Crystal Chemistry and Properties of Zintl Phases: Towards Efficient New Thermoelectrics

新化合物和晶体结构的合成仍然是追求新技术相关材料的一项极其重要的基础研究工作。这项研究由固态和材料化学计划资助，目标是合成具有技术应用的新化合物，特别是热电应用。热电材料能将热梯度转化为电。高效热电器件的设计是能量转换技术的主要目标。Zintl相是金属间化合物的一个子集，是热电应用的理想候选者，因为它们是具有复杂结构的半导体，具有低导热性，可以精确调节载流子浓度。在这个结构-性质关系研究中，将针对特定的Zintl结构来测试基于原子级修饰的性质结果的想法。长期目标是发现新的高效热电材料。短期目标包括建立对最佳Zintl结构的理解，以实现有效的热电能量转换，并为其他技术应用发现新的磁性和电子特性。有了这个NSF资助，首席研究员帮助教育下一代STEM劳动力。从高中到研究生院的学生都接受实践培训，他们的科学和社会技能通过研讨会和个人指导得到发展。下一代科学家接受的培训是考虑新材料及其对未来能源需求，特别是热电技术的影响。本基金支持基础研究工作，以制备新的Zintl相化合物并测量其性能，目的是发现新的热电材料并提高其热电性能。研究重点是研究a)在高温下有望获得高zT的14-1-11 Zintl相的新变体，以及b)具有低导热性的新型铕基材料。通过熔剂、冶金路线和火花等离子烧结，合成了单晶、高纯度粉末和颗粒状的新化合物。使用了一套物理表征技术，包括单晶和粉末x射线衍射，电子探针，电和磁测量。结构和相组成随后与电子和热输运性质相关。有了这项NSF拨款，首席研究员将指导从高中开始科学事业的学生到本科生，并与研究生合作，最终为科学事业提供专业培训。为学生提供实践培训，并通过研讨会和个人指导发展他们的科学和社会技能。这项研究在国内和国际会议上发表，研究结果发表在同行评议期刊上。

PART 1:   NON-TECHNICAL SUMMARYThe synthesis of new compounds and crystal structures remains an extremely important fundamental research endeavor in the pursuit of new technologically relevant materials. This research, funded by the Solid State and Materials Chemistry Program targets the synthesis of new compounds with technological applications, specifically thermoelectric applications. Thermoelectric materials can convert a heat gradient into electricity. The design of efficient thermoelectric devices is a major goal for energy conversion technologies. Zintl phases, which are a subset of intermetallics are ideal candidates for thermoelectric applications as they are semiconductors with complex structures which provide low thermal conductivity, which allows for precise tuning of carrier concentration. In this structure-property relationship study specific Zintl structures will be targeted to test ideas for property outcomes based on atomic-level modifications. The long-term goal is to discover new highly efficient thermoelectric materials. Short term goals include building an understanding of best Zintl structures for efficient thermoelectric energy conversion and discovery of new magnetic and electronic properties for other technological applications. With this NSF grant the principal investigator helps educate the next generation of the STEM workforce. Students from high school through graduate school are provided hands-on training and their scientific and social skills are developed through workshops and individual mentorship. The next generation of scientists is trained to consider novel materials and their impact on technology for our future energy needs and specifically thermoelectrics.PART 2:   TECHNICAL SUMMARYThis grant supports fundamental research efforts to prepare new Zintl phase compounds and measure their properties with a goal of discovering new thermoelectric materials and enhancing their thermoelectric properties. The research focuses on studying a) new variants of 14-1-11 Zintl phases for which high zT is expected at high temperatures, and b) novel Europium-based materials exhibiting low thermal conductivity. New compounds are synthesized as single crystals, high purity powders and pellets via flux, metallurgical routes, and spark plasma sintering. A suite of physical characterization techniques is utilized, including single crystal and powder X-ray diffraction, electron microprobe, electrical and magnetic measurements. Structure and phase composition is subsequently correlated with electronic and thermal transport properties. With this NSF grant the principal investigator mentors science students starting their science careers in high school to undergraduates in partnerships with graduate students, ultimately providing professional training for scientific careers. Students are provided hands-on training and their scientific and social skills are developed through workshops and individual mentorship. The research is presented at national and international meetings and the findings published in peer-review journals.