In the quest for efficient thermoelectrics, semiconducting behavior is a targeted property. Yet, this is often difficult to achieve due to the complex interplay between electronic structure, temperature, and disorder. We find this to be the case for the thermoelectric clathrate ${\mathrm{Ba}}_8{\mathrm{Al}}_{16}{\mathrm{Si}}_{30}$: Although this material exhibits a band gap in its ground state, a temperature-driven partial order-disorder transition leads to its effective closing. This finding is enabled by a novel approach to calculate the temperature-dependent effective band structure of alloys. Our method fully accounts for the effects of short-range order and can be applied to complex alloys with many atoms in the primitive cell, without relying on effective medium approximations.

• Received 18 September 2020
• Revised 14 February 2023
• Accepted 24 March 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.166402