Unravelling the progressive role of rattlers in thermoelectric clathrate and strategies for performance improvement: Concurrently enhancing electronic transport and blocking phononic transport

Intermetallic clathrates, one class of guest-host systems with perfectly crystalline structures, hold great potential to be the “phonon glass – electron crystal” thermoelectric materials. Previous studies focus on revealing the atomistic origins of blocked phononic transport, yet little attention is...

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Bibliographic Details
Published in:Applied physics letters 2017-12, Vol.111 (24)
Main Authors: Yang, Jia-Yue, Cheng, Long, Hu, Ming
Format: Article
Language:English
Subjects:
Applied physics
Barium
Blocking
Cages
Clathrates
Crystal structure
Doping
Electric bridges
Electrical resistivity
Electron transport
First principles
Lead
Phonons
Power factor
Relaxation time
Strontium
Thermal conductivity
Thermoelectric materials
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Summary:Intermetallic clathrates, one class of guest-host systems with perfectly crystalline structures, hold great potential to be the “phonon glass – electron crystal” thermoelectric materials. Previous studies focus on revealing the atomistic origins of blocked phononic transport, yet little attention is drawn to the enhanced electronic transport. In this work, we investigate the binary type-I M8Si46 (M = Sr, Ba, Tl, and Pb) clathrates and unravel how rattlers concurrently block phononic transport and enhance electronic transport from first-principles. By comparing the empty and filled clathrates, the lattice thermal conductivity is greatly reduced by a factor of 21 due to the decrease in phonon relaxation time for propagative phonons over 0–6 THz by 1.5 orders of magnitude. On the other hand, rattlers bridge charge gaps among cages by donating electrons and thus drastically increase electrical conductivity. The concurrent realization of blocked phononic transport and enhanced electronic transport boosts the figure-of-merit (ZT) of empty clathrate by 4 orders of magnitude. Furthermore, by manipulating metallic rattlers and n-type doping, the power factor is markedly improved and ZT can reach 0.55 at 800 K. These results provide a quantitative description of the guest-host interaction and coupling dynamics from first-principles. The proposed strategy of manipulating ratting atoms and in-situ doping offers important guidance to engineer clathrates with high thermoelectric performance.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.4998646