Engineering site disorder to give rise to enhanced conductivity in a scandia-stabilised zirconia electrolyte via disruption of short-range ordering

Conductivity degradation is the key limitation associated with zirconia electrolytes, especially within the scandia doped compositions. This is strongly associated with defect ordering, suggesting that introduction of cation disorder could overcome such degradation. The system Sc 0.15+x [In 0.05 Mg 0.0125 ]Zr 0.7875-x O 1.8875-x/2 , x = −0.125, 0 (IMSSZ), 0.125 addressed in this study shows an unusual conductivity degradation-recovery-enhancement profile where the conductivity degrades for a short period of time then recovers and exceeds its initial value. The conductivity at 850 °C in air was found to recover to the initial value of 0.096 S cm −1 in less than 25 h, and then it continues to improve up to 0. 11 S cm −1 after 250 h. Starting with a brief introduction on the origin of short-range ordering hence long-term conductivity degradation in the fluorite materials, this paper presents a detailed structural characterisation of this special composition with a focus on short-range structure through electron diffraction, TOF neutron diffraction and impedance spectroscopy. We conclude that the conductivity degradation is caused by pyrochlore and rare-earth C-type related short-range ordering, whereas the conductivity increase and stabilisation observed in this composition is a result of dopant segregation to grain boundaries, with the altered bulk composition destabilising and eliminating such defect short-range ordering and moving towards a stable disordered fluorite structure. • Short range order has been disrupted in fluorite oxide ion conductors via introduction of variable size cations. • An stable oxide ion conductivity of 0.11 S cm −1 at 850 °C is demonstrated over 100 s of hours of testing. • Initial conductivity degradation is caused by pyrochlore and rare-earth C-type related short-range ordering. • Conductivity then increases and stabilises as a result of dopant segregation to grain boundaries, with the altered bulk composition defect short-range order.