Synthesis and characterization of Gd3+ and Nd3+ co-doped ceria by using citric acid–nitrate combustion method

Abstract: A series of Ce0.8Gd0.2−x Nd x O2−δ (x =0–0.20) compositions have been synthesized by citric acid–nitrate combustion method. XRD measurements indicate that all the obtained materials crystallized in cubic fluorite-type structure. Lattice parameters were calculated by Rietveld method and the parameter a values in Ce0.8Gd0.2−x Nd x O2−δ system obey Vegard''s law, a (Å)=5.4224+0.1208x. The obtained powders have good sinterability and the relative density could reach above 95% after being sintered at 1400°C. Impedance spectroscopy measurements indicated that the conductivity of Ce0.8Gd0.2−x Nd x O2−δ first increased and then decreased with Nd dopant content x. The maximum conductivity, σ 700°C =6.26×10−2 S/cm, was found in Ce0.8Gd0.12Nd0.08O1.9 when sintered at 1300°C. The corresponding activation energies of conduction had a minimum value E a =0.676eV. The results tested experimentally the validity of the effective atomic number concept of recent density functional theory, which had suggested that co-dopant with effective atomic number between 61 (Pm) and 62 (Sm) was the ideal dopant exhibiting high ionic conductivity and low activation energy. [Copyright &y& Elsevier]