Accurate Atomic Structure and Symmetry Determination of New Hybrid Improper Ferroelectric Phases

非技术摘要。由于其独特的性质(自发极化)，铁电材料构成了一个70亿美元的市场，并被用于许多应用，如用于疾病诊断的医学成像、数据中心等大规模信息存储，或在这些形式的能源不可用时用于太阳能或风力发电场的高密度能量存储。最常见的铁电材料使用在自然界中很难获得和/或有毒的元素。幸运的是，随着杂化不当铁电材料的发现，铁电系统的数量已经大大增加，这种铁电材料可以由容易获得的、廉价的元素组成，并且具有低毒性。这项工作的目标是确定这些材料在高压下的原子结构，因为可以创造出新的独特的原子结构，这种结构将在信息存储或能量存储方面具有很高的技术适用性。研究生和本科生参与这项工作的所有层面，包括样品制备、实验室和基于同步加速器的测量、建模和数据分析。在研究小组和研究生的指导下，纽瓦克地区来自代表性不足群体的高中生正在接受为期七周的材料准备和先进材料表征的暑期研究和教学计划的培训。它包括为高中教师举办的为期一周的研讨会，使他们能够将该计划的组成部分落实到他们的实验室实验中。教育和研究是新泽西理工学院、罗格斯大学、密歇根大学、布鲁克海文国家实验室、阿贡国家实验室、劳伦斯·伯克利国家实验室和针对高中生的SEED计划(美国化学学会)之间的合作。技术摘要。铁电材料是高密度数据存储的关键，并用于固态驱动器，但已知材料的基本物理要求限制了可用于开发新材料的化学和结构空间。最近，随着杂化非正铁电体的发现，这一空间得到了显著的扩展，这种杂化非正铁电体具有多个非极扭曲，可以稳定极性铁电态。外部条件可以稳定新的阶段。为了充分开发这类新的铁电材料，需要它们完全依赖于压力和温度的相图。为了详细了解过渡金属氧化物基杂化铁电材料的结构变化，正在进行单晶衍射测量，作为压力和温度的函数。通过约束通过计算研究的晶体结构，导出的详细结构被用于密度泛函理论(DFT)计算。新发现的相正在以亚稳态的形式制备，并集成到基于铁电的器件中，以提高性能。该提案的社会影响将来自于扩大可用于数据存储设备应用的氧化物的范围，并允许使用无毒的富含地球的材料系统。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。

Non-Technical Abstract. Ferroelectric materials comprise a $7 billion market owing to their unique properties (a spontaneous electric polarization), and find use in many applications such as medical imaging for disease diagnosis, large-scale storage of information such as in data centers, or in high-density energy storage for solar or wind farms for times when these forms of energy are not available. The most common ferroelectric materials utilize elements that are difficult to obtain in nature and/or are toxic. Fortunately, the number of ferroelectric systems has been expanded significantly with the discovery of hybrid improper ferroelectrics, which can be composed of readily available, cheap elements and have low toxicity. The goal of this work is to determine what the atomic structures of these materials are under high pressure, as new unique ones can be created which will have high technological applicability for information storage or energy storage. Graduate and undergraduate students are involved in all levels of this work, including sample preparation, laboratory and synchrotron-based measurements, modeling, and data analysis. Under the direction of the research team and graduate students, Newark-area high school students from under-represented groups are being trained in a seven-week summer research and teaching program on material preparation and advanced materials characterization. It includes a one-week workshop for high school teachers to enable them to implement components of the program into their laboratory experiments. The education and research is a collaboration between the New Jersey Institute of Technology, Rutgers University, the University of Michigan, Brookhaven National Laboratory, Argonne National Laboratory, Lawrence Berkeley National Laboratory, and the SEED program for high school students (American Chemical Society). Technical Abstract. Ferroelectric materials are essential to high-density data storage and are used in solid-state drives, but basic physics requirements for the known materials have limited the chemical and structural space available for the development of new ones. Recently, this space has been significantly expanded with the discovery of hybrid improper ferroelectrics, which have multiple nonpolar distortions that stabilize a polar ferroelectric state. External conditions can stabilize new phases. To fully exploit this new class of ferroelectrics, their full pressure- and temperature-dependent phase diagrams are needed. To develop a detailed understanding of structural changes in the general class of transition metal oxide-based hybrid improper ferroelectrics, single-crystal diffraction measurements as a function of pressure and temperature are being carried out. The derived detail structure is being used to inform density functional theory (DFT) calculations by constraining the crystal structures investigated computationally. Newly discovered phases are being prepared as metastable forms and integrated into ferroelectric-based devices for improved performance. The societal impact of the proposal will come from broadening the range of oxides available for applications in data storage devices and enabling the use of nontoxic earth-abundant materials systems.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.