Ag9GaSe6: high-pressure-induced Ag migration causes thermoelectric performance irreproducibility and elimination of such instability

• Published in: Nature communications Vol. 13; no. 1; pp. 2966 - 10
• Main Authors: Liu, Jing-Yuan, Chen, Ling, Wu, Li-Ming
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 27.05.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301; 639/301/299/2736; Annealing; Chemical potential; Heat conductivity; High pressure; Humanities and Social Sciences; Instability; multidisciplinary; Photoelectrons; Pressure; Reproducibility; Science; Science (multidisciplinary); Single crystals; Stability; Thermal conductivity; Thermoelectric materials; Thermoelectricity; Valence band; X-ray diffraction
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-30716-7

The argyrodite Ag 9 GaSe 6 is a newly recognized high-efficiency thermoelectric material with an ultralow thermal conductivity; however, liquid-like Ag atoms are believed to cause poor stability and performance irreproducibility, which was evidenced even after the 1 st measurement run. Herein, we demonstrate the abovementioned instability and irreproducibility are caused by standard thermoelectric sample hot-pressing procedure, during which high pressure promotes the 3-fold-coordinated Ag atoms migrate to 4-fold-coordinated sites with higher-chemical potentials. Such instability can be eliminated by a simple annealing treatment, driving the metastable Ag atoms back to the original sites with lower-chemical potentials as revealed by the valence band X-ray photoelectron chemical potential spectra and single crystal X-ray diffraction data. Furthermore, the hot-pressed-annealed samples exhibit great stability and TE property repeatability. Such a stability and repeatability has never been reported before. This discovery will give liquid-like materials great application potential. The Ag 9 GaSe 6 is a high-efficient thermoelectric material yet suffers instability. Here, the authors demonstrate the instability is caused by the pressure-induced liquid-like Ag migration, which can be eliminated by a simple annealing treatment.