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Negative Thermal Expansion Materials under Pressure: a New Route for High Performance Thermoelectrics

压力下负热膨胀材料：高性能热电材料的新途径

基本信息

批准号：
313705203
负责人：
Professor Denis Music, Ph.D., since 3/2018
金额：
--
依托单位：
College of Engineering and Computing
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/313705203?language=en
关键词：
Negative Thermal Expansion Materials under

项目摘要

Thermoelectrics offer an attractive pathway for addressing an important niche in the globally growing landscape of energy demand, since they can convert heat and, in particular waste heat, to electricity. In the past decades, searching for high efficiency thermoelectrics has been guided by the concept of phonon glass electron crystal. Despite remarkable progress have been made under this concept, the energy conversion performance is still well below what is needed for thermoelectrics to compete with traditional electricity producing methods, primarily due to the nature of strong coupling between electronic and phononic transport. This proposal aims at exploring a new area where the electronic and phononic transport can be decoupled, when negative thermal expansion material, pressure, and thermoelectrics meet together.Negative thermal expansion materials have inherent nature that a large number of low frequency acoustic phonons possess strong phonon anharmonicity compared with less flexible materials, leading to very low intrinsic thermal conductivity, which is beneficial for thermoelectrics. However, they have not been extensively studied for thermoelectrics so far, due to the low thermopower or extremely low temperature range that negative thermal expansion normally occurs. Herewith we propose a new concept of applying pressure to enhance the thermoelectric coefficient by taking advantage of the unique feature that the electrical and phononic transport properties can be largely tuned in an opposite way.The overall goal of this project is to advance the fundamental science underlying the electrical and phononic transport properties of some representative negative thermal expansion materials under mechanical compression and rationally performed doping and alloying as novel strategy for high efficiency thermoelectrics. Combined anharmonic lattice dynamics based on first principles and Boltzmann transport equation are proposed as approaches to this end. The result of these investigations is likely to provide a major advancement to rational optimizing of thermoelectrics based on negative thermal expansion materials, with the potential to make a clear contribution to the energy needs of the future.The novelty of this project manifests itself in that, applying pressure to negative thermal expansion materials not only reduces the lattice thermal conductivity by augmenting phonon anharmonicity, but also largely enhances their thermopower and pushes the negative thermal expansion range upward to higher temperatures, which in turn achieves decoupling the electrical and phononic transport in thermoelectrics and results in significant improvement in thermoelectric performance. Such opposing effects have never been realized in traditional methods for optimizing thermoelectric materials, where the electrical and phononic transport is always strongly correlated and acts in unison.

热电为解决全球不断增长的能源需求格局中的一个重要利基市场提供了一条有吸引力的途径，因为它们可以将热量，特别是废热转化为电力。在过去的几十年里，声子玻璃电子晶体的概念一直指导着对高效率热电器件的研究。尽管在这一概念下已经取得了显着的进展，但能量转换性能仍然远低于热电与传统发电方法竞争所需的能量转换性能，这主要是由于电子和声子传输之间的强耦合的性质。负热膨胀材料具有固有的性质，即大量的低频声学声子具有较强的声子非谐性，与柔性较差的材料相比，具有很低的本征热导率，这对热电材料是有利的。然而，由于通常发生负热膨胀的低热功率或极低的温度范围，迄今为止还没有对它们进行广泛的热电研究。本文提出了一种利用负热膨胀材料的电学和声子输运性质可以反向调节的特点，通过施加压力来提高热电系数的新概念，旨在研究具有代表性的负热膨胀材料在机械压缩下的电学和声子输运性质的基础科学，并对其进行合理的应用掺杂和合金化作为高效热电的新策略。基于第一性原理和玻尔兹曼输运方程的组合非谐晶格动力学的方法，提出了这一目的。这些研究的结果很可能为基于负热膨胀材料的热电器件的合理优化提供重大进展，并有可能为未来的能源需求做出明确的贡献。该项目的新奇体现在，向负热膨胀材料施加压力不仅通过增加声子非谐性来降低晶格热导率，而且极大地增强了它们的热电势，并将负热膨胀范围向上推到更高的温度，这又实现了热电器件中的电和声子输运的解耦，并导致热电性能的显著改善。在优化热电材料的传统方法中从未实现过这种相反的效果，其中电和声子传输总是强烈相关并一致地起作用。