A novel quaternary Cu₂MnSnSe₄ diamondlike thermoelectric material was discovered recently based on the pseudocubic structure engineering. In this study, we show that introducing off-stoichiometry in Cu₂MnSnSe₄ effectively enhances its thermoelectric performance by simultaneously optimizing the carrier concentrations and suppressing the lattice thermal conductivity. A series of nonstoichiometric Cu_2+δMn_1−δSnSe₄ (δ = 0, 0.025, 0.05, 0.075, and 0.1) samples has been prepared by the melting–annealing method. The X-ray analysis and the scanning electron microscopy measurement show that all nonstoichiometric samples are phase pure. The Rietveld refinement demonstrates that substituting part of Mn by Cu well maintains the structure distortion parameter η close to 1, but it induces obvious local distortions inside the anion-centered tetrahedrons. Significantly improved carrier concentrations are observed in these nonstoichiometric Cu_2+δMn_1−δSnSe₄ samples, pushing the power factors to the theoretical maximal value predicted by the single parabolic model. Substituting part of Mn by Cu also reduces the lattice thermal conductivity, which is well interpreted by the Callaway model. Finally, a maximal thermoelectric dimensionless figure-of-merit zT around 0.60 at 800 K has been obtained in Cu_2.1Mn_0.9SnSe₄, which is about 33% higher than that in the Cu₂MnSnSe₄ matrix compound.

中文翻译：

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提高的热电性能在非化学计量的Cu _{2 +δ}的Mn _1-δ位SnSe ₄季化合物类金刚石

基于伪立方结构工程，最近发现了一种新型的季铵型Cu ₂ MnSnSe ₄菱形热电材料。在这项研究中，我们表明，通过同时优化载流子浓度和抑制晶格热导率，在Cu ₂ MnSnSe ₄中引入非化学计量可有效提高其热电性能。一系列的非化学计量铜_{2 +δ}的Mn _1-δ位SnSe ₄通过熔融退火法制备了（δ= 0、0.025、0.05、0.075和0.1）样品。X射线分析和扫描电子显微镜测量表明，所有非化学计量的样品都是相纯的。Rietveld的改进表明，用Cu很好地替代了Mn的一部分，可以使结构变形参数η保持接近1，但是它在以阴离子为中心的四面体内部引起了明显的局部变形。显著改进的载流子浓度在这些非化学计量铜观察_{2 +δ}的Mn _1-δ位SnSe ₄采样，将功率因数推至单个抛物线模型预测的理论最大值。用Cu代替部分Mn也会降低晶格的热导率，Callaway模型对此进行了很好的解释。最后，在Cu _2.1 Mn _0.9 SnSe _4中获得了800 K时0.60左右的最大热电无因数品质因数zT，比Cu ₂ MnSnSe ₄基体化合物高约33％。