Ag2Se to KAg3Se2: Suppressing Order–Disorder Transitions via Reduced Dimensionality
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, hexagon...
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Published in | Journal of the American Chemical Society Vol. 140; no. 29; pp. 9193 - 9202 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
25.07.2018
American Chemical Society (ACS) |
Subjects | |
Online Access | Get full text |
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Summary: | 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 R3̅m, 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. 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. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 USDOE Office of Science (SC), Basic Energy Sciences (BES) National Science Foundation (NSF) AC02-06CH11357; 5J-30161-0010A; ECCS-1542205 |
ISSN: | 0002-7863 1520-5126 1520-5126 |
DOI: | 10.1021/jacs.8b04888 |