Synthesis of Zintl Phases for Thermoelectric Applications

技术概要：该项目由固态和材料化学计划支持，重点是合成新的Zintl相，引入过渡金属，以在费米能级（通过部分填充的d轨道）实现高态密度（DOS），从而获得高塞贝克系数（功率因数）和高zT。纳米结构将被用于进一步降低导热性。相将通过熔剂和冶金途径合成。利用一套物理表征技术，包括单晶和粉末X射线衍射，SEM和TEM，元素波色散微探针和ICP-MS分析，平行的电和磁测量，结构和相组成将与电子和热输运性质相关。该项目的最终目标是发现具有高zT的新材料，用于将废热直接转化为电能。基于最近在Zintl相中证明的高zT的结果，该提议将合成策略与物理和化学性质的表征紧密联系起来，从而提供有效的反馈以指导这些热电系统的改进。用于发电的热电装置将热能直接转换成电能，需要最少的维护，并且可以在大的温度范围（室温至1000摄氏度）上操作。热电材料由品质因数zT描述，zT与材料将热流转化为电能的程度有关-值越高，效率越高。最近发现zT为1.0或更高的Zintl相，突出了继续探索新材料的重要性。Zintl相是含有碱金属、碱土金属和稀土元素等阳离子的化合物，其向由周期表第13、14和15族等主族元素构成的聚阴离子单元提供电子。这些类型的化合物自然地提供低热导率，这是热电装置的要求。随着zT的提高，废热回收固态发电的潜力为研究在高温（300摄氏度）下具有稳定性和最佳性能的新Zintl相材料提供了一个框架。该项目在初级阶段（从高中到大学，从大学到研究生院）支持少数民族和妇女，沿着培训研究生从事科学事业。学生通过实践培训，探索和向更广泛的科学界传播研究来培养科学，社会和专业技能。正在研究的主题包括材料合成和性能测量，材料合成和结构-性能相关性的基础培训，为热能到电能转换的发展和多学科研究与技术的进步提供了重要基础。这项研究将在国家和国际会议上发表，研究结果将发表在同行评审期刊上。此外，PI通过ACS SEED计划（高中），MURPPS（本科）和AGEP（研究生）计划支持学生，这些计划专注于增加校园科学中代表性不足的群体。ChemWiki将通过写作和批判性评价来提高学生的学习能力。

TECHNICAL SUMMARY: This project, supported by the Solid State and Materials Chemistry program focuses on the synthesis of new Zintl phases, incorporating transition metals in order to target a high density of states (DOS) at the Fermi level (through partially filled d orbitals) to obtain high Seebeck coefficient (Power factor) and therefore high zT. Nanostructuring will be employed to further reduce the thermal conductivity. Phases will be synthesized via flux and metallurgical routes. Utilizing a suite of physical characterization techniques including single crystal and powder X-ray diffraction, SEM and TEM, elemental wave dispersive microprobe and ICP-MS analysis, parallel electrical and magnetic measurements, the structure and phase composition will be correlated with electronic and thermal transport properties. The ultimate goal of the project is to discover new materials with high zT for the direct conversion of waste heat into electricity. Building upon recent results of demonstrated high zT in Zintl phases, this proposal closely links synthetic strategies with characterization of physical and chemical properties, thus providing efficient feedback to guide improvement of these thermoelectric systems.NON-TECHNICAL SUMMARY: Thermoelectric devices for power generation convert thermal energy directly into electrical energy, require minimal maintenance, and can be operated over a large temperature range (room temperature to 1000 degrees C). Thermoelectric materials are described by a figure of merit, zT, which relates to how well a material converts heat flow to electricity - the higher the value, the greater the efficiency. Recent discoveries of Zintl phases with zT of 1.0 or greater highlight the importance of continued exploration of new materials. A Zintl phase is a compound which contains both cations such as alkali, alkaline earth, and rare earth elements which donate electrons to polyanionic units composed of main group elements such as those from groups 13, 14, and 15 of the periodic table. These types of compounds naturally provide low thermal conductivity which is a requirement for thermoelectric devices. With higher zT, the potential for solid-state power generation from waste heat recovery provides a framework for investigating new Zintl phase materials with stability and optimal properties at high temperatures (300 degrees C). This project supports minorities and women at the initial stages (high school to college and college to graduate school), along with training graduate student for scientific careers. Students develop scientific, social, and professional skills through hands-on training, exploration, and dissemination of research to the broader scientific community. The topics under study include materials synthesis and property measurements, fundamental training in materials synthesis and structure-property correlations, providing an important foundation for the development of thermal to electrical energy conversion and the advancement of multidisciplinary research aligned with technology. The research will be presented at national and international meetings and the findings published in peer-review journals. Additionally, the PI supports students through the ACS SEED program (high school), MURPPS (undergraduate), and AGEP (graduate) programs focused on increasing underrepresented groups in science on campus. The ChemWiki will be employed to enhance student learning through writing and critical evaluation.