镍对地球内地核成核的影响量化
Quantifying the effects of nickel on Earth's inner-core nucleation
AI总结：
本研究通过原子级模拟量化镍对地球内地核成核的影响，发现Fe80Ni20中bcc相成核在约250K过冷度下即可发生，镍富集、bcc相成核及化学异质性可缩小内地核成核悖论。
AI中文摘要：
地球固态内地核的形成标志着地球深部热与化学演化的重大转变，但其起源仍存在悖论，因为初始成核似乎需要外核中达到大得不切实际的过冷度。本研究在内地核条件下，采用原子级模拟量化镍（Ni）对该过程的影响：铁-镍（Fe-Ni）合金在密排六方（hcp）与体心立方（bcc）相之间保持强烈的热力学竞争，其中bcc相始终形成更小的临界核，且比hcc相具有更低的成核势垒；熔体中镍含量的增加会进一步降低成核势垒、缩短成核等待时间；局部化学波动对宏观成核速率也有显著影响。综合上述效应，Fe80Ni20合金中的bcc相成核在约250K的过冷度下即可发生，接近地球物理约束条件。研究表明，镍富集、bcc相成核及化学异质性可大幅缩小内地核成核悖论的范围。
英文摘要：
The formation of Earth's solid inner core marks a major transition in the thermal and chemical evolution of the deep Earth, yet its origin remains paradoxical, as initial nucleation appears to require unrealistically large undercooling in the outer core. Here, we use atomistic simulations to quantify how Ni affects this process under inner-core conditions. While Fe-Ni alloys preserve strong thermodynamic competition between the hcp and bcc phases, the bcc phase consistently forms smaller critical nuclei and has lower nucleation barriers than hcp. Increasing Ni content in the melts further lowers the nucleation barrier and shortens the nucleation waiting time. Local chemical fluctuations also strongly affect the macroscopic nucleation rate. Combining these effects, bcc nucleation in Fe80Ni20 reaches about 250 K of undercooling, approaching geophysical constraints. We demonstrate that Ni enrichment, bcc nucleation, and chemical heterogeneity substantially narrow the inner-core nucleation paradox.
