Electrical properties of sol-gel-derived glass-metal nanocomposites

Composites of silica glass and metal nanoparticles of copper or nickel have been synthesized by the hot compaction of sol-gel-derived glass-metal powders. The metal particle sizes range from 5.1 to 7.2 nm. The electrical resistivity of the composites is characterized by semiconductor-like behaviour in the temperature range 235-340 K. This is believed to arise owing to electron hopping between localized states within the band gap of amorphous silica formed by the dispersed metal atoms. A low activation energy of the order of a few millielectronvolts in the specimens containing copper in the temperature range 140-235 K may occur because of a quantum size effect, the metal particles forming continuous chains with diameters of the order of 3 nm.