Solid state Si-29 NMR studies of apatite-type oxide ion conductors


Sansom, J. E. H., Tolchard, J. R., Islam, M. S., Apperley, D. and Slater, P. R., 2006. Solid state Si-29 NMR studies of apatite-type oxide ion conductors. Journal of Materials Chemistry, 16 (15), pp. 1410-1413.

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Apatite-type silicates have been attracting considerable interest as a new class of oxide ion conductor, whose conduction is mediated by interstitial oxide ions. We report here the first (29)si solid state NMR studies of these materials with a systematic investigation of thirteen compositions. Our results indicate a correlation between the silicon environment and the observed conductivity. Specifically, samples which show poor conductivity demonstrate a single NMR resonance, whereas fast ion conducting compositions show more complex NMR spectra. For the oxygen excess samples La9M(SiO4)(6)O-2.5 (M = Ca, Sr, Ba) two peaks are observed at chemical shifts of approximate to - 77.5 and - 80.5 ppm, with the second peak correlated with a silicate group adjacent to an interstitial oxygen site. On Ti doping to give La9M (SiO4)(6-x)(TiO4),O-2.5 (X = 1,2) the second peak disappears, which is consistent with the "trapping" of interstitial oxygens by Ti and the consequent lowering in oxide ion conductivity. The samples La-9.33(SiO4)(6)O-2 and La-9.67(SiO4)(6)O-2.5 show a further third weak peak at a chemical shift (approximate to -85.0 ppm) consistent with the presence of some [Si2O7](6-) units in these samples, due to condensation of two [SiO4](4-) units. The effect of such condensation of [SiO4](4-) units will be the creation of additional interstitial oxide ion defects, i.e. 2 [SiO4](4-) -> [Si2O7](6-) + O-int(2-). Overall, the results further highlight the importance of the [SiO4](4-) substructure in these materials, and additionally suggest that Si-29 NMR could potentially be used to screen apatite silicate materials for oxide ion conductivity.


Item Type Articles
CreatorsSansom, J. E. H., Tolchard, J. R., Islam, M. S., Apperley, D. and Slater, P. R.
DepartmentsFaculty of Science > Chemistry
ID Code4662
Additional InformationID number: ISI:000237202800012


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