Geometry Optimization Strategies for Dual Enhancement of Power and Efficiency in All-Mg3Sb1.5Bi0.5 Thermoelectric Devices

Sep 30, 2026

Mg3Sb2–Mg3Bi2 solid-solutions show strong thermoelectric performance for power generation and cooling, yet fully Mg3(Sb,Bi)2 device studies are limited by imbalance between p-type and n-type counterparts. The work demonstrates simultaneous maximization of device power density and conversion efficiency using an optimized geometry for a Mg3Sb1.5Bi0.5 device. Two-pair structures with Cu/Fe multilayer contacts are designed with an optimum cross-sectional area ratio An/Ap=1:2, validated by finite-element simulations and experiments achieving over 10% combined gains near 465 K.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

1. Introduction

2. Methodology and Device Design

2.1 Optimized cross-sectional area ratio (An/Ap)

3. Results and Validation

3.1 Simulation vs. experimental comparison

3.2 Dual improvement in power and efficiency

RESEARCH ARTICLE [www.small-journal.com](www.small-journal.com) Geometry Optimization Strategies for Dual Enhancement of Power and Eﬃciency in All-Mg3 Sb 1.5 Bi0.5 Thermoelectric Devices Jayachandran Babu, Raju Chetty, and Takao Mori* Mg3Sb2–Mg3 Bi2 solid-solutions exhibit excellent thermoelectric (TE) performance in power generation and cooling. However, reports on fully Mg3 (Sb,Bi)2-based TE devices remain limited, due to performance imbalance between p-type and n-type counterparts. In such cases, geometric design optimization is essential for achieving either a maximum power density (􀀂max) or maximum conversion eﬃciency (􀀃max). Simultaneous improvement is often diﬃcult due to compromises in the device ﬁll factor. In this study, simultaneous enhancement of 􀀂max and 􀀃max is demonstrated in a fully Mg3Sb1.5 Bi0.5 device through optimized design. Two-pair devices are fabricated using p-and n-type doped Mg3Sb1.5 Bi0.5 materials with Cu/Fe multilayer electrical contacts.The optimum cross-sectional area ratio (An/Ap) is calculated using the constant properties model. Accordingly, a revised device architecture is designed to accommodate the optimum An/Ap = 1:2 without compromising the ﬁll factor. Finite element simulations predict a combined improvement in 􀀂max and 􀀃max compared to a non-optimized 1:1 design. Simulations are experimentally validated with An/Ap = 1:1 and 1:2 devices, showing a“double-high” improvement more than 10 % in 􀀂max and 􀀃max at 􀀂T ≈465 K. The proposed optimization strategy provides a general approach to enhance both power output and conversion eﬃciency in various p-n thermoelectric material combinations. 1. Introduction Thermoelectric (TE) devices directly convert heat to electricity, exhibit great potential in cooling and power generation applications. [1,2] It consists of doped ptype and n-type materials connected electrically in series and thermally in parallel. The output power density (􀀂) and conversion eﬃciency (􀀃) of the device is mainly decided by the performance of the TE materials. [3] TE materials are characterized by a dimensionless parameter,ﬁgure of merit (zT), derived from the Seebeck coeﬃcient ( S), electrical conductivity (􀀄) and thermal conductivity (􀀅) at absolute temperature ( T), using the relation: S2 􀀄 zT = . T (1) 􀀅 Over the past several decades, Te-based materials (Bi2Te3 , Sb2Te3 , PbTe, GeTe, La3 − xTe4 etc.) have emerged as state-of-theart candidates for commercial/ practical TE devices because of their impressive zT. [4–8] However, the scarcity and toxicity of Te have prompted the search for alternative materials composed of earthabundant and environmentally benign J. Babu, R. Chetty, T. Mori Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) Tsukuba 305-0044, Japan [E-mail:](E-mail: MORI.Takao@nims.go.jp)[ MORI.Takao@nims.go.jp](E-mail: MORI.Takao@nims.go.jp) T. Mori Graduate School of Pure and Applied Sciences University of Tsukuba Tsukuba 305-8577, Japan The ORCID identiﬁcation number(s) for the author(s) of this article can be found under [https://doi.org/10.1002/smll.202508990](https://doi.org/10.1002/smll.202508990) © 2025 The Author(s) . Small published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modiﬁcations or adaptations are made. DOI: 10.1002/smll.202508990 elements. [9] Mg-based materials emerge as a promising alternative in this context with a comparable TE performance to the Te-based materials in the low-to-medium temperature applications. [10–13] Mg3 Sb2-Mg3 Bi2 solid solutions are zintl materials with a layered crystal structure and intrinsically low lattice thermal conductivity. Their electronic properties can be eﬀectively tuned to either n-type or p-t

FAQs

Why are geometry optimization strategies important for Mg3(Sb,Bi)2 thermoelectric devices?

Because p-type and n-type performance imbalance makes it difficult to reach both maximum power density and maximum conversion efficiency. Geometric design helps mitigate trade-offs in device fill factor.

What device design change is proposed in the study?

A revised two-pair device architecture based on optimizing the cross-sectional area ratio An/Ap. The optimum target is An/Ap=1:2 while preserving the fill factor.

How are the simulated improvements verified experimentally?

Finite element simulations predict combined improvements versus a non-optimized 1:1 design. Experiments are then conducted for both An/Ap=1:1 and An/Ap=1:2, showing a “double-high” increase of more than 10% in both metrics near 465 K.

Sep 30, 2026

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