Berlin 2005 – wissenschaftliches Programm
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DF: Dielektrische Festkörper
DF 4: Poster
DF 4.17: Poster
Samstag, 5. März 2005, 08:30–16:30, Poster TU C
Mixed Alkali Effect in (Li, Na) Niobium Silicate Glasses – Probing Cation Dynamics by Impedance Spectroscopy and by Solid-Echo and Multiple-Time Spin-Alignment Echo 7Li NMR Spectroscopy — •Muayad Masoud1, Martin Wilkening1, Rudolf Winter2, and Paul Heitjans1 — 1Universität Hannover, Institut für Physikalische Chemie und Elektrochemie, Callinstraße 3-3a, 30167 Hannover, Germany — 2University of Wales, Institute of Mathematical and Physical Sciences, Ceredigion SY23 3BZ, Wales, UK
Glasses with the composition 1/3[x Li2O,(1−x)Na2O] : 1/3Nb2O5 : 1/3SiO2 (0 ≤ x ≤ 1) were prepared by conventional quenching of the corresponding molten oxides. Conductivities σdc probed by impedance spectroscopy exhibit a typical minimum at x ≈ 0.4 whereas the corresponding activation energies (0.61(1) eV ≤ EA σdc ≤ 0.91(1) eV) show a maximum at this composition (mixed alkali effect). In contrast to the σdc measurements detecting the overall cation diffusion, with multi-pulse NMR techniques the Li and Na diffusion can be studied separately from each other. For instance, solid-echo 7Li NMR line narrowing showed an enhancement of Li diffusivity with both increasing temperature and Li content x. Consistently, lithium jump rates τecho−1, directly probed by recording two-time correlation functions via spin-alignment echoes, decrease exponentially with the introduction of Na ions. The corresponding activation energies EA echo increase with increasing Na content.