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nearly half a century has been performed, concentrating on the impact of sand and gravel mining and the recuperation of abandoned mining areas as well as on the proceeding urbanisation. Fig. 4 shows the dynamic of the urbanisation of the alluvial plains from 1977 until 1990. These analyses were accompanied by field observations including geological, pedological and environmental aspects such as the state of the recuperation of abandoned extraction areas as well as sedimentological structures. The total area of 6,68 km² of the alluvium between the road MG 424 and the road MG 010, have been subject to many drastic transformations during the last decades. Frequent changes of the riverbed, erosion at its margins, siltation and the augmentation of exposed soil in the alluvial plain could be observed. Fig.4: Proceeding urbanisation of the alluvial plain of the Riberâo da Mata between 1977 and 1990. The peak of the sand mining activities was in the decades of 1970 to 1980, when the city of Belo Horizonte was growing very rapidly and environment legislation was less strict. Still, even today, active sand and clay mines can be found in the area, showing the importance of these resources for the city. During the last decades, approximately 30% of the study area has been subject to mining (1.5 km² during the 1977 and only 0,5 km² in 1990). In some abandoned mining areas, industrial plants breaking carbonate rocks for gravel substitution have been constructed, as the alluvium offers plain construction sites. The gravel mining has stopped since, as the natural gravel resources are scarce and deep seated. The natural recuperation of abandoned mining areas is slow and exposed soil and active erosion carries away fertile soil and increases the sediment load of the river. In the 1970s, 0,4 km² of the area could be classified as exposed soil showing signs of erosion. The multi-temporal analysis of the land use in this area together with a comparison with other source areas showed that certain georesources like sand and gravel for construction purposes are heavily needed in close distance to the growing city, but competing for space with other uses and with environmental legislation. - 150 -
Planar Defects in Bixbyite, (Mn,Fe)2O3; A Prominent Diffusion Path Hans-Joachim Kleebe, Stefan Lauterbach Bixbyite is a rather uncommon manganese-iron oxide (Mn,Fe)2O3, crystallizing in the Ia3 space group [1], forming black cubic crystals with metallic lustre that are commonly truncated by small icositetrahedral faces at corners. Bixbyite normally occurs in small crystals reaching some mm in size. However, there is one location at Thomas Range (Utah), where large crystals up to 4 cm are found. These crystals occur in cavities of a rhyolite host rock associated with topaz, pseudobrookite, braunite, hematite, hausmannite and quartz [2]. In contrast to the small isomorphic crystals, most of the larger bixbyite crystals from Thomas Range show distinct re-entrant facets at halfway of every edge of the cube, linked by a band of parallel linear features, crossing at the center of each cube face. These linear features were first characterized as twin boundaries, but they cannot be a result of local twinning, since any twinning operation on {100} planes of the centrosymmetric bixbyite structure would produce an identical single crystal. High-resolution transmission electron microscopy (HRTEM) was used to study the structure of those linear features. HRTEM images showed fault planes running along {100} planes of the bixbyite structure. The interfaces are atomically sharp and planar over large areas of the crystal. TEM/EDS analyses revealed an enrichment of Si in the fault regions with a simultaneous increase in Mn. The composition of the planar defects closely corresponds to the manganese silicate braunite, Mn 2+ Mn 3+ 6SiO12 [3]. Small precipitates observed in close proximity to the planar faults suggest an increased diffusion rate along those defects. The enhanced grain growth of the larger bixbyite crystals can be rationalized by fast diffusion along those planar braunite interlayers. [1] Dachs, H. (1956): Die Kristallstruktur des Bixbyits (Fe, Mn)2O3, Z. für Kristallographie, 107, 370. [2] Eric H. Christiansen, E. H, James V. Bikun, J. V., Michael F. Sheridan, M. F., Donald M. Burt, D. M. (1984): Geochemical Evolution of Topaz Rhyolites from the Thomas Range and Spor Mountain, Utah, American Mineralogist, 69, 223. [3] De Villiers, J.P.R. & Buseck, P.R. (1989): Stacking Variations and Non-Stoichiometry in the Bixbyite- Braunite Polysomatic Mineral Group, American Mineralogist, 74, 1325. - 151 - Fig. 1: HRTEM image of the intrinsic defect structure observed in a lager bixbyite single crystal. Note the presence of small precipitates adjacent to the planar faults of braunite, Mn7SiO12.
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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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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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