Yudong Cheng

Multiple heteroatom induced carrier engineering and hierarchical nanostructures for high thermoelectric performance of polycrystalline In4Se2.5

In this paper, different atom combinations of Pb, I and Cu have been doped into the In4Se2.5 matrix and a systematic investigation has been carried out for the synergistic effect of multiple heteroatoms on the microstructure and thermoelectric properties of polycrystalline In4Se2.5. By this approach, the electron and phonon transport properties are rationally regulated and the electrical conductivity increases greatly due to the multiple doping, which result in a simultaneous increase of carrier concentration and mobility. The Seebeck coefficient also remains at a relatively high level in a high temperature range due to the energy-dependent electron scattering at the metal nanoparticle–matrix interfaces. In addition, the lattice thermal conductivity is also greatly reduced because of the wide frequency phonon scattering by the point defects and hierarchical metal nanoparticles combined with the phonon–phonon interactions. Consequently, an enhancement of the ZT with a maximum of 1.4 (723 K) has been achieved in the multiple doped In4Se2.5 sample.

Enhancement of thermoelectric properties of Yb-filled skutterudites by an Ni-Induced “core–shell” structure

Since the lattice thermal conductivity of n-type multi-filled skutterudites have been reduced below 1 W (mK−1), the development of new strategies that can further enhance the power factor while maintaining the low thermal conductivity is highly desired. In this paper, we conducted a pioneering work by introducing a “core–shell” microstructure into Yb single-filled skutterudite thermoelectric materials to realise this purpose. The “core–shell” structure formed by the thermal diffusion of well dispersed Ni nanoparticles in the Yb0.2Co4Sb12 powder during hot pressing is composed of the normal “core” grains surrounded by Ni-rich nanograin “shells”. The electrical resistivity is greatly reduced due to the increase in both carrier concentration and mobility. However, the Seebeck coefficient first increases due to the increased density of states at the Fermi energy and then decreases gradually. As a consequence, the power factor is remarkably increased for the samples with the addition of Ni nanoparticles. In addition, the lattice thermal conductivity is also reduced by the extra phonon scattering introduced by the “core–shell” microstructure. The concomitant effects enable a maximum ZT of 1.07 for the 0.2 wt% Ni sample at 723 K.

New insight into InSb-based thermoelectric materials: from a divorced eutectic design to a remarkably high thermoelectric performance

As a promising mid-temperature thermoelectric (TE) material, the main obstacle to a high TE performance of the InSb compound is its high thermal conductivity. In this article, a new strategy of eutectic melting has been employed to improve the TE properties of the compound for the first time. By addition of excess Sb into the InSb matrix, an InSb–Sb eutectic structure has been introduced. When the temperature is above the melting point of the eutectic mixture, the InSb–Sb eutectic melts into a liquid phase which inhibits the propagation of transverse acoustic phonons, and the thermal conductivity is reduced drastically. Therefore, the thermoelectric performance is remarkably enhanced after the melting of the eutectic, and an unprecedented high ZT of 1.28@773 K has been achieved for the InSb1.04 sample, which is almost 3 times higher than that of the eutectic-free InSb matrix. Moreover, the Vickers hardness of the eutectic included InSb compound is higher than those of many well-established mid-temperature TE materials, and no evident hardness degradation can be detected after several melting–solidification cycles of the eutectic.