Probing functional perovskites through scanning transmission electron microscopy and first-principles theory

The aberration-corrected scanning transmission electron microscope (STEM) can provide real space imaging and spectroscopy at atomic resolution with a new level of sensitivity to structure, bonding, elemental valence and even spin state. Coupled with first-principles theory, this represents an unprecedented opportunity to probe the functionality of complex nanoscale systems. A number of examples will be shown, including the microscopic origin of the barrier to O vacancy transport across grain boundaries in Y-stabilized ZrO$_{2}$, the strain stabilized generation of a spin state superlattice in La$_{0.5}$Sr$_{0.5}$CoO$_{3-x}$ (LSCO) [1], the unexpected ferromagnetism in ultrathin, insulating LaCoO$_{3-x}$ (LCO) films [2] due to a vacancy superlattice (Fig. 1), and finally, the origin of the 2D electron gas at a LaAlO$_{3}$/SrTiO$_{3}$ interface is shown to be not due to vacancies but to the polar nature of the substrate [3].\\[4pt] Work performed in collaboration with J. Gazquez, N. Bi\v{s}kup, J. Salafranca, C. Cantoni, M. Varela and S. T. Pantelides. \\[4pt] [1] J. Gazquez, et al., Nano Lett, \textbf{11}, 973 (2011).\\[0pt] [2] N. Bi\v{s}kup, et al., Phys. Rev. Lett. \textbf{112}, 087202 (2014).\\[0pt] [3] C. Cantoni, et al., Adv. Mater. \textbf{24}, 3952 (2012).