镁铝榴石中置换型Cr3 +的结构弛豫
Structural relaxation around substitutional Cr3+ in pyrope garnet
摘要：
利用Cr K边扩展X射线吸收精细结构（EXAFS）和X射线吸收近边结构（XANES）结合第一性原理计算，研究了天然镁铝榴石Mg3 Al 2Si 3 O 12中Cr 3+离子置换的结构环境. Cr-O距离接近于镁橄榄石Mg3 Cr2 Si 3 O 12中的距离，表明第一近邻的完全弛豫。在Cr-Al置换过程中，八面体Y位的局部C3 i对称性得以保留。第二和第三壳的邻居（镁和硅）放松只有部分。网站松弛是由应变引起的债券屈曲，与角倾斜的Si为中心的四面体周围的铬为中心的八面体，并通过径向变形的Mg为中心的十二面体。
英文摘要：
The structural environment of substitutional Cr3+ ion in a natural pyrope Mg3Al2Si3O12 has been investigated by Cr K-edge Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) coupled with first-principles computations. The Cr-O distance is close to that in knorringite Mg3Cr2Si3O12, indicating a full relaxation of the first neighbors. The local C3i symmetry of the octahedral Y site is retained during Cr-Al substitution. The second and third shells of neighbors (Mg and Si) relax only partially. Site relaxation is accommodated by strain-induced bond buckling, with angular tilts of the Si-centered tetrahedra around the Cr-centered octahedron, and by a radial deformation of the Mg-centered dodecahedra.
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