Structure refinement of a synthetic knorringite, Mg3(Cr0.8Mg0.1Si0.1)2(SiO4)3
Structure refinement of a synthetic knorringite, Mg3(Cr0.8Mg0.1Si0.1)2(SiO4)3
复制标题
合成镁菱沸石 Mg3(Cr0.8Mg0.1Si0.1)2(SiO4)3 的结构精化
DOI：
10.2138/am.2010.3243
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发表时间：
2010
影响因子：
3.1
通讯作者：
G. Calas
中科院分区：
文献类型：
--
作者：
A. Juhin;G. Morin;E. Elkaïm;D. Frost;M. Fialin;F. Juillot;G. Calas
摘要利用高分辨率同步加速器x射线粉末衍射数据，研究了在11gpa和1500℃条件下在多顶压机中合成的多晶菱长石Mg3(Cr0.8Mg0.1Si0.1)2(SiO4)3的晶体结构。结构为立方结构，空间群Ia3′d， a = 11.5935(1) Å， V = 1558.27(4) Å3, Dcalc = 3.79 g/cm3。结构式表明，在这些合成条件下，褐辉石易被多数石取代。Cr-O距离为1.959(7)Å，与含cr的Mg3Al2(SiO4)3相似。这证实了Cr-O距离的大小并不是绿绿褐辉石和红色Cr-pyrope晶体场分裂值差异的原因。与其他cr -石榴石端元的结构比较表明，随着合成压力的降低和x阳离子尺寸的增大，Cr-O距离和[4]Si-O-Cr角减小。
Abstract The crystal structure of a polycrystalline knorringite, Mg3(Cr0.8Mg0.1Si0.1)2(SiO4)3, synthesized at 11 GPa and T = 1500 °C in a multi-anvil press, has been refined from high-resolution synchrotron X-ray powder diffraction data. The structure is cubic, space group Ia3̅d, a = 11.5935(1) Å, V = 1558.27(4) Å3, Dcalc = 3.79 g/cm3. The structural formula indicates that knorringite is susceptible to majorite substitution at these synthesis conditions. The Cr-O distance, 1.959(7) Å, is similar to that in Cr-bearing pyrope Mg3Al2(SiO4)3. This confirms that the magnitude of the Cr-O distance is not responsible for the difference in crystal field splitting values between green knorringite and red Cr-pyrope. A comparison with the structure of other Cr-garnet end-members shows that the Cr-O distance and the [4]Si-O-Cr angle decrease with decreasing synthesis pressure and with increasing X-cation size.