Partial Order-Disorder Transition Driving Closure of Band Gap: Example of Thermoelectric Clathrates

TL;DR

This paper introduces a novel method to calculate temperature-dependent effective band structures in complex alloys, revealing how partial order-disorder transitions can close the band gap in thermoelectric clathrates, impacting their semiconducting properties.

Contribution

The study presents a new computational approach that accurately models the effects of short-range order on the electronic structure of complex alloys at finite temperatures.

Findings

Partial order-disorder transition closes the band gap in Ba8Al16Si30.

The method accounts for short-range order effects without effective medium approximations.

Temperature influences the electronic properties significantly in thermoelectric materials.

Abstract

On 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 Ba$_8$Al$_{16}$Si$_{30}$: Although this material exhibits a band gap in its groundstate, 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.