Sarkar Debattam, Dolui Kapildeb, Taneja Vaishali, Ahad Abdul, Dutta Moinak, Manjunatha S O, Swain Diptikanta, Biswas Kanishka
New Chemistry Unit, International Centre for Materials Science and School of Advanced Materials, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore, 560064, India.
Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
Angew Chem Int Ed Engl. 2023 Oct 2;62(40):e202308515. doi: 10.1002/anie.202308515. Epub 2023 Aug 23.
Comprehension of chemical bonding and its intertwined relation with charge carriers and heat propagation through a crystal lattice is imperative to design compounds for thermoelectric energy conversion. Here, we report the synthesis of large single crystal of new p-type cubic AgSnSbTe which shows an innately ultra-low lattice thermal conductivity (κ ) of 0.47-0.27 Wm K and a high electrical conductivity (1238 - 800 S cm ) in the temperature range 294-723 K. We investigated the origin of the low κ by analysing the nature of the chemical bonding and its crystal structure. The interaction between Sn(5 s)/Ag(4d) and Te(5p) orbitals was found to generate antibonding states just below the Fermi level in the electronic band structure, resulting in a softening of the lattice in AgSnSbTe . Furthermore, the compound exhibits metavalent bonding which provides highly polarizable bonds with a strong lattice anharmonicity while maintaining the superior electrical conductivity. The electronic band structure exhibits nearly degenerate valence-band maxima that help to achieve a high Seebeck coefficient throughout the measured temperature range and, as a result, the maximum thermoelectric figure of merit reaches to ≈1.2 at 661 K in pristine single crystal of AgSnSbTe .
理解化学键及其与电荷载流子的相互交织关系以及通过晶格的热传播对于设计用于热电能量转换的化合物至关重要。在此，我们报告了新型p型立方AgSnSbTe大单晶体的合成，该晶体在294 - 723 K温度范围内显示出固有超低的晶格热导率（κ），为0.47 - 0.27 Wm⁻¹K⁻¹，以及高电导率（1238 - 800 S cm⁻¹）。我们通过分析化学键的性质及其晶体结构来研究低κ的起源。发现Sn(5s)/Ag(4d)与Te(5p)轨道之间的相互作用在电子能带结构中费米能级以下产生反键态，导致AgSnSbTe晶格软化。此外，该化合物表现出变价键，提供具有高极化性的键以及强晶格非谐性，同时保持优异的电导率。电子能带结构呈现出近乎简并的价带最大值，这有助于在整个测量温度范围内实现高塞贝克系数，结果，在AgSnSbTe原始单晶体中，在661 K时最大热电优值达到约1.2。
