Structure of a new Al-rich phase, [K, Na]0.9[Mg, Fe]2[Mg, Fe, Al, Si]6O12, synthesized at 24 GPa
Structure of a new Al-rich phase, [K, Na]0.9[Mg, Fe]2[Mg, Fe, Al, Si]6O12, synthesized at 24 GPa
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在 24 GPa 下合成的新富铝相 [K, Na]0.9[Mg, Fe]2[Mg, Fe, Al, Si]6O12 的结构
DOI：
10.2138/am-2000-0426
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发表时间：
2000
影响因子：
3.1
通讯作者：
J. Parise
中科院分区：
文献类型：
--
作者：
T. Gasparik;A. Tripathi;J. Parise
摘要在24 GPa、1700 °C下合成了一种新的富铝相[K0.56Na0.32][Ca0.04Mg1.66Fe2+0.3][Mg0.98Fe3+0.3Al2.62Si2.1] O 12，并用X射线单晶衍射法测定了其结构。晶胞为六方晶系，空间群P63/m，a = 8.830（1），c = 2.779（1）Ω，V = 187.65（5）Ω 3，Z = 1，分子量= 448.62，计算密度= 3.970 g/cm 3。以前未知的结构包括碱和空位轴承M3网站在隧道沿着c，主要是镁轴承的三角棱柱M2网站的线性阵列，非常不寻常的地幔阶段，和边缘连接的扭曲八面体M1网站的框架充满了铝和硅。所观察到的组成变化和高密度的范围内建议复杂的固溶体行为在下地幔压力类似于辉石在上地幔和majestic石榴石在过渡带的压力。富铝相的稳定性似乎扩大到较低的铝含量，随着压力的增加，这表明一个寒武纪下地幔可以包含高达24%的新相的分子基础上。
Abstract A new Al-rich phase, [K0.56Na0.32][Ca0.04Mg1.66Fe2+0.3][Mg0.98Fe3+0.3Al2.62Si2.1]O12, was synthesized at 24 GPa, 1700 °C, and its structure was determined by single-crystal X-ray diffraction. The unit cell is hexagonal, space group P63/m, a = 8.830(1), c = 2.779(1) Å, V = 187.65(5) Å3, Z = 1, formula weight = 448.62, calculated density = 3.970 g/cm3. The previously unknown structure consists of alkali- and vacancy-bearing M3 sites in tunnels along c, mostly Mg-bearing linear arrays of trigonal prismatic M2 sites, very unusual for mantle phases, and a framework of edge-linked distorted octahedral M1 sites filled mostly with Al and Si. The observed range of compositional variations and high density suggest complex solid solution behavior at the lower-mantle pressures similar to pyroxenes at the upper-mantle and majorite garnet at the transition-zone pressures. The stability of the Al-rich phase appears to expand to lower Al contents with increasing pressure, suggesting that a chondritic lower mantle could contain up to 24% of the new phase on the molecular basis.