Gharavi M A, Armiento R, Alling B, Eklund P
1Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, 581 83 Linköping, Sweden.
2Theory and Modelling Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, 581 83 Linköping, Sweden.
J Mater Sci. 2018;53(6):4294-4305. doi: 10.1007/s10853-017-1849-0. Epub 2017 Nov 30.
Scandium nitride has recently gained interest as a prospective compound for thermoelectric applications due to its high Seebeck coefficient. However, ScN also has a relatively high thermal conductivity, which limits its thermoelectric efficiency and figure of merit (). These properties motivate a search for other semiconductor materials that share the electronic structure features of ScN, but which have a lower thermal conductivity. Thus, the focus of our study is to predict the existence and stability of such materials among inherently layered equivalent ternaries that incorporate heavier atoms for enhanced phonon scattering and to calculate their thermoelectric properties. Using density functional theory calculations, the phase stability of TiMgN, ZrMgN and HfMgN compounds has been calculated. From the computationally predicted phase diagrams for these materials, we conclude that all three compounds are stable in these stoichiometries. The stable compounds may have one of two competing crystal structures: a monoclinic structure (LiUN prototype) or a trigonal superstructure (NaCrS prototype; R mH). The band structure for the two competing structures for each ternary is also calculated and predicts semiconducting behavior for all three compounds in the NaCrS crystal structure with an indirect band gap and semiconducting behavior for ZrMgN and HfMgN in the monoclinic crystal structure with a direct band gap. Seebeck coefficient and power factors are also predicted, showing that all three compounds in both the NaCrS and the LiUN structures have large Seebeck coefficients. The predicted stability of these compounds suggests that they can be synthesized by, e.g., physical vapor deposition.
由于氮化钪具有较高的塞贝克系数，近来它作为一种有望用于热电应用的化合物而受到关注。然而，氮化钪也具有相对较高的热导率，这限制了其热电效率和优值（）。这些特性促使人们寻找其他具有氮化钪电子结构特征但热导率较低的半导体材料。因此，我们研究的重点是预测在包含较重原子以增强声子散射的固有层状等效三元化合物中此类材料的存在和稳定性，并计算它们的热电性能。通过密度泛函理论计算，我们计算了TiMgN、ZrMgN和HfMgN化合物的相稳定性。从这些材料的计算预测相图中，我们得出结论，所有这三种化合物在这些化学计量比下都是稳定的。稳定的化合物可能具有两种相互竞争的晶体结构之一：单斜结构（LiUN原型）或三角超结构（NaCrS原型；R mH）。我们还计算了每个三元化合物两种竞争结构的能带结构，并预测了在NaCrS晶体结构中所有三种化合物的半导体行为，其具有间接带隙，以及在单斜晶体结构中ZrMgN和HfMgN的半导体行为，其具有直接带隙。我们还预测了塞贝克系数和功率因子，结果表明在NaCrS和LiUN结构中的所有三种化合物都具有较大的塞贝克系数。这些化合物的预测稳定性表明它们可以通过例如物理气相沉积法合成。
