Unraveling the atomic-scale mechanisms of hydrogen defects behavior in yttria-stabilized tetragonal zirconia by first principles calculation

In hydrogen-fueled gas turbines, protons are more likely to penetrate the ceramic layer of thermal barrier coatings (TBCs) system and eventually reach the metallic bond coat. The knowledge about the atomic mechanism of proton migration in the ceramic layer of TBCs is important to evaluate the feasibility of using current TBCs in hydrogen-fueled gas turbines. In this work, the tetragonal zirconia (T-ZrO₂) and yttria-stabilized tetragonal zirconia (T-YSZ) are focused, where the configurations, formation energies and migration of hydrogen defects are studied. The orientation of O-H bond is found to be related to the length of Zr-O bond. This characteristic orientation leads to the differentiation of proton migration paths from cubic phase and further results in the anisotropy of proton migration. Moreover, the isolated Y atom and Y-Vo-Y triple are introduced into T-ZrO₂ supercell to investigate their impacts on proton migration, respectively. It is found that the former has a limited impact, while oxygen vacancy has a significant trapping effect for proton. This trapping effect is attributed to changes in the local characteristics (especially for electronic properties) of O atoms near Vo due to lattice distortion. These findings provide critical insights into the research of proton migration mechanisms in TBCs, which are essential for optimizing TBCs for hydrogen-fueled gas turbine applications.