In-situ observation of melting and recrystallization to a high-pressure phase of MoO₃ induced by nanosecond laser shock-compression

Molybdenum(VI) oxide (MoO₃) is a layered n-type wide bandgap semiconductor and has attracted attention in energy-related catalysis applications. It is important to investigate the structural response in various extreme environments. In the present study, the structural changes in MoO₃ under high-pressure and high-temperature conditions induced by laser shock compression were investigated via in situ XRD using ultra-short X-ray pulses from an XFEL. When the sample was shock-compressed at pressures above 61 GPa, the Bragg peaks in the XRD profile first weakened as the shock wave propagated through the sample, and a broad halo pattern appeared in the profile indicating melting of the sample. Recrystallization of liquid MoO₃ to α-MoO₃ phase with MoO₃-II was observed on nanosecond timescales during pressure release.