Aluminum ordering and clustering in Al-rich synthetic phlogopite: {H-1} -%26gt; Si-29 CPMAS HETCOR spectroscopy and atomistic calculations

作者：Langner Ramona^*; Fechtelkord Michael; Garcia Alberto; Palin Erika J; Lopez Solano Javier

来源：American Mineralogist, 2012, 97(2-3): 341-352.

DOI：10.2138/am.2012.3840

• HETCOR CPMAS NMR
• phlogopite
• Monte Carlo simulations
• J formalism
• total-energy calculations
• GULP
• SIESTA

The cationic ordering in the octahedral and tetrahedral sheets of Al-rich synthetic phlogopites with composition K(Mg3-xAlx)[Al1+xSi3-xO10](OH)(2) (0.0 %26lt; x %26lt; 1.0) has been investigated using a combined approach of Monte Carlo simulations based on the %26quot;J formalism%26quot; (Bosenick et al. 2001; Warren et al. 2001) and H-1, Si-29 MAS and {H-1} -%26gt; Si-29 CPMAS/HETCOR solid-state NMR spectroscopic experiments. Our results are compatible with the well-established Loewenstein%26apos;s rule of Al-Al avoidance in the tetrahedral sheets, but the Si/Al-IV and Mg/Al-VI distributions show a tendency to segregation of the excess Al atoms, and we observe a preference for Al-VI and Al-IV to occupy directly neighbored octahedral and tetrahedral sites. As a result the structure is separated into clusters of original phlogopite composition {K(Mg-3)[AlSi3O10](OH)(2)} and clusters of %26quot;eastonite%26quot; composition {K(Mg2Al)[Al2Si2O10] (OH)(2)} that encompass a whole T-O-T layer package, although Al is solved in the phlogopite structure homogeneously on a macroscopic level.

• 出版日期2012-3