Atomic-Level Investigation of Oxygen Distribution in Grain Boundaries in Yttria-Stabilized Zirconia using Graph-Order Parameter

Yttria-stabilized zirconia (YSZ) is a widely utilized ceramic material renowned for its remarkable mechanical and thermal properties. However, it is susceptible to low-temperature degradation (LTD), adversely affecting its long-term performance. This degradation process is hypothesized to be closely linked to the occurrence of oxygen vacancies within the crystal lattice. To understand the origins of LTD, Atom Probe Tomography (APT) is employed as a characterization technique to investigate the microstructure of YSZ. To analyze the sample and understand oxygen distribution, we translate the local atomistic environment characterization method from molecular dynamics into the APT field. The method is based on the graph representation of point cloud data coupled with the information theory entropy measures to capture the local environment's chaos/order and density. In this study, we learned that this method is highly sensitive to small changes in the number and connectivity of the oxygen ions. We unravel that grain boundaries are lean in the less connected oxygen ions compared to the grains, offering direct atomistic evidence of noticeable differences between grain and grain boundaries of zirconia. This knowledge contributes to developing strategies for enhancing the material's resistance to low-temperature degradation and optimizing its performance in diverse applications.