Berlin 2005 – wissenschaftliches Programm
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M: Metallphysik
M 18: Nanoskalige Materialien I
M 18.3: Vortrag
Samstag, 5. März 2005, 09:45–10:00, TU H111
Direct Determination of Cation Disorder in Nanoscale Spinels by High-Resolution Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy — •Vladimir Šepelák1, Sylvio Indris2, Klaus Dieter Becker3, and Paul Heitjans2 — 1Center for Solid State Chemistry and New Materials, University of Hannover, 30167 Hannover, Germany; on leave from Slovak Academy of Sciences, Košice, Slovakia — 2Institute of Physical Chemistry and Electrochemistry, University of Hannover, 30167 Hannover, Germany — 3Institute of Physical and Theoretical Chemistry, Technical University of Braunschweig, 38106 Braunschweig, Germany
Complex oxides AB2O4 with the spinel structure, in general, and Al-containing members of this structural group, in particular, have continuously attracted interest because of the large diversity and the practical usefulness of their physical and chemical properties. Ultrafine powders of MgAl2O4 with crystallite sizes in the nm range have been prepared by high-energy milling the bulk material in a SPEX 8000 shaker mill using grinding chamber and balls made of ZrO2. The nanoscale nature of the mechanically activated samples has been characterized by TEM, XRD and BET methods. The disorder of Mg2+ and Al3+ cations between the tetrahedral (A) and octahedral [B] sites in nanosized milled MgAl2O4 has been determined by 27Al magic-angle spinning NMR spectroscopy. Disorder, measured by the fraction of Al3+ cations on (A) sites and described by the degree of inversion, λ, increases with increasing milling time. The cation inversion parameter of the nanoscale spinels is compared with that of the bulk materials quenched from high temperatures.