Effect Of Compositing And Doping On Thermoelectric Properties Of Bi_xSb_2-xTe₃

Thermoelectric materials operate as a conversion medium between thermal energy and electric energy,no noise,no harmful substance are produced.Great progress have been made in thermoelectric research for half a century.Generally,doping and making composites are two main methods to enhance performance of thermoelectric materials.BixSb_2-xTe₃?BST?alloys are the state-of-the-art thermoelectric materials near room temperature and play an irreplaceable role in low-grade waste heat recovery and refrigeration.In this work,we researched how to improve thermoelectric performance of BST,as following.High-performance Bi_0.4Sb_1.6Te₃-x?x=0,0.05,0.1,0.15?bulk materials are prepared by combining fusion technique with hot pressing process,and their thermoelectric properties are investigated.With the decrease of tellurium content,the power factor increases significantly and the lattice thermal conductivity decreases remarkably.Therefore,a great improvement in the thermoelectric figure of merit is achieved.The maximum figure of merit value reaches 1.33 at 350 K for Bi_0.3Sb_1.7Te_2.90,which is ascribed to the vacancies in the Te sublattice and antisite defects Bi/Sb occupy the vacancies on some of the Te sites.These vacancies and defects alter the concentration of free charge carriers,affect the phonon modes,and modify transport properties.Researching of the defect structure in Bi_0.3Sb_1.7Te₃ is of important sense to enhance the thermoelectric performance.The thermoelectric properties of Ge-doped Bi_0.4Sb_1.6-xGe_xTe₃?x=0,0.01,0,015,0.02?were investigated in the temperature range from 300K to 525K.The results show that Ge doping brings about 13-52%increase in electrical conductivity due to the increase of hole concentration,and 5-11%decrease in thermal conductivity owing to enhanced phonon scattering by the dopant atoms.As a result,a maximum thermoelectric figure of merit?ZT?reaches 1.48 at 350 K for Bi_0.4Sb_1.59Ge_0.01Te₃,which is?25%larger than that of Bi_0.4Sb_1.6Te₃.Present results demonstrate that Ge doping is an effective way to enhance the thermoelectric performance of Bi_0.4Sb_1.6Te₃ alloy.Bi_0.4Sb_1.6Te₃?BST?based composites incorporated with CuInTe2 particles were prepared and their thermoelectric properties were studied in the temperature range from 300 to 500K.The results indicate that by incorporating CuInTe₂ particles in the matrix the power factor?PF?of the composite samples f?CuInTe₂?/BST?f=0.1-0.3 wt.%?enhances;specially,PF reaches 41 ?Wcm-1 K-2?at 300K?as f=0.2 wt.%,which is?14%higher than that of BST.This enhancement of PF comes from the elevating of both the electrical conductivity and thermopower from energy filtering effect.Moreover,the lattice thermal conductivity decreases monotonously with increasing content of CuInTe2 inclusions due to enhanced phonon scattering in the composite samples and reaches 0.42 Wm^-1K^-1?at 300K?that is around 40%lower than that of BST.As a result,a maximum figure of merit ZT=1.45 at 400K is achieved in the composite sample with f=0.2 wt.%,which is?45%larger than that of BST studied here,demonstrating that incorporating a proper amount of CuInTe2 in BST is an effective way to improving thermoelectric performance of BST alloys.