Cu grain boundaries, “Zener drag” of NbO, Cu2O or Fe7Nb6 particles, and a non-equilibrium state of Cu grain boundaries.

Nanocrystalline Cu and Cu–Nb alloys were prepared by the consolidation of mechanically alloyed powder. The alloys show a microstructure with a grain size below 50 nm. The microstructure of the Cu matrix remains stable even at elevated temperatures of up to 900 °C, whereas the Nb precipitates coarsen during annealing. The mechanical strength as well as the electrical conductivity depend on the grain size of the Cu matrix, which can be influenced by the temperature of the heat treatment, i.e., a mechanical strength of about 1.6 GPa is measured for a Cu–10 at.% Nb alloy which shows an electrical conductivity of about 10% IACS (international annealing copper standard) at room temperature. The main contribution to the mechanical strength of the alloys is attributed to the grain boundary strengthening in Cu referring to the Hall–Petch relation, which is quantified. The grain boundaries are also found to influence considerably the electrical resistivity.

We discuss further developments in the application of Finite Element Analysis (FEA) to the design of pulsed magnets on the basis of our latest coil design. Two areas are addressed. Firstly, we present results concerning the current distribution in the conductor during the discharge. Eddy current heating leads to thermal gradients across the layers and in the conductor; the results are compared with well established analytical codes. Significantly higher stresses result due to temperature gradients and nonuniform current distribution, which can be partly offset by pre-stressing reinforcement fibers. Secondly, we report progress in designs that facilitate much more rapid cool-downs for pulsed magnets, which can sometimes take in the order of hours between pulses.. We show that cool-down times of 20 minutes or less are achievable using copper discs (designed using FEA) that will not support eddy currents.

The phase relations of the GdCo13−x Six system have been studied by means of scanning microscopy, microprobe analysis and x-ray diffraction. Single-phase samples GdCo9±δSi4∓δ (structure type LaFe9Si4 with space group I 4/mcm) ar ef ormed in a narrow composition range |δ| 0.2, where GdCo9Si4 forms as af ully ordered ternary compound. The magnetic properties of GdCo9Si4 have been investigated by ac susceptibility, magnetization, specific heat and resistivity measurements. These experiments reveal ferrimagnetism below about 47 K, which is analysed in terms of a two-sublattice molecular field model with a local moment Gd subsystem coupling antiparallel to the itinerant ferromagnetic Co 3d sublattice. The 3d–3d exchange of the latter is the driving force for the onset of long range magnetic order. The validity of the twosublattice model is demonstrated by high field measurements, showing that the ferrimagnetic coupling starts to break up at a lower critical field µ0 Hl � 27 T. The magnetic ground state of GdCo9Si4 has been analysed on a microscopic basis via LSDA electronic structure calculations. (Some figures in this article are in colour only in the electronic version)

High strength Cu–Nb-conductors were prepared by mechanical alloying and subsequent heat treatment and deformation. The mechanical as well as electrical properties of the material were optimised by varying the Nb-content and also by the adjustment of the heat treatment parameters. Microstructure characterisation was carried out by SEM including EBSD, TEM and X-ray measurements. Optimally treated material shows an ultimate tensile strength of 1210 MPa and an electrical conductivity of about 50% International Annealing Copper Standard (IACS) at room temperature. Grain-boundary sliding as a non-conventional deformation mechanism has been observed to be active in the copper matrix, which is strongly correlated to its nanocrystalline microstructure. This is associated with grain rotation as accommodation process.

The slope is an important distance parameter for a convolutional code. It can be used to obtain a lower bound on the active burst distance and in this respect essentially determines the error-correcting capability of the code. An upper bound on the slope of rate R=b/c convolutional codes is derived. A new family of convolutional codes, called the maximum slope (MS) code family, is introduced. Tables for rate R=1/2 MS codes with memory 1/spl les/m/spl les/6 are presented. Additionally, some new rate R=(c-1)/c, 3/spl les/c/spl les/6, punctured convolutional codes with rate R=1/2 optimum free distance (OFD) and MS mother codes are presented. Simulation results for the bit error performance of serially concatenated turbo codes with MS component codes are presented.

