期刊
ADVANCED FUNCTIONAL MATERIALS
卷 29, 期 6, 页码 -出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201806534
关键词
directional negative thermal expansion; intrinsically low thermal conductivity; phonon spectrum; thermoelectric properties; vacancy
类别
资金
- Natural Science Foundation of China [51521001, 51632006]
- U.S. Department of Energy, Office of Science [DE-SC0014520, DE-AC02-06CH11357]
- U.S. Department of Energy, Office of Basic Energy Sciences [DE-SC0014520, DE-AC02-06CH11357]
A deficiency of Ga in wide band-gap AgGa1-xTe2 semiconductors (1.2 eV) can be used to optimize the electrical transport properties and reduce the thermal conductivity to achieve ZT > 1 at 873 K. First-principles density functional theory calculations and a Boson peak observed in the low temperature heat capacity data indicate the presence of strong coupling between optical phonons with low frequency and heat carrying acoustical phonons, resulting in a depressed maximum of Debye frequency in the first Brillouin zone and low phonon velocities. Moreover, the Ag-Te bond lengths and Te-Ag-Te bond angles increase with rising temperature, leading to a significant distortion of the [AgTe4](7-) tetrahedra, but an almost unmodified [GaTe4](5-) tetrahedra. This behavior results in lattice expansion in the ab-plane and contraction along the c-axis, corresponding to the positive and negative Gruneisen parameters in the phonon spectral calculations. This effect gives rise to the large anharmonic behavior of the lattice. These factors together with the low frequency vibrations of Ag and Te atoms in the structure lead to an ultralow thermal conductivity of 0.18 W m(-1) K-1 at 873 K.
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