In situ observation of the phase transformation kinetics of bismuth during shock release

Abstract

A time-resolved X-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth. Results reveal a retarded transformation from the shock-induced Bi-V phase to a metastable Bi-IV phase during the shock release, instead of the thermodynamically stable Bi-III phase. The emergence of the metastable Bi-IV phase is understood by the competitive interplay between two transformation pathways towards the Bi-IV and the Bi-III, respectively. The former is more rapid than the latter because the Bi-V to B-IV transformation is driven by the interaction between the closest atoms while the Bi-V to B-III transformation requires the interaction between the second closest atoms. The nucleation time for the Bi-V to Bi-IV transformation is determined to be 5.1± 0.9 ns according to a classical nucleation model. This observation demonstrates the importance of the formation of the transient metastable phases, which is able to change the phase transformation pathway in a dynamic process.