Mixed-alkali effect in Na–Rb borate glasses: A tracer diffusion and electrical conductivity study

摘要: The ionic transport in a series of 0.2 [X Na2O·(1 − X)Rb2O]·0.8B2O3 glasses has been studied by measuring both the electrical conductivity these and tracer diffusivities 22Na 86Rb as functions composition temperature. At constant temperature (380 °C) decrease monotonically with decreasing Na- or Rb-content, respectively. parameter X intersect near X = 0.2 (‘crossover composition’). This behaviour gives rise to minimum which appears X = 0.4. crossover are practically same within measured range resulting similar Arrhenius parameters. For each other investigated parameters for diffusion differ significantly. Comparing 22Na-diffusivity pure Na-borate glass corresponding coefficient calculated via Nernst–Einstein equation from yields temperature-independent Haven ratio. In contrast, temperature-dependent ratio was found Rb-borate glass. order compare mixed-alkali their we introduce ‘common ratio’ coincides conventional definition single-alkali glasses. On Rb-rich side common decreases Na–Rb borate (X = 0.2 X = 0.4) Rb