Perovskite oxides are widely studied for a variety of applications, from thermoelectric heat conversion to fuel cell and solar cell applications. Part of the attraction lies in the fact that perovskite ceramics are relatively easy to dope chemically over a wide range of compositions allowing for their physical properties and functionality to be efficiently tailored. Precise control of local ordering and local or extended defects can alter the local electronic structure, affecting for instance electron transport behaviour, while the precise growth control of multilayer heterostuctures can give rise to emergent properties within the interior of the multilayer structure. However, as these effects are dependent on small structural details, such as atomic arrangements at the sub-angstrom scale they are often too minute, to be detected or sufficiently characterized by bulk techniques. In this respect electron microscopy and in particular Scanning Electron Microscopy Transmission Electron Microscopy (STEM) in tandem with Electron Energy loss Spectroscopy (EELS) is probably the ultimate research tool for such systems, as it allows to probe simultaneously structural and chemical/bonding information at the atomic level. Furthermore, recent advances in instrumentation, such as the introduction of advanced, high-resolution monochromators have allowed for new exciting experiments in the electron microscope. Spectroscopic signatures of optical and acoustical phonons, excitons and defect gap states are now accessible with an atom size probe and in tandem with high precision imaging. Here, we present results on the structure and electronic structure of thermoelectric (TE) materials systems for heat recovery applications, using advanced electron microscopy. High energy STEM EELS was used to inform theoretical predictions from density functional theory electronic band-structure calculations combined with the Boltzmann transport theory.