First-principles study of electronic properties of La2Hf2O7 and Gd2Hf2O7

The structural and electronic properties of A(2)Hf(2)O(7) (A=La and Gd) pyrochlore compounds are investigated by means of first-principles total energy calculations. Also, the formation energies of defects are calculated, and the results can be used to explain the stability of pyrochlores. Hybridizations between A 5p and O 2s and between A 5d and O 2p states are observed, but the interaction between A 5p and O 2s orbitals is much stronger in Gd2Hf2O7 than that in La2Hf2O7. Gd2Hf2O7 shows a density of state distribution much different from that of La2Hf2O7. Mulliken overlap population analysis shows that the A-O-48f and A-O-8b bonds in Gd2Hf2O7 are more ionic than the corresponding bonds in La2Hf2O7, while the Hf-O-48f bond in Gd2Hf2O7 is more covalent. These calculations suggest that A-O-48f and A-O-8b bonds may play important roles in their response to irradiation-induced amorphization observed experimentally.