Sajjad Muhammad, Singh Nirpendra
Department of Physics, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
Phys Chem Chem Phys. 2021 Jul 28;23(29):15613-15619. doi: 10.1039/d1cp01967h.
We have comprehensively demonstrated the thermal transport properties of Nb2SiTe4 and Nb2GeTe4 ternary monolayers by employing first-principles calculations and the semi-classical Boltzmann transport theory, including the electron-phonon coupling. The appealing features uncovered here for the monolayers are their colossal Seebeck coefficient and power factor at a higher carrier concentration. For example, the room temperature Seebeck coefficient lasts as high as 200 μV K-1 even at an increased hole (electron) concentration 6.32 × 1020 cm-3 (5.17 × 1019 cm-3) and 1.47 × 1020 cm-3 (5.18 × 1019 cm-3) for Nb2SiTe4 and Nb2GeTe4 monolayers, respectively. Our findings disclose similar band structures and moderate indirect bandgaps of 0.55 eV and 0.41 eV for Nb2SiTe4 and Nb2GeTe4 monolayers. The absence of imaginary frequencies in phonon band dispersion confirms the dynamic stability of both monolayers. The lowest value of lattice thermal conductivity turns out to be 14.30 W m-1 K-1 (12.30 W m-1 K-1) for Nb2SiTe4 and 11.70 W m-1 K-1 (8.34 W m-1 K-1) for Nb2GeTe4 in the x(y) direction. Besides, both monolayers express tremendous potential to further reduced lattice thermal conductivity by nano-structuring without requiring a diminished sample size that is technically challenging to synthesize.
我们通过采用第一性原理计算和半经典玻尔兹曼输运理论，全面展示了Nb2SiTe4和Nb2GeTe4三元单层的热输运性质，包括电子 - 声子耦合。这里发现的单层的吸引人的特性是在较高载流子浓度下具有巨大的塞贝克系数和功率因数。例如，即使在空穴（电子）浓度增加时，室温下Nb2SiTe4和Nb2GeTe4单层的塞贝克系数分别高达200 μV K-1，空穴（电子）浓度分别为6.32 × 1020 cm-3（5.17 × 1019 cm-3）和1.47 × 1020 cm-3（5.18 × 1019 cm-3）。我们的研究结果揭示了Nb2SiTe4和Nb2GeTe4单层具有相似的能带结构和0.55 eV和0.41 eV的适度间接带隙。声子能带色散中没有虚频证实了两种单层的动态稳定性。对于Nb2SiTe4，晶格热导率在x（y）方向上的最低值为14.30 W m-1 K-1（12.30 W m-1 K-1），对于Nb2GeTe4为11.70 W m-1 K-1（8.34 W m-1 K-1）。此外，通过纳米结构化，两种单层都表现出进一步降低晶格热导率的巨大潜力，而无需减小在技术上难以合成的样品尺寸。
