Grain boundary's conductivity in heavily yttrium doped ceria

Four high purity heavily yttrium doped ceria (YDC, YxCe1 − xO2 − δ, x = 0.1, 0.15, 0.2 0.25) electrolytes were prepared and their grain boundaries (GBs) were investigated by impedance spectroscopy (IS) and transmission electron microscopy (TEM). IS data indicated that single GB's resistance and GB's thickness firstly decreased and then increased with increasing doping level. TEM investigation on GBs suggested the formation of nanodomains at GBs was responsible for the increase of GB's electrical thickness. Our work suggests in heavy doping level ceria, in addition to the space charge effect, nanodomain's blocking effect is another contribution to the high GB resistivity. According to the microstructure evolution of YDC with increasing doping level, we suggest three factors that influence nanodomain's segregation to GBs.

► GB's space charge potential is decreased with increasing doping level.
► GB's thickness is not monotonically decreased with increasing doping level.
► Nanodomain's density at GBs is higher than that in grain interior in 25YDC.
► GB's resistance and thickness are increased by the segregation of nanodomains to GB.