Valence and conduction state distributions in a series of Al-Cu-Fe and Al-Cu-Fe-Cr alloys of different structural states and nominal compositions have been investigated by means of soft X-ray emission and photoabsorption spectroscopies. A complete description of the valence band is obtained. The DOS at EF is observed to be very low which is consistent with the high resistivity values found for the icosahedral quasicrystalline phase. The existence of a wide pseudo-gap at EF is evidenced, which is higher in the quasicrystal than in be related crystalline counterparts.

Mechanical testing of micropillars is a field that involves new physics, as the behaviour of materials is non-deterministic at this scale. To better understand their deformation mechanisms we applied 3-dimensional high angular resolution electron backscatter diffraction (3D HR-EBSD) to reveal the dislocation distribution in deformed single crystal copper micropillars. Identical micropillars were fabricated by focused ion beam (FIB) and compressed at room temperature. The deformation process was stopped at different strain levels (≈ 1%, 4% and 10%) to study the evolution of geometrically necessary dislocations (GNDs). Serial slicing with FIB and consecutive HR-EBSD mapping on the (100) side was used to create and compare 3-dimensional maps of the deformed volumes. Average GND densities were calculated for each deformation step. Total dislocation density calculation based on X-ray synchrotron measurements were conducted on the 4% pillar to compare dislocation densities determined by the two complementary methods. Scanning transmission electronmicroscopy (STEM) and transmission electronmicroscopy (TEM) images were captured on the 10% pillar to visualize the actual dislocation structure. With the 3D HR-EBSD technique we have studied the geometrically necessary dislocations evolving during the deformation of micropillars. An intermediate behaviour was found at the studied sample size between bulk and nanoscale plasticity: A well-developed dislocation cell structure built up upon deformation but with significantly lower GND density than in bulk. This explains the simultaneous observation of strain hardening and size effect at this scale.

We report on experimental valence and conduction electronic distributions of quasicrystalline Al-Mn-Pd alloys probed using the soft x-ray emission and absorption spectroscopy techniques. The various partial distributions are adjusted in the binding energy scale in order to investigate the electronic interactions characteristic in the material. In the valence band, interaction exists between Al states and Mn 3d states near the Fermi level and with Pd 4d states in the middle of the band. At the Fermi level the intensity of the Al 3p states is very low and a rather wide pseudo-gap is observed. In the conduction band, interaction exists also between Al p-Mn d states in the energy range of the absorption edge. Pd d-s states are found about 2 eV beyond the Fermi level. It is suggested that unlike the case of Mn, a small charge transfer may exist from Al to Pd states. Adjustment of Al 3p and Al p distributions at the same intensity at the Fermi level shows that the density of available Al p conduction states is dramatically decreased in the quasicrystal in comparison to pure Al. We propose that this could be connected to the existence of numerous narrow gaps and spikes in the densities of states as predicted theoretically elsewhere for crystal approximant phases with very large unit cells.

We report on experimental and calculated occupied and unoccupied electronic distributions of crystalline A12Cu and various Al-Cu-Fe alloys. The experiments have been carried out by means of soft-x-rayspectroscopy and photoelectron-spectroscopy techniques. The densities of states have been calculated using either the linear-muffin-tin-orbital atomic-sphere-approximation or the augmented-plane-wave methods. The comparison between experiment and calculations is discussed. We pay special attention to the effect of Fe in the various alloys and emphasize the role of Al atom neighbors. We propose that changes in Al site occupancy that induce changes in Al p-d hybridization near the Fermi level could be responsible for the modifications of the densities of states observed in quasicrystalline Al-Cu-Fe phases with respect to the crystalline Al-Cu2Fe alloy.

No abstract

Plastic deformation of micron-scale crystalline materials differ considerably from bulk ones, because it is characterized by random strain bursts. To obtain a detailed picture about this stochastic phenomenon, micron sized pillars have been fabricated and compressed in the chamber of a SEM. An improved FIB fabrication method is proposed to get non-tapered micro-pillars with a maximum control over their shape. The in-situ compression device developed allows high accuracy sample positioning and force/displacement measurements with high data sampling rate. The collective avalanche-like motion of dislocations appears as stress drops on the stress-strain curve. To confirm that these stress drops are directly related to dislocation activity, and not to some other effect, an acoustic emission transducer has been mounted under the sample to record emitted acoustic activity during strain-controlled compression tests of Al-5% Mg micro-pillars. The correlation between the stress drops and the acoustic emission signals indicates that indeed dislocation avalanches are responsible for the stochastic character of the deformation process.

We report the results of the complex study of the bulk interior of Bursa L6 ordinary chondrite using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, electron microprobe analysis (EMPA), X-ray diffraction (XRD), magnetization measurements, and M€ ossbauer spectroscopy. The main and minor ironbearing phases and their chemical compositions were determined by these techniques. The detected iron-bearing phases in the bulk interior of Bursa L6 are the following: olivine; orthopyroxene; Ca-rich clinopyroxene; troilite; chromite; hercynite; ilmenite; the a 2-Fe(Ni, Co), a-Fe(Ni, Co), and c-Fe(Ni, Co) phases; and ferrihydrite resulting from meteorite terrestrial weathering. Using the EMPA, the values of fayalite and ferrosilite were obtained as~25.2% and~21.4%, respectively. The unit cell parameters for silicate crystals were determined from XRD, then the Fe 2+ and Mg 2+ occupations of the M1 and M2 sites in these crystals were estimated. Further calculations of the ratios of the Fe 2+ occupancies in the M1 and M2 sites in olivine and orthopyroxene based on XRD and M€ ossbauer spectroscopy appeared to be in a good agreement. The temperatures of equilibrium cation distributions for olivine and orthopyroxene obtained from these techniques are consistent: 623 K (XRD) and 625 K (M€ ossbauer spectroscopy) for olivine and 1138 K (XRD) and 1122 K (M€ ossbauer spectroscopy) for orthopyroxene.

PACS. 61.40 -Amorphous and polymeric materials. PACS. 71.20 -Electronic density of states determinations (inc. energy states of liquid PACS. 78.70D -X-ray absorption and absorption edges. semiconductors).