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DF: Dielektrische Festkörper

DF 4: Gl
äser II (gemeinsam FV DF/DY)

DF 4.6: Vortrag

Dienstag, 9. März 2004, 16:00–16:15, H23

Ionic transport in alkali-borate glasses — •F. Berkemeier, Á.W. Imre, S. Voss und H. Mehrer — Institut für Materialphysik, Wilhelm–Klemm–Str. 10, 48149 Münster, Westfählische–Wilhelms–Universität Münster, Sonderforschungsbereich 458

We studied the ionic transport in binary and ternary alkali-borate glasses of the compositions y Na₂O·(1−y) B₂O₃, y Rb₂O ·(1−y) B₂O₃ and 0.3 [x Na₂O·(1−x) Rb₂O]·0.7 B₂O₃. The total alkali content of the binary glasses ranges from y = 0.04 up to y = 0.30 while the relative composition of the mixed glasses varied in between x = 0 and x = 1. First, the ionic transport was observed by temperature dependent measurements of the dc conductivity which is connected to the long range transport of the cations. For each glass composition we observed an Arrhenius behaviour of the dc conductivity and determined an activation enthalpy Δ H. For the binary systems we found decreasing values of Δ H with increasing alkali content while for the mixed glasses we observed a maximum of the activation enthalpy at the composition range around x ≈ 0.4. Conductivity measurements only reveal the sum of the contributions of the different cations. Because of this we measured additionally the diffusivities of ²²Na and ⁸⁶Rb in the mixed glasses at 380 ^∘C using the radiotracer technique. We observed an exponential decrease of the Rb-diffusivity with decreasing Rb-content, while the Na-diffusivity also decreases with decreasing Na-content on the Na-rich side, but remains nearly constant on the Rb-rich side. Both diffusivities intersect at the composition range around x ≈ 0.2. A similar behaviour was reported from our laboratory for mixed glasses with a total alkali content of y = 0.2.