Cubic zirconia electrical conductivity

Fig. 16 Electrical conductivity of pure cubic zirconia at (a) 16.5 GPa and (b) 18GPa [56] (reprinted with permission)...

At the beginning stage of this study, we investigated the optima composition of ScSZ. It is well known that cubic phase zirconia has highest ion conductivity. Therefore, we tried to make several ScSZ samples, which have different amounts of scandium additives, and confirmed that cubic phase was obtained by addition of over 8-mol% scandium into zirconia. The electrical conductivity of 8 to 12 mol% ScSZ ranges from 0.25 to 0.38 S/cm at 1273K, which is twice or third higher than YSZ[3]. 

Room temperature monoclinic zirconia has little use as a SOFC electrolyte because it is predominantly an electronic conductor with low oxygen ion conductivity [15]. Cubic zirconia has high ionic conductivity but needs to be stabilized so that it retains its cubic structure at room temperature. Nemst discovered and reported in 1899 that mixtures of zirconia with other oxides such as magnesia showed high ionic conduction at high temperatures [16]. Two years later, he patented his further observation that the material composition (15% yttria and 85% zirconia) was suitable for electric-lamp glowers [17]. Westinghouse Electric Corporation has used a similar zirconia-based electrolyte in their SOFC development since 1962 [18]. 

Microstxuctural studies of the sintered pellet depicted highly dense grain morphology. Furthermore, conductivity analysis evidenced an Arrhenius-type thermally activated ionic conduction above 300 °C. However, the electrical conductivity of the system was foimd to increase with the bismuth content up to X = 0.05, and thereafter decreased due to less solubility of Bi " into zirconia matrix. A better conductivity, 0.019 S/cm, was achieved for 5 mol% Bi203 cal-cia-codoped cubic zirconia system at 760 °C. Thus, the cost-effective bismuth codoped calcia-stabilized zirconia might be a possible alternative to YSZ, due to its ionic conductivity comparable to that of the YSZ. 

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