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비만아 부모의 돌봄 경험: q 방법론

Physical Review B

There has been a renaissance of interest in exploring highly efficient thermoelectric materials as a possible route to address the worldwide energy generation, utilization, and management. This review describes the recent advances in designing high-performance bulk thermoelectric materials. We begin with the fundamental stratagem of achieving the greatest thermoelectric figure of merit ZT of a given material by carrier concentration engineering, including Fermi level regulation and optimum carrier density stabilization. We proceed to discuss ways of maximizing ZT at a constant doping level, such as increase of band degeneracy (crystal structure symmetry, band convergence), enhancement of band effective mass (resonant levels, band flattening), improvement of carrier mobility (modulation doping, texturing), and decrease of lattice thermal conductivity (synergistic alloying, second-phase nanostructuring, mesostructuring, and all-length-scale hierarchical architectures). We then highlight the decoupling of th...

Rationally Designing High-Performance Bulk Thermoelectric Materials

BACKGROUND Heat and electricity are two forms of energy that are at opposite ends of a spectrum Heat is ubiquitous, but with low quality, whereas electricity is versatile, but its production is demanding Thermoelectrics offers a simple and environmentally friendly solution for direct heat-to-electricity conversion A thermoelectric (TE) device can directly convert heat emanating from the Sun, radioisotopes, automobiles, industrial sectors, or even the human body to electricity Electricity also can drive a TE device to work as a solid-state heat pump for distributed spot-size refrigeration TE devices are free of moving parts and feasible for miniaturization, run quietly, and do not emit greenhouse gasses The full potential of TE devices may be unleashed by working in tandem with other energy-conversion technologies Thermoelectrics found niche applications in the 20th century, especially where efficiency was of a lower priority than energy availability and reliability Broader (beyond niche) application of thermoelectrics in the 21st century requires developing higher-performance materials The figure of merit, ZT, is the primary measure of material performance Enhancing the ZT requires optimizing the adversely interdependent electrical resistivity, Seebeck coefficient, and thermal conductivity, as a group On the microscopic level, high material performance stems from a delicate concert among trade-offs between phase stability and instability, structural order and disorder, bond covalency and ionicity, band convergence and splitting, itinerant and localized electronic states, and carrier mobility and effective mass ADVANCES Innovative transport mechanisms are the fountain of youth of TE materials research In the past two decades, many potentially paradigm-changing mechanisms were identified, eg, resonant levels, modulation doping, band convergence, classical and quantum size effects, anharmonicity, the Rashba effect, the spin Seebeck effect, and topological states These mechanisms embody the current states of understanding and manipulating the interplay among the charge, lattice, orbital, and spin degrees of freedom in TE materials Many strategies were successfully implemented in a wide range of materials, eg, V2VI3 compounds, VVI compounds, filled skutterudites and clathrates, half-Heusler alloys, diamond-like structured compounds, Zintl phases, oxides and mixed-anion oxides, silicides, transition metal chalcogenides, and organic materials In addition, advanced material synthesis and processing techniques, for example, melt spinning, self-sustaining heating synthesis, and field-assisted sintering, helped reach a much broader phase space where traditional metallurgy and melt-growth recipes fell short Given the ubiquity of heat and the modular aspects of TE devices, these advances ensure that thermoelectrics plays an important role as part of a solutions package to address our global energy needs OUTLOOK The emerging roles of spin and orbital states, new breakthroughs in multiscale defect engineering, and controlled anharmonicity may hold the key to developing next generation TE materials To accelerate exploring the broad phase space of higher multinary compounds, we need a synergy of theory, machine learning, three-dimensional printing, and fast experimental characterizations We expect this synergy to help refine current materials selection and make TE materials research more data driven We also expect increasing efforts to develop high-performance materials out of nontoxic and earth-abundant elements The desire to move away from Freon and other refrigerant-based cooling should shift TE materials research from power generation to solid-state refrigeration International round-robin measurements to cross-check the high ZT values of emerging materials will help identify those that hold the most promise We hope the renewable energy landscape will be reshaped if the recent trend of progress continues into the foreseeable future

