First-principles study of electronic properties of La2Hf2O7 and Gd2Hf2O7

The structural and electronic properties of A2Hf2O7 (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–O48f and A–O8b bonds in Gd2Hf2O7 are more ionic than the corresponding bonds in La2Hf2O7, while the Hf–O48f bond in Gd2Hf2O7 is more covalent. These calculations suggest that A–O48f and A–O8b bonds may play important roles in their response to irradiation-induced amorphization observed experimentally.