Thermoelectric Properties Of PbSe And Its Nanocomposites Derived By Mechanical Alloying

Thermoelectric materials,which can directly convert thermal energy into electricity,have been receiving increasing attention for their potential applications such as recovering waste heat in industry and reducing greenhouse gas emissions.Basically,there are two routes towards high-performing thermoelectrics.One is seeking for new compounds with excellent electrical or thermal properties,or both of them.The other is developing new strategies to enhance or improve existing materials,which seems to be more important due to its practicality,and also extendibility to other thermoelectric systems.In this study,we implemented different strategies including traditional doping and alloying,as well as novel nanocompositing methods,on thermoelectric PbSe that fabricated by mechanical alloying,in order to get a more comprehensive understanding on their influences to the electrical and thermal transport of thermoelectric materials,and also develop new compositing strategies for high-performance thermoelectrics.At first,pristine PbSe bulk materials were fabricated through mechanical alloying,and their electrical and thermal transport properties as well as thermoelectric performance were investigated in a wide temperature range.A maximum ZT of 0.8 was obtained at 673 K by utilizing compositional optimization,and the potential thermoelectric efficiency was also improved due to the enhanced low-temperature performance,showing a high average ZT of 0.6 that is even comparable to that of commercial n-type Bi2Te3 materials.Doping and alloying methods were then adopted to enhance the high-temperature thermoelectric performance of PbSe.The carrier concentration was easily optimized by doping chlorine,leading to improved power factors.However,alloying with SnSe seemed to be less effective on limiting the lattice thermal conductivity.Consequently,a maximum ZT of 1.0 was achieved at 773 K.The efficiency of different dopants in PbSe was discussed,and the assessment of beneficial disorder in PbSe was also performed.Next,chemically inert secondary phase nanoparticles were embedded into PbSe,in order to reduce the lattice thermal conductivity but unfortunately failed.Even so,systematic doping was found to be generated from the least expected nanoparticles in a composite of PbSe and SiC,which is believed due to interfaces that stabilized more defects than is allowed in bulk PbSe.Eventually,the nanoparticle-induced doping effect led to a decent thermoelectric performance with ZT over 0.9 at 800 K,comparable to optimized PbSe using conventional dopants.Aiming to further limit its lattice thermal conductivity,nanoporous PbSe-based composites were fabricated by a facile method of mechanical alloying assisted by subsequent wet-milling and then spark plasma sintering.Owing to the formation of random nanopores and additional interface scattering,the lattice thermal conductivity was reduced by 30 % at above 600 K.Besides,the room-temperature electrical transport was found to be dominated by the grain-boundary potential barrier scattering,whose effect fades away with increasing temperatures.Consequently,a maximum ZT of 1.15 at 823 K was achieved with > 20 % increase in average ZT,indicating the great potential of nanoporous structuring toward high thermoelectric conversion efficiency.