Thermoelectric materials are a kind of functional materials that can realize the direct conversion between thermoelectricity and electric energy. They can be used for semiconductor refrigeration, high-precision temperature control and thermoelectric power generation. In order to improve the thermoelectric conversion efficiency, it is necessary to increase the power factor S2σ of the material as much as possible while maintaining a low thermal conductivity. However, there is an intrinsic correlation between the Seebeck coefficient S and the conductivity σ, and it is generally difficult to achieve a significant increase in the power factor. Using "band engineering" can decouple S and σ to a certain extent to obtain higher power factor and conversion efficiency. Surrounding several types of environment-friendly new thermoelectric materials, the Institute of Optoelectronic Functional Materials and Devices of the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, has been closely integrated with theory and experiments, and has carried out a series of characteristic and fruitful studies in energy band engineering and performance optimization. jobs.
The team's researchers used the near-room-temperature new thermoelectric material α-MgAgSb as an example, advanced the theory of energy band engineering design through theory, and strongly promoted the progress of related experimental research. According to the theory of basic electronic structure, the bandgap of covalently bonded semiconductors comes from the splitting of bonding and antibonding states, and the valence band or conduction band has typical bonding or antibonding features. Researchers have designed a variety of doping schemes for the degeneracy of the α-MgAgSb pluripotency valley by exploring the inherent relationship between “doping element level—bonding/bonding strength—band dispersionâ€. This energy band engineering design idea is highly operational, not only applicable to α-MgAgSb, but also providing theoretical guidance for the regulation of other thermoelectric materials. The research was published in Adv. Energy Mater. 2017, 1700076.
SnTe is expected to replace PbTe as an environmentally friendly medium-temperature thermoelectric material. In the previous work, the team has achieved optimization of its thermoelectric performance through two energy band engineering mechanisms: “degeneration by valence band†and “resonance energy levelâ€. They recently discovered that there is a good match between the position of the resonant state in the SnTe and the energy difference between light and heavy valence bands. This indicates that the above two mechanisms can work synergistically in SnTe to achieve an overall improvement in the thermoelectric performance in the larger temperature range. . The researchers further pointed out that the co-doping scheme that achieves the synergy between the two mechanisms is a lower concentration of In and the appropriate amount of Mg, Mn, or Cd. Experimental studies confirm these theoretical predictions and related research work was published in ACS Energy Lett. 2017, 2: 1203 and J. Mater. Chem. C 2017, doi: 10.1039/C7TC02162C, and others.
SnSe is a high-performance intermediate temperature thermoelectric material reported in recent years, but its mechanical properties are poor. The team's researchers independently developed the "horizontal gradient solidification method" and obtained high-quality large-size SnSe single crystals. The related work was published in J. Cryst. Growth 2017, 460: 112 and J. Alloys Compd. 2017, 712: 857. The researchers also prepared SnSe polycrystals to overcome the shortcomings of single crystal growth conditions, long preparation cycle and other defects, and to improve its thermoelectric properties through doping design. For example, PbBr2 doping gives excellent n-type SnSe polycrystals, and Ag doping gives excellent p-type SnSe polycrystals. Related research work was published in RSC Adv. 2017, 7: 17906 and NPG Asia Mater. 2017.
The above work was supported by projects supported by the National Natural Science Foundation of China (11234012, 11404350, 11404348), the Zhejiang Outstanding Youth Fund (LR16E020001) and the Ningbo Science and Technology Innovation Team (2014B82004).
Surgical Face Mask,Tie-On Medical Masks,Disposable Surgical Mask,Disposable Medical Surgical Face Mask
Henan Diyi Medical Technology Development Co.,Ltd. , https://www.diyimedical.com