Breaking the Minimum Limit of Thermal Conductivity of Mg3Sb2 Thermoelectric Mediated by Chemical Alloying Induced Lattice Instability

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 19; no. 33
• Main Authors: Hu, Jinsuo, Zhu, Jianbo, Dong, Xingyan, Guo, Muchun, Sun, Yuxin, Shi, Wenjing, Zhu, Yuke, Wu, Hao, Guo, Fengkai, Zhang, Yi‐Xin, Ge, Zhen‐Hua, Zhang, Qian, Liu, Zihang, Cai, Wei, Sui, Jiehe
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 16.08.2023
• Subjects: Alloying elements; Anharmonicity; Bonding strength; Chemical bonds; Functional materials; giant anharmonicity; Group velocity; Heat conductivity; Heat transfer; Heavy elements; Heterogeneity; Lattice instability; Nanotechnology; phonon mode softening; Phonons; p‐type Mg3Sb2 materials; Stability analysis; Thermal barrier coatings; Thermal conductivity; Thermal management; Thermodynamic properties; thermoelectric; Thermoelectric materials; Transport properties; Zintl phase
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202301382

Thermal properties strongly affect the applications of functional materials, such as thermal management, thermal barrier coatings, and thermoelectrics. Thermoelectric (TE) materials must have a low lattice thermal conductivity to maintain a temperature gradient to generate the voltage. Traditional strategies for minimizing the lattice thermal conductivity mainly rely on introduced multiscale defects to suppress the propagation of phonons. Here, the origin of the anomalously low lattice thermal conductivity is uncovered in Cd‐alloyed Mg3Sb2 Zintl compounds through complementary bonding analysis. First, the weakened chemical bonds and the lattice instability induced by the antibonding states of 5p‐4d levels between Sb and Cd triggered giant anharmonicity and consequently increased the phonon scattering. Moreover, the bond heterogeneity also augmented Umklapp phonon scatterings. Second, the weakened bonds and heavy element alloying softened the phonon mode and significantly decreased the group velocity. Thus, an ultralow lattice thermal conductivity of ≈0.33 W m−1 K−1 at 773 K is obtained, which is even lower than the predicated minimum value. Eventually, Na0.01Mg1.7Cd1.25Sb2 displays a high ZT of ≈0.76 at 773 K, competitive with most of the reported values. Based on the complementary bonding analysis, the work provides new means to control thermal transport properties through balancing the lattice stability and instability. The traditional strategies for reducing the lattice thermal conductivity mainly rely on the introduced hierarchical architecture to impede the propagation of the phonons. Herein, the chemical alloying to balance the lattice stability and instability is subtly used, which lead to an ultralow lattice thermal conductivity that breaks the minimum limit of the Mg3Sb2 system estimated by the Cahill model.