Keywords: 
• 纳米复合 /
• 热电材料 /
• PbSe

Abstract: Thermoelectric materials can generate electricity by harnessing the temperature gradient and lowering the tem-perature through applying electromotive force. Lead chalcogenides based materials, especially PbTe-based ones, have shown extremely high thermoelectric performance. PbSe has a similar crystal structure and band structure to PbTe. Compared with the commonly-used PbTe, PbSe possesses a high melting point and has an abundant reserve of Se, making it attractive to high temperature thermoelectric applications. It has been theoretically proposed that Mn-doping in lead chalcogenide should be able to lower the temperature of band degeneracy, and experimental evidences have been represented in Mn-PbTe. However, such an experimental study as well as the investigations of influences of Mn on microstructure, mechanical, electrical and thermal properties has not been conducted in Mn-PbSe. In this work, Pb0.98?xMnxNa0.02Se (0≤x≤0.12) materials are prepared by the melting-quenching techniques combined with rapid hot-press sintering. Effects of Mn doping on the microstructures, mechanical and thermoelectric properties of PbSe samples are systematically studied. The refined lattice parameters from X-ray powder diffraction patterns show that the solubility of Mn in the matrix is in a range from 0 to 0.04. The back-scattered electron images and elemental maps reveal that the MnSe-rich impurity phases exist in the PbSe matrix, which makes the PbSe-MnSe system a nano-composite system. Pb0.96Mn0.02Na0.02Se has also such microstructures, implying that the solubility of Mn should be below 0.02. Cubic-phase MnSe-rich precipitates have the sizes ranging from 50 nanometers to 1–5 micrometers. They are well dis-persed in the PbSe-rich matrix, as round or layered microstructures. The mechanical properties of the nanocomposites can be determined by micro-hardness measurements. Interestingly, the average Vickers hardness values of the PbSe-MnSe nanocomposites are significantly improved, which are 16.6% and 51.6% harder respectively in x=0.02 and 0.06 samples than those of pristine PbSe. Smaller Mn content can optimize the figure of merit Z T due to the band con-vergence and additional phonon scattering by precipitates, while higher Mn content has little influence on ZT because of the saturated Seebeck coeffcient and anomalous increase in lattice thermal conductivity. As a result, the highest figure of merit is 0.52 at 712 K, which is achieved in the Pb0.96Mn0.02Na0.02Se sample. By further adjusting the Na content from 2%to 0.7%, the carrier concentration is optimized. Thus, the Seebeck coeffcient and power factor become higher. A figure of merit of 0.65 is achieved at 710 K in the PbSe-MnSe nano-composite with a nominal composition of Pb0.973Mn0.02Na0.007Se. We suggest that further optimizing the electrical properties may achieve a higher thermoelectric performance in the PbSe-MnSe system.