Effect of reaction path on high-pressure synthesis and stability of ruthenium hydrides

This study explores the behavior of ruthenium hydrides under high-pressure conditions through three thermodynamical paths using laser-heated diamond anvil cells. The synthesis of RuH0.9 occurs gradually exceeding the pressure of 23.5 GPa in the ambient temperature path, while RuH is successfully synthesized at pressures above 20 GPa and a temperature of 1500 K. High-temperature conditions are found to reduce the pressure required for synthesis. The results demonstrate that the hydrogen occupancy of octahedral interstitial sites in the ruthenium hydrides is found to reach saturation with complete hydrogen absorption in the high-temperature path. Moreover, the crystallinity of the ruthenium hydride samples improves at higher temperatures, with the grain size increasing from 10 nm in the ambient temperature path to submicron in the high-temperature path. However, the predicted RuH6 and RuH3 were not observed in the present work.