Copper has been mechanically alloyed with the bcc structure type elements Nb and Mo in order to obtain a material with high strength, good ductility and good electrical conductivity. In the case of alloying Cu with Nb a solid solution is formed during milling, whereas in the case of alloying Cu and Mo a fine distribution of Mo particles within the copper matrix is observed. The different behaviour of these two alloys is related to the large difference of the elastic constants of the bcc elements. Niobium precipitates from the solid solution and molybdenum particles coarsen during a subsequent heat treatment.

Nanostructured Cu–Nb composites are prepared by mechanical alloying and a subsequent heat treatment. Up to 10 at.% Nb can be brought into solid solution by milling for 30 h at liquid nitrogen temperature. Subsequent to mechanical alloying a heat treatment was applied to precipitate the niobium from the solid solution in order to enhance both strength and conductivity of the material. The atmosphere present during the milling process strongly influences the phase formation. A high oxygen content within the powder leads to the formation of niobium oxide during the late state of milling and, later, prevents the formation of niobium precipitates by heat treatment. This occurs only in powder with a low oxygen content. A temperature of 400 °C proves to be the optimum for strength, but too low to enhance the conductivity by complete precipitation of the Nb atoms. Almost all the niobium precipitates from the solid solution at 900 °C, but recrystallisation takes place at this temperature. Thus, the optimum heat treatment produces a balance between the mechanical and electrical properties and should be in the range of 600–700 °C.

Alloys with both high strength and high conductivity have been produced by mechanical alloying. In the present study, copper was mechanically alloyed with 5, 10 and 20 at.% Nb using a planetary ball mill. The Cu–Nb phase diagram shows a negligibly low mutual solubility in the solid state, but high energy ball milling can largely extend the region of solid state solution. Previously, it was observed that niobium partly dissolves in the copper lattice during milling. The present investigation demonstrates that this limit can be extended to a strongly supersaturated Cu solid solution of up to 10 at.% Nb provided the appropriate mechanical alloying method is applied. The change in the powder microstructure was followed by scanning and transmission electron microscopy (TEM) as well as by X-ray diffraction (XRD) analysis. In the case of Cu–5%Nb and Cu–10%Nb a homogeneous single-phase microstructure was obtained after 30 h of milling. Elemental Nb could no more be detected, indicating the formation of a metastable supersaturated Cu–Nb solid solution.

The effect of substitutional disorder on the superconducting properties of YNi2B2C was studied by partially replacing yttrium and nickel by Lu and Pt, respectively. For the two series of (Y, Lu)Ni2B2C and Y(Ni, Pt)2B2C compounds, the upper critical field H c2(T) and the specific heat c p(T, H) in the superconducting mixed state have been investigated. Disorder is found to reduce several relevant quantities such as T c, the upper critical field H c2(0) at T=0 and a characteristic positive curvature of H c2(T) observed for these compounds near T c. The H c2(T) data point to the clean limit for (Y, Lu) substitutions and to a transition to the quasi-dirty limit for (Ni, Pt) substitutions. The electronic specific heat contribution γ(H) exhibits significant deviations from the usual linear γ(H) law. These deviations reduce with growing substitutional disorder but remain even in the quasidirty limit which is reached in the Y(Ni1−x , Pt x )2B2C samples for x=0.1.

The challenge of the present knowledge of the electronic structure and selected thermodynamic properties on the mechanism of superconductivity in rare-earth transition metal borocarbides (nitrides) is discussed with respect to somewhat unexpected similarities with as well as to clear differences from the cuprate superconductors. The effect of substitutional nonmagnetic and magnetic disorder in the rare-earth intermediate layer in between the transition metal boron networks as well as in the network itself upon various thermodynamic properties in the superconducting state of Y x R 1− x C(Ni 1− y Pt y B) 2 R= Lu or Tb is studied theoretically as well as experimentally. The suppression of the upper critical field and its positive curvature near T c can be used as highly sensitive measures of the degree of disorder.

