Crystal Chemistry of MgAl2O4 Spinel Solid Solution-Peculiar Site Preference of Cation Observed Under Substitution and Pressure-
Crystal Chemistry of MgAl2O4 Spinel Solid Solution-Peculiar Site Preference of Cation Observed Under Substitution and Pressure-
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MgAl2O4 尖晶石固溶体的晶体化学-在取代和压力下观察到的阳离子的特殊位点偏好-
DOI：
10.5940/jcrsj.53.13
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发表时间：
2011
影响因子：
0.7
通讯作者：
K. Sugiyama
中科院分区：
文献类型：
--
作者：
A. Yoshiasa;H. Maekawa;K. Sugiyama
尖晶石族矿物或尖晶石型化合物是地壳和地幔的重要组成部分，对其结构的研究一直是人们关注的焦点。尽管它们的结构简单，许多尖晶石型化合物表现出复杂的无序现象，涉及在两个网站上的阳离子的混合，这对热力学和物理性质具有重要的后果。用27 Al MAS NMR和单晶X射线衍射研究了MgAl_（2-x）Ga_xO_4固溶体中的阳离子分布和结构变化。在固溶体中确定的局部距离对应于从有效离子半径预期的键距离，除了在四面体位置中的Al-O距离。结果表明，尖晶石固溶体中四面体位的Al-O间距比预期值长0.15埃。硼与Al、Ga是同一族元素，其离子半径相当小。在高温高压条件下合成了MgAl_（2-x）B_xO_4尖晶石单晶。在1273 K和11 GPa下，硼的最大含量约为x = 0.13。在Mg-Al-B系尖晶石固溶体中，最小的B离子优先占据八面体位置。B ~（3+）离子在压力下可以取代较大的Al ~（3+）离子。这些尖晶石固溶体在很大程度上是无序晶体。只有氧离子的位置移动才能缓和固溶体中的无序。
Considerable efforts have been devoted to the structural studies of spinel group minerals or type compounds because of their importance as constituents of the Earth’s crust and mantle. Despite their simple structures, many spinel type compounds exhibit complex disordering phenomena involving the mixing of cation on two sites, which have important consequences for both thermodynamic and physical properties. The cation distributions and the structural variation in MgAl2-xGaxO4 solid-solution have been clarified using 27Al MAS NMR measurements and single crystal X-ray diffraction. The determined local distance in the solid solution corresponds with the bond distance expected from the effective ionic radii except Al-O distance in the tetrahedral site. We have revealed that the Al-O distance in the tetrahedral site in spinel solid solution is about 0.15 A longer than the expected value. Boron is the same group element as Al and Ga and its ionic radius is considerably small. Single crystals of MgAl2-xBxO4 spinel were synthesized under high pressure and high temperature. The maximum content of boron was about x = 0.13 at 1273 K and 11 GPa. The smallest B ion occupies the octahedral site in top priority in the spinel solid solution of the Mg-Al-B systems. The B3+ ions can replace considerably bigger Al3+ ion under pressure. These spinel solid-solutions are largely disordered crystals. Only the positional shifts of oxygen ion have been relaxing the disorder in the solid solution.