The electrical conductivity of monocrystalline samples with 3.0, 9.5, 12.0 or 17.5mol%Y2O3, and of polycrystalline samples with 9.9mol%Y2O3, was studied by means of impedance spectroscopy at temperatures ranging from 250 to 1200C. The results showed that the bulk ionic conductivity was independent of the O partial pressure, but depended upon the amount of yttria. The highest conductivities were found in the case of the monocrystalline samples. These results, and published O diffusion data, suggested that various types of defect were present in the material; depending upon the temperature range and the yttria content. The behavior of the conductivity of the grain boundaries, with and without alumina, was close to that of the monocrystalline doped sample. This suggested that associated point defects controlled the grain boundary transport properties. A maximum in the conductivity, a so-called composite effect, was observed when the amount of alumina in the polycrystalline material was approximately 2mol%.

M.Filal, C.Petot, M.Mokchah, C.Chateau, J.L.Carpentier: Solid State Ionics, 1995, 80[1-2], 27-35