Alternating current conductivity and dielectric dispersion in copper-silica nanocomposites synthesized by electrodeposition

Composites of nanometer-sized copper metal with diameters varying from 3.2 to 11.4 nm dispersed in a silica gel medium were synthesized by an electrodeposition method. The ac conductivity and dielectric dispersion of these nanocomposites were measured over the frequency range 0.2 kHz-1.5 MHz at temperatures varying from 150 to 300 K, The ac conductivity showed a frequency dependence of proportional to omega(n) where omega is the angular frequency and n similar to 0.62 the latter being temperature independent. The quantum mechanical tunneling model was used to explain this result. The dielectric modulus data were analyzed on the basis of a stretched exponential relaxation function. The values of the exponent beta as extracted from such analysis were found to be in the range 0.31-0.42 and were temperature independent for different gel compositions. The activation energies were estimated from the temperature variation of frequency at which the imaginary part of the dielectric modulus was maximum. The activation energy value similar to 0.24 eV could be explained satisfactorily on the basis of an electron tunneling mechanism. (C) 1998 American Institute of Physics. [S0021-8979(98)05014-2]