Mechanisms of Nucleation and Crystal Growth of Metal Halide Networks

该项目将使用等温时间和温度分辨的二维X射线衍射（2-D t/TRXRD）技术来独立地测量内在和外在成核和晶体生长的速率，以及同时对结晶和非晶部分进行成对分布函数（PDF）分析。 这将通过使用高能X射线、时间分辨率高达30 Hz的区域探测器、速率大于500/min的熔体淬火技术的发展以及数据处理方法来实现，以适应大量数据的收集和分析。 这些研究将用一系列卤化物材料进行，这些材料的熔点在室温和350 ℃之间，这些温度很容易适用于所提出的实验方法。具体而言，将研究笼形网络（我们的halozeotypes）的结晶，探测母体二元凝聚相的结晶，并考虑通过形成分子塑性结晶相的逐步结构排序。该项目将为学生提供基础科学发现方面的宝贵培训，这些发现对大气和地质科学以及先进材料的设计和功能具有影响。快速时间分辨衍射技术正在开发中，阿贡和布鲁克海文国家实验室的设备正在用于独立测量晶体成核和生长的速率。 这项工作正在改变对晶体从熔融状态形成的机制的经典理解。 与经典理论的假设相反，该项目将证明，它是在熔融状态下的原子和分子水平结构的组织，而不是控制成核和晶体生长速率的表面能。 将开发新的仪器和数据处理工具，并进行一系列机理研究，以发展和完善新的结构有序驱动结晶（SODC）理论。 从这些晶体生长的基本机理研究的答案将有助于破译奥秘，如冰晶生长的云显着影响全球气候，并将适用于设计和功能的先进技术，如相变材料用于数据存储的快速非晶到晶体的转变的理解将导致上级性能。

This project will use isothermal time and temperature resolved two-dimensional X-ray diffraction (2-D t/TRXRD) techniques to independently measure the rates of intrinsic, and extrinsic nucleation, and crystal growth, as well as to perform simultaneous pair distribution function (PDF) analysis of the crystalline and amorphous fractions. This will be accomplished using high energy X-rays, area detectors with up to 30 Hz time resolution, development of melt-quenching techniques with rates greater than 500/min, and data processing methods to accommodate collection and analysis of massive amounts of data. The studies will be conducted with a series of halide materials that exhibit melting points between room temperature and 350 C, which are temperatures that are readily amenable to the proposed experimental methods. Specifically, the crystallization of clathrated networks (our halozeotypes), probing the crystallization of parent binary condensed phases, and considering step-wise structural ordering through the formation of molecular plastic crystalline phases will be studied. This project will provide invaluable training of students in fundamental scientific discoveries with implications for the atmospheric and geologic sciences as well as for the design and function of advanced materials. %%%Fast time-resolved diffraction techniques are being developed, and facilities at Argonne and Brookhaven National Laboratories are being used to independently measure the rates of crystal nucleation and growth. This work is transforming classical understandings of the mechanisms by which crystals are formed from the molten state. Contrary to the assumptions of classical theory, this project will demonstrate that it is the organization of atomic and molecular level structure in the molten state, rather than surface energy that controls the rate of nucleation and crystal growth. New instrumentation and data processing tools will be developed, and series mechanistic studies performed to develop and refine a new structural-order-driven-crystallization (SODC) theory. Answers from these fundamental mechanistic studies of crystal growth will help decipher mysteries such as ice-crystal growth in clouds which dramatically impact global climates, and will be applicable to the design and function of advanced technologies such as phase change materials utilized for data storage for which understanding of the rapid amorphous-to-crystal transitions will lead to superior performance.