Homogene und heterogene mechanochemische Reaktionen in Spinellen untersucht mit Hilfe von Mössbauer-Spektroskopie und kernmagnetischer Resonanzspektroskopie (NMR)
Zusammenfassung der Projektergebnisse
Spinel oxide nanoparticles of various chemistry (aluminates, ferrites, germanates, stannates) were prepared via two different mechanochemical routes: mechanical activation of corresponding bulk materials and mechanosynthesis. These nonconventional preparation methods offer several advantages over traditional processing of complex oxides, including low-temperature solid-state reactions, fewer processing steps, and suitability for the low cost, large-scale production of nanopowders. Due to the ability of Mössbauer and NMR spectroscopies to provide structural information on a local atomic scale, valuable insight into the homogeneous and heterogeneous mechanochemical processes in spinels was obtained. Oxide nanoparticles prepared by the far-from-equilibrium mechanochemical routes possess the core–shell configuration consisting of an ordered inner core surrounded by a disordered interface/surface region. The latter is found to exhibit a nonequilibrium cation distribution, deformed polyhedron geometry, and canted spin arrangements (in the case of magnetic spinels). The quantitative information on the local structural features of mechanochemically prepared nanospinels, provided by the nuclear spectroscopic techniques, was complemented by the investigation of their behavior on a macroscopic scale. Focusing on the nanomagnetism of the materials studied, their anomalous functional properties, markedly different from those of their bulk-sized counterparts, are consistently explained in terms of the core–shell model, in which a competition between the effects of spin canting and site exchange of cations in the surface shell of spinel nanoparticles plays a decisive role. The range of the thermal stability of the mechanochemically prepared nanostructured oxides was found to extend up to about 700 K. The collaborative research of German and Slovak scientists on room-temperature mechanochemical reduction processes and mechanosynthesis of solids has had a significant impact on the international mechanochemical community. In recognition of Prof. Becker’s scientific achievements in the field, in 2010, the Slovak Academy of Sciences (SAS) awarded Professor Klaus-Dieter Becker its highest honor, The SAS Prize for International Cooperation. http://www.tu-braunschweig.de/presse/medien/presseinformationen?year=2010&pinr=39 http://www.sav.sk/index.php?lang=sk&charset=&doc=services-news&news_no=3075 http://www.zfm-hannover.de/news/singleview/SASPrizeKDBecker/
Projektbezogene Publikationen (Auswahl)
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Mechanochemie: Chemie mit dem Hammer. Chemie in Unserer Zeit 39 (2005) 384-392
S. Kipp, V. Šepelák, K. D. Becker
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Nanocrystalline ferrites prepared by mechanical activation and mechanosynthesis. Zeitschrift für Anorganische und Allgemeine Chemie 631 (2005) 993-1003
V. Šepelák, I. Bergmann, S. Kipp, K. D. Becker
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Nonequilibrium cation distribution in nanocrystalline MgAl2O4 studied by 27Al magic-angle spinning NMR. Solid State Ionics 177 (2006) 2487-2490
V. Šepelák, S. Indris, I. Bergmann, A. Feldhoff, K. D. Becker, P. Heitjans
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Nonequilibrium cation distribution, canted spin arrangement, and enhanced magnetization in nanosized MgFe2O4 prepared by a one-step mechanochemical route. Chemistry of Materials 18 (2006) 3057-3067
V. Šepelák, A. Feldhoff, P. Heitjans, F. Krumeich, D. Menzel, F. J. Litterst, I. Bergmann, K. D. Becker
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Preparation of nanoscale MgFe2O4 via nonconventional mechanochemical route. Solid State Ionics 177 (2006) 1865-1868
I. Bergmann, V. Šepelák, K. D. Becker
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Direct determination of the cation disorder in nanoscale spinels by NMR, XPS, and Mössbauer spectroscopy. Journal of Alloys and Compounds 434-435 (2007) 776-778
V. Šepelák, S. Indris, P. Heitjans, K. D. Becker
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Magnetization enhancement in nanosized MgFe2O4 prepared by mechanosynthesis. Journal of Magnetism and Magnetic Materials 316 (2007) e764-e767
V. Šepelák, I. Bergmann, D. Menzel, A. Feldhoff, P. Heitjans, F. J. Litterst, K. D. Becker
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Nanocrystalline nickel ferrite, NiFe2O4: mechanosynthesis, nonequilibrium cation distribution, canted spin arrangement, and magnetic behavior. Journal of Physical Chemistry C 111 (2007) 5026-5033
V. Šepelák, I. Bergmann, A. Feldhoff, P. Heitjans, F. Krumeich, D. Menzel, F. J. Litterst, S. J. Campbell, K. D. Becker
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Spektroskopische Untersuchungen zur lokalen Struktur von mechanochemisch hergestellten nanokristallinen komplexen Oxiden. Dissertation, Technische Universität Braunschweig, Cuvillier Verlag, Göttingen, 2007, ISBN 978-3-86727-349-7
I. Bergmann
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Mechanosynthesis of nanocrystalline iron germanate Fe2GeO4 with a nonequilibrium cation distribution. Reviews on Advanced Materials Science 18 (2008) 349-352
V. Šepelák, I. Bergmann, A. Diekmann, P. Heitjans, K. D. Becker
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Particle size dependent cation distribution in lithium ferrite spinel LiFe5O8. Reviews on Advanced Materials Science 18 (2008) 375-378
I. Bergmann, V. Šepelák, A. Feldhoff, P. Heitjans, K. D. Becker
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A one-step mechanochemical route to core−shell Ca2SnO4 nanoparticles followed by 119Sn MAS NMR and 119Sn Mössbauer spectroscopy. Chemistry of Materials 21 (2009) 2518-2524
V. Šepelák, K. D. Becker, I. Bergmann, S. Suzuki, S. Indris, A. Feldhoff, P. Heitjans, C. P. Grey
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Magnetic properties of nanostructured MnZn ferrite. Journal of Magnetism and Magnetic Materials 321 (2009) 152-156
M. J. N. Isfahani, M. Myndyk, D. Menzel, A. Feldhoff, J. Amighian, V. Šepelák
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Response of the local structure of complex oxides to mechanical action. Annales de Chemie – Science des Materiaux 34 (2009) 377-390
V. Šepelák, I. Bergmann, S. Indris, A. Feldhoff, P. Heitjans, K.D. Becker
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Nanocrystalline oxides prepared by mechanochemical reactions. PhD Thesis, Technische Universität Braunschweig, 2010
M. Myndyk
