Comparison and correlation of structural disorder caused by anion Frenkel in affecting ion conduction of La₂Hf₂O₇ and La₂Mo₂O₉ as high performance electrolytes in SOFCs

Abstract

La₂Hf₂O₇ and La₂Mo₂O₉ as potential electrolytes for solid oxide fuel cells (SOFCs) have been investigated through first-principles calculations to understand the mechanism of ion motion. In La₂Hf₂O₇, three unique types of positions that can form anion-Frenkel (a-Fr) pairs have been screened out and a reasonable continuous diffusion path constructed by these migration sites has also been suggested as the dominant cause of ion conduction. On the other side, excellent ion conductivity in La₂Mo₂O₉ is more based on the short-range disorder induced by mobile structure. The thermodynamic properties comparison of La₂Mo₂O₉ and La₂Hf₂O₇ shows that the formation of a-Fr pairs in La₂Mo₂O₉ will start at lower temperature because of higher degree of structural disorder and less constraints on oxygen ions.