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 coating (TBC) 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, tetragonal zirconia (T-ZrO₂) and yttria-stabilized tetragonal zirconia (T-YSZ) are focused on, and the configurations, formation energies, and migration of hydrogen defects are studied. The orientation of O–H bond is related to the length of Zr–O bond. This characteristic orientation leads to the differentiation of proton migration paths from the cubic phase and further results in the anisotropy of proton migration. Moreover, the isolated Y atom and Y–oxygen vacancy (V_O)–Y triple are introduced into the T-ZrO₂ supercell to investigate their impacts on proton migration. The former has a limited impact, while the oxygen vacancy has a significant trapping effect on protons. This trapping effect is attributed to changes in the local characteristics (especially the electronic properties) of O atoms near V_O due to lattice distortion. These findings provide critical insights into the proton migration mechanisms in TBCs, which are essential for optimizing TBCs for hydrogen-fueled gas turbine applications.