NZGO and YSZ both are well-known ionic conductors. At lower temperatures R 2E@0 ^< R GHE ^ and at higher temperatures R 2E@0 ^> R GHE ^. Thus, two main regimes were observed in the total conductivity plot, as shown in figure . Regarding the degraded sample, the measured conductivity of the centerpiece showed values between the degraded cathode and anode terminals which is attributed to the slight sodium content concentration gradient from cathode to anode. The cathode terminal showed higher conductivity with respect to the anode terminal. Due to the high thermodynamic activity and high chemical potential of sodium, some sodium contents volatilized and caused a decrease in total conductivity. However, the mass transport of the Na ! through the sample thickness from anode to cathode could be the reason for lower measured conductivity in low-temperature regime at anode compared to cathode terminal. In the high-temperature regime (T > 550 °C), where oxygen ion conductivity is dominant, R 2E@0 ^> R GHE ^, all specimens exhibit almost identical conduction behavior, which attributed to the chemical and thermal refractory nature of the YSZ content.