Thermoelectric And Mechanical Properties Of Skutterudites With Nano-TiN Particles Or Micro-Nano-pores

Thermoelectric?TE?material is a kind of functional material that can directly convert heat to electrical energy.It has a wild application prospects in the fields of solar power generation,industrial waste heat recovery and thermoelectric refrigeration.Skutterudite materials are considered as one of most promising TE materials because of their higher power factor in the intermediate temperature range.However,it displays a relative high thermal conductivity,which hinders its practical applications.The strategy of how to reduce the thermal conductivity of the skutterudite material and improve its thermoelectric performance has been research hotpot at home and abroad.In addition,thermoelectric materials are usually suffering to high temperature loads,large temperature difference cyclic loads and alternating mechanical loads during service.Therefore,the influence of various methods on the mechanical properties of skutterudite materials should take into account while improving its TE performance.In this paper,the Te-doped skutterudite TE material Co₄Sb_11.5Te_0.5 is focused as research object.Grain refinement combined with nano-inclusions and introducing of micro-nano-pores are applied to further reduce the thermal conductivity of Co₄Sb_11.5Te_0.5 and increase its ZT value,Meanwhile,the effects of these two methods on the mechanical properties of Co₄Sb_11.5Te_0.5 are investigated.The main contents and and results are listed as follows:?1?A method of grain refinement combined with nanocomposite to reduce the thermal conductivity of skutterudite materials was proposed.Nano-Co₄Sb_11.5Te_0.5/1vol%TiN?20 nm?is prepared by solid state reaction,high energy ball milling combined with spark plasma sintering?SPS?.It is found that the room temperature thermal conductivity of the nano-Co₄Sb_11.5Te_0.5/1 vol%TiN sample decreased to 2.34Wm^-1K^-11 due to the decreased grain size of skutterudite and introduction of the nano-TiN particles,which decreased by 53%compared with the micron-sized Co₄Sb_11.5Te_0.5.The ZT value of the nano-Co₄Sb_11.5Te_0.5/1 vol%TiN sample was increased by 18.9%compared with the micro-Co₄Sb_11.5Te_0.5.In addition,the introduction of nano-TiN particles exhibits a positive effect on maintaining the structure and thermoelectric properties of nano-Co₄Sb_11.5Te_0.5 materials.However,the nano-Co₄Sb_11.5Te_0.5/1 vol%TiN sample has a poor flexural strength,which decreased by 24.2%compared with that of micro-Co₄Sb_11.5Te_0.5,but the fracture toughness is17.9%higher than that of the micro-Co₄Sb_11.5Te_0.5 sample..?2?A new method of pore-forming process is applied.Co₄Sb_11.5Te_0.5nanocomposites with homogenous nanoparticals:micro-Co₄Sb_11.5Te_0.5/10 vol%nano-Co₄Sb_11.5Te_0.5?named N10?is prepared by solid state reaction,high energy ball milling and SPS.After annealing for 100 h of N10,a stable micro-nanopore structure skutterudite sample?named N10-A100?is obtained due to the grain boundary migration of nano-Co₄Sb_11.5Te_0.5 particles during annealing.The room temperature thermal conductivity of N10-A100 is largely reduced due to strong scattering of phonons,which the mean free path of phonons is comparable to the pore size The ZT value of N10-A100 reached 1.2 at 800 K,which was increase by 33.7%than that of micro-Co₄Sb_11.5Te_0.5.The TE properties of N10-A100 exhibits good thermal stability after further annealed for 100 h.However,N10-A100 displays a poor flexural strength,which is 21.9%lower than that of micron-Co₄Sb_11.5Te_0.5,but the fracture toughness show an increased of 7%compared with micro-Co₄Sb_11.5Te_0.5.In order to optimize the mechanical properties of skutterudite with micro-nano-pores,1 vol%SiC whisker is introduced into the homogenous composites?named N10/SiCw?.The strength and fracture toughness are 26%and 21.6%higher than the N10-A100samples sfter annealing for 100 h of N10/SiC,respectively.