Spin transition of ferric iron in the calcium-ferrite type aluminous phase
Spin transition of ferric iron in the calcium-ferrite type aluminous phase
复制标题
铁酸钙型铝相中三价铁的自旋转变
DOI：
10.1002/2017jb014095
复制
发表时间：
2017
影响因子：
3.9
通讯作者：
Prakapenka Vitali B.
中科院分区：
文献类型：
--
作者：
Wu Ye;Qin Fei;Wu Xiang;Huang Haijun;McCammon Catherine A.;Yoshino Takashi;Zhai Shuangmeng;Xiao Yuming;Prakapenka Vitali B.
在室温下，我们用原子核前向散射和X射线衍射法研究了无Fe和含Fe的Cf相，并与金刚石顶压室进行了耦合。含铁Cf相中的八面体Fe3+离子在25-35 GPa时经历了高自旋到低自旋的转变，伴随着体积减小~2.0%和体声速软化高达17.6%。根据本研究和我们以前的研究结果，预测在较低的地幔压力下，占俯冲MORB的10-30%的NAL和Cf相都将经历八面体Fe3+的自旋转变。这两个铝质相中的自旋跃迁使被俯冲的MoRb的密度增加0.24%，体积声速显著软化达2.3%，在1200K时，反常弹性区扩大并移动到30-75 Gpa，vΦ降低的最大值降至约1.8%。含铁铝相在自旋过渡区的这种异常弹性行为可能与理解观测到的下地幔地震特征有关。
We investigated Fe‐free and Fe‐bearing CF phases using nuclear forward scattering and X‐ray diffraction coupled with diamond anvil cells up to 80 GPa at room temperature. Octahedral Fe3+ions in the Fe‐bearing CF phase undergo a high‐spin to low‐spin transition at 25–35 GPa, accompanied by a volume reduction of ~2.0% and a softening of bulk sound velocity up to 17.6%. Based on the results of this study and our previous studies, both the NAL and CF phases, which account for 10–30 vol % of subducted MORB in the lower mantle, are predicted to undergo a spin transition of octahedral Fe3+at lower mantle pressures. Spin transitions in these two aluminous phases result in an increase of density of 0.24% and a pronounced softening of bulk sound velocity up to 2.3% for subducted MORB at 25–60 GPa and 300 K. The anomalous elasticity region expands and moves to 30–75 GPa at 1200 K and the maximum of theVΦreduction decreases to ~1.8%. This anomalous elastic behavior of Fe‐bearing aluminous phases across spin transition zones may be relevant in understanding the observed seismic signatures in the lower mantle.