Sonderforschungsbereiche
Sonderforschungsbereich 458 - Ionenbewegung in Materialien mit ungeordneten Strukturen -
vom Elementarschritt zum makroskopischen Transport -
B8 - Prof. Dr. H. Mehrer

Tracer diffusion and ionic conduction in single and mixed alkali borate glasses

Tracer diffusion and ionic conductivity studies have been performed on single and mixed sodium-rubidium borate glasses as functions of temperature, composition and in one case also as function of pressure. The diffusivity of mobile ions deduced from the ionic conductivity via the Nernst-Einstein relation are compared with tracer diffusivities. For 0.2[XNa₂O (1-X) Rb₂O] 0.8B₂O₃ the conductivity shows minimum near X = 0.4 and a maximum in the activation enthalpy indicating a conventional mixed alkali effect. The Rb diffusivity decreases exponentially with decreasing Rb content. Respectively the Na diffusivity decreases with decreasing Na content but remains nearly constant at the Rb rich side. Both diffusivities intersect near X = 0.2. The Haven ratio is temperature independent on th Na side and decreases with decreasing temperature on the Rb side.The temperature dependencies of Na and Rb diffusion yield distinct trends for the activation enthalpies. The complementary measurements of conductivity and tracer diffusion provide detailed insight in the dynamics of ionic transport in mixed Na-Rb-borate glasses.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft

Beteiligte Wissenschaftler:

Cand.-Phys. F. Berkemeier, Dr. C. Cramer (Institut für Physikalische Chemie), Dr. A. W. Imre, Prof. Dr. Mehrer (Leiter), Dr. St. Voß

Veröffentlichungen:

Schoo, U., C. Cramer, E. Ratai, H.Mehrer: Diffusion in Single and Mixed Alkali Borate Glasses, Defect and Diffusion Forum 194 - 199, 925 - 933 (2001).

Imre, A. W., S. Voss, and H. Mehrer: Ionic transport in 0.2[XNa₂O (1-X) Rb₂O]0.8 B₂O₃ mixed-alkali glasses, Phys. Chem. Chem. Phys. 4, 3219 - 3224 (2002).

Mehrer, H., A. W. Imre, S. Voss: Diffusion and ionic conduction in sodium-rubidium borate glasses, in: “Mass and ChargeTransport in Inorganic Materials II”, edited by P. Vincenzini, V. Buscaglia, Techna, Faenza, 2003, pp. 127 - 138.