PNNL

Abstract

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 compound shows much different density of state distribution 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 responses to irradiation-induced amorphization observed experimentally.