Doping effect and vacancy formation on ionic conductivity of zirconia ceramics

Doping effect and vacancy formation on ionic conductivity of ZrO2 ceramics doped with RENbO4 (RE=Yb, Er, Y, Dy) were investigated using X-ray diffractometry, scanning electron microscope and corresponding ionic conductivity were evaluated using impedance spectroscopy in this work. The results show that defect distribution can be correlated with the phase transformation behavior modified by ionic radius of dopants. The total conductivity of 5 mol% RENbO4-doped ZrO2 (3Y) comprises the intragrain and grain boundary (GB) conductivity. The intragrain conductivity of 5 mol% RENbO4-doped ZrO2 (3Y) are lower than 3 mol% Y2O3-doped ZrO2 (3Y-TZP) and 8 mol% Y2O3-doped ZrO2 (8YSZ). The additions of Nb2O5 to ZrO2 (3Y) increase average lattice binding energy and activation energy, and the amount of oxygen vacancies was decreased. The average radius of oxygen vacancies of 5 mol% 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 contributes a maximum content of non-interfering oxygen 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.