Complete substitution of Fe2+ by Mg in Fe4O5: The crystal structure of the Mg2Fe2O5 end-member
Complete substitution of Fe2+ by Mg in Fe4O5: The crystal structure of the Mg2Fe2O5 end-member
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DOI：
10.2138/am-2015-5138
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发表时间：
2015-02-01
影响因子：
3.1
通讯作者：
Woodland, Alan B.
中科院分区：
文献类型：
--
作者：
Ballaran, Tiziana Boffa;Uenver-Thiele, Laura;Woodland, Alan B.
用X射线单晶衍射法测定了在15 GPa和1550 ℃下合成的新型Mg_2Fe_2O_5氧化物的晶体结构。该化合物与Fe_4O_5是同构的，可以被认为是这两种氧化物之间的固溶体的另一端员，涉及Fe ~（2+）取代Mg。得到的晶胞晶格参数a = 2.8889（4），B = 9.7282（4），和c = 12.5523（7）埃小于Fe 4 O 5的晶胞晶格参数。Mg和Fe 3+阳离子被发现是无序的Mg 2Fe 2 O 5结构的三个晶体学位置之间，虽然观察到的三角棱柱协调（M3）的Mg的偏好。Mg取代到Fe 4 O 5结构中减少了M1和M2位点的八面体畸变。与Mg一样，最近发现Cr替代Fe 4 O 5，使得在Mg-Cr-Fe氧化物系统中Fe 3 +/σ Fe可以在0至1.0之间变化。Mg和Cr在Fe 4 O 5中的替代也使得这一阶段更相关的预期在地球的过渡带和深部上地幔的散装组合物。因此，具有CaFe 3 O 5型结构的M4 O 5相需要被认为是在尖晶石结构相变得不稳定的压力和温度条件下对几种简单氧化物体系的相关系的新添加。
The crystal structure of a novel Mg2Fe2O5 oxide synthetized at 15 GPa and 1550 degrees C has been determined by means of single-crystal X-ray diffraction. This compound is isostructural with Fe4O5 and can be considered as the other end-member of a solid solution between these two oxides involving the substitution of Fe2+ for Mg. The resulting unit-cell lattice parameters a = 2.8889(4), b = 9.7282(4), and c = 12.5523(7) angstrom are smaller than those of Fe4O5. Mg and Fe3+ cations are found to be disordered among the three crystallographic sites of the Mg2Fe2O5 structure, although preference of Mg for the trigonal prism coordination (M3) is observed. Substitution of Mg into the Fe4O5 structure reduces the octahedral distortion of both the M1 and M2 sites. Like Mg, Cr has recently been found to substitute into Fe4O5, so that Fe3+/Sigma Fe can vary from 0 to 1.0 in the Mg-Cr-Fe oxides system. Substitution of both Mg and Cr in Fe4O5 also makes this phase more relevant for bulk compositions expected in the Earth's transition zone and deep upper mantle. M4O5 phases having the CaFe3O5-type structure, therefore, need to be considered as a new addition to the phase relations of several simple oxide systems at pressure and temperature conditions at which the spinel-structured phases become unstable.