Correlation between microstructure and electrical properties of tungsten-silica nanocomposites

The electrical properties and the microstructure of nanocomposite materials composed of nano-sized amorphous silica powder and micron-sized tungsten powder were studied as a function of composition and heat treatment temperature. The dielectric constant and the electrical conductivity of the nanocomposites are higher than those of pure silica powder at all compositions. The percolation threshold of this system is about 20% vol. W. Above this composition a sharp increase in the dielectric constant and in the electrical conductivity occurs. This increase becomes even sharper after the nanocomposites are heat treated at 950°C for 1 hour. No changes in the microstructure are observed up to this temperature. It is suggested that the electrical properties of the nanocomposites are dominated mainly by dangling bonds at the W/SiO₂ interfaces. Further research should be undertaken to investigate the factors controlling the dielectric constant and the electrical conductivity in order to obtain high capacitance materials with high dielectric constant and low electrical conductivity.