Studying the properties and phase diagram of iron at high-pressure and high-temperature conditions has relevant implications for Earth’s inner structure and dynamics and the temperature of the inner core boundary (ICB) at 330 GPa. Also, a hexagonal-closed packed to body-centered cubic (bcc) phase transition has been predicted by many theoretical works but observed only in a few experiments. The recent coupling of high-power laser with advanced x-ray sources from synchrotrons allows for novel approaches to address these issues. Here, we present a study on shock compressed iron up to 270 GPa and 5800 K probed by single-pulse (100 ps FWHM) x-ray absorption spectroscopy (XAS). Based on the analysis of the XAS spectra, we provide structural identification and bulk temperature measurements along the Hugoniot up to the melting. These results rule out the predicted transition to a high-temperature bcc phase and allow one to discriminate among existing equations of state models and melting curves. In particular, we report the first bulk temperature measurement in shock compressed iron on the melting plateau at 240(20) GPa and 5345(600) K. The melting curve resulting from our work extrapolates to a temperature of 6202(514) K at 330 GPa and represents a refined upper bound for the ICB temperature. Published by the American Physical Society 2024

中文翻译：

---

超快 X 射线吸收光谱探测高达 270 GPa 的冲击铁熔化温度和相位稳定性的新约束


研究铁在高压和高温条件下的性质和相图对地球的内部结构和动力学以及 330 GPa 的内核边界 （ICB） 温度具有相关意义。此外，许多理论著作已经预测了六边形封闭堆积到体心立方 （bcc） 相变，但仅在少数实验中观察到。最近高功率激光器与来自同步加速器的先进 X 射线源的耦合为解决这些问题提供了新的方法。在这里，我们介绍了一项通过单脉冲 （100 ps FWHM） X 射线吸收光谱 （XAS） 探测高达 270 GPa 和 5800 K 的冲击压缩铁的研究。根据对 XAS 光谱的分析，我们提供了沿 Hugoniot 的结构鉴定和整体温度测量，直到熔化。这些结果排除了预测的向高温 bcc 相的转变，并允许人们在现有的状态模型和熔融曲线方程之间进行区分。特别是，我们报道了在 240（20） GPa 和 5345（600） K 的熔化平台上冲击压缩铁的首次整体温度测量。我们工作得出的熔解曲线外推到 330 GPa 时的温度为 6202（514） K，代表了 ICB 温度的精细上限。 美国物理学会 2024 年出版