Parametric X radiation (PXR) produced by electrons with an energy of ${E}_{0}=4 \mathrm{MeV}$ interacting with the atoms in the (220) plane of a $20\ensuremath{-}\ensuremath{\mu}\mathrm{m}$ silicon and a $55\ensuremath{-}\ensuremath{\mu}\mathrm{m}$ diamond crystal and observed at an angle of $44\ifmmode^\circ\else\textdegree\fi{}$ by a Si(Li) detector has been investigated with respect to the interference with coherent bremsstrahlung (CB) that originates in the same interaction process between the incoming relativistic electron and the crystal. Since the energy of PXR and CB is identical, contributions of both types of radiation are indistinguishable. The newly derived analytical expressions describe the radiation which consists of a coherent superposition of PXR and CB. For the comparison of the experimental results with the theoretical predictions a Monte Carlo simulation taking into account all effects accompanying the radiation process has been performed. The comparison shows very good agreement between experiment and theory.

Summary In the newly changed managed care environment, psychologists can distinguish themselves both as scientists and practitioners. Psychologists have been working steadily to quantify their offerings. Researchers have not only confirmed the efficacy and effectiveness of psychotherapy, they have been studying specific in-session and out-of-session factors that will help predict when, how, and with whom, to provide which psychological services. Our knowledge of all that precedes treatment and all that is required to maintain treatment gains will help us market ourselves with more authority. Our ability to create services based on this knowledge will become our most valued offering to the payor driven medical establishment and the underwriters of medical care.

Parametric x rays (PXR) produced by bombarding silicon and diamond crystals with electrons of 30 to 87 MeV were detected at $180\ifmmode^\circ\else\textdegree\fi{}$ relative to the direction of the electron beam. It was found that the dependence of the intensity on the orientation of the crystal agrees with the predictions of the kinematical theory of PXR. The absolute intensity is twice as large as predicted. These findings can be explained considering dynamical effects that govern the x-ray crystal interaction. Additionally, x rays caused by self-diffracted transition radiation have been observed.

Magnetisation and longitudinal magnetoresistance of single-crystal samples of two compositions: stoichiometric compound U3P4 and its solid solution U3(P,As)4 (with As:P ratio close to 1) were measured in pulsed magnetic fields with strength up to 47 T, and in temperatures from 4 K up to few tens of kelvins above the Curie temperatures (135 K and 181 K for both compositions, respectively). Field was always applied along a hard magnetic direction [100]. Magnetisation experiments showed no sign of expected magnetic-moment-reorientation transition and data look quantitatively similar for both compositions. On the other hand, longitudinal magnetoresistance (MR) is remarkably different for each composition. Onset of the above mentioned transition can be held responsible for broad maxima observed in MR(B) curves for U3(P,As)4. Values of magnetic field strength corresponding to these maxima follow a linear dependence on temperature. We assume that these features of MR(B) curves are due to progressive deformation of magnetic structure of U3(P,As)4 in high magnetic fields.

