Experimental constraints on the sound velocities of cementite Fe3C to core pressures
Experimental constraints on the sound velocities of cementite Fe3C to core pressures
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DOI：
10.1016/j.epsl.2018.05.002
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发表时间：
2018-07
影响因子：
5.3
通讯作者：
Bin Chen;X. Lai;Jie Li;Jiachao Liu;Jiyong Zhao;W. Bi;E. Ercan Alp;Michael Y. Hu;Yuming Xiao-Yuming
中科院分区：
文献类型：
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作者：
Bin Chen;X. Lai;Jie Li;Jiachao Liu;Jiyong Zhao;W. Bi;E. Ercan Alp;Michael Y. Hu;Yuming Xiao-Yuming
用核共振非弹性X射线散射(NRIXS)技术在金刚石顶压室中测量了渗碳体Fe3C在300K和1.5Mbar的声速。从Fe3 C的部分声子态密度(PDO)和状态方程(EOS)出发，求出了其剪切模数、纵波(V P)和横波(V S)速度对核压的弹性参数.X射线发射光谱(XES)测量发现，粉末Fe3 C样品在10~5 0 Gpa之间逐渐发生压力诱导的自旋配对相变。在完成自旋配对相变后，低自旋Fe3 C的VP和V S随压力增加的速率明显低于高自旋Fe3 C.结果表明，在固体铁中掺入碳形成碳化铁相Fe3C和Fe7C3，可有效地降低V-S，但使泊松比分别提高0.0 5和0.0 7，接近地核的地震观测值。与初步参考地球模型(PREM)的比较表明，含有铁及其富碳合金的内核成分可以令人满意地解释观测到的内核地震性质。
Sound velocities of cementite Fe 3 C have been measured up to 1.5 Mbar and at 300 K in a diamond anvil cell using the nuclear resonant inelastic X-ray scattering (NRIXS) technique. From the partial phonon density of states (pDOS) and equation of state (EOS) of Fe 3 C, we derived its elastic parameters including shear modulus, compressional (V P) and shear-wave (V S) velocities to core pressures. A pressure-induced spin-pairing transition in the powdered Fe 3 C sample was found to occur gradually between 10 and 50 GPa by the X-ray Emission Spectroscopy (XES) measurements. Following the completion of the spin-pairing transition, the V P and V S of low-spin Fe 3 C increased with pressure at a markedly lower rate than its high-spin counterpart. Our results suggest that the incorporation of carbon in solid iron to form iron carbide phases, Fe 3 C and Fe 7 C 3, could effectively lower the V S but respectively raise the Poisson's ratio by 0.05 and 0.07 to approach the seismically observed values for the Earth's inner core. The comparison with the preliminary reference Earth model (PREM) implies that an inner core composition containing iron and its carbon-rich alloys can satisfactorily explain the observed seismic properties of the inner core.