First-principles calculation of structural and energetic properties for A(2)Ti(2)O(7) (A = Lu, Er, Y, Gd, Sm, Nd, La)

A first-principles method was used to investigate the structural and energetic properties. for A(2)Ti(2)O(7) (A = Lu, Er, Y, Gd, Sm, Nd, La), including the formation energies of the cation antisite-pair, the anion Frenkel pair that defines anion-disorder, and the coupled cation antisite-pair/anion-Frenkel. It is proposed that the < A-O-48f > interaction may have more significant influence on the radiation resistance behavior of titanate pyrochlores, although the < Ti-O-48f > interactions are relatively stronger than the < A-O-48f > interactions. It was found that the defect formation energies are not simple functions of the A-site cation radii. The formation energy of the cation antisite-pair increases continuously as the A-site cation varies from Lu to Gd, and then decreases continuously with the variation of the A-site cation from Gd to La, in excellent agreement with the radiation-resistance trend of the titanate pyrochlores. The band gaps in these pyrochlores were also measured, and the band gap widths changed continuously with cation radius.