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Title: Constructing of highly porous thermoelectric structures with improved thermoelectric performance
Award ID(s):
1905037
NSF-PAR ID:
10299264
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Nano Research
Volume:
14
Issue:
10
ISSN:
1998-0124
Page Range / eLocation ID:
3608 to 3615
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    Zintl phase thermoelectric materials have generated tremendous interest due to possessing structural features conducive to high thermoelectric performances. On the other hand, both arsenic and arsenic‐based compounds have become attractive in electronics due to having interesting properties like narrow bandgap, tunable carrier concentration, and non‐centrosymmetric structures. The structure of arsenic compounds plays a telling role in determining their efficiency as thermoelectric materials. They also show the scope to be doped as both p‐ and n‐type conduction providing exciting new materials with applications as a full module. These attributes make them appealing as thermoelectric materials for further research. This short review is an overview of the different structures of arsenic‐based Zintl ternary materials that have potential to be excellent thermoelectric materials.

     
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  2. Thermoelectric materials can convert heat into electricity. They are used to generate electricity when other power sources are not available or to increase energy efficiency by recycling waste heat. The Yb 21 Mn 4 Sb 18 phase was previously shown to have good thermoelectric performance due to its large Seebeck coefficient (∼290 μV K −1 ) and low thermal conductivity (0.4 W m −1 K −1 ). These characteristics stem respectively from the unique [Mn 4 Sb 10 ] 22− subunit and the large unit cell/site disorder inherent in this phase. The solid solutions, Yb 21 Mn 4− x Cd x Sb 18 ( x = 0, 0.5, 1.0, 1.5) and Yb 21− y Ca y Mn 4 Sb 18 ( y = 3, 6, 9, 10.5) have been prepared, their structures characterized and thermoelectric properties from room temperature to 800 K measured. A detailed look into the structural disorder for the Cd and Ca solid solutions was performed using synchrotron powder X-ray diffraction and pair distribution function methods and shows that these are highly disordered structures. The substitution of Cd gives rise to more metallic behavior whereas Ca substitution results in high resistivity. As both Cd and Ca are isoelectronic substitutions, the changes in properties are attributed to changes in the electronic structure. Both solid solutions show that the thermal conductivities remain extremely low (∼0.4 W m −1 K −1 ) and that the Seebeck coefficients remain high (>200 μV K −1 ). The temperature dependence of the carrier mobility with increased Ca substitution, changing from approximately T −1 to T −0.5 , suggests that another scattering mechanism is being introduced. As the bonding changes from polar covalent with Yb to ionic for Ca, polar optical phonon scattering becomes the dominant mechanism. Experimental studies of the Cd solid solutions result in a max zT of ∼1 at 800 K and, more importantly for application purposes, a ZT avg ∼ 0.6 from 300 K to 800 K. 
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