Electronic structure, lattice dynamics, and thermoelectric properties of bismuth nanowire from first-principles calculat
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To reveal the electron and phonon transport mechanism in bismuth nanowire (BiNW), the electronic structure, the lattice dynamics, and the thermoelectric properties of bismuth bulk (BiB) and BiNW were investigated in this paper through first-principles calculation and the Boltzmann transport theory. The results suggest that BiNW possesses an increased electrical conductivity and Seebeck coefficient, while its thermal conductivity, especially phonon thermal conductivity, is reduced significantly as compared to BiB. As a consequence, a largely enhanced figure of merit (ZT) at 300 K of 2.73 is achieved for BiNW. The enhancement in electrical conductivity and Seebeck coefficient of BiNW is originated from its high density of states and large effective mass of carriers. Such significant suppression in phonon thermal conductivity of BiNW is ascribed to the reduced phonon vibration frequency, the decreased phonon density of states, and the shortened mean free path of phonons. So BiNW should be viewed as an excellent candidate for a thermoelectric material with a high figure of merit. Moreover, we have provided a complete understanding on the relationship between the electronic structure, the dynamics, and the thermoelectric properties of BiNW.
I. INTRODUCTION
Thermoelectric materials, which can be used as solidstate Peltier cooler or power generator from waste heat, have attracted more interests in recent years because of their increasingly important role in solving global fossil energy crisis and minimizing environmental pollution.1 The thermoelectric coefficient is evaluated by a dimensionless figure of merit (ZT), ZT ¼
a2 r T je þ jp
;
ð1Þ
where a is the Seebeck coefficient, r is the electrical conductivity, je and jp are the thermal conductivity contributed from electrons and phonons respectively, and T is absolute temperature. A thermoelectric material with an excellent performance needs a high electrical conductivity, a large Seebeck coefficient, and meanwhile a low thermal conductivity. However, these thermoelectric parameters cannot be optimized at the same time due to the existed and hardly solved conflicts among the thermoelectric variations, which restrict the further improvement in ZT.2 A high electrical conductivity should have a large concentration of carriers; however, it also leads to a decreased Seebeck coefficient and an increased electron
Contributing Editor: C. Robert Kao a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.88
thermal conductivity. A large effective mass of carriers is helpful to a large Seebeck coefficient but also harmful to a high electrical conductivity for its lowered mobility of carriers. A large Seebeck coefficient is often related a broad band gap; however, it also results in a lowered mobility of carriers and thereby a decreased electrical conductivity. Strong grain-boundary scattering is beneficial to a suppressed phonon thermal conductivity but also disadvantageous to electrical conductivity due to its strengthened electron scattering effe
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