Mg3Sb1.5Bi0.5-based alloys have received much attention,and current reports on this system mainly focus on the modulation of doping.However,there lacks the explanation for the choice of Mg3Sb1.5Bi0.5 as matrix.Here in this work,the thermoelectric properties of Mg3Sb2-xBix(0.4≤x≤0.55)compounds are systematically investigated by using the first principles calculation combined with experiment.The calculated results show that the band gap decreases after Bi has been substituted for Sb site,which makes the thermal activation easier.The maximum figure of merit(ZT)is 0.27 at 773 K,which is attributed to the ultra-low thermal conductivity 0.53 W·m-1·K-1 for x=0.5.The large mass difference between Bi and Sb atoms,the lattice distortion induced by substituting Bi for Sb,and the nanoscale Bi-rich particles distributed on the matrix are responsible for the reduction of thermal conductivity.The introduction of Bi into Mg3Sb2-based materials plays a vital role in regulating the transport performance of thermoelectric materials.
Yang WangXin ZhangYan-Qin LiuJiu-Xing ZhangMing Yue
The Ba-, La- and Ag-doped polycrystalline Ca2.9M0.1Co4O9 （M=Ca, Ba, La, Ag） thermoelectric bulk samples were pre- pared via citrate acid sol-gel synthesis method followed by spark plasma sintering technique. The bulk samples were characterized and analyzed with regard to their phase compositions, grain orientations as well as microstructures. The high temperature thermoelec- tric transport properties of the bulk samples were studied in detail. All bulk samples were found to be single-phased with modified body texture. The electrical resistivity was modulated as a result of carrier concentration modification, however the carrier transport process was not influenced; the Seebeck coefficient was deteriorated simultaneously. The total thermal conductivity was remarkably reduced, on account of the decreasing of phonon thermal conductivity. The thermoelectric properties of the Ba-, La-, and Ag-doped bulk samples were optimized, and the Ba-doped Ca2.9Ba0.1Co4O9 system was found to have the highest dimensionless figure of merit ZT0.20 at 973 K, which was remarkably higher than that of the un-doped sample.
Mg_(3)Sb_(2)-based thermoelectric materials have poor electrical conductivity which is the key to limit thermoelectric performance that need to be solved.Herein we tuned the carrier concentration of Mg_(3)Sb_(2)-based materials via Ag doping at the Mg sites(at two distinct crystallographic sites)to enhance the electrical performance.Mg_(3-x)Ag_(x)Sb_(2)(0≤x≤0.05)has been prepared successfully by vacuum suspension smelting plus Spark Plasma Sintering technique.Using the vacuum suspension smelting plus Spark Plasma Sintering method,we proved that Ag doping can precisely tune the electrical transport properties and accordingly enhance the power factor.Moreover,the Ag doping leads to a low lattice thermal conductivity due to phonons scattering,and the maximal thermoelectric figure of merit ZT for Mg_(3-x)Ag_(x)Sb_(2)reaches 0.66 at 773 K.
