Using the Seebeck effect or the Peltier effect of the semiconductor, direct conversion between thermal energy and electrical energy can be realized, including two application forms of thermoelectric power generation and thermoelectric refrigeration. The thermoelectric properties are characterized by a dimensionless figure of merit ZT (=S2σT/κ), where S, σ, T, and κ are Seebeck coefficients, electrical conductivities, temperatures, and thermal conductivities, respectively, and S2σ is called a power factor. Based on semiconducting compounds with low thermal conductivity, the electro-acoustic transport can be coordinated and controlled from both electronic band engineering and multi-scale phonon scattering, which can effectively improve thermoelectric performance. For a variety of systems of thermoelectric materials, the Optoelectronic Functional Materials and Devices team of the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, has achieved a series of progress in material design and performance optimization by closely integrating theory and experiments. For SnTe thermoelectric materials, the team explained theoretically the effects of several typical dopings on the electric heat transport, and achieved a significant improvement in the thermoelectric properties of SnTe. For example, theoretical studies have shown that intrinsic Sn vacancies play an important role in the regulation of SnTe band, and the presence of Sn vacancies leads to significant bandgap increases in Mg, Mn, Cd, and Hg-doped SnTe, and light/heavy valence band energy difference decreases. The small features (shown in Figure 1) are very beneficial to improve the thermoelectric properties of SnTe. The Mn-doped SnTe polycrystalline samples were prepared by zone melting method. The experimental results confirmed the above theoretical predictions. The Mn/Sn alloying can realize the increase of the bandgap and degeneracy of the light/heavy valence band. The Seebeck coefficient of SnMnTe can reach 270 μV/K and the ZT value is 1.25. Related research results were published in J. Mater. Chem. A, 3, 19974 (2015), RSC Adv., 5, 59379 (2015), RSC Adv., doi:10.1039/c6ra02658c (2016) and Phys. Chem. Chem. Phys., 18, 7141 (2016). Although they are all IV-VI compounds, SnSe and SnTe have different crystal structures. In the last two years, SnSe single crystals have been reported to have ZT values ​​as high as 2.6. In order to overcome the disadvantages of the severe growth conditions, long preparation cycle, and poor mechanical properties of SnSe single crystals, the preparation of SnSe polycrystals and improvement of their thermoelectric properties has become a research hotspot. Recently, the team carried out research on SnSe polycrystals using theoretical calculations and zone melting growth methods. Figure 2a shows the polycrystalline SnSe textured region with power factor and ZT values ​​of 9.5 μWcm-1K-2 and 0.9@873 K, respectively (Figure 2b), which is much higher than the results reported by other similar international The single crystal results reported by Nature (2014, 508, 373) reflect the effective enhancement of the electrical transport properties of SnSe by texturing. By pulverizing and re-sintering the polycrystalline SnSe region, higher power factor can be maintained and the thermal conductivity can be reduced (Fig. 2c). First-principles calculations show that Ag doping can promote light/heavy band degeneracy in SnSe. This energy band degenerate effect is beneficial to increase Seebeck coefficient and power factor. Experimental work confirms this theoretical hypothesis that Ag doping The carrier concentration of SnSe polycrystalline was increased, the power factor was 11 μWcm-1K-2, and the ZT value was further increased to 1.3 (Fig. 2d). At the same time, the use of BiCl3 doped SnSe significantly increased the carrier concentration and conductivity of n-type SnSe, and obtained higher Seebeck coefficient and lower thermal conductivity. Its power factor is about 5 μWcm-1K-2 and the ZT value is 0.7, which provides a solution for the development of n-type SnSe thermoelectric materials. The results of related studies are published in J. Mater. Chem. C, 4, 1201 (2016), Appl. Phys. Lett., 108, 083902 (2016). In addition, the researchers studied the phonon transport properties of BiCuOSe through first-principles calculations. The calculated thermal conductivity agrees well with the experiment. The Green's Eisen constant of BiCuOSe is about 2.5 at room temperature, which indicates that it has strong anharmonicity, resulting in very low thermal conductivity. Studies have also shown that the high-frequency phonon vibrations in BiCuOSe are mainly contributed by oxygen atoms, and their contribution to the overall lattice thermal conductivity exceeds 30% (Fig. 3a). This is similar to the general material in which the thermal conductivity is usually caused by acoustic phonon vibration. The decision was very different; through further research, it was revealed that these high-frequency modes have strong dispersion, high group velocity, and weak scattering with low-frequency phonons (Fig. 3b), establishing the BiCuOSe high-frequency phonon. A physical image that has an unusually large contribution to thermal conductivity. In addition, it is also found that the phonon group velocity (Fig. 3d) and the bulk modulus of BiCuOSe in different directions have strong anisotropy, which results in significant anisotropy of the lattice thermal conductivity (Fig. 3c). The results of the relevant studies are published in Scientific Reports, 6, 21035 (2016). The above work has received strong support from the National Natural Science Foundation of China (11234012, 11304327, 11404348, 11404350), the Zhejiang Outstanding Youth Fund (LR16E020001), the Ningbo Natural Science Foundation (2014A610011) and the Ningbo Science and Technology Innovation Team (2014B82004). Gift Bags,Gift Bag Hiking Travel Pack,Eco Gift Bag,Gift String Bag Dongguan C.Y. RedApple Industrial Limited , https://www.redapplebags.com