Effect of Zr/Hf ratio on ionic conductivity of (ZrxHf1-xO2)0.9(Y2O3)0.1 ceramics

Yttria- and scandia-stabilized zirconia are pivotal in solid-state oxide fuel cell research owing to their exceptional oxide ion conduction properties. In addition, the similarity between Hf and Zr, combined with their abundance, underscores the significance of exploring yttria-stabilized hafnia as a potential alternative. In this study, we aim to enhance our understanding of the properties and potential applications of such materials in sustainable energy technologies. Thus, the effect of the Zr/Hf ratio on the oxide ionic conductivities of (ZrxHf1-xO2)0.9(Y2O3)0.1 compounds is investigated by varying the Zr/Hf ratio in the range of 1.00/0.00/0.00/1.00. We determined that the oxide ionic conductivity intragrain decreases with increasing Hf contents, and the apparent activation energy with respect to the oxide ionic conduction increases. The standard enthalpy of formation per one oxygen atom is ?572.35 and ?550.28 kJ mol-1 for Hf-O and Zr-O, respectively. In addition, it is confirmed that the Hf-O bond is stronger than the Zr-O bond. Therefore, it is assumed that oxide ion conduction does not occur easily when Hf atoms are adjacent to oxide ions.