Ion transport and dielectric relaxation studies in nanocrystalline Ce<inf>0.8</inf>Ho<inf>0.2</inf>O<inf>2-δ</inf> material

The ac electrical conductivity and dielectric relaxation properties of nanocrystalline 20 mol% Ho doped ceria (Ce0.8Ho0.2O2-δ) prepared by citrate auto ignition method, were studied in the temperature range 300-550 °C. The conductivity behaviour showed the absence of any precipitation of Ho inside the grains, even though it has the tendency of forming a C-type structure similar to Ho2O3 in association with oxygen vacancies. The frequency spectra of electric modulus M″ exhibits a single relaxation peak corresponding to relaxation reorientation of oxygen vacancy around the Ho+3 ions in the cubic nanostructured material. The migration of oxygen ions in the nanocrystalline Ce0.8Ho0.2O2-δ material takes place through hopping and the migration energy and association energy of oxygen vacancies in the long range order motion are found to be 1.02 and 0.24 eV, respectively. © 2009 Elsevier B.V. All rights reserved.