The experimental identification of structural transitions in layered black phosphorus (BP) under mechanical stress is essential to extend its application in microelectromechanical (MEMS) devices under harsh conditions. High-pressure Raman spectroscopic analysis of BP flakes suggests a transition pressure at ∼4.2 GPa, where the BP’s crystal structure progressively transforms from an orthorhombic to a rhombohedral symmetry (blue phosphorus, bP). The phase transition has been identified by observing a transition from blueshift to redshift of the in-plane characteristic Raman modes (B_2g and A_g²) with increasing pressure. Recovery of the vibrational frequencies for all three characteristic Raman modes confirms the reversibility of the structural phase transition. First-principles calculations provide insight into the behavior of the Raman modes of BP under high pressure and reveal the mechanism responsible for the partial phase transition from BP to bP, corresponding to a metastable equilibrium state where both phases coexist.

中文翻译：

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几层黑色磷中可逆的压力诱导的部分相变。

在机械应力下，层状黑磷（BP）的结构转变的实验识别对于在恶劣条件下扩展其在微机电（MEMS）器件中的应用至关重要。BP薄片的高压拉曼光谱分析表明，转变压力约为4.2 GPa，其中BP的晶体结构逐渐从正交晶体转变为菱形对称（蓝磷，bP）。通过观察面内特征拉曼模式（B _2g和A _g ²从蓝移到红移）可以识别出相变）随着压力的增加。所有三个特征拉曼模式的振动频率的恢复证实了结构相变的可逆性。第一性原理计算可洞悉高压下BP的拉曼模式的行为，并揭示负责从BP到bP的部分相变的机理，这对应于两个相共存的亚稳态平衡状态。