Ag2Se to KAg3Se2: Suppressing Order–Disorder Transitions via Reduced Dimensionality
[1];
[5]
- Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division
- Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry
- Center for High Pressure Science and Technology Advanced Research, Shanghai (China); Carnegie Inst. of Washington, Argonne, IL (United States). HPSynC. Geophysical Lab.
- Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science
- Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division; Center for High Pressure Science and Technology Advanced Research, Shanghai (China)
Here we report an order–disorder phase transition in the 2D semiconductor KAg3Se2, which is a dimensionally reduced derivative of 3D Ag2Se. At ~695 K, the room temperature β-phase (CsAg3S2 structure type, monoclinic space group C2/m) transforms to the high temperature α-phase (new structure type, hexagonal space group R$$ \overline{3}\ $$m, a = 4.5638(5) Å, c = 25.4109(6) Å), as revealed by in situ temperature-dependent X-ray diffraction. Significant Ag+ ion disorder accompanies the phase transition, which resembles the low temperature (~400 K) superionic transition in the 3D parent compound. Ultralow thermal conductivity of ~0.4 W m–1 K–1 was measured in the “ordered” β-phase, suggesting anharmonic Ag motion efficiently impedes phonon transport even without extensive disordering. The optical and electronic properties of β-KAg3Se2 are modified as expected in the context of the dimensional reduction framework. UV–vis spectroscopy shows an optical band gap of ~1 eV that is indirect in nature as confirmed by electronic structure calculations. Electronic transport measurements on β-KAg3Se2 yielded n-type behavior with a high electron mobility of ~400 cm2 V–1 s–1 at 300 K due to a highly disperse conduction band. Finally, our results thus imply that dimensional reduction may be used as a design strategy to frustrate order–disorder phenomena while retaining desirable electronic and thermal properties.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
- Grant/Contract Number:
- AC02-06CH11357; 5J-30161-0010A; ECCS-1542205
- OSTI ID:
- 1482168
- Journal Information:
- Journal of the American Chemical Society, Vol. 140, Issue 29; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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