We present a overivew of the present knowledge of the electronic structure of selected properties of quaternary intermetallic rare earth transition metal borocarbides and related boronitride compounds. The calculated highly anisotropic Fermi surfaces exhibit clear similarities such as nested regions but also significant distinctions. Electrons from the nested parts of the Fermi surface affect several properties in the superconducting state. We report theoretical calculations which emphasize the relevance of these electrons to the mechanism of superconductivity. Structural parameters for ScNi2B2C derived from total energy calculation allow to discriminate confilicting experimental structural calculation results with various electronic spectroscopies such as X-ray absorption spectroscopy (XAS). The excellent agreement with the XAS data suggests a minor importance of correlation effects compared with the cuprate super-conductors. Thermodynamic properties of these systems are analyzed within the multi-band Eliashberg theory with special emphasis on the upper critical field (H c2 (T) and the specific heat. In particular, the unusual positive curvature of H c2 (T) near T c observed for high-quality single crystals, polycrystalline samples of YNi2B2C, LuNi2B2C as well as to a somewhat reduced extent also for the mixed system Y1−x LuxNi2B2C is explained microscopically. The values of H c2 (T) and of its positive curvature near T c are intrinsic quantities generic for such samples. Both quantities decrease with growing disorder and thus provide a direct measure of the sample quality.

The suppression of superconductivity of pseudo-quaternary R{sub x}Y{sub 1{minus}x}Ni{sub 2}B{sub 2}C compounds in the dilute limit was found to be mainly caused by magnetic pair-breaking in the case of the heavy rare-earth elements (R = Tm, Er, Ho, Dy, Tb, Gd) and by lattice distortions in the case of the light rare-earth elements (R = Pr, Nd) resulting from the large difference of the ionic radii between the Y host ions and the R impurity ones.

The electronic structure of tetragonal (RC(N))m(TB)2, m=1−3, compounds, with R= Y,Lu,La, T=Ni,Pt is studied. Total and partial densities of states N(E) are calculated and compared with orbital resolved x-ray absorption data. Special attention is paid to the structure of N(E) near the Fermi-level and its consequences for thermodynamic properties in the superconducting and the normal states. A medium el-ph coupling constant 0.5≤λ≤ 1.2 is found. There is no simple correlation between N(0) and Tc. The analysis of the upper critical field reveals the presence of at least two groups of electrons with quite different Fermi velocities vFin accord with dHvA data, and with calculated distributions of vFaround the Fermi surface

Polarization properties of parametric X radiation (PXR) have been investigated theoretically and experimentally at the S-DALINAC. For the first time analytical expressions describing the polarization properties of PXR have been derived. PXR is – under ideal conditions – 100% linearly polarized in every single point of its angular distribution. In reality, however, multiple scattering of the electrons passing through the crystal, the emittance of the electron beam, the crystal mosaicity and the detector acceptance decrease the polarization degree. In the present experiment PXR was produced by E 0 =80.5 MeV electrons interacting with a (2 2 0) plane of a 13 μm silicon crystal and observed at an angle of about 20° by a CCD polarimeter. For the comparison of the experimental results with the theoretical predictions a Monte Carlo simulation taking into account the experimental conditions has been performed. The comparison shows very good agreement.

The linear polarization of Parametric X-radiation (PXR) produced by 80.5 MeV electrons in a 13 μm thick silicon single crystal has been analyzed by means of a novel method of polarimetry exploiting directional information of the photoeffect in a charge coupled device consisting of 1.3×10 6 square pixels of 6.8 μm. The experiment was carried out at the Darmstadt superconducting linear accelerator S-DALINAC providing a low-emittance electron beam. The linear polarization of the (2 2 0) reflection observed in eight narrow angular bins between 20 ∘ and 21 ∘ with respect to the electron beam direction is consistent with complete local linear polarization. The orientation of the polarization plane, within measurement errors of typically 10 ∘ , varies over the diffraction pattern in such a way as to be expected from kinematical theory. The result of this experiment is in contradiction to the only other PXR polarization measurement performed so far.

The spectral-angular and the linear polarization properties of channeling radiation emitted by 30.8 MeV electrons incident on a 13 μm thick silicon crystal at small angles with respect to various major crystal axes have been investigated. The transition from axial to planar channeling radiation properties is well described by a two-dimensional many-beam calculation based on a periodic string potential. At energies above the strongest planar channeling radiation lines coherent bremsstrahlung linearly polarized perpendicular to the polarization of the corresponding planar channeling radiation is observed and found to be well reproduced by the model calculations. Axial channeling radiation of the 〈110〉 axis shows a small amount of linear polarization due to the `double-well' potential in agreement with the calculations.

