Doping effects and vacancy formation in the ionic conductivity of ZrO2 ceramics doped with RENbO4 (RE = Yb, Er, Y, Dy) were investigated here by using X-ray diffractometry and scanning electron microscope, and with the corresponding ionic conductivity being evaluated using impedance spectroscopy. The results show that defect distribution could be correlated with the phase transformation behavior modified by ionic radius of dopants. The total conductivity of 5mol% RENbO4-doped ZrO2 (3Y) comprises the intragrain and grain boundary conductivity. The intragrain conductivity of 5mol% RENbO4-doped ZrO2 (3Y) were lower than 3mol%Y2O3-doped ZrO2 (3Y-TZP) and 8mol%Y2O3-doped ZrO2 (8YSZ). The additions of Nb2O5 to ZrO2 (3Y) increase average lattice binding energy and activation energy, and the amount of O vacancies was decreased. The average radius of O vacancies of 5mol% RENbO4-doped zirconia (3Y) were smaller than that of 8YSZ identified using hard-sphere model. The results imply that a specific doping content in zirconia which contributed a maximum content of non-interfering O vacancies, the average radius of doping ions close to that of Zr4+ and average binding energy as smaller as possible help obtain the highest conductivity of zirconia. To acquire an appropriate operation condition in the application of solid oxide fuel cell, electrical properties, phase transformation behavior and related mechanical properties need to be compromised.

Doping Effect and Vacancy Formation on Ionic Conductivity of Zirconia Ceramics. T.H.Yeh, C.C.Chou: Journal of Physics and Chemistry of Solids, 2008, 69[2-3], 386-92