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In case of the undoped sintered B6O sample, the individual B6O grains are typically well faceted with sharp edges. The grain-size distribution in this sample is bimodal with larger grains (1-2 µm) embedded in a fine-grain B6O matrix. All B6O grains typically reveal numerous stacking faults (similar to B4C particles). In the case of the doped, sintered B6O sample, the grain size was greatly increased (by a factor of about 5x). Stacking faults are a common feature of this B6O material even upon long-term anneal. A secondary phase formation was observed in the Al-containing sample. With respect to the phase diagram, the two aluminium borate compounds that are most likely to form upon sintering are Al4B2O9 and/or Al18B4O33. Conventional TEM (bright field; Figure 3) and HRTEM (Figure 4) were performed on the crystalline secondary phase in addition to selected area electron diffraction (SAD). The diffraction pattern given in Figure 4 can be indexed corresponding to a primitive orthorhombic unit cell (a,b = 0.7617 and c = 0.2827 nm; Pbma) as well as with respect to an A-centered orthorhombic symmetry (Amam). EDS analysis does not allow the distinction between both phases, because this technique is rather insensitive to boron (no quantitative analysis possible). The A-centered phase; however, should follow the extinction rules (k+l=2n). Under the assumption that the rather weak {010}-type reflections visible in the SAD-pattern (Figure 4) are a result from 2 nd -order Laue reflections, it is concluded that extinction occurs. Therefore, the secondary crystalline Al-compound observed in this material is the Al18B4O33 phase. It should be noted that the secondary phase shows an identical orientation within an area of 20-50 microns within the sample. This observation indicates that this Al-phase is characterized by a rather low nucleation rate, which is uncommon for most secondary phases. Fig. 3: TEM image of the secondary Al-phase, Al18B4O33, observed in the doped, sintered B6O sample. Fig. 4: HRTEM image of the secondary Alphase present in B6O. Note the presence of stacking faults as well the weak reflections in the SAD pattern (extinction). - 154 -
Pressure and Temperature Dependence of the Fe 2+ /Fe 3+ -Ratio in Omphacite for the Re-Calibration of the Fe-Mg Geothermometer Stefan Lauterbach, Hans-Joachim Kleebe Iron is present in omphacite, (Ca,Na)(Mg,,Al,Fe 2+ ,Fe 3+ )Si2O6, a common clinopyroxene (Figure 5), as di- and trivalent cations. Analyzing the iron content via micoprobe, the overall iron content can be determined; however, without a distinction between Fe 2+ and Fe 3+ . The commonly used geothermomenter calibration of high pressure (HP) and ultrahigh pressure (UHP) eclogites is solely based on the Fe 2+ content as the total iron content. Thereby, the determined corresponding formation temperatures may differ by up to 400 degree Celsius, since the Fe 3+ content is not considered. Mathematical corrections of the Fe 2+ /Fe 3+ -ratio in omphacite are based on stoiciometric considerations, while analytical techniques to determine the actutal Fe 3+ content are still lacking. Moreover, experimental calibration of the Fe 2+ /Fe 3+ -ratio are commonly not satisfying. Therefore, a re-calibration of the Fe 2+ /Fe 3+ -ratio is performed by measuring both the Fe 2+ and Fe 3+ content in omphacite employing the technique of electron energy-loss spectroscopy (EELS). Parallel, energy-dispersive X-ray spectroscopy (EDS) is used, in order to determine the overall Fe-content of the sample. The experimental EDS and EELS data allow a quantitative determination of the Fe 2+ and Fe 3+ content. In addition, the high lateral resolution of the transmission electron microscope (TEM), down to a few nanometer, allows the analysis of model samples that were synthesized at rather low temperatures (short diffusion profile), which are close to the formation temperature assumed for natural omphacites. Due to the high lateral resolution of the electron transmission microscopy techniques EELS and EDS, exchange equilibria at the sub-micron level are suitable for the experimental determination of the Fe 2+ /Fe 3+ -ratio, even at synthesis temperatures as low as 800 o C. Such low-temperature samples omit the normally applies extrapolation of HT data to low temperatures and add “hard data” to the lower temperature regime. Apart from synthetic samples, natural omphacites (HP-eclogites) from the Tauern Window are studied. Fig. 5: TEM bright field image of Omphacite, (Ca,Na)(Mg,,Al,Fe 2+ ,Fe 3+ )Si2O6; clinopyroxene) in an orientation which reveals typical antiphase boundaries (APB; courtesy W. Müller). - 155 -
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ANNUAL REPORT 2 0 0 6 FACULTY OF MA
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Annual Report 2006 Faculty 11 Mater
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Preface The year 2006 of the Depart
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difference of numerical and analyti
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Institute of Materials Science Phys
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Research Projects Bulk Amorphous Al
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el Dsoki, C.; Landersheim, V. ; Kau
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Das, J.; Kim, K. B.; Xu, W.; Wei, B
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Staff Members Head Prof. Dr. Jürge
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Zhou L.; Rixecker G.; Aldinger F.;
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concerned with the synthesis and ch
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Publications Fleissner, A.; Schmid,
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• Surface analysis The UHV-surfac
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T. Mayer, U. Weiler, E. Mankel and
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Thin films The Thin Film division w
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Berky, W.; Gottschalk, S.; Elliman,
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Guest Scientists Research Projects
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Hesse, S.; Zimmermann, J.; von Segg
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Structure Research The research in
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Research Projects Functional Advanc
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Dincer, I.; Elerman, Y.; Elmali, A;
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hexakis(imidazole)nickel(II)bis(for
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Chemical Analytics The chemical ana
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Collaborations The above mentioned
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Hoffmann, P.; Non-Invasive Identifi
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Ferroelectrics For this class of ma
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Materials Modelling The research ac
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Materials for Renewable Energies In
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Joint Research Laboratory Nanomater
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Collaborative Research Center (SFB)
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B7 P.I.: Prof. H. v. Seggern / Dr.
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The glass transition temperature (T
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transition allows to investigate at
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Relative density 1.00 0.95 0.90 0.8
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Fig. 2 shows the time dependencies
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Dielectric interface trap engineeri
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∆V C q th eff 12 −2 p ( VGS = 0
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Fig. 3: Schematic of the photovolta
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synthesis and analysis of interface
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Fig. 2: Resistivity vs temperature
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Fig. 2: X-ray appearance near-edge
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Capacity [mAhg -1 ] 700 600 500 400
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Texture investigations and field em
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screening effects. Gold coating of
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Figure 2 shows a selected region of
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The spectrum shows that apart from
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The effect of crystallinity on the
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Electrochemical investigation and c
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This phenomenon can be understood c
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∆ = 0 − exhibiting dominance of
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constituents. The requirement of va
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In order to assess the influence of
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