Degradation of zirconia in moisture

Zirconia especially stabilized by Y2O3 (YSZ) is an important and popularly used material. We have observed the degradation of YSZ in moisture, and have also revealed the degradation mechanism which could be related to the following three chemical processes: (1) reaction of water with the residual Y2O3 which is not incorporated into the crystal lattice of ZrO2; (2) corrosion of YSZ by water; (3) depletion of Y3+ from the crystal lattice by water molecule due to oxygen vacancies. A core/shell structure of ZrO2/Y2O3 in YSZ crystalline grains has been proved. Calcination of YSZ above 1100 degrees C can prevent the degradation.