含Mg矿物和玻璃中Mg的局部结构研究

COORDINATION AND LOCAL STRUCTURE OF Mg IN SILICATE MINERALS AND GLASSES

本文用同步辐射的MgK 边X射线近边结构谱 (XANES)研究了 9种含Mg矿物的MgK 边特征谱 ,其谱的能量位置随着配位数的增加而增大 ;建立了含Mg矿物中MgK 边的能量与Mg—O键距的关系 :CaMgSi2 O6(Di) NaAlSi3 O8(Ab)玻璃中MgK 边XANES的能量和Mg—O的键长的关系。在Di Ab玻璃中的Mg O键距是 0 .2± 0 .0 0 4nm。表明本方法可以作为研究含Mg矿物Mg的配位与局部结构新的结构探针。

The MgK\|edge peak shifts to higher energy with increasing coordination from \{\}\+\{\\}Mg in spinel, to \{\}\+\{\\}Mg in grandidierite, to \{\}\+\{\\}Mg in diopside and many other silicates containing \{\}\+\{\\}Mg, and to \{\}\+\{\\}Mg in pyrope. The correlation between the energy of MgK\|edge and Mg—O bond distance of the model minerals is also established, which can be used to estimate the average Mg—O bond distance in disordered systems. The structural role of Mg in CaMgSi\-2O\-6 (Di)\|NaAlSi\-3O\-8(Ab) glasses was studied using MgK\|edge XANES spectra. The Mg—O bond distance in these glasses is estimated to be 0.2±0.004nm. Thus, Mg in these glasses may be five coordinated with oxygen, or Mg may have multiple structural sites, \{\}\+\{\\}Mg, \{\}\+\{\\}Mg and \{\}\+\{\\}Mg. The Di\|Ab glasses may possess a medium\|range ordering structure, and have dramatically different multiple scattering (MS) paths from those of crystalline model minerals.