Maxwell-Wagner Relaxation in Ca-, Sm- and Nd-doped Ceria
Abstract
Doped ceria, i.e. Ce1-xMxO2-δ with M being dopant metal, has been a focus of great attention for 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-Vö ) possessing different MCeʺ and Vö 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-δ 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 low-temperature relaxation (R1) was argued to be a Maxwell-Wagner relaxation caused by humidity sensitivity. The high-temperature 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.