Structural and thermal property changes of yttria-stabilized zirconia under high-temperature hydrogen atmospheric conditions

Hydrogen-fueled gas turbines operate under high-temperature reducing atmospheres that can destabilize thermal barrier coatings (TBCs). However, the structural and thermal responses of yttria-stabilized zirconia (YSZ) under hydrogen environments remain insufficiently clarified. In this study, 8 wt% yttria-stabilized zirconia (YSZ) was used to prepare bulk specimens, which exhibited a porosity of ∼30%, and were heat treated at 1300, 1500, and 1600 °C under 99.995% H 2 to simulate hydrogen turbine conditions, and their microstructural, compositional, phase, and thermal property changes were systematically investigated. Hydrogen heat treatment promoted progressive densification while inducing significant oxygen loss (∼8 wt%) and a slight decrease in yttrium content, suggesting the formation of oxygen-deficient sites under reducing conditions. X-ray diffraction analysis revealed that the monoclinic phase fraction increased with temperature, reaching ∼18 mol% at 1600 °C, suggesting destabilization of the tetragonal structure. Raman spectroscopy confirmed defect-induced lattice distortion and modification of the Zr–O bonding environment. FT-IR results identified –OH species formation above 1500 °C, indicating hydrogen dissociation and adsorption at oxygen-deficient sites. Correspondingly, the coefficient of thermal expansion increased from 11.00 × 10 −6 K −1 (as-sintered) to 13.41 × 10 −6 K −1 after treatment at 1600 °C. These findings demonstrate that high-temperature hydrogen exposure induces presence of oxygen-deficient sites, phase redistribution, and increased thermal expansion in YSZ, which may accelerate structural degradation under hydrogen-fueled turbine environments. • Hydrogen atmospheres are evaluated to clarify YSZ degradation in future H 2 turbine. • High-temperature H 2 generates oxygen vacancies driving structural evolution in YSZ. • Hydrogen-induced vacancy formation promotes phase changes and lattice distortion. • Vacancy-driven reactions alter YSZ bonding behavior and thermal responses.