Solid solubility and transport properties of Ce1-xNdxO2-delta nanocrystalline solid solutions by a sol-gel route

Ce1-xNdxO2-delta (x = 0.05 to 0.55) nanocrystalline solid solutions were pr epared by a sol-gel route. X-ray diffraction analysis showed that Ce1-xNdxO 2-delta crystallized in a cubic fluorite structure. The lattice parameter f or the solid solutions increased linearly with the dopant content. The soli d solubility of Nd3+ in ceria lattice was determined to be about x = 0.40 i n terms of the nearly constant lattice parameters at a dopant level larger than x = 0.40. First-order Raman spectra for Ce1-xNdxO2-delta at a lower do pant content exhibited one band associated with the F2g mode. At higher dop ant contents, F-2g mode became broadened and asymmetric, and a new broad ba nd appeared at the higher frequency side of the F-2g mode. This new band wa s assigned to the oxygen vacancies. The electron paramagnetic resonance spe ctrum for x = 0.05 showed the presence of O-2(-) adsorbed on sample surface at g = 2.02 and 2.00 and of Ce3+ with a lower symmetry at g = 1.97 and 1.9 4. Further increasing dopant content led to the disappearance of the signal s for O-2(-). Impedance spectra showed the bulk and grain boundary conducti on in the solid solutions. The bulk conduction exhibited a conductivity max imum and an activation energy minimum with increasing dopant content. Ce0.8 0Nd0.20O2-delta was determined to give promising conduction properties such as a relatively high conductivity of sigma (700 degreesC) = 2.44 x 10(-2) S cm(-1) and moderate activation energy of E-a = 0.802 eV. The variations o f conductivity and activation energy were explained in terms of relative co ntent of oxygen vacancies V-(O) double over dot and defect associations {Ce Fe ' 'V-(O) double over dot}/{NdCe 'V-(O) double over dot}.