Structure And Thermoelectric Performance Of Cu-containing Polycomponent CuSb(Sn)Se(S) Chalcogenides

CuSb(Sn)Se(S)chalcogenides have received much attention due to earth abundance,low cost,and non-toxic of their elements.In this work,we select Cu₃SbSe₄and CuSbSe₂-based compounds as target materials and propose a co-doping strategy to improve their thermoelectric(TE)performance.The detailed compositions of the three group materials are designed as follows:(Cu₃Sb_0.9Sn_0.1Se_3.6S_0.4)(Ga₂Te₃)_x(x=0.01,0.0125,0.015,0.0175),(Cu₃Sb_1-xGa_xSe₄)_0.9(Cu_3-3xAg_3xSnS₄)_0.1(x=0.005,0.01,0.02,0.03)and Cu_1-xAg_xSbSe₂(x=0.05,0.075,0.1,0.2).The results are summarized below.In this work,we co-dope Sn and S in Cu₃SbSe_4,and then alloy Ga₂Te_3,aiming to improve its TE performance and understand the mechanism via the calculation of the band and crystal structures.The band structure calculation reveals that an impurity band creates within the bandgap after co-doping of Sn and S,which is directly responsible for the significant improvement in carrier concentration(n _H)and electrical property.Therefore,the power factor(PF)enhances from 0.52×10^-3Wm^-1K^-2to1.3×10^-3Wm^-1K^-2.Although the effect associated with the residing of Ga(Te)at Sb(Se)sites on the band structure is limited,the bond lengths and angles of the tetrahedras[SbSe₄]and[Se Cu₃Sb]alters remarkably,thus yielding a significant distortion of local lattice structure.Therefore,the lattice thermal conductivity(?_L)reduces from 1.23 WK^-1m^-1to 0.81 WK^-1m^-1at 691 K,preventing the total thermal conductivity(?)from rapid enhancement.As a consequence,the highest ZT value of0.64 is attained,which is much higher than that of the pristine Cu₃SbSe₄.We co-dope Sn and S in Cu₃SbSe₄,and then dope Ag and Ga to prepare solid solutions(Cu₃Sb_1-xGa_xSe₄)_0.9(Cu_3-3xAg_3xSnS₄)_0.1(x=0?0.03).Through co-doping of Sn and S,the carrier concentration(n _H)and electrical property has been improved significantly.When we dope Ag and Ga in succession,the carrier concentration increases slightly while the electrical properties remains almost unchanged.However,after doping Ag and Ga,the thermal conductivity reduces,which enables the TE performance to be improved.As a consequence,the highest ZT value of 0.55 is attained at 691 K,which is much higher than that of the pristine Cu₃SbSe₄.Upon an addition of Ag in CuSbSe₂,only a limited effect has been made on the Seebeck coefficient and electrical conductivity at high temperatures for the solid solutions Cu_1-xAg_xSbSe₂(x=0,0.05,0.075,0.1,0.2),so does the power factor.However,the scattering to phonons on the point defects strengthens as the Ag content increases,which can effectively reduces the lattice thermal conductivity from 0.69WK^-1m^-1(600 K)to 0.53 WK^-1m^-1(621 K).As a consequence,the highest ZT value of0.21 is attained at 621 K,which is 16%higher than that of the pristine CuSbSe₂.