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 Bi-III, respectively. The former is more rapid than the latter because the Bi-V to B-IV transformation is driven by interaction between the closest atoms while the Bi-V to B-III transformation requires 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 can change the phase transformation pathway in a dynamic process.

中文翻译：

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冲击释放过程中铋相变动力学的原位观察

采用时间分辨 X 射线衍射技术来监测激光冲击铋的结构转变。结果表明，在冲击释放过程中，从冲击诱导的 Bi-V 相到亚稳态 Bi-IV 相的转变被延迟，而不是热力学稳定的 Bi-III 相。亚稳态 Bi-IV 相的出现可以通过两种分别向 Bi-IV 和 Bi-III 转化途径之间的竞争性相互作用来理解。前者比后者更快，因为 Bi-V 到 B-IV 的转变是由最接近的原子之间的相互作用驱动的，而 Bi-V 到 B-III 的转变需要第二最近的原子之间的相互作用。根据经典成核模型，Bi-V 到 Bi-IV 转变的成核时间确定为 5.1±0.9 ns。这一观察结果证明了瞬态亚稳态相形成的重要性，它可以改变动态过程中的相变途径。