Maxwell-Wagner Relaxation in Ca-, Sm- and Nd-doped Ceria

Abstract

Doped ceria, i.e. Ce1-xMxO2-with M being dopant metal, has been a focus of great attention for solid oxide fuel cells (SOFCs) due to their high oxygen conduction. In the past literature, the dielectric relaxations in these materials have been ascribed to be caused by defect associates (MCeʺ-V̈) possessing different MCeʺ and V̈ distances. But we believe that with changing measurement and analysis techniques, it is necessary to invest our time to re-examine the already reported materials and take a detailed investigation of the underlying phenomenon behind their dielectric relaxations again. Thus, we have used solid-state reaction to prepare Ce1-xMxO2- with M=Ca, Sm, and Nd in x=0.1, 0.2, and 0.3 ratios, respectively. The as-prepared and post annealed samples were tested for dielectric properties from 300-1080 K with varying frequencies. The lowtemperature relaxation (R1) was argued to be a Maxwell-Wagner relaxation caused by humidity sensitivity. The hightemperature relaxation (R2) was ascribed to be caused by the hopping motion of oxygen vacancies. This fact was also supported by a detailed analysis of impedance spectra. While according to the previous reports, this relaxation is because of the oxygen-vacancy-dopant defect pair.

Non-classical electrostriction in calcium-doped cerium oxide ceramics

“…[18][19][20] Dielectric properties of cerium dioxide at room temperature are rarely reported and oen depend on the unpredictable presence of defect-induced dipoles in the lattice. [21][22][23] For A 3+ -doped ceria electrostriction, Varenik et al described that the electric eld-assisted rearrangement of the elastic dipole involves a slight change in the Ce À V $$ O distance and could be enough to trigger the relaxation behaviour. 24 Experimental ndings show that trivalent doped ceria leads to higher M 33 values at low operating frequencies and at 5-10 mol% doping levels.…”