Ionic Conductivity Enhancement in Nanostructured Heavily Doped Ceria Ceramics

M. G. BELLINO; D. G. LAMAS; N. E. WALSÖE DE RECA

Cancún, México

Congreso; XV international Materials Research Congress; 2006

Academia Mexicana de Ciencia de Materiales

Nanostructured materials are widely investigated because of the enhancement of different properties compared to those of bulk materials. Particularly, in case of nanostructured ceramics, the presence of  a large fraction of grain boundary can lead to unusualy better mechanical, electrical, optical, sensing, magnetical and biomedical properties. A growing area of investigation is "nanoionics": the ionics transport in nanostructured solid electrolytes because of thear useful applications: lithium batteries, gas sensors, fuel cells, etc. An intensive research has been conducted to find new electrolyte and electrode materials allowing the reduction of the operating temperature of SOFCs with Ceria-based ceramics among the most promising electrolytes for intermediate temperature SOFCs (IT-SOFCs) since their ionics conductivity is higher than that of traditional circonia-based electrolites used in SOFCs. This materials exhibit electronic conductivity in reducing atmosphere being this effect negligible for T < 600ºC with a consequent efficient behavior at internediated temperatures. In the last decade,transport properties of Ceria-based electrolytes have been investigated particularly, the influence of microstructured and impurities on the grain boundary (intergrain) ionic conductivity, concluding that the maximun total ionic conductivity is the grain interior (intrinsic or bulk) conductivity (independent of microstructure). On the other hand, a enhancement the of one or two orders of magnitud in the total ionic conductivity was found for nanostructured CeO2-Gd2O3 and Yttria-stabilized circonia (YSZ) thin films, compared to that of microcrystal or single-crystal, being this behavior  not confirmed yet for nanostructured heavely-doped ceria or YSZ dense pellets. In this work, electrical properties of nanostructured CeO2-10mol% Y2O3 (CYO) and CeO2-10mol% Sm2O3 (CSO) ceramics have been studied by electrochemical impedance spectroscopy (EIS) in funtion of grain size. Samples were nanostructured densified ceramics with high-specifics surface area. EIS results demostrated an enhancement (one order of magnitud) in the total ionoc conductivity of nanostructured hevily Y2O3 or Sm2O3 - doped CeO2 pelled in comparation with the grain interior conductivity of these materials. This fact is attribuited to the predominance of grain boundary conductivity in nanostructured materials coupled with the faster grain boundary diffusion with decreasin grain size.