High-pressure transitions in MgAl2O4 and a new high-pressure phase of Mg2Al2O5
High-pressure transitions in MgAl2O4 and a new high-pressure phase of Mg2Al2O5
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DOI：
10.1016/j.jssc.2008.11.015
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发表时间：
2009-02
影响因子：
3.3
通讯作者：
A. Enomoto;H. Kojitani;M. Akaogi;H. Miura;H. Yusa
中科院分区：
文献类型：
--
作者：
A. Enomoto;H. Kojitani;M. Akaogi;H. Miura;H. Yusa
在21-27 GPa和1400-2500℃条件下，用多砧仪检测了MgAl{sub 2}和{sub 4}的相变。MgAl{sub 2}O{sub 4}尖晶石高压解离产物MgO与Al{sub 2}O{sub 3}刚玉的混合物在26 ~ 27gpa和1400 ~ 2000℃下结合成铁酸钙型MgAl{sub 2}O{sub 4}。在温度高于2000℃，压力低于25.5 GPa的条件下，Al{sub 2}O{sub 3}刚玉与Mg{sub 2}Al{sub 2}O{sub 5}组成的新相的混合物稳定存在。两个场之间的过渡边界具有很强的负压-温度斜率。根据粉末x射线衍射谱对Mg{sub 2}Al{sub 2}O{sub 5}相进行了结构分析和Rietveld细化，结果表明，该相是一种具有正交对称（Pbam）的新型结构，其晶格参数为a=9.3710(6) a, b=12.1952(6) a, c=2.7916(2) a， V=319.03(3) a {sup 3}， Z=4。该结构由边共享和角共享（Mg, Al）O{sub 6}八面体组成，包含沿c轴运行的边共享八面体链。部分Mg原子被安置在六配位的三角棱柱位上，这些棱柱位被共边的（Mg, Al）O{sub 6}八面体链包围。其结构与铁辉石（Mg, Fe{sup 2+}）{sub 2}(Fe{sup 3+}, Al)(BO{sub 3})O{sub 2}有关。Mg{sub 2}Al{sub 2}O{sub 5}相的摩尔体积比2MgO和Al{sub 2}O{sub 3}刚玉的摩尔体积之和小0.18%。在各种A{sup 2+}B{sup 3+}{sub 2}O{sub 4}化合物中，仅在MgAl{sub 2}O{sub 4}化合物中发现高压解离为刚玉型相和具有ludwigite相关结构的相的混合物。-图解摘要：MgAl{sub 2}O{sub 4}在高压和高温下解离成Al{sub 2}O{sub 3}刚玉和Mg{sub 2}Al{sub 2}O{sub 5}的新高压相的混合物。Mg{sub 2}Al{sub 2}O{sub 5}相代表了一种新的正交对称结构类型，呈现出到（0 0 1）平面的投影。该结构由边共享和角共享（Mg, Al）O{sub 6}八面体组成，并包含沿c轴运行的边共享八面体链。
Phase transitions in MgAl{sub 2}O{sub 4} were examined at 21-27 GPa and 1400-2500 deg. C using a multianvil apparatus. A mixture of MgO and Al{sub 2}O{sub 3} corundum that are high-pressure dissociation products of MgAl{sub 2}O{sub 4} spinel combines into calcium-ferrite type MgAl{sub 2}O{sub 4} at 26-27 GPa and 1400-2000 deg. C. At temperature above 2000 deg. C at pressure below 25.5 GPa, a mixture of Al{sub 2}O{sub 3} corundum and a new phase with Mg{sub 2}Al{sub 2}O{sub 5} composition is stable. The transition boundary between the two fields has a strongly negative pressure-temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg{sub 2}Al{sub 2}O{sub 5} phase indicated that the phase represented a new structure type with orthorhombic symmetry (Pbam), and the lattice parameters were determined as a=9.3710(6) A, b=12.1952(6) A, c=2.7916(2) A, V=319.03(3) A{sup 3}, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O{sub 6} octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O{sub 6} octahedra. The structure is related with that of ludwigite (Mg, Fe{sup 2+}){sub 2}(Fe{sup 3+}, Al)(BO{sub 3})O{sub 2}. The molar volume of the Mg{sub 2}Al{sub 2}O{sub 5} phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al{sub 2}O{sub 3} corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl{sub 2}O{sub 4} among various A{sup 2+}B{sup 3+}{sub 2}O{sub 4} compounds. - Graphical abstract: MgAl{sub 2}O{sub 4} dissociates into a mixture of Al{sub 2}O{sub 3} corundum and a new high-pressure phase of Mg{sub 2}Al{sub 2}O{sub 5} at high pressures and temperatures. The Mg{sub 2}Al{sub 2}O{sub 5} phase represents a new structure type with orthorhombic symmetry, showing the projection to (0 0 1) plane. The structure consists of edge- and corner-shared (Mg, Al)O{sub 6} octahedra, and contains chains of edge-shared octahedra running along the c-axis.