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J Am Chem Soc. 2018 Nov 21;140(46):15883-15888. doi: 10.1021/jacs.8b09375. Epub 2018 Oct 11.

Vacancy Manipulation for Thermoelectric Enhancements in GeTe Alloys.

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Interdisciplinary Materials Research Center, School of Materials Science and Engineering , Tongji University , 4800 Caoan Road , Shanghai 201804 , China.
Department of Mechanical Engineering , The University of Hong Kong , Pokfulam Road , Hong Kong SAR , China.


Optimization of carrier concentration plays an important role on maximizing thermoelectric performance. Existing efforts mainly focus on aliovalent doping, while intrinsic defects (e.g., vacancies) provide extra possibilities. Thermoelectric GeTe intrinsically forms in off-stoichiometric with Ge-vacancies and Ge-precipitates, leading to a hole concentration significantly higher than required. In this work, Sb2Te3 having a smaller cation-to-anion ratio, is used as a solvend to form solid solutions with GeTe for manipulating the vacancies. This is enabled by the fact that each substitution of 3 Ge2+ by only 2 Sb3+ creates 1 Ge vacancy, because of the overall 1:1 cation-to-anion ratio of crystallographic sites in the structure and by the charge neutrality. The increase in the overall Ge-vacancy concentration facilitates Ge-precipitates to be dissolved into the matrix for reducing the hole concentration. In a combination with known reduction in hole concentration by Pb/Ge-substitution, a full optimization on hole concentration is realized. In addition, the resultant high-concentration point defects including both vacancies and substitutions strongly scatter phonons and reduce the lattice thermal conductivity to the amorphous limit. These enable a significantly improved thermoelectric figure of merit at working temperatures of thermoelectric GeTe.


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