Atomic Structure of the Initial Nucleation Layer in Hexagonal Perovskite BaRuO₃ Thin Films

Abstract

Hexagonal perovskites are an attractive family of materials due to their various polymorphs and rich structure–property relationships. BaRuO3 (BRO) is a prototypical hexagonal perovskite, in which the electromagnetic properties are significantly modified depending on its lattice structure. Whereas thin‐film synthesis would allow the study of the diverse properties of hexagonal perovskites by epitaxially stabilizing various metastable polymorphs, the epitaxial growth of hexagonal perovskites, especially at the initial growth stage, is yet to be addressed. In this study, it is shown that an intriguing nucleation behavior takes place during the initial stabilization of a hexagonal 9R BRO thin film deposited on a (111) SrTiO3 (STO) substrate. It is found that a nanoscale strained layer composed of different RuO6 octahedral stacking is initially formed at the interface followed by a relaxed single crystal 9R BRO thin film. Within the interface layer, hexagonal BRO is nucleated on the (111) STO substrate by both face‐ and corner‐sharing octahedra. More interestingly, it is found that boundaries between differently stacked nucleation layers (heterostructural boundaries) facilitate strain relaxation, in addition to the formation of conventional misfit dislocations evolved from homostructural boundaries. The observations reveal an important underlying mechanism to understand the thin‐film epitaxy and strain accommodation in hexagonal perovskites.

Atomic Reconstruction and Oxygen Evolution Reaction of Mn3O4 Nanoparticles

“…Bright dots indicate Mn columns, and their brightness was roughly determined by the density of Mn ions in each atomic column. Meanwhile, oxygen columns were generally not detected in the HAADF STEM images because the HAADF STEM provides the scattering intensity that is approximately proportional to the square of the atomic number. , The atomic configurations of the surfaces differed significantly in the HAADF STEM images from those observed in the bulk Mn 3 O 4 , clearly demonstrating that surface reconstruction occurred on each facet of the Mn 3 O 4 nanoparticles. In the (101) surface, an additional Mn column always appeared in each period, which is denoted by the gray arrow in Figure (c).…”