Abstract
Valley anisotropy is a favorable electronic structure feature that could be utilized for good thermoelectric performance. Here, taking advantage of the single anisotropic Fermi pocket in p-type Mg3Sb2, a feasible strategy utilizing the valley anisotropy to enhance the thermoelectric power factor is demonstrated by synergistic studies on both single crystals and textured polycrystalline samples. Compared to the heavy-band direction, a higher carrier mobility by a factor of 3 is observed along the light-band direction, while the Seebeck coefficient remains similar. Together with lower lattice thermal conductivity, an increased room-temperature zT by a factor of 3.6 is found. Moreover, the first-principles calculations of 66 isostructural Zintl phase compounds are conducted and 9 of them are screened out displaying a pz-orbital-dominated valence band, similar to Mg3Sb2. In this work, we experimentally demonstrate that valley anisotropy is an effective strategy for the enhancement of thermoelectric performance in materials with anisotropic Fermi pockets.
Highlights
Valley anisotropy is a favorable electronic structure feature that could be utilized for good thermoelectric performance
The conversion efficiency is governed by the dimensionless figure of merit zT of the used TE materials, zT = S2σ/(κL + κe), where S, σ, κL, and κe stand for Seebeck coefficient, electrical conductivity, lattice and electronic component of the thermal conductivity κ, respectively[2]
To facilitate the analysis of the relation between the valley direction in the reciprocal space and the crystallographic direction in the real space, an anisotropic Fermi pocket locates at the center of the Brillouin zone (BZ) is desirable
Summary
Valley anisotropy is a favorable electronic structure feature that could be utilized for good thermoelectric performance. This low-dimensionality strategy sparked the studies of TE materials with nanostructures, such as quantumwell superlattice structures[4], nanowires[6]. Apart from distorting the DOS with the resonant level, converging the electronic bands to achieve high valley degeneracy Nv was demonstrated as a general strategy to boost the TE performance of bulk materials, such as PbTe1−xSex[8] and Mg2Si1−xSnx[9]. From the view of band structure engineering, both resonant level and band convergence strategies target the enhanced DOS near EF, leading to the improvement of S, similar to the low-dimensionality strategy
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