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Figure 1. (a) Thermoelectric figure of type n AgInSe2 diamond-like structural compound; (b) Thermoelectric device of the first diamond-like structure compound Figure 2. (a) phonon spectrum of n-type AgInSe2 diamond-like structural compound; (b) lattice Thermal conductivity
Shanghai Institute of Silicate has made progress in the research of n-type high performance diamond-like structure thermoelectric materials
In recent years, with the introduction and development of some new effects and new mechanisms of thermoelectric transport, many new high-performance thermoelectric material systems have also been discovered. Among them, the diamond-like structural compound is derived from the diamond structure. Due to the atomic radius and chemical valence state of the constituent elements, the lattice of the material is distorted, transforming from the cubic structure of the diamond to the non-cubic structure. The intrinsic low thermal conductivity and regulatable electrical properties of diamond-like structural compounds make it an excellent thermoelectric material. Since 2009, the thermoelectricity research team of the Shanghai Institute of Ceramics of the Chinese Academy of Sciences first reported the thermoelectric properties of the quaternary compounds Cu2CdSnSe4 and Cu2ZnSnSe4, and the diamond-like structural compounds have gained extensive attention in the field of thermoelectric research. So far, the thermoelectric properties of more than 20 kinds of diamond structural compounds have been reported, and the thermoelectric figure of many p-type materials is higher than 1, which is comparable to traditional thermoelectric materials. However, the thermoelectric figure of the n-type diamond-like structural compound is generally low, which limits the development of high-efficiency diamond-like structural compound thermoelectric devices. Recently, Xie Pengfei, a researcher at the Shanghai Institute of Silicate, researcher Shi Xun and Chen Lidong collaborated with Professor Yang Lan of Shanghai University to discover a high-performance n-type class with intrinsic extremely low lattice thermal conductivity and electrical properties. Diamond structure compound AgInSe2. At 900K, the highest thermoelectric figure of the AgInSe2-based compound reaches 1.1, which is comparable to the best p-type diamond-like structural compounds such as CuGaTe2 and CuInTe2 which have been reported so far. On this basis, the research team first prepared a diamond-like structural compound thermoelectric component that showed good application prospects. The forbidden band width of AgInSe2 is about 1.2 eV. Previous studies on AgInSe2 have focused on the application in the field of optoelectronics. The discovery that AgInSe2 has a lattice thermal conductivity that is much lower than other diamond-like structural compounds. At room temperature, the lattice thermal conductivity of AgInSe2 is only 0.99W m-1K-1, which is comparable to amorphous glass. The first-principles calculations show that there are a large number of low-frequency optical branches in the phonon spectrum of AgInSe2, and strongly scatter the lattice phonons close to their frequencies, which is the root cause of the low lattice thermal conductivity of AgInSe2. Further studies have found that these low frequency optical branches are derived from the coordinated vibration of "Ag-Se cluster". In the crystal structure of AgInSe2, Ag and Se are combined by strong chemical bonds, and the chemical bonds of In and the above two atoms are weak. Therefore, Ag and Se can form an "Ag-Se cluster" having a large overall mass, and the binding force thereof is weak, and thus exhibits a low phonon vibration frequency. On the other hand, by introducing a Se vacancy in AgInSe2 or introducing a Cd element at the Ag site for doping, an increase in the order of magnitude of material conductivity can be achieved. Preliminary studies have shown that the thermoelectric figure of merit of AgInSe2 compounds with a small amount of Se vacancies reaches 1.1 at 900K. Based on the high-performance n-type AgInSe2 compound and the p-type CuInTe2-based compound previously reported by the research team (J. Mater. Chem. A, 2016, 4, 1277), this study was the first to prepare a diamond-like structure with two pairs of thermoelectric monocouples. Compound thermoelectric components. Using the electroplating and brazing techniques, the Ni and Mo-Cu electrodes were successfully connected to the cold and hot ends of the thermocouple. Preliminary test results show that the maximum output power of the device is 0.06W at a temperature difference of 520K. If the contact resistance and contact thermal resistance at the device interface can be further optimized, the performance will be further improved. Related research results are published in Advanced Science. The research was funded by the National Natural Science Foundation of China, the Chinese Academy of Sciences Key Deployment Project, the Youth Innovation Promotion Association, and the Shanghai Excellent Academic Leadership Program.