From stoichiometric to off-stoichiometric GeTe: Phase diagram reconstruction and thermoelectric performance reassessment

Yi Fen Tsai; Ying Chun Chao; Cheng Rong Hsing; Kuang Kuo Wang; Yung Hsiang Tung; Chun Chuen Yang; Sinn Wen Chen; G. Jeffrey Snyder; Hung Wei Yen; Ching Ming Wei; Pai Chun Wei; Hsin Jay Wu

doi:10.1016/j.actamat.2023.119644

From stoichiometric to off-stoichiometric GeTe: Phase diagram reconstruction and thermoelectric performance reassessment

Yi Fen Tsai, Ying Chun Chao, Cheng Rong Hsing, Kuang Kuo Wang, Yung Hsiang Tung, Chun Chuen Yang, Sinn Wen Chen, G. Jeffrey Snyder, Hung Wei Yen, Ching Ming Wei^*, Pai Chun Wei, Hsin Jay Wu

^*Corresponding author for this work

Materials Science and Engineering

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Abstract

This study investigates the structure, microstructure, and transport properties of off-stoichiometric GeTe (off-GeTe). In a narrow range of 50–53 at% Te, both the rhombohedral a-GeTe and orthorhombic g-GeTe phases coexist. Despite their similar chemical composition, GeTe and off-GeTe alloys exhibit distinct microstructural and thermal/electronic properties. Theoretical density functional theory (DFT) calculations were employed to verify that changes in the Ge/Te ratios influence the concentration of Ge vacancies, leading to a significant alteration in transport properties despite minor variations in chemical compositions. The off-GeTe alloy, which is free of Ge precipitates, displays defective domain boundaries, showcasing a non-typical herringbone nanostructure that is unprecedented for GeTe-based materials. Notably, the phase transition temperature of off-GeTe, at 620K, differs from its peak zT temperature of 698K. Moreover, a TE device incorporating off-GeTe demonstrates superior interfacial stability and higher energy conversion efficiency compared to its stoichiometric GeTe counterpart. Consequently, off-GeTe demonstrates superior TE performance and enhanced interfacial stability compared to stoichiometric GeTe. The addition of Sb to off-GeTe further improves its potential for TE applications by lifting the single-leg conversion efficiency greater than 3%.

Original language	English (US)
Article number	119644
Journal	Acta Materialia
Volume	265
DOIs	https://doi.org/10.1016/j.actamat.2023.119644
State	Published - Feb 15 2024

Funding

We acknowledged the financial support from the National Science and Technology Council (NSTC) in Taiwan under Grant NSTC 111–2628-E-A49–012, NSTC 111–2628-E-A49–017-MY4, NSTC 111–2112-M-008–034, NSTC-111–2119-M-002–020-MBK, MOST 108–2112-M-001–043-MY3, MOST 111–2112-M-001–084-MY3, and MOST 111–2112-M-006 −034 -MY3. The support of award 70NANB19H005 from U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD).

Keywords

Defective domain boundaries
Off-stoichiometric GeTe
Theoretical density functional theory (DFT)
Thermoelectric

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Ceramics and Composites
Polymers and Plastics
Metals and Alloys

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10.1016/j.actamat.2023.119644

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title = "From stoichiometric to off-stoichiometric GeTe: Phase diagram reconstruction and thermoelectric performance reassessment",

abstract = "This study investigates the structure, microstructure, and transport properties of off-stoichiometric GeTe (off-GeTe). In a narrow range of 50–53 at% Te, both the rhombohedral a-GeTe and orthorhombic g-GeTe phases coexist. Despite their similar chemical composition, GeTe and off-GeTe alloys exhibit distinct microstructural and thermal/electronic properties. Theoretical density functional theory (DFT) calculations were employed to verify that changes in the Ge/Te ratios influence the concentration of Ge vacancies, leading to a significant alteration in transport properties despite minor variations in chemical compositions. The off-GeTe alloy, which is free of Ge precipitates, displays defective domain boundaries, showcasing a non-typical herringbone nanostructure that is unprecedented for GeTe-based materials. Notably, the phase transition temperature of off-GeTe, at 620K, differs from its peak zT temperature of 698K. Moreover, a TE device incorporating off-GeTe demonstrates superior interfacial stability and higher energy conversion efficiency compared to its stoichiometric GeTe counterpart. Consequently, off-GeTe demonstrates superior TE performance and enhanced interfacial stability compared to stoichiometric GeTe. The addition of Sb to off-GeTe further improves its potential for TE applications by lifting the single-leg conversion efficiency greater than 3%.",

keywords = "Defective domain boundaries, Off-stoichiometric GeTe, Theoretical density functional theory (DFT), Thermoelectric",

author = "Tsai, {Yi Fen} and Chao, {Ying Chun} and Hsing, {Cheng Rong} and Wang, {Kuang Kuo} and Tung, {Yung Hsiang} and Yang, {Chun Chuen} and Chen, {Sinn Wen} and Snyder, {G. Jeffrey} and Yen, {Hung Wei} and Wei, {Ching Ming} and Wei, {Pai Chun} and Wu, {Hsin Jay}",

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AU - Hsing, Cheng Rong

AU - Wang, Kuang Kuo

AU - Tung, Yung Hsiang

AU - Yang, Chun Chuen

AU - Chen, Sinn Wen

AU - Snyder, G. Jeffrey

AU - Yen, Hung Wei

AU - Wei, Ching Ming

AU - Wei, Pai Chun

AU - Wu, Hsin Jay

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AB - This study investigates the structure, microstructure, and transport properties of off-stoichiometric GeTe (off-GeTe). In a narrow range of 50–53 at% Te, both the rhombohedral a-GeTe and orthorhombic g-GeTe phases coexist. Despite their similar chemical composition, GeTe and off-GeTe alloys exhibit distinct microstructural and thermal/electronic properties. Theoretical density functional theory (DFT) calculations were employed to verify that changes in the Ge/Te ratios influence the concentration of Ge vacancies, leading to a significant alteration in transport properties despite minor variations in chemical compositions. The off-GeTe alloy, which is free of Ge precipitates, displays defective domain boundaries, showcasing a non-typical herringbone nanostructure that is unprecedented for GeTe-based materials. Notably, the phase transition temperature of off-GeTe, at 620K, differs from its peak zT temperature of 698K. Moreover, a TE device incorporating off-GeTe demonstrates superior interfacial stability and higher energy conversion efficiency compared to its stoichiometric GeTe counterpart. Consequently, off-GeTe demonstrates superior TE performance and enhanced interfacial stability compared to stoichiometric GeTe. The addition of Sb to off-GeTe further improves its potential for TE applications by lifting the single-leg conversion efficiency greater than 3%.

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From stoichiometric to off-stoichiometric GeTe: Phase diagram reconstruction and thermoelectric performance reassessment

Abstract

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Keywords

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