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

第1部分：非技术概述能够对外界刺激(如磁场或电场)做出反应的材料非常适合广泛的技术应用，包括与电子和能源行业相关的应用。虽然许多材料有能力对一种类型的外部刺激做出反应并与之相互作用，但只有少数材料可以同时与多种刺激相互作用，发现和理解这种材料是一个活跃的研究领域。在NSF材料研究部固态和材料化学项目的支持下，贝茨学院的Laurita教授的团队致力于了解原子的排列如何允许与外部刺激相互作用，这是一种被广泛研究但知之甚少的材料家族，称为焦绿石。从这项工作中获得的理解和原则最终将为广泛的技术上重要的特性提供设计考虑。本科教育和研究是这项工作的核心，这项工作解决了教育和培训未来几代材料科学家的国家需求。拟议的教育部分在研究密集型机构的研究生学习和以本科生为主的本科院校的本科教育生涯之间建立了一座桥梁。通过在URM服务的研究生院有针对性的广告，首席调查员促进来自历史上被排斥和代表性不足的群体的个人的参与。此外，该项目还发挥了长期和更广泛的目标，以多样化的学术人员，特别是在PUI。在这笔助学金的支持下，将为高水平研究生创造身临其境的实习体验，以研究为重点的PUI。这项活动为研究生在PUI的职业生涯提供信息，在研究生和本科生参与者之间提供有价值的互动和共同指导，并通过合作研究努力促进助学金和研究生论文工作的科学目标。第二部分：技术概述烧绿石晶体结构显示出无数与技术相关的性质，包括超导、铁电、光催化和受挫磁性。虽然有大量关于焦绿石的研究，但这个系统的错综复杂留下了许多关于故意操纵化学和结构以实现所需功能的问题。由于两个相互穿透的子网络，焦绿石结构本质上是复杂的，结构变化可以由任一网络上的替代或空位来驱动。此外，由于几何约束，每个亚晶格上阳离子的三角形排列导致了结构和行为问题。根据这一职业奖开展的研究建立在之前关于焦绿石结构扭曲的驱动因素的研究基础上。现在，首席研究员研究了这项工作产生的两个假设：(1)无论长程有序性如何，磁性阳离子在局域和晶体尺度上的磁电相互作用中都起着作用；(2)空位/掺杂的结晶学有序性决定了电偶极子的有序性，是驱动长程极性结构的关键。目前的工作集中在焦绿石结构中磁偶极子和电偶极子的汇合以及空位在这些相互作用中的作用。具体地说，这项研究调查了：(1)有可能形成电偶极(d0或s2电子组态)的阳离子的取代，(2)未配对的d或f电子对磁性阳离子的取代，以及(3)阴离子空位的存在；从而旨在帮助我们理解焦绿石的复杂结构行为，帮助我们在局域和结晶学尺度上理解磁偶极子和电偶极子的行为和相互作用，并最终设计用于多铁性应用的新型材料。在这笔助学金的支持下，将为高水平研究生创造身临其境的实习体验，以研究为重点的PUI。这项活动为研究生在PUI的职业生涯提供信息，在研究生和本科生参与者之间提供有价值的互动和共同指导，并通过合作研究努力促进助学金和研究生论文工作的科学目标。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.