Positional disorder of Ba in the thermoelectric germanium clathrate Ba6Ge25

TL;DR

This study investigates the local atomic structure of Ba6Ge25, revealing temperature-dependent positional disorder of barium atoms using advanced diffraction techniques.

Contribution

It provides the first detailed evidence of Ba atom displacement and split-site locking in Ba6Ge25 at low temperatures, enhancing understanding of its local structure.

Findings

Two types of Ba atoms move off their sites at low temperature

Ba atoms become locked in split sites at 40 K

Structural disorder affects thermoelectric properties

Abstract

The local structure of Ba6Ge25 has been studied by x-ray diffraction and the atomic pair distribution function technique at 40 K and room temperature. Unambiguous evidence has been found that two out of three types of Ba atoms in Ba6Ge25 move off their positions and become locked in split sites at low temperatures.