Users of High Magnetic Field Facility (SHMFF), Professor TANG Guodong’s group from Nanjing University of Science and Technology, synthesized a new Se quantum dot/Sn0.99Pb0.01Se nanocomposite using an in situ high magnetic field-assisted hydrothermal method and achieved high thermoelectric performance.

Thermoelectric materials are a kind of functional materials that can directly convert heat to electrical energy or vice versa. They have immense application prospects in the fields of thermoelectric power generation and portable refrigeration due to many superiorities such as no noise, no pollution, small size, and etc.

An effective strategy to improve the performance of thermoelectric materials is microstructure manipulation while magnetic field is an important means to control the microstructure.

TANG’s group fabricated Se quantum dot/Sn0.99Pb0.01Se nanocomposites using in situ high magnetic field-assisted hydrothermal synthesis and studied the influence of magnetic field on their microstructure and thermoelectric performance.

The preparation of the samples was accomplished in two steps: hydrothermal synthesis was first carried out under different magnetic fields, and then the reaction products were sintered by spark plasma.

High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imaging results indicated that magnetic field had pronounced effects on the microstructures of the materials.

Firstly, a high magnetic field reduced the grain size. Secondly, the magnetic field had a significant effect on the nanoscale precipitates in terms of shape, size and spatial distribution. Lastly and more importantly, the magnetic field also led to the formation of Se quantum dots.

These changes of microstructures were well illustrated by the analysis of nucleation free energy in a magnetic field.

The Seebeck coefficient of the samples synthesized under magnetic field was greatly increased, which could be mainly attributed to the changes in electronic structure caused by the formation of Se quantum dots.

Ultra violet photoelectron spectroscopy (UPS) measurements showed that Se quantum dots resulted in higher electron density of states near Fermi energy , which improved the Seebeck coefficient and power factor of the materials.

On the other hand, the Se quantum dots, smaller nanograins and nanoprecipitates depressed the thermal conductivity. As a result, a remarkable high ZT value of2.0 was achieved in the nanocomposites, which was enhanced by 47% compared with that synthesized without a magnetic field.

The results were published in Journal of Materials Chemistry A entitled "Nanostructured SnSe integrated with Se quantum dots with ultrahigh power factor and thermoelectric performance from magnetic field-assisted hydrothermal synthesis".