A research team led by Prof. QIN Xiaoying from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has found that the thermoelectric properties of N-type Bi₂Te_2.7Se_0.3 (BTS) could be improved by introducing a small amount of Ag₉AlSe₆ nanoparticles into BTS matrix.

The thermal conductivity of the composite sample with 0.35vol.% Ag₉AlSe₆ was significantly reduced, resulting in a maximum ZT (figure of merit) of 1.2 (423K) and an average ZT of 1.1 in the 300-473K temperature range.

Relevant results were published in Inorganic Chemistry Frontiers.

Thermoelectric devices are composed of P-type and N-type thermoelectric materials. At present, great progress has been made in the improvement of P-type room temperature thermoelectric material ZT. However, developing high-performance (large ZT) N-type thermoelectric materials near room temperature is more challenging, which hinders the conversion efficiency of thermoelectric devices and prevents them from being widely used.

Bi₂Te₃ is currently recognized as one of the well-known alloys that can both generate electricity and cool at room temperature. However, the low thermoelectric value ZT and energy conversion efficiency of N-type Bi₂Te₃ limit its commercial application. Therefore, improving the thermoelectric properties of N-type Bi₂Te₃ is of great significance to promote its industrial application.
Finding the optimal second phase is the first and key task to design and manufacture a composite system material with excellent performance (including function and structure). Studies have explored different dispersed phases of BTS to obtain better thermoelectric performance.

In this study, the researchers investigated the thermoelectric properties of BTS-xvol % Ag₉AlSe₆ (x= 0, 0.15, 0.25, 0.35, 0.50 and 0.70) samples by introducing N-type nanoparticles Ag₉AlSe₆ into BTS.

According to the researchers, when Ag₉AlSe₆ nanoparticles were added to BTS, the phonon scattering and phase boundary were enhanced, the Seebeck coefficient was enhanced and the thermal conductivity was reduced.

In addition, the thermoelectric performance of composite sample BTS-0.35vol% Ag₉AlSe₆ was improved by about 40% compared with the original BTS.

This work shows that the addition of Ag₉AlSe₆ nanoparticles is an effective way to improve the thermoelectric properties of BTS, which is of great significance for the regulation of the thermoelectric properties of N-type bismuth telluride alloys.

(a). The low magnification TEM image; (b). the medium magnification TEM image; (c). the high magnification TEM image for BTS-0.35Vol% Ag₉AlSe₆; (d). the selected area electron diffraction (SAED) (false-colored); (e-l). the medium magnification TEM image and the EDS mapping for Bi, Te, Se, Ag and Al. (Image by CHEN Tao)