Defect Engineering in the Crystal Lattice for Higher Thermoelectric Performance

Inorganic solids inevitably involve a certain level of defects or imperfection, which are embedded in the bulk crystal matrix. Defects can be atomic-level point defects induced by the generation of vacancies and chemical doping and alloying. They can be further extended to form one-dimensional dislocations or multiple-dimension nanostructures. According to the structure and dimension of defects ranging from Å to micron scale, they uniquely interact with charge carrier and heat-carrying phonon, significantly affecting physical properties of solids. Consequently, understanding formation mechanisms of defects is essential for proper design and stabilization of desirable defect structures in the bulk crystal matrix, leading to the discovery of inorganic solids with unusual physical properties. However, they are hardly detected and analyzed by conventional X-ray diffraction methods. In this talk, I will discuss our recent efforts on rational design of multiscale defect structures stabilized in the bulk crystal matrix. Effective design principles for the representative structure type of PbSe, SnSe₂, and SnSe systems will be introduced. I will present our direct observations on their local defect architectures employing atomic-resolution scanning transmission electron microscopy and atom probe tomography. These results help to understand defect formation mechanisms and designing desirable defect structures in the bulk crystal matrix. The effects of defect structures on charge carrier and thermal transport properties will be also discussed.