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Understanding the response of ceramics operating in extreme environments isof interest for a variety of applications. Ab initio molecular dynamicsimulations have been used to investigate the effect of structure and $B$-site(=Ti, Zr) cation composition of lanthanum-based oxides (La$_2$$B_2$O$_7$) onelectronic-excitation-induced amorphization. We find that the amorphoustransition in monoclinic layered perovskite La$_2$Ti$_2$O$_7$ occurs for alower degree of electronic excitation than for cubic pyrochloreLa$_2$Zr$_2$O$_7$. While in each case the formation of O$_2$-like moleculesdrives the structure to an amorphous state, an analysis of the polyhedralconnection network reveals that the rotation of TiO$_6$ octahedra in themonoclinic phase can promote such molecule formation, while such octahedralrotation is not possible in the cubic phase. However, once the symmetry of thecubic structure is broken by substituting Ti for Zr, it becomes less resistantto amorphization. A compound made of 50% Ti and 50% Zr (La$_2$TiZrO$_7$) isfound to be more resistant in the monoclinic than in the cubic phase, which maybe related to the lower bandgap of the cubic phase. These results illustratethe complex interplay of structure and composition that give rise to theradiation resistance of these important functional materials.

Effect of structure and composition on the electronic excitation induced amorphization of La$_2$Ti$_{2-x}$Zr$_x$O$_7$ ceramics