Insights into Energy Materials through Aberration-Corrected STEM

Abstract

The recent introduction of next-generation aberration correctors has propelled the capabilities of the scanning transmission electron microscope (STEM) to even higher levels. Several case studies of complex oxides for energy applications will be presented, showing how microscopy data can be compared to the results of density functional calculations to provide microscopic insights into functionality. Nanometer thick layers of Yttria-stabilized zirconia (YSZ) in YSZ/strontium titanate (STO) epitaxial heterostructures have been shown to poses ionic conductivities up to eight orders of magnitude higher than that of bulk YSZ near room temperature [1]. Density functional simulations predict O to be in a disordered form in the strained YSZ, with a greatly reduced migration energy barrier consistent with experiment [2]. Spectroscopic imaging directly confirms the theoretical predictions [3]. ADF images of LiFePO4 are able to resolve Li columns. Many of these columns show anomalous intensities, suggesting occupation by Fe. Spectroscopic analysis of such sites confirms the presence of Fe, and shows it to be in a +2 configuration instead of the expected +1 for Li. Theoretical simulations indicate the origin of the effect and explain the anisotropic Li diffusivity in the plane. Insights into solid oxide fuel cell cathodes include the imaging of O vacancy clustering, the formation of an amorphous phase on cycling, as well as the generation of voids and cracks. In the case of multiferroics, the influence of interfaces on local properties will be shown, mediated by the suppression of octahedral rotations that cause local changes in lattice parameters and electronic structure [4].