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

J E H Sansom, J R Tolchard, M S Islam, D Apperley, P R Slater

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Abstract

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.
LanguageEnglish
Pages1410-1413
Number of pages4
JournalJournal of Materials Chemistry
Volume16
Issue number15
DOIs
StatusPublished - 2006

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Apatites
Apatite
Oxides
Nuclear magnetic resonance
Ions
Silicates
Chemical shift
Oxygen
Condensation
Silicon
Chemical analysis
Doping (additives)
Defects

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Sansom, J. E. H., Tolchard, J. R., Islam, M. S., Apperley, D., & Slater, P. R. (2006). Solid state Si-29 NMR studies of apatite-type oxide ion conductors. DOI: 10.1039/b600122j

Solid state Si-29 NMR studies of apatite-type oxide ion conductors. / Sansom, J E H; Tolchard, J R; Islam, M S; Apperley, D; Slater, P R.

In: Journal of Materials Chemistry, Vol. 16, No. 15, 2006, p. 1410-1413.

Research output: Contribution to journalArticle

Sansom, JEH, Tolchard, JR, Islam, MS, Apperley, D & Slater, PR 2006, 'Solid state Si-29 NMR studies of apatite-type oxide ion conductors' Journal of Materials Chemistry, vol. 16, no. 15, pp. 1410-1413. DOI: 10.1039/b600122j
Sansom JEH, Tolchard JR, Islam MS, Apperley D, Slater PR. Solid state Si-29 NMR studies of apatite-type oxide ion conductors. Journal of Materials Chemistry. 2006;16(15):1410-1413. Available from, DOI: 10.1039/b600122j
Sansom, J E H ; Tolchard, J R ; Islam, M S ; Apperley, D ; Slater, P R. / Solid state Si-29 NMR studies of apatite-type oxide ion conductors. In: Journal of Materials Chemistry. 2006 ; Vol. 16, No. 15. pp. 1410-1413
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AU - Tolchard,J R

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AU - Slater,P R

N1 - ID number: ISI:000237202800012

PY - 2006

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N2 - 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.

AB - 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.

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JF - Journal of Materials Chemistry

SN - 0959-9428

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