The pressure scale at multimegabar and the implication to the center of the Earth

我们将NaCl-B2压缩到304 Gpa，并根据Birch-Murnaghan和Vinet状态方程给出了该相的压力标度。在273(6)Gpa和4490(560)K、250(19)Gpa和2730(110)K、304(3)Gpa和2780(210)K范围内，分别研究了Fe、Fe_<90>Ni_<10>和Fe_<87.9>、Ni_<4.4>Si_<7.7>的相关系，发现在所研究的压力和温度条件下，这些化合物都具有稳定的六方密实排列结构。高温条件下，hcp-Fe-Ni-Si合金轴比的温度依赖性较弱，表明c轴仍比a轴硬。因此，hcp-Fe-Ni-Si合金与地球自转轴平行的c轴排列可以解释观测到的内核地震波各向异性。另一方面，Fe_<88.1>Ni_<9.1>S_<2.8>合金被压缩到335 Gpa，并保持稳定的六边形密排结构。我们的结果表明，hcp Fe-5在。% Ni-7.9-10.3 at。假设密度与镍和硫含量之间存在线性关系，则% S合金可以解释330 Gpa时的内芯密度。

We compressed NaCl-B2 to 304 Gpa and presented a pressure scale based on the Birch-Murnaghan and Vinet equations of state for this phase. The phase relations of Fe, Fe_<90>Ni_<10> and Fe_<87.9>Ni_<4.4>Si_<7.7> were investigated up to 273(6) Gpa and 4490(560) K, 250(19) Gpa and 2730(110) K and 304(3) Gpa and 2780(210) K, respectively, and the hexagonal close-packed structure was found to be stable in all of these compounds under the pressure and temperature conditions studied. The weak temperature dependency of the axial ratio of hcp-Fe-Ni-Si alloy indicates that the c-axis is still harder than the a-axis at high temperature condition. Therefore the alignment of hcp-Fe-Ni-Si alloy with the c-axis parallel to the Earth's rotation axis could account for the observation of the seismic wave anistropy of the inner core. On the other hand, Fe_<88.1>Ni_<9.1>S_<2.8> alloy was compressed up to 335 Gpa, and the hexagonal close-packed structure was found to be stable. Our results indicate that the hcp Fe-5 at.% Ni-7.9-10.3 at.% S alloy can account for the density of the inner core at 330 Gpa, assuming a linear relationship exists between the density and the nickel and sulfur content.