ABSTRACT

Heavily acceptor-doped Cu₂SnS₃ (CTS) shows promisingly large power factor (PF) due to its rather high electrical conductivity (σ) which causes a modest ZT with a high electronic thermal conductivity (κ_e). In the present work, a strategy of carrier compensation through Sb-doping at the Sn site in Cu₂Sn_0.8Co_0.2S₃ was investigated, aiming at tailoring electrical and phonon transport properties simultaneously. Rietveld analysis suggested a complex polymorphic microstructure in which the cation-(semi)ordered tetragonal phase becomes dominant over the coherently bonded cation-disordered cubic phase, as is preliminarily revealed using TEM observation, upon Sb-doping and Sb would substitute Sn preferentially in the tetragonal structure. With increasing content of Sb, the σ was lowered and the Seebeck coefficient (S) was enhanced effectively, which gave rise to high PFs maintained at ~10.4 μWcm⁻¹K⁻² at 773 K together with an optimal reduction in κ_e by 60–70% in the whole temperature range. The lattice thermal conductivity was effectively suppressed from 1.75 Wm⁻¹K⁻¹ to ~1.2 Wm⁻¹K⁻¹ at 323 K while maintained very low at 0.3–0.4 Wm⁻¹K⁻¹ at 773 K. As a result, a peak ZT of ~0.88 at 773 K has been achieved for Cu₂Sn_0.74Sb_0.06Co_0.2S₃, which stands among the tops so far of the CTS-based diamond-like ternary sulfides. These findings demonstrate that polymorphic microstructures with cation-disordered interfaces as an approach to achieve effective phonon-blocking and low lattice thermal conductivity, of which further crystal chemistry, microstructural and electrical tailoring are possible by appropriate doping.

摘要

重掺杂受主的Cu ₂ SnS的₃（CTS）所示大好，大的功率因子（PF），由于其相当高的电导率（σ）引起适度ZT具有高电子热导率（κ _ë）。在目前的工作中，通过在 Cu ₂ Sn _0.8 Co _0.2 S ₃中的 Sn 位点掺杂 Sb 来补偿载流子的策略进行了研究，旨在同时定制电和声子传输特性。Rietveld分析表明，一种复杂的多晶型微观结构，其中阳离子（半）有序四方相在相干键合的阳离子无序立方相中占主导地位，这是通过TEM观察初步发现的，在Sb掺杂中，Sb优先取代Sn。四方结构。随着 Sb 含量的增加，σ降低，塞贝克系数（S）有效提高，这导致在 773 K 时保持在 ~10.4 μWcm ^-1 K ^{-2 的}高PF s以及κ _e的最佳降低在整个温度范围内降低 60-70%。晶格热导率在 323 K 时从 1.75 Wm ^-1 K ^-1被有效抑制到~1.2 Wm ^-1 K ^-1，同时在 773 K 时保持在 0.3-0.4 Wm ^-1 K ^-1非常低。因此，Cu ₂ Sn _0.74 Sb _0.06 Co _0.2 S ₃在 773 K 达到了 ~0.88 的峰值ZT，它是迄今为止基于 CTS 的类金刚石三元硫化物的佼佼者。这些发现表明，具有阳离子无序界面的多晶微结构是实现有效声子阻挡和低晶格热导率的一种方法，通过适当的掺杂可以进一步实现晶体化学、微观结构和电学定制。