Rational Design of Thermoelectric Materials and Material Processing Approaches Based on Microwave Processing of Silicides

热电材料是当材料的两侧暴露在不同的温度下或反之亦然时能够产生电流的材料(即，向热电材料提供电压和电流可以改变其表面的温度)。热电材料是一种很有前途的技术，应用范围从发电到供暖和制冷。今天，大多数电力都是通过燃烧燃料来产生热量的过程产生的，这些热量将水转化为蒸汽，然后用于推动发电机，而低温蒸汽则被作为废物排放出去。这样的过程效率相对较低，只将燃料能量的30%到40%转化为有用的电力。热电材料可以用来将这些浪费的热能转化为有用的电能。该团队将设计和构建高效热电材料和器件，这些材料由非晶态(即非晶态、分子无序)和晶态材料的组合构成，可以最大限度地提高材料的导电性，同时将材料的导热系数降到最低，这是有效热电的理想组合。该项目将通过开发与纳米技术有关的大学课程，以及通过代表人数不足的学生直接参与研究，产生广泛的教育影响。工作的主要重点将是使用复合硅化物(即将硅与其他元素如金属结合的材料)来制造高效热电材料。更高效的热电材料的目标是实现大的热电效应，以便从废热源和环境之间相对较小的温差中产生大量电力。该项目是一项以计算为指导的材料设计工作，涵盖了非晶态材料的理论和实验两个方面。该程序解决了扩展态和局域态的电荷载流子的多模输运，以及无序多组分非晶结构中的声子输运性质。基于硅化物合金非晶态-晶态复合材料的新型材料结构有望显著提高材料的热电功率因数，同时降低材料的导热系数。这个研究概念是一种纳米尺度的效应，只有当载流子的能量分布函数不松弛到晶体中的主体材料的能量分布函数时才会发生。在大多数热电材料中，这种状态要求微晶尺寸小于10 nm，而现有的材料加工方法往往难以达到这一要求。本项目将开发一种新的材料合成方法，该方法基于微波腔中的场去结晶，可以制备非平衡硅化物材料。将首次研究氢化对热电性能的影响，并将展示材料生长技术的可扩展性。

Thermoelectric materials are materials that can produce an electric current when two sides of the material are exposed to different temperatures or vice-versa (i.e., supplying an electric voltage and current to a thermoelectric material can change the temperature of its surfaces). Thermoelectric materials are a promising technology for a range of application from electric power generation to heating and cooling. Most electric power today is produced from processes where fuel is burned to produce heat that turns water into steam that is then used to turn electric power generators, and low temperature steam is exhausted as waste. Such processes are relatively inefficient, converting only about 30 to 40 percent of the fuel's energy into useful electric power. Thermoelectric materials could be used to convert this wasted thermal energy into useful electric power. The team will design and construct high efficiency thermoelectric materials and devices from composite materials constructed from combinations of amorphous (i.e., non-crystalline, molecularly disordered) and crystalline materials that can maximize the material's electrical conductivity while minimizing the material's thermal conductivity, an ideal combination for effective thermoelectricity. The project will have broad educational impacts through both development of nanotechnology related university-level coursework and through the direct involvement of underrepresented students in the research.The primary focus of the work will be on the use of composite silicide (i.e., materials that combine silicon with other elements such as metals) to create highly efficient thermoelectrics. The target of more efficient thermoelectric materials is to achieve a large thermoelectric effect so that large amounts of electric power can be generated from relatively small temperature differences between waste heat sources and the environment. This project is a computationally guided material design effort which encompasses both theoretical and experimental aspects of amorphous based materials. The program addresses the multi-mode transport of charge carriers in extended and localized states, along with phonon transport properties in disordered multi-component amorphous structures. It is expected that new material structures based on amorphous-crystalline composites of silicide alloys developed in this work should result in significant nonlinear enhancement of the thermoelectric power factor, along with the reduction of the thermal conductivity of the materials. This research concept is a nanoscale effect that happens only if the energy distribution function of the carriers does not relax to that of the bulk material in the crystallites. This state requires crystallite sizes of sub-10 nm in most thermoelectric materials, which is often difficult to reach with the existing material processing methods. This project will develop a new material synthesis method based on field decrystallization in a microwave cavity that can produce non-equilibrium silicide materials. The effect of hydrogenation on thermoelectric properties will be investigated for the first time, and the scalability of the material growth technique will be demonstrated