Suppression of vacancies boosts thermoelectric performance in type-I clathrates

TL;DR

This study demonstrates that filling vacancies in type-I clathrates with gallium significantly improves their thermoelectric performance, achieving a high figure of merit of 0.9 at 900 K.

Contribution

It reveals the structural role of vacancies and shows how Ga filling enhances charge mobility and thermoelectric efficiency in Ba8(Cu,Ga,Ge,v)46.

Findings

Vacancies are present at the 6c site in Ba8(Cu,Ga,Ge,v)46.

Ga substitution fills vacancies and increases charge carrier mobility.

Achieved a ZT of 0.9 at 900 K in Ga-filled Ba8Cu4.6Ga1.0Ge40.4.

Abstract

Intermetallic type-I clathrates continue to attract attention as promising thermoelectric materials. Here we present structural and thermoelectric properties of single crystalline Ba8(Cu,Ga,Ge,v)46, where v denotes a vacancy. By single crystal X-ray diffraction on crystals without Ga we find clear evidence for the presence of vacancies at the 6c site in the structure. With increasing Ga content, vacancies are successively filled. This increases the charge carrier mobility strongly, even within a small range of Ga substitution, leading to reduced electrical resistivity and enhanced thermoelectric performance. The largest figure of merit ZT =0.9 at 900 K is found for a single crystal of approximate composition Ba8Cu4.6Ga1.0Ge40.4. This value, that may further increase at higher temperatures, is one of the largest to date found in transition metal element-based clathrates.