CAREER: Confluence of magnetic and electric dipoles on the pyrochlore lattice

第一部分：非技术概述对于各种各样的技术应用，包括与电子和能源工业相关的应用，非常需要能够响应外部刺激（例如磁场或电场）的材料。虽然许多材料具有响应和与一种类型的外部刺激相互作用的能力，但已知只有少数材料可以同时与一种以上的刺激相互作用，并且发现和理解这种材料是一个活跃的研究领域。有了这个职业奖，由NSF材料研究部的固态和材料化学计划支持，贝茨学院的Laurita教授的小组专注于了解原子的排列如何允许与外部刺激相互作用在一个广泛研究但知之甚少的材料家族中称为pyrophores。从这项工作中获得的理解和原则，最终将提供广泛的技术上重要的性能的设计考虑。本科教育和研究是这项工作的核心，它解决了国家需要教育和培训未来几代材料科学家。拟议的教育部分建立了研究密集型机构的研究生学习和主要本科院校（PUI）的本科教育职业之间的桥梁。通过有针对性的广告，在URM服务的研究生院，主要研究员促进参与的个人从历史上被排斥和代表性不足的群体。该计划还在长期和更广泛的目标中发挥作用，以使学术教师多样化，特别是在PUI。在这项资助的支持下，将为高水平研究生创造以研究为重点的PUI的沉浸式实习体验。这项活动告知研究生在PUI的职业生涯，提供研究生和本科生参与者之间有价值的互动和共同指导，并通过合作研究工作推进补助金的科学目标和研究生的论文工作。技术概述烧绿石晶体结构表现出无数的技术相关性质，包括超导性、铁电性、铁电性，和挫败的磁性。 虽然存在大量关于焦烧体的研究，但该系统的复杂性留下了许多关于有意操纵化学和结构以实现所需功能的问题。烧绿石结构由于两个互穿的子网络而固有地复杂，并且结构变化可以由任一网络上的取代或空位驱动。此外，由于几何约束，每个子晶格上的阳离子的三角形排列导致结构和行为问题。在这个职业奖下进行的研究建立在以前对火辉石结构扭曲驱动因素的研究基础上。现在，主要研究人员研究了这项工作中产生的两个假设：（1）磁性阳离子，无论长程有序与否，在局部和晶体学尺度上的磁电相互作用中发挥作用;（2）空位/掺杂剂的晶体学有序决定了电偶极子的有序性，是驱动长程极性结构的关键。目前的工作集中在磁偶极子和电偶极子的汇合在烧绿石结构和空位在这些相互作用中的作用。具体而言，本研究探讨：（1）取代阳离子的倾向，形成电偶极子（d 0或s2电子构型），（2）磁性阳离子被未成对的d或f电子取代，和（3）阴离子空位的存在;从而有助于我们理解火辉石的复杂结构行为，我们的行为和磁和电偶极子在本地和晶体尺度上的相互作用的理解，并最终走向多铁性应用的新型材料的设计。在这项资助的支持下，将为高水平研究生创造以研究为重点的PUI的沉浸式实习体验。该活动告知研究生在PUI的职业生涯，为研究生和本科生参与者提供有价值的互动和共同指导，并通过合作研究努力推进资助的科学目标和研究生的论文工作。该奖项反映了NSF的法定使命，并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，被认为值得支持。

Part 1: Non-Technical SummaryMaterials that can respond to external stimuli (such as magnetic or electrical fields) are highly desirable for a wide variety of technological applications, including those relevant to the electronics and energy industries. While many materials have the ability to respond and interact with one type of external stimulus, only a few materials are known that can simultaneously interact with more than one stimulus and the discovery and understanding of such materials is an active area of research. With this CAREER award, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, Prof. Laurita’s group at Bates College focuses on understanding how the arrangement of atoms allows for interaction with external stimuli in a widely studied yet poorly understood family of materials called pyrochlores. The understanding and principles obtained from this work will ultimately offer design considerations for a broad range of technologically important properties. Undergraduate education and research are central to this work, which addresses a national need to educate and train future generations of material scientists. The proposed educational component establishes a bridge between graduate studies at research-intensive institutions and a career in undergraduate education at a primarily undergraduate institution (PUI). Through targeted advertisement at URM-serving graduate institutions, the principal investigator promotes participation of individuals from historically excluded and underrepresented groups. This program additionally plays a role in long-term and broader goals to diversify academic faculty, particularly at PUIs. With support from this grant hands-on, immersive internship experience at a research-focused PUI for upper-level graduate students will be created. This activity informs graduate students on a career at a PUI, provides valuable interaction and co-mentoring between graduate and undergraduate participants, and advances the science objectives of the grant and the graduate students’ dissertation work through collaborative research efforts.Part 2: Technical SummaryThe pyrochlore crystal structure exhibits a myriad of technologically relevant properties including superconductivity, ferroelectricity, photocatalysis, and frustrated magnetism. While there exists a wealth of studies on pyrochlores, the intricacies of this system leave many questions about intentionally manipulating the chemistry and structure for the desired functionality. The pyrochlore structure is inherently complex due to two interpenetrating subnetworks, and structural changes can be driven by substitution or vacancies on either network. Additionally, the triangular arrangement of cations on each sublattice leads to structural and behavioral questions due to geometrical constraints. The research carried out under this CAREER award builds on previous studies on the drivers of structural distortions in pyrochlores. Now the principal investigator investigates two hypotheses that arose from this work: (1) magnetic cations, regardless of long-range ordering, play a role in magnetoelectric interactions on both a local and crystallographic scale and (2) the crystallographic ordering of vacancies/dopants dictates the ordering of electric dipoles and is key to driving long range polar structures. The current work focuses on the confluence of magnetic and electric dipoles in the pyrochlore structure and the role of vacancies in these interactions. Specifically, the research investigates: (1) substitution of cations with the propensity to form electric dipoles (d0 or s2 electronic configurations), (2) substitution of magnetic cations with unpaired d or f electrons, and (3) the presence of anion vacancies; and thereby aims to contribute to our understanding of the complex structural behavior of pyrochlores, our understanding of the behavior and interaction of magnetic and electric dipoles on both a local and crystallographic scale, and ultimately towards the design of novel materials for multiferroic applications. With support from this grant hands-on, immersive internship experience at a research-focused PUI for upper-level graduate students will be created. This activity informs graduate students on a career at a PUI, provides valuable interaction and co-mentoring between graduate and undergraduate participants, and advances the science objectives of the grant and the graduate students’ dissertation work through collaborative research efforts.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.