Abstract
A high power factor and low lattice thermal conductivity are two essential ingredients of highly efficient thermoelectric materials. Although monolayers of transition-metal dichalcogenides possess high power factors, high lattice thermal conductivities significantly impede their practical applications. Our first-principles calculations show that these two ingredients are well fulfilled in the recently synthesized Pd2Se3 monolayer, whose crystal structure is composed of [Se2]2- dimers, Se2- anions, and Pd2+ cations coordinated in a square-planar manner. Our detailed analysis of third-order interatomic force constants reveals that the anharmonicity and soft phonon modes associated with covalently bonded [Se2]2- dimers lead to ultralow lattice thermal conductivities in Pd2Se3 monolayers (1.5 and 2.9 W m-1 K-1 along the a- and b-axes at 300 K, respectively), which are comparable to those of high-performance bulk thermoelectric materials such as PbTe. Moreover, the "pudding-mold" type band structure, caused by Pd2+ (d8) cations coordinated in a square-planar crystal field, leads to high power factors in Pd2Se3 monolayers. Consequently, both electron- and hole-doped thermoelectric materials with a considerably high zT can be achieved at moderate carrier concentrations, suggesting that Pd2Se3 is a promising two-dimensional thermoelectric material. Our results suggest that hierarchical chemical bonds, that is, coexistence of different types of chemical bonds, combined with a square-planar crystal field is a promising route for designing high-efficiency thermoelectric materials.
Original language | English (US) |
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Pages (from-to) | 5639-5647 |
Number of pages | 9 |
Journal | Chemistry of Materials |
Volume | 30 |
Issue number | 16 |
DOIs | |
State | Published - Aug 28 2018 |
Funding
S.S.N. (electronic structure, thermoelectric, and phonon calculations and analysis) acknowledges support from the Center for Hierarchical Materials Design and from the U.S. Department of Commerce, National Institute of Standards and Technology, under award no. 70NANB14H012. J.H. and C.W. (electronic structure and thermoelectric calculations and analysis) acknowledge support by the U.S. Department of Energy, Office of Science and Office of Basic Energy Sciences, under Award No. DE-SC0014520. The authors acknowledge computing resources provided by the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231. J.H. acknowledges Junhao Li for sharing the crystal structure.
ASJC Scopus subject areas
- General Chemistry
- General Chemical Engineering
- Materials Chemistry