Interface and matrix effects on light-switchable solid-state spin transitions

第1部分：非技术概述。使用光在宏观尺度上诱导运动有时被称为光到工作的直接转换，预计将在从人造肌肉到光能收集再到无线机器等领域带来新技术。自旋过渡固体是一类已知的材料，当暴露在包括光在内的特定刺激下时，体积会发生变化。这种体积变化本身就可以用来引起运动，但通过将复合材料中的自旋过渡固体与其他材料结合起来，这种影响会大大放大。该项目由NSF的固态和材料化学计划支持，探索当自旋转变固体与其他材料结合在一起形成复合材料时，与光引起的体积变化相关的基本材料化学问题。理论模型预测了矩阵中的自旋跃迁应该如何变化，但目前还缺乏实验来验证这些预测，而且矩阵效应的大小还没有被量化。佛罗里达大学的研究人员开发了新的合成方法，将定义明确的自旋转变固体粒子放置在不同材料的基质中，从而能够定量测量与自旋转变相关的体积变化是如何传递到支持基质并被支撑基质放大的。该项目利用国家科学用户设施，包括阿贡国家实验室的高级光子源和布鲁克海文国家实验室的NSLS II，并为学生提供这些先进技术的培训。该项目的成果将使更好地设计用于直接将光转化为工作的下一代材料。这个项目与这些正在开发的技术的关系在一个计划中的展览中得到了强调，该展览的主题是用光创造运动，将在当地的教育和公共推广论坛上展示。第二部分：技术概述在固态自旋转变期间伴随着金属-配体结合的重大体积变化开启了为机械执行器技术收获这些效应的前景。这些新出现的应用要求自旋跃迁材料与其他材料组分物理耦合，但材料界面会影响自旋跃迁的特性，特别是在纳米或介观尺度的高表面与体积比特性时。该项目由美国国家科学基金会的固体和材料化学计划支持，量化了基质或界面属性及其对中尺度粒子自旋转变的影响。在实验上，研究了铁氰化钴作为光开关核心的电荷转移诱导自旋跃迁(CTIST)，其周围基质是化学结构不同的氰基金属氰酸盐。理论模型预测了磁芯的弹性性质是决定相变顺序和动力学的关键因素。这些性质可以受壳的刚度、核和壳的相对晶格常数以及壳厚度的影响；所有这些都是可以综合改变的参数。用X射线衍射法和磁强计监测了光诱导和温度相关的相行为，以提供活化能和有关组份变化时转变的有序性和协同性的信息。用核非弹性散射(NIS)和加压X射线衍射法测量了其弹性性质，并将其与相变行为进行了关联，以量化基质效应。同时，范围扩大到化学上不相似的基质。这些研究为光诱导机械驱动的主题领域提供了信息，其潜在的应用是利用光直接执行工作和新的光能收集方案。这个项目与这些正在开发的技术的关系在一个计划中的展览中得到了强调，该展览的主题是用光创造运动，将在当地教育和公共宣传论坛上展示。研究任务旨在成为研究生和本科生教育的平台，提供在材料化学相关高科技专业中具有竞争力所需的技术专长和知识以及一般技能。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 Summary.Using light to induce motion on a macroscopic scale is sometimes referred to as the direct conversion of light to work and is expected to lead to new technologies in areas ranging from artificial muscles to light energy harvesting to wireless machines. Spin transition solids are a class of materials known to change volume when exposed to certain stimuli, including light. This volume change alone can be used to cause motion, but the effects are greatly amplified by combining the spin transition solid in a composite with other materials. This project, supported by the Solid State and Materials Chemistry program at NSF, explores the fundamental materials chemistry questions associated with light induced volume changes when spin transition solids are combined in a matrix with other materials to form a composite. Theoretical models predict how the spin transition should change in a matrix, but experiments to verify these predictions are currently lacking, and the magnitude of matrix effects have not been quantified. Researchers at the University of Florida develop new synthetic methods to place well-defined particles of the spin transition solid in matrices of different materials enabling quantitative measurements of how the volume change associated with the spin transition is transmitted to and amplified by the supporting matrix. The project utilizes national scientific user facilities including the Advanced Photon Source at Argonne National Labs and the NSLS II at Brookhaven National Labs, and provides students training in these advanced technologies. Results of the project will enable better design of the next generation of materials used for directly converting light to work. The relationship of this project to these developing technologies is highlighted in a planned exhibit themed Creating Motion with Light, to be displayed at local education and public outreach forums.Part 2: Technical SummaryThe significant volume change accompanying alterations in metal-ligand bonding during a solid-state spin transition opens the prospect of harvesting these effects for mechanical actuator technology. These emerging applications require the spin transition material to physically couple to other material components, yet the material interface can influence the characteristics of a spin transition, especially at high surface to volume ratios characteristic of the nanoscale or mesoscale. This project, supported by the Solid State and Materials Chemistry program at NSF, quantifies matrix or interface attributes and their influence on spin transitions in mesoscale particles. Experimentally, the charge transfer induced spin transition (CTIST) of rubidium cobalthexacyanoferrate as the light-switchable core with isostructural but chemically distinct cyanometallate shells as surrounding matrix are studied. Theoretical models predict the elastic properties of the core are the key determinants of the order and kinetics of the phase transition. These properties can be affected by the stiffness of the shell, the relative lattice constants of the core and shell, and the shell thickness; all are parameters that can be synthetically altered. Light-induced and temperature-dependent phase behavior is monitored with X-ray diffraction and magnetometry to provide activation energies and information about the order and cooperativity of the transition as components are changed. The elastic properties are measured using nuclear inelastic scattering (NIS) and X-ray diffraction under pressure, and they are correlated with the phase change behavior to quantify the matrix effects. In parallel, the scope extends to chemically dissimilar matrices. These studies inform the subject area of light-induced mechanical actuation, potential applications of which are the use of light to directly perform work and new light energy harvesting schemes. The relationship of this project to these developing technologies is highlighted in a planned exhibit themed Creating Motion with Light, to be displayed at local education and public outreach forums. The research tasks are designed to be platforms for graduate and undergraduate student education, providing technical expertise and knowledge along with general skills needed to be competitive in materials chemistry related high-technology professions.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.