The fracture behavior of non-stoichiometric gadolinia-doped ceria solid electrolytes using molecular dynamics simulations

Gadolinia-doped ceria (GDC) electrolytes create non-stoichiometric oxygen vacancies and reduce mechanical properties under reducing conditions. Especially when there are crack defects in the material, an excess of oxygen vacancies create and propagate cracks to the point of ultimate failure of the electrolyte membrane. In this paper, we investigate the effect of crack defects on anisotropic mechanical behavior of non-stoichiometric GDC by using the molecular dynamics (MD) method. It is found that in the [100] and [110] crystal orientations, crack defects cause a change from ductile to brittle fracture. For non-stoichiometric GDC with low doping concentration, oxygen vacancies increase fracture stress by increasing critical nucleation stress of phase transformation. However, for non-stoichiometric GDC with high doping concentration, excess oxygen vacancies reduce the strength of fluorite phase. The fracture stress exhibits anomalous characteristics that first increases and then decreases with increasing oxygen vacancies. Due to the electrostatic repulsion between the adjacent oxygen ion layers in the [111] crystal orientation, the material strength decreases with increasing oxygen vacancies and crack defects.