Abstract
We studied the narrow band-gap (0.55 eV) semiconductor K2.5Bi8.5Se14 as a potential thermoelectric material for power generation. Samples of polycrystalline K2.5Bi8.5Se14 prepared by spark plasma sintering exhibit exceptionally low lattice thermal conductivities (κlat) of 0.57-0.33 W m-1 K-1 in the temperature range of 300-873 K. The physical origin of such low κlat in K2.5Bi8.5Se14 is related to the strong anharmonicity and low phonon velocity caused by its complex low symmetry, large unit cell crystal structure, and mixed occupancy of Bi and K atoms in the lattice. High-resolution scanning transmission electron microscopy studies and microanalysis indicate that the K2.5Bi8.5Se14 sample is a single phase without intergrowth of the structurally related K2Bi8Se13 phase. The undoped material exhibits an n-type character and a figure-of-merit (ZT) value of 0.67 at 873 K. Electronic band structure calculations indicate that K2.5Bi8.5Se14 is an indirect band-gap semiconductor with multiple conduction bands close to the Fermi level. Phonon dispersion calculations suggest that K2.5Bi8.5Se14 has low phonon velocities and large Grüneisen parameters that can account for the observed ultralow κlat. The degree of n-type doping can be controlled by introducing Se deficiencies in the structure, providing a simple route to increase the ZT to ∼1 at 873 K.
Original language | English (US) |
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Pages (from-to) | 5943-5952 |
Number of pages | 10 |
Journal | Chemistry of Materials |
Volume | 31 |
Issue number | 15 |
DOIs | |
State | Published - Aug 13 2019 |
Funding
This work was supported by the Department of Energy, Office of Science Basic Energy Sciences under grant DE-SC0014520, DOE Office of Science (sample preparation, synthesis, XRD, TE measurements, TEM measurements, DFT calculations). Z.-Z.L. and Q.Y. gratefully acknowledge the National Natural Science Foundation of China (61728401). This work made use of the EPIC facility of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the MRSEC program (NSF DMR-1720139) at the Materials Research Center, the International Institute for Nanotechnology (IIN), the Keck Foundation, and the State of Illinois, through the IIN. User Facilities are supported by the Office of Science of the U.S. Department of Energy under Contract Nos. DE-AC02-06CH11357 and DE-AC02-05CH11231. Access to facilities of high-performance computational resources at Northwestern University is acknowledged. The authors also acknowledge Singapore MOE AcRF Tier 2 under Grant Nos. 2018-T2-1-010 and MOE2017-T2-2-069, Singapore A*STAR Pharos Program SERC 1527200022, and the support from FACTs of Nanyang Technological University for sample analysis.
ASJC Scopus subject areas
- General Chemistry
- General Chemical Engineering
- Materials Chemistry