Study of the relationship between structure and O-17 electric field gradient parameters in some aluminosilicates

摘要

The relation between O-17 quadrupolax parameters and the local structure in silicates is of considerable interest if these parameters are to be used as a local probe. Although there are a number of investigations and some theoretical work on Si-O-Si bonds, there seems to be very little experimental data on Si-O-Al bonds. We have therefore investigated a number of sodalites with a general formula of M-8[AlSiO4]Cl-2 where M is an alkali cation. They have only one oxygen site and a Si:Al ratio of one. By varying the alkali we were able to change the Si-O-Al bond angle about five degrees steps from 125 to 152 degrees. The value of the electric field gradient (EFG), C-Q of O-17, followed a roughly similar angular dependence to that found for Si-O-Si bonds with C-Q180 = 4.2 MHz. The asymmetry parameter of O-17 also behaved in a similar fashion to that found for Si-O-Si bonds although it increased more rapidly at small angles.