Anomalous conductivity and microstructure in gadolinium doped ceria prepared from nano-sized powder

The temperature and the oxygen partial pressure dependences of the electron and hole conductivities were measured by the dc polarization method using a Hebb–Wagnerʹs ion blocking cell for Gd0.2Ce0.8O1.9 polycrystalline bodies with grain size of 0.5 μm prepared by sintering of nano-sized powder. A significant enrichment of gadolinium was observed in the vicinity of the grain boundary by TEM/EDS analyses. The electron conductivity were comparable with those of conventional Gd0.2Ce0.8O1.9 polycrystalline body with grain size of 2 μm, and it followed p(O2)− 1/4 dependence at temperatures T = 973–1273 K. However, the observed hole conductivity was higher than that of conventional Gd0.2Ce0.8O1.9, and it did not follow p(O2)1/4 dependence. This anomalous p(O2) dependence disappeared after the sample was treated at T = 1773 K for 38 h and grain size was enlarged to 2–10 μm.