Theoretical modelling of cis?-vacant and trans?-vacant configurations in the octahedral sheet of illites and smectites |
| |
| Authors: | C I Sainz-Diaz A Hernández-Laguna M T Dove |
| |
| Institution: | (1) Department of Earth Sciences and Environmental Chemistry, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008 Granada, Spain e-mail: sainz@eez.csic.es, ES;(2) Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ UK, GB |
| |
| Abstract: | The cis-vacant configurations of smectites and illites have been studied theoretically by using transferable empirical interatomic
potentials. A wide range of compositions of octahedral and tetrahedral cation and interlayer charge has been considered. All
results have been compared with the trans-vacant configurations in each sample. The calculated values reproduce the differences in the lattice parameters between the
cis- and trans-vacant configurations of experimental studies. Taking into account the cis-/trans-vacant proportion, the calculated structures agree with experiment for the main structural features of the crystal lattice.
The effect of the cation substitution in the octahedral and tetrahedral sheets on the cell parameters has been also studied,
finding good linear relationships. The calculated cation substitution effects are consistent with experimental results. Although
the energy difference between the cis- and trans-vacant configurations is small, the cis-vacant is more stable when the composition of clays is more smectitic, like the experimental behaviour. Similar trends of
the cation substitution effect on the cis-/trans-vacant proportion to the experimental results are found. The structure of the hydroxy groups has also been analysed. The
OH bond length, the orientation of the O–H bond with respect to the (001) plane and the non-bonding H...O distances have been
studied.
Received: 4 September 2000 / Accepted: 29 January 2001 |
| |
| Keywords: | Cis- trans-vacant configurations Smectite Illite H-atom positions Cation substitution effect |
| 本文献已被 SpringerLink 等数据库收录！ |
|
