Yangyang Ren

Multiple effects of Bi doping in enhancing the thermoelectric properties of SnTe

We studied the effect of doping with Bi on the thermoelectric properties of SnTe-based materials. Doping with Bi reduced the density of holes and increased the Seebeck coefficient over a wide temperature range as a result of modulation of the carrier concentration and an increase in the density of states effective mass. The lattice thermal conductivity was also greatly reduced as a result of the wide frequency range of phonon scattering by multiscale architectures derived from Bi doping. A maximum ZT value of c. 1.1 at 873 K was obtained in Sn0.94Bi0.06Te, an enhancement of 165% compared with the undoped sample.

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.

Synergistic effect by Na doping and S substitution for high thermoelectric performance of p-type MnTe

Pristine MnTe is a p-type semiconductor with a relatively low hole concentration of 1018 cm−3, low electrical conductivity, and thus poor TE performance at room temperature owing to the broad direct band gap of 1.27 eV. In this study, Na2S was employed to be doped into the MnTe matrix to synergistically tune the electrical and thermal transport properties of the semiconductor via point defect engineering. On the one hand, Na substitution effectively improved the electrical transport properties by increasing the carrier concentration via the formation of acceptor-like defects, Na−Mn. On the other hand, thermal conductivities of the Na2S-doped samples were also sharply reduced via mass fluctuation and strain field fluctuation from the point defects introduced through Na doping and S substitution. Consequently, a maximum ZT of ∼1.09 was achieved for the 0.5 at% Na2S-doped sample at 873 K, which was the highest ZT value ever reported for p-type MnTe-based thermoelectric materials. Moreover, the high performance 0.5 at% Na2S-doped sample also exhibited good thermal stability and mechanical stability (Vickers microhardness) of ∼122 Hv, which was higher than those of other promising thermoelectric materials such as Bi2Te3, PbTe, PbSe, Cu2Se, and SnTe.

Combination of Carrier Concentration Regulation and High Band Degeneracy for Enhanced Thermoelectric Performance of Cu3SbSe4

The effect of Al-, Ga-, and In-doping on the thermoelectric (TE) properties of Cu3SbSe4 has been comparatively studied on the basis of theoretical prediction and experimental validation. It is found that tiny Al/Ga/In substitution leads to a great enhancement of electrical conductivity with high carrier concentration and also large Seebeck coefficient due to the preserved high band degeneracy and thereby a remarkably high power factor. Ultimately, coupled with the depressed lattice thermal conductivity, all three elements (Al/Ga/In) substituted samples have obtained a highly improved thermoelectric performance with respect to undoped Cu3SbSe4. Compared to the samples at the same Al/In doping level, the slightly Ga-doped sample presents better TE performance over the wide temperature range, and the Cu3Sb0.995Ga0.005Se4 sample presents a record high ZT value of 0.9 among single-doped Cu3SbSe4 at 623 K, which is about 80% higher than that of pristine Cu3SbSe4. This work offers an alternative approach to boost the TE properties of Cu3SbSe4 by selecting efficient dopant to weaken the coupling between electrical conductivity and Seebeck coefficient.

A new method for simultaneous measurement of Seebeck coefficient and resistivity

A new method has been proposed and verified to measure the Seebeck coefficient and electrical resistivity of a sample in the paper. Different from the conventional method for Seebeck coefficient and resistivity measurement, the new method adopts a four-point configuration to measure both the Seebeck coefficient and resistivity. It can well identify the inhomogeneity of the sample by simply comparing the four Seebeck coefficients of different probe combinations, and it is more accurate and appropriate to take the average value of the four Seebeck coefficients as the measured result of the Seebeck coefficient of the sample than that measured by the two-point method. Furthermore, the four-point configuration makes it also very convenient to measure the resistivity by using the Van der Pauw method. The validity of this method has been verified with both the constantan alloy and p-type Bi2Te3 semiconductor samples, and the measurement results are in good agreement with those obtained by commercial available equipment.