Tiffany Kaspar | Searcharxiv

arXiv2021

Percolation of Ion-Irradiation-Induced Disorder in Complex Oxide Interfaces

Mastery of order-disorder processes in highly non-equilibrium nanostructured oxides has significant implications for the development of emerging energy technologies. However, we are presently limited in our ability to quantify and harness these processes at high spatial, chemical, and temporal resolution, particularly in extreme environments. Here we describe the percolation of disorder at the model oxide interface LaMnO$_3$ / SrTiO$_3$, which we visualize during in situ ion irradiation in the transmission electron microscope. We observe the formation of a network of disorder during the initial stages of ion irradiation and track the global progression of the system to full disorder. We couple these measurements with detailed structural and chemical probes, examining possible underlying defect mechanisms responsible for this unique percolative behavior.

cond-mat.mtrl-sci↗

arXiv2018

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

Understanding the response of ceramics operating in extreme environments is of interest for a variety of applications. Ab initio molecular dynamic simulations 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$) on electronic-excitation-induced amorphization. We find that the amorphous transition in monoclinic layered perovskite La$_2$Ti$_2$O$_7$ occurs for a lower degree of electronic excitation than for cubic pyrochlore La$_2$Zr$_2$O$_7$. While in each case the formation of O$_2$-like molecules drives the structure to an amorphous state, an analysis of the polyhedral connection network reveals that the rotation of TiO$_6$ octahedra in the monoclinic phase can promote such molecule formation, while such octahedral rotation is not possible in the cubic phase. However, once the symmetry of the cubic structure is broken by substituting Ti for Zr, it becomes less resistant to amorphization. A compound made of 50% Ti and 50% Zr (La$_2$TiZrO$_7$) is found to be more resistant in the monoclinic than in the cubic phase, which may be related to the lower bandgap of the cubic phase. These results illustrate the complex interplay of structure and composition that give rise to the radiation resistance of these important functional materials.

cond-mat.mtrl-sci↗