Mechanical and electrical properties of ZrO₂ (3Y) doped with RENbO₄ (RE = Yb, Er, Y, Dy, YNd, Sm, Nd)

Abstract
Mechanical and electrical properties of specimens of ZrO₂ (3Y) doped with RENbO₄ (RE = Yb, Er, Y, Dy, YNd, Sm, Nd) were investigated using micro-indentation and impedance spectroscopy in this work. The results show that ZrO₂ (3Y) doped with RENbO₄ (RE = Yb, Er, Y, Dy) possess outstanding mechanical properties, and specimens with RENbO₄ (RE = Y, Nd, Sm) exhibit increasing amount of the monoclinic phase after fabrication, but still show fairly good mechanical bebavior compared to those of 3Y-TZP and 8YSZ, indicating that mechanical properties 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 conductivity and grain boundary (GB). The intragrain conductivity of 5 mol%RENbO₄-doped ZrO₂ (3Y) are lower than 3Y-TZP and 8YSZ. The addition of RENbO₄ to ZrO₂ (3Y) increases average binding energy and activation energy, and reduces the amount of oxygen vacancies. 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 to achieve the highest conductivity of zirconia. The conditions deviate from those possessing the best mechanical properties, suggesting that to obtain an appropriate electrolyte in the application of a solid oxide fuel cell, mechanical properties and electrical properties of zirconia need to be compromised.