RUI: Developing Insight and Control of Polarity in the Pyrochlore Lattice

许多能源和技术驱动的应用依赖于利用铅的化学特性的材料。然而，铅的已知毒性和随后的法规促使人们研究用于技术应用的替代元素。在材料研究部门的固态和材料化学计划以及刺激竞争研究的既定计划（EPSCoR）的共同支持下，该项目旨在了解原子的排列和相互作用，这些原子产生了应用所需的物理特性，并将重点关注广泛研究但知之甚少的称为烧绿石氧化物的材料家族。通过这项工作发现的原则将加深对烧绿石氧化物的理解，为实现铅基技术的替代品提供新的知识。本科教育和接触固态化学是这项研究的核心，提供一种促进兴奋和包容所有人的体验是至关重要的。在贝茨学院，主要是本科院校的地方，这项工作非常适合对化学，材料科学，能源和电子应用的可持续方法感兴趣的学生。通过参与这项研究，学生将接触到本科化学课程中通常没有涉及的技术，并在本科院校经常未充分利用的设施中进行尖端实验。除了独立的研究，这项工作将促进专业发展的参与者通过有目的的讨论的职业道路，与外部科学家的互动，并在整个参与活动进行反思。技术摘要极性晶体结构包括一类材料，具有广泛的技术应用，特别是作为电子设备中的组件。虽然这些材料的使用很广泛，但它们通常依赖于Pb的电子孤对化学，因此寻找不牺牲性能的替代无铅材料非常重要。 目前的研究主要集中在钙钛矿氧化物，由于高温稳定性，易于制备和广泛的化学取代基。然而，关于钙钛矿氧化物的大量文献没有提供绕过Pb的使用的明确方法。改变烧绿石氧化物中金属阳离子和阴离子化学计量的能力为获得无铅极性晶体结构提供了通用平台。由于其复杂的晶体结构，钙钛矿的研究较少，但测量和计算技术的最新发展使得研究和确定这些材料中长程极性的原因成为可能。这项研究得到了材料研究部的固态和材料化学计划以及刺激竞争研究的既定计划（EPSCoR）的支持，将应用钙钛矿极性原因的知识来系统地调查和确定火辉石中极性的基本驱动因素。在烧绿石结构中发现的互穿网络将通过不同金属阳离子的系统取代而解耦，即那些可以引起二阶Jahn-Teller畸变（s2或d 0电子构型）的金属阳离子。将具有可能导致结构扭曲的金属离子的材料的详细结构与具有不会导致扭曲的阳离子的材料进行比较，将提供对导致长程极性的潜在化学的见解。除了阳离子取代，这项工作将调查结构，局部扭曲和整体极性的阴离子化学计量的影响。 结构观察将通过介电常数和非线性光学行为的表征与物理性质测量相关联。本科生研究人员将主要参与贝茨学院（一个主要的本科院校）的现场样品制备和表征，以及国家实验室用户设施的场外表征。 通过合作，该小组将获得计算计算，以支持实验测量。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Non-Technical SummaryMany energy and technology-driven applications rely on materials that utilize the chemical properties of lead. However, the known toxicity of lead and subsequent regulations prompt the investigation of alternative elements for technological applications. With joint support from the Solid State and Materials Chemistry program in the Division of Materials Research and the Established Program to Stimulate Competitive Research (EPSCoR), this project seeks to understand the arrangement and interactions of atoms that give rise to the desired physical properties for applications, and will focus on a widely studied yet poorly understood family of materials called pyrochlore oxides. The principles discovered through this work will deepen the understanding of pyrochlore oxides, offering new knowledge for achieving properties that offer alternatives to lead-based technologies. Undergraduate education and exposure to solid state chemistry is at the heart of this research, and providing an experience that promotes excitement and is inclusive to all is of paramount importance. Taking place at Bates College, a primarily undergraduate institution, this work is well-suited for students interested in chemistry, materials science, and sustainable approaches for energy and electronic applications. Through participation in this research, students will be exposed to techniques not typically covered in undergraduate chemistry curricula, as well as perform cutting-edge experiments at facilities that are often underutilized by undergraduate institutions. In addition to independent research, this work will promote professional development of participants through purposeful discussion of career paths, interaction with outside scientists, and reflection on activities performed throughout their involvement.Technical SummaryPolar crystal structures comprise a class of materials with a broad range of technological applications, particularly as components in electronic devices. While widespread in their use, these materials often rely on the electron lone-pair chemistry of Pb, and finding alternative Pb-free materials that do not sacrifice performance is of considerable importance. Current research focuses broadly on perovskite oxides due to high temperature stability, facile preparation, and a wide range of chemical substituents. However, the vast literature on perovskite oxides provides no clear way to get around the use of Pb. The ability to alter the metal cations and anion stoichiometry in pyrochlore oxides provides a versatile platform for obtaining Pb-free polar crystal structures. Pyrochlores have been less studied than perovskites due to their complex crystal structure, but recent developments in measurement and computational techniques make it possible to study and determine the causes of long-range polarity in these materials. This research, supported by the Solid State and Materials Chemistry program in the Division of Materials Research and the Established Program to Stimulate Competitive Research (EPSCoR), will apply knowledge of the causes of polarity in perovskites to systematically investigate and determine the fundamental drivers of polarity in pyrochlores. The interpenetrating networks found in the pyrochlore structure will be decoupled through systematic substitution of different metal cations, namely those that can cause second-order Jahn-Teller distortions (s2 or d0 electronic configurations). Comparing detailed structures of materials with metal ions that can cause structural distortions to materials with cations that will not cause distortions will provide insights into the underlying chemistry that leads to long-range polarity. In addition to cation substitution, the work will investigate the influence of anion stoichiometry on structure, local distortions, and overall polarity. Structural observations will be correlated to physical property measurements through characterization of the dielectric constant and nonlinear optical behavior. Undergraduate student researchers will be the primary participants in on-site preparation and characterization of samples at Bates College, a primarily undergraduate institution, and off-site characterization at national laboratory user facilities. Through collaboration, the group will obtain computational calculations to support experimental measurements.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.