Comparative study of fluorite-type ceria-based Ce1-x Ln (x) O2-delta (Ln = Tb, Gd, and Pr) mixed ionic electronic conductors densified at low temperatures

It has been reported that peak mixed conducting performance can only be obtained in doped ceria-based fluorite ceramics that contain cobalt sintering additives, when these materials are sintered below 1100 A degrees C. Hence, this article provides a comparative analysis of the electrochemical behavior of such materials formed under the aforementioned conditions. The transport properties of Ce0.8Tb0.2O2-delta (CTO), Ce0.8Gd0.2O2-delta (CGO), and Ce0.8Pr0.2O2-delta (CPO) with 2 mol% Co sintering aid were analyzed for samples prepared and sintered under similar conditions. The total conductivities of these samples were characterized by impedance spectroscopy under air atmosphere in the temperature range of 200-850 A degrees C. Oxide-ion transference numbers were determined by the modified electromotive force method under oxygen/air gradient. Ionic and electronic conductivities were calculated from transference numbers and total conductivity measurements and compared. CTO + Co and CPO + Co ceramic materials show higher relative contribution of the electronic transport compared to CGO + Co. Among these materials, CPO + Co shows the highest total and partial electronic conductivities, as well as the highest oxygen permeability, with essentially the same partial oxide-ion conduction as CGO + Co

Structural-Transport Properties Relationships on Ce(1-x)Ln(x)O(2-delta) System (Ln = Gd, La, Tb, Pr, Eu, Er, Yb, Nd) and Effect of Cobalt Addition

A large series of doped cerias have been prepared by the coprecipitation method combined with impregnation and completely characterized in order to have an overall understanding of the structural, oxygen vacancy concentration, and transport properties relationships. Several lanthanides were incorporated in the fluorite structure, and the effects of the final sintering temperature (1073 and 1573 K) and the addition of cobalt oxide on the structural properties were studied. The chosen lanthanides (Gd, La, Tb, Pr, Eu, Er, Yb and Nd) included a large range of ionic radii and different metals exhibiting variable oxidation states under the typical operating conditions for these materials. The materials have been characterized by powder XRD, high-temperature XRD, micro- Raman spectroscopy, helium pycnometry, and dc conductivity. Transport properties were correlated with structural features induced by the different ionic radii and variable oxidation state of the dopants. The highest ionic conductivity was obtained for the less distorted cells (Gd- and Nd-doped ceria) which represent the optimum balance between Coulomb interactions, steric effects, and vacancy distribution. The lowest Ea value was found for materials with long cell parameters.Financial support by the Spanish Ministry for Science and Innovation (Project ENE2008-06302, ENE2011-24761 and Grant BES-2009-015835), Spanish Industry Ministry (Project IAP-560620-2008-17), and Instalaciones Inabensa S.A. is kindly acknowledged. Dr. Jose L. Jorda contributed to this work with HT-XRD diffraction experiments.Balaguer Ramírez, M.; Solis Díaz, C.; Serra Alfaro, JM. (2012). Structural-Transport Properties Relationships on Ce(1-x)Ln(x)O(2-delta) System (Ln = Gd, La, Tb, Pr, Eu, Er, Yb, Nd) and Effect of Cobalt Addition. Journal of Physical Chemistry C. 116(14):7975-7982. https://doi.org/10.1021/jp211594dS797579821161