Composition-dependent intrinsic defect structures in pyroclore RE2B2O7 (RE = La, Nd, Gd; B = Sn, Hf, Zr)

Point defects are closely correlated with various properties of pyrochlore oxides and therefore play a key role on their engineering applications. Here, the native point defect complexes in RE2B2O7 (RE = La, Nd, Gd; B = Sn, Hf, Zr) under stoichiometric and nonstoichiometric compositions are studied by first-principles calculations. The O Frenkel defect complex is predicted to be the predominant defect structure in stoichiometric zirconates and hafnates, whereas the cation antisite defect complex is the predominant one in stannates. In the case of BO2 excess, the formation of the B-RE antisite defect together with the RE vacancy and the oxygen interstitial is energetically favorable, whereas the RE-B antisite defect together with the oxygen vacancy and the RE interstitial is preferable under the RE2O3 excess environments. Additionally, the formation energies of the native defect complexes are greatly affected by the B-site and/or RE-site cations. The strategy on tailoring the intrinsic defect structures of these pyrochlore oxides is proposed. It is expected to guide the experiments on the defect-related property optimization through stoichiometric and nonstoichiometric compositions, so as to meet the specific engineering requirements and promote their commercial applications.