Oxygen partial pressure dependence of creep on yttria-doped ceria ceramics

A creep test was performed on yttria-doped ceria (YDC), which was investigated as an electrolyte for solid oxide fuel cells (SOFC). The test was performed using a four-point bending method and with testing conditions including a constant load under a temperature range of 1050-1125 °C, an applied stress of 20-50 MPa, and an oxygen partial pressure of P(O2)=0.21-10−15.2 atm. The results showed that the creep rate increased with decreasing P(O2), and showed a peak at P(O2)=10−13.6 atm. The activation energy for creep was increased from 264 to 333 kJ/mol with decreasing P(O2) from 0.21 to 10−14.5 atm. These values were much higher than the reported activation energy of oxygen anion diffusion in ceria. Thus, it could be suggested that the creep mechanism is controlled by cation diffusion. The creep mechanism changed from Nabarro-Herring creep to grain boundary sliding in a reducing atmosphere when the P(O2) was lower than 10−14.5 atm.