Destabilization and ion conductivity of yttria-stabilized zirconia for solid oxide electrolyte under thermal stress

The degradation behavior of yttria-stabilized zirconia under thermal stress was investigated in terms of phase transformation, local atomic structure, and electrical conductivity. The average grain size of 8YSZ were increased from 20.83 µm to 25.81 µm with increasing aging temperature. All 8YSZ samples degraded at different temperatures had a predominantly cubic structure. The (400) peak of 8YSZ deteriorated at 1300 and 1400°C shifted to high angle, and the peak of tetragonal was not indexed. For 8YSZ degraded at 1500°C, the (400) peak shifted to a lower angle, and the peak of tetragonal was identified. In the local atomic structure of the aged 8YSZ with extended X-ray absorption fine structure, the intensity of the Zr-O peak gradually increased, and the intensity of the Zr-Cation peak decreased as the aging temperature increased. The changes in the peaks indicate that the oxygen vacancies were reduced and Y3+ ions escaped from the lattice, leading to destabilization of 8YSZ. The activation energies of 8YSZ at 1300°C and 1400°C were derived to be 0.86 and 0.87 eV, respectively, and the activation energy of 8YSZ at 1500°C increased significantly to 0.92 eV. With the thermal deterioration of 8YSZ, the cation (Y3+) escaped from the lattice and the number of oxygen vacancies decrease, resulting in the formation of a tetragonal structure and high activation energy at 1500°C.