The melting curve of vanadium at high pressure and temperature (P-T) is of great interest to our understanding of $d$-orbital transition metals with simple crystal structures at extreme P-T conditions. Here we have investigated the melting curve and crystal structures of polycrystalline vanadium at high P-T using synchrotron x-ray diffraction (XRD) in laser-heated diamond anvil cells (LH DACs) up to ∼100 GPa and ∼4400 K, a two-stage light-gas gun with in situ shock temperature measurements up to ∼256 GPa and ∼6200 K, and ab initio molecular dynamics (AIMD) with density functional theory computations up to ∼200 GPa. The occurrence of the diffuse scattering signals in high P-T XRD patterns is used as the primary criterion to determine the melting curve of body-centered cubic (bcc) vanadium up to ∼100 GPa in LH DACs. Analysis of thermal radiation spectra of shocked vanadium using a quasispectral pyrometer constrains the melting curve up to ∼246 GPa and ∼5830 K, which is consistent with our static results using the Simon equation. The present static and dynamic experiments on the melting curve of vanadium are consistent with our AIMD simulations with the two-phase melting modeling, and are overall consistent with other theoretical simulations using the Z method. The results reconcile the recently reported theoretical discrepancy, and refute a higher melting curve report given by self-consistent ab initio lattice dynamics calculations. The consistencies among our studies indicate that one does not have to invoke superheating as a hypothesis to describe the solid-liquid equilibrium boundary of vanadium as an explanation for static vs dynamic experimental results. Our static and dynamic results with in situ diagnostics of melting and two-phase AIMD simulation have implications for studying melting curves of other $d$-orbital transition metals and their alloys at extreme P-T conditions.

中文翻译：

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最高256 GPa的钒的熔融曲线：实验与理论之间的一致性

钒在高温高压下的熔融曲线（PT）对我们的理解非常感兴趣。 $d$-在极端PT条件下具有简单晶体结构的轨道过渡金属。在这里，我们使用同步加速器X射线衍射（XRD）在高达约100 GPa和约4400 K（两阶段）的激光加热金刚石砧座中研究了高PT下多晶钒的熔融曲线和晶体结构。轻气枪，其原位冲击温度测量高达256 GPa和约6200 K，并且从头开始分子动力学（AIMD），具有高达200 GPa的密度泛函理论计算能力。高PT XRD图谱中出现的散射信号被用作确定LH DAC中高达100 GPa的体心立方（bcc）钒的熔化曲线的主要标准。使用准光谱高温计分析冲击钒的热辐射光谱，可将熔融曲线限制在约246 GPa和约5830 K，这与我们使用西蒙方程得出的静态结果相符。当前钒熔融曲线的静态和动态实验与我们的两相熔融模型的AIMD模拟是一致的，并且总体上与使用Z的其他理论模拟是一致的方法。结果调和了最近报道的理论差异，并驳斥了由自洽的从头算晶格动力学计算给出的更高的熔解曲线报告。我们研究的一致性表明，不必以过热为假设来描述钒的固液平衡边界，从而可以解释静态和动态实验结果。我们的静态和动态结果以及熔化的原位诊断和两相AIMD模拟对研究其他合金的熔化曲线具有重要意义$d$-极端PT条件下的轨道过渡金属及其合金。