Preparation And Characterization Of Low-Dimensional Nano-Silver Dispersed Bi₂Te₃-Based Thermoelectric Composites

Thermoelectric (TE) materials are a kind of new functional materials, which can be used for direct conversion between thermal and electrical energy. They have wide application in the fields of thermoelectric cooling and power generation. Bi2Te3-based material has by far been considered to be the most suitable TE material for energy conversion at room temperature. How to further enhance the figure of merit of Bi2Te3has become a research hotspot. Although low-dimensional thermoelectric materials have made great progress in improving thermoelectric performance, yet from an application perspective, preparation of bulk TE materials is more practical. Low-dimensional nanocomposite TE materials could reduce the lattice thermal conductivity and simultaneously improve the power factor, which are expected to be the main trend in the future development of TE materials.In this paper, we attempt to construct a kind of novel low-dimensional nanocomposite TE materials by introducing low-dimensional silver nanowires (AgNWs) and silver nanoparticles (AgNPs) into the three-dimensional Bi2Te3matrix, respectively. With the introduction of low-dimensional nano-phase, we could not only obtain much higher interphase density to cause strong scattering of long wavelength phonon, and therefore reduce the lattice thermal conductivity, but also enhance the power factor by energy filtering of carriers. Here, AgNWs and AgNPs are obtained by using polyol reduction of silver nitrate. The Bi2Te3nanopowders are synthesized by using the surfactant-mediated hydrothermal method. Then the two nanopowders are mixed uniformly through ultrasound and subsequently sintered into bulk materials by the spark plasma sintering (SPS) technique. The main studies are as follows:(1) AgNWs and AgNPs were obtained by using polyol reduction of silver nitrate and the Bi2Te3nanopowders were synthesized by the surfactant-mediated hydrothermal method. The results show that AgNWs have a mean diameter of50nm and length of50μm and AgNPs have a mean diameter of50nm as well. The Bi2Te3nanopowders possess some ball-like and flake-like structure and are well agglomerated with the average size of about50nm.(2) The synthesized AgNWs and Bi2Te3were mixed at different proportion through ultrasound and stirring. The as-prepared AgNWs-dispersed Bi2Te3composite powders were sintered using spark plasma sintering. The influence of different concentration of AgNWs on the morphology and thermoelectric properties of n-type Bi2Te3was fully studied. The results show that AgNWs were uniformly dispersed in the Bi2Te3matrix. The dispersed AgNWs effectively suppressed the grains growth and formed new interfaces with the Bi2Te3matrix. Consequently, the maximum ZT reached0.71when1.5vol%AgNWs were added, which was3.4times higher than that of the pure Bi2Te3(ZT=0.16) at475K.(3) The synthesized AgNPs and Bi2Te3were mixed at different proportion through ultrasound and stirring. The as-prepared AgNPs-dispersed Bi2Te3composite powders were sintered using spark plasma sintering. The influence of different concentration of AgNPs on the morphology and thermoelectric properties of n-type Bi2Te3was fully studied. The results show that AgNPs were uniformly dispersed in the Bi2Te3matrix. The dispersed AgNPs effectively suppressed the grains growth and formed new interfaces with the Bi2Te3matrix. Consequently, the maximum ZT reached0.77when2.0vol%AgNPs were added, which was3times higher than that of the pure Bi2Te3(ZT=0.19) at475K.