Huaihong Guo, Teng Yang, Peng Tao, Yong Wang, Zhidong Zhang
We systematically study the effect of high pressure on structure, electronic structure and thermoelectric properties of 2H-MoS$_2$, based on first-principles density functional calculations and the Boltzmann transport theory. Under pressure, cross-plane lattice size reduces much faster than in-plane one due to weak van der Waals interaction and it gets more difficult to shrink the size as external pressure goes higher than 20 GPa, which agrees with experimental observation. A conversion from van der Waals bonding to covalent-like is found from charge density calculation. Concurrently, the dependence of band structure on pressure shows that a transition from semiconductor to metal occurs at 30 GPa. Band features close to Fermi level are discussed, such as narrow band from $\Gamma$ to A and pressure-induced decrease of the band dispersion, which are advantageous for high values of thermopower. Our transport calculations also find that pressure-enhanced electrical conductivities, as well as high values of thermopower (up to a few hundred $\mu$V/K), lead to significant values of thermoelectric figure of merit (above 0.10 for high pressure and even up to 0.65 at 30 GPa) over a wide temperature range. Our study supplies a new practical route to improve the thermoelectric performance of MoS$_2$ and of other transition metal dichalcogenides by applying hydrostatic pressure.
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http://arxiv.org/abs/1208.5941
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