Controllable Synthesis And Properties Study Of CoSb₃-base Skutterudite Thermoelectric Materials

Recently,thermoelectric materials have attracted extensive research attention because of their environment friendly applications in waste heat recovery with the Seebeck effect and refrigeration with the Peltier effect.The efficiency of thermoelectric materials can be evaluated by the dimensionless figure of merit ZT?ZT=S²?T/k?,where S is the Seebeck coefficient,?is the electrical conductivity,T is the absolute temperature,k_L is the lattice thermal conductivity,and k_e is the electronic thermal conductivity.Although thermoelectric materials have been studied for decades,their relatively low energy conversion efficiency has been an important factor restricting its commercial development.At present,the energy conversion efficiency of thermoelectric materials that have been commercialized is only about 10%,which is a certain gap compared with the traditional fossil energy utilization rate.Therefore,how to improve the energy conversion efficiency of thermoelectric materials has become the goal of researchers all over the world.The skutterudite thermoelectric material is recognized as the most promising medium-temperature thermoelectric material due to its excellent electrical transport properties,mechanical properties and rich content of raw materials.In this paper,the materials were prepared by melt-annealing-high energy ball milling combined with DC rapid hot pressing sintering.The n-type filled and doping skutterudite Ga_xCo₄Sb_12.32.3 and Ga_0.2Co₄Sb_11.3Te composites with the well-distributed GaSb nanoinclusions were synthesized by an in-situ method through the manipulation of metastable Ga fillers and enrichment of Sb by a proper annealing procedure.The Ga fillers are able to fill the icosahedron cages of skutterudite at high temperature but driven out of the lattice voids and dispersed on grain boundary in the form of antimonides second phase as temperature is lowered.The presence of the GaSb second phase effective scattering low-energy electrons by the GaSb-related boundary energy barriers and reduce the thermal conductivity.In addition,this experiments also have found that Te-doping can suppress the bipolar effect of Ga-filled skutterudite at 600 K while significantly increasing the carrier concentration,resulting in the room-temperature thermal conductivity of Ga_0.2Co₄Sb_11.3Te is 3.35 Wm^-1K^-1,which is 20%lower than the Ga_0.2Co₄Sb_12.3,and the electrical conductivity increased from 286.68 S cm^-1 for Ga_0.2Co₄Sb_12.3 to 1281.65 S cm^-1 for Ga_0.2Co₄Sb_11.3Te.Benefiting from the greatly increased the electrical conductivity and decreased the thermal conductivity,the highest dimensionless thermoelectric figure of merit ZT value was increased from 0.56 for the Ga_0.2Co₄Sb_12.3 sample at 573 K to 1.48 for the Ga_0.2Co₄Sb_11.3Te sample at 873 K.This result is the maximum value of the current single element filled skutterudite thermoelectric material,which is very significant for improving the energy conversion efficiency of the skutterudite thermoelectric material.