Examination of the mixed-alkali effect in (Li,Na) disilicate glasses by nuclear magnetic resonance and conductivity measurements.
Results from 29Si, 23Na and 7Li magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, 7Li NMR relaxation and electrical conductivity in a series of [Li(1-x).Nax]2O.2SiO2 (disilicate) glasses are used to investigate the mixed-alkali effect. From the 29Si NMR spectra there is relatively little change of the network with alkali composition. 23Na and 7Li NMR linewidths and shifts change continuously as a function of composition, indicating that the alkali ions are intimately and uniformly mixed rather than separated into lithium and sodium-rich domains. The activation energy from electrical conductivity shows a distinct maximum at the central composition (x = 0.5), whereas the local activation energy for lithium motion determined from NMR shows only a smaller but monotonic increase as the lithium-content decreases.
Ali
F
F
Chemical Laboratory, University of Kent, Canterbury, UK.
Chadwick
A V
AV
Greaves
G N
GN
Jermy
M C
MC
Ngai
K L
KL
Smith
M E
ME
D004553:Electric Conductivity; D005898:Glass / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy