Phase stability and ionic conductivity of cubic xNb2O5-(11-x)Sc2O3-ZrO2 (0 ≤ x ≤4)

The present work looks at the effect of Nb2O5 co-doping on the structure and conductivity of 11 mol.% Sc2O3 stabilized ZrO2 solid electrolyte for intermediate temperature solid oxide fuel cells. XPS analysis confirmed that niobium exists in 5+ valence state in the sintered stabilized ZrO2 samples. SEM study performed on sintered samples revealed that the addition of Nb2O5 not only assists in the densification of Sc2O3-ZrO2 but also leads to exaggerated grain growth. Both XRD and Raman analysis confirmed that addition of up to 1 mol.% of Nb2O5 suppresses the formation of low-conductivity rhombohedral b-phase and leads to the stabilization of cubic phase. For compositions with > 1 mol.% Nb2O5, a mixture of tetragonal and monoclinic phases was identified. Impedance spectroscopy showed that the total ionic conductivity increases significantly on co-doping with 1 mol.% Nb2O5. This increase is attributed to the enhanced sinterability and decrease in space-charge potential of Nb2O5 co-doped samples. While > 1 mol.% Nb2O5 compositions have low conductivity due to the formation of low conductivity secondary phases. (C) 2017 Elsevier B.V. All rights reserved.