Complex structured "electron-poor" framework semiconductors with potential for thermoeletric application

热电装置将热量清洁地转化为电能，在满足未来全球对高效能源管理的需求方面发挥着重要作用。然而，存在改进热电装置的显著障碍，这就是热电材料本身。最有希望的候选材料是具有低热导率的（重掺杂）窄隙半导体。虽然晶体化学机制已被确定为降低热导率，导致块体窄隙半导体的组成和结构的合理选择还没有很好地建立。我们提出了一个国际和跨学科的研究计划，旨在推进热电材料研究，以发现有前途的材料，并提供边界/重叠金属和半导体材料的新的科学认识。以最先进的热电Zn 4Sb 3为起点，我们在概念上将这种材料整合到一个更大的化合物类别中-贫电子框架半导体（EPFS）-其中包括元素硼。EPFS材料由金属和半金属原子制成，形成包含多中心键合结构实体的常见弱极性框架。局部多中心键合特征被认为是结构复杂半导体的关键。二元和三元EPFS材料，迄今已被确定和表征显示出有前途的热电性能，特别是显着的是他们的低热导率。通过化学合成，结构分析，计算建模和物理性能测量的组合，我们系统地探索EPFS材料的组成和结构潜力，并分析其键合性能及其独特的，但理想的，低导热率背后的机制。这项工作将作为三个机构之间的合作活动进行，亚利桑那州立大学（美国亚利桑那州立大学）、奥格斯堡大学（德国）和慕尼黑工业大学（德国）组成了一个研究小组，由化学和物理系的教职员工和学生组成。拟议活动的主要智力价值将是预测、制备和表征具有理想热电性能的新型窄隙半导体。此外，将实现对边界/重叠金属和半导体（包括硼基耐火半导体）的化学系统的复杂结构和键合机制的新的和结论性的见解。我们的研究将大大提高对热电性能的微观机制的理解，特别是晶格热导率。这将被用来制定原则，用于合理设计优秀的热电材料。通过国际合作，拟议研究项目的实验和理论方面将紧密结合。这对于揭示高热电性能背后的决定性结构-性质相关性至关重要。德国高通量中子源FRM-II（慕尼黑）的独特仪器将可供该项目使用。拟议活动产生的更广泛影响：能源技术已成为社会上要求最高、最具挑战性的问题之一。这里描述的项目通过与热电能量转换优化相关的基础研究为能源技术做出贡献。特别是，它利用了金属间化合物的潜力，将联合收割机结构复杂性与窄的电子带隙结合起来。金属间化合物是一大类无机固体，具有一系列不同的物理和化学性质。该项目推进了对复杂金属间化合物中的键合和结构-性能相关性的理解，为将这类化合物作为有用的材料用于能源技术的其他领域奠定了基础。为了加速这一努力，将组织一个讲习班，汇集金属间化合物化学键合方面的国际专门知识。通过向K-12学生（通过开发清晰但适当针对性的教室演示并为教师提供支持）和专业科学硕士（PSM）学生（通过将纳米科学研讨会课程中的主题纳入亚利桑那州的新兴技术领导者）传播拟议研究的各个方面，进一步解决能源技术日益增加的社会影响。拟议研究的国际/跨学科性质为学生培训提供了独特的机会。国际交流计划旨在整合研究（通过对合作实验室和设施的扩展研究访问）和教育（通过访问德国合作伙伴的着名国际硕士课程）。其目的是教育研究生对当今材料研究的复杂性，并沉浸在跨学科和国际研究。

Thermoelectric devices cleanly convert heat into electricity and play an important role in satisfying the future global demand for efficient energy management. However, there exists a significant barrier to improving thermoelectric devices and that is the thermoelectric materials themselves. The most promising candidate materials are (heavily doped) narrow-gap semiconductors with low thermal conductivity. While crystal chemical mechanisms have been identified for reducing the thermal conductivity, a rationale selection of compositions and structures leading to bulk narrow-gap semiconductors is not well established. We present an international and interdisciplinary research program aimed at advancing thermoelectric materials research to uncover promising materials and provide new scientific understanding of materials that border/overlap metals and semiconductors. Taking the state-of-the-art thermoelectric Zn4Sb3 as a starting point, we conceptually integrate this material into a larger class of chemical compounds – electron poor framework semiconductors (EPFSs) – which includes elemental boron at one extreme. EPFS materials, made from metal and semimetal atoms, form a common, weakly polar framework containing multi-center bonded structural entities. The localized multi-center bonding feature is thought to be the key to structurally complex semiconductors. Binary and ternary EPFS materials that have so far been identified and characterized show promising thermoelectric properties; especially remarkable is their low thermal conductivity. Through a combination of chemical synthesis, structure analysis, computational modeling, and physical property measurements we explore systematically the compositional and structural potential of EPFS materials, and analyze their bonding properties and the mechanisms behind their peculiar, but desirable, low thermal conductivity. The effort will be carried out as collaborative activity among three institutions, Arizona State University (ASU, USA), Augsburg University (Germany), and Technical University Munich (Germany) assembling a research group with faculty, staff and students from Chemistry and Physics departments.Intellectual merit of the proposed activity: The major intellectual merit of the proposed activity will be the prediction, preparation and characterization of new narrow gap semiconductors with desirable thermoelectric properties. Additionally, new and conclusive insights into the intricate structure and bonding mechanisms of chemical systems that border/overlap metals and semiconductors – including boron-based refractory semiconductors – will be achieved. Our research will yield a significantly improved understanding of the microscopic mechanisms fundamental to thermoelectric properties, especially lattice thermal conductivity. This will be used to formulate principles to be used in the rational design of outstanding thermoelectric materials. Through the international collaboration, the experimental and theoretical aspects of the proposed research project will be closely integrated. This is paramount for unveiling the decisive structure-property correlations behind high thermoelectric performance. Unique instrumentation at the German high flux neutron source FRM-II (Munich) will become accessible to the project.Broader impacts resulting from the proposed activity: Energy technology has become one of the most demanding and challenging issues of society. The project described here contributes to energy technology through fundamental research related to optimization of thermoelectric energy conversion. In particular, it exploits the potential of intermetallic compounds to combine structural complexity with a narrow electronic band gap. Intermetallic compounds are a large class of inorganic solids, with a range of distinct physical and chemical properties. This project advances the understanding of bonding and structure-property correlations in complex intermetallics, laying the groundwork for opening up this class of compounds as useful materials also for other areas of energy technology. To accelerate the effort, a workshop assembling international expertise on chemical bonding in intermetallic compounds will be organized. The increasing societal impact of energy technology is further addressed by disseminating aspects of the proposed research to K-12 students (by developing lucid but appropriately targeted class room demonstrations and providing support to teachers) and professional science master’s (PSM) students (by incorporating the topic in the nanoscience seminar course to these emerging technology leaders in` Arizona). The international/interdisciplinary character of the proposed research offers unique opportunities for student training. An international exchange program has been designed to integrating research (through extended research visits to collaborating laboratories and facilities) and education (through accessing the renowned international masters program of the German partners). The aim is to educate graduate students on the complexity of today’s materials research and immerse them in interdisciplinary and international research.