Mechanismen der Bildung metastabiler Hydride und Nitride mittels in situ-Neutronenbeugung von Fest-Gas-Reaktionen

了解反应途径是合成亚稳态化合物的基础。因此，针对固体与氢(氢)或氨气的反应，我们研制了用于原位中子衍射的气体压力和气体流动池。对于前者，由于蓝宝石单晶管作为样品容器的适当取向，可以在极低的衍射背景下获得160巴的气压和400°C的温度。更高的温度(1000°C)是使用像气体流动池中的二氧化硅管来实现的。两者都是用双面激光系统加热的，温度是用校准的高温计测量的。利用法国格勒诺布尔ILL的高强度衍射仪D20上的两个池，现已很好地建立了氢气或氨气与固气反应的原位中子衍射，时间分辨率为1分钟。研究了各种体系，其中包括钯的氢化物、锌相、金属间化合物Li-Al化合物、稀土金属间化合物、VN、V2N以及通过中间体Fe3N形成的Fe4N。对于富钯金属间化合物，可以提出一个完整的反应机理，从而可以有计划地合成新的亚稳态化合物。我们成功的现场气室概念将根据温度-压力范围(密封和容器材料)、自动压力-温度程序并将其安装在Garching FRM-II的衍射仪SPODI上进行优化。利用已知的富钯金属间化合物的反应机理，将合成新的金属M=T11-xPbx，In1-xSnx，As，Sb，Se，Mn的亚稳氢化物。此外，还将研究混合价Yb氢化物形成过程中的亚稳中间体以及用于储氢的轻质金属间化合物的氢化反应。对于氮化物，已经获得的关于钒和铁的知识将被深化并扩展到铬、锰、钴、镍和铜，以便生产和表征亚稳态化合物，如Fe16N2、Fe8N或Co3N，其中一些化合物由于其磁性而非常有趣。亚稳氮化物的其他合成策略包括使用预离解氨、前体材料的分解和金属氢化物的氨解。亚稳氧化物和氧化物氮化物的形成将进行研究，以扩大材料的范围并加强SPP内部的合作。Ta_2O_5氨解反应的原位中子衍射图将详细描述光催化剂Ta_3N_5是如何通过瞬时发生的TaN及其亚稳态修饰形成的。我们还将跟踪亚稳的二尖晶石型V2O的形成和黑磷的形成。实验研究将得到SPP内外合作的量子力学计算的支持。

Understanding of reaction pathways is a fundamental basis in the synthesis of metastable compounds. Therefore, we have developed gas-pressure and gas-flow cells for in situ neutron diffraction aiming on the reaction of solids with hydrogen (deuterium) or ammonia gas. With the former 160 bar gas pressure and 400 °C are accessible in combination with extremely low diffraction background due to proper orientation of a sapphire single crystal tube as a sample container. Higher temperatures (1000 °C) are achieved using silica tubes like in the gas-flow cell. Both are heated with a two-sided laser system and the temperature is measured with a calibrated pyrometer. In situ neutron diffraction on solid-gas reactions with hydrogen or ammonia gas with a time resolution of one minute is now well established with both cells on the high-intensity diffractometer D20 at the ILL in Grenoble, France. A variety of systems was studied, amongst them the formation of deuterides of palladium, Zintl phases, intermetallic Li-Al compounds, lanthanide intermetallics, VN, V2N, and of Fe4N via intermediate Fe3N. For palladium rich intermetallic phases a complete reaction mechanism could be proposed, which allowed the planned synthesis of new metastable compounds. The successful concept of our in situ gas cells will be optimized in view of the temperature-pressure range (seal and container materials), automated pressure-temperature programs and installing them on the diffractometer SPODI at the FRM-II, Garching. Using the known reaction mechanism for palladium rich intermetallics, new metastable hydrides will be synthesized for metals M = Tl1-xPbx, In1-xSnx, As, Sb, Se, Mn. Metastable intermediates in the formation of mixed-valent ytterbium hydrides and the hydrogenation of light-weight intermetallics of interest for hydrogen storage will be studied as well. For nitrides the knowledge already acquired on vanadium and iron will be deepened and extended to chromium, manganese, cobalt, nickel and copper, in order to yield and structurally characterize metastable compounds, such as Fe16N2, Fe8N or Co3N, some of them are highly interesting in view of their magnetic properties. Other synthetic strategies to metastable nitrides include the use of predissociated ammonia, decomposition of precursor materials and the ammonolysis of metal hydrides.The formation of metastable oxides and oxide nitrides will be studied, in order to widen the range of materials and to strengthen collaboration within the SPP. In situ neutron diffraction on the ammonolysis of Ta2O5 will give a detailed picture of the formation of the photocatalyst Ta3N5 via transiently occurring TaON and its metastable modification. We will also follow the formation of metastable bixbyite type V2O3 and the formation of black phosphorous. Experimental studies will be backed up by quantum mechanical calculations in cooperation within and outside the SPP.