Density Functional Analysis of Fluorite-Structured (Ce, Zr)O<inf>2</inf>/CeO<inf>2</inf> Interfaces

The structures and properties of Ce1-xZrxO2 (x = 0-1) solid solutions, selected Ce1-xZrxO2 surfaces, and Ce1-xZrxO2/CeO2 interfaces were computed within the framework of density functional theory corrected for strong electron correlation (DFT+U). The calculated Debye temperature increases steadily with Zr content in (Ce, Zr)O2 phases, indicating a significant rise in microhardness from CeO2 to ZrO2, without appreciable loss in ductility as the interfacial stoichiometry changes. Surface energy calculations for the low-index CeO2(111) and (110) surfaces show limited sensitivity to strong 4f-electron correlation. The fracture energy of Ce1-xZrxO2(111)/CeO2(111) increases markedly with Zr content, with a significant decrease in energy for thicker Ce1-xZrxO2 films. These findings suggest the crucial role of Zr acting as a binder at the Ce1-xZrxO2/CeO2 interfaces, due to the more covalent character of Zr-O bonds compared to Ce-O. The impact of surface relaxation upon interface cracking was assessed and found to reach a maximum for Ce0.25Zr0.75O2/CeO2 interfaces.