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Aberration-corrected scanning transmission electron microscopy (STEM) is one of the most versatile experimental techniques to explore materials at the atomic level. In a single experiment, the crystalline structure, chemical composition and bonding configuration of a material can be reveled with an unparallel (sub-angstrom) spatial resolution and with single-atom sensitivity. Density functional theory (DFT) is the established state-of-the-art theoretical method for investigating the physical properties of structurally and chemically complex materials from parameter-free calculations.

Superconductivity, antiferromagnetism, spin-density waves and structural deformation are some of the known phase transformations that occur at relatively low temperatures in the recently discovered high-Tc iron-based superconductors. The performance of devices made of silicon nitride ceramics depends upon the behavior of the interfaces under high temperature and pressure conditions. The next generations of batteries (based on Li) depend upon the reliability of these materials to stand high volume changes under, a property intrinsically related the atomic structure of the bulk material, grain boundaries, interfaces and defects in general.

In this talk, I will present a combination of experiments (atomic resolved Z-contrast, bright-field imaging, and electron energy-loss spectroscopy) and total-energy first-principles calculations within DFT that were utilized to study : (i) the interfaces of silicon nitride ceramics, (ii) the magnetic and structural phase transitions of the parent compound NdFeAsO —an iron-based superconductor which shows one of the highest TC when doped—, (iii) the visualization of antisite defects (Fe substitution in Li sties) in LiFePO4.