New sample environments and techniques specifically designed for in situ powder X‐ray diffraction studies up to 1000 bar (1 bar = 105 Pa) gas pressure are reported and discussed. The cells can be utilized for multiple purposes in a range of research fields. Specifically, investigations of gas–solid reactions and sample handling under inert conditions are undertaken here. Sample containers allowing the introduction of gas from one or both ends are considered, enabling the possibility of flow‐through studies. Various containment materials are evaluated, e.g. capillaries of single‐crystal sapphire (Al2O3), quartz glass (SiO2), stainless steel (S316) and glassy carbon (Sigradur K), and burst pressures are calculated and tested for the different tube materials. In these studies, high hydrogen pressure is generated with a metal hydride hydrogen compressor mounted in a closed system, which allows reuse of the hydrogen gas. The advantages and design considerations of the in situ cells are discussed and their usage is illustrated by a case study.

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To enhance the dehydrogenation/rehydrogenation kinetic behavior of the LiBH 4 −MgH 2 composite system, TiF 4 is used as an additive. The effect of this additive on the hydride composite system has been studied by means of laboratory and advanced synchrotron techniques. Investigations on the synthesis and mechanism upon hydrogen interaction show that the addition of TiF 4 to the LiBH 4 −MgH 2 composite system during the milling procedure leads to the in situ formation of well-distributed nanosized TiB 2 particles. These TiB 2 nanoparticles act as nucleation agents for the formation of MgB 2 upon dehydrogenation process of the hydride composite system. The effect of TiB 2 nanoparticles is maintained upon cycling.

We report on the first in situ synchrotron radiation powder X-ray diffraction study (SR-PXD) of the ammonolysis reaction of selected alkaline and alkaline earth metal hydrides (i.e., LiH, NaH, KH, MgH 2 , and CaH 2 ). The investigation was performed using an in situ SR-PXD pressure cell at an initial NH 3 pressure of 6.5 bar in a range of temperature between room temperature (RT) and 350 °C. The results of this work give new important insights into the formation of metal amides and imides starting from the corresponding metal hydrides. LiH was observed to react with NH 3 to form LiNH 2 already at RT, and then it decomposes into Li 2 NH at 310 °C through the formation of nonstoichiometric intermediates of the Li 1+x NH 2−x form. The formation of NaNH 2 takes place nearly at RT (28 °C), and it melts at 180 °C. As for LiH, KH reacts with NH 3 at RT to surprisingly form, what it seems to be, cubic KNH 2 . However, we believe this phase to be a solid solution of KH in KNH 2 . At high temperature, the possible formation of several solid solutions of K(NH 2 ) 1−y H y with defined composition is also observed. The formation of Mg(NH 2 ) 2 was observed to starts at around 220 °C, from the interaction γ-MgH 2 and NH 3 . At 350 °C, when all γ-MgH 2 is consumed, the formation of Mg(NH 2 ) 2 stops and MgNH is formed by the reaction between β-MgH 2 and NH 3. Our results indicate that the formation of the γ-MgH 2 is a key step in the synthesis of Mg(NH 2 ) 2 at low temperature (e.g., via ball milling technique). CaH 2 was observed to react with NH 3 at around 140 °C to form CaNH. At higher temperature the appearance of new reflections of possible Ca 1+x NH phases, with the same crystalline structure of CaNH but with a smaller cell parameter was observed.

We report for the first time the formation of a metal amide-hydride solid solution. The dissolution of KH into KNH leads to an anionic substitution, which decreases the interaction among NH ions. The rotational properties of the high temperature polymorphs of KNH are thereby retained down to room temperature.