Thermoelastic property and high-pressure stability of Fe7C3: Implication for iron-carbide in the Earth’s core
Thermoelastic property and high-pressure stability of Fe7C3: Implication for iron-carbide in the Earth’s core
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DOI：
10.2138/am.2011.3703
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发表时间：
2011-07
影响因子：
3.1
通讯作者：
Y. Nakajima;E. Takahashi;N. Sata;Yu Nishihara;K. Hirose;K. Funakoshi;Y. Ohishi
中科院分区：
文献类型：
--
作者：
Y. Nakajima;E. Takahashi;N. Sata;Yu Nishihara;K. Hirose;K. Funakoshi;Y. Ohishi
摘要为了研究Fe 7 C3的物理性质，我们用Kawai型多顶砧装置和金刚石对顶砧装置在71.5GPa和1973 K下进行了原位X射线衍射实验。发现碳化物在这些实验条件下是稳定的。然而，我们发现它的等温压缩和热膨胀的异常行为。这些异常可能是由于Fe 7 C3从铁磁（FM）到顺磁（PM）相的磁相变。1 bar时的居里温度为523 K（Tsuzuki et al. 1984），随着压力的增加而降低，压力诱导的磁转变估计发生在~18 GPa和300 K。通过Mie-Grüneisen-Debye（MGD）状态方程（EOS）拟合pm-Fe 7 C3的压力-体积-温度（P-V-T）数据集，并获得以下参数：晶胞体积V0 = 184.2 ± 0.3 × 10 - 3，体积弹性模量K 0 = 253 ± 7 GPa，体积弹性模量的压力导数K ′ 0 = 3.6 ± 0.2，零压时的格吕奈森参数γ0 = 2.57 ± 0.05，德拜温度θ0 = 920 ± 140 K，q = 2.2 ± 0.5。Fe 7 C3的计算密度为从地震观测获得的地球内核密度提供了很好的解释。
Abstract To investigate the physical property of Fe7C3, we carried out in situ X‑ray diffraction experiments using a Kawai-type multi-anvil apparatus and a diamond anvil cell up to 71.5 GPa and 1973 K. The carbide was found to be stable under these experimental conditions. However, we found anomalous behavior in its isothermal compression and thermal expansivity. These anomalies could be due to the magnetic phase transition in Fe7C3 from a ferromagnetic (fm) to a paramagnetic (pm) phase. The Curie temperature of 523 K at 1 bar (Tsuzuki et al. 1984) decreases with pressure, and the pressure-induced magnetic transition is estimated to occur at ~18 GPa and 300 K. The pressure-volume-temperature (P-V-T) data set for the pm-Fe7C3 was fitted by the Mie-Grüneisen-Debye (MGD) equation of state (EOS) and the following parameters were obtained: unit-cell volume V0 = 184.2 ± 0.3 Å3, bulk modulus K0 = 253 ± 7 GPa, the pressure derivative of bulk modulus K'0 = 3.6 ± 0.2, Grüneisen parameter γ0 = 2.57 ± 0.05, Debye temperature θ0 = 920 ± 140 K, and q = 2.2 ± 0.5, respectively, at zero pressure. The calculated density for Fe7C3 provides a good explanation for the density of the Earth’s inner core obtained from seismological observations.