Understanding Cu Incorporation in the $\mathrm{Cu_{2x}Hg_{2-x}GeTe_4}$ Structure using Resonant X-ray Diffraction
Abstract
The ability to control carrier concentration based on the extent of Cu solubility in the alloy compound (where 0 x 1) makes an interesting case study in the field of thermoelectrics. While Cu clearly plays a role in this process, it is unknown exactly how Cu incorporates into the crystal structure and how this affects the carrier concentration. In this work, we use a combination of resonant energy X-ray diffraction (REXD) experiments and density functional theory (DFT) calculations to elucidate the nature of Cu incorporation into the structure. REXD across the edge facilitates the characterization of Cu incorporation in the alloy and enables direct quantification of anti-site defects. We find that Cu substitutes for Hg at a 2:1 ratio, wherein Cu annihilates a vacancy and swaps with a Hg atom. DFT calculations confirm this result and further reveal that the incorporation of Cu occurs preferentially on one of the z = 1/4 or z = 3/4 planes before filling the other plane. Furthermore, the amount of anti-site defects quantified by REXD was found to be directly proportional to the experimentally measured hole concentration, indicating that the defects are the driving force for tuning carrier concentration in the alloy. The link uncovered here between crystal structure, or more specifically anti-site defects, and carrier concentration can be extended to similar cation-disordered material systems and will aid the development of improved thermoelectric and other functional materials through defect engineering.
Keywords
Cite
@article{arxiv.2010.04784,
title = {Understanding Cu Incorporation in the $\mathrm{Cu_{2x}Hg_{2-x}GeTe_4}$ Structure using Resonant X-ray Diffraction},
author = {Ben L. Levy-Wendt and Brenden R. Ortiz and Lìdia C. Gomes and Kevin H. Stone and Donata Passarello and Elif Ertekin and Eric S. Toberer and Michael F. Toney},
journal= {arXiv preprint arXiv:2010.04784},
year = {2021}
}