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Solid State NMR Studies of Cation Distributions in Glasses

Solid State NMR Studies of Cation Distributions in Glasses. Hellmut Eckert Institut für Physikalische Chemie WWU Münster. network modifier. network former. B,Si,P. O. Li-Cs. directly bonded neighbors. 0.1-0.3 nm, MAS-NMR. Coordination numbers and symmetries. Site quantification.

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Solid State NMR Studies of Cation Distributions in Glasses

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  1. Solid State NMR Studies of Cation Distributions in Glasses Hellmut Eckert Institut für Physikalische Chemie WWU Münster

  2. network modifier network former B,Si,P O Li-Cs directly bonded neighbors 0.1-0.3 nm, MAS-NMR Coordination numbers and symmetries Site quantification Short-range order in glasses

  3. B, Si, P O Li-Cs Spatial distribution of modifiers 0.3-0.6 nm Dipolar NMR Network former-network modifier correlation Network former connectivity Medium-range order in glasses

  4. Cation distributions in silicate glasses: MD - Simulations Huang and Cormack, J. Chem. Phys. 1990

  5. Cation Clustering in Silicate Glasses .....also implies nbo-clustering and strong Cation-nbo interactions O Li+ SiO- O O Si Li+ -OSi O O O O Si O- Li+ O -O Si Si Li+ O O Li+ O O Si O- O O O Li+ -O Si Si Q(3) – Li interactions: strong Q(4) – Li interactions: weak

  6. Modulation of HD under sample rotation + I - Tr S + + Tr I-channel p pulse Magic- Angle Spinning (MAS) 7Li Rotational Echo Double Resonance (REDOR) 29Si

  7. p p/2 2 0 1 3 4 DS DS = S0 S0 p/2 p [ Tr ] REDOR Pulse Sequence 29Si 7Li - S S0 S0 29Si 7Li depends on: strength of interaction (# neighbors, distance) dipolar evolution time N . Tr

  8. Analysis of REDOR curves in glasses .

  9. 29Si-{7Li}-REDOR Curve of Li2SiO3 Crystal structure: Voellenkle, ZEKRD 154 (1981) 77-81

  10. 29Si {7Li}-REDOR in lithium silicate glass Q3 Q4

  11. Compositional dependence of M2( 7Li-29Si) In lithium silicate glasses Q(3) Q(4) M2 = K Srij-6 ~ Nj <rij>-6

  12. Combination NMR/MD Simulations (H. Lammert, A. Heuer) MD: R(Q(3)-Li) = 320 pm NMR: M2 = 12 kHz2 NLi ~ 3

  13. Cation clustering in lithium silicate glasses O Li+ SiO- O O Si Li+ -OSi O O O O Si O- Li+ O -O Si Si Li+ O O Li+ O O Si O- O O O Li+ -O Si Si Q(3) : 3 Li neighbors at distance 320 pm Q(4) : interaction with Li negligible

  14. Li+ O- O Li+ SiO- O O Si Li+ -OSi O O O O Si O- Li+ O -O Si Si Li+ O O Li+ O O Si O- O O O Li+ -O Si Si Lithium-lithium interaction measured by 7Li{6Li} SEDOR d(Li-NBO) = 1.93 Å 4 Li-Li distances at 2.73 Å M26Li-7Li = 9.9 kHz2

  15. 2BO3/2 + Na2O = 2 BO4/2 Na clustering implies difference in dipolar couplings for the two boron sites 23Na-11BO3/2 23Na-11BO4/2 Approach: 11B{23Na}-REDOR BO3 BO4 Anionic compensation mechanism in borate glasses

  16. 11B{23Na} REDOR in sodium borate glass (Na2O)0.2 (B2O3)0.8 BO4- BO3

  17. 11B - 23Na dipolar M2 -values in sodium borate glasses d(Na-BO4) = 316 pm

  18. B,Si,P O Li-Cs Network modifier-network modifier correlations Spatial cation distribution

  19. 23Na spin echo decay spectroscopy M2 = 0.9562 (µo/4p)2g4h2 Srij-6 Regime of Validity:HQ(2) ~ HD << H1 << HQ(1) (selective excitation) low Temperature (~100 K) (no dynamic contribution)

  20. Dependence of M2(23Na-23Na) on Sodium Number Density in Sodium Borate Glasses Model: Statistical Distribution of Na ions in a truncated NaCl lattice with R(Na-B) = 316 pm

  21. Comparison between different glass systems

  22. Conclusions Dipolar NMR reveals new quantitative information on cation distribution in silicate and borate glasses Lithium and sodium silicate Glasses: Li -Silicate glasses: clustering at low alkali (< 33 mole% Li2O) 3 Q(3)...Li distances at 320 pm; 4 Li...Li distances 270 pm Sodium silicate glasses: clustering at < 20 mole% Na2O Lithium and sodium borate glasses: Na+....BO4- pair correlation: 316 pm Cation distribution close to homogeneous

  23. Acknowledgments Wenzel Strojek Stefan Puls Jan-Dirk Epping Ulrike Voigt Prof. Andreas Heuer Heiko Lammert Deutsche Forschungsgemeinschaft: SFB 458 MWF Nordrhein-Westfalen

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