Structure And Thermoelectric Properities Of Filled Skutterudites

Medium-temperature thermoelectric materials CoSb₃ based skutterudites display great potential for applications due to good thermoelectric properties,environment friendly and excellent mechanical properties.Element filling has been considered as one of the most effective methods to control the thermoelectric properties of skutterudites.Yb has been proved to be the best choice among so many doping elements.Currently,Materials preparation mainly includes long-period annealing,ball milling and melt spinning.The optimum filling amount of rare earth varies even with the same preparation method.Cobalt is one of the constituted elements for skutterudites,which is a kind of strategic resources.Therefore,it is particularly necessary to develop Yb filled and cobalt-free skutterudites thermoelectric materials to further improve thermoelectric performance and save Co strategic resources.In this paper,n-type and p-type skutterudites were prepared by melt spinning,and their thermoelectric transport performance was studied by means of conductivity/Seebeck coefficient test system and laser thermal conductivity meter.The research results are as follows:Filled CoSb₃ based skutterudites with Yb as filling element was synthesized by melt-spinning,which shortened preparation cycle greatly.The electrical conductivity increased while the Seebeck coefficient decreased with the increment of filling fraction of Yb.As a result,the power factor of Yb_0.25Co₄Sb₁₂ reached the maximum value54.2?W·cm^-1·K^-2.The simple harmonic motion Yb presented in the intrinsic holes scattered phonon effectively,the lattice thermal conductivity was decreased due to the enhanced phonon scattering caused by Yb filling,and then the ZT value was increased.Finally,the ZT value of Yb_0.25Co₄Sb₁₂ reached 1.32 at 873 K.This work lay a foundation for further improvement of thermoelectric performance.Combing melt-spinning and hot-pressing sintering preparation technology,utilization of Fe,Ni instead of Co in the preparation of cobalt free skutterudites,Ce_0.45Nd_0.45Fe_3.75Ni_0.25Sb₁₂2 was obtained using Fe and Ni to completely substitute Co.Compared with cobalt containing skutterudites Ce_0.45Nd_0.45Fe_3.5Co_0.5.5 Sb₁₂ sample,we found that cobalt-free alloy showed higher electric conductivity,and lower Seebeck coefficient,leading to that power factor of cobalt containing and cobalt free sukterrudites were almost equal.In terms of thermal conductivity,the total thermal conductivity and lattice thermal conductivity of cobalt-free alloy were higher than that of cobalt-containing alloy.Therefore,the ZT value of cobalt-free alloy was slightly lower in the high temperature range.The ZT value of cobalt-free alloy could still reach1.07 at 773K.