Topochemical fluorination reactions in the context of fluoride ion batteries, tailored properties and for the modification of thin films

该项目旨在研究钙钛矿类型和类似结构（AxByOz, A =碱或碱土，B =过渡金属）内氧化物的拓扑化学氟化反应。这种反应类型在氟离子电池、定制材料特性以及薄膜技术领域具有特殊的意义。据此，本项目分为三个子项目。(a)部分讨论了新的电化学氟化反应。我们的目标是寻找并表征能够进行这种反应的新化合物（例如SrFeO2—> SrFeO2F或LaSrMnO4—> LaSrMnO4F2-d）。为了证明氟化物的掺入，我们的目标是使用Mössbauer以及x射线吸收光谱和XRD实验。与化学氟化方法（XeF2、F2）相比，电化学氟化反应有望精确调整氟含量和平均过渡金属氧化态（对磁性、导电性、超导性等性质起着至关重要的作用）。特别感兴趣的是确定能够可逆插入和脱插氟的化合物，这将有助于建立完全插入的氟离子电池。关于(a)部分，将在(b)部分研究使用还原性化学剂（例如金属有机化合物、碱金属）和氟氧化合物的化学除氟方法。我们的目标是投资更多材料的氟化行为，其中包括Bi1-xAxFeO3-y和La1 xSrxMnO3，其中材料性能（磁性，电导率，铁电性能）的强烈变化是预期和研究的。如果后一种系统的氟化显示是可逆的，该项目将进一步扩大到电化学可调材料特性。研究铁电性能需要制备致密的氟化氧薄膜。这是因为氟氧化物在热力学上是不稳定的，因此不能烧结。我们的目标是在子项目(c)中研究脉冲激光沉积制备的钙钛矿薄膜的氟化和随后的表征。我们将研究衬底应变和氟化引起的化学应变对外延生长薄膜结构和性能的相互作用。此外，将研究与固体氧化物燃料电池技术相关的多孔氟化薄膜的特性（稳定性、导电性、极化电阻）。最后，我们努力通过基于DFT的计算对所有三个子项目的实验结果进行理论验证。

The project aims to investigate topochemical fluorination reactions of oxides within the perovskite type and similar structures (AxByOz, A = alkali or alkali earth, B = transition metal). This reaction type is of special interest in the fields of fluoride ion batteries, tailored material properties as well as thin film technologies. According to this, the project is structured in three subprojects. New electrochemical fluorination reactions are under concern in part (a). We aim to find and characterize new compounds which are capable for this type of reaction (e. g. SrFeO2--> SrFeO2F or LaSrMnO4 --> LaSrMnO4F2-d). To prove fluoride incorporation we aim to use Mössbauer as well as X-ray absorption spectroscopy in addition to XRD experiments. In contrast to chemical fluorination methods (XeF2, F2), electrochemical fluorination reactions can be expected to have the potential to adjust fluorine contents and average transition metal oxidation states (which play a crucial role on properties such as magnetism, conductivity, superconductivity) precisely. A special interest is located in the identification of compounds which are capable for reversible fluorine intercalation and deintercalation, which would facilitate building completely intercalation based fluoride ion batteries. In relation to part (a), chemical defluorination methods will be investigated in part (b) using reductive chemical agents (e. g. metal organic compounds, alkali metals) with oxyfluoride compounds. We target to invest the fluorination behavior of further materials, among them Bi1-xAxFeO3-y and La1 xSrxMnO3, where a strong change of material properties (magnetism, conductivity, ferroelectric properties) is to be expected and investigated. If fluorination of the latter systems will show to be reversible, the project will be additionally expanded towards electrochemically adjustable material properties. Investigation of ferroelectric properties requires the preparation of dense thin film oxyfluoride films. This is explained due to the fact that oxyfluorides are thermodynamically unstable and therefore cannot be sintered. We aim to investigate the fluorination and subsequent characterisation of thin perovskite films prepared by pulsed laser deposition in subproject (c). We will study the interplay between substrate strain and chemical strain due to fluorination on structure and properties of epitaxial grown films. In addition, thin porous fluorinated films will be investigated regarding their properties which are relevant for solid oxide fuel cell technologies (stability, conductivity, polarization resistances). Finally, we strive for theoretical validation of experimental results by means of DFT based calculations for all three subprojects.