Electrical Conductivity of 10 mol% Sc ₂ O ₃ –1 mol% M ₂ O ₃ – ZrO ₂ Ceramics

The oxide‐ion conductivity behavior of 10 mol% Sc 2 O 3 – ZrO 2 co‐doped with 1 mol% trivalent metal oxide has been determined from 350°C to 700°C in air. All the powders were synthesized using conventional solid‐oxide route. XRD patterns collected at room temperature show the presence of β ‐phase in the predominant cubic phase in 1 Sc 10 Sc SZ , 1 Yb 10 Sc SZ , and 1 Y 10 Sc SZ , although 1 In 10 Sc SZ consist entirely of β ‐phase at ambient temperature. As evident from the cubic symmetry of 1 Gd 10 Sc SZ and 1 Sm 10 Sc SZ , the β ‐phase can be suppressed by the slight addition of co‐dopant elements of larger ionic radius. The total conductivity of 1 M 10 Sc SZ initially increases with increasing size of the co‐dopant, reaches a maximum at ~0.95 Å and thereafter decreases. At 600°C, 1 Yb 10 Sc SZ exhibits the highest total conductivity, namely 14 mS/cm. The grain interior and the grain boundary follow similar conductivity trends with the maximum at 1 In 10 Sc SZ and 1 Y 10 Sc SZ , respectively. Around 475°C, 1 In 10 Sc SZ but not other compositions exhibits an abrupt drop in the conductivity on cooling, due to the cubic to β ‐phase transformation. At 600°C, the activation energy for the oxide‐ion conductivity in 1 M 10 Sc SZ compositions ranges from 1.06 to 1.15 eV, with 1 Yb 10 Sc SZ exhibiting the smallest value. Long‐term stability studies of the conductivity were performed on the sintered pellet of 1 Yb 10 Sc SZ in both oxidizing and reducing conditions at 600°C. After 2000 h of exposure to air and reducing conditions, the 1 Yb 10 Sc SZ composition shows 9.1% and 12.0% loss in the total conductivity, respectively. After the first 1000 h, 1 Yb 10 Sc SZ exhibited a degradation rate of ~1.1%/1000 h in both the conditions. From impedance studies, it was shown that, during annealing, the grain interior resistivity remains almost stable, while only grain boundary contributes toward the rise in total resistivity in both the conditions.