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

本项目将回答两个中心问题：1)沉淀反应中小晶体成核和生长过程中结构性质的演变应通过SAXS(颗粒形态)、WAXS(相干体积、晶体结构和相变)和总散射(非周期排列、缺陷和相变)在原位可见，10μS反应物混合后。这一方法将为散射方法在成核和早期结构形成领域开辟一个迄今未被探索的时间区域。这三种方法的信息内容部分重叠。这确保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)要采用他的成年结构，晶体的最小尺寸必须是多少？小团聚体或微晶可能具有非晶态或非周期性排列，例如具有高密度的堆积缺陷，这通常被称为结构缺陷。我们关心的问题是，这些观察到的非晶序是否代表非平衡相，或者它们是否应该被视为小粒子的内在属性。D.Zahn的计算(离子团簇从二聚体到数百个离子的聚集体的结构演化，包括结构成熟)和R.Wehrich的计算(关于晶核的结构、动力学和稳定性的非常高质量的从头计算)对这一讨论是至关重要的。根据我们的经验，我们打算开始研究从水溶液中合成的硫化物(CDS，PBS，ZnS，Ag2S)。然而，我们新的实验方法也将适用于项目内外的其他样品系统。混合室的构建是实验计划的重要部分。应获得结晶开始后的早期数据点(10μS)，并且必须确保结晶时间的高分辨率(结晶时间短时为15%，结晶时间长于1 ms时最好为1%)。这是通过一个带有产品自由喷射的快速混合单元来实现的。自由喷流进一步显著减少了背景散射，从而确保了高数据质量。

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.