Size-dependent ionic conductivity observed for ordered mesoporous alumina-LiI composite

Ordered mesoporous Al2O3 was synthesized by a solution sol-gel method using neutral copolymer surfactants as templates. The pore size was controlled over the range of 2.8-12.5 nm by using different surfactant copolymers under different synthetic conditions. By utilizing cyclohexane as a cosolvent, mesoporous Al2O3 having relatively monodispersed particle size was obtained. Composites composed of the synthesized mesoporous Al2O3 and the lithium ion conductor (LiI) was prepared by heating the composite in a sealed Pyrex tube at 773 K. Composition dependence of the dc conductivity was determined from a single are in the observed impedance spectra. The maximum dc electrical conductivity, 2.6 x 10(-4) S cm(-1) at 298 K, was observed for 50 LiI . 50 Al2O3 composite with 4.2 nm averaged mesoporosity, which was considerably higher than the previously reported LiI-alumina composites. A systematic dependence of conductivity upon pore size was observed, in which the conductivity increased with decreasing the pore size. (C) 2004 Elsevier B.V. All rights reserved.