High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys
High pressure thermoelasticity and sound velocities of Fe-Ni-Si alloys
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DOI：
10.1016/j.pepi.2019.05.011
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发表时间：
2019-09-01
影响因子：
2.3
通讯作者：
Toellner, Thomas S.
中科院分区：
文献类型：
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作者：
Morrison, Rachel A.;Jackson, Jennifer M.;Toellner, Thomas S.
众所周知，地球以铁为主的核心含有来自宇宙化学分析的镍，以及地球物理对密度和地震波速度的限制所产生的一些轻元素。虽然已经有一些关于限制铁合金热弹性能的研究，但还没有人用相同的实验方法和数据分析方法系统地研究镍和轻元素对铁合金性能的影响。我们对体心密排(HCP)的Fe0.91Ni0.09和Fe0.8Ni0.1Si0.1分别进行了高达104 Gpa和86 Gpa的核共振非弹性X射线散射和X射线衍射实验，并与在高达171 Gpa的HCP-Fe上进行的类似测量进行了比较。具体地说，我们使用为每种材料确定的状态方程和一种利用信息准则和概率分布的新方法，从(部分)声子态密度(DOS)的低能量转移区域确定德拜声速。镍降低了铁的剪切速度，而10at%Si对Fe0.91Ni0.09的剪切速度几乎没有影响。我们观察到，随着压力的增加，这些合金的声子DOS形状保持相似。因此，在测量的压缩范围内，我们用一个广义标度定律来描述声子DOS的体积依赖关系，发现HCP-Fe0.91Ni0.09的振动Gruneisen参数与HCP-Fe的振动Gruneisen参数几乎没有区别，而Fe0.8Ni0.1Si0.1的振动Gruneisen参数则呈下降趋势。从振动自由能出发，我们约束了热压的简谐振动分量，这与地核压力和温度下hcp-Fe的理论计算有显著的正偏差。总而言之，我们的结果表明，在模拟富铁行星核时，应该考虑镍的影响。
The Earth's iron-dominant core is known to contain nickel from cosmochemical analysis and some amount of light elements from geophysical constraints on density and seismic wave velocities. Although there have been several studies to constrain thermoelastic properties of iron-alloys, there has been no systematic study on the effects of nickel and light elements on properties of iron using the same experimental methods and data analysis approach. We conducted nuclear resonant inelastic X-ray scattering and X-ray diffraction experiments on body-centered cubic and hexagonal close-packed (hcp) Fe0.91Ni0.09 and Fe0.8Ni0.1Si0.1 up to 104 GPa and 86 GPa, respectively, and compare to similar measurements conducted on hcp-Fe up to 171 GPa. Specifically, we determine the Debye sound velocity from the low-energy transfer region of the (partial) phonon density of states (DOS) using the equation of state determined for each material and a new approach which utilizes information criteria and probability distributions. Nickel decreases the shear velocity of iron, while 10 at% Si has little to no effect on the shear velocity of Fe0.91Ni0.09 We observe that the shape of the phonon DOS of these alloys remains similar with increasing pressure. In the measured compression range, we therefore apply a generalized scaling law to describe the volume dependence of the phonon DOS and find that the vibrational Gruneisen parameters of hcp-Fe0.91Ni0.09 are nearly indistinguishable from those hcp-Fe and those for Fe0.8Ni0.1Si0.1 trend lower. From the vibrational free energy, we constrain the harmonic vibrational component of thermal pressure, which shows a significant positive deviation from theoretical calculations of hcp-Fe at pressures and temperatures of Earth's core. Collectively, our results demonstrate that the effects of nickel should be considered when modeling iron-rich planetary cores.