Non-equilibrium phases during the early growth of crystals - an ultrafast in-situ SAXS, -WAXS, and -PDF analysis

晶体早期生长过程中的非平衡相 - 超快原位 SAXS、-WAXS 和 -PDF 分析

• 批准号: 233885349
• 负责人: Professor Dr. Andreas Magerl
• 金额: --
• 依托单位: Institut für Materials Resource Management
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2016-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/233885349?language=en
• 关键词: Non; equilibrium; phases; during; early

Two central questions shall be answered within this project:1) The evolution of the structural properties during nucleation and growth of small crystals in precipitation reactions shall be made visible in-situ already 10 μs after mixing of the reactants by SAXS (morphology of the particles), WAXS (coherence volumina, crystal structure and phase transitions), and Total Scattering (non-periodic arrangements, defects and phase transitions). This approach will opened up a so far unexplored time regime in the field of nucleation and early structure formation for scattering methods. The information content of the three methods is in part overlapping. This assures a reliable interpretation of the experimental data and it provides further a solid foundation for model calculations.2) What is the minimum size a crystal must have in order to adopt his adult structure? Small agglomerates or crystallites may have amorphous or non-periodic arrangements e. g. with a high density of stacking faults which are usually referred to structural defects. We are concerned with the question if these observed non-crystalline orderings represent non-equilibrium phases or if they should be considered as an intrinsic property of small particles. The calculations by D. Zahn (structural evolution of ion clusters from dimers to aggregates with hundreds of ions including structural ripening) and by R. Weihrich (very high quality ab initio calculations of crystal nuclei regarding their structure, dynamics, and stability) are of fundamental importance for this discussion.Based on our experience we intend start out with investigations on sulfides synthesized from aqueous solutions (CdS, PbS, ZnS, Ag2S). However, our novel experimental approach will be also made available to other sample systems within the project and beyond.The construction of a mixing cell is an essential part of the experimental program. An early data point after the beginning of the crystallization shall become accessible (10 μs) and a high resolution for the crystallization time must be assured (15 % for short crystallization times, better 1 % for crystallization times longer 1 ms). This is achieved by a rapid mixer cell with a free jet for the product. The free jet further reduces background scattering significantly thus assuring a high data quality.

本项目将回答两个核心问题：1)在混合后10 μs，通过SAXS（颗粒形貌）、WAXS（相干体积、晶体结构和相变）和全散射（非周期排列、缺陷和相变），可以在原位观察到沉淀反应中小晶体成核和生长过程中结构性质的演变。这种方法将为散射方法的成核和早期结构形成领域开辟一个迄今尚未探索的时间范围。三种方法的信息内容部分重叠。这保证了对实验数据的可靠解释，并进一步为模型计算提供了坚实的基础。2)晶体的最小尺寸是多少才能形成成人结构？小的团块或晶体可能具有无定形或非周期性排列，例如具有高密度的层错，通常称为结构缺陷。我们关心的问题是，这些观察到的非晶有序是否代表非平衡相，或者它们是否应该被认为是小颗粒的固有性质。D. Zahn的计算（离子簇从二聚体到包含数百个离子的聚集体的结构演化，包括结构成熟）和R. Weihrich的计算（关于晶体核的结构、动力学和稳定性的非常高质量的从头计算）对本讨论具有重要意义。根据我们的经验，我们打算开始研究从水溶液合成的硫化物（CdS, PbS, ZnS, Ag2S）。然而，我们的新实验方法也将提供给项目内外的其他样品系统。混合池的构造是实验方案的重要组成部分。结晶开始后的早期数据点必须是可访问的（10 μs），并且必须保证结晶时间的高分辨率（短结晶时间为15%，长于1 ms的结晶时间为1%）。这是通过一个带有自由射流的快速混合池来实现的。自由射流进一步显著降低了背景散射，从而保证了高数据质量。