The longitudinal sound wave (P‐wave) velocity of liquid Fe₇₅P₂₅ alloy is determined up to 60 GPa using inelastic X‐ray scattering with laser‐heated diamond anvil cell. Phosphorus is found to have negligible effect on the P‐wave velocity of liquid Fe under high‐pressure conditions. Based on the P‐wave and pressure data, an adiabatic Murnaghan equation of state for liquid Fe₇₅P₂₅ is constructed, yielding to the adiabatic bulk modulus K_S0 = 94.9 ± 7.1 GPa and its pressure derivative K’_S = 3.56 ± 0.18, respectively, at 1 bar with the density of 5.94 g cm⁻³ at 2000 K. The addition of phosphorus decreases the bulk modulus and density of liquid Fe under high‐pressure conditions, which minimizes the effect on the velocity. Using the equation of state, the P‐wave velocity and density of liquid Fe₇₅P₂₅ are estimated under Earth's liquid outer core conditions. Comparison with seismological observations suggests an upper limit of phosphorus in liquid core of 14.6 ± 3.9 wt%.

中文翻译：

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高压下液态Fe–P的声速

液态Fe ₇₅ P ₂₅合金的纵向声波（P-wave）速度是使用激光加热的金刚石砧盒通过非弹性X射线散射确定的，最高可达60 GPa。发现在高压条件下，磷对液态铁的P波速度的影响可忽略不计。根据P波和压力数据，状态的用于液体的Fe绝热Murnaghan状态方程₇₅ P ₂₅被构造，产生的绝热体积模量ķ _S0  = 94.9±7.1 1GPa以上，并且压力衍生物ķ '_小号 = 3.56±0.18，分别在1 bar下的密度为5.94 g cm ^-3在2000 K下，磷的添加降低了高压条件下液态Fe的体积模量和密度，从而最大程度地减小了对速度的影响。使用状态方程，可以估算出地球液态外核条件下液态Fe ₇₅ P ₂₅的P波速度和密度。与地震观察结果的比较表明，液芯中磷的上限为14.6±3.9 wt％。