Study On Thermoelectric Transport Properties Of Cu₂SnSe₃ Based Complex Solid Soluations Alloyed With Multicomponent Compounds

Over the last 20 years,with the deepening of study on solid state physics,semiconductor physics,materials science,chemistry and microscopy,the research of thermoelectric materials has attracted wide attentions and been rapidly developed.Meanwhile,remarkable achievements have been made in the optimization of thermoelectric properties.However,traditional thermoelectric materials are mainly concentrated on compounds with special structures,toxic elements,high price or Earth-scarce storage,such as Pb Te,Ge Te,skutterudites,half-Heusler alloys,etc.Diamond-like compounds have attracted extensive attentions due to the advantages such as simple structures,low price,environmental friendliness and good electrical properties.However,the relatively high lattice thermal conductivity of diamond-like compounds limits the further improvement in their thermoelectric performance.Besides,the traditional solid solution methods with single atomic substitution is not effective in reducing the lattice thermal conductivity of these compounds.Therefore,it is worth investigating the effect of making diamond-like compounds solid solutions with multicomponent alloys on their thermal conductivities and thermoelectric performance.In order to solve this problem,this work taking p-type Cu₂SnSe₃-based diamond-like compounds as an example,aims to rationally design and systematically study the influences of multicomponent alloys with different crystal structures on thermoelectric properties of diamond-like compounds.Additionally,combined with transport coefficient theory,the electric transport mechanisms of a series of solid solutions are explored.This study shed light on the further study on thermoelectric transport properties of similar systems.The details are summarized briefly as follows:(1)The lattice thermal conductivity of Cu₂SnSe₃-based materials is effectively reduced by alloying with binary compounds with different crystal structures.The binary compounds used as alloying components include In₂Se₃(sphalerite structure)with intrinsic cation vacancy,Sn Te with rock salt structure and In Sb with sphalerite structure.By studying the thermoelectric properties of a series of solid solutions,it is found that the compounds with rock salt structure and sphalerite structure can be used as alloying components to form solid solutions with compounds with diamond-like structure.In addition,among the series of solid solution samples,alloying with In₂Se₃exhibits the most significant optimization effect on thermoelectric properties of Cu₂SnSe₃based compounds.Moreover,In₂Se₃can synergistically decrease the lattice thermal conductivity and increase power factor of Cu₂SnSe₃based compounds.When the alloying content of In₂Se₃reaches 9%,a lattice thermal conductivity of?0.52 Wm^-1K^-1can be obtained,?40%reduction for pristine Cu₂SnSe₃.In addition,the intrinsic thermoelectric properties of(Cu₂SnSe₃)_1-x(In₂Se₃)_xsolid solutions are evaluated by quality factor analysis,and the most promising sample is found to be(Cu₂SnSe₃)_0.91(In₂Se₃)_0.09.Furthermore,In and Ga are selected as dopants on Sn sites to increase the carrier concentration.Finally,both the peak and average thermoelectric figure of merits of solid solutions are greatly promoted to?0.85 and?0.30,respectively,?500%enhancement compared with the pristine Cu₂SnSe₃.(2)Considering that the lattice thermal conductivity of Cu₂SnSe₃based compounds is greatly reduced by alloying with the binary compound In₂Se₃,we are motivated to further optimize the thermoelectric properties of Cu₂SnSe₃system by alloying the Cu-Se based ternary alloy Cu In Se₂with sphalerite structure.Additionally,the simultaneous optimization of electrical and thermal transport properties can be successfully achieved by alloying with Cu In Se₂for Cu₂SnSe₃based compounds.Finally,combined with the further carrier regulation,the maximum figure of merit of?0.98 and the maximum average figure of merit of?0.35over the whole working temperature are obtained in the 3%Ga doped sample.Compared with the reported p-type Cu₂SnSe₃based compounds,this result is among the best reported values.(3)Considering that the electrical performance of(Cu₂Sn_0.97Ga_0.03Se₃)_0.80(Cu In Se₂)_0.20solid solution is still lower compared with the reported results,the thermoelectric performance of Cu₂SnSe₃based compounds is optimized by adjusting the carrier concentration through allovalent element doping on Sn sites firstly and then alloying with complex solid solutions.Firstly,the electrical transport properties of Cu₂SnSe₃based compounds are greatly improved by using Cd as the dopant on Sn site.When the doping content of Cd reaches 9%,the peak power factor at?723 K is?11.49?Wcm^-1K^-2,which increases by?5 times compared with the pristine Cu₂SnSe₃.Moreover,Cd doping can also significantly decrease the lattice thermal conductivity.When the doping content of Cd reaches7%,the minimum lattice thermal conductivity at?723 K is?0.47 Wm^-1K^-1,which is reduced by 46%compared with the pristine Cu₂SnSe₃.Besides,the intrinsic thermoelectric properties of Cu₂Sn_1-xCd_xSe₃samples are evaluated by quality factors analysis,and the optimal doping ratio of Cd is determined to be 7%.Furthermore,Cu-Se based ternary alloy Cu Ga Se₂with sphalerite structure is selected as alloying component to optimize the thermoelectric properties of Cu₂Sn_0.93Cd_0.07Se₃based compounds.Finally,both the peak and average figure of merits of solid solutions are promoted to?0.75,and?0.28,which are?300%and?500%enhancement compared with the pristine Cu₂SnSe₃,respectively.(4)Keeping Cd as the dopant on Sn site,the influence of alloying with Cu-Te sphalerite ternary compounds Cu In Te₂and Cu Ga Te₂on the thermoelectric properties of Cu₂Sn_0.93Cd_0.07Se₃based compounds are been further systematically studied.Finally,the highest average figure of merit of?0.30 is obtained over the whole working temperature in(Cu₂Sn_0.93Cd_0.07Se₃)_0.91(Cu In Te₂)_0.09and(Cu₂Sn_0.93Cd_0.07Se₃)_0.94(Cu Ga Te₂)_0.06,and the thermoelectric conversion efficiencies are both?6%,which is improved by?300%compared with the pristine Cu₂SnSe₃.