15-18 March 2021
DESY
Europe/Berlin timezone

Tunable bonding in the incipient metal thermoelectric GeTe

15 Mar 2021, 15:25
20m
DESY

DESY

Oral contribution Disordered Materials, complex crystal structures and aperiodic crystals, diffuse scattering and 3D-PDF Disordered Materials, complex crystal structures and aperiodic crystals, diffuse scattering and 3D-PDF

Speaker

Simon Kimber (Université Bourgogne Franche-Comté)

Description

The group IV-VI chalcogenides have important thermoelectric applications. GeTe has emerged as a promis- ing non-toxic candidate, especially when the high-temperature cubic phase is suppressed to room tempera- ture. However, even the mechanism of phase transition is disputed, as is the presence of disorder. Here we combine ab initio MD with synchrotron X-ray and dynamic neutron pair distribution function (PDF) analysis. We show that previous reports of disorder and symmetry breaking are entirely due to highly damped and anharmonic phonons. As predicted by metavalent bonding theories, this arises due to a softening in local bonding on heating, which strengthens long-range <100>c correlations. This picture is consistent with reported changes in resistivity and dielectric constant, and shown to be ubiquitously present in other polarisable binary chalcogenides and hR6 structured elements. Our results unify the results of local probes and spectroscopy as applied to binary chalcogenides, and should inspire a re-examination of other highly anharmonic energy materials such as hybrid perovskites and ’rattling’ thermoelectrics.

Primary authors

Simon Kimber (Université Bourgogne Franche-Comté) Dr Jiayong Zhang (Brookhaven National Laboratory) Dr Yongiang Cheng (Oak Ridge National Laboratory) Dr Douglas Abernath (Oak Ridge National Laboratory) Dr Timmy Ramirez-Cuesta (Oak Ridge National Laboratory) Dr Jessica Hudspeth (ESRF) Dr Zhong-Zhen Luo (Northwestern University) Prof. Mercouri Kanatzidis (Northwestern University) Prof. Simon Billinge (Columbia University) Dr Tapan Chatterji (Institut Laue Langevin)

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