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Enhanced thermoelectric properties of n-type Bi2Te2.7Se0.3 semiconductor by manipulating its parent liquid state

Zhu, Bin, Yu, Yuan, Wang, Xiao-yu, Zu, Fang-qiu, Huang, Zhong-yue
Journal of materials science 2017 v.52 no.14 pp. 8526-8537
air, alloys, cooling, glass, melting, methodology, nanoparticles, pressing, semiconductors, thermal conductivity
To enhance the properties of bulk thermoelectric (TE) materials, preparation methods have been intensively developed with advanced techniques, e.g., zone-melting, Bridgman or Czochralski unidirectional methods, hot pressing or spark plasma sintering, that follow various complicated synthesis steps. However, these innovative methods remain less competitive than conventional techniques for large-scale production and application. Here, we report that, by manipulating the liquid state of the Bi₂Te₂.₇Se₀.₃ alloy doped with KI, n-type bulk specimens with desired TE performance can be simply solidified by air cooling and without costly equipments. The specimens solidified from the parent melt experienced temperature-induced liquid–liquid structural transition, which is indicated by the resistivity behavior of the liquid, the presence of a refined matrix and eutectics, and the observation of more nanoparticles and a higher density of lattice defects. It was confirmed these refined multiscale refined structures lead to a “phonon glass electron crystal” effect, i.e., a much lower lattice thermal conductivity but a much higher power factor (PF). The present method, which synergistically obtains higher PF and lower thermal conductivity, could also be applied to other TE compounds.