非平衡条件下热致结构竞争性与体心立方铁的亚稳性
Thermal Induced Structural Competitiveness and Metastability of Body-centered Cubic Iron under Non-Equilibrium Conditions
AI总结：
本研究通过ab initio计算揭示，在非平衡高温条件下，BCC铁因能量下降、声子稳定及高振动熵而具有结构竞争性与亚稳性，为理解地球内核及实验中的铁相变与凝固提供了理论框架。
摘要：
在数百万巴压力下，铁在近熔点处的结构和稳定性在高压物理学以及地球与行星科学中备受关注。尽管体心立方（BCC）相普遍被认为在较低温度下不稳定，但相对于六方密排（HCP）相，其在地球内核（IC）高温（约0.5 eV）下的稳定性仍是理论和实验上持续争论的话题。我们的ab initio计算显示，能量显著下降，势能面上出现平台和局部极小值，且在升高的电子温度（>1-1.5 eV）下所有声子模式均稳定。这些效应加剧了BCC、HCP和面心立方（FCC）相之间的竞争，并导致BCC结构的亚稳性。此外，BCC铁的显著晶格振动熵增强了其热力学稳定性。这种非平衡条件下热致结构竞争性与亚稳性，为理解铁相变关系和凝固过程提供了清晰的理论框架，适用于实验和IC环境。
英文摘要：
The structure and stability of iron near melting at multi-megabar pressures are of significant interest in high pressure physics and earth and planetary sciences. While the body-centered cubic (BCC) phase is generally recognized as unstable at lower temperatures, its stability relative to the hexagonal close-packed (HCP) phase at high temperatures (approximately 0.5 eV) in the Earth's inner core (IC) remains a topic of ongoing theoretical and experimental debate. Our ab initio calculations show a significant drop in energy, the emergence of a plateau and a local minimum in the potential energy surface, and stabilization of all phonon modes at elevated electron temperatures (>1-1.5 eV). These effects increase the competition among the BCC, HCP, and the face-centered cubic (FCC) phases and lead to the metastability of the BCC structure. Furthermore, the thermodynamic stability of BCC iron is enhanced by its substantial lattice vibration entropy. This thermally induced structural competitiveness and metastability under non-equilibrium conditions provide a clear theoretical framework for understanding iron phase relations and solidification processes, both experimentally and in the IC.
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