Recently, probing the reaction under extreme conditions from both kinetic and dynamic perspectives in an unprecedented time scale has been realized by taking advantage of the state-of-the-art XFEL facilities. The high-brilliant X-ray (~10¹⁰ photons per pulse in ~20 fs) can penetrate and heat high-atomic number (Z) materials thoroughly, providing a more extreme condition than traditional near-IR laser heating in diamond anvil cells (DACs). In addition, the reduction of heating time to nanoseconds can prevent the carbon contamination from anvils and is beneficial for determining accurate structures.
High-Z materials, such as tungsten and tungsten nitrides, are ideal subjects for studying the X-ray heating effect and fast reactions. Tungsten nitrides are exceptionally important materials for their unique chemical and mechanical properties, such as high hardness, incompressibility, and high energy density. The high-pressure high-temperature synthesis usually results in complex structures from N-poor to N-rich compounds, while the formation process is unclear.
In this study, the reaction between tungsten and nitrogen under high pressure was investigated in a temporal resolution of 222 ns at European XFEL. The experiments were performed in collaboration with more than 15 research groups from different countries under community proposal. At 80 GPa, hexagonal W₇N₁₂ was successfully synthesized via direct reaction between W and ζ-N₂ via pulsed X-ray heating above 3000 K. The formation, melting, and recrystallization of W₇N₁₂ were observed through real-time XRD images on nanosecond scales. Our findings demonstrate XFEL as a new approach to investigate the time-resolved ultrafast physical and chemical phenomena under high pressure and high temperature in DACs.

high temperature and high pressure,XFEL,tungsten nitride,time-resolved XRD