First-Principles Study On Skutterudite Based Thermoelectric Materials

Industrial combustion produces a lot of waste heat,and it has wasted energy and ruined the ecological environment.Thermoelectric material,as a secondary functional material that can convert heat and electric energy,can reuse waste heat and convert it into electric energy.In this process,the waste heat utilization is completed,and it is harmless and pollution-free.Therefore,thermoelectric materials have broad prospects and are worth of further exploration in the area of new material research.CoSb3 is mainly studied in skutterudite based thermoelectric materials.Due to its environmentally friendly chemical composition,good thermoelectric mechanical properties and large reserves,CoSb3 thermoelectric materials have become a research hotspot.In this paper,the electronic structure and related thermoelectric properties of CoSb3 materials under different strain conditions and doping conditions are are calculated,using the first principle combined with Boltzman transport theory,and the changes of thermoelectric properties of CoSb3 materials under different performance control methods are studied.The main work of this paper is as follows:(1)We have studied the effect of uniaxial strain on the electronic structure and thermoelectric properties of CoSb3.It is proved that strain regulation is an effective method to improve the thermoelectric properties of CoSb3 system,and the corresponding strain value under the condition of the best regulation effect is found.we can see from the results that both tensile and compressive strain lead to the decrease of the band gap.The steepness of the density of states near the Fermi level is changed.The thermoelectric properties of CoSb3 are also greatly improved by the application of external strain.The calculation results show that the maximum power factor increases by 23.77% at 700 k temperature and-1% compressive strain;At 700 k temperature and 3% tensile strain,the maximum power factor increases by 47.63%.(2)The effects of external biaxial strain on the electronic structure and related thermoelectric properties of CoSb3 system were studied.Similar to the uniaxial strain condition,the energy band structure and electronic structure of CoSb3 system under biaxial strain condition are also greatly affected,but the effect of biaxial strain condition on CoSb3 system is different from that under uniaxial strain condition,its band gap fluctuation is greater,and the overall shift of partial wave density of States is obvious.The results show that ± 1% biaxial strain has a great effect on the improvement of thermoelectric properties of CoSb3 system,and biaxial compressive strain has a higher effect on the improvement of thermoelectric properties of CoSb3 system than biaxial tensile strain;Compared with uniaxial strain regulation,-1%biaxial strain regulation and 3%uniaxial tensile strain regulation have the same peak value,about 45%.(3)The 3% uniaxial strain condition combined with Fe and Ni single atom doping is studied to jointly control the thermoelectric properties of CoSb3 system.The calculation results show that the double regulation improves the conductivity of the system,but reduces the Seebeck coefficient of the system,so the final regulation effect is not good.(4)The effects of three relative doping positions of Co site on the thermoelectric properties of CoSb3 system were studied.The energy band structure diagram and total density of states at each relative position were selected to compare and analyze the influence mechanism.The calculated results of thermoelectric properties show that the conductance relaxation time ratio in the case of the same side is relatively the largest,the face angle is the second,and the conductance relaxation time ratio in the case of the body diagonal is the lowest.In the case of the same side,the Seebeck coefficient is the smallest,and the peaks of the other two are similar.The power factor corresponding to the diagonal of body near the carrier concentration 2e20 is the largest;The power factor corresponding to the same side near the carrier concentration 2e21 is the largest.