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The mixed-alkali effect is studied in  Y  [ X  Na 2 O · (1− X ) Rb 2 O] · (1− Y ) B 2 O 3  glasses as a function of the total alkali content  Y . To this aim the ionic transport in glasses with  Y  = 0.3 was investigated by impedance spectroscopy and by the radiotracer diffusion technique. The results are compared with data obtained earlier by our group on a glass system with  Y  = 0.2. In both systems the relative compositions  X  = Na/(Na + Rb) are varied from 0.0 to 1.0 in steps of 0.2. The dc electrical conductivity is higher in  Y  = 0.3 glasses than in  Y  = 0.2 glasses and exhibits a minimum in each system near  X  = 0.4. Also near  X  = 0.4 a pertaining maximum in activation enthalpy occurs being more pronounced for  Y  = 0.3 as compared to  Y  = 0.2. The glass-transition temperature  T  g  is almost identical for glasses with  Y  = 0.2 and 0.3 with a minimum near  X  = 0.2. The diffusivities of  22 Na and  86 Rb measured at a constant temperature (380 °C) show in both glass systems ( Y  = 0.3 and  Y  = 0.2) a similar dependence on the composition parameter  X . The  86 Rb diffusivity decreases exponentially with decreasing Rb content. The  22 Na diffusivity decreases with decreasing Na content but reaches an almost constant plateau on the Rb-rich side. For each relative composition  X  the diffusivities of the two isotopes increase by nearly the same constant factor, when  Y  is increased from 0.2 to 0.3. In both systems  22 Na- and  86 Rb-diffusivities as functions of the composition parameter  X  intersect near  X  = 0.2 explaining the minimum in dc-conductivity. Composition dependent common Haven ratios were obtained by comparing the conductivity with the diffusion data.

Mixed-Alkali Effect of Tracer Diffusion and Ionic Conduction in Na-Rb Borate Glasses as a Function of Total Alkali Content