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DF: Dielektrische Festkörper

DF 5: Gl
äser II (gemeinsam FV DF/DY)

DF 5.9: Vortrag

Dienstag, 25. März 2003, 16:45–17:00, HSZ/403

Ionic transport in Na-Rb-borate glasses — •S. Voß, Á.W. Imre, and H. Mehrer — Institut für Materialphysik, Wilhelm-Klemm-Str. 10, 48149 Münster, Sonderforschungsbereich 458

We studied the ionic transport on a series of 0.2[X Na₂O (1-X) Rb₂O]0.8B₂O₃ glasses with X ranging from 0 to 1 in steps of 0.2. To this aim we measured the conductivity by impedance spectroscopy. The dc conductivity σ_dc is connected to the long range transport of the ions and exhibits a deep minimum for the composition range at X ≃ 0.4. Since conductivity measurements only reveal the sum of the contributions of the Na- and the Rb-ions to the ionic transport it cannot distinguish between the specific contributions. To overcome this drawback we measured additionally the diffusivities of ²²Na and ⁸⁶Rb as functions of composition and temperature using the radiotracer technique. At the highest temperature (T=380^∘C), which is for all compositions below the glass-transition temperature, the Rb-diffusivity decreases exponentially with decreasing Rb-content. Respectively, on the Na-rich side the Na-diffusivity also decreases with decreasing Na-content, but remains nearly constant on the Rb-rich side. Both diffusivities intersect near the composition X=0.2. The temperature dependences of the measured ²²Na and ⁸⁶Rb diffusivities obey each an Arrhenius law yielding distinct trends for the corresponding activation enthalpies with composition. The complementary measurements of conductivity and tracer diffusivities provide detailed insight in the dynamics of ionic transport in mixed NaRb-borate glasses.