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

我们将NaCl-B2压缩到304 Gpa，并提出了基于Birch-Murnaghan和Vinet状态方程的压力标度。研究了Fe、Fe_ Ni<90>_3<10>和Fe_<87.9>Ni_<4.4>Si_4<7.7>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排结构。hcp-Fe-Ni-Si合金轴比的温度依赖性较弱，表明高温下c轴硬度仍高于a轴。因此，hcp-Fe-Ni-Si合金与平行于地球自转轴的c轴的排列可以解释内核地震波各向异性的观测。而Fe_<88.1>Ni_<9.1>S_<2.8>合金在335 Gpa的压力下仍保持六方密排结构。我们的研究结果表明，hcp Fe-5at.% Ni-7.9-10.3原子%假设密度与镍和硫含量之间存在线性关系，S合金可以解释330 Gpa下的内核密度。

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.