Unraveling the role of defect induced exciting charge and heat transport phenomena in thermoelectric clathrates

Thermoelectric clathrates are generally referred to have a semiconducting cage like framework of group -IV (host) elements enclosing metal (guest) atoms, whereby the electronic and vibrational transport can be decoupled by means of the host and guest respectively. Density functional theory calculations are perfectly suitable to analyse the electronic and vibrational transport phenomena in this class. Using the simple binary [1] and complex ternary clathrates [2] as examples, we unravel the role of rattling of guest, mutual coupling of guest and host, and implications of defects on the charge and heat transport of this material class. Our study reveals the complex interplay of materials phenomena that goes beyond the usual concepts in this field.
[1] Amrita Bhattacharya, Christian Carbogno, Bodo Bohme, Michael Baitinger, Yuri Grin, and Matthias Scheffler. “Formation of vacancies in Si/Ge Clathrates: The importance of broken symmetries”, Phys. Rev. Lett. 118, 236401 (2017).
[2] Amrita Bhattacharya and Saswata Bhattacharya. Unraveling the role of vacancies in the potentially promising thermoelectric clathrates Ba₈Zn_xGe_46-x-y■_y clathrates. Phys. Rev. B, 94, 094305 (2016).