Oxygen Vacancies at Grain Boundaries in Doubly-Doped Ceria Determined using EELS

In oxygen conducting ceramics such as cerium-based oxides, O 2diffusion occurs via vacancy hopping. The vacancy concentration can be modulated through doping with aliovalent cations such as Gd 3+ or Pr 3+ . Sluggish ionic conductivity in these electrolytes has been attributed to various defects which increase the activation energy for anion migration. The association of mobile oxygen vacancies with dopant cations, and the presence of highly resistive grain boundaries in polycrystalline electrolytes are well-accepted mechanisms which degrade total ionic conductivity [1]. The predominant explanation for high grain boundary resistivity in ceramics of high purity is the space charge double layer (SCDL) which results in vacancy-depleted regions emanating from grain boundary cores [2]. Recently it was shown that addition of 0 – 2 at% transition metal (TM) ions such as Cr, Fe, Ni and Cu to high purity gadolinium-doped ceria (GDC) enhanced grain boundary electrical conductivity by as much as 15 times by reducing the SCDL potential barrier [3]. Here we use a combination of impedance spectroscopy (EIS) and electron energy-loss spectroscopy (EELS) to characterize the electrical conductivity and vacancy concentration of grain boundaries in ceria doubly-doped with Gd and Pr.