Mechanical properties of yttria-stabilized zirconia: A study by ReaxFF molecular dynamics simulations

Yttria-stabilized zirconia (YSZ) used as the electrolyte in solid oxide fuel cells usually relies on the complicated chemical reactions at an extremely high temperature. In this paper, the impact of the reaction on the mechanical properties of YSZ is investigated with the aid of reactive force-field (ReaxFF) molecular dynamics simulations. The obtained results show that before the reaction, the intrinsic Young's modulus of YSZ is almost independent of the crystal orientation, while different Poisson's ratios are detected in different crystal orientations. After the reaction, both Young's modulus and Poisson's ratio of YSZ are greatly reduced, since the oxygen in the surface can be deboned and thus escapes from YSZ. Specifically, the largest difference of the mechanical properties before and after the reaction is observed in [111]-oriented YSZ, since it has a unique zigzag surface structure. A decrease of Young's modulus and Poisson's ratio is also observed in YSZ with increasing the temperature and the doping concentration, though the reduction in the mechanical properties is different in different crystal orientations. Based on the obtained simulation results, predictive equations were proposed for quickly predicting the Young's modulus and the Poisson's ratio of YSZ at different temperatures and with different doping concentrations.