The Effects of Oxygen Vacancy Concentration on the Mechanical Properties of Zirconia and Ceria-Based Electrolytes for SOFCs

Abstract

In this paper, we discuss the effects of different oxygen partial pressures on the deformation property and fracture characteristics of representative constituent materials for solid oxide fuel cells (SOFCs). The elastic modulus and fracture strength of 8 mol% yittria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC) treated under different oxygen partial pressures were evaluated using the small-punch testing method in this study. The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 °C under an oxygen partial pressure in the range of 0.21 to 10−22 atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10−15 atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ. The elastic modulus and fracture strength of 10GDC for the treatment under 10−22 atm was reduced down to 10–20% of those treated under the atmospheric pressure. SEM observations revealed that the fracture surface of the 10GDC specimens was changed from transgranular mode to intergranular mode when the oxygen partial pressure was reduced, whereas the fracture surface of the 8YSZ specimens was transgranular regardless of the different oxygen partial pressures.

Effect of Gd content on mechanical properties and erosion durability of sub-stoichiometric Gd2Zr2O7

“…The literature has shown that annihilation of vacancies via Ta 5+ and Nb 5+ doping in tetragonal zirconia can improve toughness [20] indicating the sensitivity of this material in the ferroelastic regime, though this is not active in the fluorite regime. For the fluorite phase, experiments on gadolinia doped ceria for fuel cell applications showed that decreasing oxygen partial pressure and increasing vacancy content yielded lower fracture stresses and a change in failure from transgranular to intergranular [21]. The reason for this transition is unclear, though it is possible a similar mechanism occurs in zirconia as rare earth content and vacancy content increase.…”