Defect chemistry of (Nd,Tm)- and (Nd,Dy)-doped ceria as revealed by Raman and electrochemical impedance spectroscopy

A Raman and electrochemical impedance spectroscopy (EIS) joint study was performed on the (Nd,Tm)- and (Nd, Dy)-doped ceria systems, members of a promising class of materials to be used as electrolytes in solid oxide cells operating at intermediate temperatures (IT-SOCs). Raman and EIS data were collected in the 573-1073 K temperature range, i.e. in the operating temperature range of IT-SOCs, and analyzed with the aim to correlate ionic conductivity and defect chemistry. Defect aggregates growing within the CeO2-based matrix tend in fact to reduce and even suppress oxygen transport. A slope change in the trend of Raman shift of the Ce- O vibration, as well as of the FWHM/intensity ratio of the same signal, occurs around the temperature where also the activation energy to ionic conduction changes its value. This common evidence is discussed in the light of defect aggregates stability, and in more detail in terms of decomposition of the 1Voo2RE? trimers.