Regensburg 2004 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 4: Gl
äser II (gemeinsam FV DF/DY)

DF 4.9: Vortrag

Dienstag, 9. März 2004, 16:45–17:00, H23

Mixed-alkali effect in sodium rubidium borate glasses: ionic conductivity and diffusivity — •Árpád W. Imre, Stephan Voss, and Helmut Mehrer — Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster, Germany and Sonderforschungsbereich 458

Measurements of the tracer diffusion coefficient and ionic conductivity have been made in a series of 0.2[X Na₂O·(1−X)Rb₂O]·0.8 B₂O₃  glasses where X=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 in order to investigate the mixed-alkali effect. The glasses were characterised with differential scanning calorimetry, density measurements and X-ray diffraction experiments. Both ²²Na and ⁸⁶Rb tracer diffusion coefficients were determined as a function of temperature and composition. For each composition the temperature dependence of the tracer diffusion coefficients and dc conductivity times temperature σ_dc × T follow the Arrhenius law. The manifestations of the mixed-alkali effect were observed: i) the ionic conductivity shows a minimum with composition near X=0.4, ii) the activation enthalpy of σ_dc × T has a maximum near X=0.4, iii) the glass-transition temperature has a minimum near X=0.2, iv) the diffusivities of ²²Na and ⁸⁶Rb crossover near X=0.2. The diffusivity crossover is found to be temperature independent. The composition dependence of the tracer diffusivities has an asymmetric character. The tracer diffusion coefficients are compared with ionic conductivity and the corresponding Haven ratios obtained. In contrast to 0.2Na₂O · 0.8 B₂O₃ glass, the Haven ratio in the 0.2Rb₂O · 0.8 B₂O₃ depends on temperature.