Electrical and optical properties of dense composites

Effective cluster models have been developed that treat disordered suspensions of monodisperse metal spheres as mixtures of isolated spheres and compact clusters of spheres using the Clausius-Mossotti equation [Phys. Rev. B 42, 9319 (1990); J. Appl. Phys. 71, 3926 (1992)] and the Bruggeman equation [J. Appl. Phys. 78, 6165 (1995)]. These effective cluster models are adapted to suspensions of dielectric particles with arbitrary complex permittivity. The models are compared with the coated sphere model of Sheng [Phys. Rev. Lett. 45, 60 (1980); J. Opt. Soc. Am. B 15, 1022 (1998)]. Model calculations are compared with the measurements of the optical transmission spectra and low frequency electrical conductivity of Au-SiO2 films by Cohen, Cody, Coutts, and Abeles [Phys. Rev. B 8, 3689 (1973)], and with the low frequency permittivity measurements on suspensions of Ag spheres in KCl of Grannan, Garland, and Tanner [Phys. Rev. Lett. 46, 375 (1981)]. The models accurately predict the percolation thresholds seen in the electrical measurements and are in good agreement with all of the experiments over the entire range of volume loading. (C) 1999 American Institute of Physics. [S0021-8979(99)05504-8].