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- Carbon black (2)
- Sol-gel (2)
- Electrical resitivity (1)
- Nanomaterials (1)
- Percolation (1)
- Percolation phenomena (1)
- Ruthenium dioxide (1)
- Thin films (1)
The electrical properties of solgel-derived films can be tailored by embedding conductive particles of ruthenium dioxide or carbon black in an insulating amorphous SiO2 silica matrix. The preparation process included an acid hydrolysis of tetraethoxysilane and methyltrimethoxysilane. Then alcohol solutions of ruthenium chloride or carbon black were added. Films of filler concentration up to 60 vol.% were prepared by dip coating and then dried and heat-treated at various temperatures up to 600_°C. The D.C. resistance of the films can be varied within the range of 109 to 102 OHgr sdot cm. A non-linear dependence on filler composition in the films was observed for both systems, which is explained by a modified percolation theory. A percolation threshold of 5.5 vol.% for SiO2-RuO2 or 50 vol.% for SiO2-C films, whereby the resistance drastically decreases, was determined. Moreover the temperature dependency of resistance and the current-voltage characteristics of the films can also be explained by this geometric model.
The preparation of sol-gel derived silica-based nanomaterials containing electrical conductive carbon fillers in an extensive composition range is described and their electrical properties are presented. Nanomaterials of carbon filler concentrations up to 60% (v/v) were obtained by dip coating or screen-printing from precursors of hydrolysed alkoxysilanes. Nanostructured morphology could be identified to consist of homogeneously dispersed carbon black particles or carbon fibres of 30 to 500 nm in size in a modified silica matrix. The electrical resistivity of the films changes drastically from 1010 to 10?1 O?cm, according to the amount of dispersed conductive particles. A threshold between 5 and 50% (v/v), at which the resistance abruptly decreases, was determined. A geometrical model related to percolation theory explains this non-linear dependence on the filler composition in the materials. Moreover the temperature dependence of resistance and the current-voltage characteristics of the nanomaterials can also be illustrated using this geometric model.