Main Content

Structure relaxation in depletion zones

 The foreign ion CAIT experiment developed in the Weitzel group builds on enforcing the replacement of native ions by foreign ions provided in an attachment experiment. Our main interest is focused on replacing one (mono-valent) alkali ion by another alkali ion or a proton or a deuteron. By now we have studied a considerable number of materials. We never found evidence for structural relaxation of the solid material upon ion replacement.

Such hints at structural relaxation have only been observed in cases where a native di-valent ion, e.g. Ca++, was replaced by a mono-valent alkali ion, e.g. K+. Such a study has been reported by Hein et al. [1]. There an alkali-calcium-phosphate glass had been irradiated by a K+ ion beam. Charging up of the surface induced the transport of Na+ and Ca++ (!) away from the charged surface and subsequent replacement by external K+ ions. Concomitant with the electrodiffusion profile we observed a change in the P+ and PO4+ ion signals in the ToF-SIMS analysis, which was interpreted as an indication of local structure changes [1].

Fig. 1     Normalized ToF-SIMS concentration profiles. Signals depicted are particle densities of the mobile ion species normalized considering charge conservation of the glass material. Additionally P+ and PO4+ signals are shown for illustration of structural changes in the glass. The glass surface is at 0.

[1]          A. Hein, J. Martin, M. Schäfer, K.-M. Weitzel
Electrodiffusion versus Chemical Diffusion in Alkali Calcium Phosphate Glasses: Implication of Structural Changes
J. Phys. Chem. C, 121, 3203−3211, (2017)