The intensity of channeling radiation (CR) was compared for diamond and ruby crystals and also with the intensity of parametric X-radiation (PXR) originating from the same diamond. The investigations were carried out with relativistic electrons provided by the injector of the S-DALINAC at energies between 3.0 and 9.0 MeV. Both types of radiation were observed by means of Si(Li) detectors placed at 0° and 44° with respect to the electron beam axis for CR and PXR, respectively. The highest photon flux Φ = 2 × 108 photons/(smm2) was found to result from CR of diamond crystals. Ruby crystals exhibit somewhat narrower X-ray lines but less intensity. A comparison with PXR reveals that — against predictions — its intensity is three orders of magnitude weaker than CR under the same conditions. The possibility to use the CR and PXR as intense tunable photon sources is discussed.

In order to increase the mechanical strength of copper while retaining its high electrical conductivity the copper matrix is strengthened by Nb particles. For thermodynamical reasons the mutual solubility of Nb in copper is negligible. Therefore, a Cu-Nb alloy is prepared by mechanically alloying and subsequent hot pressing. The formation of a solid solution in a first step and of precipitates in a Cu-10 at.%Nb alloy in the second one as well as the effect of these precipitates on the mentioned properties is discussed. The influence of different temperatures during hot pressing on density, mechanical and electrical properties, etc. is investigated.

Ultrafine-grained materials produced by different severe plastic deformation methods show very high strengths but their tensile ductility is often very low. In the present work, we demonstrate an approach for retaining high strength while recovering ductility in a Cu-3 at.% Ag alloy through cold rolling and short-time annealing. X-ray line profile analysis of cold-rolled and annealed samples reveals the development of a heterogeneous solute atom distribution due to the dissolution of nanosized Ag particles in some regions of the matrix. In regions with higher solute (Ag) content, the high dislocation density present following rolling is stabilized, while in other volumes the dislocation density is decreased. High-resolution scanning electron microscopy confirms the presence of regions of varying Ag content in the matrix. Microstructure analysis of the rolled and annealed samples revealed bimodal grain size, dislocation density and solute Ag distributions as well as nanosized Ag precipitation. The as-rolled samples exhibit high tensile strengths of ?600-700 MPa with negligible uniform elongation (?1%). After short-time annealing the strength decreases only slightly to ?550-620 MPa with significant improvement in uniform elongation (from 1 to 10%); this is mainly attributed to the bimodal microstructure. � 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Investigating the anisotropy of superconductors permits an access to fundamental properties. Having succeeded in the fabrication of epitaxial superconducting LaFeAs(O,F) thin films we performed an extensive study of electrical transport properties. In face of multiband superconductivity we can demonstrate that a Blatter scaling of the angular dependent critical current densities can be adopted, although being originally developed for single band superconductors. In contrast to single band superconductors the mass anisotropy of LaFeAs(O,F) is temperature dependent. A very steep increase of the upper critical field and the irreversibility field can be observed at temperatures below 6K, indicating that the band with the smaller gap is in the dirty limit. This temperature dependence can be theoretically described by two dominating bands responsible for superconductivity. A pinning force scaling provides insight into the prevalent pinning mechanism and can be specified in terms of the Kramer model., 7 pages, 13 figures

The effectiveness of the cryogenic (CT) rolling vis-�-vis room temperature (RT) rolling on strengthening is significantly affected by stacking fault energy (SFE) and there is an optimum SFE at which CT rolling is most effective. Studies on Al, Al alloy AA6061, Cu, Cu-4.6Al, Cu-9Al and Cu-15Al (in at.%) alloys revealed that in metals with very high and very low SFEs, the strength difference between CT and RT rolled samples is