http://science.sciencemag.org/content/sci/357/6358/eaak9997.full.pdf

Advances in thermoelectric materials research: Looking back and moving forward

The past two decades have witnessed the rapid growth of thermoelectric (TE) research. Novel concepts and paradigms are described here that have emerged, targeting superior TE materials and higher TE performance. These superior aspects include band convergence, "phonon-glass electron-crystal", multiscale phonon scattering, resonant states, anharmonicity, etc. Based on these concepts, some new TE materials with distinct features have been identified, including solids with high band degeneracy, with cages in which atoms rattle, with nanostructures at various length scales, etc. In addition, the performance of classical materials has been improved remarkably. However, the figure of merit zT of most TE materials is still lower than 2.0, generally around 1.0, due to interrelated TE properties. In order to realize an "overall zT > 2.0," it is imperative that the interrelated properties are decoupled more thoroughly, or new degrees of freedom are added to the overall optimization problem. The electrical and thermal transport must be synergistically optimized. Here, a detailed discussion about the commonly adopted strategies to optimize individual TE properties is presented. Then, four main compromises between the TE properties are elaborated from the point of view of the underlying mechanisms and decoupling strategies. Finally, some representative systems of synergistic optimization are also presented, which can serve as references for other TE materials. In conclusion, some of the newest ideas for the future are discussed.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201702816

Compromise and Synergy in High-Efficiency Thermoelectric Materials.

Thermoelectric materials could be used to convert waste heat into useful electricity, but the ideal substance needs to both optimize the electrical power factor and suppress thermal conductivity. Here, the authors report a high figure of merit of 1.5 at 1,200 K in the p-type half-Heusler alloy FeNbSb.

/pdf/realizing-high-figure-of-merit-in-heavy-band-p-type-half-i1ey9au6d0.pdf

Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials.

We report new p-type FeNb1−xTixSb (0.04 ≤ x ≤ 0.24) half-Heusler thermoelectric materials with a maximum zT of 1.1 at 1100 K, which is twice that of the ZrCoSb half-Heusler alloys. The electrical properties are optimized by a tradeoff between the band effective mass and mobility via a band engineering approach. A high content of Ti up to x = 0.2 optimizes the power factor and reduces the lattice thermal conductivity. In view of abundantly available elements, good stability and high zT, FeNb1−xTixSb alloys could be promising materials for high temperature power generation.

Band engineering of high performance p-type FeNbSb based half-Heusler thermoelectric materials for figure of merit zT > 1

Half-Heusler (HH) compounds have gained ever-increasing popularity as promising high temperature thermoelectric materials. High figure of merit zT of ≈1.0 above 1000 K has recently been realized for both n-type and p-type HH compounds, demonstrating the realistic prospect of these high temperature compounds for high efficiency power generation. Here, recent progress in advanced fabrication techniques and the intrinsic atomic disorders in HH compounds, which are linked to the understanding of the electrical transport, is discussed. Thermoelectric transport features of n-type ZrNiSn-based HH alloys are particularly emphasized, which is beneficial to further improving thermoelectric performance and comprehensively understanding the underlying mechanisms in HH thermoelectric materials. The rational design and realization of new high performance p-type Fe(V,Nb)Sb-based HH compounds are also demonstrated. The outlook for future research directions of HH thermoelectric materials is also discussed.

High Efficiency Half-Heusler Thermoelectric Materials for Energy Harvesting

Electron and phonon transport characteristics determines the potential of thermoelectric materials for power generation or refrigeration. This work shows that, different from most of high performance thermoelectric materials with dominant acoustic phonon scattering, the promising ZrNiSn based half-Heusler thermoelectric solid solutions exhibit an alloy scattering dominated charge transport. A low deformation potential and a low alloy scattering potential are found for the solid solutions, which is beneficial to maintain a relatively high electron mobility despite of the large effective mass, and can be intrinsic favorable features contributing to the noticeably high power factors of ZrNiSn based alloys. A quantitive description of the different phonon scattering mechanisms suggests that the point defect scattering is the most important mechanism that determines the phonon transport process of the solid solutions. The present results indicate that alloying can be an effective approach for such materials systems to enhance thermoelectric figure of merit ZT by reducing phonon thermal conductivity, while minimizing the deterioration of charge mobility due to the low alloy scattering potential.

Chenguang Fu

Papers

Compromise and Synergy in High-Efficiency Thermoelectric Materials.

Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials.

Band engineering of high performance p-type FeNbSb based half-Heusler thermoelectric materials for figure of merit zT > 1

High Efficiency Half-Heusler Thermoelectric Materials for Energy Harvesting

Beneficial Contribution of Alloy Disorder to Electron and Phonon Transport in Half-Heusler Thermoelectric Materials