Optimization of the Electronic Band Structure and the Lattice Thermal Conductivity of Solid Solutions According to Simple Calculations: A Canonical Example of the Mg2Si1–x–yGexSny Ternary Solid Solution

Yin, Kang; Su, Xianli; Yan, Yonggao; You, Yonghui; Zhang, Qiang; Uher, Ctirad; Kanatzidis, Mercouri G.; Tang, Xinfeng

doi:10.1021/acs.chemmater.6b02308

Cited by 56 publications

(28 citation statements)

References 80 publications

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“…4a. 70 A PF as high as~50 μW cm −1 K −2 is reached in both quasi-binary and quasi-ternary solid solutions of Mg 2 X-Mg 2 Sn when the alloy compositions are tuned within the convergence range.…”

Section: Valley Degeneracymentioning

confidence: 98%

Valleytronics in thermoelectric materials

et al. 2018

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The central theme of valleytronics lies in the manipulation of valley degree of freedom for certain materials to fulfill specific application needs. While thermoelectric (TE) materials rely on carriers as working medium to absorb heat and generate power, their performance is intrinsically constrained by the energy valleys to which the carriers reside. Therefore, valleytronics can be extended to the TE field to include strategies for enhancing TE performance by engineering band structures. This review focuses on the recent progress in TE materials from the perspective of valleytronics, which includes three valley parameters (valley degeneracy, valley distortion, and valley anisotropy) and their influencing factors. The underlying physical mechanisms are discussed and related strategies that enable effective tuning of valley structures for better TE performance are presented and highlighted. It is shown that valleytronics could be a powerful tool in searching for promising TE materials, understanding complex mechanisms of carrier transport, and optimizing TE performance.npj Quantum Materials (2018) 3:9 ; doi:10.1038/s41535-018-0083-6 INTRODUCTIONThe demand for renewable energy harvesting has been growing because of the limited fossil fuels and increasing worldwide energy consumption. Thermoelectric (TE) materials, which have the capability of converting heat directly into electricity under a temperature gradient, have been regarded as an alternative option to alleviate energy shortage.1 Though TE devices have already been applied in deep space exploration and solid state cooling, 2,3 the relatively low energy conversion efficiency limits their wide commercialization, 4 which is mainly constrained by the performance of TE materials as characterized by the dimensionless figure of merit, zT = α 2 σT/(κ e + κ L ), where α is the Seebeck coefficient, σ is the electrical conductivity, κ e and κ L are, respectively, the electronic and lattice contributions to the total thermal conductivity κ, and T is the absolute temperature.5 Since all three physical properties (α, σ, and κ) are carrier concentration dependent, zT could reach its maximum value at an optimized carrier concentration. zT max is determined by a combination of intrinsic physical parameters as well as the temperature, all of which integrated into a term called the TE quality factor, B. Higher quality factor B leads to higher zT max at a fixed temperature. With a single parabolic band model in the nondegenerate limit, B could be expressed as:

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Section: Valley Degeneracymentioning

confidence: 98%

Valleytronics in thermoelectric materials

et al. 2018

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“…In general, the Carnot conversion efficiency of thermoelectric materials is governed by the figure of merit ZT = S 2 σT /(κ e + κ L ), where T is the absolute temperature, S is the thermopower, σ is the electrical conductivity, while e and κ L are the electronic and lattice thermal conductivities, respectively (79). Optimal values for the power factor σS (PF) can be achieved in heavily doped semiconductors with a carrier concentration in the range of 1 × 10 19 cm −1 (80,81), with a narrow band gap which gives rise to large values of σ, while a sharp increase in the DOS around the Fermi level leads to an enhanced S according to Mott's theory (82). Due to their chemical and structural complexity, Zintl compounds exhibit inherently low lattice thermal conductivities together with favorable power factors (83)(84)(85).…”

Section: Properties For Energy Applicationsmentioning

confidence: 99%

Ternary mixed-anion semiconductors with tunable band gaps from machine-learning and crystal structure prediction

Amsler

Ward

Hegde

et al. 2019

Phys. Rev. Materials

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We report the computational investigation of a series of ternary X4Y2Z and X5Y2Z2 compounds with X={Mg, Ca, Sr, Ba}, Y={P, As, Sb, Bi}, and Z={S, Se, Te}. The compositions for these materials were predicted through a search guided by machine learning, while the structures were resolved using the minima hopping crystal structure prediction method. Based on ab initio calculations, we predict that many of these compounds are thermodynamically stable. In particular, 21 of the X4Y2Z compounds crystallize in a tetragonal structure with I-42d symmetry, and exhibit band gaps in the range of 0.3 and 1.8 eV, well suited for various energy applications. We show that several candidate compounds (in particular X4Y2Te and X4Sb2Se) exhibit good photo absorption in the visible range, while others (e.g., Ba4Sb2Se) show excellent thermoelectric performance due to a high power factor and extremely low lattice thermal conductivities.

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“…Mechanical alloying reduces the Mg losses to practically zero, due to it being conducted at low temperature and in Ar atmosphere 53 . This process is often used as a mixing and homogenization step, before reaction through other methods 56,95,99 , boron nitride 32 , and graphite 60 . Magnesium-based thermoelectric materials are also reported to have been synthesized through less common techniques such as melt spinning 112 , where the molten materials are injected onto a .…”

Section: Synthesis Methodsmentioning

confidence: 99%