Synthesis and Mechanistic Studies of New Series of Ferroelastic and Ferroelectric Crystals

现代晶体工程的主要目标之一是设计、合成和优化具有特定功能的新材料。这项研究计划集中在铁弹性和铁电域转换的技术上的有用的性质，其中可以通过施加各向异性应力(铁弹性)或电场(铁电性)来改变晶体中域或区域的理论取向。这类材料(可用作光门或存储器件)的合理设计需要更深入地了解磁畴转换的机制，这是一种可见的宏观现象，可在分子、纳米和介观尺度上进行控制。在铁弹性分子决定因素的基础上，这项工作将集中于铁弹性和铁电系列晶体中的磁畴转换的机制研究，其中磁畴转换和铁电有序的协同弹性势垒可以被优化和定制。由于可以产生和比较如此大量的密切相关的结构，所以它集中在一系列表现出铁弹性和/或铁电区切换的包合物、共晶和有机盐的设计、合成和机理研究。由于它们可以提供关于磁区切换障碍的见解，这项工作将利用各种技术(例如，X射线衍射、同步白光X射线形貌术、固态核磁共振、超快视频显微镜、双折射映射)来探索“记忆效应”或“类橡胶行为”的现象，其中，由应力(或电场)产生的子磁区自发地回复到母体取向。更透彻地了解这种记忆效应将有助于采用有针对性的迭代方法来形成一系列具有明确性质的铁电晶体。广泛的影响：由于他们将被要求整合各种方法的结果，并在新材料的设计中利用这些结果，本研究计划将为将从事材料化学职业的本科生、研究生和博士后提供广泛的培训。通过综合一系列密切相关的结构的大量实验结果，应该有可能对控制各种铁电材料中的磁畴转换和记忆效应的因素有一个更基本的理解。这项工作将在论文和演示文稿中广泛传播，并用于研究生课程和本科生实验室。

One of the principal goals of modern crystal engineering is the design, synthesis and optimization of new materials with specified function. This research program focuses on the technologically useful properties of ferroelastic and ferroelectric domain switching, in which theorientations of domains or regions within a crystal can be changed by application of anisotropic stress (ferroelasticity) or electric fields (ferroelectricity). The rational design of such materials (which can act as light gates or memory devices) requires a deeper understanding of the mechanisms of domain switching, a visible, macroscopic phenomenon that is controlled at the molecular, nanoscopic and mesoscopic scales. Building upon earlier work on the molecular determinants of ferroelasticity, this work will focus on mechanistic studies of domain switching in series of ferroelastic andferroelectric crystals in which the cooperative, elastic barriers to domain switching and ferroelectric ordering can be optimized and tailored. Because such a large number of closely related structures can be generated and compared, it concentrates on the design, synthesis and mechanistic studies ofseries of inclusion compounds, co-crystals and organic salts that exhibit ferroelastic and/or ferroelectric domain switching.Because of the insights they can provide about the barriers to domain switching, this work will utilize a variety of techniques (e.g., X-ray diffraction, synchrotron white beam X-ray topography, solid state nuclear magnetic resonance, ultrafast videomicroscopy, birefringence mapping) to probethe phenomenon of "memory effects" or "rubber-like behavior," in which the daughter domain that is generated by stress (or electric field) spontaneously reverts back to the parent orientation. A more thorough understanding of such memory effects will facilitate a targeted and iterative approach toforming series of ferroelectric crystals with well-defined properties.Broader Impacts: Because they will be required to integrate results from various methods and to utilize these results in the design of new materials, this research program will provide a broad-based training for undergraduate, graduate and postdoctoral students who will pursue careers in materialschemistry. By integrating numerous experimental results on a series of closely related structures,it should be possible to develop a more fundamental understanding of the factors controlling domain switching and memory effects in a variety of ferroelectric materials. This work will be disseminatedwidely in papers and presentations and utilized in graduate-level courses and undergraduate laboratories.