In situ high-pressure high-temperature X-ray powder diffraction studies of the cobalt-hydrogen system reveal the direct synthesis of both the binary cobalt hydride (CoH) and a novel cobalt dihydride (CoH₂). We observe the formation of fcc CoH at pressures of 4 GPa, which persists to pressures of 45 GPa. At this pressure, we see the emergence with time of a further expanded fcc lattice, which we identify as CoH₂, where the hydrogen atoms occupy the tetrahedral vacancies. We have explored alternative synthesis routes of CoH₂ and can lower the synthesis pressure to 35 GPa by the application of high temperature. CoH₂ is stable to at least 55 GPa and decomposes into CoH below 10 GPa, releasing molecular hydrogen before further decomposing completely into its constituent elements below 3 GPa. As a first-row transition metal, cobalt has a relatively lower mass than other hydride-forming transition metals, and as a result, CoH₂ has a high hydrogen content of 3.3 wt. % and a volumetric hydrogen density of 214 g/l.

中文翻译：

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高压合成和氢化钴的稳定性

钴-氢系统的原位高压X射线粉末衍射研究表明，直接合成了二元氢化钴（CoH）和新型二氢化钴（CoH ₂）。我们观察到在4 GPa的压力下会形成fcc CoH，并持续到45 GPa的压力。在此压力下，随着时间的推移，我们看到了进一步扩展的fcc晶格的出现，我们将其标识为CoH ₂，其中氢原子占据了四面体空位。我们已经探索了CoH _2的替代合成路线，并且通过施加高温可以将合成压力降低到35 GPa。CoH ₂稳定在至少55 GPa并在低于10 GPa时分解为CoH，释放出分子氢，然后进一步分解为低于3 GPa的组成元素。作为第一行过渡金属，钴的质量要比其他形成氢化物的过渡金属的质量低，因此，CoH ₂的氢含量较高，为3.3 wt％。％和体积氢密度为214g / l。