Structural and conductivity characteristics of Bi4MgxV2−xO11−δ (0 ⩽ x ⩽ 0.3) as solid electrolyte for intermediate temperature SOFC application

A novel material family for electrolyte in intermediate temperature solid oxide fuel cells (SOFC), i.e., BIMGVOX, Bi4MgxV2−xO11-δ (0 ⩽ x ⩽ 0.3), were synthesized by solid state reaction. In order to examine the effects of dopant cation concentration on γ-phase stability (vacancy disordering phenomena) and ionic conductivity, structure and electrical conductivity of BIMGVOX were investigated using X-ray diffraction, scanning electron microscopy and AC impedance spectroscopy. Compositional dependence of the conductivity behavior as a function of temperature was found. The change of slopes observed in the Arrhenius plots was in agreement with the phase transitions for all the compositions. The stabilisation of highly conducting γ-phase was found when x ⩾ 0.2. The highest low temperature ionic conductivity (σ300 = 1.18 × 10−3 S cm−1) of the Mg-substituted compound was observed for the composition of x = 0.2 as compared with other doped samples of the same series, attributing to its low activation energy. Since the grain size and its phase distribution had great influence on the conductivity, various sintering parameters were also investigated for all samples.