Dear researchers,
I'm trying to understand how ion-exchange reactions affect the crystal structure of olivine mineral. I observed that regardless of the ion-exchange mechanism (Mg-H or Si-OH exchange), some miller planes of olivine mineral increased in height and tightened whereas, some of them decreased in height and widened. I wonder why XRD pattern of olivine after ion-exchange showed both well-crystallization and amorphization at the same time. Could you kindly advise me solving this problem or at least lead me to specific researches involving how ion-exchange affected XRD pattern of inorganic materials ?
Thank you for your attention.
A very non-detailed view: In x-ray diffraction, the various planes of diffractions are defined by the unit cell. So, as long as you do not change the actual crystal structure of olivine (and it is a very hardy structure) you will not change the actual diffraction peak positions. However, the intensity of the diffracted beams are dependent on the electron density in the system. So, by doing ion exchange, you are changing the electron density and so you are changing the heights of the peaks. The homogeneity, or lack thereof, of the ion exchange will result in peaks that may be more or less broad.
Olivine is an orthosilicate and not a sheet silicate. In general: ion exchange modifies the chemical composition and, consequently the crystal structure. Therefore it is normal to observe changes in the intensity and the position of the diffraction peaks. The intensiy is a function of the atoms scattering powers and of their atomic coordinated as expressed by the strcuture factor. The peak position is a function of the cell parameters that, in their turn, depends from the atomic coordinates.
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