Preparation And Thermoelectric-mechanical Properties Of Co Sb₃-based Composite Materials

Thermoelectric material is a functional material that can directly achieve a mutual conversion of thermal energy and electrical energy,which should be widely applicable in the fields of thermoelectric power generation and refrigeration.And the skutterudite material is identified as one of the most promising middle-temperature thermoelectric materials thanks to its excellent electrical performance.Yet its application is restricted seriously by its high thermal conductivity.Processing excellent mechanical performance is also one of the prerequisites of applying skutterudite materials by taking into account the complex service conditions of thermoelectric materials.Nano-composite as a hotspot in the thermoelectric research is one of the most effective methods to improve the thermoelectric and mechanical properties of skutterudite materials.In-situ nano-composite skutterudite materials and one-dimensional nano-wire composite skutterudite materials were prepared rapidly by MQ?Melt Quenching?,HTHP?High Temperature and High Pressure?and SPS?Spark Plasma Sintering?in this paper.Moreover,the influence of in-situ prepared nano-particles or the introduced nano-wires on thermoelectric and mechanical properties of skutterudite materials was also studied.Main research contents and achievements are shown as follows:1.Co₄Sb₁₁Ge_xTe_1-x?x=0.2,0.25,0.3?materials were prepared by MQ-SPS and HTHP-SPS,spending 6 hours and 1 hour,respectively.The whole preparation process took 6 h and 1 h,respectively.GeO₂ nano-particles were formed in situ at the grain boundary of the sample prepared by HTHP-SPS with the increase of a phonon scattering center.When x=0.2,the lattice thermal conductivity of the sample decreased to 1.12 Wm^-1K^-1 at 800 K,lowered by about 52%in comparison to the sample prepared by MQ-SPS.The ZT value of the Co₄Sb₁₁Ge_0.2Te_0.8 sample prepared by HTHP-SPS reached 1.05 at 800 K.2.Skutterudite materials doped with group IV elements?Si,Ge,Sn,Pb?were prepared by HTHP-HP.Of which,nanoparticles were formed in situ in samples of Gex-Co₄Sb₁₂ and Sn_x-Co₄Sb₁₂.As Ge/Sn contents increase,nano-particles in the sample are increased obviously.The lowest lattice thermal conductivity at room temperature was about 1.80 Wm^-1K^-1 in the Sn₁-Co₄Sb₁₂ sample.The ZT value of the sample reached0.28 at 800 K.Also,the bending strength of the Sn₁-Co₄Sb₁₂ sample reached 143.4 MPa due to the pinning effect between nano-particles formed in situ,which was approximately improved by 98.6%compared to the pure Co4Sb12 sample.3.CoSb₃/x vol%K₂Ti₆O₁₃?x=0,0.5,1,2?composites were prepared by two HTHPs.K2Ti6O13 whiskers were primarily distributed at the grain boundary of the sample after the first high pressure.Micro-cracks were found on the surface of the one-step HTHP sample that was treated thermally at 600°C for 6 hours as clusters emerged with the increased content of K₂Ti₆O₁₃ whiskers.After the second high pressure,K₂Ti₆O₁₃3 whiskers were dispersed more evenly with some K₂Ti₆O₁₃ whiskers interspersed in skutterudite grains.No significant change was found on the surface of the sample after thermally treating at 600°C for 6 hours.To be specific,the bending strength,the fracture toughness and hardness of the CoSb₃/1 vol%K₂Ti₆O₁₃ sample reached 92.46 MPa,1.38 MPa m^1/2 and 719.26 HV,respectively,which were improved by 24.3%,35.3%,and 30.1%respectively,compared to the pure CoSb₃ sample.