The presence of high crystallographic symmetry and nanoscale defects are favorable for thermoelectrics. With proper electronic structures, a highly symmetric crystal tends to possess multiple carrier channels and promote electrical conductivity without sacrificing Seebeck coefficient. In addition, nanoscale defects can effectively scatter acoustic phonons to suppress thermal conductivity. Here, it is reported that the triple doping of Cu₂SnSe₃ leads to a high ZT value of 1.6 at 823 K for Cu_1.85Ag_0.15(Sn_0.88Ga_0.1Na_0.02)Se₃, and a decent average ZT (ZT_ave) value of 0.7 is also achieved for Cu_1.85Ag_0.15(Sn_0.93Mg_0.06Na_0.01)Se₃ from 475 to 823 K. This study reveals: 1) Ag doping on Cu sites generates numerous point defects and greatly decreases lattice thermal conductivity. 2) Doping Mg or Ga converts the monoclinic Cu₂SnSe₃ into a cubic structure. This symmetry enhancing leads to an increase in the effective mass from 0.8 m_e to 2.6 m_e (m_e, free electron mass) and the power factor from 4.3 µW cm⁻¹ K⁻² for Cu₂SnSe₃ to 11.6 µW cm⁻¹ K⁻². 3) Na doping creates dense dislocation arrays and nanoprecipitates, which strengthens the phonon scattering. 4) Pair distribution function analysis shows localized symmetry breakdown in the cubic Cu_1.85Ag_0.15(Sn_0.88Ga_0.1Na_0.02)Se₃. This work provides a standpoint to design promising thermoelectric materials by synergistically manipulating crystal symmetry and nanoscale defects.

中文翻译：

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通过三重掺杂类金刚石化合物 Cu2SnSe3 的晶体对称性增强实现高热电性能

高晶体对称性和纳米级缺陷的存在有利于热电。通过适当的电子结构，高度对称的晶体往往具有多个载流子通道并在不牺牲塞贝克系数的情况下促进导电性。此外，纳米级缺陷可以有效地散射声学声子以抑制热导率。在这里，据报道，Cu ₂ SnSe ₃的三重掺杂导致Cu _1.85 Ag _0.15 (Sn _0.88 Ga _0.1 Na _0.02 )Se _{3 的}ZT值在 823 K 时达到 1.6的高值，并且具有良好的平均ZT ( ZT _ave)从 475 到 823 K ，Cu _1.85 Ag _0.15 (Sn _0.93 Mg _0.06 Na _0.01 )Se _{3 的}) 值也达到了 0.7 。这项研究表明：1) 在 Cu 位点上掺杂 Ag 会产生许多点缺陷并大大降低晶格热导率。2)掺杂Mg或Ga将单斜Cu ₂ SnSe ₃转变为立方结构。这种对称性增强导致有效质量从 0.8 me _e增加到 2.6 me _e（me _e，自由电子质量）以及Cu的功率因数从 4.3 µW cm ^-1 K ^-2₂ SnSe ₃至 11.6 µW cm ^-1 K ^-2。3) Na 掺杂会产生密集的位错阵列和纳米沉淀，从而加强声子散射。4) 对分布函数分析显示立方体Cu _1.85 Ag _0.15 (Sn _0.88 Ga _0.1 Na _0.02 )Se ₃中的局部对称破坏。这项工作为通过协同操纵晶体对称性和纳米级缺陷来设计有前途的热电材料提供了一个观点。