New insight into the material parameter B to understand the enhanced thermoelectric performance of Mg2Sn1−x−yGexSby

Liu, Weishu; Zhou, Jiawei; Qi, Jie; Li, Yang; Kim, Hee Seok; Bao, Jiming; Chen, Gang; Ren, Zhifeng

doi:10.1039/c5ee02600h

Cited by 91 publications

(88 citation statements)

References 52 publications

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“…According to our recent understanding [30], in the Sn-poor region (purple in Fig. 1a), it would have a light band (C L -band) at the bottom which is mainly from the hybridized 3p orbital of Mg with the s-orbital and d-e g orbital of IV elements (i.e., Sn, Ge, Si) as shown in Fig.…”

Section: Introductionmentioning

confidence: 91%

Thermoelectric properties of materials near the band crossing line in Mg2Sn–Mg2Ge–Mg2Si system

et al. 2016

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Thermoelectric properties of Mg 2 (Sn 0.765 Ge 0.22 Sb 0.015 ) 1-x (Sn 0.685 Si 0.3 Sb 0.015 ) x materials with compositions on and near the line connecting Mg 2 Sn 0.765 Ge 0.22 Sb 0.015 and Mg 2 Sn 0.685 Si 0.3 Sb 0.015 in the Mg 2 Sn-Mg 2 Ge-Mg 2 Si system are investigated. Although ZTs are very similar, power factors are different. On the line, the power factor decreases from Mg 2 Sn 0.765 Ge 0.22 Sb 0.015 to Mg 2 Sn 0.685 Si 0.3 Sb 0.015 , and off the line, the power factor also decreases. The output power and energy conversion efficiency are calculated using engineering power factor (PF) eng and figure of merit (ZT) eng . It is shown that although similar energy conversion efficiency of ~11% could be achieved for all compositions studied, the output power are different, increasing from ~9.1 W cm -2 for Mg 2 Sn 0.685 Si 0.3 Sb 0.015 to ~10.3 W cm -2 for Mg 2 Sn 0.765 Ge 0.22 Sb 0.015 , due to the different power factors.

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Section: Introductionmentioning

confidence: 91%

Thermoelectric properties of materials near the band crossing line in Mg2Sn–Mg2Ge–Mg2Si system

et al. 2016

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“…66,67 In Mg 2 X, above the conduction band minimum, there exists another sub-band which usually does not contribute to the transport due to large splitting energy from the band minimum (−0.4 eV for Mg 2 Si, 68 0.16 eV for Mg 2 Sn 69 ). As the two conduction band edges (one heavier and another lighter) are reversely positioned in Mg 2 Sn, compared with that in Mg 2 Si and Mg 2 Ge, it is possible to converge these two band edges (with splitting energy ≈0) through alloying, as revealed in Fig.…”

Section: Valley Degeneracymentioning

confidence: 99%

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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“…Amongst the binary compounds, n -type Mg 2 Si 9, 10 and Mg 2 Sn 11 exhibit inherently higher thermoelectric performance than Mg 2 Ge 12 . Following the high z T of 1.1 reported for the pseudo-binary Mg 2 Si-Mg 2 Sn system 8 , originating from mass-difference phonon scattering and conduction band convergence 8 , considerable efforts have been devoted to fabricating and characterising complex ternary 2, 13, 14 and quaternary 2, 15, 16 compounds. Whereas, binary Mg 2 Ge has received very limited attention, with only two experimental reports on n -type Sb-doped samples 12, 17 and a single report on p -type Ag-doped Mg 2 Ge thin films 18 .…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric performance of n-type Mg2Ge

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et al. 2017

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Magnesium-based thermoelectric materials (Mg2X, X = Si, Ge, Sn) have received considerable attention due to their availability, low toxicity, and reasonably good thermoelectric performance. The synthesis of these materials with high purity is challenging, however, due to the reactive nature and high vapour pressure of magnesium. In the current study, high purity single phase n-type Mg2Ge has been fabricated through a one-step reaction of MgH2 and elemental Ge, using spark plasma sintering (SPS) to reduce the formation of magnesium oxides due to the liberation of hydrogen. We have found that Bi has a very limited solubility in Mg2Ge and results in the precipitation of Mg2Bi3. Bismuth doping increases the electrical conductivity of Mg2Ge up to its solubility limit, beyond which the variation is minimal. The main improvement in the thermoelectric performance is originated from the significant phonon scattering achieved by the Mg2Bi3 precipitates located mainly at grain boundaries. This reduces the lattice thermal conductivity by ~50% and increases the maximum zT for n-type Mg2Ge to 0.32, compared to previously reported maximum value of 0.2 for Sb-doped Mg2Ge.

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New insight into the material parameter B to understand the enhanced thermoelectric performance of Mg₂Sn_1−x−yGe_xSb_y

Cited by 91 publications

References 52 publications

Thermoelectric properties of materials near the band crossing line in Mg2Sn–Mg2Ge–Mg2Si system

Thermoelectric properties of materials near the band crossing line in Mg2Sn–Mg2Ge–Mg2Si system

Valleytronics in thermoelectric materials

Thermoelectric performance of n-type Mg2Ge

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