S. Indris et al., Nanocrystalline versus microcrystalline Li2O : B2O3 composites: Anomalous ionic conductivities and percolation theory, PHYS REV L, 84(13), 2000, pp. 2889-2892
We study ionic transport in nano- and microcrystalline (1 - x)Li2O:xB(2)O(3
) composites using standard impedance spectroscopy. In the nanocrystalline
samples (average grain size of about 30 nm), the ionic conductivity sigma(d
c) increases with increasing content x of B2O3 up to a maximum at x approxi
mate to 0.5. Above x approximate to 0.92, sigma(dc) vanishes. By contrast,
in the microcrystalline samples (grain size about 10 mu m), sigma(dc) decre
ases monotonically with x and vanishes above x approximate to 0.55. We can
explain this strikingly different behavior by a percolation model that assu
mes an enhanced conductivity at the interfaces between insulating and condu
cting phases in both materials and explicitly takes into account the differ
ent grain sizes.