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Shawon AKA, Guetari W, Ciesielski K, Orenstein R, Qu J, Chanakian S, Rahman MT, Ertekin E, Toberer E, Zevalkink A. Alloying-Induced Structural Transition in the Promising Thermoelectric Compound CaAgSb. Chem Mater 2024; 36:1908-1918. [PMID: 38533450 PMCID: PMC10961731 DOI: 10.1021/acs.chemmater.3c02621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Revised: 01/25/2024] [Accepted: 01/26/2024] [Indexed: 03/28/2024]
Abstract
AMX Zintl compounds, crystallizing in several closely related layered structures, have recently garnered attention due to their exciting thermoelectric properties. In this study, we show that orthorhombic CaAgSb can be alloyed with hexagonal CaAgBi to achieve a solid solution with a structural transformation at x ∼ 0.8. This transition can be seen as a switch from three-dimensional (3D) to two-dimensional (2D) covalent bonding in which the interlayer M-X bond distances expand while the in-plane M-X distances contract. Measurements of the elastic moduli reveal that CaAgSb1-xBix becomes softer with increasing Bi content, with the exception of a steplike 10% stiffening observed at the 3D-to-2D phase transition. Thermoelectric transport measurements reveal promising Hall mobility and a peak zT of 0.47 at 620 K for intrinsic CaAgSb, which is higher than those in previous reports for unmodified CaAgSb. However, alloying with Bi was found to increase the hole concentration beyond the optimal value, effectively lowering the zT. Interestingly, analysis of the thermal conductivity and electrical conductivity suggests that the Bi-rich alloys are low Lorenz-number (L) materials, with estimated values of L well below the nondegenerate limit of L = 1.5 × 10-8 W Ω K-2, in spite of the metallic-like transport properties. A low Lorenz number decouples lattice and electronic thermal conductivities, providing greater flexibility for enhancing thermoelectric properties.
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Affiliation(s)
- A. K.
M. Ashiquzzaman Shawon
- Department
of Chemical Engineering and Material Science, Michigan State University, East Lansing, Michigan 48824, United States
| | - Weeam Guetari
- Department
of Chemical Engineering and Material Science, Michigan State University, East Lansing, Michigan 48824, United States
| | - Kamil Ciesielski
- Department
of Physics, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Rachel Orenstein
- Department
of Physics, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Jiaxing Qu
- Department
of Mechanical Science and Engineering, University
of Illinois at Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Sevan Chanakian
- Department
of Chemical Engineering and Material Science, Michigan State University, East Lansing, Michigan 48824, United States
| | - Md. Towhidur Rahman
- Department
of Mechanical Engineering, Michigan State
University, East Lansing, Michigan 48824, United States
| | - Elif Ertekin
- Department
of Mechanical Science and Engineering, University
of Illinois at Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Eric Toberer
- Department
of Physics, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Alexandra Zevalkink
- Department
of Chemical Engineering and Material Science, Michigan State University, East Lansing, Michigan 48824, United States
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