多组元掺杂提升Cu_(3)SbSe_(4)基固溶体的热电性能

Polycomponent doping improved thermoelectric performance of Cu_(3)SbSe_(4)-based solid solutions

Cu_(3)SbSe_(4)是一种具有黄铜矿结构的三元p-型半导体材料,在热电领域颇受重视.本次工作采用在Cu_(3)SbSe_(4)中先掺杂Sn与S,然后再掺杂Ga_(2)Te_(3)这一多组元掺杂方式,通过能带及晶体结构计算,了解多组元掺杂后热电性能提升的结构因素.能带计算表明,共掺杂Sn与S后,禁带区域萌生出杂质带,导致材料的载流子浓度(n_(H))和电学性能大幅提高.在691 K时,功率因子(PF)从本征的5.2μW·cm^(-1·)K^(-2)增大到13.0μW·cm^(-1)·K^(-2).虽然Ga占位在Sb或Te占位在Se位置对能带结构作用甚少,但四面体[SbSe_(4)]和[SeCu_(3)Sb]的键长和键角发生了改变,从而产生了明显的局部点阵畸变.因此,在691 K时,晶格热导率(k_(L))从1.23 W·K^(-1)·m^(-1)降低到0.81 W·K^(-1)·m^(-1),有效地抑制了总热导率(k)的提高.最终,材料的最大热电优值(ZT)为0.64,而本征Cu_(3)SbSe_(4)的ZT值为0.26.

Cu_(3)SbSe_(4),one of the ternary p-type semiconductor materials with chalcopyrite structure,has aroused much interest in thermoelectrics due to its inherent large effective mass and narrow bandgap.Therefore,many researches have been done,which cover the single and/or multi-element doping to manipulate its band structure and introduce the point defects.Although great achievements have been made in recent years,the mechanism in Cu_(3)SbSe_(4) with respect to the phonon and electronic transport properties needs further investigating.In this work,first,Sn and S are co-doped into Cu_(3)SbSe_(4) and then the resulting compound is alloyed with Ga_(2)Te_(3),to improve its TE performance and understand the mechanism by calculating the band structure and crystal structure.The calculation of band structure reveals that an impurity band is created within the bandgap after co-doping Sn and S due to their contributions to the density of the states(DOS),which is directly responsible for the significant improvement in carrier concentration(nH)and electrical property.Therefore,the power factor(PF)is enhanced from 0.52×10^(-3) to 1.3×10^(-3) W·m^(-1)·K^(-2).Although the effect associated with the Ga(Te)residing at Sb(Se)sites on the band structure is limited due to the fact that both the single Ga-and single Te-doped band structure remain almost unchanged,the structural parameters(bond lengths and angles)of the polyhedrons[SeCu_(3)Sb]and[SbSe_(4)]before and after Te and Ga residing at Se and Sb sites respectively change remarkably.This yields the significant distortion of local lattice structure on an atomic scale.Therefore,the phonon scattering is enhanced and the lattice thermal conductivity(kL)decreases from 1.23 to 0.81 W·K^(-1)·m^(-1) at 691 K.The reduction in kL prevents the total thermal conductivity(k)from being enhanced rapidly.As a consequence,the highest ZT value of 0.64 is attained,which is much higher than that of the pristine Cu_(3)SbSe_(4)(ZT=0.26).In addition,we not only present a synergistic strategy to separately optimize the phonon and electronic properties,but also fully elaborate its mechanism and better understand that this strategy is an effective way to improve the TE performance of the Cu3SbSe4-based solid solutions.