Segregation effects at grain boundaries in fluorite-structured ceramics

The atomic-scale structure, composition, and chemistry of grain boundaries in two fluorite-structured ceramic materials were characterized by a combination of Z-contrast imaging and electron energy-loss spectroscopy (EELS). In the case of a symmetric 24degrees [001] tilt bicrystal of yttria-stabilized-zirconia (YSZ), a shift in the zirconium M-edge onset and a change in the yttrium and zirconium M-edge ratios at the boundary indicate an increase in the number of electrons in the boundary plane. A detailed study of the structure and composition indicates that this is caused by an increase in the number of oxygen vacancies in the grain boundary core that is partially compensated by yttrium segregation. Studies of grain boundaries in an industrial Gd-doped ceria ceramic reveals similar changes in vacancy/dopant profiles indicating that these effects may be generic to grain boundaries in fluorite-structured materials.