Mechanisms for enhancing n-type polaronic transport in transition metal oxides: ionic size, pair formation/clustering, and valence effects

非技术摘要该奖项支持一个专注于研究一组称为过渡金属氧化物材料的项目。这些材料是制造储能设备（如锂离子电池）和转换能量（如太阳能电池）的有希望的候选材料。然而，它们的效率从根本上受到它们中负电荷和正电荷的缓慢移动的限制，限制了它们在实际应用中的使用。这些电荷运动受限的主要原因是它们被材料原子结构的扭曲所捕获。该项目将研究使用掺杂剂来改善这些过渡金属氧化物的代表氧化铁中的电荷的流动性。它将确定“良好”掺杂剂的设计原则，这些掺杂剂可以改善这些氧化物中电荷的传输，以便它们可以用于实际能源应用。本项目将培养本科生和研究生，并将开展涉及高中生的推广活动，重点是扩大代表性不足的学生的参与。技术摘要本研究项目旨在定量研究限制电荷传输的机制，包括外部n型掺杂剂的聚集如何发生，电子小极化子和（成簇的）掺杂剂之间的相互作用如何影响电子输运性质，以及什么步骤可能增加过渡金属氧化物中的载流子浓度。该项目将首先使用具有代表性的极化氧化物赤铁矿，掺杂锡和其他4+/5+离子作为研究的模型系统。掺杂剂聚集被认为是由于离子尺寸失配，并因此限制了载流子电导率。研究团队将采用“共掺杂”策略，提高掺杂剂的溶解度，避免成团，并相应提高载流子迁移率作为掺杂浓度的函数。在这个项目中的一个关键步骤是确定本地环境的外部掺杂剂和掺杂剂集群，如果/如何修改时，第二掺杂剂被纳入，这项工作将结合联合收割机物理测量与第一原理模拟。本项目的研究结果可以为合理设计具有改善输运性质的极化氧化物提供规则，更重要的是，对决定孤立掺杂剂是否具有良好的导电性的关键因素有了基本的了解，掺杂剂簇或共-该奖项反映了NSF的法定使命，并通过利用基金会的智力价值进行评估，更广泛的影响审查标准。

Non-Technical Abstract This award supports a project focused on studying a group of materials called transition metal oxides. These materials are promising candidates for making devices for storing energy such as lithium-ion batteries and for converting energy such as solar cells. However, their efficiency has been fundamentally limited by the slow movement of negative and positive charges in them, restricting their use in practical applications. The main reason for the restricted movement of these charges is that they get trapped by the distortions in the materials’ atomic structure. This project will investigate the use of dopants to improve the mobility of the charges in iron oxide, a representative of these transition metal oxides. It will determine the design principles of “good” dopants that improve the transport of charges in these oxides so that they can be used in practical energy applications. The project will train undergraduate and graduate students and will engage in outreach activities involving high school students, emphasizing in broadening participation of underrepresented students.Technical Abstract This research project aims to quantitatively investigate the mechanisms that limit charge transport, including how the clustering of extrinsic n-type dopants takes place, how the interaction between electron small polarons and (clustered) dopants affects the electronic transport properties, and what steps might increase the carrier concentration in transition metal oxides. This project will initially use hematite, a representative polaronic oxide, doped with tin and other 4+/5+ ions as a model system for the study. The dopant clustering is believed to be due to ionic size mismatch, and consequently limit the carrier conductivity. The research team will use a “co-doping” strategy to improve the solubility of dopants and avoid clustering and correspondingly enhance carrier mobility as a function of doping concentration. A crucial step in this project is determining the local environment about extrinsic dopants and dopant clusters and if/how they are modified when the second dopants are incorporated; this work will combine physical measurements with first-principles simulations. The findings in this project can provide rules for rational design of polaronic oxides with improved transport properties, and more importantly, develop a fundamental understanding of key factors determining whether an isolated dopant, dopant cluster or co-doping can be beneficial or harmful for transport properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.