Ionic conductivity and relaxation in ZrF4–BaF2–YF3 glasses: effect of substitution of BaF2 by NaF

The ionic conductivity and relaxation of 50ZrF4–(40−x)BaF2–10YF3–xNaF glasses for varying x have been investigated in the frequency range 10 Hz–2 MHz and in the temperature range from 300 K to just below the glass transition temperature. It is observed that the conductivity decreases with an increase in the NaF content, which is interpreted as arising from the trapping of F− ions by Na+ ions. The relaxation data have been analyzed in the framework of the electric modulus formalism. The values of the stretching exponent β obtained from the fits of the experimental data to the prediction of this formalism are almost independent of temperature and composition. The values of the decoupling index decrease with an increase of the NaF content, which is consistent with the decrease in the conductivity.