Ionic Conductivity of Gd- and Y-Doped Ceria-Zirconia Solid Solutions

Abstract

The total conductivity of the solid solutions (Ce1−xZrx)0.8Gd0.2O1.9 and (Ce1−xZrx)0.8Y0.2O1.9 was measured in air as a function of temperature (T = 300 °C- 600 °C) and composition (x = 0.0 - 0.9). A deep minimum of the bulk ionic conductivity was found for equal fractions of ceria and zirconia. It indicates enhanced defect association and ordering of the oxygen vacancies around x = 0.5. X-ray analysis (Guinier technique) showed the diffraction pattern of the cubic fluorite structure for all investigated compositions 0 < x < 1. The lattice parameter decreased linearly with increasing zirconia content x.

The model case of an oxygen storage catalyst – non-stoichiometry, point defects and electrical conductivity of single crystalline CeO2–ZrO2–Y2O3solid solutions

“…Here, the decrease in conductivity is more than one order of magnitude. This behaviour has been reported by several other groups for polycrystalline samples as well, 27,29,30 which is therefore in good agreement with single crystals investigated in the present work. However, such a strong decrease in conductivity with respect to the ceria content is surprising at first glance, since the charge carrier concentration (oxygen vacancies) is fixed in the whole composition range by yttria doping.…”

“…The lattice parameters determined by Rietveld refinements are in good agreement with literature data. 29,53 An increasing ceria content results in a shift of the observed reflections to smaller 2y values. Since the ionic radius r(Ce 4+ ) = 0.97 Å of cerium ions is larger in comparison to the radius of zirconium ions r(Zr 4+ ) = 0.84 Å, the lattice parameters expand with increasing ceria content resulting in a shift of the reflections to smaller diffraction angles.…”

“…the system appears to be fully miscible in the entire composition range as already reported by several authors. 27,29,31,55,56 In contrast, Sammes et al 57 found a local maximum of the cell parameter vs. x in the system (CeO 2 ) 1Àx (8YSZ) x for x E 0.5 and drew the conclusion that CeO 2 has a limited solubility in YSZ. Similar results from Hinatsu et al 58 and Sakai et al 53 indicate a miscibility gap for In addition to phase analysis by X-ray diffraction (XRD), Raman spectroscopy on small single crystals of each composition was performed (Fig.…”

“…[21][22][23] As well shown by Chiodelli et al, 24 Lee et al 25 and Kuhn et al, 26 defect chemical modelling is essential for the fundamental understanding of the OSC and for further improvement. The solid solution system CeO 2 -ZrO 2 -Y 2 O 3 has already been examined in polycrystalline form with regard to total conductivity, 25,[27][28][29][30][31][32][33] partial electronic conductivity 34 and nonstoichiometry 26,35 as a function of temperature and oxygen partial pressure. Reviewing these studies, three questions remain open: (a) it was observed by Cales and Baumard, 31 Lee et al 32 and Xiong et al 34 that the course of the total and the partial electronic conductivity as a function of oxygen partial pressure deviates strongly from the ''classical'' point defect model for acceptor doping (see Section 2), especially at low pO 2 .…”

Ceria: Recent Results on Dopant-Induced Surface Phenomena

“…In the framework of the current investigation the standard phenomenological treatment could recently be extended [33,34]. Because of the open questions on the nature of the K-D correlation we will only consider publications which present data for both K and D and will not discuss other, though interesting, studies like electrical conductivity measurements where electrodes are used and which, at best, supply the oxygen ion conductivity (which would yield the oxygen self-diffusivity) but no information on the surface exchange coefficient (see, e.g., [35]) nor, respectively, electrical conductivity relaxation studies which yielded only surface exchange coefficients but no diffusion coefficients (see, e.g., [36]). …”