{"title":"Crystal symmetry-driven structural design for enhanced thermoelectric performance in lead-free cubic GeTe","authors":"Fang Xu , Bo Liu , Ran Ang","doi":"10.1016/j.actamat.2025.121266","DOIUrl":null,"url":null,"abstract":"<div><div>GeTe-based materials have emerged as promising candidates for medium-temperature thermoelectric (TE) applications. However, their phase transition near ∼700 K significantly degrades mechanical properties. In this study, we present a novel approach to stabilize the cubic rock-salt phase of lead-free GeTe at room temperature through co-doping with Tb and Sb, which completely solves the phase transition problem. Tb substitution at Ge sites not only alters the valence band structure but also promotes the formation of orthorhombic Tb<sub>2</sub>Te<sub>3</sub>, effectively reducing the <em>c</em>/<em>a</em> lattice ratio. Simultaneously, Sb doping optimizes the carrier concentration, enhances band convergence, and suppresses the stereochemical activity of Ge<sup>2+</sup> 4<em>s</em><sup>2</sup> lone pair electrons, thereby improving the overall symmetry of GeTe. The introduction of hierarchical nano- and meso-structures, including nanoprecipitates (e.g., solid-solution point defects, Ge, Tb<sub>2</sub>Te<sub>3</sub>, and Sb<sub>2</sub>Te<sub>3</sub>) and an increased density of grain boundaries, further augments the material's performance. As a result, the optimized composition, Ge<sub>0.89</sub>Tb<sub>0.01</sub>Sb<sub>0.10</sub>Te, achieves a peak <em>ZT</em> of ∼2.0, an average <em>ZT</em> (<em>ZT</em><sub>avg</sub>) of ∼1.24, a theoretical conversion efficiency of ∼16.50%, and a Vickers hardness of ∼203.16 <em>H</em><sub>v</sub>. This study demonstrates that inducing orthorhombic structure and manipulating lone-pair electrons can effectively enhance the crystal symmetry of lead-free GeTe-based materials, offering valuable insights for the development of high-performance cubic-phase GeTe materials.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"296 ","pages":"Article 121266"},"PeriodicalIF":9.3000,"publicationDate":"2025-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Acta Materialia","FirstCategoryId":"88","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S1359645425005531","RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATERIALS SCIENCE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
GeTe-based materials have emerged as promising candidates for medium-temperature thermoelectric (TE) applications. However, their phase transition near ∼700 K significantly degrades mechanical properties. In this study, we present a novel approach to stabilize the cubic rock-salt phase of lead-free GeTe at room temperature through co-doping with Tb and Sb, which completely solves the phase transition problem. Tb substitution at Ge sites not only alters the valence band structure but also promotes the formation of orthorhombic Tb2Te3, effectively reducing the c/a lattice ratio. Simultaneously, Sb doping optimizes the carrier concentration, enhances band convergence, and suppresses the stereochemical activity of Ge2+ 4s2 lone pair electrons, thereby improving the overall symmetry of GeTe. The introduction of hierarchical nano- and meso-structures, including nanoprecipitates (e.g., solid-solution point defects, Ge, Tb2Te3, and Sb2Te3) and an increased density of grain boundaries, further augments the material's performance. As a result, the optimized composition, Ge0.89Tb0.01Sb0.10Te, achieves a peak ZT of ∼2.0, an average ZT (ZTavg) of ∼1.24, a theoretical conversion efficiency of ∼16.50%, and a Vickers hardness of ∼203.16 Hv. This study demonstrates that inducing orthorhombic structure and manipulating lone-pair electrons can effectively enhance the crystal symmetry of lead-free GeTe-based materials, offering valuable insights for the development of high-performance cubic-phase GeTe materials.
期刊介绍:
Acta Materialia serves as a platform for publishing full-length, original papers and commissioned overviews that contribute to a profound understanding of the correlation between the processing, structure, and properties of inorganic materials. The journal seeks papers with high impact potential or those that significantly propel the field forward. The scope includes the atomic and molecular arrangements, chemical and electronic structures, and microstructure of materials, focusing on their mechanical or functional behavior across all length scales, including nanostructures.