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The role of the synthesis route for the defect formation in BaLiF3 and the investigation of the collective ion motion in fluorite structured materials with the help of molecular dynamic simulations

BaLiF3 缺陷形成的合成路线的作用以及借助分子动力学模拟研究萤石结构材料中的集体离子运动

基本信息

批准号：
319059311
负责人：
Dr. Andre Düvel
金额：
--
依托单位：
Institut für Nanotechnologie (INT)
依托单位国家：
德国
项目类别：
Research Fellowships
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/319059311?language=en
关键词：
role synthesis route defect formation

项目摘要

Ceramic ion conductors are of increasing relevance for science and technology, especially in the area of energy storage where they promise an increase in power, safety and versatility. For an aimed synthesis of ceramic fast ion conductors suitable for applications, however, a more in-depth understanding of the conduction mechanisms as well as the influence of the crystal structure and especially the local structure, which depends on the synthesis route, on the ionic conductivity is needed.Experimental investigations show that only a small amount of the Li and F ions in mechanosynthesized BaLiF3 are highly mobile at temperatures exceeding 600 K, while in thermally prepared, micro or monocrystalline BaLiF3 almost all Li and F ions are highly mobile at these temperatures. MD simulations of BaLiF3 revealed that there is no ion mobility in a perfectly ordered BaLiF3 crystal, but only in defective regions that are, for instance, characterized by a site exchange of Ba and Li ions. Accordingly, micro and monocrystalline BaLiF3 would be rich in defects, while, counterintuitively, there should be almost no such defects in the mechanosynthesized material. MD simulation of the crystallisation of Ba1-xSrxLiF3 indicate that the elimination of site exchange defects can only happen if those defects are in direct contact with the surface of the crystallite. Hence, such defects cannot be eliminated when they are located deep within the crystal. In the case of ball milling, however, the formed crystallites are repeatedly in part destroyed which should lead to an exposure of almost all atomic planes to the surface several times during the milling process, such that the defects could be eliminated. This shall be investigated by mimicking mechanosynthesis using MD simulation.The second part of the project deals with the investigation of collective ion motion in crystalline solids. This conduction mechanism, which was observed in MD simulations of Ba1-xSrxLiF3, BaF2, CaF2 and Ba1-xCaxF2, and is also mentioned in a few publications, is based on jumps of ions towards, in this sublattice, neighbouring occupied sites, which causes the ions residing at that sites to jump towards their neighbouring sites and so on. This way long chains of jointly moving ions are formed which end in vacancies or form closed loops. This mechanism probably allows the explanation of the transition to superionic conduction in fluorite structured materials occuring at temperatures of approximately 0.8 x Tmelt. This assumption shall be tested and the mechanism be investigated with the help of MD simulations on diverse systems.

陶瓷离子导体与科学和技术的相关性越来越大，特别是在能量存储领域，它们有望提高功率，安全性和多功能性。然而，为了有目的地合成适合应用的陶瓷快离子导体，需要更深入地理解导电机制以及晶体结构，特别是局部结构的影响，这取决于合成路线，实验研究表明，在机械合成的BaLiF 3中，只有少量的Li和F离子在温度下是高度移动的超过600 K，而在热制备的微或单晶BaLiF 3中，几乎所有Li和F离子在这些温度下都是高度移动的。MD模拟BaLiF 3显示，有没有离子迁移率在一个完美有序的BaLiF 3晶体，但只有在有缺陷的区域，例如，其特征在于由Ba和Li离子的网站交换。因此，微米和单晶BaLiF 3将富含缺陷，而与直觉相反，在机械合成材料中应该几乎没有这种缺陷。MD模拟的Ba 1-xSrxLiF 3的结晶表明，只有当这些缺陷与微晶的表面直接接触时，才能消除位置交换缺陷。因此，当这些缺陷位于晶体深处时，它们不能被消除。然而，在球磨的情况下，形成的微晶被重复地部分破坏，这将导致几乎所有原子平面在研磨过程中多次暴露于表面，从而可以消除缺陷。这将通过使用MD模拟来模拟机械合成来研究。该项目的第二部分涉及结晶固体中集体离子运动的研究。在Ba 1-xSrxLiF 3、BaF 2、CaF 2和Ba 1-xCaxF 2的MD模拟中观察到并且在一些出版物中也提到的这种传导机制是基于离子朝向该子晶格中的相邻占据位置的跳跃，这使得驻留在该位置的离子向其相邻位置跳跃，以此类推。这样，形成了长链的共同运动的离子，其末端是空位或空位。形成闭合回路。这种机制可能允许在约0.8 x Tmelt的温度下发生的萤石结构材料中的超离子传导的转变的解释。这一假设应进行测试，并与不同系统的MD模拟的帮助下，机制进行调查。