In this work, the composition-dependent point defect types and formation energies of
RE2Hf
2O
7 (
RE = La, Ce, Pr, Nd, Pm, Sm, Eu and Gd) as well as the oxygen diffusion behavior are systematically investigated by first-principles calculations. The possible defect reactions and dominant defect complexes under stoichiometric and non-stoichiometric conditions are revealed. It is found that O Frenkel pairs are the predominant defect in stoichiometric pyrochlore hafnates. Hf-
RE cation anti-site defects, accompanied by
RE vacancies and/or oxygen interstitials, are stable in the non-stoichiometric case of HfO
2 excess. On the other hand,
RE-Hf anti-site defects together with oxygen vacancies and/or
RE interstitials are preferable in the case of
RE2O
3 excess. The energy barriers for the migration along the V
O48f - V
O48f pathway of pyrochlore hafnates were calculated to be between 0.81 eV and 0.89 eV. Based on these results, a defect engineering strategy is proposed and the pyrochlore hafnates investigated here are predicted to exhibit potential oxygen ionic conductivity.
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