Localized atomic vibrations in complex-oxide structures by monochromated EELS and theory

Atomic vibrations in crystals, namely phonons, are directly correlated to atomic arrangements and bonding and underlie a wide range of thermal, optical, and other properties. They especially reflect the structure and bonding at interfaces and defects. Here we combine density-functional-theory (DFT) calculations and monochromated electron-energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) to investigate atomic vibrations at interfaces and grain boundaries in complex oxides. Local symmetry (octahedral tilts) and phonons at interfaces differ markedly in short- and long-period SrTiO₃/CaTiO₃ superlattices and dominate properties in ultrashort periods¹. At a low-angle grain boundary in SrTiO₃, we directly correlate the structure, composition, and chemical bonding with atomic vibrations within the dislocation cores². Theory and experiments provide mutual validation of results. Such quantification of atomic-scale vibrational properties is necessary to link macroscopic properties to atomic structure.

¹E. R. Hoglund, D.-L. Bao, et al. Nature 601 556 (2022)

²E. R. Hoglund, D.-L. Bao, et al. arXiv:2208.00309