During in-situ XRD on sodium titanate nanotubes, {h00} planes intensity decrease and d(hkl) increase. Can sodium migrate from interlayers positions to the (outer/inner) surface, driven by thermal motion? Furthermore, can sodium react with CO2 to form Na2CO3, driven by the same thermal motion?
Do you expect the migration of Na atoms in a crystal structure? Can this be possible without a chemical reaction? Consider a piezoelectric BaTiO3 structure. Ti is located at (1/2, 1/2, z). Ti moves a bit when a potential applied to the lattice. But it never goes to a corner site. However a thermal vibration can not be responsible such amount of displacement.
There are my own opinions.
Sodium titanate (Na2Ti2O4(OH)2) has a layered structure with Na, H, OH or H3O ions located between TiO6 octahedra layers. Sodium can be removed by ion-exchange to become a protonic titanate or else, depending on the used ions. This structure can not be associated with BaTiO3 type structure
In principle, it is possible.
We studied the effect of temperature on valence state of Mn in YMnO3 by XPS. The sample contained a small amount of contaminating Bi (0.3 at%). After heating, the amount of Bi in the near-surface region increased up to 2.8 at%. Well, at least Bi can do it.
See A.G. Kochur, A.T. Kozakov, K.A. Googlev, A.V. Nikolskii J. Electron Spectrosc. Relat. Phenom. 195 (2014) 1-7
In the layered structures containing alkali metals different ionic exchange reactions are quite usual. For example, we observed that Na2CO3 is formed on surface of NaNdTiO4 after exposure to air. And when this compound is placed into water, about half of the Na+ ions are substituted by H+ in a few minutes.
Thank you! The ion-exchange procedure is used also for doping with different cations. But, can thermal energy (heating) determine such a migration?
From the very general point of view, rate of the most of heterogeneous reactions is determined by diffusion of the reacting species (Na+ ions in our case) to the surface. And diffusion will surely become faster when heating is applied.
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction