Density functional theory study of La₂Ce₂O₇: disordered fluorite vs pyrochlore structure

Abstract

The crystal structure of lanthanum cerium oxide (La₂Ce₂O₇) is investigated using ab initio density functional theory calculations. The relative stability of fluorite- and pyrochlore-like structures is studied through comparison of their formation energies. These formation energies show the pyrochlore structure to be favored over the fluorite structure, apparently contradicting the conclusions based on experimental neutron and x-ray diffraction (XRD).
By calculating and comparing XRD spectra for a set of differently ordered and random structures, we show that the pyrochlore structure is consistent with diffraction experiments. For these reasons, we suggest the pyrochlore structure as the ground-state crystal structure for La₂Ce₂O₇.